AOAC Official Method 935.50 Lead Suitability of Methods and Precautions
A. Principle
Instrumental methods, polarography and atomic absorption (AA) spectrophotometry, are generally more reliable than colorimetric method at lower concentrations. Method 972.25 (see 9.2.19) is particularly applicable to samples containing high Ca concentration. Special instrumental methods optimized for evaporated milk and fish are given in 973.35 (see 9.2.14), 974.13 (see 9.2.15), 979.17 (see 9.2.16), 972.23 (see 9.2.17), and 972.24 (see 9.2.18).
General colorimetric method calls for ashing, 934.07«B (see 9.2.20), separation of Pb, either as dithizone complex, 934.07«D(see 9.2.20), or as sulfide, 934.07«E (see 9.2.20), followed by colorimetric dithizone determination, 934.07«F(see 9.2.20), in comparator tubes, or with spectrophotometer. Interference is treated separately, 934.07«G–I (see 9.2.20), and analyst should become familiar with details of these sections before applying method. Special methods of material preparation are given in 934.07«J andK(see 9.2.20).
