8-Hydroxyquinoline-5-sulfonic acid as the modifier for the determination of trace elements in cereals by slurry sampling electrothermal vaporization ICP-MS

Abstract

Ultrasonic slurry sampling electrothermal vaporization inductively coupled plasma mass spectrometry (USS-ETV-ICP-MS) has been applied to determine V, Cr, Co, Ni, Cu, Zn, Se, Cd, Hg and Pb in cereal samples. 8-hydroxyquinoline-5-sulfonic acid (8-HQ-5-SA) was used as the modifier to increase the volatility of the elements studied which makes the quantification possible using external calibration. The influences of instrument operating conditions and slurry preparation on the ion signals were studied to get better sensitivity of the elements studied and also similar sensitivity between slurry and aqueous solution. In this study, Cr, Cu, Zn and Se were determined under dynamic reaction cell (DRC) mode, while V, Co, Ni, Cd, Hg and Pb were determined under standard mode separately. The background ions at the masses m/z 52 and 80 were reduced in intensity significantly by using 1.0 mL min⁻¹ CH₄ as reaction cell gas in the DRC. This method has been applied to the determination of V, Cr, Co, Ni, Cu, Zn, Se, Cd, Hg and Pb in NIST SRM 1568a Rice Flour and SRM 1567a Wheat Flour reference materials and two cereal samples purchased from the local market. Analysis of the reference material agreed with the certified values. The results for the real world cereal samples were also found to be in good agreement with the pneumatic nebulization ICP-MS results of the sample solutions. The method detection limit was 1.3, 2.1, 3.6, 4.3, 6.8, 16, 1.7, 0.6, 0.8 and 2.6 ng g⁻¹ for V, Cr, Co, Ni, Cu, Zn, Se, Cd, Hg and Pb, respectively, in original cereal samples.