Rice Slurry Analysis Using Mixed-Gas Plasma and Axially Viewed ICP OES

Abstract

This study deals with determination of essential and toxic elements in slurry of rice using axially viewed inductively coupled plasma optical emission spectrometry (ICP OES) and mixed gas plasma (N2-Ar ICP). Nitrogen was added (flow rate of 20 mL min−1) to the nebulizer gas through the spray chamber. It was observed that the addition of N2 increased the ICP robustness and mitigated the slurry matrix effects. Several parameters associated with the slurry preparation (extractant concentration, dispersant concentration, mass volume ratio of the slurry and sonication) were evaluated. The slurry was prepared in 10 % (m/v) HNO3 + 0.2 % (m/v) Triton X-100. Calibration was carried out with aqueous standards whereas Y(II) (371.029 nm) was used as internal standard (IS) in order to overcome matrix effects. The IS and sample solutions were mixed online. Accuracy was evaluated by the analysis of certified reference materials and by comparison with an independent method of sample preparation (acid digestion). The concentrations were consistent with those certified or found in digested rice sample. Calcium, Mg, K, Cd Cu, Fe, Mn, Mo, Cr, Zn, Co, Pb and Ni were investigated whose limits of detections were 0.080, 0.033, 0.050, 0.048, 0.050, 0.015, 0.005, 0.107, 0.036, 0.056, 0.040, 0.367 and 0.132 mg kg−1, respectively. The RSD (relative standard deviation) was typically lower than 10 %. Samples of parboiled, white, and brown rice were analysed and the concentrations found corroborate with those reported. It was concluded that calibration with aqueous standard is feasible, making the analysis simpler. The method is robust and can be routinely applied.