A novel strategy for medical foods digestion and subsequent elemental determination using inductively coupled plasma optical emission spectrometry

A sample preparation method using only H2O2 in the single reaction chamber system (SRC-H2O2) for medical foods (MFs) digestion and further elemental determination by inductively coupled plasma optical emission spectrometry (ICP OES) was proposed. Digestion of some refractory substances (RS), such as, histidine, linoleic acid, phenylalanine and tryptophan, was also investigated. For the method development important parameters, such as, maximum temperature and pressure of SRC system, volume of H2O2 and sample mass were evaluated. Digestion efficiency was evaluated based on the concentration of residual carbon (RC) of final digests. The optimized method conditions were 1 g of sample, 6 mL of 50% H2O2 and maximum temperature and pressure of 250 degrees C and 160 bar, respectively. The digests obtained using the optimized conditions presented concentration of RC lower than 720 mg L-1. The accuracy of SRC-H2O2 method was evaluated by analysis of reference material (RM) NIST 8435 (whole milk powder) and by comparison between results obtained using the proposed method and those obtained by digestion with concentrated HNO3(SRC-HNO3). Significant differences were not observed comparing the results of SRC-H2O2 with reference values of RM and SRC-HNO3. Limits of detection obtained by the proposed method ranged from 0.01 to 88 mu g g(-1) for all elements determined by ICP OES. SRC-H2O2 method provided digests of individual constituents (sodium caseinate, corn syrup and sunflower oil) of MFs and RS with residual carbon content (RCC) lower than 10% (calculated based on molar and sample masses), except for linoleic acid (RCC of 17%). These same compounds were also digested using SRC-HNO3 method and the RCC values were significantly lower than than those found by SRC-H2O2, except for aromatic amino acids (tryptophan and phenylalanine). The final acidity of digests obtained using SRC-H2O2 was negligible that is convenient for elemental determination using ICP-based techniques and agrees with green analytical chemistry requirements.