CORRESPONDENCE Re: “Criteria for Judging Acceptability of Analytical Methods” SIR: Earl F. McFarren, Raymond J. Lishka, and John H. Parker ( I ) , the authors of this paper, propose a procedure for determining acceptability of an analytical method based on
The “total error” has been calculated for a number of successful collaborative studies (2-5). These are summarized in Table I. As you will note, the results indicate that with
Table I. Summary of AOAC Collaborative Study Data for Pesticides (2-5) No. of True, ppm Mean, ppm Mean error, ppm Std dev, ppm results Butterfat (2) Heptachlor epoxide Dieldrin White potatoes (3) Aldrin DDE Methoxychlor Aldrin DDE Methoxychlor Endive (4 Lindane Heptachlor DDD(TDE) Lindane Heptachlor DDD(TDE) Cauliflower (4 Lindane Heptachlor DDD(TDE) Lindane Heptachlor DDD(TDE) Apricots ( 5 ) BHC DDT Endrin BHC DDT Endrin Strawberries (5) BHC DDT Endrin BHC DDT Endrin
20 20
0.261 0.266
0.293 0.255
+O. 032 -0.011
0.039 0.051
42.15 42.48
10 10 10 10 10 10
0.12 4.90 6.80 0.04 0.70 0.60
0.124 4.95 6.35 0.0399 0.704 0.558
$0.004 +O. 050 -0.450 -0.0001 +0.004 -0.042
0.013 0.530 0.750 0.0039 0.064 0.050
25.00 22.65 28.68 19.75 18.86 23.67
8 8 8 8 8 8
10.00 0.10 7.00 1.00 0.05 1.OO
9.17 0.082 5.50 0.936 0.044 0.861
-0.830 -0.018 -1.500 -0.064 -0.006 -0.139
0.780 0.015 1.030 0.105 0.006 0.120
23.90 48.00 50.86 27.40 36.00 37.90
8 7 6 7 7 5
10.00 0.10 7.00 1.oo 0.05 1.00
9.57 0.094 5.98 0.883 0.041 0.864
-0.430 -0.006 -1.020 -0.117 -0.009 -0.136
1.730 0.012 0.620 0.154 0.005 0.137
38.90 30.00 32.29 42.50 38.00 41.00
12 12 13 12 12 13
4.04 6.299 0.198 0.879 0.208 0.0496
4.18 6.37 0.187 0.93 0.202 0.049
+O. 140 +0.071 -0.011 +0.051 -0.006 -0.0006
0.950 0.580 0.023 0.190 0.020 0.006
50.50 19.54 28.79 49.03 22.12 25.40
12 12 13 12 12 13
4.219 6.580 0.207 0.918 0.217 0.0518
4.31 6.77 0.193 0.96 0.227 0.052
+0.091 fO. 190 -0.014 $0.042 +0.010 +0.0002
1.100 0.680 0.022 0.180 0.023 0.010
54.30 23.56 28.02 43.79 25.81 38.99
calculation of “total error.” They then apply this proposed criteria to several analytical studies selected from the literature. One such study involved analysis of pesticide residues in water. The authors concluded in part: “. . . none of the pesticides studied could be determined satisfactorily by gas chromatography.” They were, of course, referring only to the study results referenced in their paper but, by unfortunate inference, gave the impression that general pesticide residue GLC analysis was suspect. This is not true. There are, in fact, many published studies which have demonstrated the reliability of pesticide residue analysis and which produced acceptable results using the author’s own criteria. (1) E. F. McFarren, R. J. Lishka, and J. H. Parker, ANAL.CHEM., 42, 358 (1970). 156
Total error,
few exceptions, pesticide residue GLC methodology is s?.tisfactory, but could be improved.
TERRYL J. FARRELL Department of Health, Education, and Welfare Food and Drug Administration 1521 West Pic0 Boulevard Los Angeles, Calif. 90015
RECEIVED for review June 12, 1970. Accepted August 31, 1970. (2) (3) (4) (5)
ANALYTICAL CHEMISTRY, VOL. 43, NO. 1, JANUARY 1971
L. Y.Johnson, J. Ass. Ofic.Agr. Chew., 48, 668 (1965). R. T. Krause, ibid., 49, 460 (1966). J. Gaul, ibid., p 463. A. Davidson, ibid., p 468.
