Mass spectrometers interfaceable currently available

Currently, HPLC/fiuorescence is still the most common technique for the determination of residues of oxime carbamates. With the introduction of ESI and APCI MS interfaces, HPLC/MS analysis for oxime carbamates in various sample matrices has become widespread. However, for a rapid, sensitive, and specific analysis of biological and environmental samples, HPLC/MS/MS is preferred to HPLC/MS and HPLC/fiuorescence. With time, improved and affordable triple-quadrupole mass spectrometers will be available in more analytical laboratories. With stricter regulatory requirements, e.g., highly specific and conclusive methods with lower LOQ, HPLC/MS/MS will be a method of choice for oxime carbamates and their metabolites. 

Different options are available for LC-MS instruments. The vacuum system of a mass spectrometer typically will accept liquid flows in the range of 10-20 p,L min-1. For higher flow-rates it is necessary to modify the vacuum system (TSP interface), to remove the solvent before entry into the ion source (MB interface) or to split the effluent of the column (DLI interface). In the latter case only a small fraction (10-20 iLrnin ) of the total effluent is introduced into the ion source, where the mobile phase provides for chemical ionisation of the sample. The currently available commercial LC-MS systems (Table 7.48) differ widely in characteristics mass spectrometer (QMS, QQQ, QITMS, ToF-MS, B, B-QITMS, QToF-MS), mass range m/z 25000), resolution (up to 5000), mass accuracy (at best <5ppm), scan speed (up to 13000Das-1), interface (usually ESP/ISP and APCI, nanospray, PB, CF-FAB). There is no single LC-MS interface and ionisation mode that is readily suitable for all compounds... 

Over the past few years interfaces have been developed to couple an HPLC to a mass spectrometer. At first sight the mass spectrometer is an ideal HPLC detector, giving both quantitative (total ion current, TIC) and structural information at the same time. There are, however, drawbacks to the two commercially available interfaces ... 

There are numerous ionization methods that allow formation of ions to carry out mass spectrometry however, in this chapter we will only focus on those most common in LC-MS. The challenge in coupling HPLC to mass spectrometry is that the chromatography operates with liquids and under high pressure, while the detector operates under high vacuum. The device between the chromatograph and the mass spectrometer is called the interface. Here, ionization and transition from liquid to gas phase of the compounds occur. The development of the first commercial available interfaces started as early as in the 1970s. Since then numerous interfaces have been introduced. Table 3.6 shows a list of current interfaces and their acronyms. 

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