Enzymatic Digestion for the Determination of Trace Elements in Blood Serum by Inductively Coupled Plasma Mass Spectrometry

Abstract

A non-specific protease enzyme (pronase) was used to demonstrate the potential of enzymatic digestion as an alternative sample preparation method for the determination of trace elements in blood serum by ICP-MS. By measuring the number of peptide bonds in solution, it was found that this digestion led to a 40% reduction in the level of plasma protein in the samples. Based on the data obtained, it appears that the majority of these proteins were broken down into smaller polypeptides. Using this digestion technique, a high degree of instrument stability was achieved during the continuous analysis of blood serum over a 3 h period. Selective enhancement of the selenium signal was observed during these analyses. A charge-exchange mechanism between C ⁺ ions and selenium atoms in the plasma, which leads to the formation of excited Se ⁺ ions, is proposed and is supported by data related to the ionization/excitation energies of the various species involved in this reaction. It was also demonstrated that in order to achieve good accuracy, calibration must be conducted using matrix-matched standards. Finally, the accuracy of the technique is demonstrated by showing excellent agreement between the experimental results and the certified values for Seronorm certified serum reference material.