Liquid chromatography/mass spectrometry chromatograms

Figure 5.67 Reconstructed ion chromatograms for Idoxifene and internal standard (ds-Idoxifene using LC-ToF-MS for (a) double-blank human plasma extract, (b) extract of blank human plasma containing internal standard (IS), and (c) control-blank human plasma spiked with Idoxifene at 5 gml , the LOQ of the method. Reprinted from 7. Chromatogr., B, 757, Comparison between liquid chromatography-time-of-flight mass spectrometry and selected-reaction monitoring liquid chromatography-mass spectrometry for quantitative determination of Idoxifene in human plasma , Zhang, H. and Henion, J., 151-159, Copyright (2001), with permission from Elsevier Science.

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. 

As an example, consider a chromatogram in which a number of compounds are detected with different elution times, at the same time as a their spectra (such as UV or mass spectra) are recorded. Coupled chromatography, such as high-performance chromatography-diode array detection (HPLC-DAD) or liquid chromatography-mass spectrometry (LC-MS), is increasingly common in modern laboratories, and represents a rich source of multivariate data. These data can be represented as a matrix as in Figure 4.3. 

Figure 3 SPE-LC-APCI-MS chromatogram of 200 ml tap water spiked with 0.04 ng ml of pesticides and 0.05 ng ml IS tert-butylazine in positive-ion mode and dinoterb in negative-ion mode). Peak identification 1, bentazone 2, Vamidothion 3,4-nitrophenol 4, MCPA 5, mecoprop 6, dinoseb 7, atrazine 8, isoproturon 9, ametryn 10, malathion 11, fenotrothion 12, molinate 13, prometryn 14, terbutryn and 15, parathion-ethyl. (Reprinted with permission from Aguilar C, Ferrer I, Bormll F, Marce RM, and Barcelo D (1998) Comparison of automated on-line solid-phase extraction followed by liquid chromatography-mass spectrometry with atmospheric-pressure chemical ionization and particle-beam mass spectrometry for the determination of a priority group of pesticides in environmental waters. Journal of Chromatography A 794 147-163 Elsevier.)...

Figure 9.4 High-pressure liquid chromatography separation of 50 pg of a natural phosphatidylcholine mixture from egg yolk. The reconstructed ion chromatograms of diglyceride ions were selected from data acquired by full mass scanning from 120 amu to 820 amu. The relative intensity is shown based on the peak height. Column 3 pm Ultrasphere-ODS (4.6 mm x 7.5 cm). Mobile phase MeOH/hexane/0.1 m NH4OAC (71 5 7), 1 mlmin . Reprinted with permission from Kim, H. Y. and Salem, N. Jr, Phospholipid molecular species analysis by thermospray liquid chromatography/mass spectrometry. Anal. Chem., 58 (1), 9-14, 1986.

Figure 9.7 Ion chromatograms of 22 6n3 containing phospholipids obtained after incubation of C-6 glioma cells with 100 iu 22 6n3 for 24 h. Reprinted with permission from Kim, H. Y., Wang, T, C. L. and Ma, Y. C., Liquid chromatography/mass spectrometry of phospholipids using electrospray ionization. Anal. Chem., 66 (22), 3977-82, 1994.

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. 

Different liquid chromatography modes in polymer analysis were successfully interfaced with electrospray ionisation time-of-flight mass spectrometry in a single experimental set-up the mass spectrometry data from size exclusion chromatography/mass spectrometry of PMMA were used as absolute calibration points in the size exclusion chromatography/refractive index chromatogram, and monomer mass and end groups were inferred from the isotopically resolved mass spectra. 44 refs. 

Either gas chromatography (GC) or liquid chromatography (LC) can be used as a separation technique coupled with a variety of detection methods. Mass spectrometry (MS) is one of the most popular means of detection. When using GC-MS, a capillary column should be used, while any suitable LC column can be used for LC-MS. It is advisable to obtain a print-out of the chromatogram so that the shapes of individual peaks can be assessed. Electronically produced data using integrators should be treated with some suspicion and always examined visually to check the selected baseline, start- and end-points of peak integration, etc. 

Zissis, K.D., Dunkerley, S., and Brereton, R.G. 1999. Chemometric techniques for exploring complex chromatograms Application of diode array detection high performance liquid chromatography electrospray ionization mass spectrometry to chlorophyll a allomers. Analyst 124 971-979. 

Figure 13.13 On-line trace enrichment-RPLC-diode-array detection (DAD) chromatogram (at 230 nm) obtained from 200 ml of tap water spiked with various pesticides at levels of 1 jxg L1. Reprinted from Chromatographia, 43, C. Aguilar et al., Determination of pesticides by on-line trace enrichment-reversed-phase liquid chromatography-diode-array detection and confirmation by particle-beam mass spectrometry , pp. 592-598,1996, with permission from Vieweg Publishing.

Figure 13.14 LC-diode-array detection (DAD) chromatogram (at 220 nm) obtained after preconcentration of 50 ml of ground water sample spiked with various pollutants at levels of 3 p.g l-1 passed through (a) a PLRP-S cartridge and (b) an anti-isoproturon cartridge. Peak identification is as follows 1, chlortoluron 2, isoproturon plus diuron 3, linuron 4, diben-zuron , water matrix. Reprinted from Journal of Chromatography, A 777, I. Ferrer et al. Automated sample preparation with extraction columns by means of anti-isoproturon immunosorbents for the determination of phenylurea herbicides in water followed by liquid chromatography diode array detection and liquid chromatography-atmospheric pressure chemical ionization mass spectrometry , pp. 91-98, copyright 1997, with permission from Elsevier Science.

Figure 7 Liquid chromatography inductively coupled plasma mass spectrometry (LC-ICP-MS) chromatogram of a standard mixture of organolead and inorganic lead compounds (Pb2+, TML, and TEL) using reversed-phase HPLC. Mobile phase, 0.1 M ammonium acetate, and 0.1 M acetic acid at pH 4.6, 30% ethanol. Flow rate 1 mL/min. (From Ref. 26.)...

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