Green microwave-assisted wet digestion method of carbohydrate-rich foods with hydrogen peroxide using single reaction chamber and further elemental determination using ICP-OES and ICP-MS

Abstract

A sample preparation method using only H2O2 in the single reaction chamber system (SRC-UltraWave™) was proposed for carbohydrate-rich foods (CRFs) digestion and further elemental determination by inductively coupled plasma (ICP) based techniques. The greenness of the proposed method was evaluated based on the Analytical Eco-Scale. Additionally, the digestion efficiency, obtained under different conditions (temperature and volume of H2O2), was evaluated based on the concentration of residual carbon (RC). Determination of RC and major elements (Ca, Fe, Mg and Na) were carried out using inductively coupled plasma optical emission spectrometry (ICP-OES), while the minor and toxic elements (As, Ba, Cd, Co, Cu, Mn, Mo, Pb, Sr and Zn) were determined by inductively coupled plasma mass spectrometry (ICP-MS). Digests with lower RC were obtained using 8mL of 50% H2O2, 250°C and 199bar. Residual carbon lower than 250 and 400mgL−1 were obtained for honey and different flours (wheat, corn, cassava and potato), respectively. Maxima sample masses of 0.75g and 1.25g were efficiently digested (without insoluble residues) for different flours and honey, respectively. Reference materials (RMs) and certified reference material (CRM) with carbohydrate-rich matrices: corn bran (RM NIST 8433), cotton cellulose (RM IAEA V9) and rice flour (CRM NIST 1568a) were used to evaluate the accuracy of the proposed method. Additionally, accuracy was also evaluated by comparison between results obtained using proposed method and those obtained by microwave-assisted wet digestion (MAWD) with concentrated HNO3. Significant differences were not observed when comparing the results of the proposed method with reference values of RMs, CRM and MAWD. Limits of detection obtained by the proposed method were suitable for the quality control analysis of CRFs and ranging from 0.0001μgg−1 to 30μgg−1. As water and oxygen are the main products of H2O2 with CRFs, final digests are suitable for ICP-based techniques analysis due to its low acidity and consequent reduction of physical interferences on nebulization devices. Finally, according to the Analytical Eco-Scale, the proposed method was considered an excellent green analysis with final score of 85.