Optimization of the operating conditions of solid sampling electrothermal vaporization coupled to inductively coupled plasma optical emission spectrometry for the sensitive direct analysis of powdered rice

• 4-mg aliquots of rice powder can be accurately analysed in 87 s by SS–ETV–ICP-OES.
• The total analysis time, including grinding, weighing and analysis is 5 min.
• As accurate results are directly obtained as with ICP-MS following acid digestion.
• Detection limits of 0.01–6 ng g−1 were achieved in the solid, depending on the element.
• Al, As, Co, Cu, Fe, Mg, Pb, Se and Zn levels in organic brown and white rice are reported.

Two different approaches were used to improve the capabilities of solid sampling (SS) electrothermal vaporization (ETV) coupled to inductively coupled plasma optical emission spectrometry (ICP-OES) for the direct analysis of powdered rice. Firstly, a cooling step immediately before and after the vaporization step in the ETV temperature program resulted in a much sharper analyte signal peak. Secondly, point-by-point internal standardization with an Ar emission line significantly improved the linearity of calibration curves obtained with an increasing amount of rice flour certified reference material (CRM). Under the optimized conditions, detection limits ranged from 0.01 to 6 ng g−1 in the solid, depending on the element and wavelength selected. The method was validated through the quantitative analysis of corn bran and wheat flour CRMs. Application of the method to the multi-elemental analysis of 4-mg aliquots of real organic long grain rice (white and brown) also gave results for Al, As, Co, Cu, Fe, Mg, Se, Pb and Zn in agreement with those obtained by inductively coupled plasma mass spectrometry following acid digestion of 0.2-g aliquots. As the analysis takes roughly 5 min per sample (2.5 min for grinding, 0.5–1 min for weighing a 4-mg aliquot and 87 s for the ETV program), this approach shows great promise for fast screening of food samples.

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