Direct analysis of wheat flour by inductively coupled plasma mass spectrometry with flow injection, slurry nebulization, and a mixed-gas plasma

Abstract

Inductively coupled plasma mass spectrometry (ICPMS) is well suited for vegetation analysis. Slurry nebulization offers an attractive alternative to traditional digestions that increase the risk of sample contamination and analyte loss. By simply grinding the sample very finely and suspending it in solution the material can be nebulized directly. While ICPMS has been used for slurry nebulization, it is susceptible to matrix effects. Mixed-gas plasmas have been shown to reduce or eliminate these matrix effects by increasing energy transfer between the bulk plasma and the central channel. This contribution uses flow injection and slurry nebulization for sample introduction into an Ar–N₂–H₂ mixed-gas plasma for analysis of wheat flour by ICPMS. 1% (m/v) aerosol–OT was used as a dispersing agent to stabilize the 1% (m/m) wheat flour slurry without additional grinding. To form the mixed-gas plasma, 462 mL min⁻¹ of N₂ gas was added to the 18.5 L min⁻¹ Ar plasma flow. The normal Ar sheath gas was replaced with 4 mL min⁻¹ H₂ gas. External calibration without internal standardization was performed using aqueous standard solutions prepared in 1% (m/v) aerosol–OT. Accurate concentrations were determined for K, Fe, Zn, Cu, Mo, and Cd despite analysis being conducted in a 0.05% Na solution. Detection limits between 0.02 and 40 mg kg⁻¹ of bulk sample were obtained. However, severe polyatomic interferences induced by the mixed-gas plasma prevented accurate determination of Al. Nonetheless, this method should be applicable to the analysis of any dried and finely ground plant material.