Bioanalytical mass spectrometry as applied to organic acid profiling and steroid reference methodology

Gas chromatography-mass spectrometry (GC-MS) is a versatile and powerful diagnostic tool in clinical chemistry. Instrumental aspects of the technique are considered. The use of GC-MS for identification purposes is exemplified by the metabolic profiling of organic acids for the diagnosis of inborn errors of metabolism. Quantitative GC-MS is discussed with particular emphasis on the choice of the internal standard. For highest precision and accuracy, isotope dilution GC-MS is the most suitable technique; the application of ID-GC-MS to reference methods and reference materials is discussed in relation to the analysis of steroid hormones. The principles involved in devising calibration procedures and measurement protocols in quantitative GC-MS are outlined.