Quantitative Analysis of Urinary Organic Acids by Gas Chromatography-Mass Spectrometry

Kim, Jeong Uk; Choi, Tae Yeal; Kim, Dae Won; Keum, Dong Geuk; Kim, Jong Won

Abstract

BACKGROUND: Analysis of urinary organic acids is an important procedure for the diagnosis of inherited disorders of amino acid and organic acid metabolism. Analysis of urinary organic acids by gas chromatography-mass spectrometry (GC-MS) were initially developed for qualitative purposes, and quantitative anlytical procedure have seldom been extensively studied if at all. The purpose of this study is to evaluate a quantitative procedure for profiling organic acids with GC-MS.
METHODS
Urine samples (1.5 mL) were extracted with ethylacetate, and derivated to trimethylsilyl derivatives. The compounds were analysed with MD-800 GC-MS (Fisons, Manchester, U.K.). The quantitation was done by establishment of calibration curves with the standard solutions of 74 organic acids. A response factor for internal standard was used to quantify organic acids of which the standards were not available. Extraction efficiencies for 51 organic acids were evaluated. Interassay and intraassay imprecisions were estimated from the analysis of two quality control specimens with the different concentrations of organic acids.
RESULTS
Extraction efficiencies varied from 7.9 0.2% to 182.7 4.8% according to organic acids. Interassay imprecisions of specimen I and II were 4.1~60.7% and 10.7~84.9%, respectively. Intraassay imprecisions were 1.7~24.3% and 2.8~38.1%, respectively. But interassay imprecisions for clinically important analytes were below 20%.
CONCLUSIONS
The described method for quantification of urinary organic acids with GC-MS is a acceptable routine method for screening of urinary organic acids. The result that imprecisions of clinically significant organic acids were less than 20% suggests that the method would be acceptable not only for diagnosis, but also for follow-up.