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ANALYTICAL CHEMISTRY, VOL. 52, NO. 4, APRIL 1980
CORRECTIONS Maximum Likelihood Estimation Evaluation of a Material with Unequal Number of Replicates In this article by D. C. Jordan and L. R. de Alvare, Anal. Chem., 51, 1079 (1979), there are errors in Table I1 in the “maximum likelihood” column. The table should be: Table 11. Estimates of Parametersa Procedure parameter h ow U B
ir
“2
Mandel & Paule
maximum likelihood
3.240 0.04289 0 . 1 3898 7.466 0.142
2.980 0.04200 0.12517 7.465 0.135
Initial estimates of p = 7.28, u B 2 = 0.19946, u w 2 = 0.04289 were used t o start the Gauss-Newton iterations. a
The authors thank J. Kenneth Casey and Lars H. Sjodahl for raising a question which led to the discovery of the computational error.
Air-Sampling and Analytical Method for 4,4’Methylenebis(2-chloroaniline) In this article by Stephen M. Rappaport and Raul M o d e s , Anal. Chem. 1979, 51, 19-23 (January), the units indicated in Table I and in the sixth line of the second paragraph of page 20 should read pg/m3. Loss of Polychlorinated Biphenyl Homologues during Chromium Trioxide Extraction of Fish Tissue
There is an unfortunate error in this article by Michael J. Szelewski, David R. Hill, Stuart J. Spiegel, and Edwin C. Tifft, Jr., Anal. Chem. 1979, 51, 2405 (December). The notation, Cr?O,, which appears four times in the article, should be replaced with CrO?. The hexavalent chromium compound was used in all experiments. The authors thank Waldo E. Kallenberger of the University of Cincinnati, Cincinnati, Ohio, for bringing the error to their attention.
ADDENDUM Sampling of Isocyanates in Air
Sir: I wish to add two improvements to the paper ( I ) I coauthored with Jurgen Keller: (1) On page 1868, under “Absorption Tubes“, we suggest reducing the amount of cotton from 200 mg to 40 mg to improve the air flow through the tubes. (2) On page 1868 under “TLC Analysis of the Derivatized Isocyanates” and in the footnote ( b ) of Table I, we suggest using methylene chloride in place of cyclohexane as an eluting solvent. We have found methylene chloride to be a bet,ter solvent for the nitroreagent-urea derivatives. LITERATURE CITED (1) Keller, Jurgen; Sandridge. R. L. Anal. Chem. 1979, 51, 1868-1870.
R. L. Sandridge Mobay Chemical Corporation Analytical Group New Martinsville, West Virginia 26155
