EP0346387A1 - Improved automatic atomic-absorption spectrometer - Google Patents

Improved automatic atomic-absorption spectrometer

Info

Publication number
EP0346387A1
EP0346387A1 EP88902653A EP88902653A EP0346387A1 EP 0346387 A1 EP0346387 A1 EP 0346387A1 EP 88902653 A EP88902653 A EP 88902653A EP 88902653 A EP88902653 A EP 88902653A EP 0346387 A1 EP0346387 A1 EP 0346387A1
Authority
EP
European Patent Office
Prior art keywords
lamp
arm
carousel
pulse
drum
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
EP88902653A
Other languages
German (de)
French (fr)
Other versions
EP0346387A4 (en
Inventor
Thomas J. Scuitto
Theodore J. Scuitto
Al E. Bernhard
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Leeman LLC
Original Assignee
Leeman LLC
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Leeman LLC filed Critical Leeman LLC
Publication of EP0346387A1 publication Critical patent/EP0346387A1/en
Publication of EP0346387A4 publication Critical patent/EP0346387A4/en
Ceased legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
    • G01J3/02—Details
    • G01J3/06—Scanning arrangements arrangements for order-selection
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
    • G01N21/3103—Atomic absorption analysis
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2201/00—Features of devices classified in G01N21/00
    • G01N2201/06—Illumination; Optics
    • G01N2201/069—Supply of sources
    • G01N2201/0696—Pulsed

Definitions

  • the analytical instrument consists of a means for generating a vapor such as a nebulizer; a burner assembly to disassociate into free atoms the vapor delivered by the nebulizer: a source of monochromatic light such as a hollow cathode lamp which light is directed through the atomized vapor, and a device for isolating and measuring the monochromatic light after it has passed through the atomized vapor.
  • the quantitative measurement of the elements present in the vapor and thus the liquid sample from which the vapor was derived is made by comparing the intensity of the monochromatic light characteristic of an element after absorption in the burner flame to the unabsorbed intensity of the light source.
  • the spectrometer system consists of the following basic parts:
  • a light source that has up to 16 different hollow cathode lamps mounted in a carousel so that each lamp can be rapidly and accurately positioned into the optical path when it is needed.
  • a sampling system that converts a sample into an atomic vapor so that the absorption of the atoms can be determined and related to the concentration in the original sample.
  • a monochromator that isolates the wavelength region of interest, converts the light into an electronic signal via a photomultiplier tube and displays and records the results. 4. A computer system that controls the system and processes and displays the meas urements.
  • the monochromator has a grating that disperses light of different wavelengths in different directions.
  • the wavelength of light that passes through the monochromator is determined by the rotational position of the grating.
  • the rotational position of the grating is determined by a unique drive mechanism.
  • FIG. 1 is a schematic diagram of the grating and its unique drive mechanism.
  • the grating is mounted so that its front surface G pivots about an axis at point P.
  • An arm A is attached to the grating mount to allow the grating to be rotated as the taut band or wire B pulls on the arm.
  • the taut band or wire is connected to the arm at a hinge point H.
  • a spring S helps to keep the band or wire taut.
  • the band is connected to a drum D at point C and wraps around drum, less than one time or up to many times around the drum.
  • the drum is rotated about its axis M by a motor (stepping, synchronous, or servo). This mechanism is unique for at least two reasons:
  • the drum could be shaped so that the angle of the drum position could be directly proportional to the energy of the light passing through the monochromator (that is, inversely proportional to the wavelength). Or the drum could be shaped so that the angle of the drum position is directly proportion to wavelength.
  • the deviation can be corrected by the computer supplying an offset number for the position of the motor.
  • the offset number can be calculated more quickly when the deviation has the simplest mathematical form.
  • Prior art consist of the sine-bar mechanism for driving a grating arm.
  • This drive requires a worm gear that is highly accurate throughout its length, and it requires a point of contact between the carriage that rides on the worm gear and the arm that slides along the arm. The worm gear and the sliding contact are both subject to wear.
  • the taut band system is not subject to such wear because there are no gears if the motor is connected directly to the drum shaft M, and there is no sliding contact that moves along the arm A.
  • the taut band system also allows the wavelength to be changed much more rapidly than would be reasonable (because of rapid wear) for the worm gear system.
  • the worm gear in this application must have a very fine pitch because the grating must be positioned with great accuracy to achieve a reproducible wavelength setting that is better than 0.1 nanometers.
  • the fine pitch requires exceptionally high speed rotation for rapid scanning.
  • Prior art also consists of mounting the grating directly on a motor shaft. This does not have the wearing surfaces that the sine-bar has and it allows rapid scanning of the wavelength. Connecting the motor shaft directly to the grating shaft produces only one mathematical relationship between the motor position and the wavelength passing through the monochromator: the relationship is nonlinear in wavelength and the inverse of wavelength (frequency or photon energy).
  • a special high precision motor is required to achieve the necessary wavelength precision and accuracy, and the motor must be driven in such a manner that the nonlinearity is compensated for when wavelength scanning is recorded on a strip chart recorder for example.
  • the taut band system does not require a motor with such high precision when the diameter of the drum D is considerably less than the length of the arm A.
  • the demand on precision is decreased by approximately the ratio of these two dimensions.
  • Prior art also consists of a nonlinear drum or cam (mounted on a motor shaft) that is in direct contact with the grating arm.
  • the wavelength range covered is limited by the extent of the motion of the arm as the cam rotates through one full revolution. A compromise is necessary between the range of the wavelength region covered and the accuracy and precision with which the wavelength can be set.
  • the taut band system is able to cover a wide wavelength range with accuracy, especially when a circular drum is used and the diameter of the drum is smaller than the length of the arm. (In this case the taut band wraps around the drum more than once during a wide wavelength scan.)
  • the functional relationship between motor position and wavelength is determined not only by the shape of the drum, but as mentioned above also by the length of the arm A, the length of the taut member B, the average diameter of the drum D, and the distance between the pivot points of the drum M and the grating P.
  • the taut band system has no member that rubs against the grating arm as does the cam system.
  • Another advantage is that this is more efficient than the acme lead screws and therefore energy required and drive costs are lower for the same performance.
  • Each different chemical element whose absorption is to be determined requires a different hollow cathode lamp. In a few cases one lamp may suffice for a few different elements. Up to 16 lamps are mounted on a lamp carousel that rapidly rotates each lamp into an accurately determined position in the optical path when the lamp is needed.
  • a unique (and necessary) feature of the carousel is its ability to accurately and rapidly position each lamp that is present in the carousel. It does this rapidly because of the way that the carousel is pivoted about two points P1 and P2 In Figure 2. Pivoting about P1 moves the proper lamp into position and positions it accurately in a substantially vertical direction. Pivoting about P2, which occurs essentially during the same time that the movement about P1 occurs, positions the lamp accurately in a substantially horizontal direction.
  • Figure 2 shows the motion about P2 being done with a worm gear W driven by a motor K2.
  • Other driving methods are possible, such as a direct connection of the shaft of E2 to a motor shaft.
  • a unique feature of the carousel is the use of pivoting around two pivots to align the lamp in the horizontal and vertical directions. Pivoting can be done more rapidly and with a simpler mechanism than moving the entire carousel horizontally along a linear translation stage for example.
  • the computer system that controls the spectrometer scans the lamp alternately about P1 and P2 two or three times in each direction to determine when the lamp is centered on the optical axis.
  • the two motor positions (for the motors that drive the carousel about P1 and P2) are then stored in memory for later use to position the lamp when the lamp is needed during a chemical analysis.
  • Prior art Includes a carousel Chat is moved around a pivot P1, and where the accuracy of alignment is done by manual adjustments on the mount for each individual lamp.
  • One claim here is for a pulsed means of removing atoms from the surface of a solid sample (and keeping the atoms in a substantially free state long enough for them to be observed) that combines the removal effects of (a) at least one jet of gas disposed adjacent such sample surface and pointing at a substantially nonzero angle toward such surface and (b) a low pressure electrical discharge.
  • This special type of discharge (1) pulse the electrical discharge, (2) pulse the gas jet, and (3) pulse both simultaneously.
  • pulsing the atom source has the advantage of getting high absorption generated by high current pulses without the instability associated with high current DC operation. This also permits better limits of detectability for less power costs.
  • Prior art includes pulsing a hollow cathode lamp, which is a glow discharge. It is not obvious however from this prior art that this special combined discharge can be pulsed. For example, it would be reasonable to expect that a gas jet when suddenly turned on would blow out the electrical discharge. It would also be reasonable to expect that the presence of a jet prior to turning on the electrical discharge would make it impossible to rapidly establish during the electrical pulse an electrical discharge in the rapidly moving jet. Even if it were not possible to establish a pulsed mode of operation (where the jet or electrical discharge are suddenly turned on) it is still possible to establish the previously known continuous mode of operation of the combined discharge by the different means of slowly turning on the jet.
  • An absorption measurement requires knowledge of the light source signal both in the presence of and in the absence of the absorber. This is usually done by physically placing a cell containing a nonabsorbing substance in the light path and recording the signal, and then physically removing the nonabsorber and physically placing a cell containing the absorber in the light path and recording the signal. This is done rather frequently to compensate for changes in the light source intensity with time. This method is also used to compensate for changes in the light source intensity with wavelength during a spectral scan.
  • This pulsed method also has the advantage of observing the same part of the beam from the lamp for both signals, and with the same optical components in the beam.
  • Double beam systems either observe different parts of the beam at the same time, or the same part of the beam with different optical components in each beam. When different parts of the beam are observed, each part may behave somewhat differently, and the compensation will not, then, be completely accurate. When the same part is observed by different optical components, then the optical components may not be identical, causing the compensation to be somewhat inaccurate.
  • Another embodiment of this claim is the use of a pulsed light source Chat is synchronized with the pulsed absorbing source so that a nonabsorber light measurement pulse occurs just prior to the pulse of the absorbing source, and another occurs after the absorbing source is pulsed on.
  • the separation of the atomization process from the absorption measurement temporally also eliminates the emission noise from the absorption measurement thus improving detection limits.
  • high intensity light source pulses reduce front end noise improving detection limits.
  • an important limitation of absorption methods is the limited dynamic range (of absorbance values and therefore concentrations) over which accurate measurements can be made.
  • the use of a pulsed source of absorbing atoms allows the dynamic range to be easily extended without changing wavelength and without a significant loss of time or sample. This unique method involves making measurements at a known delay time after the absorber pulse is turned off (and the absorption has had a chance to decay) when the absorption is too high during the pulse.
  • a continuous light source When a continuous light source is used, then many measurements can be made at fixed delay-time intervals after each pulse. The data for the best delay-time interval are then selected for use after the measurements have been completed.
  • a pulsed light source When a pulsed light source is used, then a measurement made during a previous absorber pulse can be used to select the delay time to pulse the lamp for the present absorber pulse. Alternatively, the delay time can be set before a sample is run if some previous knowledge of the approximate range of concentration is available for the sample.
  • the relationship between delay time and absorbance relative to the absorbance that occurs during the absorber pulse is determined by measurement. This relationship is used to establish a large dynamic range over which concentrations can be accurately compared; that is, the delay time and the measured absorbance are both entered into this relationship to obtain an effective absorbance (or parameter with some other name) for comparison purposes over a large dynamic range of concentrations.
  • the Analyte 16 differs in two fundamental ways from currently existing multielement AA instruments. First, it analyzes each sample completely for all the desired elements, before moving on to the next sample. Conventional multielement
  • AA's analyze a group of, say, 50 samples by determining a single element in all of them, then going to a second element, and so on.
  • the Analyte 16 is intended for use with the Analyte Atomsource tm non-thermal Atomizer, which is designed for the analysis of solid, undissolved samples.
  • Conventional AA's use either a flame or a furnace atomizer, both of which are most suitable for the analysis of liquids.
  • the Analyte 16 preserves the flame AA advantages of specificity and ease of use, but provides even better precision (0.12 RSD), and the ability to determine a wide range of concentrations, from ppm to constituent levels, with little or no sample preparation.
  • the Analyte 16 Analyte 16 AA - 2 also has good sensitivity for refractory elements such as B, Si, Ti, and W, which give problems by conventional AA.
  • a laboratory might therefore consider the use of an Analyte 16 AA Spectrophotometer instead of, or as a supplement to, an X-ray fluorescence or an arc/spark emission spectrometer.
  • the Analyte 16 is equipped with a turret that can hold sixteen hollow-cathode lamps, some of which can be multielement sources. If the first element to be determined in a given sample is, say, silver, and the second is iron, the automated operation is as follows:
  • the source optics of the instrument set themselves to accept the light from the silver hollow cathode lamp, while the drives to the preselected silver wavelength. Immediately after the silver has been determined, the optics move to select the emission from the iron lamp, while the monochromator moves to the iron wavelength, and so on until the sample has been completely analyzed.
  • the time for each determination can be as low as 5 seconds per element. A sample can be analyzed for ten elements in 60 seconds, and for 20 elements in under two minutes.
  • the Analyte 16 consists of three modules.
  • the optical module includes the lamp turret, monochromator, power supplies, and microprocessor controllers.
  • the second module is the Atomsource Atomizer.
  • the third module is an IBM-compatible personal computer, which provides all the required control and intelligence for instrument and atomizer.
  • the Analyte 16 can also be provided with a conventional atomic absorption flame atomizer. In the flame mode, the Ana Analyte 16 AA - 3 lyte 16 has performance that is approximately equivalent to that of a good sequential ICP (inductively coupled plasma) spectrometer. The Analyte 16 has, however, far fewer spectral interferences, and can use all the well-established atomic absorption methods that have been developed over the past 25 years. The Analyte 16 is therefore worth considering as an alternative to sequential ICP instruments.

Abstract

Spectromètre d'absorption atomique dans lequel chaque échantillon est analysé pour tout élément désiré avant de commencer l'échantillon suivant. De nouvelles caractéristiques incluent une commande de réseau de diffraction, un alignement de carrousel à lampe, une source d'atomes pulsée, une compensation de dérive de lampe, et un contrôle de taux d'intensité. Le réseau de diffraction (G) est mû par un bras (A), le bras (A) par un ruban tendu (B) enroulé sur un tambour (D), et le tambour directement par un moteur. Le carrousel à lampe (C) monte sur un levier en forme de ''L'' ayant un bras horizontal et un bras vertical. Le carrousel (C) pivote sur un axe horizontal (P1) à l'extrémité du bras vertical. Le levier pivote lui-même sur un axe horizontal (P2) à l'angle du L; il est entraîné autour de son axe par un moteur (M2) et vissé (W) à l'autre extrémité du L. La rotation du carrousel (C) sur son axe fait prendre position à la lampe de droite et la règle avec précision dans la direction verticale. Le fait de pivoter le levier simultanément sur son axe d'angle positionne la lampe avec précision dans la direction horizontale. Le source d'atomes pulsée est une combinaison d'un brûleur à jet de gaz d'angle et d'une unité de décharge. Pendant les impulsions il produit une haute absorption avec des limites de détectabilités meilleures; la puissance moyenne est inférieure. Le compensateur de dérive de lampe remplit les deux fonctions de pulsation d'absorbeur pour obtenir une lecture d'intensité de lampe entre les impulsions. Le contrôle de taux d'intensité est obtenu en exploitant encore plus au-delà la pulsation, c'est-à-dire en prenant des mesures à une temporisation (et à un temps de remise à zéro) connue, après chaque impulsion.Atomic absorption spectrometer in which each sample is analyzed for any desired element before starting the next sample. New features include diffraction grating control, lamp carousel alignment, pulsed atom source, lamp drift compensation, and intensity rate control. The diffraction grating (G) is moved by an arm (A), the arm (A) by a stretched ribbon (B) wound on a drum (D), and the drum directly by a motor. The lamp carousel (C) mounts on a lever in the shape of an "L" having a horizontal arm and a vertical arm. The carousel (C) pivots on a horizontal axis (P1) at the end of the vertical arm. The lever itself pivots on a horizontal axis (P2) at the angle of the L; it is driven around its axis by a motor (M2) and screwed (W) to the other end of the L. The rotation of the carousel (C) on its axis causes the right lamp to take position and adjusts it precisely in the vertical direction. Rotating the lever simultaneously on its angle axis precisely positions the lamp in the horizontal direction. The pulsed atom source is a combination of a corner gas jet burner and a discharge unit. During the pulses it produces a high absorption with better limits of detectability; the average power is lower. The lamp drift compensator fulfills the two absorber pulse functions to obtain a reading of lamp intensity between the pulses. The intensity rate control is obtained by exploiting the pulse even further, that is to say by taking measurements at a known delay (and reset time), after each pulse.

Description

IMPROVED AUTOMATIC ATOM IC-ABSORPTION SPECTROMETER
General background information.
A commonly used instrumental analysis method for the elemental analysis of various materials for trace and minor elements is the atomic absorption method. In the most used manifestation the analytical instrument consists of a means for generating a vapor such as a nebulizer; a burner assembly to disassociate into free atoms the vapor delivered by the nebulizer: a source of monochromatic light such as a hollow cathode lamp which light is directed through the atomized vapor, and a device for isolating and measuring the monochromatic light after it has passed through the atomized vapor. The quantitative measurement of the elements present in the vapor and thus the liquid sample from which the vapor was derived is made by comparing the intensity of the monochromatic light characteristic of an element after absorption in the burner flame to the unabsorbed intensity of the light source.
DISCLOSURE.
The spectrometer system consists of the following basic parts:
1. A light source that has up to 16 different hollow cathode lamps mounted in a carousel so that each lamp can be rapidly and accurately positioned into the optical path when it is needed.
2. A sampling system that converts a sample into an atomic vapor so that the absorption of the atoms can be determined and related to the concentration in the original sample.
3. A monochromator that isolates the wavelength region of interest, converts the light into an electronic signal via a photomultiplier tube and displays and records the results. 4. A computer system that controls the system and processes and displays the meas urements.
There are 5 improvements over prior art which we claim as inventions:
1. Grating drive
2. Lamp carousel optical alignment method
3. Pulsed atom source
4. Compensation method for lamp intensity drift
5. Dynamic range control
These will be discussed in order.
1. Grating Drive.
The monochromator has a grating that disperses light of different wavelengths in different directions. The wavelength of light that passes through the monochromator is determined by the rotational position of the grating. The rotational position of the grating is determined by a unique drive mechanism.
Figure 1 is a schematic diagram of the grating and its unique drive mechanism. The grating is mounted so that its front surface G pivots about an axis at point P. An arm A is attached to the grating mount to allow the grating to be rotated as the taut band or wire B pulls on the arm. The taut band or wire is connected to the arm at a hinge point H. A spring S helps to keep the band or wire taut. The band is connected to a drum D at point C and wraps around drum, less than one time or up to many times around the drum. The drum is rotated about its axis M by a motor (stepping, synchronous, or servo). This mechanism is unique for at least two reasons:
(1)because a taut band or wire connects the arm of the grating drive to a motorized drum and
(2)because the particular arrangement of the parts causes the angular position of the grating, and more importantly the wavelength that passes through the monochromator, to be related by a unique mathematical function to the angle of drum D; no other grating drive mechanism relates the angle of a motor shaft to the angle of the grating drive by this same mathematical function. This mathematical function depends upon the length of the arm A, the length of the taut member B, the diameter of the drum D, the distance between the pivot points of the drum M and the grating P, and the shape of the drum. The drum may be circular in shape, or it may be machined to have a shape that produces a particular desirable mathematical relationship. For example, the drum could be shaped so that the angle of the drum position could be directly proportional to the energy of the light passing through the monochromator (that is, inversely proportional to the wavelength). Or the drum could be shaped so that the angle of the drum position is directly proportion to wavelength.
When the functional relationship between motor position and
wavelength deviates from a desired relationship, the deviation can be corrected by the computer supplying an offset number for the position of the motor. In this case the offset number can be calculated more quickly when the deviation has the simplest mathematical form. The versatility of the taut band system to adjust the functional relationship by selecting dimensions listed in the previous paragraph helps to achieve a deviation with the simplest mathematical form.
Prior art consist of the sine-bar mechanism for driving a grating arm.
This produces a drive whose angular rotation of the motor is substantially directly proportional to the wavelength passing through the monochromator. This drive requires a worm gear that is highly accurate throughout its length, and it requires a point of contact between the carriage that rides on the worm gear and the arm that slides along the arm. The worm gear and the sliding contact are both subject to wear.
The taut band system is not subject to such wear because there are no gears if the motor is connected directly to the drum shaft M, and there is no sliding contact that moves along the arm A. The taut band system also allows the wavelength to be changed much more rapidly than would be reasonable (because of rapid wear) for the worm gear system.
(The worm gear in this application must have a very fine pitch because the grating must be positioned with great accuracy to achieve a reproducible wavelength setting that is better than 0.1 nanometers. The fine pitch requires exceptionally high speed rotation for rapid scanning.)
Prior art also consists of mounting the grating directly on a motor shaft. This does not have the wearing surfaces that the sine-bar has and it allows rapid scanning of the wavelength. Connecting the motor shaft directly to the grating shaft produces only one mathematical relationship between the motor position and the wavelength passing through the monochromator: the relationship is nonlinear in wavelength and the inverse of wavelength (frequency or photon energy). A special high precision motor is required to achieve the necessary wavelength precision and accuracy, and the motor must be driven in such a manner that the nonlinearity is compensated for when wavelength scanning is recorded on a strip chart recorder for example.
In addition to being more versatile than the direct drive motor system in the functional relationship between motor shaft position and wavelength, the taut band system does not require a motor with such high precision when the diameter of the drum D is considerably less than the length of the arm A. The demand on precision is decreased by approximately the ratio of these two dimensions.
Prior art also consists of a nonlinear drum or cam (mounted on a motor shaft) that is in direct contact with the grating arm. In this case the wavelength range covered is limited by the extent of the motion of the arm as the cam rotates through one full revolution. A compromise is necessary between the range of the wavelength region covered and the accuracy and precision with which the wavelength can be set.
The taut band system is able to cover a wide wavelength range with accuracy, especially when a circular drum is used and the diameter of the drum is smaller than the length of the arm. (In this case the taut band wraps around the drum more than once during a wide wavelength scan.) Unlike the cam drive, when a nonlinear drun is used with the taut band system, the functional relationship between motor position and wavelength is determined not only by the shape of the drum, but as mentioned above also by the length of the arm A, the length of the taut member B, the average diameter of the drum D, and the distance between the pivot points of the drum M and the grating P. The taut band system has no member that rubs against the grating arm as does the cam system.
Another advantage is that this is more efficient than the acme lead screws and therefore energy required and drive costs are lower for the same performance.
2. Lamp carousel optical alignment method.
Each different chemical element whose absorption is to be determined requires a different hollow cathode lamp. In a few cases one lamp may suffice for a few different elements. Up to 16 lamps are mounted on a lamp carousel that rapidly rotates each lamp into an accurately determined position in the optical path when the lamp is needed.
A unique (and necessary) feature of the carousel is its ability to accurately and rapidly position each lamp that is present in the carousel. It does this rapidly because of the way that the carousel is pivoted about two points P1 and P2 In Figure 2. Pivoting about P1 moves the proper lamp into position and positions it accurately in a substantially vertical direction. Pivoting about P2, which occurs essentially during the same time that the movement about P1 occurs, positions the lamp accurately in a substantially horizontal direction.
Figure 2 shows the motion about P2 being done with a worm gear W driven by a motor K2. Other driving methods are possible, such as a direct connection of the shaft of E2 to a motor shaft.
A unique feature of the carousel is the use of pivoting around two pivots to align the lamp in the horizontal and vertical directions. Pivoting can be done more rapidly and with a simpler mechanism than moving the entire carousel horizontally along a linear translation stage for example.
In operation, when a lamp is first mounted in the carousel, the computer system that controls the spectrometer scans the lamp alternately about P1 and P2 two or three times in each direction to determine when the lamp is centered on the optical axis.The two motor positions (for the motors that drive the carousel about P1 and P2) are then stored in memory for later use to position the lamp when the lamp is needed during a chemical analysis.
Prior art Includes a carousel Chat is moved around a pivot P1, and where the accuracy of alignment is done by manual adjustments on the mount for each individual lamp.
3. Pulsed atom source
One claim here is for a pulsed means of removing atoms from the surface of a solid sample (and keeping the atoms in a substantially free state long enough for them to be observed) that combines the removal effects of (a) at least one jet of gas disposed adjacent such sample surface and pointing at a substantially nonzero angle toward such surface and (b) a low pressure electrical discharge. There are three ways to pulse this special type of discharge (1) pulse the electrical discharge, (2) pulse the gas jet, and (3) pulse both simultaneously.
Another claim iε that pulsing the atom source has the advantage of getting high absorption generated by high current pulses without the instability associated with high current DC operation. This also permits better limits of detectability for less power costs. Prior art includes pulsing a hollow cathode lamp, which is a glow discharge. It is not obvious however from this prior art that this special combined discharge can be pulsed. For example, it would be reasonable to expect that a gas jet when suddenly turned on would blow out the electrical discharge. It would also be reasonable to expect that the presence of a jet prior to turning on the electrical discharge would make it impossible to rapidly establish during the electrical pulse an electrical discharge in the rapidly moving jet. Even if it were not possible to establish a pulsed mode of operation (where the jet or electrical discharge are suddenly turned on) it is still possible to establish the previously known continuous mode of operation of the combined discharge by the different means of slowly turning on the jet.
4. Compensation method for lamp intensity drift
Prior art. An absorption measurement requires knowledge of the light source signal both in the presence of and in the absence of the absorber. This is usually done by physically placing a cell containing a nonabsorbing substance in the light path and recording the signal, and then physically removing the nonabsorber and physically placing a cell containing the absorber in the light path and recording the signal. This is done rather frequently to compensate for changes in the light source intensity with time. This method is also used to compensate for changes in the light source intensity with wavelength during a spectral scan.
It is uniquely possible when using a pulsed atom source to supply the absorbing atoms from the sample material, to obtain these two signals by recording the signal before each pulse and then recording the signal after the pulsed atom source has been turned on and the absorbing sample atoms are in the optical path. The general claim here is either (a) this method of obtaining these two signal before and during each pulse or/and (b) the use of a pulsed absorber to allow this method to be used without using an external force to physically manipulate the nonabsorber and absorber between these measurements.
By making these two measurements for each pulse, it is possible to compensate for relatively rapid changes with time in the light source intensity. If the measurement of the nonabsorber signal is made just prior to (within microseconds of) turning on the sampling pulse, then the compensation can be achieved on a time scale that is considerably shorter than can be done with the methods that involve physical manipulation (even with mechanically vibrating systems); more rapid changes in the lamp intensity can thereby be tolerated.
This pulsed method also has the advantage of observing the same part of the beam from the lamp for both signals, and with the same optical components in the beam. Double beam systems either observe different parts of the beam at the same time, or the same part of the beam with different optical components in each beam. When different parts of the beam are observed, each part may behave somewhat differently, and the compensation will not, then, be completely accurate. When the same part is observed by different optical components, then the optical components may not be identical, causing the compensation to be somewhat inaccurate.
The claims presented here are not restricted to solid sample atomization but apply to flame atomization as well.
Another embodiment of this claim is the use of a pulsed light source Chat is synchronized with the pulsed absorbing source so that a nonabsorber light measurement pulse occurs just prior to the pulse of the absorbing source, and another occurs after the absorbing source is pulsed on.
Also the separation of the atomization process from the absorption measurement temporally, also eliminates the emission noise from the absorption measurement thus improving detection limits.
In addition high intensity light source pulses reduce front end noise improving detection limits.
5. Dynamic range control.
As mentioned in the previous patent application, an important limitation of absorption methods is the limited dynamic range (of absorbance values and therefore concentrations) over which accurate measurements can be made. The use of a pulsed source of absorbing atoms allows the dynamic range to be easily extended without changing wavelength and without a significant loss of time or sample. This unique method involves making measurements at a known delay time after the absorber pulse is turned off (and the absorption has had a chance to decay) when the absorption is too high during the pulse.
When a continuous light source is used, then many measurements can be made at fixed delay-time intervals after each pulse. The data for the best delay-time interval are then selected for use after the measurements have been completed. When a pulsed light source is used, then a measurement made during a previous absorber pulse can be used to select the delay time to pulse the lamp for the present absorber pulse. Alternatively, the delay time can be set before a sample is run if some previous knowledge of the approximate range of concentration is available for the sample.
In practice, the relationship between delay time and absorbance relative to the absorbance that occurs during the absorber pulse is determined by measurement. This relationship is used to establish a large dynamic range over which concentrations can be accurately compared; that is, the delay time and the measured absorbance are both entered into this relationship to obtain an effective absorbance (or parameter with some other name) for comparison purposes over a large dynamic range of concentrations.
The Analyte 16 differs in two fundamental ways from currently existing multielement AA instruments. First, it analyzes each sample completely for all the desired elements, before moving on to the next sample. Conventional multielement
AA's analyze a group of, say, 50 samples by determining a single element in all of them, then going to a second element, and so on.] Second, the Analyte 16 is intended for use with the Analyte Atomsourcetm non-thermal Atomizer, which is designed for the analysis of solid, undissolved samples. [Note to Ed: Conventional AA's use either a flame or a furnace atomizer, both of which are most suitable for the analysis of liquids.]
Equipped with the Atomsource Atomizer, the Analyte 16 preserves the flame AA advantages of specificity and ease of use, but provides even better precision (0.12 RSD), and the ability to determine a wide range of concentrations, from ppm to constituent levels, with little or no sample preparation. The Analyte 16 Analyte 16 AA - 2 also has good sensitivity for refractory elements such as B, Si, Ti, and W, which give problems by conventional AA. A laboratory might therefore consider the use of an Analyte 16 AA Spectrophotometer instead of, or as a supplement to, an X-ray fluorescence or an arc/spark emission spectrometer.
The Analyte 16 is equipped with a turret that can hold sixteen hollow-cathode lamps, some of which can be multielement sources. If the first element to be determined in a given sample is, say, silver, and the second is iron, the automated operation is as follows:
The source optics of the instrument set themselves to accept the light from the silver hollow cathode lamp, while the drives to the preselected silver wavelength. Immediately after the silver has been determined, the optics move to select the emission from the iron lamp, while the monochromator moves to the iron wavelength, and so on until the sample has been completely analyzed. The time for each determination can be as low as 5 seconds per element. A sample can be analyzed for ten elements in 60 seconds, and for 20 elements in under two minutes.
Physically, the Analyte 16 consists of three modules. The optical module includes the lamp turret, monochromator, power supplies, and microprocessor controllers. The second module is the Atomsource Atomizer. The third module is an IBM-compatible personal computer, which provides all the required control and intelligence for instrument and atomizer.
The Analyte 16 can also be provided with a conventional atomic absorption flame atomizer. In the flame mode, the Ana Analyte 16 AA - 3 lyte 16 has performance that is approximately equivalent to that of a good sequential ICP (inductively coupled plasma) spectrometer. The Analyte 16 has, however, far fewer spectral interferences, and can use all the well-established atomic absorption methods that have been developed over the past 25 years. The Analyte 16 is therefore worth considering as an alternative to sequential ICP instruments.

Claims

WE CLAIM :
All of the novel apparatus, methods, and other subject matter hereinabove disclosed.
EP19880902653 1987-02-17 1988-02-12 Improved automatic atomic-absorption spectrometer Ceased EP0346387A4 (en)

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DE3809212A1 (en) * 1988-03-18 1989-10-05 Bodenseewerk Perkin Elmer Co ATOMIC ABSORPTION SPECTROMETER
JPH06100538B2 (en) * 1989-08-02 1994-12-12 株式会社日立製作所 Atomic absorption spectrophotometer
US6587196B1 (en) * 2000-01-26 2003-07-01 Sensys Medical, Inc. Oscillating mechanism driven monochromator

Citations (2)

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US3655288A (en) * 1970-07-30 1972-04-11 Technicon Instr Optical system for use in automatic, simultaneous multielement atomic spectroscopy sample analysis apparatus
EP0091137A2 (en) * 1982-01-18 1983-10-12 Philips Electronics Uk Limited Lamp mount for optical apparatus

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AU414987B2 (en) * 1968-05-01 1971-07-13 Commonwealth Scientific And Industrial Research Organization Improvements in or relating to atomic absorption spectroscopy
SU734510A1 (en) * 1977-03-11 1980-05-15 Новосибирский институт органической химии СО АН СССР Device for turning diffraction grating
GB2109922B (en) * 1981-11-11 1985-03-20 Philips Electronic Associated Atomic resonance line source lamps and spectrophotometers for use with such lamps
GB2113829B (en) * 1982-01-19 1985-07-10 Philips Electronic Associated Atomic absorption spectrophotometer

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Publication number Priority date Publication date Assignee Title
US3655288A (en) * 1970-07-30 1972-04-11 Technicon Instr Optical system for use in automatic, simultaneous multielement atomic spectroscopy sample analysis apparatus
EP0091137A2 (en) * 1982-01-18 1983-10-12 Philips Electronics Uk Limited Lamp mount for optical apparatus

Non-Patent Citations (2)

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Title
APPLIED SPECTROSCOPY, vol. 22, no. 6, November-December 1968, pages 797-799, Baltimore, US; D.R. DEMERS: "Atomic fluorescence flame spectrometry: Potential tool for trace analycis" *
See also references of WO8806280A1 *

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AU623851B2 (en) 1992-05-28
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AU1396388A (en) 1988-09-14
JPH02502402A (en) 1990-08-02

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