Liquid chromatography-mass systems

LC/MS/MS. LC/MS/MS is used for separation and quantitation of the metabolites. Using multiple reaction monitoring (MRM) in the negative ion electrospray ionization (ESI) mode, LC/MS/MS gives superior specificity and sensitivity to conventional liquid chromatography/mass spectrometry (LC/MS) techniques. The improved specificity eliminates interferences typically found in LC/MS or liquid chro-matography/ultraviolet (LC/UV) analyses. Data acquisition is accomplished with a data system that provides complete instmment control of the mass spectrometer. 

Liquid chromatography/mass spectrometry (LC/MS) analysis Quantitation system Agilent Series 1100 liquid chromatograph Chromsep Omnispher 3 Cig HPLC column, 100 x 4.6-mm i.d., 3- am diameter particle size... 

Nagele, E., Vollmer, M., Horth, P. (2003). Two-dimensional nano-liquid chromatography— mass spectrometry system for applications in proteomics. J. Chromatogr. A1009,197-205. 

Masuda, J., Maynard, D.M., Nishimura, M., Ueda, T., Kowalak, J.A., Markey, S.P. (2005). Fully automated micro- and nanoscale one- or two-dimensional high-performance liquid chromatography system for liquid chromatography-mass spectrometry compatible with nonvolatile salts for ion exchange chromatography. J. Chromatogr. A 1063, 57-69. 

Jandera, P., Holcapek, M., Theodoridis, G. (1998). Investigation of chromatographic behavior of alcohol ethoxylate surfactants in normal-phase and reversed-phase systems using high-performance liquid chromatography-mass spectrometry. J. Chromatogr. A 813(2), 299-311. 

Chromatographic methods are also often used as part of systems that are called hyphenated methods, (see Chapter 15) where the output of the chromatographic section is used as the input for an identification method such as mass spectrometry. These hyphenated methods are also most often referred to by their acronyms, for example, GC-MS—gas chromatography-mass spectrometry and HPLC-MS—high-performance liquid chromatography-mass spectrometry. Note that although ultraviolet-visible (UV-Vis) is hyphenated, it is not a hyphenated method in that it does not consist of two different methods of analysis. Hyphenated methods will be discussed fully in Chapter 15. 

Based on a new technology, particle beam enhanced liquid chromatography-mass spectrometry expands a chemist s ability to analyse a vast variety of substances. Electron impact spectra from the system are reproducible and can be searched against standard or custom libraries for positive compound identification. Chemical ionization spectra can also be produced. Simplicity is a key feature. A simple adjustment to the particle beam interface is all it takes. 

The different ways a particle beam liquid chromatography mass spectrometer can be configured reflect the versatility of the system in accommodating both the application and the availability of existing instrumentation. The system consists of these elements ... 

While the alkyl chain distribution is determined on a non-polar RP8 and RP18, EO homologue distribution is determined using a polar phase. AEOs are not UV-absorbing species, so they cannot be directly determined by HPLC followed by standard optical detection systems (UV and FL), unless suitable derivatives are prepared [2], Because of this, methods based on liquid chromatography-mass spectrometry [77-79] are currently considered as the benchmark procedure that gives sufficiently high selectivity and sensitivity. 

Many of the more established techniques have been validated through collaborative studies which becomes of greater importance as laboratories seek to become accredited via ISO, EN or related systems where the use of official or well validated methods is mandatory. New instrumental techniques are constantly being reported in the literature but it often requires many years before procedures are introduced, validated and then applied within the food industry. Recent techniques that can be included in this category are capillary electrophoresis and liquid chromatography-mass spectrometry (LC-MS). In time procedures based on these techniques will also become accepted as routine methods and are likely to be adopted by some of the official international bodies like the AOAC International, CEN, ISO, etc. 

Jenkins et al. developed a capillary electrophoresis system for the measurement of iohexol as a marker of the glomerular filtration rate (GFR) with a run time of 5.25 min and a coefficient of variation (CV) of 4.3% at 80 mg L" [121]. The GFR, calculated from the plasma clearance, had a reproducibility of 5.47 %. A similar approach (liquid chromatography-mass spectrometry with positive electrospray ionization after enrichment by solid phase extraction) was applied by Putschew et al. for the determination of iodinated contrast agents in treatment plant effluents and surface waters [118]. 

Dohta, Y, Yamashita, T, Horiike, S., Nakamura, T. and Kukami, T. (2007) A system for logD screening of 96-weIl plates using a water-plug aspiration/ injection method combined with high-performance liquid chromatography-mass spectrometry. Analytical Chemistry, 79, 8312-8315. 

Davis, M. T., Stahl, D. C., and Lee, T. D., Low-flow high-performance liquid-chromatography solvent delivery system designed for tandem capillary liquid-chromatography mass-spectrometry. Journal of the American Society for Mass Spectrometry 6(7), 571-577, 1995. 

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... 

The system relies upon preliminary fractionation of the microbial crude extract by dualmode countercurrent chromatography coupled with photodiode array detection (PDA). The ultraviolet-visible (UV-Vis) spectra and liquid chromatography-mass spectrometry (LC-MS) of biologically active peaks are used for identification. Confirmation of compound identity is accomplished by nuclear magnetic resonance (NMR). Use of an integrated system countercurrent chromatography (CCC) separation, PDA detection, and LC-MS rapidly provided profiles and structural information extremely useful for metabolite identification (dereplication, Figure 14.1). 

Figure A.3A.2 Selection of chromatography-mass spectrometry system for the analysis of a sample. Abbreviations APCI, atmospheric pressure chemical ionization CF, continuous flow Cl, chemical ionization El, electron impact FAB, fast atom bombardment GC/MS, gas chromatogra-phy/mass spectrometry LC/MS, liquid chromatography/mass spectrometry.

Duffin, K. L., Wachs, T., and Henion, J. D. (1992). Atmospheric pressure ion-sampling system for liquid chromatography/mass spectrometry analyses on a benchtop mass spectrometer. Anal. Chem. 64 61-68. 

Gu, M., Wang, Y., Zhao, X. G., and Gu, Z. M. (2006). Accurate mass filtering of ion chromatograms for metabolite identification using a unit mass resolution liquid chromatography/ mass spectrometry system. Rapid Commun. Mass Spectrom. 20 764-770. 

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