Liquid chromatography LC/MS

An EPA method was created for measuring NDMA and six additional nitrosamines in drinking water (EPA Method 521) [55]. This method uses GC/ chemical ionization (CI)-MS/MS and enables the measurement of NDMA and six other nitrosamines (N-nitrosomethylethylamine, N-nitrosodiethylamine, N-nitroso-di-n-propylamine, N-nitroso-di- -butylamine, N-nitrosopyrrolidine, and N-nitrosopiperidine) in drinking water at detection limits ranging fi om 1.2 to 2.1 ng/L. A liquid chromatography (LC)/MS/MS method [56] can also be used to measure nine nitrosamines, including N-nitrosodiphenylamine, which is thermally unstable and cannot be measured using the EPA Method. 

Several new brevetoxin derivatives have been isolated and identified in K. brevis and natural blooms by solid-phase extraction and liquid chromatography (LC)-MS(MS) techniques <2006MI104>. These analogues are more polar than the previously reported brevetoxin derivatives and are poorly extractable by nonpolar solvents. They are novel derivatives and result from the hydrolysis of the A-ring and/or oxidation of the formyl group of some known derivatives. 

These additives are essentially high boiling point liquids and so the most appropriate technique to use is liquid chromatography (LC-MS). A range of synthetic plasticisers such as phthalates, adipates, mellitates and sebacates can be detected using the atmospheric pressure chemical ionisation (APCl) mode. Process oils are hydrocarbon mineral oils and require either the atmospheric pressure photoionisation (APPl) head (which can ionise nonpolar species) or, where the oil contains sufficient aromatic character, the use of in-line UV or fluorescence detectors. A fluorescence detector is particularly sensitive in the detection of polyaromatic hydrocarbon (PAH) compounds in such oils. 

It is a feature of current developments in mass spectrometry that this method of analysis can be coupled or interfaced with other techniques. The interfacing may in fact be with further MS equipment (MS/MS), or with various separation techniques such as high-performance liquid chromatography (LC/MS), gas chromatography (GC/MS), electrophoresis, particularly high-resolution capillary electrophoresis (CE/ MS), and biomolecular interaction analysis (BIA/MS) (Krone 1997). 

Although MALDI applications for quantitative analysis of biopolymers have been shown recently, most applications involve qualitative studies [21—23]. Limitations in the quantitative addition of matrix to analyte and online configurations of MALDI, compared to gas chromatography/MS and liquid chromatography (LC)/MS systems, have kept the primary focus on qualitative applications. 

Electrospray is surely the ionization method most widely employed for the liquid chromatography (LC)-MS coupling (Cappiello, 2007). The possibility of performing ionization at atmospheric pressure [also obtained in the case of atmospheric pressure chemical ionization (APCI) and atmospheric pressure photoionization (APPI), allows the direct analysis of analyte solutions. However, some problems arise from the intrinsically different operative conditions of the two analytical methods. First, there are the high-vacuum conditions that must be present at the mass analyzer level. Second, the mass spectrometers generally exhibit a low tolerance for the nonvolatile mobile-phase components, usually employed in LC conditions to achieve high chromatographic resolution. 

Mass spectrometry (MS) is a powerful method for the identification of very small amounts of organic compounds and there is great interest in combining it with liquid chromatography (LC), MS serves as a sensitive method for the detection and identification of substances separated by LC. The combination of a nass spectrometer and a liquid chromatograph can be realized by either off-line or on-line coupling. 

Capillary column gas chromatography (GC)/mass spectrometry (MS) has also been used to achieve more difficult separations and to perform the structural analysis of molecules, and laboratory automation technologies, including robotics, have become a powerful trend in both analytical chemistry and small molecule synthesis. On the other hand, liquid chromatography (LC)/MS is more suitable for biomedical applications than GC/MS because of the heat sensitivity exhibited by almost all biomolecules. More recent advances in protein studies have resulted from combining various mass spectrometers with a variety of LC methods, and improvements in the sensitivity of nuclear magnetic resonance spectroscopy (NMR) now allow direct connection of this powerful methodology with LC. Finally, the online purification of biomolecules by LC has been achieved with the development of chip electrophoresis (microfluidics). 

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