Criteria for the Determination of Analytes by Selected Techniques

It is always worth trying another solvent to check if you can get any discrimination or separation. 

Either gas chromatography (GC) or liquid chromatography (LC) can be used as a separation technique coupled with a variety of detection methods. Mass spectrometry (MS) is one of the most popular means of detection. When using GC-MS, a capillary column should be used, while any suitable LC column can be used for LC-MS. It is advisable to obtain a print-out of the chromatogram so that the shapes of individual peaks can be assessed. Electronically produced data using integrators should be treated with some suspicion and always examined visually to check the selected baseline, start- and end-points of peak integration, etc. 

Chromatographic conditions should be optimized wherever possible to achieve baseline separation of the analyte peak from other peaks produced by co-extracted compounds. The retention time of the analyte should be at least twice the column 

The MS detection system can be such that the full mass spectrum is observed (at least five peaks) or just selected ions monitored (SIM) with three or four identification points. For some analyses, it may be necessary to use MS-MS techniques [8]. In LC-MS, it is important to make sure that ionization of the compounds of interest has been achieved. For all of these approaches, the criteria for matching of the analyte with the standard should be established during validation studies. 

Gas chromatography can also be used with other detection systems, e.g. electron-capture detection (GC-ECD) and flame-ionization detection (GC-FID). The optimization will have been carried out during validation studies. The peak separation criterion is the same as that given for LC above. Once again, cochromatography can be used for confirmation. 

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