HPLC-hyphenated techniques

LC separation is to bring about the physical separation of sample constituents; however, as the sample complexity increases this becomes more difficult. Hyphenation and the application of selective detection, for example, can estab- lish the separation of species according to information, but not necessarily in a physical sense. A DAD may be tuned to a particular wavelength such that the desired species are visible but the undesired species are not, or an MS can be tuned to respond to a particular mass ion. So, if the phy- sical collection of sample constituents is a requirement of the separation process, attention must be paid to the chromatography. Furthermore, some hyphenated methods of analysis are best served when good chromatography is applied, such as LC-NMR methods, whereby the interpre- tation of the NMR information is made easier as the purity of the sample constituent is improved.