Sample pre-treatment techniques for use with ICP-MS hyphenated techniques for elemental speciation in biological samples

The biochemical reactions involving trace elements depend on the nature and form of their chemical species in a biological system. Consequently, the study of the chemical speciation of a given element in biological samples has become essential for understanding their bioavailability and toxicity. Inductively coupled plasma-mass spectrometry (ICP-MS) hyphenated techniques are the most powerful and widely used for elemental speciation combining both high sensitivity and good selectivity for the determination of ultra-trace elements in biological samples. However, direct analysis of biological samples can suffer from matrix interferences, and both the low concentrations of chemical species, and in some cases, the limited amount of sample available can present analytical challenges. Therefore, there is a need to develop sample pre-treatment methods that can be used to remove the matrix and pre-concentrate the species of interest prior to analysis. This review will focus specifically on the state-of-the-art sample pretreatment methods published in the last ten years including liquid and solid phase micro-extraction, and chip-based manifolds that can be coupled to ICP-MS hyphenated techniques. The different methods are evaluated for their ability to be deployed for the pre-treatment of actual biological samples. The development trends in this area of research are discussed, and integrated automated miniaturized systems are also reviewed.