Development of a quantitative chemical ionization gas chromatography-mass spectrometry method to detect tuberculostearic acid in body fluids.

We developed a mass spectral method to verify the detection of free tuberculostearic acid (TSA) by frequency-pulsed electron-capture gas chromatography (FPEC-GC) in cerebrospinal fluid (CSF), serum, pericardial fluid, ascites fluid and pleural fluid of patients infected with Mycobacterium tuberculosis. To obtain satisfactory sensitivity and specificity for comparison of the test using mass spectrometry (MS) in the single ion monitor (SIM) mode to the FPEC-GC test, we developed a specific, sensitive, quantitative chemical ionization mass spectrometry capillary gas chromatography (QCIGC-MS) test. The procedure maximized the molecular ion (i.e., made it the base peak) for increased specificity and sensitivity, and instrument parameters for increased sensitivity. The procedure uses a computerized approach, requiring an internal standard (nonadecanoic acid) for precise measurement of the retention time and quantitation of the molecular ion of TSA. Data from this study suggest that QCIGC-MS analysis could be a valuable tool to confirm FPEC-GC identification of TSA in CSF, serum, and in pleural, ascites, and pericardial fluids.