US3852604A

US3852604A - Mercury analysis system and method

Info

Publication number: US3852604A
Application number: US00279820A
Authority: US
Inventors: W Grengg
Original assignee: POLLUTION CONTROL Tech I
Current assignee: POLLUTION CONTROL Tech I
Priority date: 1972-08-11
Filing date: 1972-08-11
Publication date: 1974-12-03
Anticipated expiration: 1991-12-03
Also published as: JPS4987391A

Abstract

The system and method utilize a vessel, such as a test tube, having a predetermined interior side surface area coated with gold. The closed end of the tube is uncoated. Mercury from a fluid sample is adsorbed by the gold coating, such as by passing a gas through the tube or by placing a liquid in the tube and shaking the tube for a short period of time. After mercury from a given amount of sample has been adsorbed by the gold coating, the test tube is placed in an inverted generally upright position with the closed end of the tube above the open end and with the open end vented. Then the tube is rapidly heated to a temperature in excess of 400* centigrade to vaporize the mercury from the gold coating. The mercury vapor will rise in the test tube to the closed end thereof and form a bubble of mercury vapor mixed with hot air. Ultraviolet light in the 2537 angstrom wave length band is passed endwise through the test tube. Some of the ultraviolet light is absorbed by the mercury vapor in the test tube and the transmitted light is detected and measured. Next, the mercury vapor laden air is flushed from the test tube with mercury free air. Ultraviolet light is again passed through the test tube, this time through mercury-free air and the amount of light transmitted through the mercury-free air is detected and measured. The difference between the light transmission measurements is indicative of the concentration of mercury in the fluid sample. In addition to the test tube, the system includes structure for carrying out the method steps described above.

Description

United States Patent 191 Grengg MERCURY ANALYSIS SYSTEM AND METHOD [75] Inventor:

Walter M. Grengg, Madison, Wis.

Pollution Control Technology, Inc., Madison, Ill.

Aug. 11, 1972 App]. No.: 279,820

Assignee:

[22] Filed:

References Cited UNITED STATES PATENTS 3,173,016 3/1965 Williston an. 250/218 3,178,572 4/1965 Williston 3,544,789 12/1970 Wieder 250/373 Primary Examiner.lames W. Lawrence Assistant Examiner-C. E. Church Attorney, Agent, or Firm-Silverman & Cass,-Ltd.

[57] ABSTRACT The system and method utilize a vessel, such as a test tube, having a predetermined interior side surface area coated with gold. The closed end of the tube is uncoated. Mercury from a fluid sample is'adsorbed by the gold coating, such as by passinga gas through the tube or by placing a liquid in the tube and shaking the tube for a short period of time. After mercury from a given amount of sample has been adsorbed by the gold coating, the test tube is placed in an inverted generally upright position with the closed end of the tube above the open end and with the open end vented. Then the tube is rapidly heated to a temperature in excess of 400 Centigrade to vaporize the mercury from the gold coating. The mercury vapor will rise in the test tube to the closed end thereof and form a bubble of mercury vapor mixed with hot air. Ultraviolet light in the 2537 angstrom wave length band is passed endwise through the test tube. Some of the ultraviolet light is absorbed by the mercury vapor in the test tube and the transmitted light is detected and measured. .Next, the mercury vapor laden air is flushed from thetest tube with mercury free air. Ultraviolet light is again passed through the test tube, this time through mercury-free air and the amount of light transmitted through the mercury-free air is detected and measured. The difference between the light transmission measurements is indicative of the concentration of mercury in the fluid sample.

In addition to the test tube, the system includes structure for carrying out the method steps described above.

33 Claims, 9 Drawing Figures I PATENTELDEB 3:974

' sum 10? s PATENTEL DE!) 31974 SHEET 2 BF 3 FIG. 7

us V

2 MEMORY I22 M I I B AMPLIFIER a r LOGARITHMIC RY f CONVERTER STORED MULT-IPLICAND MERCURY ANALYSIS SYSTEM AND METHOD BACKGROUND AND SUMMARY OF THE INVENTION The present invention relates to a method and system for analyzing the mercury concentration in a fluid sample which may be either a gas or a liquid. The field of the invention includes chemical analysis methods and systems, particularly methods and systems which optically measure ray energy which passes through a fluent material. Methods and systems of this type have been classified at this time in Class 23, subclasses 232 and' 253, and Class 250, subclass 218.

More specifically, the present invention relates to a method and system which include (a) adsorbing mercury in a noble metal from a fluid sample, (b) vaporizing the mercury from the noble metal by heating the same, (c) passing ultraviolet light in the mercury vapor adsorption wave length band of 2537 angstroms through the mercury vapor, and (d) measuring the amount of ultraviolet light absorbed by the mercury vapor to obtain an indication of the concentration of mercury in the fluid sample.

The technique of measuring the concentration of a gas or vapor by passing radiant energy or light having a specific discrete wavelength band which is absorbed by the particular gas or vapor being studied, is well known. Examples of such procedures or techniques are disclosed in the following US patents:

US. Patent 3,174,037

US. Patent 3,589,814

US. Patent 3,589,868

Also, procedures have heretofore been proposed for measuring the concentration of mercury vapor in a gas sample such as air by passing radiant energy in the 2537 angstrom wavelength band through gas being analyzed, and then measuring the amount of radiant energy absorbed by the gas, theamount of absorbed radiant energy being related to the concentration of mercury vapor in the gas being analyzed. In this respect reference may be had to US. Pat. No. 3,173,016 issued to S. H. Williston et al. on Mar. 9, 1965 and to Trace Mercury Determination by J. B. Brooks and W. E. Wolfram which appeared in Chemical & Engineering News, Volume 48, Page 37 (June 22, 1970).

One of the disadvantages incurred with previously proposed methods and systems for mercury analysis, is the problem of loss of mercury from the sample and contamination of the sample (carryover) when measuring minute amounts of mercury. As for losses, it is well known that mercury is adsorbed by many different elements and in systems where the sample being analyzed is transferred through tubing or otherwise from one chamber or container to another chamber or container, there is danger of loss of mercury from the sample by reason of the mercury being adsorbed in the walls of the vessel, container or tubing by which it is transferred. Y

As for contamination, it will be understood that afte adsorbing mercury, the transfer vessel, container or tubing may later give off mercury toa succeeding fluid sample and thereby cause an erroneous measurement of the concentration of mercury in the succeeding sam- I ple. These problems of losses and contamination are mercury are being measured such as concentrations in the order of 0.05 parts per billion (PPB).

Another problem incurred with known methods and systems for analyzing mercury concentration in fluid samples by passing ultraviolet light through the sample or through mercury vapors obtained from the samples, is brought about by the fact that the gaseous medium containing the mercury vapor may also contain other gases or vapors such as organic vapors which also ab sorb radiant energy in the band width of radiant energy absorbed by mercury. When this occurs, an erroneous measurement indicating a larger concentration of mer-' cury than actually exists, will be obtained.

Still another disadvantage incurred with prior art mercury analysis systems and methods is the fact that for measuring very small concentrations of mercury in a fluid sample, a large quantity of the sample must be analyzed and this takes a significant amount of time. It is desirable, therefore, to providea method and system for analyzing mercury in which the time period for making the analysis is relatively short.

The method and system of the present invention overcome many of the disadvantages incurred with prior art mercury analysis systems and methods by eliminating transfer means such as vessels, containers or tubings, and by eliminating losses between the collection of mercury from a sample and the analysis of the mercury collected. The method and system of the present invention are also very versatile and enable one quickly to make accurate determinations of minute concentrations of mercury in liquids, gases and solids. The method andsystem of the invention achieve the aforementioned advantages by utilizing one vessel having a predetermined interior surface area thereof coated with a noble metal, such as gold, for the collecting vessel, the vaporizing vessel and the mercury vapor absorption vessel. Heretofore, the use of a vessel, such as a test tube, lined with gold has been proposed but for an altogether different purpose, namely, to provide the interior surface of the tube with an essentially chemically inert lining. In this respect reference may be had to US. Pat. No. 3,475,131.

According to the invention, there is provided for use in a mercury analysis system, a test tube having an open end adapted to be stoppered, an interior side surface area coated with a noble metal, and an uncoated closed end.

Also, according to the invention, there is provided a method for analyzing the concentration of mercury in a fluid including the steps of placing a given amount of fluid sample in a vessel having a noble-metal coating therein, removing the sample for the vessel, positioning the vessel in an inverted generally upright position with the closed end above the open end and with the open end vented, heating the vessel to a given temperature to release mercury vapor from the noble metal coating, passing ultraviolet light of awave-length band which is absorbed by mercury vapor endwise through the vessel, measuring the amount of light transmitted through the mercury vapor laden air within the vessel, flushing the mercury vapor laden air from the vessel with mercury free air, again passing ultraviolet light endwise through the vessel now having mercury-free air therein, measuring the amount of light transmitted through the mercuryfree air, and comparing the'first light transmission measurement with the second light transmission measurement, the difference between the measurements being indicative of the concentration of mercury in the fluid sample.

Further according to the invention there is provided a mercury analysis system including a vessel supported in a generally upright position with a first end of the vessel above a second end and with the second end vented, a mechanism for .vaporizing mercury stored in the noble metal coating on the interior surface of the vessel, and apparatus for analyzing the mercury vapor, the analyzing apparatus including a source of ultraviolet light which is positioned to pass ultraviolet light endwise through the vessel, a detector for detecting the amount of light transmitted through the vessel, and a mechanism for flushing mercury vapor laden air from the test tube. Preferably the mercury analysis system also includes electronic circuitry for converting the signals generated by the detector into signal values directly related to the numerical concentration of mercury in the fluid sample in parts per billion (PPB).

Further, according to the invention there is provided for use in a mercury analysis system a device for sampling a gas including a vessel positioned to receive a gas therein, a suctionmechanism for drawing a gas through the vessel and a'control mechanism for controlling the rate of flow and the time period of flow of the gas through the vessel.

' BRIEF DESCRIPTION'OF THE DRAWlNGS 7 FIG. I is a sectional elevational view of the test tube of the invention.

FIG. 2 is aperspective view of a device for obtaining multiple samples of a gas by drawing the gas through FIG. 6 is a fragmentary sectional elevational view DESCRIPTION'OF THE PREFERRED EMBODIMENTS In FIG. 1 is illustrated a test tube 10 made in accordance with the teachings of the present invention. The test tube 10 is basically of conventional design having a closed generally.semi-spherical end 12, a generally cylindrical elongate side wall 14,and an opened end 16 defined by an outwardly flared flange 18 extending from the cylindrical side wall 14. According to the in,- vention a portion of interior side-surface 20 of the tube 10 is coated with a noble metal 22. Any one of the noble metals which have a strong afinity for mercury can be utilized for the noble metal coating 22. One

noble metal which has worked very well is gold, and hereinafter the noble metal coating 22 will be simply referred to as the gold coating 22.

The gold coating 22 extends along the length of the side wall I4 starting at a point at or adjacent the junction between the closed end 12 and the side wall 14, and extending toward the open end 16. Empirical tests have shown that good results are obtained when the ratio of the length of the gold coating 22 to the length of the tube 10 is a number equal to approximately 0.4. The limitations on the length of the gold coating 22 will be explained in greater detail in connection with the description of FIG. 6.

' The gold coating or film 22 on the interior surface 20 of the tube 10 can be applied by several methods which are as follows: (a) high vacuum vapor deposition; (b) ionic sputtering in a low pressure inert gas electrical discharge; (c) chemical reduction of a solution initially containing the metal in soluble form; and (d) thermal decomposition of a metal-organic compound which has been applied to the inside by painting a solution of the metal-organic compound in an organic solvent on the interior surface 20 of the test tube 10, drying the solvent, and then converting the remaining film to metallic gold (or other noble metal) by heating the test tube 10 above the decomposition temperature of the metalorganic compound.

To facilitate heating of the test tube for purposes to I be described hereinafter, outer surface 24 of the test tube 10 preferably has a black coating thereon. Such a black coating can consist of a black oxide coating which is applied to the outer surface 24 after the outer surface 24 has been sandblast roughened. After being applied, the black oxide coating is fused in place.

According to the teachings of the invention, the test tube is preferably made from a glass which transmits infra-red radiation and ultraviolet light radiation. In this respect the test tube 10 is preferably'made from high'silica 2537 angstrom transmitting glass. I

The flared flange 18 at the open end 16 facilitates the insertion of a stopper 26 in the tube 10 as shown in FIG. 4. However, for practicing the method or for utilizing the system of theinvention, a flared open end is not essential. r

The test tube 10 with the gold coating 22 enables one to utilize a very simple and accurate procedure for analyzing the concentration of mercury in a sample. Briefly this procedure involves the placing of a sample, or the passing of a given amount of sample through the test tube 10 in such a way that at least a portion, if not substantially all of the mercury in the sample, is adsorbed by the gold coating 22. Then the sample is removed from the tube 10 and the tube 10 is stoppered as shown in FIG. 4. It is now ready for making an analysis of the mercury in the sample by analyzing the mercury adsorbed by the gold'coating 22. This is accomplished by rapidly heating the test tube 10 to vaporize the mercury from the gold coating 22. Ultraviolet light in the mercury absorption band width, namely, 2537 angstrom ultraviolet light is passed axially through the tube and the amount of light which is transmitted through the tube is detected and compared with a measurement of light through the tube with mercury-free air therein. The difference in the light transmission measurements is indicative of the concentration of mercury in the sample.

As will be described hereinafter, the sample can be a liquid or gas. A device 30 is shown in FIG. 2 for sampling a gas. The device 30 includes a housing 32 having a plurality of openings or ports 34 which extend through the upper surface of the housing 32. In FIG. 2, the housing 32 has eight such ports 34. Each of the ports 34 is adapted to receive one of the test tubes in inverted position, that is to say, with the closed end 12 up, as shown in FIG. 2.

Positioned within each one of the openings 34 is a pipe 36, a portion of which extends above the upper surface of the housing 32 such that an upper end 38 of each pipe 36 extends into a test tube 10 received in the associated opening 34 and opens at the upper end 38 into the test tube adjacent the closed end 12 of the test tube 10. In this way gas sample which'is injected into the tube 10 through the pipe 36 will enter the test tube 10 adjacent the closed end 12 and flow downwardly therefrom along and past the gold coating 22 in the test tube 10 as best shown in FIG. 3. It will be appreciated that by injecting the gas sample into the test tube 10 with the pipe 36 one is assured that substantially all of the gas sample will flow past the gold coating 22 on the inner surface of the test tube 10. i

In FIG. 3 is illustrated the structure within the housing 32 beneath one of the openings 34. This structure for receiving and holding a test tube in proper location relative to the pipe 36 includes a block 40. The block 40 has a top side 41 and a bottom side 43 with an inlet opening 44 opening onto the bottom side 43 and a cavity 46 which opens onto the top side 41. Extending between and communicating with the cavity 46 and the inlet opening 44 is a passageway 48 in which an inner end 50 of the pipe 36 is received and fixed in place. As

shown in FIG. 3 the block 40 has a spigot 52 and an outlet opening or passageway 54 .which extends through the spigot 52. The spigot 52 has a valve member 56 mounted therein for controlling the flow of gas through the outlet passageway 54. A constriction 58 between the cavity 46 and the passageway 54' limits the rate of flow when the valve member 56 is fully open. As shown in FIG. 3, the inverted test tube 10 is supported on the block 40 with the flange 18 resting on the top side 41 and with the open end 16 of the test tube 10 positioned over the cavity 46. To facilitate proper locating of the test tube 10 over the cavity 46, a tubular guide member or pipe 64 is positioned in and extends outwardly from the cavity 46. In this respect one end 66 of the pipe 64 is received and fixed in the cavity 46 with the remainder of the pipe 64 extending outwardly from the cavity 46. The pipe 64 is shorter in length than the pipe 36 such that an outer end 68 of the pipe 64 is located beneath the upper end 38 of the pipe 36 and beneath the gold coating 22 in the test tube 10 when the test tube 10 is positioned as shown in FIG. 3. Thus, the outer pipe 64 serves as a means for supporting and holding the test tube 10 in a desired location with the upper end 38 of the inner, smaller pipe coaxial with the test tube 10.

Since it is not necessary to eject gas toward the closed end 12 of the test tube 10, the upper end 38 of the pipe 36 ejects air through ports or holes 70 in the side walls of the pipe adjacent the upper end 38 as shown in FIGS. 2 and 3. In this way a gas is injected into the test tube 10 radially outwardly from the center of the test tube 10 toward the gold coating 22 on the interior surface 20 of the test tube 10.

The cavity 46 and associated openings located beneath each housing opening 34 can be formed in an individual block or in a large block which contains a plurality of cavities and associated openings.

To minimize undesired adsorption and crosscontamination between samples, it is desirable to coat the gas conducting channels, such as the interior of the pipe 36, which carry the gas to be analyzed into the test tube 10 with a material which has a very low adsorption of mercury. It has been discovered that fluorocarbon plastic such as plastic sold under the trademark Teflon is one such material which adsorbs very little mercury.

Thus, according to the teachings of the invention the fluid conducting channels in a mercury analysis apparatus, e.g., in the sampling device 30, are coated with or made of a fluoro-carbon plastic such as Teflon.

The device 30 is particularly adapted for sampling ambient air by drawing air from the underside of the housing 32 into the opening 44 through the pipe 36 and into the interior of the test tube 10. This is accomplished by applying a suction to the outlet passageway 54. The rate of flow of air drawn through the test tube 10 is determined by the size of the flow limiting cons triction 58 and the partial vacuum in the outlet passageway 54. The initiation and termination of the sample air flow is provided by a 90 rotation of the valve the test tubes 10 in one of the openings 34 and over the" outer pipe 64 within the housing 32.. Then the operator sets the appropriate timer 74 to initiate the known rate of air flow at the desired time, arid to terminate the air flow after a predetermined interval.

It will be understood that since theair or other gas which is sampled is passed through the test tube 10, not

all of the mercury in the gas or air is adsorbed by the gold coating 22. However, it has been found that for a particular gas, a specific percentage of mercury will be adsorbed by the gold coating 22 from the gas depending upon the flow rate. Accordingly, in practicing the method of the invention, an operator will first draw a sample of air containing a known quantity of mercury through the test tube at a known flow rate. Then after determining the amount of mercury adsorbed by the gold coating 22, and knowing the amount of air which has been passed through the test tube 10, the operator can calibrate the sample analyzing device accordingly. Empirical tests have shown that measurements of a standard can be reproduced very accurately with not more than plus or minus 6% error.

With one working model of the test tube 10 and-sampling device 30, a time period of 200 seconds was found to be very adequate for sampling air.The testv of course, an immediate analysis of the contents of the test tube is to bemade. It is contemplated that the device 30 may be used at various locations far removed from analysis equipment hereinafter to be described. Thus, it is contemplated that after the sample is collected in the gold coating 22 of a test tube 10, the tube .10 will be stoppered as shown in FIG. 4, and then sent,

such asby mail, to an analyzing station or laboratory.

dissolving the solid with an acid, diluting the dissolved solidacid mixture and placing the aqueous solution into test tube 10 and adding a reducing agent to obtain free mercury. Likewise, for making an analysis of a liquid, one can simply place liquid in an aqueous solution into test tube 10 and add a reducing agent. Empirical tests have shown'thatalmost all of the mercury in the solution will be picked up by the gold coating if the solution is agitated, such as by shaking, for at least minutes. In this respect empirical tests have shown that shaking for 20 minutesor more results in an adsorbtion of practically all of the mercury in the liquid by the gold coating 22. Of course, when analyzing a liquid sample one would first make an analysis of a liquid having a known concentration of mercury therein in order to properly calibrate the analyzing equipment hereinafter to be described. v V I Onesprocedure which worked very well for analyzing the mercury concentration in a water sample involved the placing of ten cubic centimeters of the water sample directly into the test tube and then adding 2 cubic centimeters of a 1.5 percent hydroxylamine hydrochloride solution. The'test tube 10 was then stoppered and shaken for at least fifteen minutes.

When a liquid sample isbeing analyzed, the test tube' 10 is rinsed after the sample is removed therefrom and then dried before being-stopperedor beforejmaking an analysis of the mercury picked up and adsorbed by the gold coating 22.

Since mercuryis vaporized from the gold coating 22 for ultraviolet light'absorption within the tube10, the tube 10 can be referred to as an absorption cell inaddition to a sample. collecting tube. By combining the absorption cell into the collecting and sampling tube, the present invention obviates, if not altogether eliminates, the problems incurred with previously proposed mercury analysis systems. In this respect, there is no transferring of a fluid sample from a collecting container or tube to an absorption cell for analysis of the mercury concentration in the fluid sample.

After each sample is made, the test tube will be given an identification marking or number to identify what was sampled, where and when. This information will preferably be in a code which can be sensed and then printed with the analysis of the mercury adsorbed by the gold coating 22.

As previously described, the analysis involves driving out or vaporizing the mercury from the gold coating 22 and then making an analysis of the amount of mercury vapor driven from the gold coating 22. This is accomplished according to the method and system of the invention with a vaporizing and analyzing apparatus shown in FIG. 5. The apparatus 80 includes a housing 82 in which are mounted components of the apparatus 80 including electronic circuit elements. The apparatus 80 also includes a test carrier 84 in which a plurality of test tubes 10 are carried in a generally inverted upright position. The carrier is received in an opening 86 in the front side of the housing 82. Preferably the housing 86 includes a suitable mechanism for indexing the carrier 84 into and through the housing 82 each time the analysis of the mercury in the gold coating 22 in one of the test tubes 10 is completed whereby a plurality of test tubes 10 can be analyzed automatically. Also the apparatus 80 includes a printer 87 (FIG. 7) which provides a print-out tape 88 on which the analysis of the mercury adsorbed by the gold coating 22 in each of the test tubes 10 is printed together with identifying code information carried by each test tube 10.

A generally cylindrical device 90 for vaporizing mercury from the gold coating 22 in each of the test tubes 10 carried by the carrier 84 is situated above the opening 86. The interior diameter of the device 90 is slightly larger than the outer diameter of the test tube 10, so that the device 90 can be easily received over the closed end 12 of the test tube 10. Also, the device 90 is movablymounted in the opening 86 for movement from a raised position shown in FIG. 5 to a lowered position shown in FIG. 6 where the vaporizing device 90 is received over the portion of one of the test tubes 10 extending upwardly from the carrier 84. 1

The vaporizing device 90 consists essentially of an infra-red heater which includes a heating coil or element 94 imbedded in a material 96 having high emissivity in the infrared spectral region. The vaporizing device or heater 90 is designed to rapidly heat the upper portion of the inverted test tube including the closed end 12 and the portion of the tube 10 which has the gold coating 22 on'the inner surface 20 thereof. It will be appreciated that the black coating on the exterior surface 24 of the test tube 10 enhances the rapid heating of the portion of the test tube 10 located within the heater 90. Also the black coating prevents undesirable reflection, of the infra-red heat applied to the test tube able in view of the heat-dissipation problems incurred therewith. Very good results have been obtained however, by utilizing an electric current through the heating element 94 which is sufficient to raise the temperature of the test tube 10 to approximately l000 centigrade.

The rapid heating of the test tube 10 to a temperature on the order of I,OOO centigrade produces very desirable results in that a thin film of hot air and mercury vapor is quickly generated along the surface of the gold coating 22. This vapor rises in the inverted test tube 10 and forms a bubble of hot air and mercury vapor at the closed end 12 of the test tube 10. Although mercury vapor is heavier than air, the heated air and mercury vapor mixture is buoyant on the cooler air within the 9 test tube. As a result, the mercury vapor tends to remain at the upper end of the test tube 10 as shown in FIG. 6.

During the heating of the test tube 10, the heated gas within the upper part of test tube 10 expands and it is desirable to allow the displaced cooler gas (air) to escape from the test tube 10. For this reason, the test tube 10, when positioned underneath the heater 90, has the lower end thereof in communication with a passageway 100 in a block 102 as shown in FIG. 6. The passageway 100 extends vertically downwardly into a block 102 and then communicates with an outlet or vent passageway 104 in the block 102. Typically, the passageway 104 vents to atmosphere.

From the foregoing description it will be understood that when a test tube is indexed to a position beneath the heater 90, the lower open end 16 of the test tube 10 is in registry with the passageway 100 so that the test tube is vented. Then, when the upper portion of the inverted test tube '10 is heated and the gases in the test tube expand, the cooler gas or air within the test tube is forced out of the test tube by the expanding heated gases and mercury'vapor.

It will be appreciated that if the gold coating 22 on the interior surface 20 of the test tube 10 extended further toward the open end 16 thereof, a greater amount of mercury vapor would be vaporized from the gold coating 22 into the test tube 10, and very possibly forced out of the test tube 10 through the vent passageway 104 by the heated expanding gases within the test tube 10. This possibility of losing some of the mercury vapor creates a limitation on the length of the gold coating 22 relative to the overall length of the test tube 10. As described previously, a gold coating length to tube length'ratio of approximately 0.40 has been found to work quite satisfactorily for obtaining a significant sample of mercury none of which is lost during heating of the test tube 10.

After the mercury in the gold coating 22 has been vaporized, an analysis of the amount of mercury vapor to determine the concentration of mercury in the sample from which the mercury vapor was originally obtained,

is made by passing ultraviolet light axially through the test tube 10 and the mercury vapor therein. In the illustrated embodiment of the apparatus 80, this is accomplished with a light source 106 which directs light to a prism 108 mounted above the heater 90 in position to reflect light downwardly through an opening 110 in the top of the heater 90. The prism 108 is located to direct light downwardly along the axis of the test tube 10.

The ultraviolet light from thesource 106 is in the 2537 angstrom band width which is the band width of ultraviolet light that is absorbed by mercury vapor. To

minimize any optical aberrations which may be in curred as a result of passing the ultraviolet light through the heated closed end 12 of the test tube 10 and the heated gases within the test tube 10, a quartz diffuser 112 is situated between the source 106 and the prism 108 for diffusing the light that is passed through the test tube 10. As shown in FIG. 6, the light passing through the test tube 10 passes through the passageway 100 and thence through an ultraviolet band width pass filter 114 to a photodetector 116. The filter 114 prevents any extraneous light or radiant energy from reaching the photodetector 116 such as light from the heated gold coating 22. Typically the light source 106 is continuously on such that ultraviolet light is continuously passing through the test tube 10. The detector 116, however, is only switched on at certain times. In

carrying out the method, the apparatus is programmed to heat the test tube 10 for a predetermined period of time and then to switch on the photodetector 116 which will immediately sense the amount of ultraviolet light passing through the mercury vapor in the test tube 10. Then, after a measurement has been made of the ultraviolet light passed through the test tube 10, the detector 116 will be turned off. Next, the mercury vapor laden air is flushed from the test tube 10 with mercury-free air. This is accomplished by injecting mercury-free air into the test tube 10 from a nozzle 118 mounted in the block 102 in position to direct air there from upwardly along one side of the test tube 10 as best shown in FIG. 6. The flow of air through the nozzle 118 is controlled by a valve shown schematically at 120. Typically, the flushing air is ambient air which is passed through a filter 122. The filter 122 can contain manganese dioxide and/or activated charcoal.

After the mercury vapor laden air has been flushed from the test tube 10 and only mercury free air is therein, the photodetector 116 is again activated and another measurement of ultraviolet light reaching the photodetector 116 is made. The difference between these measurements is indicative of the. amount of mercury vapor in the test tube 10. I

In FIG. 7 is illustrated a schematic block diagram of an electronic circuit for comparing the light transmission measurements and then converting the difference to a signal value which is related to the numerical value in parts per billion (PPB) of mercury in the fluid samtained from ultraviolet light passing through the merv cury vapor laden air is identified as V and is stored in a first memory M The second voltage signal derived from ultraviolet light passing through mercuryfree air in the test tube 10, is designated V and is stored in a memory M The twovoltage signals V and V are then applied to a subtractor S A where the first voltage signal V is subtracted from the second voltage signal V The difference signal V -V is then applied to a multiplier 124. A stored :rnultiplicand which is determined from the measurement of a fluid sample standard having a known concentration of mercury therein is applied to the multiplier 124 for multiplying the difference signal to obtain an output signal from the multiplier 124 which is directly related to the numerical value of the concentration of mercury in parts per billion. This signal is then applied to the printer 97 which prints out the numerical value of the tape 88.

Ultraviolet light is also absorbed by some organic vapors and, to avoid inaccurate measurements of light intensity as may be occasioned by the absorption of some of the ultraviolet light by organic vapors in the test tube 10, it may be desirable to make measurements of ultraviolet light of a wavelength which is not absorbed by mercury. For this purpose the apparatus 80 of the mercury analysis system can include a second light source 130 as shown in FIG. 6. Also the electronic circuit can be modified to include the additional memories M and M and an additional subtractor 8,, as shown in FIG. 8 connected between the subtractor S A and the multiplier 124. The light from the source 130 is preferably of a wavelength band which is near to the 2537 angstrom band but which does not include the 2537 angstrom wavelength which is absorbed by mercury vapor.

air to obtain a second signal V which is stored in the memory M The difference V V, is determined by the subtractor S and the result stored in the memory M Then, after the mercury laden air has been flushed from the test tube 10 by mercury free air, a third signal V is obtained by passing lightv from the source 106 through the mercury free air and the logarithmic signal value V is'stored in the memory M,,. Then a fourth signal V is obtained by passing light from the source 130 through the mercury free air and stored in the memory M The difference V V is determined by the subtractor S and the result stored in the memory M The two difference signals stored in the, memories M and M are then applied to the subtractor 5;, where the second difference signal (V -V is subtracted from v necessary since in most cases the vapors in the tube are oxidized by the heat from the infra-red heater 90 and the oxidized organic vapors generally do not absorb ultraviolet light in the mercury absorption band width of 2537 angstroms. g

- in F 10. 9 there is illustrated a modified mercury analysis system or apparatus 180 where a fixed cell or vessel 210 is utilized in place of movable tubes 10. The apparatus 180 is particularly useful for on-the-spot analysis of food (by thermal decomposition) or gases. The

' vessel 210 is positioned in a generally upright positionand has an upper end 212, a lower end 216,. an inner surface220 with a gold coating or film 222 thereon and an infra-red absorbing, layer 224 on theouter surface of the vessel 210. Agas input line 230 is connected to the upper end 212. A vacuum line 232 also is connected to the upper end 212. A second vacuum line 1234 and aclean air input line 236 are connected to the lower end 216. An infrared heater 290 surrounds the vessel 210 in the general area of the gold coating 222. A reflector 292 surrounds the heater 290 and has a quartz window 310 therein above the upper end 212. An ultraviolet light source 312 issituated above the quartz window. Beneath the lower end 216 is a 2537 angstrom band pass filter 314 and a photo detector 316. Cooling air is supplied to the interior of the reflector through line 318.

' also minimizes, if not altogether eliminates, losses'and Each gas or air line has a suitable control valve therein and by programming the operation ofthe valves, the heater 290 and the detector 316, mercury from a given amount of a gas sample first can be concentrated in the gold coating 222 followed by the thermal release of mercury vapor from the coating 222 and buoyant maintenance of the vapor in the generally vertical optical path between light source 312 and photodetector 316. Then a first light transmission measurement is made, the vessel 210 is flushed with mercuryfree air, a second light transmission measurement is made and the measurements are compared to determine the concentration of mercury in the gas sample.

It has been found that the mercury analysis system of the present invention utilizing the apparatus 80 or 180 enables an operator to make a mercury concentration analysis in a time period from three to five minutes which is a much faster time than obtained with many of the previously proposed mercury analysis systems. Also it has been found that the mercury analysis system of the present invention is very sensitive in that readings of 0.01 parts per billion (PPB) can be obtained therewith.

From the foregoing description it will be readily apparent that the mercury analysis system and method of the present invention provide a number of advantages some of which have been described above and others of which are inherent in the invention. Some of these advantages are as follows: l The system is very sensitive. (2) It is very flexible and enables one to make analysis of gases, liquids and solids such as food stuffs. (3) The system is very simple and the simplicity is enhanced by combining the sample collection tube and absorption cell into one test tube. (4) This simplicity cross-contamination. (5) The fluid sampling time and the analysis time are very short, thereby facilitating the analysis of numerous samples. (6) The system is very economical in that one vaporizing and analyzing apparatus can be used for any number of field collecting test tubes 10. (7) The results obtained are readily reproducible within a plus or minus 6 percent error.

From the foregoing description it will also be apparent that modifications and variations can be made to the test tube, method and system of the present invention without departing from the spirit or scope of the invention. Accordingly, the present invention is only to be limited as necessitated by the accompanying claims.

What it is desired to be secured by Letters Patent of the United States is:

l. A method for analyzing the concentration of mercury in a fluid including the steps of: placing a given amount of a fluidsample in a vessel having a predetermined interior side surface area coated with a noble metal which has a strong affinity for mercury, such that at least a portion of the mercury in said sample is adsorbed by said noble metal coating; removing said sample from said vessel; positioning said vessel in a generally upright position with a first end of said vessel above a second end of said vessel and with said second end vented; heating said vessel to a given temperature to release mercury vapor from said noble metal coating; passing endwise through said vessel an ultraviolet light of a wave length band which is absorbed by mercury vapor; measuring the amount of said light transmitted through the mercury vapor laden air within said vessel; flushing said mercury vapor laden air from said vessel with mercury-free air; passing said ultraviolet light endwise through said vessel having mercury-free air therein; measuring the amount of said light transmitted through said mercury-free air; and comparing the first light transmission measurement with the second light transmission measurement, the difference between said measurements being indicative of the concentration of mercury in said fluid sample.

2. The method according to claim 1 wherein said fluid is a gas and said steps of placing sample and removing sample from said vessel consists in passing said gas through said vessel at a given flow rate for a given time period.

3. The method according to claim 2 wherein said gas is injected into said vessel at a point near said first end of said vessel so that said gas flows along and adjacent the interior noble-metal-coated surface of said vessel and out said second end of said vessel.

4. The method according to claim 2 wherein said gas is injected into said vessel through a pipe which extends into said vessel at said second end and opens into said vessel adjacent said first end and said gas is caused to flow through said pipe into said vessel along and adjacent the interior noble-metal-coated, surface of said vessel and out said second end of said vessel by applying a vacuum to said second end of said vessel.

5. The method according to claim 2 wherein said vessel is positioned in a generally upright position while said gas is being passed through said vessel.

6. The method according to claim 1 wherein said fluid sample is an aqueous solution and said method includes the steps of adding a reducing agent to the given amount of aqueous solution in said vessel; sealing said vessel; and agitating said aqueous solution and reducing agent for a given period of time to facilitate reduction of mercury compounds to free metal mercury and to facilitate adsorption of said mercury by said noble metal coating.

7. The method according to claim 6 wherein said aqueous solution sample includes dissolved solids and said method includes the initial steps of;dissolving a solid in an acid and diluting the acid-dissolved solid with water to form the aqueous solution sample.

8. The method according to claim 7 wherein said solid is a foodstuff. a

9. The method according to claim 6 wherein said step of agitating said solution consists essentially in shaking said vessel.

10. The method according to claim 6 wherein said aqueous solution is agitated for at least five minutes.

11. The method according to claim 6 including the steps of rinsing and drying said vessel prior to heating said vessel.

12. The method according to claim 6wherein said sample consists essentially of approximately ten cubic centimeters of water and said reducing agent consists essentially of approximately two cubic centimeters of an approximately 1.5 percent hydroxylamine hydrochloride aqueous solution.

13. The method according to claim 1 wherein said fluid sample is a gas sample including vapors from a thermally decomposed solid and said method includes the initial step of thermally decomposing a solid to obtain vapors which form said fluid sample.

14. The method according to claim 1 wherein said noble metal is gold. I g

15. The method according to claim 1 wherein said vessel is heated to a temperature between 400C and l,300C.

16. The method according to claim 1 wherein said vessel is heated by infra-red radiation.

17. The method according to claim 2 including the initial step of filtering said gas to remove undesirable particles therefrom.

18. The method according to claim 1 wherein said ultraviolet light is diffused before being passed endwise through said vessel.

19. The method according to claim 1 including the step of preheating said fluid sample to vaporize mercury in any solid particles carried in said sample.

20. The method according to claim 1 including the steps of amplifying and logarithmically converting the light measurements to signal values which are directly related to the concentration of mercury in said fluid sample. 1

21. The method according to claim 20 including the steps of subtracting said first signal value from said second signal value; multiplying the difference by a predetermined multiplicand to obtain a numerical value in parts per billion; and printing said numerical value.

22. The method according to claim 1 including the steps of: passing through said mercury vapor laden air ultraviolet light of a second wavelength band which is near to, but which does not include, said mercury absorption band; measuring the amount of said light having said second wave' length which is transmitted through said mercuryvapor laden air to obtain a light transmission measurement; passing said light having said second wave length band through said mercuryfree air; measuring the amount of said light having said second wave length band which is transmitted through said mercury-free air to obtain a light transmission measurement; amplifying and logarithmically converting said light transmission measurements to signal values proportional to the logarithm of said light transmission measurements; subtracting said first signal value derived from the measurement of transmission through said mercury vapor laden air of ultraviolet light of a wavelength band which is absorbed by mercury vapor, from said signal derived from the measurement of transmission through said mercury vapor laden air of ultraviolet light of said second wave length band to obtain a first difference signal; subtracting said signal value derived from the measurement of transmission through said mercury-free air of ultraviolet light of said wave length band which is absorbed by mercury vapor from said signal derived from the measurement of transmission through said mercury-free air of ultraviolet light of said second wave length band to obtain a second difference signal; and subtracting said second difference signal from said first difference signal to obtain a signal value which is related to the concentration of mercury in said fluid sample and which has had subtracted therefrom the undesired effects of ultraviolet light absorption by other vapors which may be in said vessel in addition to mercury vapor.

23. The method according to claim 22 including the steps of multiplying said last signal value by a given multiplicand to obtain a numerical value in parts per billion; and printing said numerical value.

24. A mercury analysis system including a vessel having a noble metal-coating on an interior side surface thereof and being supported in a generally upright position with an upper end of the vessel above a lower end and with the lower end of the vessel vented, means for vaporizing mercury stored in said noble metal coating, and means for analyzing the mercury vapor, said analyzing means including a source of ultraviolet light of a wave length band which is absorbed by mercury vapor, said source of ultraviolet light being positioned to pass ultraviolet light endwise through the vessel, means for detecting the amount of light transmitted through the vessel, and means for flushing mercury vapor laden air from the vessel.

25. The system according to claim 24 including an electronic circuit connected to said detecting means, said electronic circuit including means for amplifying signals generated by light detected by said detecting means and for logarithmically converting the generated signals to signal values related to the concentration of mercury in the mercury vapor laden air, means for obtain difference signal directly related to the concentration of mercury in the mercury vapor laden air.

26. The system accordingto claim 25 includingmeans for printing the mercury analysis measurement in parts per billion and wherein said electronic circuit includesa multiplying means connected between said 27. The system according to claim 25 including a sec ond source ofuitraviolet light of a wavelength band which is near, but which does not include, the mercury vapor absorption band, said second source being positio ned to pass ultraviolet light endwise. through the vessel at predetermined times, and wherein a memorizing means is operable to memorize a generated signal obtained when ultraviolet light from said second source is passed through the mercury vapor laden air in the vessel; a memory means is operable to memorize a generated signalobtained when ultraviolet light from said second source is passed through mercury-free air in the vessel, said subtracting means being operable to subtract. said first signal obtained when ultraviolet light from said first source is passed through the mercury vapor laden air in the vessel from said signal obtained when ultraviolet light from said second source is passed through the mercury vapor laden air in the vessel to obtain a first difference signal, memory means operable to memorize a third signal obtained when ultraviolet light from said first source is passed through mercuryfree air in the vessel, memory means operable to memorize a fourth signal obtained when ultraviolet light from said second source is passed through mercuryfree air in the vessel, said subtracting means being operable to subtract said third signal from said fourth signal to obtain a second difference signal, and said electronic circuit includes a means for memorizing said first difference signal and a means for memorizing said second difference signal and a second subtracting means for subtracting said second difference signal from said first difference signal to obtain a third difference signal which is directly related to mercury vapor vaporized in the test tube and which has had subtracted therefrom the undesired effects of ultraviolet light absorption by other vapors which may be in the vessel in addition to mercury vapor.

28. The system according to claim 27 including means for printing the mercury analysis of a fluid sample in parts per billion and wherein said electronic circuit includes multiplying means connected between said second subtracting means and said printing means for multiplying said third difference signal by a predetermined multiplicand to obtain a numerical value in parts per billion of the mercury concentration in the fluid sample. i

29. The system according to claim 24 wherein said flushing means includes a filter for removing mercury vapors from air used as a flushing medium, and a flush nozzle having its outlet orifice arranged to inject flushing air into the lower'end of the vessel adjacent one side of the vessel and in a direction generally parallel to the longitudinal axis of the vessel. a

l 30. The system according to claim 24 including an ultraviolet bandpass filter situated between one end of the vessel and said detecting means.

31. The system according to claim 24 wherein said vaporizing means is an infra-red heater.

32. The system according to claim 24 wherein said light source is horizontally spaced from the upper end of the vessel and a prism is situated above the upper 1 end of the vessel for reflecting light from said light source downwardly through vessel. v

33. The system according to claim 24 including means interposed between said light source and the vessel for diffusing the light from said light source.

Claims

1. A method for analyzing the concentration of mercury in a fluid including the steps of: placing a given amount of a fluid sample in a vessel having a predetermined interior side surface area coated with a noble metal which has a strong affinity for mercury, such that at least a portion of the mercury in said sample is adsorbed by said noble metal coating; removing said sample from said vessel; positioning said vessel in a generally upright position with a first end of said vessel above a second end of said vessel and with said second end vented; heatinG said vessel to a given temperature to release mercury vapor from said noble metal coating; passing endwise through said vessel an ultraviolet light of a wave length band which is absorbed by mercury vapor; measuring the amount of said light transmitted through the mercury vapor laden air within said vessel; flushing said mercury vapor laden air from said vessel with mercury-free air; passing said ultraviolet light endwise through said vessel having mercury-free air therein; measuring the amount of said light transmitted through said mercury-free air; and comparing the first light transmission measurement with the second light transmission measurement, the difference between said measurements being indicative of the concentration of mercury in said fluid sample.

4. The method according to claim 2 wherein said gas is injected into said vessel through a pipe which extends into said vessel at said second end and opens into said vessel adjacent said first end and said gas is caused to flow through said pipe into said vessel along and adjacent the interior noble-metal-coated surface of said vessel and out said second end of said vessel by applying a vacuum to said second end of said vessel.

7. The method according to claim 6 wherein said aqueous solution sample includes dissolved solids and said method includes the initial steps of; dissolving a solid in an acid and diluting the acid-dissolved solid with water to form the aqueous solution sample.

8. The method according to claim 7 wherein said solid is a foodstuff.

12. The method according to claim 6 wherein said sample consists essentially of approximately ten cubic centimeters of water and said reducing agent consists essentially of approximately two cubic centimeters of an approximately 1.5 percent hydroxylamine hydrochloride aqueous solution.

14. The method according to claim 1 wherein said noble metal is gold.

15. The method according to claim 1 wherein said vessel is heated to a temperature between 400*C and 1,300*C.

20. The method according to claim 1 including the steps of amplifying and logarithmically converting the light measurements to signal values which are directly related to the concentration of mercury in said fluid sample.

22. The method according to claim 1 including the steps of: passing through said mercury vapor laden air ultraviolet light of a second wavelength band which is near to, but which does not include, said mercury absorption band; measuring the amount of said light having said second wave length which is transmitted through said mercury vapor laden air to obtain a light transmission measurement; passing said light having said second wave length band through said mercury-free air; measuring the amount of said light having said second wave length band which is transmitted through said mercury-free air to obtain a light transmission measurement; amplifying and logarithmically converting said light transmission measurements to signal values proportional to the logarithm of said light transmission measurements; subtracting said first signal value derived from the measurement of transmission through said mercury vapor laden air of ultraviolet light of a wavelength band which is absorbed by mercury vapor, from said signal derived from the measurement of transmission through said mercury vapor laden air of ultraviolet light of said second wave length band to obtain a first difference signal; subtracting said signal value derived from the measurement of transmission through said mercury-free air of ultraviolet light of said wave length band which is absorbed by mercury vapor from said signal derived from the measurement of transmission through said mercury-free air of ultraviolet light of said second wave length band to obtain a second difference signal; and subtracting said second difference signal from said first difference signal to obtain a signal value which is related to the concentration of mercury in said fluid sample and which has had subtracted therefrom the undesired effects of ultraviolet light absorption by other vapors which may be in said vessel in addition to mercury vapor.

24. A mercury analysis system including a vessel having a noble metal coating on an interior side surface thereof and being supported in a generally upright position with an upper end of the vessel above a lower end and with the lower end of the vessel vented, means for vaporizing mercury stored in said noble metal coating, and means for analyzing the mercury vapor, said analyzing means including a source of ultraviolet light of a wave length band which is absorbed by mercury vapor, said source of ultraviolet light being positioned to pass ultraviolet light endwise through the vessel, means for detecting the amount of light transmitted through the vessel, and means for flushing mercury vapor laden air from the vessel.

25. The system according to claim 24 including an electronic circuit connected to said detecting means, said electronic circuit including means for amplifying signals generated by light detected by said detecting means and for logarithmically converting the generated signals to signal values related to the concentration of mercury in the mercury vapor laden air, means for memorizing a first generated signal related to the light transmitted throUgh mercury-laden-vapor, means for memorizing a second generated signal related to the light transmitted through mercury-free air, and means for subtracting the first signal from the second signal to obtain difference signal directly related to the concentration of mercury in the mercury vapor laden air.

26. The system according to claim 25 including means for printing the mercury analysis measurement in parts per billion and wherein said electronic circuit includes a multiplying means connected between said subtracting means and said printing means for multiplying the difference signal by a predetermined multiplicand.

27. The system according to claim 25 including a second source of ultraviolet light of a wavelength band which is near, but which does not include, the mercury vapor absorption band, said second source being positioned to pass ultraviolet light endwise through the vessel at predetermined times, and wherein a memorizing means is operable to memorize a generated signal obtained when ultraviolet light from said second source is passed through the mercury vapor laden air in the vessel; a memory means is operable to memorize a generated signal obtained when ultraviolet light from said second source is passed through mercury-free air in the vessel, said subtracting means being operable to subtract said first signal obtained when ultraviolet light from said first source is passed through the mercury vapor laden air in the vessel from said signal obtained when ultraviolet light from said second source is passed through the mercury vapor laden air in the vessel to obtain a first difference signal, memory means operable to memorize a third signal obtained when ultraviolet light from said first source is passed through mercury-free air in the vessel, memory means operable to memorize a fourth signal obtained when ultraviolet light from said second source is passed through mercury-free air in the vessel, said subtracting means being operable to subtract said third signal from said fourth signal to obtain a second difference signal, and said electronic circuit includes a means for memorizing said first difference signal and a means for memorizing said second difference signal and a second subtracting means for subtracting said second difference signal from said first difference signal to obtain a third difference signal which is directly related to mercury vapor vaporized in the test tube and which has had subtracted therefrom the undesired effects of ultraviolet light absorption by other vapors which may be in the vessel in addition to mercury vapor.

28. The system according to claim 27 including means for printing the mercury analysis of a fluid sample in parts per billion and wherein said electronic circuit includes multiplying means connected between said second subtracting means and said printing means for multiplying said third difference signal by a predetermined multiplicand to obtain a numerical value in parts per billion of the mercury concentration in the fluid sample.

29. The system according to claim 24 wherein said flushing means includes a filter for removing mercury vapors from air used as a flushing medium, and a flush nozzle having its outlet orifice arranged to inject flushing air into the lower end of the vessel adjacent one side of the vessel and in a direction generally parallel to the longitudinal axis of the vessel.

30. The system according to claim 24 including an ultraviolet band pass filter situated between one end of the vessel and said detecting means.

32. The system according to claim 24 wherein said light source is horizontally spaced from the upper end of the vessel and a prism is situated above the upper end of the vessel for reflecting light from said light source downwardly through vessel.