Acidified acetonitrile and methanol extractions for quantitative analysis of acylcarnitines in plasma by stable isotope dilution tandem mass spectrometry

We have compared two sample preparation methods for the analysis of plasma acylcarnitines by tandem mass spectrometry. Extraction from liquid plasma using acetonitrile was compared with the widely used methanol extraction from plasma spotted on filter paper. The recovery and reproducibility of the acetonitrile extraction were improved by acidification with 0.3% formic acid. The acidified acetonitrile and methanol extractions have the same limit of detection and upper linearity limit for all acylcarnitine species studied. The correlation coefficients between the two methods were greater than 0.988 and the slopes of the linear regressions ranged from 0.901 to 1.070. The extraction of acylcarnitines by acidified acetonitrile from liquid plasma yielded results comparable to those obtained by methanol extraction from plasma spotted on filter paper.