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ANALYTICAL CHEMISTRY, VOL. 50, NO. 14, DECEMBER 1978
technique for quantitative analysis for trace amount>s of arsenic' Of detection limits 'I1) demonstrates that the ESCA-volatilization technique is quite competitive with other trace analytical methods. Likewise, our analytical method shows both good accuracy and precision. Further, volatilization can be performed in the field making remote sampling facile. T h e possibility of doing quantitative simultaneous multielement analysis a t trace levels also has been demonstrated.
ACKNOWLEDGMENT T h e authors express their gratitude to F. LV. Plankey and E. M. Heithmar for loan of the atomic absorption standards and for some helpful discussions; also t o S.Erickson for her assistance.
LITERATURE CITED (1) T. A. Carison, "Photoelectron and Auger Spectroscopy", Plenum Press. New York, 1975 p 268. (2) J. S. Brinen and J. E. McClure, Anal. Lett., 5, 737 (1972). (3) J. S. Brinen and J. E. McClure, J . Electron Spectrosc. Relat. Phenom.. 4, 243 (1974). (4) D. M. Hercules, L. E. Cox, S . Onisick, G. D. Nichols, and J. C. Carver, Anal. Chem., 45, 1973 (1973). (5) M. Czuha and W. M. Riggs, Anal. Chem., 47, 1836 (1975). (6) G. M. Bancroft, J. R. Brown, and W. S . Fyfe, Anal. Chem., 49, 1044 119771. \ ~ , (7) D. Briggs, V. A. Gibson, and J. K. Becconsall, J . Electron. Spectrosc. Relat. Phenom., 11, 343 (1977). (8) H. F. Walton, "Principles and Methods of Chemical Analysis", 2nd ed., Prentice-Hall, Englewood Cliffs, N.J., 1964, Chap. 9. (9) H. s. Satterlee and G. Blodgett, h d . h g . Chem., Anal. Ed., 16,400 (1944). (10) J. A. Fiorino, J. W. Jones, and S. G. Capar, Anal. Chem., 48, 120 (1976). (1 1) U.S. Public Health Service, "Drinking Water Standards', U.S. Dept. of Health, Education, and Welfare, Washington D.C., 1962.
(12) R. S. Braman, L. L. Justen, and C. C. Foreback, Anal. Chem.,44,2195 (1972). (13) N. G. Elenkova, R. A. Tconeva, and Tc. K. Nedeitcheva, Talanta, 23, 726 (1976). (14) "Arsenic in the Environment - An Annoted Bibliography", Oak Ridge National Laboratory, Oak Ridge, Tenn., ORN-E1S-73-16 (1973). (15) "Official Methods of Analysis of the Association of Official Analytical Chemists", 11th ed., 1970, p 399. (16) T. F. Jula, "Inorganic Reductions with Sodium Borohydride: Principles and Practice", Ventron Corp., 1974. (17) K. T. Kan, Anal. Lett., 6,603 (1973). (18) F. J. Fernandez, At. Absorp. News/., 12, 93 (1973). (19) H. H. Walker, J. H. Runnels, and R. Merryfield, Anal. Chem., 48,2056 (1976). (20) F. J. Schmidt and J. L. Roger, Anal. Lett., 6, 17 (1973). (21) K. M. Mackay, "Hydrogen Compounds of the Metallic Elements", Spon, London, 1966, p 133. (22) H. I. Schlesinger, H. C. Brown, A. E. Finhoit, J. R. Gilbreath, H. R. Hockstra, and E. K. Hyde, J . Am. Chem. SOC.,75, 215 (1953). (23) H. C. Brown and A. C. Boyd, Anal. Chem., 27, 156 (1955). (24) A. E. Smith, Analyst (London) 100,300 (1975). (25) R . Belcher, S. L. Bogdanski, E. Henden, and A. Townshend. Analyst (London),100, 522 (1975). (26) F. D. Pierce and H. R. Brown, Anal. Chem., 48, 693 (1976). (27) J. E. Drinkwater, Analyst (London), 101,672 (1976). (28) K . G. Brodie, Am. Lab., 3, 73 (1977). (29) E. M. Heithmar, Ph.D. Thesis, University of Pittsburgh, 1976. (30) R. S . Braman et al., Anal. Chem., 49. 621 (1977). (31) L. E. Wangen and E. S. Gladney, Anal. Chim. Acta, 96,271 (1978). (32) G. Forsberg, J. W. O'Laughlin. and R. G. Megargle, Anal. Chem.. 47, 1586 (1975). (33) R. D. Kadeg and G. D. Christian, Anal. Chim. Acta, 88, 117 (1977).
RECEIVED for review May 17, 1978. Accepted September 1,
1978, presented at the 29th Pittsburgh conference on Analytical Chemistry and Applied SPeCtroSCopY, Cleveland, Ohio, Feb. 27-March 3, 1978, paper no. 229. This work was by the Science Foundation under Grant CHE76-19452.
Quantitative Ion Probe Analysis of Glasses by Empirical Calibration Methods J. D. Ganjei and G. H. Morrison* Department of Chemistry, Cornell University, Ithaca, New York
74853
The range of applicability of the empirical sensitivity factor approach in ion probe analysis of glasses was investigated. Accurate results were achieved only when the standards and sample contained the same major element (excluding oxygen) in the glass matrix. With the above criterion satisfied, modification of the basic external standard approach was not necessary since other interelement matrix effects were minimal. Analyses in the range of error factors of 1.15 were obtained using average relative sensitivity factors.
Secondary ion mass spectrometry (SIMS) is one of the most sensitive techniques for surface elemental analysis. However, the potential of SIMS, particularly in the ion probe mode, is currently limited by the difficulty in quantification of the secondary ion signals. This problem has been previously discussed ( 1 ) but, briefly, t h e uncertainty in secondary ion interpretation is mainly due to the variability of the ratio of measured ion intensities to sputtered atoms. T h e relative secondary ion ratios can be affected by residual gas surface adsorption, primary bombarding ion species, sampling con0003-2700/78/0350-2034$01 O O / O
ditions, and the sample composition (commonly called the matrix effect). Of these factors, the matrix effect is certainly the most perplexing since the analyst can regulate instrumental parameters, whereas sample composition is beyond his control. In attacking the problem of quantitative analysis, the authors have selected an empirical approach utilizing external standards to calibrate the elemental secondary ion signals. The accuracy of external standards derived sensitivity factors is critically dependent on the matrix effect. If the sample matrix is sufficiently different from the standard, the change in secondary ion ratios between the matrices will result in large analytical errors. In fact, the popularity of semitheoretical quantitation methods which are accurate only to a factor of 2 or 3 is due to the uncertainty of the empirical standards' approach. Many SIMS users have rejected the empirical approach for analyses because of the difficulty of obtaining standards whose elemental sensitivity factors will be applicable to the sample. As Christie and Smith (2) have recently pointed out, criteria for sample-standard matrix match currently do not exist. C 1978 American Chemical Society
ANALYTICAL CHEMISTRY, VOL 50, NO. 14, DECEMBER 1978
I n a previous study, Ganjei, Leta, and Morrison (3) found t h a t a modified external standard approach could achieve accuracies on the order of fl0Oic in the ion probe analysis of metal samples. T h e criteria for application of their matrix ion species ratio method (MISR) are sample and standard containing a common matrix element in major concentrations, and oxygen surface adsorption affecting the sampling environment. By indexing t h e sampling environment with a matrix ion species ratio, the MISR method compensates for minor matrix effect differences between metal alloys whose major matrix element is the same. T h e present study is an investigation of empirical methods for quantifying insulator matrices, and in particular glasses, by secondary ion mass spectrometry. The presence of oxygen at greater than 50 atomic percent concentration within the matrix precludes the use of the MISR method, but its presence should also reduce the effect of matrix elemental differences. T h e samples chosen were the recently issued National Bureau of Standards Research Material (RM 30) specially prepared as microprobe standards. Included in the study is a discussion of the importance of matrix effect in these glasses and the limit it places on t h e empirical approach to quantitation. Other experimental factors discussed include electrical charging of samples a n d differences in relative elemental sensitivity between t h e CAMECA IMS-300 ion microanalyzer used in this study and t h e Applied Research Laboratories Ion Microprobe Mass Analyzer (IMMA) used by previous investigators for t h e analysis of these glasses ( 4 , 5').
2035
a
b
EXPERIMENTAL Instrumentation. The study was accomplished with a CAMECA IMS-300 ion microanalyzer and PDP-11/20 computer interface. These have been previously described (6). Samples. The samples used in the study were the recently issued National Bureau of Standards Research Material 30 series, glasses K-251 and K-309 prepared by NBS for a round-robin survey and the NBS SRM-610 glass for trace elements analysis. Sample Preparation. The samples were cut to approximately 2 X 2 X 10 mm, mounted in Sn-Bi eutectic and polished with alumina paste. They were then ultrasonically cleaned with methanol and, immediately after drying, a layer of aluminum approximately 1 pm thick was vapor deposited on the surface. Procedure. A small square, roughly 100 X 100 pm. was sputtered through the vapor deposited Al film with a finely focused rastered (Ox+) primary beam of 5.5 keV. During the analysis, the primary beam was defocused and rastered in order to produce a uniform low beam density (approximately 1&100 pA/cm2). The 100-pm square was further apertured by a 50-pm field aperture which reduced signal from the A1 film. Data collection was accomplished with peak height measurement using a 5-s integration time counted by the PDP-l1/20 computer interfaced to the coincidence photomultiplier pulse counting detection system. The magnet was manually switched from peak to peak. At each new magnet setting, the secondary ion signal was maximized by realigning the field aperture image onto the photomultiplier target using the secondary ion optics. This procedure was necessary because the image position changes with mass and realignment improved reproducibility of the measurements. Standards' homogeneity and instrumental reproducibility were evaluated by measuring signals from five sampling areas of glasses K-489 and K-493, chosen as representative glasses of the RM 30 series. The average relative standard deviations of the elemental ion intensity ratioed to the %Sit signal were 13.7% for glass K-489 and 9.2% for K-493. Experimental measurement error in the analyses then is in the neighborhood of 10 to 15%. The secondary ion ratios presented in Table I1 are averages of measurements from three sampling areas. The analysis of SRM-610 was a special case since heterogeneous elemental distributions have been previously reported (7). Only the major elements Al, Na, Si, and Ca and two trace elements B and P b were analyzed since other elements were either not certified or their signals were interfered with by molecular ions. Signal averaging from five sampling areas produced relative
Figure 1. Ion micrographs. Field of view, 250-pm diameter. (a) "AI' from vapor deposited film. (b) "Si' image of sampling area; (c) *'Si' image of sampling area under electrically charged conditions
standard deviations under 20%.
RESULTS AND DISCUSSION I n s u l a t o r C h a r g i n g . One of t.he main experimental problems in ion probe analysis of insulators is local sample charging induced by the bombarding primary ion beam. T h e amount of charging can range from several volts to thousands of volts. Severe charging causes deflection of the primary beam and total loss of signal. More intermediate charging results in loss of mass resolution, secondary ion image degradation, and distortion of the low energy spectrum. Several methods have been suggested to alleviate the problem; surface coating with vapor deposited conducting films (8) and grids ( 9 ) , negative primary ion beam bombardment ( I O ) , neutralization by surface electron flooding ( 1 1 , 12),sample bias voltage adjustment (13), and placement of a conducting diaphragm on the surface (14). Blanchard et al. (15)have also noted the use of surface oxygen in reducing charge effects. T h e effect of intermediate charging (30-70 volts) is illustrated in Figure l. Ion micrograph a shows the ziAlf background image surrounding the sq'uare dark sampling area. T h e second micrograph b is the image of *%if signal under low current density ion bombardment. When a higher density beam is used the results are as shown in micrograph c. In this micrograph the uniformity of the secondary ion signal has disappeared and charging has produced a voltage gradient. T h e potential a t a given point on the sampling area is determined by the primary beam density and t h a t point's distance from the conducting film. Ions from regions charged to a different potential will be separated by the magnet even though their initial escape energy and mass are equivalent. Thus, only equipotential regions are imaged a t particular magnet settings as illustrated in micrograph c. When t h e charging is greater than t h e instrument's voltage bandpass,
2036
ANALYTICAL CHEMISTRY, VOL. 50, NO. 14, DECEMBER 1978
t h e effect can sharply decrease experimental measurement reproducibility. W e have adopted the procedure as outlined in the Experimental section. Charging is minimized by utilizing a low density uniform primary beam and a small area surrounded by a vapor deposited conducting film. T h e small sampling area (loo00 bm2 or less) keeps the entire sampling region fairly close to t h e conducting film. During primary beam bombardment, the charging was measured by adjusting the sample accelerating high voltage independently of the high energy cutoff electrostatic mirror until the mirror cuts off all the secondary ion signal. Since the mirror is set a certain potential above the sample high voltage, t h e secondary ion signal disappears when t h e sample high voltage is incremented t o t h e mirror potential. T h e charging is equivalent to the difference in sample high voltage incrementation necessary t o eliminate signal in a charged sample compared to a conducting sample. During the analyses, the charging was found t o be typically less than five volts. A positive primary beam was utilized since t h e sample charging was minimal. Experimental reproducibility was significantly worse under negative primary beam bombardment, probably due to the nonuniform beam density of the negative beam as compared t o the positive. T h e main limitation of the procedure was the restriction on primary beam current density (100 pA/cm2) due t o charging and A1 film sputtering. However, instrumental sensitivity was high enough to enable detection of the elements present in t h e glasses. Results. T h e data from t h e glass analyses are presented in Table I. The elemental secondary ion intensities are ratioed t o t h a t of t h e matrix element of highest atomic percent concentration excluding oxygen; these majors, Si. B , P, and Ge, are assigned a ratio of 1.0. Even though oxygen comprises t h e major atomic fraction of the samples the 160tsignal was ignored because of its low intensity and instability in the positive secondary ion spectrum. Mass interferences prevented measurement of some elements; 27A1H+dominated the weak 28Sit signals from low silicon content glasses K-490, K-491, and K-497. I n glass K-489, 48TiOt and 132Ba2fsecondary ions masked t h e @Znt and 66Zn+signals, respectively. T h e Is1Tat intensity in K-251 was measured using isotopic abundances t o subtract 13iBa28Si0+and 138Ba2iA10+interferences. A similar correction was unfeasible in glass K-489 because of low signal-to-noise ratios. T h e N B S nominal compositions of t h e samples are given in Table I1 in atomic percent. T h e interpretation of the secondary ion intensities and the elemental concentrations is accomplished by the use of relative sensitivity factors. The relative sensitivity factor is defined as (16) where i is the measured secondary ion intensity, c is the atomic concentration, f is the isotopic abundance and subscript x refers to the analyte element while ref is the reference element. T h e reference element is included in t h e sensitivity factor equation t o compensate for experimental fluctuations such as sputtering rates. Matrix Effect. The purpose of this study was to evaluate t h e applicability of t h e relative sensitivity factor method in ion probe analysis of glasses. T o accomplish this, one set of relative sensitivity factors was used to calculate the elemental concentrations of all t h e samples. T h e calculated error is a measure of t h e fit between the analyzed sample and the standards used t o derive t h e sensitivity factors. T o a first approximation, t h e glasses can be easily divided into four matrix types, classified by their major constituent, excluding oxygen. These include S O 2 , B203,P205,and GeOz. As a result, t h e average relative sensitivity factors of one type matrix, the silicates, which comprised the largest group of
m m
9 ri
Y
z
zz t-
m t-
8
m
m
0
8
W
w
0
8 ri
0 i
0 i m
Y?i
m
8 ri
ri ri
0
hl
r!
0
ANALYTICAL CHEMISTRY, VOL. 50, NO. 14, DECEMBER 1978
m
m
f z
(9
m
f
M
2:
ed3 N
d:
m
rl
2037
samples, were used to calculate the samples' elemental concentrations. Table I11 presents the results of using the average silicate sensitivity factors to calibrate the secondary ion signals of the individual silicate samples. In each case, silicon was utilized as the known reference element. The errors are given in terms of the error factor F where F equals the ratio of the calculated concentration to the actual concentration ( 5 ) . Underestimates are presented as negative reciprocals for easy comparison. T h e absolute average error factor of 1.15 shows a narrow range of relative sensitivity factors within the silicate matrix. The largest error occurred with the cerium sensitivity factor which seemed to be affected by the increase in barium concentration between K-493 and K-489. A mass scan proved that the error was not caused by mass interferences. Aluminum exhibited the only other systematic error which was an increa5e in elemental sensitivity as the AI concentration decreased. However, this trend is due to background signal from vapor deposited A1 film, which is only significant in the low A1 concentration glass K-489 and K-493. This interference was partially corrected by determining the AI background in K-456 which does not contain Al, ratioing it to t h e silicon signal (ratio was approximately 2 . 2 % ) and subtracting the ratio from the A1 ratio in K-489 and K-493. The numbers in Tables I1 and I11 reflect t h e correction. T h e correction was found to be insignificant in the other glasses. In order to analyze the nonsilicate glasses, aluminum was chosen as the reference element since silicon was either absent or its secondary ion signal contained a mass interference. The accuracy of the average silicate sensitivity factors decreases considerably when applied to these glasses as shown in Table IV. T h e absolute average error factor was 1.90, making the analyses' accuracy approximately a factor of two-not acceptable for most applications. In addition. there was no apparent order to the fluctuations whirh would enable a simple matrix correction. T h e significance of the error is also emphasized by comparing the relative sensitivity factors from the glasses which contain the same major element. These results are shown in Tahle V where K-490 is matched with K-495 (high boron). K-496 with K-497 (high phosphorus), and K-453 is compared with K-491 (high germanium). -4lthough only four elements are determined. the average error factor is 1.08, close to the silicate matrix results. It should also he pointed out that there exists a definite statistical bias in this treatment since the analyzed sample elemental sensitivity factor is used to hiiild the average relative sensitivity factors in the case of Tables I11 and V while this is not true when the average silicate sensitivity factors are used to analyze the nonsilicate samples in 'Table TV. However, the bias does not account for the large jump in error between the analyses. In previous studies of metal matrices it was found that oxygen concentration within the sampling volume considerably enhanced secondary ion ratios. However, even with surface oxide formation, relative elemental sensitivity factors were consistent only within one type of metal matrix. T h e above results in Tables 111. IV, and V show t h a t the sampling environment is determined by t h e major elemental oxide in glasses. Just as steel standards do not successfully calibrate other metal alloys, silicate sensitivity factors are not correct for boron, phosphorus, and germanium oxides. Instrumental Discrimination. T h e above results have been given in terms of atomic percent concentration in order to facilitate comparison of these results with those of Christie and Smith ( , 5 ) . This comparison is presented in Table VI which contains the average relative sensitivity factors of the CAMECA instrument and the ARL IMMA for the silicate glasses. As Bradley et al. ( I 7 ) have discussed, the CAMECA
2038
ANALYTICAL CHEMISTRY, VOL. 50, NO. 14, DECEMBER 1978
-
Table 111. Error FactorC Analysis for Silicate Glasses sample Li K-251 K-309 K-456 K-458 K-489 -1.12 K-493 1.11 SRM-61 0 32.5 av. Sf rel. t o Sib a Background corrected.
B
A1 1.03 1.0
Si
Ca
Ti
Fe
Zr
Ba 1.29 1.14
-1.22
-1.10
Ce
Ta
Pb -1.02
-1.18
- 1.16
- 1.34
-1.08 1.05
-1.23'
-1.12
l.Oa
1.09
-1.20 1.25
1.13
1.0
-1.33 1.47
1.21 1.11 1.13 0.59 7.4 1.0 21.6 6.8 5.1 2.25 35.9 6.3 Average sensitivity factor compiled from silicate glasses. Av. Error Factor
1.44 1.10
1.04
=
-1.11 - 1.02
0.11 2.1 36.8132 = 1.15.
Table IV. Error Factorb Analysis for Nonsilicate Glasses Using Silicate Sensitivity Factors sample Li B A1 Si P K-490 1.61 2.10 K-495 1.46 -2.23 K-496 K-497 -1.35 -1.28 X-491 -1.54 4.47 K-453 av. Sf rel. to Ala 3.7 ,067 1.0 0.114 ' Average sensitivity factor compiled from silicate glasses.
Ti -1.16
Fe -1.78
-1.56 1.54
-2.83 2.64
0.77 0.58 Av. Error Factor
Ge
Zr -1.31
Ce 1.09
Ta -1.92
-1.38
1.07 2.77
-2.16 3.91
-1.15
=
0.26 0.72 49.2126 = 1.89.
0.0125
Pb 1.11
-2.65 1.11
0.245
Table V . Error Factorsa of B, Ge, and P Matrix Glasses Li 17.2
A1 Mg Pb av. Sf rel. to B 7.0 K-490 Error factor 1.01 - 1.06 K-495 Error factor - 1.01 1.04 av. Sf rel. to P 87.0 134.0 K-496 Error factor 1.12 1.17 K-497 Error factor -1.10 -1.15 av. Sf rel. to Ge 23.3 K-453 Error factor 1.07 K-491 Error factor -1.07 a Av. Error Factor lO.S/lO = 1.08. Table VI. Comparison of Silicate Relative Sensitivitya Factors between the CAMECA IMS-300 and the ARL IMMA CAMECA ARL element Sf Sfb CAMECAIARL 3.5 9.3 Li 32.5 0.45 1.3 B 0.59 3.8 1.95 A1 7.4 Ca 21.6 9.5 2.3 3.7 1.8 Ti 6.8 Fe 5.1 2.0 2.6 0.18 0.61 Zn 0.11 1.8 1.25 Zr 2.25 10.3 3.5 Ba 35.9 0.21 0.52 Ta 0.11 0.78 2.7 Pb 2.1 1.0 1.0 Si 1.0 Compiled a Measured relative to the silicon signal. from Christie and Smith ( 5 ) . instrument shows a much higher relative sensitivity for alkalis and alkaline earths. The results of the present study support their conclusion that t h e phenomenon can be explained by the energy discrimination factors of the two instruments. The CAMECA's secondary ion optics discriminate against high energy ions while the ARL IMMA geometry favors high energy ions. As a result, secondary ions which have different energy distributions will show different sensitivities for the two instruments. Energy spectra have been recorded of t h e elemental secondary ions and it was found that high CAMECA sensitive ions show low energy maxima and narrow peaks while
Figure 2. Corrected secondary ion energy spectrum for %a+ K-251. Average energy equals 14.0 h 1.0 eV
in glass
Figure 3. Corrected secondary ion energy spectrum for '*Si+ in glass K-251. Average energy equals 24.5 1.0 eV
*
silicon, boron, and other elements have higher energy maxima and relatively broad distributions. T h e difference in energy distribution is illustrated in Figures 2 and 3 where Figure 2 shows the 13'Ba+ energy distribution and Figure 3 illustrates the %i+ curve. These energy spectra have been corrected for the CAMECA's discrimination factor (18). T h e results in
ANALYTICAL CHEMISTRY, VOL. 50, NO. 14. DECEMBER 1978
Table VI are, therefore, due to different secondary ion energy distribution. Ions which exhibit lower average energy than silicon show higher CAMECA relative sensitivity than the ARL IMhfA while elemental ions of higher average energy than silicon show higher IMhfA sensitivity.
CONCLUSION T h e results of this study show that the use of relative sensitivity factors for ion probe analyses of glasses can achieve accurate results ( h l 5 relative percent) provided the samples contain t h e same major matrix element, excluding oxygen. T h e criterion for matrix match seems therefore to depend on the major elemental oxide, and other interelemental matrix effects are minimal. This is substantiated by t h e fact that t h e analyzed silicate glasses, while comprising a wide range of elemental compositions, generate very similar relative sensitivity factors. Modification of the empirical method, as in the author's MISR method (3)for ion probe metal analyses, is not necessary, probably because of the presence of oxygen in high concentrations within t h e glass matrices. However, t h e accuracy of the sensitivity factor method decreases so sharply when the standard does not contain the same major element as the sample that we seriously doubt the usefulness of such comparisons. I n general, the applicability of t h e sensitivity factor approach in quantitative analysis seems limited to the above criterion; a match between the standard and sample in t h e major matrix element. This, however. is not a serious limitation in many applications, as has been previously suggested since bulk analyzed standards are available for many matrix compositions and statistical analysis can minimize possible standards' sampling error (19, 20). Minor interelemental matrix effects are either minimal, as in the silicate glasses, or can be calibrated, as in the MISR method of metals analysis. As a result, quantitative ion probe analysis is
2039
certainly possible for a wide range of applications.
LITERATURE CITED (1) J. A. McHugh, "SeconQry Ion Mass Spectromeby" in "Methods of Surface Analysis", S. P. Wolsky and A. W. Czanderna, Ed., Elsevier, New York, 1976. (2) W. H. Christie, D. H. Smith, R. E. Elby, and J. A. Carter, A m . Lab., 10 (3), 19 (1978). (3) J. D. Ganjei, D. P. Leta, and G. H. Morrison, Anal. Chem.,50. 285 (1978). (4) D. E. Newbury, K. F. J. Heinrich, and R. L. Myklebust, "Surface Analysis Techniques for Metallurgical Applications", ASTM STP-576, Americai; Society for Testing and Materials, Philadelphis, Pa., 1976, pp 101-1 13. (5) D. H. Smith and W. H. Christie, Int. J . Mass Specfrom. lor?Phys.. 26, 61 (1978). (6) G. H. Morrison and G. Slodzian, Anal. Chem., 47, 932A (1975). (7) A. E. Morgan and H. W. Werner, Anal. Chem., 49, 927 (1977). (8) Y. Veda and J. Okana, Mass Spectrosc., 20, 185 (1972) (9) G. Slodzian, Ann Phys. (Paris),9, 591 (1964). (10) C. A. Andersen, H. J. Roden, and C. F. Robinson, J . A p p l . Phys., 40, 3419 (1969). (1 1) K . Nakamura, Y. Hirahara, A. Shibata, and H. Tamura, Mass Specbosc., 24, 163 (1976). (12) B. Blanchard, P. Carrier, N. Hilleret, J. L. Marguerite, and J. C: Rocco, Analusis, 4 (4), 180 (1976). (13) R. D. Fralick and T. A. Whatley, 25th Annual Conference on Mass Spectroscopy and Allied Topics, May 19-June 3, 1977, p 315. (14) H. W. Werner and A. E. Morgan, J . Appl. Phys., 47, 1232 (1976). (15) B. Blanchard, J. C. Brun, and N. Hilleret. Analusis, 3 (6). 312 (1975). (16) D. Newbury, Proceedings of 13th Anntial Conference of Microbeam Analysis Society, June 19-23, 1978, p 6-A. (17) J. G. Bradley, D. Y. Jerome, and C. A. Evans, Jr., "A Comparison of Mass Spectra from Three Ion Probes" in "Secondary Ion Mass Spectrometry", K . F. J. Heinrich and D. E. Newbury, Ed., NBS Spec. Publ. 427, U.S. Govt. Printing Office, Washington, D.C., 1975, pp 69-79. (18) M. A. Fudat and G. H. Morrison, "Energy Spectra of Ions Sputtered by an 0, Ion Beam", Materials Science Center Report #3056. Cornell University, Ithaca, N.Y.. 1978. (19) G. J. Scilla and G. H. Morrison, Anal. C'hem., 49, 4529 (1977). (20) D. M. Drummer, J. D. Fassett, and G. H. Morrison, Anal. Chim. Acta. 100, 15 (1978).
RECEIVED for review July 19, 1978. Accepted August 18, 1978. Financial support was provided by the National Science Foundation under Grant No. CHEV-04405 and through the Cornell Materials Science Center.
Analysis of Organophosphorus Insecticide and Formulations for Contaminants by Phosphorus-31 Fourier Transform Nuclear Magnetic Resonance Spectrometry R. Greenhalgh Chemistry and Biology Research Institute, Agriculture Canada, Ottawa, Ontario, K 1A OC6, Canada
J. N. Shoolery Varian Associates, Palo Alto, California 94303
Technical grade samples and formulations of fenitrothion were analyzed by "P Fourier transform nuclear magnetic resonance spectrometry. The precision of the method was acceptable with a standard analysis time of 8.3 min in the presence of a relaxing agent. Rapid assay (1 min) of the technical grade samples was also useful as a screening procedure. Up to eight phosphorus contaminants were detected, the major ones being bis(fenitrothi0n) and S-methylfenitrothion. The quantitated NMR data agreed reasonably well with that obtained by high performance liquid chromatography. The latter technique detected fewer contaminants but revealed the cresol as another major contaminant.
As evidence of the toxic nature of microcontaminants 0003-2700/78/0350-2039$01 . O O / O
present in some pesticide technical products and formulations accumulates, so the need arises for adequate methodology for determination of the levels of these impurities. Current procedures for the analysis of technical grade organophosphorus insecticides employ a variety of techniques. In the case of fenitrothion (F), [O.O-dimethyl 0-(nitro-rntolyl)phosphorothioate] these include colorimetric, ultraviolet (UV),gas-liquid chromatographic (GLC), and high performance liquid chromatographic ( H P L C ) methods ( I ) . However, they are mainly concerned with the determination of the active ingredient rather than contaminants. In a recent H P L C study, it was shown that traces of bis(fenitrothi0n) (BF). S-methylfenitrothion (SMF). S-methylbis(fenitrothion) (SMBF), fenitrooxon (FO) and 3-methyl-4-nitrophenol (cresol) were present in some technical samples of fenitrothion (2). These contaminants consist of both byproducts formed during C 1978 American Chemical Society
