Potential sources of error in capillary electrophoresis–inductively coupled plasma mass spectrometry for chemical speciation†

Abstract

The distribution concentration of chemical species in a sample is dictated by the physical and chemical properties of the matrix. As such, when a sample is pre-treated, in any way, there is a potential for redistribution of homologous species. The extent of this analyte redistribution is determined by both thermodynamic properties of species (e.g., changes in concentrations of species according to their equilibrium expressions) and kinetic properties (e.g., the rate of the reactions compared with the duration of sample preparation and analysis). The redistributions of analyte species as a function of several experimental parameters (e.g., time, solution pH, injection methods and calibration methods) are illustrated in this paper. Whereas rabbit metallothionein protein showed a stability of more than a few days under certain storage conditions, coenzyme-B₁₂ was rapidly degraded in less than 2 h. pH studies showed that the migration of free Cd²⁺ ions in rabbit metallothionein was not significantly affected unless the pH of the solution exceeds the solubility limit of the metal hydroxide. However, pH-sensitive compounds such as vitamin B₁₂ showed significant changes in the migration time and analyte composition. The injection studies suggested that electrokinetic injection may produce biased results, in favor of species that have higher electrophoretic mobility. Hydrodynamic injection will produce a result that is more representative of the initial sample composition.