A N A L Y T I C A L 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
2040
A N A L Y T I C A L CHEMISTRY, VOL. 50, NO. 14, DECEMBER 1978
Table I. 3 ' P NMR Chemical Shifts of Fenitrothion Artifacts and Degradation Products Relative to Triphenyl Phosphateo,b , c compound O,O,O.trimethyl phosphorothioate dimethyl phosphorothiochloridate fenitrothion ( F ) fenitrothion aldehyde bis(fenitrothion) ( B F ) tetramethyl dithiopyrophosphate aminofenitrothion 0,O-dimethyl S-methylphosphorothioate
shift, ppm
compound
shift, ppm
91.01 89.85 - 83.21 - 82.23 -75.31 -73.55 ~- 7 1.96 - 49.1 8
dimethyl phosphorothioic acid S-methyl fenitrothion (SMF) S-methylbis(fenitrothi0n)(SMBF) demethylfenitrothion O,O,O-trimethyl phosphate demethylfenitrooxon fenitrooxon ( F O ) dimethyl phosphoric acid
- 44.2d
-
Values correct to iO.01 ppm. Condition; 50% w/v solutions in benzene-d,, 90" pulses, 500 transients. shift of triphenyl phosphate + 1 7 . 1 ppm rel. t o H,PO,. D:O + methanol. e D,O acetone. D,O. manufacture as well as rearrangement products formed on storage. For the complete analysis of organophosphorus technical products for contaminants, both GLC and H P L C have a limited capability because of the lack of volatility or chromophoric moieties in some molecules. Since all the potential contaminants in the technical samples of fenitrothion, with the exception of the cresol, contain a phosphorus atom, t h e samples should be amenable to analysis by 31P nuclear magnetic resonance spectrometry (NMR). This technique is rapidly gaining recognition in analytical chemistry when used in conjunction with Fourier transform (FT). It has been employed to analyze for both inorganic and organophosphorus compounds and their metabolites in various matrices (3-51, in one case determining parathion a t the ppm level (6). In this paper, the feasibility of using 31PF T / N M R for t h e analysis of fenitrothion technical materials and formulations is examined and the results are compared with those obtained by HPLC.
EXPERIMENTAL NMR. All the spectra were determined using a Varian CFT-20 NMR spectrometer fitted with a 32.2-MHz 31Pprobe. For routine analysis, 1K transients (pulse-width 15 ps, 90" pulse, repetition time 0.5 s) were applied using a spectral Ridth of 8000 Hz, and collecting 8192 data points during a total acquisition time of 8.33 min. A pulsed deuterium lock (benzene-d6) was used. For rapid assay, 200 transients of 0.30-s duration were employed giving a total acquisition time of 1 min. Samples were analyzed in 8 mm NMR tubes with a probe temperature of 32 "C. All chemical shifts were referenced to the internal standard triphenyl phosphate. T1 values were determined by the inversion recovery method, from the slope of the linear log plot of signal intensity 17s. time. Sample Preparation. A 5070 w/v benzene-d, solution of technical fenitrothion was prepared and the internal standard (100 mg/g sample) and chromyl acetonyl acetonate [CAA] (10 mg/g sample) were weighed in. In the case of rapid scans, 60% w/v samples in benzene-d, were prepared containing relaxing agent (20 mg/g sample). HPLC. The analyses were carried out using a Waters hl6000 pumping system with a stop flow introduction valve, an Altex UV detector (280 nm) and a 0.4 X 30 cm SI-60, 10 pm silica gel (E. M. Merck) column. The solvent was varied from 0.25-4070 butanol/isooctane by a Waters solvent programmer (profile 9) and a flow of 2 mL/min was maintained. Chemicals. Triphenyl phosphate (TPP) was purchased from Aldrich Chemicals, Milwaukee, Wis. BF and SMBF were obtained from the Research Institute of Agrochemical Technology, Bratislava-Predmestie, Czechoslovakia;other fenitrothion metabolites were prepared as previously reported (7). Technical grade samples of fenitrothion were obtained from suppliers in Canada and included Bayer, Cyanamid, BASF, and Sumitomo products.
RESULTS AND DISCUSSIONS T h e three most pertinent factors to be considered in the use of 31P F T / N M R for quantitative purposes are the chemical , the nuclear Ovshift, spin-lattice relaxation time ( T I ) and erhauser effect (NOE) of the compounds ,8). T h e chemical shifts (relative to triphenyl phosphate) of known contaminants
- 44.06 - 41.82 - 32.46"
-~ 20.33 -
12.64f
- 12.60
-4.37f Chemical
and degradation products of fenitrothion are listed in Table I. It can be seen that the 31Presonances of F, BF, S M F , SMBF, and FO are well separated, with the phosphorothioates at lower field than the phosphates. Triphenyl phosphate was used as an internal standard because its chemical shift (+17.1 ppm relative to H 3 P 0 4 ) is upfield from those of dimethyl phosphoric acid and phosphate esters. T h e spin-lattice relaxation time (T,) determines the repetition rate for FT, since for good quantitative data all nuclei should be fully relaxed before applying the next pulse. It can be compensated for by using a small flip angle pulse or by the addition of a paramagnetic relaxing agent (9). Gurley and Ritchie (6) reported on t h e use of acetylacetonate complexes with iron and other transition metal ions for this purpose with organophosphorus pesticides. The iron complex had a greater effect on phosphates than phosphorothioates because of the greater degree of complexing with t h e P=O bond. T h e T I for fenitrothion (85% in benzene-d6) is 5 s , as compared to 3 s for B F and SMF. Addition of equimolar amounts of chromyl acetonyl acetonate reduced the value to 0.15 s without any significant changes in the chemical shift of fenitrothion or any of the known impurities in technical materials. Proton decoupling can produce NOE effects, which result in enhancement of signal intensities so that they are not proportional to the number of nuclei. The NOE (1 + h) values for F, BF, SMF, SMBF and FO are 1.22, 1.20, 1.23, 1.09 and 1.00, respectively. T o determine whether T l were shortened enough and NOE effects adequately quenched by the addition of CAA, a mixture of F, BF, S M F , SMBF, and FO was analyzed two different ways. T h e first involved t h e use of continuous proton decoupling, with 1K 90" pulses and a repetition rate of 0.5 s, and the second procedure used gated decoupling with a 1-s pulse delay giving a repetition rate of 1.5 s. T h e results were not significantly different, indicating that both T I and NOE effects were small. The NMR spectrum of technical grade fenitrothion is shown in Figure 1 as obtained with 1K transients, 90" pulses, and 0.5-s repetition rate. Improvement in the signal-to-noise ratio and precision could be obtained with increased number of transients, but for 10K the increase in precision was not significant. In addition to the expected contaminants FB, S M F , S M B F , and FO, another major impurity can be seen at 49.17 ppm, which was identified as O,O-dimethyl S-methyl phosphorothioate (ODMSMPT). The minor impurity a t 73.4 ppm was not characterized but is thought to be O,O,O,Otetramethyl thiopyrophosphate. T h e precision determined from repeated analyses of this sample is given in Table 11. In the first procedure, both fenitrothion and the internal standard (TPP) were weighed, and in the second procedure only the sample was weighed and t h e results of repeated analyses were normalized t o give a constant value for the standard. T h e precision of both procedures is quite good. T h e larger standard deviation for B F could be due to its proximity to
ANALYTICAL CHEMISTRY, VOL. 50, NO. 14, DECEMBER 1978
enitrothion
2041
Trip heny I
phosphate S-methyl fenitrothion
c I
100
6
5 '0 CHEMICAL SHIFT ( p p m )
Flgure 1. 3'P FT/NMR spectrum of a technical grade fenitrothion sample
Table 11. ) ' P FT/NMR Analysis of Technical Grade Fenitrothion Samplea,b conditions
-
X ( n = 4) std. dev. X(n=4) std. dev. X ( n = 5) std. dev.
F
BF
ODMSMP
SMF
FO
TPP
0.405 0.196 0.492 0.059 8.086 0.031 0.004 0.007 0.005 0.002 2 0.435 0.213 0.481 0.06 0.025 0.013 0.005 0.006 0.37 0.195 0.498 0.073 rapid assay 0.03 0.011 0.049 0.018 HPLC 97.86 0.52 n.d.c 0.52 0.05 F, fenitrothion; BF, bis(fenitrothion);ODbISMP, 0,O-dimethyl S-methylphosphate; FO, fenitrooxon; TPP, triphenyl phosphate. Conditions; 1, sample and standard weighed, 1000 90" pulse, 0 . 5 s repetition time; 2, sample only weighed data normalized on TPP standard, 1000 90" pulse, 0.5-s repetition time; rapid assay, sample weighed, integrator set to 98 for F , 200 90" pulses, 0 . 3 s repetition time. n.d. = not detectable. 1
97.83 0.269 97.72 0.13
Table 111. Comparison of 3 ' P FT/NMR and HPLC Analysis of Artifacts in Technical Grade Fenitrothiona*b,c,d sample
TMPT
DMPTC
BF
ODMSMPT
SMF
Shl BF
cresol
FO
( n . d . ) 0.14 (0.13) 0.18 (n.d.j 1 . 1 3 ( 1 . 5 0 ) 0.04 (0.02) 0.263 (0.'15) n.d. (0.63) 2 0.02 (n.d.) (n.d.) 0.40 (0.52) 0.20 (n.d.) 0.49 (0.54) 0.01 (0.02) 0.06 (0.04) n.d. (0.22) 3 0.21 (n.d.) (n.d.) 0.55 (0.36) 0.11 (n.d.) 3.32 (3.08) 0.09 (0.05) 0.06 (0.04) n.d. (0.72) 4 2.09 (n.d.) 0.14 (n.d.) 0.27 (0.16) 0.31 ( n . d . ) 1.74 (1.81) 0.10 (0.15) (0.O:l) n.d. (0.89) 5 (n.d.) (n.d.) 0.84 (0.50) 0.18 (n.d.1 2.64 (2.59) 0.11 (0.13) 0.03 (O.O!j) n . d . (0.36) 6 (n.d.) (n.d.) 0.78 (0.42) 0.02 (n.d.1 0.06 (0.11) 0.08 (0.0'7) n.d. (0.28) 7 (n.d.) ( n . d . ) 0.87 (0.61) 0.05 (n.d.) 0.12 (0.14) 0.03 (0.0'7) n . d . (0.33) 8 (n.d.) (n.d.) 0.60 (0.34) 0.06 ( n . d . ) 0.42 (0.60) 0.04 ( 0 . 0 6 ) n.d. (0.24) a HPLC results in parentheses. TMPT, trimethyl phosphorothioate; DMPTC, dimethyl phosphorothiochloridate; BF, bis(fenitrothion);ODMSMPT, 0,O-dimethyl S-methylphosphorothioate; SMF, S-methylfenitrothion;SMBF, S-methylbis(fenitrothi0n); FO, fenitrooxon; cresol, 3-methyl-4-nitrophenol. Conditions; 50% w/v in benzene-d, 1 0 mg/mL CAA, 100 mg/mL TPP, 1 K 90" pulses, repetition time 0.5 s. Composition % by weight. e n.d. = not detectable. 1
(n.d.)e
-
the resonance of fenitrothion, which because of the large amount present, affects the base line. T h e total acquisition time for the rapid assay was only 1 min (200, 90' pulses, repetition time 0.3 s). T h e fenitrothion concentration was increased to 60% and the amount of relaxing agent doubled to further reduce T I . Although the precision of the data is poorer than for procedures 1 and 2, the results illustrate the potential of the technique for the rapid screening of large numbers of samples. Analysis by HPLC gave higher levels of the contaminants than by NMR, except in the case of FO; otherwise the agreement is acceptable.
A number of technical grade fenitrothion samples were analyzed by "P F T / N M R (lK, 90' pulses, 0 . 5 s repetition time) and HPLC, the results are listed in Table 111. T h e major contaminants present in samples 1-5 were SMF, BF, ODMSMPT, and cresol (which is not detected by NMR), whereas SMBF and FO are only minor contaminants. TMPT (91.00 ppm) and DMPTC (89.87 ppni) were identified in samples 2, 3, and 4 and their presence suggests the omission of a step in the manufacturing process for the removal of low boiling materials. Samples 6, 7. and 8 were freshly prepared technical materials from one manufacturer. It will be noticed
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0
ANALYTICAL CHEMISTRY, VOL. 50, NO. 14, DECEMBER 1978
Table IV. 3 1 P FT/NMR Analysis of Fenitrothion Formulationsarb, c sam-
ples
F
1 2
BF
SMF
SMBF
FO
15.56 ( 1 4 . 7 ) d
0.15 0.16 0.12
0.10 0.09 0.05
0.01
0.12
3 4
9.85 ( 9 . 8 ) 1 1 , 7 5 (11.70) 16.25 (10.25)
5
12.60 (11.6)
0.18 0.10
0.07 0.05
F, fenitrothion; BF, bis(fenitrothi0n); SMF, S methylfenitrothion; SMBF S-methylbis(fenitr0Conditions; 33% emulsion in thion); FO, fenitrooxon. acetone-d6, 10 mg/mL CAA, 1 0 m g TPP standard, 10K 90" pulses, and 0.5-s repetition time. Composition wt %. GLC results in parentheses. that the levels of S M F and ODMSMPT are much lower than in samples 1-5$which had been stored for a t least two years. This difference suggests that these two compounds result mainly from rearrangement on storage. Although HPLC did not detect T M P T , DMPTC, and ODMSMPT, it did detect cresol which also appears to increase on storage. In general, the amounts determined by NMR were higher than by HPLC for BF, and lower for SMF, SMBF, and FO. Fenitrothion formulations prepared from emulsifiable concentrates were also analyzed by 31PF T / N M R . Because of the dilution factor involved, iOK transients were necessary. The results are given in Table IV. All the samples analyzed contained both B F and SMF as contaminants. Sample 2 with the lowest amount of fenitrothion also contained some FO. The levels of fenitrothion were also determined by GLC, and varied from 0.5-3670 lower than by 31PFT/XNIR. No explanation could be found for the large discrepancy in sample 4?for which direct NMR analysis of formulation gave a value of 16.3'7%. Of the contaminants detected in technical grade fenitrothion, only SMF and FO are potent inhibitors of cholinesterase ( I O ) . However, FO and, in particular, SMF are also susceptible
to enzymatic hydrolysis by mammalian plasma and hepatic aryl esterases (11). Based on these facts and the amounts present in the technical material and formulations, it is thought that they do not represent any special hazard to personnel handling these materials. In summary, 31PF T / N M R is a rapid facile procedure for the analysis of phosphorus-containing contaminants present in organophosphorus pesticide technical material and formulation. In technical grade fenitrothion, the main contaminants found were BF, SMF, and ODMSMPT with traces of T M P T , SMBF, and FO. BF. SMPF, T M P T , FO, and some S M F and ODMSMPT appear to be byproducts of t h e manufacturing process. In stored samples the amounts of S M F and ODMSMPT were significantly greater than in recently prepared materials, suggesting that they were also formed on long term storage. This technique should find wide application both for rapid assay and detailed analysis of pesticide formulations in the future.
ACKNOWLEDGMENT .The authors thank M. A. LVilson for her technical assistance.
LITERATURE CITED Y. Takimoto, A. Murano, and J. Mjamoto, ResidueRev., 60, 11-28 (1976). W. D. Marshall, R. Greenhalgh, and V. Batora, Pestic. Sci., 5, 781-789 (1974). C.T. Burt, T. Glonek, and M. Barany, Soence, 195, 145-149 (1977). S. A. Sojka and R. A. Wolfe, Anai. Chem., 50, 585-587 (1978). I . K. O'Neil and M. A. Pringler, Anal. Chem., 49, 588-590 (1977). T W. Gurley and W. M. Ritchie, Anai. Chem., 48, 1137-1141 (1976). R. Greenhalgh and W. D. Marshall, J . Agric. FoodChem., 24, 708-712 (1976). P Yeagie, W. C. Hutton, and R. E.Martin, J Am. Chem. Soc.. 97, 7175-7 181 (1975). T. W. Guriey and W. M. Ritchie, Anai. Chem., 47, 1444-1448 (1975). J. Miyamoto. N. Mikami, K. Mihara. Y . Takimoto, H. Kohda, and H. Suzuki, J , Pestic. Sci., 3, 35-42 (1978). G. L. Myatt, D. J. Ecobichon. and R . Greenhalgh, Environ. Res., IO, 407-414 (1975).
RECEIVED for review June 22, 1978. Accepted September 8, 1978.
Microcomputer-Controlled Monochromator Accessory Module for Dual Wavelength Spectrochemical Procedures J. D. Befreese,' K. M. Walczak, and H. V. Malmstadt" s^chcol of Chemical Sciences, University of Il/inois at Urbana-Champaign, Urbana, Illinois 6 780 7
A relatively inexpensive microcomputer-controlled monochromator accessory module has been developed which provides split beam, dual wavelength capability as well as ratiometric compensation for source fluctuation at a single wavelength. The two wavelengths can be keyboard selected and are focused at exit slits widely separated in space. This wide spatial separation of the slits facilitates the attachment of the accessory module without any modification to the basic programmable monochromator. The microcomputer controls the selection of both wavelengths and also performs other control and computation functions for the spectrometer system. The versatility of the dual wavelength system is demonstrated by its application to a wide variety of analytical techniques.
*Present address, Department of Chemistry, University of Kansas, Lawrence, Kan. 66045. 0003-2700/78/0350-2042$01.00/0
LVhere commercial instruments have been either too expensive or not suited for the particular situation, various methods have been used in the laboratory to implement dual wavelength measurements. These methods have included modulation of a monochromator sine bar ( I ) , introduction of quartz refractor plates (2-4) and oscillating mirrors (5) into the optical path, vibration of the exit slit ( 6 ) ,etc. However, these instrumental modifications have generally been designed with one analysis problem in mind. Therefore, they do not represent versatile solutions to the wide range of analysis problems for which a dual wavelength approach would be advantageous. It is believed that the monochromator accessory module (MAM) described in this paper does represent such a significant solution because it is microcomputer controlled for maximum versatility and reproducibility, it has a wide wavelength programming range which is particularly useful for molecular spectrochemical methods, it offers the C 1978 American Chemical Society
