Ion suppression effects

Marcomini et al. [25] performed the protonation of the carboxylic groups of the SPC. This technique termed ion suppression effect chromatography enabled the individual elution of the SPC contained in a primary sludge from a wastewater treatment plant. The quantification of the SPC was performed under the assumption that the signals detected by fluorescence before the elution of the LAS (with the exception of NPEC) correspond solely to SPC. 

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

One has to emphasize that MS also is associated with several drawbacks when it comes to bioactivity screening. First of all, the optimum, native conditions for bioactivity screening (pH 7.2, addition of 150 mM sodium chloride) are entirely incompatible with optimum conditions for MS detection which, for ESI-MS, typically require acidic pH values and the presence of organic modifiers to enhance ionization properties of the analytes. Assay development for MS-based assays therefore mainly requires the testing of different assay conditions, particularly the replacement of nonvolatile buffers with MS-compatible volatile buffers. Furthermore, it is essential to monitor ion suppression effects, for example, by the... 

Larger, P. J. Breda, M. Fraier, D. Hughes, H. James, C. A. Ion-suppression effects in liquid chromatography-tandem mass spectrometry due to a formulation... 

From a practical point of view this definition can be interpreted as being imposed by the linear boundary of the calibration curve (quadratic behavior) due to saturation of the detector or/and ion suppression effect and/or contamination for low-level samples (carryover) (see Section 8.3.7). 

Weaver, R., and Riley, R. J. (2006). Identification and reduction of ion suppression effects on pharmacokinetic parameters by polyethylene glycol 400. Rapid Commun. Mass Spectrom. 20 2559-2564. 

Alternative approaches to improve chromatography and thereby enhance signal-to-noise ratio include the use of ultrapressure liquid chromatography (UPLC) (Dear et al., 2006), where chromatographic resolution can be dramatically increased (Castro-Perez et al., 2004, 2005 Plumb et al., 2004), or nano-HPLC (Schmidt et al., 2003), which may serve to reduce ion suppression effects. For offline use, the 96-well plate approach (typically the Scintiplate) will normally be used in combination with direct mass spectrometric infusion at conventional flow rates (5-10 xL/min). This approach enables multiple experiments to be performed in order to... 

Figure 10.1. Ion suppression effects from protein precipitated plasma (a) blank injection (50/50 methanol-water) (b) Injection of protein precipitated rat plasma.

Figure 10.3. Ion suppression effects from turbulent-flow LC (a) blank injection of buffered water (b) neat rat plasma.

Although well designed LC-MS/MS assays generally outperform immunoassays due to their accuracy, sensitivity, precision, and inherent multiplexing capability, they are not free from analytical problems. Besides limitations in selectivity— isobaric analytes cannot be distinguished—sudden and unpredictable ion yield attenuations, often known as ion suppression effect, have to be considered the Achilles heel of quantitative bio-analytical mass spectrometry. Ion yield attenuation is compromising both the accuracy of an assay and its precision. It can easily lead to gross errors in analyte quantification. 

This assay was tested with respect to potential ion suppression effects (matrix effect) as well as with respect to the extraction recovery of the sample preparation procedure. 

Ion suppression effects, due to coeluting compounds or the mobile phase, need to be identified. 

TheAPCImode may be preferable to E SI in terms of enhancing the sensitivity by reduction of ion suppression effects. 

Relative to GC-MS, the application of LC-MS within the metabolomics held is still at a preliminary stage. Reproducibility is a major concern, and true quantification can be hindered by ion suppression effects whereby one co-eluting metabolite affects the ionization of another (26). The lack of electrospray ionization mass spectral libraries also makes identification by LC-MS a particularly challenging problem. Nevertheless, the technique is developing fast and has benefited from several technological advancements such as the acquisition of accurate mass data by the use of ion cyclotron resonance Fourier transform MS (26). 

Spectra acquired from PE membranes are of equal or better quality as those acquired from metal sample stages under standard sample preparation conditions. The PE membrane provides access to higher molecular weights than the more common transfer membrane materials (PVDF, nylon, and nitrocellulose). This permits the mass analysis of the large proteins for which MALDI-TOF MS is ideally suited. Mass accuracy and reproducibility approaches that obtained with standard sample preparations. Furfeermore, the use of PE reduces the severe ion suppression effects typically observed in the MALDI analysis of high mass mixtures. This also permits more accurate mass measurements to be made via the use of internal calibration. 

Cf-FAB has some distinct advantages in terms of analyte ionization over static FAB, introduced by Barber et al. [49] in 1981, e.g., improved detection limits and reduced ion suppression effects [50]. On the other hand, the mass range in Cf-FAB appears to be more limited compared to static FAB. In comparison to static FAB, the Cf-FAB technique is more convenient and easier to use. The system can be used in column-bypass mode, enabling a high sample throughput. 

Multiple sprayers from several liquid streams were used to study gas-phase ion-ion and ion-molecule reactions in the ESI source. A seven-channel ESI device was applied to study gas-phase reactions of proteins [59], but also to facilitate the protonation of highly reactive pyrolytically-produced ketenes [60]. The analyte is fed through the centre capillary, while a reagent solution is introduced through the outer six channels A dual-sprayer device was used to study the mechanism of matrix-related ion-suppression effects in quantitative analysis (Ch. 11.5.1, [61]). 

C.R. MaUet, Z. Lu, J.R. Mazzeo, A study of ion suppression effects in ESI from mobile phase additives and SEE, Rapid Commun. Mass Spectrom., 18 (2004) 49. 

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