GC-MS determination of organic acids with solvent extraction after cation-exchange chromatography

We combined column and partition chromatography to isolate, purify, and quantify biological organic acids in urine and cerebrospinal fluid (CSF). Urine and CSF samples were introduced onto a preconditioned cation-exchange column (Dowex 50 W x 8 resin) to remove the biological interferences. The effluent with water was extracted with ethyl acetate two times (pH 1 and 3) and the organic acids were quantitatively converted into their trimethylsilyl derivatives for detection by gas chromatography-mass spectrometry. The good quality-control data were obtained through precision and accuracy tests. Inter- and intraassay CVs were 0.01-10.2% and 0.02-12.2%, respectively. Analytical recoveries compared favorably with results from the commonly used solvent extraction method. This method was used for the measurement of the 14 organic acids in the urine and CSF of healthy volunteers. The values obtained were in the range of the published data.