[18] LC-MS LC-MS or HPLC-MS refers to the coupling of an LC with a mass spectrometer (MS) [Figure 3]. The separated sample emerging from the column can be identified on the basis of its mass spectral data. A switching valve can help make a working combination of the two techniques. kinase inhibitor KPT-330 A typical automated LC-MS system consists of double three-way diverter in-line with an autosampler, an LC system, and the mass spectrometer. The diverter generally operates as an automatic switching valve to divert undesired portions of the eluate from the LC system to waste before the sample enters the MS. Figure 3 Schematic of an LC-MS (electrospray ionization interface) system An LC-MS combines the chemical separating power of LC with the ability of an MS to selectively detect and confirm molecular identity.

MS is one of the most sensitive and highly selective methods of molecular analysis, and provides information on the molecular weight as well as the fragmentation pattern of the analyte molecule. The information obtained from MS is invaluable for confirming the identities of the analyte molecules. This qualitative analysis makes it possible to reconstruct an unknown compound from MS data. The ionization techniques used in LC-MS are generally soft ionization techniques that mainly display the molecular ion species with only a few fragment ions. Hence, the information obtained from a single LC-MS run, on the structure of the compound, is rather poor. However, this problem has now been tackled by the introduction of tandem mass spectrometry (MS-MS), which provides fragments through collision-induced dissociation of the molecular ions produced.

[19] The use of LC-MS-MS is increasing rapidly. Hyphenated techniques such as HPLC coupled to UV and mass spectrometry (LC-UV-MS) have proved to be extremely useful in combination with biological screening for a rapid survey of natural products. Nowadays, various types of LC-MS systems incorporating different types of interfaces are available commercially. The interfaces are designed in such a way that they offer adequate nebulization and vaporization of the liquid, ionization of the sample, removal of the excess solvent vapor, and extraction of the ions into the mass analyzer. The two most widely used interfaces, especially in relation to natural product analysis, are electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI).

The latter is considered as ��the chromatographer’s LC-MS interface�� Brefeldin_A because of its high solvent flow rate capability, sensitivity, response linearity, and fields of applicability. With these interfaces, various types of analyzers, e.g., quadrupole, ion trap, or TOF, can be used. Each of these analyzers, however, offers varying degree of mass accuracy and resolution. In the LC-UV-MS mode, thermospray (LC-TSP-MS) and continuous-flow FAB (LC-CF-FAB) interfaces can also be applied.