Quantitative determination and confirmatory analysis of N-acetylneuraminic and N-glycolylneuraminic acids in serum and urine by solid-phase extraction on-line coupled to liquid chromatography-tandem mass spectrometry

N-acetylneuraminic acid (Neu5Ac) and N-acetylglycolylneuraminic acid (Neu5Gc), two acylated derivatives of 9-C carboxylated monosaccharides, are involved in a number of biological processes as modulators of glycoconjugates. A partially automated method is here presented for determination of these sialic acids in the two most important biofluids for clinical analysis: serum and urine. For this purpose, a solid-phase extraction (SPE) workstation was on-line connected to an LC-MS/MS triple quadrupole mass detector. Hydrolysis to release sialic acids bound to glycoconjugates and derivatization were the two steps implemented as sample preparation prior to SPE-LC-MS/MS analysis. Following thorough optimization of the SPE and LC-MS/MS conditions, the analytical method was validated using the standard addition approach to assess the presence of matrix effects. The proposed method affords detection limits of 0.03 ng/mL and 0.04 ng/mL for Neu5Ac and Neu5Gc, respectively. The precision (expressed as relative standard deviation) was 1.7 and 4.6% for within-day variability, and 4.8 and 7.2% for between-days variability. Accuracy, estimated using spiked (between 1 and 50 ng/mL) and non-spiked samples of both biofluids, ranged from 95.2 to 99.6%. The method was applied to human serum and urine of healthy volunteers, thus showing its suitability for application in both clinical and research laboratories.