| Abstract | Liquid chromatography with mass spectrometry (LC-MS) or UV absorbance (LC-UV) detection is used for the analysis of a wide range of compounds. Retention times, along with mass or UV spectra, are essential for identification of analytes in complex samples. Unfortunately, absolute retention times can be highly variable between different laboratories and instruments, and even between days in the same laboratory. This usually requires the analysis of chemical reference standards with each batch of samples to allow a good match of retention times for conclusive identification. This can be particularly important when dealing with isomers, which are often not well distinguished by mass spectra. Development of modern LC-MS methods based on techniques like scheduled selected reaction monitoring also requires the availability of standards to set retention windows. Not every laboratory can stock all standards as analysts may be concerned with the monitoring for hundreds of possible analytes. It would be helpful to have a better way of cataloging retention data so that analytes can be more easily identified through a match of retention times without the use of in-house standards. A better way to report retention data is to use “retention index (RI)” values. In this procedure, a series of homologous reference compounds are co-injected with the analytes. |
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