Multivariate Optimization of Method of Slurry Sampling for Determination of Iron and Zinc in Starch Samples by Flame Atomic Absorption Spectrometry

A slurry sampling procedure has been developed for determination iron and zinc in starch sample by using flame atomic absorption spectrometry. The optimization step was performed using univariate methodology for mass of sample and multivariate methodology using Box-Behnken design involving the other variables: type extractor, final concentration of extracting solution, and sonication time. The established conditions were with 100 mg of sample, extracting solution composed of mixture (1:1) HCl:HNO3 at a final concentration of 2.0 mol L-1, sonication time of 17 min, and a slurry volume of 10.0 mL. This procedure allows the determination of iron and zinc with quantification limits of 5.68 and 1.36 mg kg(-1), respectively, and a precision expressed as relative standard deviation (%RSD) of 6.1 and 4.7 % (both, n = 10) for the concentrations of iron and zinc of 19.5 and 2.9 mg kg(-1). The accuracy of the procedure was confirmed by analysis of certified reference material wheat flour NIST 1567a. A statistical evaluation using student t test showed that there is no significant difference between the value obtained with the use of the proposed procedure and the certified value, at 95 % confidence level. The proposed procedure was applied for determination of iron and zinc in samples of corn starch, rice starch, potato starch, cassava starch, and starch mix of rice and corn. The obtained concentrations in samples analyzed varied between 17.2 and 152 mg kg(-1) of iron and 1.6 and 23.8 mg kg(-1) of zinc, and can conclude that these starches are an important source of iron and zinc.