ZINC DETERMINATION IN HUMAN-MILK BY FLAMELESS ATOMIC-ABSORPTION SPECTROMETRY AFTER DRY ASHING

A zinc determination method, using a dry ashing step and flameless atomic absorption spectrometry is described. Milk samples were dry ashed at 400-degrees-C. Then, the ash was dissolved in 0.1 M nitric acid (final dilution = 1 + 99). The within-run precision was found to be 8%. The between-run was found to be 5%. The recovery of standard addition was found to be 109 +/- 9%. The linear range was 122 nmol litre-1 to 2-mu-mol litre-1. The analytical variables (dry ashing temperature, dilution rate, acid, furnace, calibration) are discussed. A significant loss of zinc was observed at temperature < 450-degrees-C. The dilution rate and acid used for dissolution of dry ash had an important effect on the validity of the method. A comparison of the proposed method with a direct method without an ashing step was performed. The results obtained from these two methods were similar. From these results, it is concluded that flameless atomic absorption spectrometry after dry ashing is a reliable technique for the determination of zinc in solid foods or tissues.