Liquid chromatography/mass spectrometry detectors with

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). ... 

Liquid chromatography/mass spectrometry analyses were performed with an ion trap mass spectrometer (LCQ, Thermo Fisher Scientific Inc., MA) equipped with an HPLC system (Agilent, CA Model 1100) connected with a diode-array detector (DAD, G1315A). The sample solution (1-5 p,L) was applied on an Inertsil ODS-3 column (2.1 x 150 mm, 3 p,m, GL... 

Liquid chromatography mass spectrometry (LC-MS) is now routinely used in analytical laboratories. Traditional IPRs are non-volatile salts that are not compatible with MS techniques because they play a major role in source pollution that is responsible for reduced signals. Moreover the final number of charged ions that reach the detector is impaired by ion-pair formation actually IPRs added to the mobile phase to improve analytes retention exert a profound effect on analyte ionization. Chromatographers who perform IPC-MS must optimize the eluent composition based on both chromatographic separation and compatibility with online detection requirements. 

The most commonly used analytical technique for sugars is HPLC with a refractive index detector (RID). Although the HPLC-RID method is simple, the RID lacks sensitivity and selectivity. Therefore, UV and fluorescence detection is frequently used, coupled with pre- or postcolumn derivatization, for analysis with higher sensitivity. Liquid chromatography-mass spectrometry (LC-MS) using electrospray ionization also requires pre- or postcolumn derivatization. LC-MS using atmospheric pressure chemical ionization does... 

Figure 5 Reversed phase HPLC (linear gradient of 10-90% isopropanol in acetonitrile at 25°C) of natural (top) and rearranged (bottom) butterfat triacylglycerols as obtained with light-scattering detector. Peak identification by carbon and double bond number. (Reproduced with permission from Marai L, Kuksis A, and Myher JJ (1994) Reversed-phase liquid chromatography-mass spectrometry of the uncommon triacylglycerol structures generated by randomization of butteroil. Journal of Chromatography A 672 87-99.)...

When two compounds with very close, or even superimposable, retention times and identical UV spectra are found in a chromatogram, more sophisticated detectors that can yield much more structural information are required. Liquid chromatography-diode array detection (LC-DAD) is still the main technique used for phenolics quantification, a parameter not usually determined by other techniques, such as liquid chromatography-mass spectrometry (LC-MS), given its poor sensibility. 

Initially, simple methods such as ultraviolet-visible (UV-Vis), fluorescence or infrared (IR) spectroscopy were proposed in order to estimate the total amount of antioxidants in various food samples. However, coupled methods such as gas chromatography-mass spectrometry (GC-MS), high performance liquid chromatography with ultraviolet-visible (HPLC-UV-Vis) or nuclear magnetic resonance detector (HPLC-NMR) and liquid chromatography-mass spectrometry (LC-MS) are employed more to quantify individual tocols or carotens from various corn-based food samples. In this chapter all these methods of analysis will be briefly described. 

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