Abstract
Abstract A collaborative study was performed with 8 Magruder samples to evaluate a new zincon colorimetric method, an alternative to 2.137. The previous zincon method was modified, but the basic principle remains: 0.5N HCl retains a stable Zn(II) chloro-complex ion on an anion exchange resin but not interfering cations; 0.005N HCl elutes the Zn(II) ion which is determined colorimetrically in the presence of the indicator, zincon. Overall estimate of precision, Sr = 0.033, is similar to Sr = 0.030 for atomic absorption. Sb values (0.074 at 0.05%, 0.035 at 0.25%, and 0.054 at 1%) compare favorably with atomic absorption Sb values (0.072 at 0.05%, 0.036 at 0.25%, and 0.063 at 1%). F- and t-test results at the 95% confidence level indicate systematic error by both methods but do not discern a difference in the true value each method can measure. Average single sample values agree better with Magruder grand averages than corresponding averages by atomic absorption. While applicable to samples containing 0.05% zinc and higher, the method is quite time consuming when samples are low in zinc and have high iron—zinc ratios. This method has been adopted as official first action.
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