Liquid chromatography ionisation methods

Kasprzyk-Hordern B, Dlnsdale RM, Guwy AJ (2007) Multi-residue method for the determination of basic/neutral pharmaceuticals and illicit dmgs in surface water by solid-phase extraction and ultra performance liquid chromatography-positive electrospray ionisation tandem mass spectrometry. J Chromatogr A 1161 132-145... 

Whilst these methods are informative for the characterisation of synthetic mixtures, the information gained and the nature of these techniques precludes their use in routine quantitative analysis of environmental samples, which requires methods amenable to the direct introduction of aqueous samples and in particular selective and sensitive detection. Conventionally, online separation techniques coupled to mass spectrometric detection are used for this, namely gas (GC) and liquid chromatography (LC). As a technique for agrochemical and environmental analyses, high performance liquid chromatography (HPLC) coupled to atmospheric pressure ionisation-mass spectrometry (API-MS) is extremely attractive, with the ability to analyse relatively polar compounds and provide detection to very low levels. 

MS techniques have met this need in the analysis of involatile, polar surfactants after coupling techniques of liquid chromatographic methods with MS became available. Different types of interfaces for off-line and on-line coupling of liquid chromatography (LC) and MS in the analyses of surfactants had been in use [7,16] while the methods applied at present were performed predominately with soft-ionising atmospheric pressure ionisation (API) interfaces [16-19],... 

Dahlmann, J., Budakowski, W.R. and Luckas, B., Liquid chromatography-electrospray ionisation-mass spectrometry based method for the simultaneous determination of algal and cyanobacterial toxins in phytoplankton from marine waters and lakes followed by tentative structural elucidation of microcystins, /. Chromatogr., 994, 1-2, 45, 2003. 

Ylinen et al. [53] developed an ion-pair extraction procedure employing tetrabutylamonium (TBA) counter ions for determination of PFOA in plasma and urine in combination with gas chromatography (GC) and flame ionisation detection (FID). Later on, Hansen et al. [35] improved the sensitivity of the ion-pair extraction approach using methyl tertiary butyl ether (MTBE) and by the inclusion of a filtration step to remove solids from the extract making it amenable to liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) determination. Ion-pair extraction procedure has been the basis of several procedures for biota [49,54-58] and food samples [50,59,60]. However, this method has shown to have some limitations, such as (1) co-extraction of lipids and other matrix constituents and the absence of a clean-up step to overcome the effects of matrix compounds and (2) the wide variety of recoveries observed, typically ranging. 

Muller, C., Schafer, P., Stortzel, M., Vogt, S., and Weinmann, W. (2002). Ion suppression effects in liquid chromatography-electrospray-ionisation transport-region collision induced dissociation mass spectrometry with different serum extraction methods for systematic toxicological analysis with mass spectra libraries. J. Chromatogr. B Anal. Technol. Biomed. Life Set 773 47—52. 

Singh SS, Shah H, Gupta S et al (2004) Liquid chromatography-electrospray ionisation mass spectrometry method for the determination of escitalopram in human plasma and its application in bioequivalence study. J Chromatogr B Anal Technol Biomed Life Sci 811 209-215... 

Gambert, P., Lallemant, C., Archambault, A., Maume, B. F., and Padieu, P. (1979). Assessment of serum cholesterol by two methods gas liquid chromatography on capillary columns and chemical ionisation mass fragmentography with isotope dilution of 3,4-13C-cholesterol as internal standard. J. Chromatogr. 162, 1-6. 

Jensen, A. G. Ndjoko, K. Wolfender, J. L. Hostettmann, K. Camponovo, E Soldati, F. Liquid chromatography-atmospheric pressure chemical ionisation/mass spectrometry A rapid and selective method for the quantitative determination of ginkgolides and hilohalide in Ginkgo leaf extracts and phytopharmaceuticals. Phytochem. Anal., 2002, 13 31-38. 

Co-authors of these studies have recently published a method for the specific determination of 20 primary aromatic amines in aqueous food simulants by liquid chromatography-electrospray ionisation-tandem mass spectrometry... 

The final determination of the PAHs was performed by capillary gas chromatography using flame ionisation or mass selective detection, or by high-performance liquid chromatography using fluorescence or absorption detection. Each participant had validated its method by performing experiments on recovery, extraction efficiency, procedure blanks and detector linearity. 

Three soft ionisation methods are in use for earbohydrates, fast atom bombardment (FAB), eleetrospray ionisation (ESI) and matrix-assisted laser desorption/ionisation (MALDI). FAB is the oldest and involves directing a high-energy beam of Cs" ions or Xe atoms at the sample dissolved in a nonvolatile solvent such as m-nitrobenzyl alcohol. The atoms sputter the sample and matrix [M + H] or [M + Na]" ions are commonly observed. With an upper limit of M of about 2000, FAB is not that soft, and is usually used for small oligosaccharides it has the further disadvantage that the sample is prepared and then directly introduced into the mass spectrometer, so that it cannot be combined with liquid chromatography. 

The strong points of MALDl include the very low amount of sample necessary for analysis, a few fmol are sufficient. Unlike other ionisation methods, MALDl tolerates moderate concentrations of buffer and salts in the analyte mixture. Sample preparation is relatively easy and the spectra obtained are simple, so that even mixtures can be analysed without the need to separate the components prior to MALDl analysis. However, in contrary to ESI, MALDl cannot be directly coupled to liquid chromatography (LC) or capillary electrophoresis (CE) as it is not a continuous but a batch ionisation method. 

Besides the direct insertion probe, liquid chromatography (LC) has also been interfaced to FAB-MS [27]. This rapid and simple ionisation method is relatively tolerant of variations in sampling and is suitable for a large variety of compounds. 

Current analytical methods for the determination of PAH in environmental samples require the separation of individual compounds, either by thin layer or high performance liquid chromatography with fluorescence detection, or better, by gas chromatography on capillary columns, coupled to a flame ionisation detector or a mass spectrometer. Modern thermostable capillary columns will allow the elution of PAH in the molecular weight range above coronene. Prior isolation of PAH as a compound class by liquid-liquid partition and column chromatography is necessary before most of these techniques can be applied. 

Flury K, Rivier L, Dienes-Nagy A, et al. (2001) Method for confirmation of synthetic corticosteroids in doping urine samples by liquid chromatography-electrospray ionisation mass spectrometry. Journal of Chromatography B. 926 87-95. 

Edkins and co-workers [34] have described a direct capillary GC method to monitor residual methylmethacrylate in polymethylmethacrylate. A short (5 m) crosslinked methyl silicone fused-silica capillary column with flame ionisation detection gave good separation efficiency and parts per million detection limits. Capillary gas-liquid chromatography was superior to packed column analysis (SP 1000) in terms of both analytical utility and ease of use. 

Recent work includes extraction studies of aqueous extractants from acrylate coatings and adhesives using liquid chromatography LC)-mass spectrometry MS)/LC-MS-MS detection methods [21], extractant studies on elastomeric materials using MS techniques [22], and studies on rubbers using LC-atmospheric pressure chemical ionisation MS [23]. 

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