Evaluation of metal ions in rice samples: extraction and direct determination by ICP OES

Abstract

A method for extraction of metal ions present in rice samples using ammoniacal EDTA solution, pH > 10, as extractor agent is proposed under the following optimized conditions: 0.20 g of rice sample and 5.00 mL of ammoniacal EDTA (ethylenediaminetetraacetic acid) solution, with 5 min of ultrasound exposure time. Using robust ICP OES (inductively coupled plasma atomic emission spectrometry) conditions, direct analysis of the extraction solution was allowed, and the recovery values obtained were above 90% for most of the studied elements (P, K, Mg, Ca, Zn, Mn, Cu and Mo) with RSD < 5%. The results were in good agreement with those obtained by microwave-assisted extraction and for the reference material of rice flour (NIST SRM 1568a). The limits of detection of method were in the range of 0.007 mg kg-1 (Mn) - 48.68 mg kg-1 (K), showing adequate detectability for the determination of the analytes. The analysis of different samples indicated that Brazilian integral rice contains higher contents of the constituents studied, followed by parboiled rice, and the agulhinha rice a long and thin grain type.