AU2768692A

AU2768692A - Rapid assay for gold and instrumentation useful therefor

Info

Publication number: AU2768692A
Application number: AU27686/92A
Authority: AU
Inventors: Myron A. Beigler; Herbert L. Berman; Georges P. Derbalian; Huey-Rong Christina Jaw; John Junes Lee
Original assignee: BIOMYNE TECHNOLOGY Co
Current assignee: BIOMYNE TECHNOLOGY Co
Priority date: 1991-10-01
Filing date: 1992-09-30
Publication date: 1993-05-03
Also published as: JPH07501882A; BR9206580A; EP0606374A1; HU9400943D0; CZ76194A3; CA2119134A1; HUT66407A; WO1993007472A1

Description

RAPID ASSAY FOR GOLD AND INSTRUMENTATION USEFUL THEREFOR

The present invention relates to analytical methods. In a particular aspect, the present invention relates to methods and apparatus useful for performing a rapid assay of gold or other elemental concentrations, especially low concentrations of gold in rock and soil samples. In another aspect, the present invention relates to analytical methods and apparatus that are both rapid and portable, so as to be useful in field applications.

Background of the Invention

Most of the gold deposits being discovered today are made up of gold grains that are invisible by normal microscopy. These gold particles are often smaller than one micron in size. Because the gold is not detectable by any readily available, portable means, prospecting presently depends almost completely upon reliable analytical techniques which can only be carried out in large analytical laboratories. Such facilities are, by necessity (due to the nature of their equipment), large, stationary facilities. Exploration crews must, therefore, label and ship geologic samples to these stationary facilities for analysis, and must then wait a week or longer until analytical results are obtained. This method of exploring for valuable mineral content is laborious, slow, inefficient, and expensive. A gold analysis method (and apparatus useful therefor) which could be carried out at or near the exploration site, and which could provide rapid and reliable analyses of very small quantities of gold in rock matrices, would constitute a major improvement in the field of gold exploration.

At the current price of gold, rock bodies containing concentrations as low as one part per million of gold are economically minable. However, during the exploration process subeconomic amounts of gold may act as a tracer to lead the geologist toward an economic deposit. Typically, gold values as low as 5 parts per billion may constitute significant hints that other, higher values might be found nearby. Therefore, an analytical technique that is sensitive in the range of parts per billion levels of gold would be useful for this purpose.

Most gold analyses presently performed in commercial laboratories utilize the fire assay technique. Fire assay laboratories are large, labor-intensive facilities which consume large quantities of power and water, and frequently emit hazardous lead fumes. Another drawback to the fire assay method of analysis is the fact that cross contamination can readily occur between samples.

At the present time, the only commercially viable modern analytical technique for the analysis of gold is neutron activation. The requirement for access to a nuclear research reactor makes neutron activation even less readily available than fire assaying. Also, neutron activation inherently requires an eight day "cool down" period for short-lived radioisotopes to decay before counting the gold. Thus, in addition to being available only where a nuclear reactor is available, it is impossible for neutron activation to satisfy the need in the field for a rapid analytical technique.

Summary of the Invention

In accordance with the present invention, an assay method is provided which is capable of measuring gold concentrations over a broad range (i.e., from a few parts per billion up to approximately 30 thousand parts per billion or higher). The invention assay method comprises solubilizing the gold content of the sample, if necessary, then generating a photo-responsive complex with the gold, e.g., a Rhodamine B-gold complex. The gold concentration in the sample is then determined by analysis of the gold complex using optical means.

In accordance with another aspect of the present invention, a portable fluorometer instrumentation apparatus is provided that performs a rapid analysis of rocks, soil and other samples to determine the concentration of gold therein. Advantageously, the apparatus is easily transportable to those locations where the rock or soil samples are found. The instrumentation apparatus is easy to operate, and provides an accurate indication of the gold concentration within the samples in a relatively short time, e.g., in less than about three hours. Further, the instrumentation apparatus is capable of measuring gold concentrations over a broad range from a few parts per billion (ppb) to approximately 30 thousand ppb.

In accordance with another aspect of the invention, there is provided a system for determining the concentration of gold in a field sample, such as a rock or soil sample.

One embodiment of the present invention may thus be characterized as a method for determining the concentration of gold in solutions containing the same. Such method comprises carrying out the following steps: (a) contacting the gold- containing solution with: (i) an oxidizing agent, and (ii) at least one crown ether polymer; wherein the contacting is carried out in acidic media under conditions suitable to convert substantially all of the gold ions in solution into their highest oxidation state, and for a time sufficient to allow capture of substantially all of the gold ions in the solution by the crown ether polymer; (b) separating the gold-crown ether complex from the remaining components of the solution; (c) recovering the gold ions from the gold-crown ether complex; (d) contacting the metal-containing solution prepared as described in step (c) with label means, wherein the label means is capable of binding to the gold in its highest oxidation state, and wherein the label means is capable of ready analysis; wherein the contacting is carried out in acidic media under conditions sufficient to allow substantially all of the gold in the solution to become bound to the label means, and then separating unbound label means from the solution; and thereafter (e) measuring the amount of bound label means in the solution.

In accordance with another embodiment, the invention may be further characterized as a method for determining the concentration of gold in a matrix. Such method comprises the steps: (a) contacting the matrix with an aqueous cyanide- containing solution in the presence of an oxidizer in alkaline condition; (b) contacting the solution obtained from step (a) with: (i) hydrochloric acid in the presence of an oxidizing agent, and (ii) at least one crown ether polymer; wherein the contacting is carried out under conditions suitable to convert substantially all of the gold ions in solution into their highest oxidation state, and for a time sufficient to allow capture of substantially all of the gold ions in the solution by the crown ether; (c) separating the gold-crown ether complex from the remaining components of the solution; (d) recovering the gold ions from the gold-crown ether complex; (e) contacting the gold-containing solution prepared as described in step (d) with label means, wherein the label means is capable of binding to the gold in their highest oxidation state, and wherein the label means is capable of ready analysis; wherein the contacting is carried out in acidic media under conditions sufficient to allow substantially all of the gold in the solution to become bound to the label means, and then separating unbound label means from the solution; and thereafter (f) measuring the amount of label means in the solution.

A further embodiment of the invention may be characterized as instrumentation apparatus useful in the practice of the present invention. Such instrumentation apparatus includes: (a) means for generating radiant energy within a first narrow band of wavelengths; (b) coupling means for coupling the radiant energy to a prepared sample under investigation; and (c) detection means radiantly coupled to the sample for detecting any transmissive light that passes through the sample and falls within the first narrow band of wavelengths, or any fluoresced light emitted from the sample that falls within a second narrow band of wavelengths.

In operation of the instrumentation apparatus, the presence of the transmissive or fluoresced light within the first or second narrow band of wavelengths, respectively, indicates the presence of a particular element, e.g. gold, within the sample. The intensity or magnitude of the detected transmissive or fluoresced light provides a measure of the concentration of the particular element within the sample. As required or desired, a conversion chart or table is generated, e.g., by measuring samples containing known concentrations of the particular element, that allows for the direct conversion of the measured fluoresced light to a concentration value of the element within the sample. Hence, by merely measuring the intensity or magnitude of the transmissive and/or fluoresced light within the first and/or second narrow band of wavelengths, a convenient and quick measurement is provided as to the concentration of the particular element within the sample.

Advantageously, in one embodiment of the instrumentation apparatus, a fiber optic bundle is used to couple radiation energy to and from the sample under test avoids the problem of "inner filter effect" commonly found in prior art fluorometer devices. The inner filter effect, when present, produces ambiguous results in the signal output from the detector.

Yet another embodiment of the invention may be characterized as an analysis system for determining the concentration of gold in a field sample. Such system includes: (a) binding means for binding a portion of the field sample to a suitable label means, such as Rhodamine B, thereby producing a radiation complex of the label means plus gold; (b) irradiating means for irradiating the label means to which the sample is bound with radiation energy falling within a first narrow band of wavelengths, this irradiating means including fiber optic means for directing radiation to and collecting radiation emitted from the sample complex; and (c) detecting means coupled to the fiber optic means for detecting radiation emitted from the sample within a second narrow band of wavelengths.

In operation of the analysis system, the metal-label means complex emits radiation energy within the second narrow band of wavelengths in response to irradiation with radiation energy within the first narrow band of wavelengths only when the field sample bound to the label means contains the particular metal being assayed. Further, because the amount or intensity of the radiation thus emitted is proportional to the amount of metal bound to the label means, the magnitude of the detected radiation provides a simple and quick measure of the metal concentration within the field sample. Additional enhancements of the system optionally include processing means for automatically converting the detected radiation within the specified band to a measure of the gold concentration within the field sample.

It is thus a feature of the invention to provide portable apparatus that includes all the instrumentation and other components needed to carry out the method of the invention.

It is another feature of the invention to provide fluorometer instrumentation apparatus for assaying a sample complex for the presence of gold. The sample complex comprises a suitable ligand to which a portion of a soil or rock sample believed to contain gold has been bound. An advantageous feature of such instrumentation apparatus is that fluorescence and transmissive readings may be obtained over a wide dynamic range. A related feature provides good proportionality between the fluorescence/ transmissive readings and the gold concentrations. Other features of such apparatus include an overall accuracy of ± 15%.

It is another feature of the invention to provide such fluorometer/transmissive instrumentation apparatus that avoids the "inner filter effect."

It is a further feature of the invention to provide fluorometer/transmissive instrumentation apparatus that is relatively insensitive to variations in the intensity of the source radiation.

It is still another feature of the invention to combine process methodology with a novel fluorometer/transmissive instrumentation apparatus comprising a particular selection of chemicals, treatment conditions, instruments, circuits and shielding configuration that effectively eliminates the effects of extraneous signals and background radiation, thereby permitting noise repression and the reading of very small signals.

Brief Description of the Drawings

The above and other aspects, features and advantages of the present invention will be more apparent from the following more particular description thereof, presented in conjunction with the following drawings and appendix wherein: FIG. 1 is a block diagram illustrating the basic operation of a first embodiment of a fluorometer instrumentation apparatus made in accordance with the present invention;

FIG. 2 is a more detailed block diagram of the first embodiment of the fluorometer instrumentation apparatus of the present invention as generally illustrated in HG. 1;

FIG. 3 is a graph illustrating the transmissivity of the two filters used within the apparatus of FIG. 2;

FIG. 4 is a representative calibration graph used with or by the apparatus of FIG. 2 in order to convert the measured intensity of the fluoresced light to a measure of gold concentration; FIG. 5 is a top view block diagram illustrating the basic operation of a combined fluorometer/transmissive instrumentation apparatus made in accordance with the preferred embodiment of the present invention;

FIG. 6 is a more detailed top view block diagram of the combined fluorometer/transmissive instrumentation apparatus of the preferred embodiment as generally illustrated in FIG. 5; and

FIG. 7A and 7B are a flow diagram showing the steps taken when utilizing the preferred embodiment, as shown in FIG. 6, to measure gold concentration in a sample. Like components or elements are referred to with like reference numerals throughout the various views of the drawings.

Detailed Description of the Invention

The following description is of the best mode presently contemplated for carrying out the invention. This description is not to be taken in a limiting sense, but is made merely for the purpose of describing the general principles of the invention. The scope of the invention should be determined with reference to the claims.

The present invention provides a method, and instrumentation apparatus for rapidly carrying out the method, for determining the concentration of a specific element, e.g., gold, in a material (field sample). The method and instrumentation apparatus have been summarized above. Advantageously, the invention method can be carried out in both batch and continuous modes. Where the material to be analyzed is in particulate form such as an ore, rock, or the like, it is desirable to first crush the particulate material into a fine powder to improve the contacting of reagents with the components of the particulate material. The ore powder is then roasted under an oxidizing atmosphere in the temperature range of 500-800 °C for up to one hour to remove volatile elements, thereby minimizing the likelihood of false positives.

To ensure that substantially all of the gold in the particulate material is taken up into solution, the finely ground particulate is suspended in an aqueous cyanide-containing solution in the presence of an oxidizer e.g. calcium peroxide, sodium peroxide, potassium permaganate, bromine, chlorine and hydrogen peroxide.

Cyanide compounds contemplated for use in this solubilization step include sodium cyanide, potassium cyanide, and the like. Potassium cyanide is presently preferred. The quantity of cyanide employed can vary widely, so as to provide a final cyanide concentration in the metal-containing aqueous solution which typically falls in the range of about 0.001 M - 0.5 M. Currently, final cyanide concentrations in the range of about 0.1 M are employed. In order to prevent the loss of cyanide by hydrolysis or reaction with CO₂ and to neutralize the acidic components in the ore, a base, e.g., potassium hydroxide, is added to the cyanide solution.

Contacting of the optionally crushed metal-containing matrix with cyanide and oxidizer is carried out under conditions suitable to allow solubilization of substantially all the metal contained in the matrix. Once the gold is leached into the cyanide solution, it is treated with an oxidizer (e.g., Ηβ^) and hydrochloric acid. The oxidizer oxidizes gold from +1 to +3 valence state. The function of hydrochloric acid is two-fold: one is to destroy cyanide, the other is to provide a chloride ligand to the Au³⁺ ions. After this step, gold is in the form of AuCV which is appropriate for the next interference removal step by the use of crown ether polymer. AuCl complex molecules can be trapped into the cavities of the crown ether polymers in the HCI concentration of 0.1-6 M. By selecting 0.6 M HCI concentration, for example, AuCl ^~ is adsorbed by the polymer, letting most other metal species pass by.

A key element of this invention is the discovery that the crown ether polymer available from all commercial sources must be pretreated in order to obtain consistent recovery of the gold complex, especially when the sample gold concentration is below about 1000 ppb. The variation in gold recovery percentage is caused by adsorption sites of other than the gold complex dimension that would trap Au complex molecules but not release them at a later stage. The pretreatment invention requires filling the crown ether polymer with some metal species (e.g. , Ga, As, Fe, Au) that fill the adsorption sites, and then extracting most of the metal species out of the cavities leaving the "bad sites" that are filled. This treatment gives about 40% improvement in consistency of recovering gold complex concentration in the range of 100 ppb.

Any crown ether polymer capable of complexing with the metal to be assayed is contemplated for use in the practice of the present invention. Exemplary crown ether polymers include poly(dibenzo-18-crown-6) [poly(DB18C6)], and the like. The amount of crown ether polymer employed is in the range of about 20-100 mg/ml of metal-containing solution.

The crown ether polymer bound-metal material is then separated from the remaining components of the solution. This separation can readily be carried out by removal of the liquid from the particulate material using standard techniques such as decantation, filtration, aspiration or the like. It is preferred, to insure removal of substantially all extraneous species, to then wash the particulate material with 0.6 M HCI. It is preferred that the crown ether polymer separation be used in the column form. This is because the time to perform the separation is reduced dramatically when the column form is used from what would be required if other separation techniques, e.g., tumbling, were employed. For example, the crown ether separation may take 2V_ hours when tumbling is used, but may only require 30 minutes when the column form is used.

Once the gold-crown ether complexes have been separated from the remaining components of the metal-containing solution, the gold ions are recovered from the complex. This is done, for example, by extracting the ions from the complex with a polar oxygen-containing organic solvent such as alcohol, ketone, etc. Acetone (a ketone) is preferred.

When the gold ions have been recovered apart from the crown ether, the organic extractant is driven off of the sample by gentle heating in the presence of an oxidizer (e.g. H₂0₂) to prevent Au-reduction, and the material is contacted with a label means. As employed herein, "label means" refers to a chemical species which is capable of binding to AuCV, and which is also capable of ready analysis. Exemplary label means include chromophores, metal-complexing agents which are capable of fluorescing when excited with incident light of proper wavelength, and the like.

Exemplary label means include I_ιc amine B (i.e., N-(9-(2- carboxyphenyl)-6-(diethylamine)-3H-xanthen-3-ylidene)-N-ethyl ethanaminium chloride; also known as tetraethyl rhodamine), Brilliant Green,

PQPP (i.e., 2-phenylbenzo-[8,9]-quinolizino[4,5,6,7-fed]phenanthridinylium cation), and the like. Rhodamine B is the presently preferred label means because it gives very low levels of background fluorescence when gold concentrations are determined.

Substantial binding between AuCV and the dye is obtained by vortexing the mixture for a few seconds at room temperature. Following such treatment, it is desirable to separate substantially all unbound label means from the sample so as to reduce background noise in the invention analytical method. Such removal can be carried out, for example, by extraction of the label means-metal complex with an organic solvent (e.g. CβHβ, ether, preferably diisopropyl ether) from the aqueous media in which the complex is generated.

The above-described removal of unbound label means should be done with care so that substantial quantities of unbound label means do not remain in the sample to be analyzed.

Once sample preparation has been completed, it is desirable to analyze the sample relatively promptly so that the opportunity for sample degradation is niinirnized. A sample thus prepared is ready for analysis of the gold content therein. Metal analysis in accordance with the present invention is accomplished by determining the amount of label means incorporated by the sample. Where the label means is capable of emitting fluorescent radiation upon excitation, analysis can be accomplished by exciting the label means at a specified wavelength, then measuring the intensity of the emissions at a specified wavelength different from the wavelength used for excitation. Various means for carrying out such analysis employs novel instrumentation apparatus described hereinbelow. Alternatively, where the label means is a chromophore, analysis can be accomplished by spectrophotometric means, i.e., by measuring the amount of radiation absorbed by the sample when radiation of known intensity is passed through the sample. A first embodiment of the apparatus of the present invention facilitates the practice of the above-described assay method by providing portable fluorometer instrumentation apparatus that allows the assay method to be quickly carried out_.in the field at or near the location of the soil or rock samples being assayed for the presence of gold. A block diagram illustrating the basic components of fluorometer apparatus 10 made in accordance with the invention is shown in FIG. 1. These basic components include a source of radiant energy 14, a dichroic mirror 16, a fiber optic bundle 18, and a detector 20. A second detector 15 may also be employed. The dichroic mirror 16 is positioned so as to direct radiant energy generated by the source 14 into the fiber optic bundle 18. The detector 20 is positioned relative to the dichroic mirror 16 so as to receive radiant energy emitted from the fiber optic bundle 18. The detector 15 is positioned to receive radiant energy generated by the source in order to detect variations in the intensity thereof that occur over time. Such variations, if not corrected, could introduce an error in the measurements made by the apparatus.

A sample complex 12, comprising a suitable label means, such as Rhodamine B, to which a desired element, such as gold (when present) has been bound, is prepared as described above in connection with the method of the present invention. When the complex 12 contains gold, the gold-Rhodamine B complex fluoresces in the spectral region of 560 to 580 nanometers (nm) when excited by radiant energy (light) in the spectral region of 540 to 550 nm. When gold-containing complex 12 is a gold-PQPP complex, exaltation in the range of about 300 nm leads to fluorescence in the spectral region of about 460 nm. Advantageously, the amount of emitted fluorescence is a monotonically increasing function of the gold concentration in the complex.

To determine the concentration of gold in a given sample complex 12, the fluorometer instrumentation apparatus 10 operates as follows: The source of radiant energy 14 generates radiation of a first wavelength λ where λ, for the gold- Rhodamine B complex falls within the range of 540 to 550 nm (about 300 nm for gold-PQPP). This radiation is directed into the fiber optic bundle 18 using the dichroic mirror 16, and is also directed into the detector 15. The sample complex, in response to the λ, radiation, fluoresces radiation of a second wavelength λ , where λ₂ (for the gold-Rhodamine B complex) falls within the range of 560 to 580 nm (about 460 nm for gold-PQPP complex). The λ₂ radiation is directed from the sample complex 12 through the fiber optic bundle 18, through the dichroic mirror 16 and to the detector 20. The detector 20 is configured to detect the amount of radiation of wavelength λ₂. This detection thus provides a direct measure of the gold concentration within the sample complex 12.

The output intensity of the source 14 will vary to some degree during the measurement of a group of references and samples. In order to mirtimize the error due to source intensity variation, the detector 15 allows the source intensity to be monitored so that appropriate corrections in the determination of the gold concentration can be made, as described below.

Fiber optic bundles are widely available, and can be constructed of a variety of materials, including silica, glass, polymethyl methacrylate, polycarbonate, polystyrene, and the like. Commercially available fiber optic bundles can be used as received, without the need for any special treatment and/or preparation prior to use. Typically, the only modification made is to remove the cladding from the bundle from that part of the bundle which will be directly exposed to sample.

The primary considerations in selecting a particular fiber optic bundle are the stability of the probe material when exposed to the solvent system containing the metal to be analyzed, and the degree, if any, to which the probe material and sample components are prone to interact, thereby introducing interference into the analysis. Where unstable signal is observed, it is advisable to consider the use of a different fiber optic bundle, a different solvent system for the analytes, and or a different label means to overcome the problem. Referring next to FIG. 2, a more detailed block diagram of one embodiment of fluorometer instrumentation apparatus made in accordance with the present invention is shown. (It is noted that like numerals are used to represent like parts in FIG. 2 and FIG. 1). As seen in FIG. 2, the apparatus includes the same basic components shown in FIG. 1, i.e., a source of radiant energy 14, a dichroic mirror 16, a fiber optic bundle 18, a detector 20, and a second detector 15. As with FIG. 1, the fiber optic bundle 18 directs radiation to and from the sample complex 12 under test. As shown in FIG. 2, the source of radiant energy 14 comprises a power supply 22 coupled to a broad band light source 24. The light generated by the broad band light source 24 is directed through a suitable optical system 27 to a filter 30. The optical system 27 includes any suitable means for efficiently coupling the radiant energy from the broad band light source 24 to the filter 30. The filter 30 is a narrow band filter and filters out all of energy except that of the desired wavelength λt. (It is to be understood that X, may comprise a narrow band of wavelengths as well as a single wavelength, depending upon the bandwidth of the filter 30.)

As shown in FIG. 2, the optical system 27 includes a fiber optic coupler 26 having one end optically coupled to the light source 24 and the other end at the focal point of a lens 28. Radiant energy from the light source 24 is thus directed through the fiber optic coupler 26 to the lens, where it is directed to the filter

30.

After passing through the filter 30, only a narrow band of radiant energy remains, e.g, of wavelength λ,. The λ, radiant energy is optically reflected from the dichroic mirror 16 to an additional lens 32 so as to be directed or focused into the fiber optic bundle 18.

Still referring to FIG. 2, fluoresced light from the complex sample 12 is emitted from the fiber optic bundle 18 and is focused through the lens 32 back to the dichroic mirror 16. This fluoresced light passes through the mirror 16 to the detector 20. The detector 20 includes a narrow band filter 34 configured to pass only radiation having a wavelength λ₂. (It is to be understood that λ₂ may comprise a narrow band of wavelengths, as well as a single wavelength.) That is, radiation or light of wavelengths other than λ₂ is significantly attenuated by the filter 34. Hence, if the radiation fluoresced from the complex sample 12 includes the desired element, e.g., gold, it will fall within the wavelength band λ₂, and such radiation will pass through the filter 34.

After passing through the narrow band filter 34, the radiation is directed or focused through a second lens 36 to a photodetector 38. The photodetector 38 operates in conventional manner and detects the amount of radiation incident thereon. Thus, any radiation of wavelength λ₂ that makes its way through the filter 34 is detected by the photodetector 38. In response to such detection, the photodetector 38 generates an electrical signal. The amplitude of this signal is proportional to the intensity of the detected radiation. The electrical signal generated by the photodetector is amplified by amplifier 40. The output signal of the amplifier 40 may then be monitored to determine how much, if any, radiation or light of wavelength λ₂ was detected by the photodetector 38. A large output signal indicates λ₂ radiation of a high intensity, which in turn indicates a high concentration of the particular element within the complex sample (assuming a uniform volume of the sample). Similarly, a small output signal indicates λ₂ radiation of a low intensity, which in turn indicates a low concentration of the particular element within a uniform volume of the sample complex. Advantageously, as explained more fully below in connection with FIG. 4, the output signal from the amplifier 40 may be calibrated to provide a direct measure (indicated, e.g., in parts per billion, or ppb) of the concentration of the element within the sample complex.

As seen in FIG. 2, the output signal from the amplifier 40 is measured with a digital voltmeter (DVM) 42. Further, as desired, this output voltage may be recorded and/or stored in a data logger 44, or equivalent device. Moreover, for some applications, it may be desirable to couple a suitable processor 46, such as a portable personal computer (PC), to the output voltage of the amplifier 40. Such coupling may be accomplished directly from the output signal of the amplifier 40 if the processor 46 includes internal analog-to-digital (A/D) conversion means (for converting the analog output signal from the amplifier 40 to a digital signal suitable for use with the PC); or, alternatively, if the DVM 42 includes a digital output port, as many commercially available DVM's do, the coupling may be made from the DVM 42 to the processor 46.

The processor 46, when used, performs various processing functions associated with the amplifier output signal. For example, the processor may include a "look-up table" or equivalent (e.g., an equation) that is stored therein that allows the measured output voltage of the amplifier 40 to be converted directly to a concentration value of the desired element. Further, the processor may include various digital processing steps that analyze the output voltage data obtained from the amplifier 40 over a specified period of time in order to further enhance such data, e.g., by removing noise therefrom using conventional digital filtering techniques. Still referring to FIG. 2, it is seen that the detector 15 is positioned to sense the incident radiation of wavelength λ, generated by the source 14. Such radiation is directed through a suitable lens 29 to a photodetector 39. The photodetector 39 operates in conventional manner and detects the amount of radiation incident thereon. Thus, any radiation of wavelength λ, from the source 14 that makes its way through the filter 30 is detected by the photodetector 39. Additional filters, positioned in front of the lens 29, for filtering out all radiation except that of wavelength λj may also be used, as required. In response to detection of the \_t radiation, the photodetector 39 generates an electrical signal. The amplitude of this signal is proportional to the intensity of the detected radiation. The electrical signal generated by the photodetector is amplified by amplifier 41. The output signal of the amplifier 41 is then monitored to determine how much radiation or light of wavelength was detected by the photodetector 39. A large output signal indicates λj radiation of a high intensity. Similarly, a small output signal indicates λ, radiation of a low intensity.

The output signal from the amplifier 41 is measured with a digital voltmeter (DVM) 43. Further, if desired, this output voltage may be recorded and/or stored in a data logger 45, or equivalent device. Moreover, for most applications, it is adequate to couple the output of the amplifier 41 directly to the processor 46, such as a portable personal computer (PC). Such output signal may then be used to provide a reference signal that indicates variations that may have occurred in the intensity of the λi radiation.

In operation, the detector 15 thus monitors the intensity of the λ, source. When an initial sample is measured, the measured intensity thus represents a reference signal, S_Ref. For subsequent measurements, the intensity of the λ₂ fluoresced signal is another signal, S_F. Advantageously, the signal S_F may be corrected for variations that may have occured in the intensity of the λ, source as follows:

Scorr ⁼ (Sp ^• S_Ref)/S_λl where Sc_~- represents the correction of the signal S_F, and S_λ, represents the current intensity measurement of the source 14 as made by the detector 15. Advantageously, by storing the signal S_Ref in the processor 46, or equivalent device, the described correction can be made by the processor for each measurement made.

An additional embodiment of the detector 20 may include a plurality of filter-photodetector-amplifier sets, each adapted to sense radiation of a particular wavelength. The output signals from all of such sets may then be monitored, e.g., using the processor 46, to provide an overall assay report of the contents of the sample complex, including an indication of the concentrations of a plurality of elements within the sample complex.

As an alternative embodiment of the source of radiant energy 14, a conventional laser may be used, e.g, a He-Ne laser that provides an output wavelength of 543.5 nm. The narrow output of such He-Ne laser may be coupled through any suitable means directly into the fiber optic bundle 18, with a small portion thereof being coupled directly into the detector 15. Typically, such coupling will utilize at least the dichroic mirror 16 and the lens 32, thereby allowing the laser to be positioned off axis from the fluoresced radiant energy traveling out from the complex sample 12.

FIG. 3 is a graph illustrating the transmission properties through the two filters 30 and 34 used within the apparatus of FIG. 2. These transmission properties are selected for the detection of gold as a gold-Rhodamine B complex. It is to be understood, of course, that similar properties may be selected for the detection of other gold complexes. A first peak or band 70 is centered approximately at 545 nm. This peak or band 70 represents the desired transmission properties of the filter 30 coupled to the broad band energy source 24. A second peak or band 72 is centered approximately at 580 nm. This peak or band 72 thus represents the desired transmission properties of the filter 34 placed prior to the photodetector 38. If a He-Ne laser is used in place of the broad band energy source 24, the wavelength of the He-Ne laser is 543.5 nm, which is roughly centered in the desired peak or band 70.

If other complexes are being detected, the location of the band 70 and the band 72 would be selected accordingly. For example, if a given complex were to fluoresce radiation having a wavelength of 590 nm in response to being irradiated with radiation having a wavelength of 520 nm, then the first band 70 would be centered at 520 nm, and the second band 72 would be centered at 590 nm.

Referring next to FIG. 4, there is shown a representative calibration graph used with or by the apparatus of FIG. 2 in order to convert the measured intensity of the fluoresced light to a measure of gold concentration. It is to be noted that equivalent calibration techniques, such as using a look-up table, or an equation, may also be used to convert measured intensity to gold concentration. The graph of FIG. 4, or equivalent table or equation, is generated by measuring the fluorescent signal amplitude for a series of samples of uniform volume containing known concentrations of gold. That which is shown in FIG. 4 is only a portion of the overall calibration curve that can be obtained. In general, good calibration data is obtained using the fluorometer apparatus of the invention over a wide dynamic range, e.g., of from 10 ppb to 3,000 ppb. Moreover, with a system response time on the order of one second, the fluorometer apparatus is able to measure concentration differences on the order of 1 ppb. The accuracy of the combined chemical and optical method from the original samples is approximately ±15%.

Advantageously, the use of the fiber optic bundle 18 avoids a measurement problem, known as the "inner filter effect," common in spectro- fluorometers of the prior art. This problem results in the amount of emitted fluorescent light reaching a peak level at low metal concentrations, and thereafter decreasing with increasing metal concentration. This "inner filter effect" thus results in a double-valued output and ambiguous readings over the range of metal concentration of interest. See, for example, Yuan et al., "Calculation for Fluorescence Modulation by Absorbing Species and Its Application to Measurements Using Optical Fibers," Analytical Chemistry. Vol. 59, No. 19, 2391-94 (October 1, 1987).

With reference to FIG. 2, it is noted that the light source 24 may be realized with a Xenon Arc (ILC No. 131), an incandescent lamp, such as the Gilway Technical Lamp No. L7394, or a Helium-Neon laser (No. LSGR-0150M, obtained from Particle Measuring Systems (PMS)). As indicated below, the He-Ne is preferred, but the other sources may also be used. The light source 24 is positioned at the focal point of the lens 28, which may be an aspheric lens No. 06-3097, available from Spindler & Hoyer. Alternatively, the light may be transmitted to the focal point of the lens 28 by the fiber optic bundle 26. If used, the fiber optic bundle 26 may be realized using 1000 micron diameter fibers available from, e.g., Ensign- Bickford. The collimated (focused) beam from the light source 28 is transmitted through the filter 30, which may be obtained from Omega Optical Inc., as Part No. 546BP10. The dichroic mirror 16 may also be obtained from Omega Optical Inc. as Part No. 440 DES P. The lens 32 focuses the light onto the end of the fiber optic bundle 18. This lens 32 may be realized with an aspheric lens, No. 06-3097, obtained from Spindler & Hoyer. The fiber optic bundle 18 is preferably comprised of 1000 micron diameter fibers obtained from, e.g., Ensign-Bickford. The filter 34, through which the fluoresced light is directed, may further be obtained from Omega Optical Inc as Part No. 577BP10. The lens 36 may be the same as the lens 32. The photodetector 38 may be any suitable photodetector, such as a photodiode detector, of which numerous types are commercially available, e.g., a silicon photodiode No S2386, manufactured by Hamamatsu.

The electrical signal from the photodiode detector is amplified by the amplifier 40. A low noise, low drift operational amplifier is preferable for this purpose. A Burr-Brown No. OPA128LM amplifier is well suited for this purpose. The amplified output from the amplifier 40 is preferably printed and stored using the data logger 44, which data logger may be obtained from Omega Engineering Inc as Part No. OM-550. The DVM 42 may be obtained from any suitable manufacturer. The components of the detector 15 may be the same as corresponding components of the detector 20. The particular selection of components described above in connection with HG. 2 advantageously permits the reading of exceptionally low values of fluoresced light by repressing noise. The preferred amplifier 40, for example, (Burr- Brown No. OPA128LM) has ultra-low bias current, very high signal-to-noise ratio and common-mode rejection, and thus allows extremely small signals (electrical currents) to be received from the photodetector 38, which small signals correspond to small sample values. The amplifier 40 converts such small signals to a relatively large output voltage. In addition to suppressing noise, it is important in the construction of the fluorometer apparatus to select optical components that provide large amounts of light energy and yet can function within a very narrow band without extraneous signals (which extraneous signals would be seen as noise). The preferred filters 30 and 34, the photodetector 38, the lenses 28 and 36, as well as the He-Ne laser (if used), as identified above, are all selected with these considerations in mind. For example, by utilizing a He-Ne laser as the radiant energy source 14 in FIG. 2 (in lieu of broadband light source 24) to generate a narrow band energy at 543.5 nm having an output power level of approximately 1.5 milliwatts, the photodetector 38 may respond to very low power incident radiation levels from test samples having extremely low amounts of the metal of interest. For this reason, the use of a He-Ne laser as the radiation source 14 is preferred over the use of a broad-band source, as shown in HG. 2.

In view of the very small signals and the necessity of low accompanying noise, the fluorometer apparatus of the present invention further utilizes appropriate shielding in the packaging of the components. Such shielding is necessary to avoid radiative and electrical interference, e.g., background radiation, and is especially needed in packaging the photodetector 38 and the amplifier 40. Such shielding thus includes a special enclosure 39 in which the photodetector 38, the operational amplifier 40, and related components (e.g., a source of electrical power for these components) are housed. The enclosure 39 may be made from any suitable metal, such as copper or aluminum, that prevents low level radiation from passing therethrough and that is a good electrical conductor.

In addition, in order to further reduce noise and extraneous signals, the size of the fiber optic bundle 18 should be selected for maximum delivery of the λ, and λ₂ signals with minimum noise. In the preferred embodiment, this requirement is met by utilizing fiber bundles having a diameter of about 1000 microns.

Advantageously, all of the components of the apparatus 10 are sufficiently small and lightweight so that they may be easily transported, e.g., in a trailer, truck, van, by backpack, or the like, thereby allowing the entire apparatus to be portable and easily transported to a field location where soil or rock samples are to be assayed. A second embodiment of the apparatus of the present invention facilitates the practice of the above-mentioned assay method by providing a combined portable fluorometer/transmissive instrumentation apparatus that, like the first embodiment, allows the assay method to be quickly carried out in the field or near the location of the soil or rock samples being assayed for the presence of gold. The second embodiment further improves upon the first embodiment by providing a fluorometer/transmissive instrumentation apparatus that detects a wide range of gold concentrations (e.g., from a few parts per billion (ppb) to about thirty-thousand ppb) without the use of a fiber-optic bundle. By etiminating the need for the fiber-optic bundle, various problems associated with positioning the fiber-optic bundle within the sample complex are eliminated. By combining a fluorometer instrumentation apparatus and a transmission measurement apparatus, a much wider range of desired element concentrations can be measured.

A block diagram of a combined fluorometer/transmissive instrumentation apparatus 11, made in accordance with the second embodiment of the invention is shown in HG. 5. As seen in HG. 5, the apparatus 11 includes a source of radiant energy 14, a source detector 15, a florescence detector 20, and a transmission detector 21. The florescence detector 20 is positioned relative to the sample 12 so as to receive radiant energy fluoresced from the source 14 by the sample 12. The source detector 15 is positioned relative to a suitable dichroic mirror 17 so as to receive a small portion of the radiation emitted by the source 14. The transmission detector is positioned relative to the source 14 so as to receive radiant energy transmitted through the sample 12.

It is noted that with optically dense solutions, for example, samples with high ppb of gold, the linear range of the fluorescence signal is limited. To increase this range, a light shield 13 with a narrow slit 19 is placed on the side of the cuvette that faces the fluorescence detector 20. This in effect, reduces the path length of the incident light and allows the fluorescence intensity to be proportional to the exciting light over an expanded range. As with the first embodiment, a sample complex 12 comprising a suitable label means to which gold (when present) has been bound, is prepared as described above in connection with the method of the present invention. When the complex 12 contains gold, the gold-complex fluoresces in the spectral range at about 577 nm and transmits radiant energy at 543.4 nm in response to a radiant energy source that emits radiation at 543.5 nm. At low gold concentrations (e.g., below 2000 ppb), the intensity of the fluoresced radiant energy is a monotonically increasing function of the gold concentration in the complex whereas at higher gold concentrations (e.g., above 2000 ppb), the intensity of the transmitted radiant energy is a monotonically decreasing function of the gold concentration in the complex.

To determine the gold concentration in the sample complex 12, the combined fluorometer/transmissive instrumentation apparatus 11 operates as follows: The source of radiant energy 14 generates radiation of a first wavelength λ,, where λi for the gold-Rhodamine B complex is about 543.5 nm. This radiation is directed into the sample 12. The sample complex, in response to the λ, radiation, fluoresces radiation of a second wavelength λ₂, where λ₂ for the gold-Rhodamine complex is about 577 nm. The λ₂ radiation is detected by the detector 20. The detector 20 is configured to detect the amount of radiation of wavelength λ₂. Additionally, the sample complex transmits the λ_! radiation. The transmitted radiation has been designated λ,' in FIG. 5 so as to distinguish it from the incident radiation λ, and so as to indicate that the transmitted radiation λ,' is of a lower intensity than the incident radiation λ,. However, the wavelengths of incident radiation λ_t and transmitted radiation X,' are the same. The λ,' radiation is detected by the detector 21. The λi radiation is detected by the detector 15. The detector 21 is configured to detect the amount of radiation of wavelength λ,\ The combined detections of λ₂ and λ,' thus provide a direct measure of the gold concentration within the sample complex 12. The detection of the incident radiation by the detector 15 allows a suitable correction to be made to the measurments made by the detectors 20 and 21 so as to correct for variations in the intensity of the source 14.

Referring next to FIG. 6, a more detailed block diagram of the second embodiment of the combined fluorometer/transmissive instrumentation apparatus 11 is shown. (It is noted that like numerals are used to represent like parts in HG. 6, HG. 5, HG. 2, and HG. 1). As seen in HG. 6, the apparatus includes the basic components shown in HG. 5, i.e., a source of radiant energy 14, a calibration detector 15, a fluorescence detector 20, and a transmission detector 21. As further shown in HG. 6, the source of radiant energy 14 comprises a power supply 22 coupled to a narrow band laser light source 25. Incident light generated by the laser 25 is directed through an electro stop or solenoid-controlled shutter 29. The electro shutter 29 is controlled by a solenoid 23 to be either open or closed. Operation of the solenoid in response to a programmed personal computer (PC) or equivalent processor 46, or other control means, is explained more fully below with respect to HGS. 7A and 7B. When the electro stop is open, the light generated by the laser is further directed through neutral density (ND) filter 31 and aperture 33 into the sample complex 12. The neutral density filter 31 reduces the intensity of the light generated by the laser 25 to an appropriate level,; and the aperture 33 is used to confine the light beam to the sample 12.

Also referring to HG. 6, the fluoresced light or radiation from the sample complex 12, generated in response to the incident light, passes to the fluorescence detector 20. The detector 20 includes a light shield 13 with a narrow slit 19 as described above in connection with HG. 5. The detector 20 further includes a first fluorescence band filter 35 configured to pass only radiation having a wavelength λ₂. In the preferred embodiment λ₂ is 577 nm. That is, radiation or light of wavelengths other than λ₂ is significantly attenuated by the filter 35. Hence, if the sample includes the desired element, e.g. gold, the radiation fluoresced from the complex sample 12 will fall within the wavelength band λ₂, and such radiation will pass through the filter 35.

After passing through the first band filter 35, the radiation passes through a second fluorescence band filter 37. The second fluorescence band filter 37 is also configured to pass only radiation having wavelength λ₂. Hence, the second fluorescence band filter functions in a manner similar to the first fluorescence band filter so as to further attenuate light of wavelengths other than wavelength λ₂ that passes through the first fluorescence band filter 35.

After passing through the second fluorescence band filter 37, the radiation is directed to a photodetector 38. The photodetector 38 operates in a conventional manner and detects the amount of radiation incident thereon. Thus, any radiation of wavelength λ₂ that makes its way through the first fluorescence band filter 35 and the second fluorescence band filter 37 is detected by the photodetector 38. In response to such detection, photodetector 38 generates an electrical signal wherein the amplitude of the signal is proportional to the intensity of the detected radiation. The electrical signal generated by photodetector 38 is amplified by amplifier 40. The output signal of the amplifier 40 may then be monitored to determine how much, if any, radiation or light of wavelength λ₂ was detected by the photodetector 38. A large output signal indicates λ₂ radiation of high intensity, which in turn indicates a high concentration of the particular element within the complex sample (assuming uniform volume of the sample). Similarly, a small output signal indicates radiation of low intensity, which in turn indicates a low concentration of the particular element within a uniform volume of the sample complex. Advantageously, as explained more fully below, the output signal may be calibrated to provide a direct measure (indicated, e.g., in parts per billion, or ppb) of the concentration of the element within the sample complex.

As seen in HG. 6, the output signal from the amplifier 40 may be measured with a digital voltmeter (DVM) 42. As desired, this output may be recorded or stored in a data logger 44, or equivalent device.

Still referring to HG. 6, any light that passes through the sample 12, referred to as "transmitted light", passes from the sample to the transmission detector 21. The transmission detector 21 includes an aperture 43 to collimate the transmitted light and direct it to a desired detection location. Further, the aperture helps minimize scattering into the detector from outside sources. Light entering through the aperture 43 is directed through a transmission band filter 45. The filter 45 is configured to pass only radiation having a wavelength of λi'. In the preferred embodiment, the filter 45 is centered at about 546 nm so as to readily pass transmitted radiation having a frequency of λ, (543.5 nm). That is, radiation or light of wavelengths other than λi' is significantly attenuated by the filter 45. Hence, the radiation fluoresced from the complex sample 12, which has wavelength λ₂, will be significantly attenuated and therefore have minimal effect on the transmission measurements made by the transmission detector 21. However, the radiation transmitted through the sample 12, which has wavelength λ,', will pass through the filter 45. The light passing through the filter 45 is directed through an ND filter 47, which ND filter 47 reduces the intensity of the light transmitted therethrough by a controlled amount.

After passing through the ND filter 47, the radiation is directed to a photodetector 48. The photodetector operates in a conventional manner and detects 5 the amount of radiation incident thereon. Thus, any radiation of wavelength λ that makes its way through the transmission filter 45 and the ND filter 47 is detected by the photodetector 48. In response to such detection, photodetector 48 generates an electrical signal wherein the amplitude of the signal is proportional to the intensity of the detected radiation. The electrical signal generated by photodetector 48 is 10 amplified by amplifier 50. The output signal of the amplifier 50 is then monitored to determine how much, if any, radiation or light of wavelength λ,' is detected by the photodetector 48. A decreasing signal indicates a high concentration of the particular element within the complex sample (assuming uniform volume of the sample). Similarly, a higher output signal indicates a lower concentration of the particular ^' 15 element within a uniform volume of the sample complex. Advantageously, the output signal may be calibrated to provide a direct measure (indicated, e.g., in parts per billion, or ppb) of the concentration of the element within the sample complex.

As seen in HG. 6, the output signal from the amplifier 50 may be measured with a digital voltmeter (DVM) 52. As desired, this output may be recorded 20 or stored in a data logger 44, or equivalent device.

It is noted that all of the elements shown in HG. 6, e.g., the photodetectors, amplifiers, DVM's, data loggers, laser source, etc., may be realized using the same types of devices and equipment as described previously in connection with HG. 2. 25 In the second embodiment, a personal computer (PC) 46, or equivalent processor, is coupled to the output of the amplifier 40 and the output of the amplifier 50. Such coupling may be direct if the computer 46 includes internal analog-to-digital (AID) conversion means (for converting the analog output signal from the amplifier 40 and the amplifier 50 to a digital signal suitable for use with the PC 46); or, 30 alternatively, if the DVM's 42 and 52 include a digital output port, as many commercially available DVM's do, the coupling may be made from the DVM's 42 and 52 to the processor 46. Further details associated with the operation of the embodiment shown in Fig. 6 may be found in Applicants' copending U.S. patent application Serial No. 07/769,531, filed October 1, 1991, incorporated herein by reference.

Advantageously, the signals received by the processor 46 from the amplifiers 40 and 50 are used to automatically calculate the concentration of the desired element, e.g. gold, present in the complex sample. As in the first embodiment, a calibration graph, such as that shown in HG. 4, can be generated (or mathematically expressed) by analyzing complex samples from known desired element concentrations, e.g. known gold concentrations. In accordance with the present invention, a first calibration curve is generated based on the fluorescence detector 20 output, and a second calibration curve is generated based on the transmission detector 21 output. (As used herein, the term "calibration curve" refers to any means, whether a mathematical equation, or equivalent, that relates one variable, i.e., the detector output, to another variable, i.e., the gold concentration.) The first calibration curve is generated, based on known complex sample concentrations, and may be mathematically expressed as:

K C = (1/α.,) x ln [ -] (1)

K - (S - So)

where C, is the gold concentration, S is the fluorescence detector output, is an intrinsic absorption constant for the material, £_t is the effective length of the cuvette, and K, and S₀ are constants. The constants are determined empirically using samples containing known concentrations of gold. Representative values of such constants are al, = .00035, K=0.755, and S₀=0.0045 (volts). Unfortunately, the ability of Eq.

(1) to accurately estimate the gold concentration is limited to a lower range of concentrations, e.g., about 0 ppb to 3,000 ppb.

If the range of concentrations is higher than this range, then the second calibration curve is used. The second calibration curve is also derived from known complex sample concentrations, and may be mathematically expressed as:

C = (Vat _j) x ln (T₀ / T) (2) where C is the gold concentration, T is the transmissive detector output, and l/α£₂ and T₀ are constants. Again, the constants are determined empirically using complex samples containing known concentrations of gold. Representative values of such constants are α£₂ ^~~ .0000751; and T₀ ^~~1.75 (volts). The ability of Eq. (2) to accurately approximate the second calibration curve is limited to a higher range of concentrations, e.g. 1,000 ppb to 25,000 ppb.

Hence, in operation, after the amplifier 40 output signal and the amplifier 50 output signal are generated, the processor 46 calculates a first concentration, based on the fluorescence formula, Eq. (1), and a second concentration, based on the transmission formula, Eq. (2). Because the range of accuracy for the fluorescence formula, equation (1) is limited to approximately 3000 ppb or less, equation (2) is used for concentrations in the range from 2000 ppb to approximately 30,000 ppb. In the overlap range between 2,000 to 3,000 ppb either equation may be used. In this way, this second embodiment provides a significant increase in the dynamic range over the first embodiment.

Advantageously, use of the source detector 15 allows the signals detected by the detectors 39 and 49 to be corrected for variations that occur in the intensity of the incident source 14. The mirror 17 functions as a beam splitter and directs a small portion of the incident radiation (e.g., approximately 4%) to the detector 15. An initial reading of the source intensity is represented as the signal S_Ref; a current reading of the source intensity is represented as a signal S_M; a current reading of the fluoresced radiation is represented as a signal S_F; and a current reading of the transmitted radiation is represented as a signal S_T. Both the fluorescence and transmission signals S_F and S_τ may then be corrected by utilizing the following relationships:

S_P(Corτ) = (S_F-S_Ref)/S_λl and S_τ(Corr) = (S_T«S_Ref)/S i .

A more detailed description of the steps taken by the processor 46 in calculating an accurate gold concentration is presented below with respect to HGS. 7A and 7B.

It is noted that the transmission properties of the filters 35, 37 and 45 used with the apparatus of HG. 6 are selected for the detection of gold as a gold- Rhodamine B complex in the same manner as used in connection with the filters 30 and 34 associated with the apparatus of FIG. 2. The filter 45 includes a first peak or band centered at approximately 546 nm. The filters 35 and 37 include a second peak or band centered at approximately 577 nm. The laser radiant energy source 25 provides radiant energy of approximate wavelength 543.5 nm, which is roughly centered in the peak or band of the filter 45.

Referring next to HGS. 7A and 7B, a flow diagram is shown that illustrates the manual and programmed steps used to measure the concentration of the desired element within the sample 12 using the fluorometer/transmissive instrumentation apparatus of the second embodiment. Each main step of the method shown in FIGS. 7A and 7B is depicted as a "block". It is submitted that those skilled in the art can readily perform the steps shown in HGS. 7A and 7B (if manual) or write an appropriate program or code for use by the processor 46 (if automatic).

Referring then to HG. 7A, block 110 represents the preparation, as described above in connection with the method of the present invention, of the sample complex 12, including contacting the prepared material with a suitable label means to which gold, when present, has been bound. After preparing the desired element- label means complex, e.g., gold-Rhodamine B complex, the solution is transferred into a cuvette, or transparent container, through which the sample solution can be irradiated. Further, during the reading of hte initial reference sample, a measurement is made of the intensity of the radiation source 14 in order to obtain the signal S^, as described above.

After applying power to the apparatus 11, the processor 46 monitors a switch 60 (FIG. 6). The switch 60 assumes an open position or a closed position responsive to the opening or closing of a door to a test chamber that holds the cuvette containing the sample 12 while the sample 12 is tested for the desired-element concentration. Alternatively, other manual or automatic means for detecting whether the cuvette has been put in the test chamber and/or the test chamber door has been closed may be used, e.g., using optoelectronic sensors, load cells or by displaying a message and requesting operator confirmation that the cuvette is in place and the test chamber door is closed. Thus, as soon as possible after applying power to the apparatus 11 (e.g., after a suitable warmup period), the switch 60 or the other detection means detects whether the test chamber is empty or whether the test chamber door is open. Responsive to the "open" or "empty" detection, the processor 46, under the control of a suitable control program, signals the operator to put a cuvette containing a known concentration of desired element-label means complex into the test chamber. Such signalling is achieved by displaying a message on a CRT display terminal, or by using other signalling means, e.g. lights or audible alarms. Block 120 of HG. 7A represents the signalling of the operator to place the cuvette in the test chamber and to close the test chamber door.

Upon detecting that the cuvette is in the test chamber, as represented by block 130, the processor 46, responsive to the control program, activates solenoid 23 which opens electro shutter 29 (HG. 6) thereby directing radiant energy into the sample-containing cuvette as explained hereinabove. After a sufficient delay to allow transient responses to dissipate, as represented by block 150, a measurement is made of the intensity of the radiation source 14 is made in order to obtain the signal S^ (block 152), as described above. Next, the source intensity is checked to obtain the signal S_M (block 154), the output of the fluorescence detector 20 is read to obtain the fluorescence signal S_F (block 160), the output of the t__msmission detector 21 is read to obtain the transmissive signal S_T (block 170), and such signals (which are read as output voltages) are then corrected as required (block 172). (As mentioned above, the recordation of the output voltages may be achieved via analog-to-digital conversion means coupled to the PC 46 or by the digital output ports of the DVM's 42 and 52.) After recording the output voltages generated in response to the known- desired-element-concentration sample, the electro shutter 29 is closed. If sufficient known samples have been measured, the processor 46 uses the voltages to mathematically calculate values for the above mentioned constants, i.e., l/ctt _ϊt K, S₀, and T₀. This calculation is represented by block 190. In the preferred embodiment, the steps indicated at blocks 120, 130,

140, 150, 152, 154 160, 170, 172 and 180 are repeated or iterated 12 times, thereby achieving highly accurate approximated constants, as indicated at block 190. In this way the apparatus 11 is calibrated to measure unknown desired element concentrations.

Next, as represented by block 200, the processor or PC 46 signals the operator to put the cuvette containing the unknown concentration of desired element- label means in the test chamber. The operator then places the cuvette containing the unknown sample into the test chamber. After sensing that the cuvette is in place and that the test chamber door is closed, represented by block 210, that the cuvette is in place and that the test chamber door is closed, the processor 46 (as controlled by the control program) activates solenoid 23 which opens the electro stop 29, thereby directing radiant energy into the cuvette containing the sample 12. The opening of the electro stop is represented by block 220. After a sufficient time delay to allow transient responses to dissipate, as represented by block 230, the processor 46 reads and stores the output voltage or signal S_λl from the source detector 15, the output voltage or signal S_F from the fluorescence detector 20, and the output voltage or signal S_τ from the transmission detector 21, after which the electro stop is closed. Such reading and storing is represented by blocks 232, 240 and 250 in HG. 7B.

After reading the output voltages of the source detector 15, the fluorescence detector 20, and the transmission detector 21, the processor 46 corrects such readings for any variations that may have occurred in the intensity of the source radiation using the above-described correction method. Such correction is represented by block 252. Next, the processor calculates the desired element concentration using the above-mentioned formulas, Eqs. (1) and (2), or uses other means for approximating the desired element concentration based on the amplifier output voltages. That is, the processor 46 calculates a first concentration based on the fluorescence detector output, and a second concentration based on the transmission detector output. The processor 46 then compares the first and second concentrations with a reference value as mentioned above. The reference value is selected to be a desired element concentration in the overlap range or in the range of accuracy for both the fluorescence formula and the transmission formula. If the concentrations are below the reference value, the first concentration, based on the fluorescence detector output, is used or selected as an indication of the concentration. If the concentrations are above the reference value, the second concentration, based on the transmission detector output, is used or selected as an indication of the concentration. The selection of the appropriate concentration is represented by block 260. In this way, the more accurate concentration is used as an indication of the gold (or other metal) concentration. The appropriate equation is then used to calculate the concentration 5 (block 270). This selected concentration is then displayed by the processor 46 (block 280) and/or suitably recorded by the processor 46.

Finally, the processor 46 signals the operator to indicate whether additional unknown-desired-element-concentration samples to be tested (block 280) If the operator indicates that additional samples are to be tested, the steps represented 10 by blocks 200, 210, 220, 230, 232, 240, 250, 252, 260, 270 and 275 are repeated or iterated. Such repetition continues until the operator indicates that there are no more samples to be tested. In this way, multiple unknown samples can be accurately tested for desired element concentrations, and the most accurate detection means, i.e. fluorescence detection or transmission detection, can be utilized in response to a ^* 15 programmable controlled processor 46.

Advantageously, all of the components of the preferred embodiment 11 are sufficiently small and light weight so that they may be easily transported, e.g., in a trailer, truck, van, by backpack or the like, thereby allowing the entire apparatus to be portable and easily transported to a field location where soil or rock samples are 20 to be assayed. Further, the second embodiment advantageously eUminates the need for the fiber optic bundle, thereby eliminating the problems associated with the use of a fiber optic bundle, e.g., cracking, while providing a larger overall range of accuracy by using both a fluorescence detector 20 and a transmission detector 21. Hence, by using the second embodiment, the advantages of the first embodiment and 25 other advantages are maximized and the disadvantages of the first embodiment are minimized.

In one embodiment of the invention, a small and light weight device is provided that is adapted for transport in a back pack. Such small, portable unit (hereafter the "back-pack unit") is thus readily carried to a desired field location 30 where the sample analysis is to be performed. Advantageously, such back-pack unit is battery powered, thereby allowing the analysis to be carried out at remote locations where other power sources are not readily available. In order to conserve the limited energy available from the battery of the back-pack unit, a flashlamp is used as the source of radiant energy 14 (FIG. 5) rather than a laser. The flashlamp provides a very short pulse or "flash" of intense radiation, similar to the flash provided from a flash camera. Such pulse or flash of radiation is then optically filtered, as needed, in order to significantly attenuate all wavelengths except the wavelength of interest, λ,. (It is noted, of course, that even a laser may be pulsed.)

As described above in connection with HGS. 5 and 6, the back-pack unit also employs three separate sensors or detectors. A first sensor detects the intensity of the radiation from the source 14 (λ, detector 15). A second sensor detects the intensity of the radiation that fluoresces from the sample (λ₂ detector 20). A third sensor detects the intensity of the radiation transmitted through the sample (λι detector 21). Because the intensity of the source 14 from a typical flashlamp varies a great deal from flash to flash, the use of the λ, detector 15 to detect the intensity of the λj radiation at the source, thereby allowing the readings at the λj transmissive detector 21 and the λ₂ fluoresced detector 20 to be corrected for such variations as described above, becomes extremely important to the successful operation of the back-pack unit.

A typical flashlamp that may be used with the back-pack unit is the XLS-542 flashlamp, available from Xenon Corp. of Wobum, Massachusetts. The weight of the back-pack unit is less than about four (4) kg (8 lbs.); and its approximate volume, including battery, is no more than about 16000 cm³ (1000 in³). The flashlamp is powered using a conventional power supply that steps up the voltage from the battery (e.g., 9 volts) to a suitable flashlamp operating voltage (e.g., 600 volts). Advantageously, the sensors 15, 20 and 21 consume very little power, and the PC (computer) 46, when used, may be of a laptop or notebook size, which computers are already made for portability.

The invention will now be described in greater detail by reference to the following non-limiting examples. EXAMPLES The general procedure followed for each of the analyses described below is as follows:

Samples are prepared carefully to obtain representative ore samples. The ore samples are roasted under oxidizing atmosphere in the temperature range of 600-800°C for about one hour. Gold (Au) is leached out by turribling the ore in potassium cyanide/potassium hydroxide solution in the presence of hydrogen peroxide. The cyanide extract is then acidified with hydrochloric acid in the presence of hydrogen peroxide at about 90°C. The resulted AuCl₄ ^" complex is removed from interference ions by tumbling with pretreated poly(dibenzo 18-crown-6) beads in 0.6 M HCL The polymer beads selectively trap AuCI ^~ complex leaving the interference ions in HCL After several washes, AuCV is recovered by tumbling the AuCV loaded beads with acetone, the acetone is further evaporated in the presence of H^ leaving AuCV in HCL The AuClf is labelled with Rhodamine B dye. The AuCV- dye complex is further extracted into diisopropylether, and the fluorescence transmittance of the complex is measured.

Example 1:

To explore the range of the signal obtained with the invention apparatus and method when the amount of gold is increased, a range of gold concentrations were studied (0, 100, 2000, and 20000 ppb of gold). The results in millivolts response per sample, are set forth below in Table 1.

The results of Table 1 are plotted in Figure 4, which reveals a smooth non-linear response over a wide range of concentrations.

These results demonstrate that the invention method and apparatus are useful over a wide concentration range.

Example 2:

The invention technique was employed to estimate the amount of gold present in two rock samples; these sample were designated samples "A" /and "B", and were independently determined by fire assay analysis to contain about 1325 and 1660 ppb of gold, respectively. The signals obtained for 0, 500, 1000, 2000, and

4000 ppb of gold were 0, 410, 770, 1430, and 2080 millivolts, respectively. When plotted, these values give a smooth non-linear response over the entire concentration range evaluated.

The fluorescent signals for samples "A" and "B" were 970 and 1120 MV (after subtracting the values for a zero control sample), corresponding to about

1325 and about 1660 ppb of gold, respectively.

Example 3:

The fluorescent/transmissive apparatus described above in connection with HGS. 5, 6, 7A and 7B was employed to measure the gold concentration of four test samples, labeled "1", "2", "3" and "4", having ppb gold concentrations of 0, 100, 2000 and 20000, respectively. The results obtained are summarized below in Table 2.

TABLE 2

CALCULATED PPB OF TEST SAMPLES FROM THEIR MEASURED READINGS

MITTANCE (VOLTS)

CALCULATED CURVE CONSTANTS

c.£, K al₂ ^so T₀

0.000493 0.636 7.41E-05 0.00346 1.711

GOLD CALCULATIONS OBTAINED USING EQUATIONS (1) AND (2)

TEST SAMPLE GOLD(PPB) S(VOLTS) T(VOLTS) CAL GOLD(PPB)

The invention method and apparatus are seen to rapidly provide results which agree quite well with values obtained by traditional analytical means. While the invention herein disclosed has been described by means of specific embodiments and applications thereof, numerous modifications and variations could be made thereto by those skilled in the art without departing from the spirit and scope of the invention set forth in the claims.

Claims

CLAIMSWhat is claimed is:

1. Instrumentation apparatus for measuring the concentration of an element in a sample solution placed in a cuvette, comprising: means for irradiating said sample solution with radiant energy within a first band of wavelengths; first detection means for detecting fluoresced radiant energy within a second band of wavelengths that is fluoresced from the sample solution as a result of said irradiation, said second band of wavelengths not including any wavelengths within said first band of wavelengths; second detection means for detecting transmitted radiant energy within said first band of wavelengths that is transmitted through said sample solution as a result of said irradiation; and processing means responsive to said first and second detection means for determining the concentration of a prescribed element within said sample solution.

2. The instrumentation apparatus as set forth in Claim 1 further including third detection means for detecting the intensity of the radiant energy within said first band of wavelengths; and wherein said processing means includes means for correcting the detected radiant energy of said first and second detection means to account for variations in the intensity of the radiant energy detected by said third detection means.

3. The instrumentation apparatus as set forth in Claims 1 or 2 wherein said means for irradiating comprises a laser source that generates laser energy within a band of wavelengths centered about 544 nm, and wherein said first detection means comprises, means for detecting radiant energy within a band of wavelengths centered about 577 nm.

4. The instrumentation apparatus as set forth in Claim 3 wherein said first detection means includes first filter means for blocking radiant energy not within said first band of wavelengths; and a first photodetector optically coupled to receive radiation passing through said first filter means, said first photodetector generating a first output signal representative of the intensity of the radiation received by said photodetector.

5. The instrumentation apparatus as set forth in Claim 4 wherein said second detection means includes second filter means for blocking radiant energy not within said second band of wavelengths; and a second photodetector optically coupled to receive radiation passing through said second filter means, said second photodetector generating a second output signal representative of the intensity of the radiation received by said photodetector.

6. The instrumentation apparatus as set forth in Claim 5 wherein said processing means includes: means for measuring a first concentration of said element within said sample solution as a function of said first output signal; means for measuring a second concentration of said element within said sample solution as a function of said second output signal; and means for selecting either said first or second concentration measure as the best measure of the concentration of said element within said sample solution.

7. The instrumentation apparatus as set forth in Claim 6 wherein said means for measuring said first concentration includes means for computing 1 K C, = x ln [ ] αl K - (S - So)

where C, is the estimate of the first concentration, S is said first output signal, and

K, αl and S₀ are constants.

8. The instrumentation apparatus as set forth in Claim 6 wherein said means for measuring said second concentration includes means for computing

C₂ = (1/αl) x ln (To / T)

where C₂ is the estimate of the second concentration, T is said second output signal, and T₀ and al are constants.

9. Apparatus for optically analyzing a sample solution comprising: means for irradiating said sample solution with radiant energy of a first wavelength; means for measuring the amount of radiant energy having said first wavelength that is transmitted through said sample solution; and means for measuring the amount of radiant energy that fluoresces from said sample solution at a second wavelength as a result of said radiant energy of said first wavelength; the amount of radiant energy transmitted through said sample solution and the amount of radiant energy fluoresced from said sample solution each providing a measure of the concentration of a prescribed element within said sample solution.

10. The apparatus as set forth in Claim 9 further including means for correcting the measured amounts of radiant energy transmitted through and flouresced from the sample solution as a function of variations in the intensity of the radiant energy that irradiates the sample solution.

11. The apparatus as set forth in Claim 9 further including processing means for automatically analyzing said transmitted radiant energy and said fluoresced radiant energy and determining which of said two measurements represents the most accurate representation of the concentration of the prescribed element within said sample solution.

12. A method of measuring the concentration of an element in a sample solution comprising:

(a) irradiating said sample solution with incident radiant energy within a first band of wavelengths;

(b) detecting fluoresced radiant energy within a second band of wavelengths that is fluoresced from the sample solution as a result of said irradiation, said second band of wavelengths not including any wavelengths within said first band of wavelengths;

(c) detecting transmitted radiant energy within said first band of wavelengths that is transmitted through said sample solution as a result of said irradiation;

(d) determining a first measurement of the concentration of a prescribed element within said sample solution based on the detected fluoresced radiant energy, and determining a second measurement of the concentration of said prescribed element within said sample solution based on the detected transmitted radiation; and

(e) selecting said first or second measurement as the best measurement of the concentration of said prescribed element within said sample solution.

13. The method as set forth in Claim 12 wherein step (e) of selecting the first or second estimate as the best estimate of the concentration of said prescribed element comprises comparing the first and second measurements to a reference value, selecting the first measurement as the best measurement if the first and second measurements are less than said reference value, and selecting the second measurement as the best measurement if the first and second measurements are greater than said reference value.

14. The method as set forth in Claim 13 further including correcting the detected fluoresced radiant energy and the detected transmitted radiant energy to account for variations in the intensity of the incident radiant energy.