Liquid chromatography combined methods

Gas or liquid chromatography combined with tandem mass spectro-metry are the methods of choice for unequivocal identification at trace levels. 

Liquid chromatography combined with triple-quadrupole mass spectrometers has been used extensively as the analytical method of choice to determine the plasma concentration of compounds. 

Straub et al. (76) reported a method for the identification and quantification of penicillin G, ampicillin, amoxicillin, cephapirin, cloxacillin, and ceftiofur residues in milk using perfusive-particle liquid chromatography combined with ultrasonic nebulization electrospray mass spectrometry. According to this method, a 0.5 ml milk sample is diluted with an equal volume of a solution consisting of acetonitrile/water (1 1), and ultrafiltrated in a microseparation system with a 10000 da molecular mass cut-off filter. An aliquot of the ultrafiltrate is then analyzed on a 15 cm porous II R/H LC (7-8 m) perfusion analytical column using the chromatographic conditions shown in Table 29.3. Concentrations as low as 10 ppb could be readily determined in milk by electrospray mass spectrometric detection. 

LC-NMR. Separations using reverse-phase (RP) liquid chromatography are potentially more powerful because samples can be studied without derivatization. Numerous attempts have been made to separate NOM and while most studies exhibit some degree of separation, to date the complete separation of a NOM sample has not been accomplished. Even only partial separation is possible, and it is worth to hyphenate a separation method with structure information-oriented analytical applications. Liquid chromatography combined with nuclear magnetic resonance and preliminary studies with solid-phase extraction were conducted on NOM isolated from freshwater and soil (Simpson et al., 2004). 

As a new class of materials, ionic liquids require special analytical methods. In the case of imidazolium halides and similar compounds the most common impurities are amines, alkyl halides and of course water. Seddon et al. described a method for the detection of residual amines using the strong UV absorbance of copper tetramine complexes. These complexes are readily formed by the addition of Cu2+ ions [24]. The detection of both amines and alkyl halides is possible by NMR spectroscopy but with limited resolution [25]. By far the most powerful analytical method is liquid chromatography combined with UV detection. This sensitive method allows the detection of traces of amines and halides [26]. Unreacted amines can be also detected by ion chromatography combined with a suppressor module. In this case detection is achieved using a continuous flow conductivity cell since amines are protonated and thus detectable. For traces of other ionic impurities ion chromatography is also the most powerful analytical tool [27]. Finally, residual water can be quantified using Karl Fischer titration or coulometry [28]. 

Adducts with macromolecules, particularly proteins, offer long-lived biological markers of exposure to Chemical Warfare Agent (CWA), possibly up to several months. Gas or liquid chromatography combined with tandem mass spectrometry, are the methods of choice for unequivocal identification of these adducts or metabolites at trace levels. Several... 

Sensitive analytical methods should be used such as liquid chromatography combined with mass spectroscopy, microbore liquid chromatography and capillary electrophoreses. 

A number of suitable immunoassays and radioimmunoassays are available for measuring the major hormones testosterone, estrogen, LH, and FSH. Some of these assays may need adjustments to ensure that the majority of values fall within the optimal part of the measuring range because the ranges differ between laboratory animal species. Given the similarities in the structures of FSH and LH, some assays can be used for both rats and mice if the antisera are suitable (Jarrell et al. 1988). A number of methods have been described that use gas liquid or liquid chromatography combined with mass spectrometry, which can be used to measure several of the steroid hormones. The development of various contraceptives has often been helped by these hormone measurements as biomarkers of efficacy rather than markers of toxicity in animal models. 

Of the many analytical techniques now available to the lipid chemist, mass spectrometry (MS), is probably the one that has experienced the fastest growth in the last two decades. This is due both to the development of new techniques (gas and liquid chromatography combined with MS, soft-ionization MS, field desorption MS, atmospheric pressure MS etc.) and to the refinement of more traditional methods and their successful application to very complex problems, e.g. the elucidation of glycolipid structure, or the study of structures in lipid mixtures. Much progress has been made since the pioneering work of Ryhage and Stenhagen (1963) on fatty acid methyl esters. 

Zhang, Y, Jiao, J., Cai, Z., Zhang, Y, and Ren, Y. 2007. An improved method validation for rapid determination of acrylamide in foods by ultra-performance liquid chromatography combined with tandem mass spectrometry, J. Chromatogr. A 1142 194—198. 

Great advances in elucidating the variability of the lipophilic ceramide portion of the glycosphingolipids have been achieved by introducing new and refined methods of gas-liquid chromatography combined with mass spectrometry. 

Cassidy and Niro [13] have applied high-speed liquid chromatography combined with infrared spectroscopy to the analysis of polyoxyeihylene surfactants and their decomposition products in industrial process waters. Molecular sieve chromatography combined with infrared spectrometry give a selective method for the analysis of trace concentrations of these surfactants. These workers foimd that liquid-solid chromatography and reversed phase chromatography are useful for the characterisation and analysis of free fatty acids. 

We studied conditions for the determination of tiametoxam (TM), the active component of the fungicide Actai a (Syngenta, Switzerland) by the method of thin layer chromatography with use of the Perkin-Elmer liquid chromatograph combined with spectrophotometric detector. The 250 mm-long and 4.6 mm in diameter steel column filled with Silasorb was used. 

Epichlorhydrin (ECH) detection starts with detecting epoxide cycle using hydrochloric acid in combination with sodium chloride the reaction product - 1,3-dichlorhydrin - is extracted in diethyl ether and concentrated by removing the latter. Gas-liquid chromatography with a flame-ionization detector is used to detect glycerin 1,3-dichlorhydrin. The sensitivity of the method is 0.01 mg/dm. ... 

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