Simultaneous determination of multiple amino acids in plasma in critical illness by high performance liquid chromatography with ultraviolet and fluorescence detection

• A sensitive and reliable method for quantitation of 33 amino acids was developed and validated.
• This method was applied to small plasma volumes from patients with critical illness.
• Simultaneous determination of Arg, Cit, Kyn, Try and Phe which have been linked to pathogenesis of severe malaria and sepsis.

There is increasing recognition that the host response to critical illness includes derangement of multiple amino acid pathways, including amino acids (AAs) central to metabolism and immune, endothelial and neurological function. To characterise concentration changes of these plasma amino acid we report the development and validation of a method for the quantification of AAs in small volumes of plasma (50 μL) using HPLC with simultaneous UV and fluorescence (FL) detection. Protein precipitation and pre-column derivatization with 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate (AQC) is followed by reversed phase HPLC separation. Calibration curves were built with norleucine as an internal standard. Thirty-three (including the 20 proteinogenic) AAs, were selected as standards and their corresponding concentrations in the plasma of healthy human controls and patients with severe falciparum malaria were quantified. This method enables the detection of perturbations in arginine metabolism, aromatic amino acid pathways, methionine transsulfuration and transmethylation pathways and other metabolic pathways.