TABLE VII. Representative printout of the results of the anal- ysis of three lines by the SQANAL program. Peak wavelength (A): 3600.170 Location of center of peak (in.): 2.57583 Maximum peak density (%): 4.5 Position error (in.}: 0.00027 Position error (A): -0.02239 Peak width (in.): 0.0035 Background correction factor: 0.8397 Peak wavelength (~): 3510.720 Location of center of peak (in.): 3.58142 Maximum peak density (%): 13.4 Position error (in.): 0.0004 Position error (•): -0.00319 Peak width (in.): 0.0027 Background correction factor: 0.8300 Peak wavelength (~): 3440.510 Location of center of peak {in.): 4.35768 Maximum peak density (%): 20.1 Position error (in): 0.00009 Position error (/~.): -0.00725 Peak width (in.): 0.0023 Background correction factor: 0.8332 V. SUMMARY. The completed system has demonstrated performance which meets or exceeds our initial design criteria. Exten- sions, for example, to do Abel inversion deconvolution of emission profiles, are not based strictly on a need for continued and improved software development. It is in this direction that our efforts are currently directed. ACKNOWLEDGMENTS The Wayne State University Laboratory Computer Network (Departments of Chemistry and Psychology) was funded by National Science Foundation RIAS Grant SER77-06874. This research was partially supported by the National Science Foundation under Grant CHE 8016148. Appreciation is expressed to Dr. Eric Johnson, former director of the WSU LCN system, for generous assistance in software development. Conversations with John S. Beaty, who implemented a similar system for routine spectrochem- ical analysis at Globe Union, Milwaukee, are especially valued. Portions of this work were conducted as part of the requirements for the Master of Science (M.E.G.) and Doctor of Philosophy (M.A.S.) degrees in Chemistry at Wayne State University. 1. R. A. Burdo, J. R. Roth, and G. H. Morrison, Anal. Chem. 46, 701 (1974). 2. D. M. Desiderio, Jr. and T. E. Mead, Anal. Chem. 40, 2090 (1968). 3. U. W. Amdt, R. A. Crowther, and J. F. W. Mallett, J. Physics E., Series 2, 510 (1967). 4. J. F. W. Mailett, J. N. Champness, A. R. Faruqi, and T. H. Gossling, J. Physics E. 10, 351 (1977). 5. L. J. Rigby, Adv. Mass. Apec. 7B, 1074 (1978). 6. J. D. Fassett, J. R. Roth, and G. H. Morrison, Anal. Chem. 49, 2322 (1977). 7. A. Scheeline and J. P. Walters, Anal. Chim. Acta 95, 59 (1977). 8. A. Scheeline and J. P. Walters, Anal. Chem. 48, 1519 (1976). 9. A. Savitzky and M. J. E. Golay, Anal. Chem. 36, 1627 (1964). 10. J. R. Chapman, Computers in Mass Spectroscopy. (Academic Press, London, 1978). 11. Sourcebook for Programmable Calculators. Texas Instruments Electronics Series, (McGraw-Hill, New York, 1979). 12. G. Forsythe and C. B. Moler, Computer Solution of Linear Algebraic Systems. (Prentice Hall; New Jersey, 1967). 13. J. R. Woodyard, B. C. Piper, and K. R. Stever, Appl. Spectrosc. 33, 25 (1979). 14. D. M. Coleman, M. A. Sainz, and H. T. Butler, Anal. Chem. 52, 746 (1980). Direct Aerosol Introduction in Constant-temperature Furnace Atomic Absorption Spectroscopy DENNIS R. JENKE* and RAY WOODRIFF Department of Chemistry, Montana State University, Bozeman, Montana 59717 Combination of a sample introduction/desolvation system with a Woodriff-type constant temperature furnace atomizer allows for the rapid, direct analysis of aqueous samples with precisions comparable to and detection limits 5 times lower than those obtained by conventional flame analysis. The introduction sys- tem consists of a pneumatic nebulizer, a spray chamber for collection of large aerosol particles, a heated chamber for sol- vent evaporation, and a condenser for solvent removal. Under optimized operating conditions, detection limits obtainable for Ag, Cd, Zn, and Pb are 0.14, 0.50, 0.64, and 8.3 ppb, respectively, whereas precision at a concentration level 50 times the detection limit is 2.7%, 5.3%, 7.0%, and 5.5% relative standard deviation. The system is relatively free from chloride and nitrate matrix interferences, whereas interferences resulting from the pres- ence of 1% sulfate and phosphate ions appear to be related to the nebulization process and can be greatly reduced by modifi- cation of these conditions. Received 15 March 1982; revision received 14 June 1982. * Author to whom correspondence should be addressed. Volume 36, Number 6, 1982 Index Headings: Atomic absorption; Graphite furnace atomiza- tion; Methods, analytical. INTRODUCTION The utilization of the graphite furnace as an excitation source for atomic analysis of aqueous samples is limited by the ease with which samples can be reproducibly introduced into the excitation cavity and means for re- moving the interference of sample solvent and matrix. Direct introduction of sample in the form of an aerosol into the furnace, which would greatly decrease per sam- ple analysis time and cost, is limited by factors which include (a) excessive graphite decay in the presence of corrosive or oxidizing agents in the sample matrix and (b) reduced absolute sensitivity when compared with nonaerosol introduction methods due to the dependance on the magnitude of the atom population in the atomizer APPLIED SPECTROSCOPY 657
Transcript
T A B L E VII. R e p r e s e n t a t i v e pr intout o f the resu l t s o f the a n a l - y s i s o f t h r e e l i n e s b y t h e S Q A N A L p r o g r a m .
Peak wavelength (A): 3600.170 Locat ion of center of peak (in.): 2.57583 M a x i m u m peak dens i ty (%): 4.5 Posi t ion error (in.}: 0.00027 Posi t ion error (A): -0.02239 Peak width (in.): 0.0035 Background correction factor: 0.8397
Peak wavelength (~): 3510.720 Locat ion of center of peak (in.): 3.58142 M a x i m u m peak densi ty (%): 13.4 Posi t ion error (in.): 0.0004 Posi t ion error (•): -0.00319 Peak width (in.): 0.0027 Background correction factor: 0.8300
Peak wavelength (~): 3440.510 Locat ion of center of peak {in.): 4.35768 M a x i m u m peak densi ty (%): 20.1 Posi t ion error (in): 0.00009 Posi t ion error (/~.): -0.00725 Peak width (in.): 0.0023 Background correction factor: 0.8332
V. SUMMARY.
The completed system has demonstrated performance which meets or exceeds our initial design criteria. Exten- sions, for example, to do Abel inversion deconvolution of emission profiles, are not based strictly on a need for
continued and improved software development. It is in this direction that our efforts are currently directed.
ACKNOWLEDGMENTS The Wayne State University Laboratory Computer Network (Departments of
Chemistry and Psychology) was funded by National Science Foundation RIAS Grant SER77-06874. This research was partially supported by the National Science Foundation under Grant CHE 8016148.
Appreciation is expressed to Dr. Eric Johnson, former director of the WSU LCN system, for generous assistance in software development. Conversations with John S. Beaty, who implemented a similar system for routine spectrochem- ical analysis at Globe Union, Milwaukee, are especially valued. Portions of this work were conducted as part of the requirements for the Master of Science (M.E.G.) and Doctor of Philosophy (M.A.S.) degrees in Chemistry at Wayne State University.
1. R. A. Burdo, J. R. Roth, and G. H. Morrison, Anal. Chem. 46, 701 (1974). 2. D. M. Desiderio, Jr. and T. E. Mead, Anal. Chem. 40, 2090 (1968). 3. U. W. Amdt, R. A. Crowther, and J. F. W. Mallett, J. Physics E., Series 2,
510 (1967). 4. J. F. W. Mailett, J. N. Champness, A. R. Faruqi, and T. H. Gossling, J.
Physics E. 10, 351 (1977). 5. L. J. Rigby, Adv. Mass. Apec. 7B, 1074 (1978). 6. J. D. Fassett, J. R. Roth, and G. H. Morrison, Anal. Chem. 49, 2322 (1977). 7. A. Scheeline and J. P. Walters, Anal. Chim. Acta 95, 59 (1977). 8. A. Scheeline and J. P. Walters, Anal. Chem. 48, 1519 (1976). 9. A. Savitzky and M. J. E. Golay, Anal. Chem. 36, 1627 (1964).
10. J. R. Chapman, Computers in Mass Spectroscopy. (Academic Press, London, 1978).
11. Sourcebook for Programmable Calculators. Texas Instruments Electronics Series, (McGraw-Hill, New York, 1979).
12. G. Forsythe and C. B. Moler, Computer Solution of Linear Algebraic Systems. (Prentice Hall; New Jersey, 1967).
13. J. R. Woodyard, B. C. Piper, and K. R. Stever, Appl. Spectrosc. 33, 25 (1979). 14. D. M. Coleman, M. A. Sainz, and H. T. Butler, Anal. Chem. 52, 746 (1980).
Direct Aerosol Introduction in Constant-temperature Furnace Atomic Absorption Spectroscopy
DENNIS R. JENKE* and RAY WOODRIFF Department of Chemistry, Montana State University, Bozeman, Montana 59717
Combinat ion o f a s a m p l e i n t r o d u c t i o n / d e s o l v a t i o n s y s t e m w i t h a Woodri f f - type cons tant t empera ture f u r n a c e a t o m i z e r a l l o w s fo r t h e r a p i d , d i r e c t a n a l y s i s o f aqueous sample s w i t h p r e c i s i o n s c o m p a r a b l e to and de tec t ion l imits 5 t imes l o w e r than those obta ined b y c o n v e n t i o n a l f l a m e a n a l y s i s . T h e in troduct ion sys- t em cons i s t s o f a p n e u m a t i c n e b u l i z e r , a s p r a y c h a m b e r f o r co l lec t ion o f l a r g e a e r o s o l p a r t i c l e s , a h e a t e d c h a m b e r for sol- v e n t evaporat ion , and a condenser for so lven t removal . U n d e r opt imized opera t ing condit ions , de tec t ion l imi ts obta inable for Ag, Cd, Zn, and Pb are 0.14, 0.50, 0.64, and 8.3 ppb, r e s p e c t i v e l y , w h e r e a s p r e c i s i o n a t a c o n c e n t r a t i o n l eve l 50 t imes the de tec t ion l i m i t i s 2.7%, 5.3%, 7.0%, a n d 5.5% r e l a t i v e s t a n d a r d d e v i a t i o n . T h e s y s t e m is r e l a t i v e l y f r e e f r o m chloride and n i t r a t e m a t r i x i n t e r f e r e n c e s , w h e r e a s i n t e r f e r e n c e s r e s u l t i n g f r o m t h e pres- ence o f 1% sul fate and p h o s p h a t e ions appear to be re la ted to the nebul i za t ion process and can be great ly reduced b y modif i - cat ion o f these condit ions .
Received 15 March 1982; revision received 14 June 1982. * Au tho r to w h o m correspondence should be addressed.
Volume 36, Number 6, 1982
Index Headings: Atomic absorpt ion; G r a p h i t e f u r n a c e atomiza- t ion; Methods , a n a l y t i c a l .
INTRODUCTION
The utilization of the graphite furnace as an excitation source for atomic analysis of aqueous samples is limited by the ease with which samples can be reproducibly introduced into the excitation cavity and means for re- moving the interference of sample solvent and matrix. Direct introduction of sample in the form of an aerosol into the furnace, which would greatly decrease per sam- ple analysis time and cost, is limited by factors which include (a) excessive graphite decay in the presence of corrosive or oxidizing agents in the sample matrix and (b) reduced absolute sensitivity when compared with nonaerosol introduction methods due to the dependance on the magnitude of the atom population in the atomizer
APPLIED SPECTROSCOPY 657
on the efficiency of the aerosol-producing mechanism. Since in most applications the sample solvent is the primary source of corrosive agents, the first limitation is effectively combated by heat desolvation and solvent removal by recondensation. By coupling an aerosol pro- duction/desolvation system described by Veillon and Margoshes 1 with a small graphite rod type atomizer, Murphy, Clyburn, and Veillon 2 were able to detect con- centrations of 0.14, 4.0, and 0.03 tLg/ml for Zn, Cu, and Bi by atomic fluorescence. Molnar and Winefordner 3 report excellent sensitivities for several metals using a vitreous carbon furnace/continuous sample introduction combi- nation for fluorescence spectrometry. The utilization of combined graphite furnace/continuous introduction sys- tems for atomic absorption spectrometry is reported by several researchers. 4' ~ Using an atomizer equipped with graphite tubes 20 mm long with a bore diameter of 4 ram, a steel concentric flow nebulizer, and a similar desolva- tion system, Chamsaz, Sharp, and West 4 were able to detect subpart per million quantities of Ca, Cd, Co, Mg, Pb, and Fe by atomic absorption. Whereas precision at a concentration level 100 times the detection limit was typically 2% relative standard deviation (RSD), these researchers document severe matrix interferences. Poor detection limits and interferences were attributed to the low atomization efficiency of the apparatus and illustrate the type b limitations of direct aerosol introduction noted above.
The constant temperature graphite tube furnace de- sign of Woodriff 6 can, by virtue of its long tube length (~35 cm) and large bore diameter (8 mm) which forms a proportionately larger atom reservoir, effectively de- crease the magnitude of type b limitations. Previous application of constant aerosol introduction into this type of atomizer by Woodriff, Culver, and Olsen 7 utilized ultrasonic nebulization and a methanol sample matrix; sensitivities documented for Cr and Ag are 0.3 and 0.45 ttg/l, respectively. Using a similar experimental system,
8 Stone reports sensitivities between 1 and 10 ppb for Cu, Mn, and Co. The purpose of this paper is to document the performance of a system combining continuous aer- osol introduction/desolvation system with the Woodriff furnace atomizer in atomic spectroscopy.
I. E X P E R I M E N T A L
A. A ppa ra tu s . The analytical system used consists of three major components: the spectrometer/detector, the furnace atomizer, and the sample introduction sys- tem. The spectrometer used was a Varian model AA6 interfaced with a variable span Sargent Welch model XKR strip chart recorder. An optical path of 40 cm is produced between the hollow cathode source and the monochromator/detector and is defined by the use of two focusing lenses mounted between the atomizer and both the source and monochromator. All measurements are made with a monochromator spectral band of 0.5 nm and without background correction.
The atomizer is a modified single-phase Woodriff-type constant temperature graphite tube furnace design. The internal design used is illustrated in Fig. 1 and is de- scribed in greater detail elsewhere. 9 Design modifications that allow for direct introduction of aerosols are limited to modification of side tube connections to both the
658 Volume 36, Number 6, 1982
heater tube and the external sampling port. All graphite tubes and parts are constructed using POCO-type AXF- SQ graphite. Welders grade argon is used as both the purge and carrier gas. Furnace temperature is monitored with an optical pyrometer focused through the side tube entrance.
The sample introduction apparatus used is illustrated in Fig. 2 and consists of a nebulizer, a heated spray chamber, condenser, and viewing vent. The basic design is similar to that reported by Veillon and Margoshes. 1 Pneumatic nebulizers used in this study include a Varian standard variable (part number 01-100067-00) nebulizer, a modified Meinhardt glass concentric (model T-230-A2) nebulizer, and an Instruments SA Pt t ip/Teflon (model 48P-Zr-2) cone concentric nebulizer. The spray chamber consists of a 20-cm piece of 22 mm o.d. Pyrex glass tubing bent at a 135 ° angle 80 mm from the nebulizer end with a stopcock drain at the bend. Heat is supplied by heat tape tightly wrapped around the last 12 cm of the bent tube. Large particles produced by the nebulizer are effec- tively scavenged by the chamber prior to complete de- solvation. The desolvated aerosol passes through a Tygon tubing connector to a water cooled condenser; the con- nection is equipped with a pinch clamp whose tension can be modified to control the rate of aerosol introduction to the condenser. After solvent removal in the condenser, the aerosol is directed into the furnace optical path past a quartz port that allows for viewing of the furnace entry port. The condensed solvent proceeds by gravity flow to the drain located in the spray chamber. Sample is intro- duced to the nebulizer at a constant rate using a Cole Palmer Masterflex model 7013 tubing peristaltic pump and argon carrier gas flow rate is measured both on the high pressure side upstream from the nebulizer and at the low pressure furnace exit port.
B. Measu remen t . Sample analysis proceeds in a manner similar to conventional flame atomic absorption analysis in that samples are consecutively analyzed with
A
I
( f /
E
C
Fro. 1. Single-phase Woodriff furnace constant temperature atomizer. Components include (a) furnace shell, {b) graphite heater tube, (c) graphite insulating support, (d) graphite side tube, (e) desolvator con- nect, (f) aerosol inlet, and (g) heater/side tube support.
I t G
II i
J
D
FIG. 2. Schematic diagram of the introduction system. Large view shown facing furnace atomizer; view A shown looking down over viewing port. System components include (a) nebulizer, (b) argon inlet, (c) drain outlet, (d) heat tape, (e) flow control clamp, (f) condenser, (g) auxiliary argon purge, (h) furnace view port, (i) furnace heater tube, (j) furnace wall, and (k) sample inlet from condenser.
continuous aspirat ion of deionized water be tween sam- ples to ensure complete sys tem washout . Sys t em re- sponse is optimized by statistical compar ison of tr iplicate analysis of a sample capable of producing an absorbance response a t least 10 t imes the background peak- to-peak noise using various sys tems characteristics; var iables ex- amined include carrier gas flow rate bo th to and f rom the nebulizer, back pressure, solution up take rate, and fur- nace wall t empera ture . In all exper iments of this type, the t empera tu re in the desolvation chamber is main- tained at 100 ° C. For the glass concentric nebulizer carrier flow is only changed at the gas source while bo th AA and Pt -Tef lon nebulizers are of variable flow design and can be manipu la ted at bo th the source and by the nebulizer itself. An addit ional control on flow rate f rom the neb- ulizer is achieved by cr imping of the Tef lon connect ion between the spray chamber and the condenser. Absorb- ance is measured at 328.8, 228.0, 217.0, or 283.0 and 328.0 nm for Ag, Cd, Pb, and Zn determinat ions. All s tandards and solutions are p repared f rom doubly distilled water; s tandard stock solutions are p repared by dissolution of salts in a 1% (v/v) matr ix of HNO~. The chloride salt is used for Cd, Pb, and Zn, whereas the silver salt used was the nitrate. Mul t ie lement working solutions are p repared by appropr ia te dilution of the single e lement stocks and adjusted, when necessary, to the appropr ia te anion con-
ten t by addit ion of 1% (v/v) concent ra ted acid. Acids and salts used are Baker reagent grade.
II . R E S U L T S A N D D I S C U S S I O N
Optimized conditions producing m a x i m u m analyte sig- nal level for the sys tem and the various nebulizers used are summar ized in Tab le I. A tom populat ion in the excitation chamber is opt imized by coupling of m i n i m u m carrier gas flow rate and modera t e solution up take ra te with m a x i m u m nebulizer efficiency. Whereas all neb- ulizers studied are capable of operat ing at solution up take rates greater than those documented, the posit ive effect of increasing up take ra te is l imited to the product ion of sharper (in t e rms of t ime it takes to establish an equilib- r ium a tom populat ion in the atomizer) recorder peaks. Increasing sample up take ra te produces no increase on analytical sensitivity, has no noticeable effect on washout t ime and can conceivably accelerate a tomizer tube deg- radation. Absorbance and furnace t empe ra tu r e display a roughly l inear relat ionship at t empera tu re s below those documented in Tab le I; utilization of t empera tu re s up to 200°C higher than those noted produced no increase in sensitivity. When one considers tha t the furnace temper - a ture is measured at the hea ter tube center and t ha t the single-phase Woodriff furnace has a documented temper - a ture gradient of a t least 300°C f rom center to tip, s'l° it is probable tha t absorbance is l imited a t these high carrier flow rates by rapid m o v e m e n t of analyte to the cooler tube ends. Grea te r analyt ical sensitivity, therefore, could possibly be a t ta ined a t m u c h higher hea te r tube t empera tu re or th rough utilization of a tube design which facilitates the rmal equil ibrium in the optical path. Un- fortunately, the sys tem used for this s tudy is incapable of producing these conditions. T h e Tef lon nebulizer was used both with a sample mat r ix which is only deionized water and one which is 35% (v/v) e thanol in water. Since the major source of tube degradat ion was expected to be graphite oxidation by residual water escaping the con- denser column, the e thanol was added in hope of pro- mot ing the gaseous conversion of the water to a nonreac- t ive hydrocarbon. Specifically, it was desired tha t the vapor s ta te oxidation of the ethanol would provide an effective sink for all residual oxygen in t roduced as water
TABLE I. Optimized operating conditions. Solu-
Carrier Carrier tion up- gas gas flow take Tempera-
A. Varian nebulizer Ag 20 3500 3.1 1750 Cd 20 3500 3.1 1450 Pb 20 3500 3.1 1750 Zn 20 3500 3.1 1500
B. Glass nebulizer Ag 35 2500 5.0 1775 Cd 35 2000 4.5 1430 Pb 35 2500 4.5 1750 Zn 35 2500 5.0 1650
C. Pt Teflon nebulizer Ag 35 1100 5.0 1725 Cd 40 800 5.0 1450 Pb 35 1100 5.0 1670 Zn 40 800 5.0 1650
APPLIED SPECTROSCOPY 659
by producing mixed carbon oxides which are immediately flushed from the system with the carrier gas. An increase in tube life was not noted using the ethanol matrix; in fact, system performance was decreased because of the buildup of carbon material in the optical path when the ethanol solution was used continuously.
Of the design variables documented in Table I, both carrier gas flow rate (effecting analyte residence time in the optical path) and atomization temperature (effecting atomization efficiency) are critical in defining systems sensitivity. Whereas the effect of temperature on sensi- tivity appears to be species dependent, one generally notes a 10% to 30% change in sensitivity as furnace temperature is decreased from the documented value in 100°C steps. The change in sensitivity with changes in carrier gas flow rate are less pronounced; generally if the minimum operational flow for the nebulizer is exceeded relatively large changes in flow rate (25%) produce small (5% to 10%) changes in analytical sensitivity.
Detection limits, defined in this study as the concen- tration equivalent to 2 times the peak to peak height of the absorbance signal recorded during aspiration of the blank solution, are summarized in Table II. The Teflon nebulizer, by virtue primarily of its ability to operate at relatively low carrier gas flow rates, is capable of produc- ing the largest atom population in the optical path. Whereas the glass concentric nebulizer was capable with its original design of operation at flows less than half of that used for the Teflon device, its low efficiency of 0.01 limits its application to the graphite furnace. Please note that efficiency is defined as the ratio of sample mass delivered to the condenser and the total mass of sample aspirated. Modification of the length and width of the thin capillary tube in the nebulizer, although it increased carrier gas flow rate, increased efficiency sufficiently (to 0.05) to produce detection limits similar to those obtained in conventional flame analysis. Although the Varian neb- ulizer used had an efficiency 0.06 under the conditions noted in Table I, its much higher carrier flow rate effec- tively limits the sensitivity of a system using it. Using the high efficiency (0.04) low flow rate Teflon nebulizer, detection limits approximately 5 times lower than those documented for conventional flame analysis can be achieved for Ag, Cd, Pb, and Zn. The poorer detection limits obtained for the ethanol matrix reflects both the presence of small concentrations of Ag, Cd, Pb, and Zn as contaminants in the ethanol (producing a higher and less reproducible blank absorbance) and the carbon buildup noted earlier.
Table III documents the reproducibility that can be obtained by the system. The data, presented as the percent RSD of at least five replicate analyses, were obtained by repeated analysis of a sample of appropriate concentration over the course of a period of 3 h of continuous utilization under optimum conditions and is comparable to that which can be obtained at these con- centrations by other analytical techniques. The repro- ducibility appears to be unrelated to the nebulizer used and is relatively immune to changes in operating condi- tions. It is therefore expected that the precision docu- mented reflects reproducibility of the system as a whole and is not controlled by individual components.
The susceptibility of both flame and furnace atomic
660 Volume 36, Number 6, 1982
TABLE H. Detection limits.
Detection limit (ppb)
Ele- Flame" Carbon b Present study (nebulizer type) ment AA rod Varian Glass Teflon c Teflon d
b Using 5-/zl sample. 7 c Using 35% (v/v) EtOH matrix. d Using deionized water.
TABLE III. Reproducibility. % Relative standard deviation
Element Varian Glass" Teflon" Teflon nebulizer nebulizer nebulizer nebulizer
Ag 6.5 5.6 6.6 2.7 Cd 7.0 5.9 5.0 5.3 Pb 7.5 4.6 6.7 7.0 Zn 8.9 4.7 4.4 5.5
" 35% EtOH matrix.
absorption analysis to matrix effects is well documented. The susceptibility of the furnace/introduction system described herein to acid interference was studied at an- alyte concentrations of 500, 200, and 100 ppb and acid concentrations of 1% (v/v). Anions used include chloride, nitrate, phosphate, and sulfate; all solutions are charac- terized under the conditions described in Table I. The results of this study, summarized in Table IV, are docu- mented by comparing reagent blank-corrected absorb- ances obtained using the acid matrix with those obtained using deionized water as the matrix. Regardless of neb- ulizer used, no significant interference was noted for either hydrochloric or nitric acid matrices. The behavior of the analyte in the sulfuric and phosphoric acid matrix is, as a function of nebulizer used and operating condi- tions, quite different than in the water matrix. Utilization of the glass concentric nebulizer or the Teflon nebulizer with a matrix modified to be 35% (v/v) ethanol resulted in no sulfate or phosphate interference; however, when the Teflon nebulizer is used under optimal conditions without the ethanol, the sulfate matrix decreases both Cd and Pb absorption by 20%, whereas the Ag signal is unaffected and Zn absorbance is reduced by 50%. For phosphate, the effect is more profound with minimum decrease occurring for Cd (~20%) and maximum for Zn (80%). In order to study the interference phenomenon in greater detail, the effect of changing conditions in the sample introduction system on the sulfate and phosphate interference in the Zn determination was noted. As illus- trated in Table V, changing the carrier gas flow rate out of the introduction system changed the magnitude of the interference, although it could not be completely elimi- nated. Changing the power to the heat tape and thereby changing the temperature of the desolvation chamber has quite an effect on the sulfate interference, with increasing temperature increasing sulfate recovery by 95%, whereas the phosphate interference is immune to the temperature changes noted. In all experiments, Zn recovery in the hydrochloric and nitric acid solutions
T A B L E IV. M a t r i x e f fec t s .
% Relat ive peak he igh t Coneen- t ra t ion Varian nebulizer Glass nebulizer (ppb)
B. Changing desolvator t empera tu re 1150 1500 20 18 18 1150 1500 25 33 19 1150 1500 30 93 19
remains 100%. At the present time, there is insufficient data to establish the significance of the interference trends noted; however, the phenomenon appears to be
related to the sample introduction system and is not affected, as in the case of the phosphate effect on Ag, by changing the temperature of the atomizer.
ACKNOWLEDGMENT
The authors wish to thank the Montana Fisheries Bioassay Laboratory, Montana State University, for utilization of the furnace and spectrophotometer and the Montana College of Mineral Science and Technology for loan of the nebulizers.
1. V. Veillon and M. Margoshes, Spectrochim. Acta 23B, 553 (1967). 2. M. K. Murphy, S. A. Clyburn, and C. Veillon, Anal. Chem. 45, 1468 (1973). 3. C. J. Molnar and J. D. Winefordner, Anal. Chem. 46, 1419 (1974). 4. M. Chamsaz, B. L. Sharp, and T. W. West, Talanta 27, 867 (1980). 5. T. Kantor, S. A. Clyburn, and C. Veillon, Anal. Chem. 46, 2205 (1979). 6. R. Woodriff, Appl. Spectrosc. 98, 413 (1974). 7. R. Woodriff, B. R. Culver, and K. Wolsen, Appl. Spectrosc. 24, 530 (1970). 8. R. W. Stone, PhD. thesis, Montana State University, Bozeman, Montana,
1974. 9. D. Shrader and R. Woodriff, Anal. Chem. 43, 1918 (1971).
10. H. R. Howell, MS thesis, Montana State University, Bozeman, Montana, 1978.
Computer-assisted Spectral Identification of Unknown Mixtures
P. C. GILLETTE, J. B. LANDO, and J. L. KOENIG Department of Macromolecular Science, Case Western Reserve University, Cleveland, Ohio 44106
Procedures are described which permit the qualitative analysis of spectral mixtures by using factor analysis in conjunction w i t h a spectral reference library. Index Headings: Computer, applications; I n f r a r e d .
INTRODUCTION
Computer-based spectral identification of unknown compounds has already revolutionized the field of quail-
Volume 36, Number 6, 1982
tative analysis. The success of existing techniques can be attributed to the availability of digitized spectra of a large number of reference compounds. Although a wide range of searching algorithms/spectral identification pro- cedures have been proposed, 1-22 only one program at- tempts to analyze spectra of mixtures. 22 If one is able to obtain a series of mixtures in which the relative concen- trations vary and a spectral reference library is available, then qualitative identification of the pure components
