Liquid chromatography/mass sample preparation method

The need to understand the fate of pesticides in the environment has necessitated the development of analytical methods for the determination of residues in environmental media. Adoption of methods utilizing instrumentation such as gas chro-matography/mass spectrometry (GC/MS), liquid chromatography/mass spectrometry (LC/MS), liquid chromatography/tandem mass spectrometry (LC/MS/MS), or enzyme-linked immunosorbent assay (ELISA) has allowed the detection of minute amounts of pesticides and their degradation products in environmental samples. Sample preparation techniques such as solid-phase extraction (SPE), accelerated solvent extraction (ASE), or solid-phase microextraction (SPME) have also been important in the development of more reliable and sensitive analytical methods. 

In this review we have summarized the results obtained by different chromatographic techniques and a variety of sample preparation methods for the analysis of antioxidants in polymers and in solutions. Efficient techniques including liquid and gas chromatography, mass spectrometry, traditional low pressure extraction techniques and newer high pressure techniques have been developed. These have made possible the accurate quantification and identification of antioxidants. The newer techniques offer versatile tools for further developments in this area of polymer analysis. 

Cross-validation is conducted when two validated bioanalytical methods are used within the same study or submission, for example, ELISA assay to Biacore and ELISA to a liquid chromatography/mass spectrometry. It is recommended that test samples (spiked and/or pooled incurred samples) be used to cross-validate the bioanalytical methods. Data should be evaluated using an appropriate predefined acceptance criteria or statistical method [12,13]. It should be cautioned that many times the methods that are being cross-validated may not have the same range of quantification. In these situations, it is necessary to prepare spiked samples within the range that are common to both methods for comparison. 

Abdel-Rehim, M. Hassan, Z. Skansen, P. Hassan, M. Simultaneous determination of busulphan in plasma samples by liquid chromatography-electrospray ionization mass spectrometry utilizing microextraction in packed syringe (MEPS) as on-line sample preparation method. J. Liq. Chromatogr. Relat. Technol. 2007, 30, 3029-3041. 

Fig. 9.2 Relative concentrations of P450 in human liver microsomes. a P450s in 60 liver samples were estimated using immunochemical methods (electrophoresis/immunoblot-ting) [52]. Because of cross-reactivity, the individual P450s in subfamilies are not distinguished. The unknown fraction is the difference between the sum of the immunochemi-cally determined forms and the total amount, calculated from Fe -CO versus Fe " difference spectroscopy [53]. b-d Estimates were made using liquid chromatography-mass spectrometry (LC-MS) proteomic analysis with heavy-atom peptides, b Results of an analysis of 50 pooled human liver samples (XenoTech, HLM610 preparation) [54]. c Results reported in the same reference as Part 5 [54] as means from analysis often individual human samples, d Analysis of a pooled set of 23 human liver samples by another laboratory [55]...

Bu H-Z, Poglod M, Micetich RG, Khan JK. Novel sample preparation method facilitating identification of urinary drug metabohtes by liquid chromatography-tandem mass spectrometry. J Chromatogr B 2000 738 259-265. 

Traditional analytical methods to analyze amphetamines include gas chromatography-mass spectrometry where derivatization is often required to fecilitate analysis. Besides sample preparation issues, it has been demonstrated that injection port chemistry in the GC can lead to misleading results with some members of the amphetamine class. To circumvent these issues, liquid chromatography-mass spectrometry (LC-MS/ MS) offers the promise of a simpler sample preparation procedure and fewer analytical concerns. This chapter describes an LC-MS/MS technique for the analysis of 14 ATSs in blood, serum/plasma, and urine. The method is quantitative and has reporting limits in the low ng/mL range. Electrospray ionization is used in the positive ion mode. Two transitions for each compound are monitored along with ion ratios. 

Supercritical Fluid Chromatography (SFQ and Supercritical Fluid Extraction (SFE) A separation technology similar to other extraction and chromatographic methods, but in which the mobile phase is actually a fluid in its supercritical fluid state. A supercritical fluid is a fluid that is held above its critical temperature and pressure, and for which no application of additioncJ pressure can result in the development of a liquid phase. Supercritical fluids are unique in that while they possess liquid-like densities, the mass transfer behavior is superior to that of liquids. Supercritical fluid chromatography remains a niche method that is applicable to pharmaceuticals and other high relative molecular mass solutes. Supercritical extraction, on the other hand, is more widely used as a sample preparation method, especially in pharmaceutical analyses, polymers, and environmental analyses. 

Specifically for triazines in water, multi-residue methods incorporating SPE and LC/MS/MS will soon be available that are capable of measuring numerous parent compounds and all their relevant degradates (including the hydroxytriazines) in one analysis. Continued increases in liquid chromatography/atmospheric pressure ionization tandem mass spectrometry (LC/API-MS/MS) sensitivity will lead to methods requiring no aqueous sample preparation at all, and portions of water samples will be injected directly into the LC column. The use of SPE and GC or LC coupled with MS and MS/MS systems will also be applied routinely to the analysis of more complex sample matrices such as soil and crop and animal tissues. However, the analyte(s) must first be removed from the sample matrix, and additional research is needed to develop more efficient extraction procedures. Increased selectivity during extraction also simplifies the sample purification requirements prior to injection. Certainly, miniaturization of all aspects of the analysis (sample extraction, purification, and instrumentation) will continue, and some of this may involve SEE, subcritical and microwave extraction, sonication, others or even combinations of these techniques for the initial isolation of the analyte(s) from the bulk of the sample matrix. 

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