Liquid chromatography tandem mass process

Ethylenethiourea (ETU) is a toxic decomposition product/metabolite of alky-lenebis(dithiocarbamates). This compound could be generated during processing of treated crops at elevated temperature. Different chromatographic methods to determine the residue levels of ETU have been published. After extraction with methanol, clean-up on a Gas-Chrom S/alumina column and derivatization (alkylation) with bro-mobutane, ETU residues can be determined by GC with a flame photometric detector in the sulfur mode. Alternatively, ETU residues can also be determined by an HPLC method with UV detection at 240 nm or by liquid chromatography/mass spectrometry (LC/MS) or liquid chromatography/tandem mass spectrometry (LC/MS/MS) (molecular ion m/z 103). ... 

Tiller, PR. Romanyshyn, L.A. Liquid Chromatography/Tandem Mass Spectrometric Quantification with Metabolite Screening as a Strategy to Enhance the Early Drug Discovery Process, Rapid Commun. Mass Spectrom. 16(12), 1225-1231 (2002). 

Tiller PR and Romanyshyn LA (2002) Liquid chromatography/tandem mass spectrometric quantification with metabolite screening as a strategy to enhance the early drug discovery process. Rapid Commun Mass Spectrom 16 1225-1231. 

Mottier P, Hure I, Gremaud E, Guy P, Analysis of four 5-nitroimidazoles and their corresponding hydroxylated metabolites in egg, processed egg, and chicken meat by isotope dilution liquid chromatography tandem mass spectrometry, J. Agric. Food Chem. 2006 54 2018-2026. 

Sample Preparation Normally, biological samples are not directly compatible with LC-MS/MS analysis, and they need to be processed before delivery to the LC-MS system. Effective sample preparation procedures can clean up the sample and concentrate the analytes of interest. Conventional sample preparation is often the most labor-intensive and time-consuming step in a liquid chromatography-tandem mass spectrometry (LC-MS/MS) analytical method. Introduction of automated 96-well extraction techniques, and advances in sample preparation techniques, have greatly improved the efficiency of sample preparation. 

The solvent used for reconstitution is often the same as the mobile phase used in the liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis. Either Teflon seals (mats) or aluminum foil has been used to cover plates to prevent evaporation of solvent prior to injection of sample. A schematic of the entire sample preparation process is summarized in Figure 13.7. 

One attempt to overcome these disadvantages has been to use multidimensional liquid chromatography (LC) followed directly by tandem mass spectrometry to separate, fragment and identify proteins (Link et al., 1999). In this process, a denatured and reduced protein mixture is digested with a protease to create a collection of peptides (Fig. 2.6). The peptide mixture is applied to a cation exchange column and a fraction of these peptides are eluted based on charge onto a reverse-phase column. The... 

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