Atmospheric pressure chemical ionization matrix effects

ESI is more likely to exhibit matrix effects than is atmospheric pressure chemical ionization (APCI), Mei et al. [115, 124] reported that matrix effects could be seen in both APCI and ESI assays. In general, these matrix effects can be detected by using the post-column infusion technique as described above. 

Tesche, F. Pickard, V. Matrix effects during analysis of plasma samples by electrospray and atmospheric pressure chemical ionization mass spectrometry practical approaches to their elimination. Rapid Commun Mass Spectrom 2003, 17, 1950—1957. 

Hou W, Watters JW, McLeod HL (2004) Simple and rapid docetaxel assay in human plasma by protein precipitation and high-performance liquid chromatography-tandem mass spectrometry. Journal of Chromatography B 804 263-267 Schuhmacher J, Zimmer D, Tesche F, Pickard V (2003) Matrix effects during analysis of plasma samples by electrospray and atmospheric pressure chemical ionization mass spectrometry practical approaches to their elimination. Rapid Communications in Mass Spectrometry 17 1950-1957 Shah PW (2001) Guidance for Industry Bioanalytical Method Validation U.S. Department of Health and Human Services, Food and Drug Administration... 

Marchi et al. [64] reported on the utility of various sample cleanup procedures for reducing the matrix effects that are caused by various plasma constituents. They found that the best sample preparation procedure was to use PPT followed by an online SPE system. The authors also stated that with this sample preparation procedure, atmospheric pressure photoionization (APPI) was the least affected by matrix effects, followed by atmospheric pressure chemical ionization (APCI) and then electrospray ionization (ESI). 

The quantitation of small-sized therapeutic proteins or peptides in plasma can be conducted with EC—MS/MS detection of the intact proteins. Electrospray ionization (ESI) is the most widely used ionization technique for quantitative EC—MS/MS analysis of proteins or peptides. There are some occasions where atmospheric pressure chemical ionization (APCI) was used to circumvent matrix effects (Volosov et al., 2001). ESI typically generates multiply-charged protein or peptide ions, depending upon the number of basic charges in the polypeptide backbone. For small proteins, high abundance peaks of multiply... 

Matrix effects can be avoided by using MS. Mass spectrometry is characterized by being highly selective and sensitive and, in addition, it oHers spectral iirformation that permits the imequivocal identification of target compounds. LC/MS with atmospheric pressure chemical ionization (APCl) and electrospray ionization (ESI) interfaces have been applied to monitor pesticides and produce chemical ionization mass spectra with molecular information, depending on set-up conditions. Limits of detection at ng/L and the linear response range over two orders of magnitude have been reported. 

Suppression of ionization efficiency is important when the total ionizing capability of the ionization technique is limited, so that there is a competition for ionization among compounds that are present in the ion source simultaneously. In principle such a saturation effect must be operative for all ionization techniques, but in practice it is most important for electrospray ionization (Section 5.3.6), slightly less important for atmospheric pressure chemical ionization (Section 5.3.4), atmospheric pressure photoionization (Section 5.3.5) and matrix assisted laser desorption ionization (Section 5.2.2) it does not appear to be problematic under commonly used conditions for electron ionization and chemical ionization (Section 5.2.1) or thermospray (Section 5.3.2). Enhancement of ionization efficiency for an analyte by a co-eluting compound is less commonly observed and is, in general, not well understood. 

Other API techniques, such as atmospheric pressure photoionization (APPI) and atmospheric pressure chemical ionization (APCI) have been marginally applied. Although providing advantages over ESI, such as reduced matrix effects, APCI has been rarely applied for PFC analysis. Analytes measured with APCI comprise various ethoxylated PFC [40, 55] and PFOA [56]. However, no investigations with respect to matrix effects were made in these articles. 

The MS ion source which has been almost exclusively used for the ionization of dmgs and metabolites is electrospray (ESI). This source gives better analytical performances, however it suffers the problem of matrix effect, a phenomenon in which the presence of coeluting substances causes suppression or enhancements of the ionization signal of analytes. This is particularly evident with more complex samples, such as wastewater influents and effluents, than with cleaneT samples, such as river or lake water samples. The atmospheric pressure chemical ionization source (APCf) is considered to be less susceptible to matrix interferences, however, it is not suitable for all substances, in particular, the more polar ones (morphine, morphine-3 p-D-glucuronide, and ecgonine metltyl ester). 

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