594
Anal. Chem. 1982, 5 4 , 594-595
Table 11. Collection Efficiencies for Semivolatile Pesticides %
pesticide aldrin p,p'-DDE p,p'-DDT mirex tech. chlordane a-chlordane 7-chlordane diazinon methyl parathion ethyl parathion malathion
calcd air concn, ng/m 0.3-3.0 0.6-6.0 1.8-18 1.8-18
15-1 50 1.5-15 1.5-15 3.0-30 1.8-18 3.6-36 0.9-9.0 a Average 6 to 1 2 determinations.
PUF alone 28
89 83 93 73 114 126 63 91 96 97
sorbent types and combinations for high-volume air sampling. Since 300 m3 or more of air can be sampled in a 24-h period, even relatively poorly trapped chemicals can be accumulated in sufficient quantities to allow reliable measurement of very low air concentrations.
LITERATURE CITED Lewls, R. G.; Brown, A. R.; Jackson, M. D. Anal. Chem. 1977, 4 9 , 1688-1872. Jackson, M. D.; Lewls, R. G. Bull. Environ. Contam. Toxlcol. 1979, 21, 202-205. Jackson, M. D.; Lewls, R. G. I n "Sampling and Analysis of Toxic OrganiCS in the Atmosphere"; Verner, s. s., Ed.; American Society for Testing and Materlals: Philadeiphla, PA, 1980; pp 38-47; ASTM Specia1 Technical Publlcation 721. Rhoads, J. W.; Johnson, D. E.; Lewis, R. G. "Abstracts of Papers", 173rd National Meeting of the American Chemical Society, New Orleans, LA, March 1977; Americai Chemical Society: Washington, DC, 1977; PEST 77.
collecteda after 24 h at 225 L/min
PUF/ Chromosorb 102 34 83 77 94 85 108 104 72 82 85 88
PUF/ PorapakR 35 93 89 95 74 96 91 59 72 72 78
PUF/ XAD-2 33 135 138 132 87 102 96 71 80 81
89
PUF/ Tenax GC 71 69 78 73 100 93 76 87 86 91
PUF/ Florisi1 PR 40 138 119 123 97 98 100 72 83 83 81
(5) Andersson, K.; Levln, J.-0.; Nilsson, C.-A. Chemosphere 1961, 10, 137-142. (6) Lewis, R. G.; MacLeod, K. E. Anal. Chem. 1962, 5 4 , 310. (7) Lewls, R. 0. I n "Air Pollution from Pesticides and Agricultural Processers"; Lee, R. E., Jr., Ed.; CRC Press: Cleveland, OH, 1978; Chapter 3.
Robert G. Lewis* Merrill D. Jackson U.S. Environmental Protection Agency Research Triangle Park, North Carolina 27711 RECEIVED for review August 24, 1981. Accepted November 9, 1981. This paper has been reviewed by the Health Effects Research Laboratory, U.S. Environmental Protection Agency, and approved for publication. Mention of trade names or products does not endorsement Or recommendation for use.
Exchange of Comments on the Quantitative Determination of Mirex and Its Degradation Products by Capillary Gas Chromatography/Mass Spectrometry Sir: The recent paper by Onuska et al. (1) on the quantitative determination of mirex and its degradation products by high-resolution capillary gas chromatography/mass spectrometry is misleading in its conclusions concerning mirex determinations. The authors report a quantitative procedure for mirex and its major environmental degradation products that yields mass spectrometric selected-ion-monitoring (MSSIM) results which the authors claim are not significantly different from those obtained by electron capture gas chromatography (EC-GC). However, the conclusions concerning mirex determinations are not adequately supported by the information presented. An examination of Onuska's quantitative data for mirex, which is reported in terms of pg/pL, reveals that significant differences exist between the results obtained by MS-SIM and EC-GC, when these data are converted to pg/g wet weight of tissue as is generally done in such analyses. We present a comparison of these data in Table I. The MS-SIM results at m/z 546, a major ion in the molecular ion cluster for mirex, mirex levels reported for the same organisms by the other show that the mean mirex concentrations in the trout and 0003-2700/82/0354-0594$01,25/0
lamprey are at the most only 0.03 and 0.004 pg/g wet weight of tissue, respectively. Therefore, these mirex levels by MSSIM at m / z 546 are approximately 21 times lower than the three techniques employed. Thus, the reporting of the mirex data in terms of pg/pL by Onuska et al. conceals the true differences which exist among the data derived by the four techniques described. In this particular case, the converted data show that the mirex determinations by the techniques of EC-GC, MS-SIM a t mlz 272, and MS-SIM at four ions (mlz 203, 237, 238, and 272) are in error. The differences in data from all four techniques suggest the presence of coeluting compounds in the sample extracts which interfere with the proper quantification of mirex. Similar observations have been previously reported for Lake Ontario fish by Laseter et al. (2, 3) and by Kaiser (4). In addition to misleading the readers with the way in which the mirex results are presented, Onuska et al. do not provide conclusive, unequivocal mass spectral evidence for the presence of mirex in any of the samples reported, nor do they stress the importance of confirmatory evidence for mirex determinations in environmentally derived samples. Instead, the 0 1982 American Chemical Society
Anal. Chem. 1982, 54,595-596
Table I. Comparison of the Mean Mirex Concentra. tions in Lake Trout and Lamprey by Four Different Techniquesa trout lamprey rereported mirex ported mirex mean,“ concn,b mean: concn,b technique PgIwL wglg PgIwL wglg EC-GC 12!3 0.65 17.2 0.086 MS-SIM 1113 0.03 17.2 0.004 m/z 546 MS-SIM 12’7 0.64 16.5 0.083 m/z 272 MS-SIM 126 0.63 14.4 0.0’72 4 ions ( m / z 203, 237, 238, 272) a The mean mirex concentrations are reported for 10 trout and 5 larnprey samples in Table I1 of Onuska et al. ( 1 ). Converted from the reported mean for trout and lamprey in Table I1 of Onuska et al. (1 ) using the sample sizes, final volumes, aliquot volumes, and injected volumes described in the Experimental Section.
!595
which we present in Table I clearly illustrate the fact that the EC-GC technique, and the MS-SIM at m / z 272 and at four ions (mlz 203, 237,238, and 272) techniques are not suitable substitutes for the MS-SIM at m / z 546 technique for the determination of mirex in biological samples from the environment. The determinatioln of mirex in fish and other environmeiital samples from heavily contaminated water cannot be talken lightly and must be supported by confirmatory mass spectral evidence. Under ordinary conditions, the acquisition of adequate full mass spectral data to unequivocally establish the presence of mirex is difficult. Even the interpretation of diata for its quantification can be complicated. Therefore,judicious scrutiny of all confirmatory and quantitative data for mirex is essential in order to minimize the release of reports which are in error.
LITERATURE CITED Onuska. F. I.: Comba, M. E.; Coburn, J. A. Anal. Chem. 1980, 52, 2272-2275. Laseter, J. L.: DeLeon, I. R.; Remele, P. C. Anal. Chem. 1978, 5 0 , 1. 169-1 . - - . 172. . . -. DeLeon, I. R.; Warren, V.: Laseter, J. L. Ouant. Mass Specfrom. Life Sci. 1978, 2, 483-492. Kaiser, K. L. E. Sclence 1974, 186, 523. Norstrom, R. J.: Nallet, D. J.; Onuska, F. I.; Comba, M. E. Environ. Scl. Techno/. 1980, 14, 860-886.
authors evade the issue of providing conclusive mass spectral data for mirex by stating that the mass spectra of mirex and its degradation products are presented elsewhere (5). However, the mass spectral data for mirex is not presented as alleged (5). The issue is further complicated by the presentation of,selected-ion-detection traces for the m / z 203, 237, 238, and 272 ions, whereas the selected-ion-detection traces for the m/z 546 are selectively omitted. On the basis of our experience with mirex analysis (2, 3) and the data presented, it is our opinion that Onuska et al. have not successfully shown that the method described is appropriate far mirex determinations. The corrected data
Center for Bio-Organic Studies University of New Orleans Lakefront New Orleans, Louisiana 70148
Sir: With regards to our paper “QuantitativeDetermination of Mirex and Its Degradation Products by High Resolution Capillary Gas Chromatograph/Mass Spectrometry” ( I ) , we wish to express our views on the comments by J. L. Laseter and I. R. DeLeon. The first point of concern is their calculation of mirex concentrations on a p g / g basis. With reference to the calculations performed by Laseter on the data in our Table 11, we hope to provide some clarification. The choice of pg/pL as an expression of concentration was used to avoid any specific implication or reference to mirex levels in Lake Ontario biota, since this was not the intent of the article. In hindsight this may have been unfortunate, since, as in Laseter’s case, the data may be misinterpreted. However it should be noted that none of the original reviewers, including Laseter, questioned this presentation. The data on extrapolated values (pg/g) presented in Table I by Laseter et al. are incorrect for the m / z 546 technique. He has taken data which have already been normalized to enable comparison with the other three techniques and reapplied the volume coirrection factor of 20 (1 mL to 50 pL) to give a result of 0.03, which should read 0.60 pg/g. The data presented in our Table I1 on the mirex levels in lamprey samples were also normalized. Analyses again were performed on concentrated portions for the m/z 546 SIM
analysis and the four ion SIM analysis and on unconcentrated portions for the other two techniques as indicated by the footnotes in Table 11. It is incorrect to reapply this volume factor in calculating the corresponding concentrations expressed on a pg/g Ibasis. The procedures used in this paper do not reflect a 20-fold difference in resultla implied by Laseter and DeLeon and we have not experienced the interferences on the m / z 546 ion mentioned by them. Our data on m / z 546 revealed none of these interferences, perhaps due to superior cleanup and fractionation techniques used in our laboratory. Our other concern deals with the issue of “conclusivetividence for the presence of mirex”. We feel that the data and the mass spectrometry ideintification is conclusive for mirex. Millard (2) estimates a probability greater than loe for single ion determinations on mlz values higher than m/z 200, with one retention time. Our MS data indicated that the ion ratios were the same for the environmental samples as for our reference standard, since quantitation on all ions produced the same results. The correct ratios for the four selected ions and an ion from the molecular cluster present to us conclusive evidence for the presence and level of mirex reported in our paper. The additional confirmation of retention indices on four different chromatographic columns strengthens our position.
0003-2700/82/0354-0595$01.25/0
John L. Laseter* Ildefonso R. DeLeon
RECEIVED for review March 23, 1981. Resubmitted October 19, 1981. Accepted October 19, 1981.
0 1982 American Chemlcel Soclety
