Comparison of orthogonal liquid and gas chromatography-mass spectrometry platforms for the determination of amino acid concentrations in human plasma.

Concentrations of amino acids in a human plasma pool were determined using four independent quantification methods. Orthogonal separation schemes (LC, GC, or GC x GC) and detection systems (triple quadrupole or time-of-flight mass spectrometry) are shown to demonstrate excellent consistency among platforms for quantifying 18 amino acids in NIST Standard Reference Material (SRM) 1950 Metabolites in Human Plasma using a well-characterized isotope dilution (ID) quantification method. Measured levels were consistent with reference values in plasma from the literature. Individual amino acid concentrations in plasma varied by over an order of magnitude ranging from 1.83 microg/g to 28.0 microg/g (7.78 micromol/L to 321 micromol/L). Average variability (coefficient of variation) between experimental amino acid concentrations (excluding cysteine) among all methods was 6.3%. Certified mass fraction values for amino acids in NIST SRM 1950 will be established from statistically weighted means of all experimental results.