Evaluation of GC-APCI/MS and GC-FID as a complementary platform

With a development of the metabolomics field, complementary cross-platform approaches started to attract attention, as none of the contemporary analytical methods had the capacity to cover the entire space of the human metabolome. In the current manuscript, we have evaluated an online coupling of gas chromatography (GC)-mass spectrometry (MS) and flame ionization detector (FID) as ways of cross-detector analysis. The possible value of this combination was recognized from the very first days of GC-MS history but was never explored in detail. We have compared the basic analytical parameters of both detectors, such as limit of detection (LOD) and limit of quantification, with intra- and interday reproducibility. We show that for the majority of the tested compounds, MS detector demonstrates lower LOD. At the same time, FID appeared to be more robust, showing lower relative standard deviations (RSDs) for intra- and interday reproducibility. We conclude that the gain of this dual detector acquisition appears to be most evident for complex biological samples, where wide dynamic range and predictable response of FID are useful for an initial quantitative overview of sample composition and estimation of molar proportions of different metabolites. MS provides reliable, structural information and superior, at least in the case of atmospheric pressure chemical ionization, sensitivity. Taken together, both detectors represent a flexible tool for explorative studies and if supported by a powerful data-processing algorithm, would appear to be useful in any metabolic profiling study.