Biological sulphur-containing compounds – Analytical challenges

This review covers analytical methods applied to the determination of none volatile sulphur-containing biological compounds. The classes of S-compounds include amino acids, proteins, lipids, carbohydrates and sulphur-containing metabolites. Techniques covered include element specific detectors as well as molecular specific detectors from X-ray absorption near-edge structure (XANES) to elemental and molecular mass spectrometers. The major techniques used are inductively coupled plasma mass spectrometry (ICP-MS) and high-resolution electrospray mass spectrometry (ESI-MS) in their various forms. Both techniques either individually or combined require the sample to be present in liquid form and therefore involve sample preparation usually extraction and depending on sample and molecular class studied potentially also derivatisation in addition to generally requiring chromatographic separation. Over recent years, detection limits achieved by elemental methods and computational methods to extract signals of sulphur-containing compounds out of the mass of data produced by molecular high-resolution mass spectrometers made significant gains. Still the determination of sulphur-containing compounds is challenging, but nowadays the methods have been developed well enough to allow application to real samples for absolute quantification of biomolecules such as proteins or lipids.