Simultaneous on-line preconcentration and determination of toxic elements in rice and rice-based products by SPE–ICP–MS: Multiple response optimization

Abstract

Simultaneous preconcentration of five toxic elements (Cd, Hg, Mn, Pb, and Sb) was carried out using a hyphenated system by on-line coupling of flow injection (FI), solid phase extraction (SPE) and inductively coupled plasma mass spectrometry (ICP–MS). The analytes were simultaneously preconcentrated on a microcolumn filled with oxidized multiwalled carbon nanotubes (ox-MWCNTs). During the method development, SPE conditions were optimized using a chemometric approach with experimental design and desirability function by multi-response surface methodology. An enrichment factor of 104 was obtained when 50 mL of sample were passed through the microcolumn. After optimizing the FI–SPE–ICP–MS system, detection limits were calculated varying from 0.8 ng L−1 for Mn to 0.09 μg L−1 for Hg. The relative standard deviations (RSD) for all elements were < 5%. For checking accuracy two standard reference materials NIST1568b (Rice Flour) and NIST 1643f (Trace Elements in Water) were analyzed and results were in good agreement with certified values. The proposed method was successfully applied to the determination of Cd, Hg, Mn, Pb and Sb in real samples of rice and rice-based products. The concentration of the analytes spanned in the range (ng g−1): Cd, 0.18–23.5; Hg, <4.6-6.0; Mn, <0.04–744; Pb, <0.16–462 and Sb, 5.9–47.