Since the sample container represents one of the earliest and potentially one of the largest sources of sample contamination, much of the analytical accuracy will depend upon the choice of container materials and the method of cleaning containers. Twelve different plastics have been examined by gravimetry, isotope dilution mass spectrometry, and neutron activation analysis. The present study examines the levels of impurities present in the various plastics as well as the quantities of impurities leached from the plastics by acid cleaning. A suggested method of cleaning containers is presented.

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ertheless, the xror wm always less than 0 . 8~ and was typically less than 0 'm.The anr,lytical method presented is shown to be rapid and accurate. The procedure is very well suited for black chromium :dating bath solutions and can be readily adapted for chromium(II1) determination at the milligram level even in the presence of high chromium(V1) concentrations. LITERATURE CITED(1) Soweil, R. R.; Pettit, R. 8. Plating and Surface Finishing 1978, 65, 42.(2) Willard, H. H.; Young, P. Trans. Necfrochem. SOC. 1935 67, 347.(3) Monnier D.; Zwahlen, P. Helv. Chim. Acta 1956, 39, 1859. (4) Lingane, J. J. "Electroanalytical Chemistry" 2nd ed.; Interscience: New York, 1958. p 155. chromate solution. Because the result is well within 1g of the theoretical value, it is apparent that the nitrite-ceric titration is unaffected by chromium(V1) at these levels. This is important in that it indicates that one can determine the sodium nitrite titer without considering the possible chromium(V1) content of the analyte. Also, the accuracy of the technique shows no apparent dependence upon the chromium(V1) to chromium(II1) ratio. For example, the largest and the smallest errors (experiments 12 and 15, respectively) were observed a t virtually the same chromium(V1) to chromium(II1) ratios while the remaining analyses produced fairly constant errors which were near the average error of 46 kg.At these low chromium(II1) levels, precision tended to be somewhat of a problem. When the analyses were performed in triplicate (experiments 10-13), the standard deviation was usually quite large, but the precision was improved markedly by performing the determination with five analyses. Nev-

The need for reliable and accurate measurements of elements at trace and ultratrace concentrations is now well established. Less well known is the fact that, often the key to successful analysis of a sample is found to be in the control of the analytical blank. As shown by Murphy (1), the analytical clean room used to produce a particulate-free environment is one of the major tools available to the analyst. The potential for trace element contamination from the air has been examined by Murphy (1), Patterson and Settle (2), Zief and Mitchell (3), Zief and Nesher (4), and many others.Such particulate contamination may be controlled by the high-efficiency particulate (HEPA) filter (5), which was developed during World War II for the Manhattan Project (6) and was used to provide absolute con-This article not subject to U.

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