Rapid amino acid quantitation with pre-column derivatization; ultra-performance reverse phase liquid chromatography and single quadrupole mass spectrometry.

Background: We optimized a quantitative amino acid method with pre-column derivatization, norvaline (nva) internal standard and reverse phase ultra-performance liquid chromatography by replacing the ultraviolet detector with a single quadrupole mass spectrometer (MS).

Method: We used CN isotopically labeled amino acid internal standards and a C18 column with 1.6μm particles to optimize the chromatography and to confirm separation of isobaric compounds (MS).

Reference ranges and biological variation of free and total serum indoxyl- and p-cresyl sulphate measured with a rapid UPLC fluorescence detection method.

Introduction: The uremic toxins indoxyl sulphate (IS) and p-cresyl sulphate (pCS) are absorbed bacterial metabolites of tryptophan and tyrosine respectively and may be predictive of clinical outcome. Long chromatography times, incomplete data on the reference ranges of the free and total fractions and the biological variation limit wider clinical application.

Methods: An UPLC method with fluorescence detection was developed and reference ranges and biological variation were investigated in healthy volunteers.