Matrix effect chromatogram

Figure 13.14 is an example of two superimposed matrix effect chromatograms, one generated with ESI and the other with APCI. These data highlight a common observation that suppression effects are more serious and more commonly observed with ESI than APCI. The suppression effects are actually serious in both cases, but the retention time characteristics of the suppressing materials with APCI are more readily predicted ... 

Figure 13.13. The continuous trace is an ESI matrix effect chromatogram of a 10- iL injection of protein-precipitated plasma while post-column infusing beclomethazone. The dashed chromatogram is an injection of standard beclomethazone and metabolite superimposed to indicate retention times of the analytes. MRM data 466 376, 2.1 mm x 5 cm CIS column, 200 pL/min, isocratic conditions 60740 CH3CN/H2O 2 mM NH4OAC.

Figure 13,14. Electrospray and APCI matrix effect chromatograms of a 20-pL injection of rat urine while post-column infusing Minoxidil, MRM 210 — 195, 2.1-mm x 5-cm C18 column, 200pL/min, isocratic conditions 70/30 CH3CN/H2O 2mM NH4OAC.

Compare the mass chromatograms—differences are due to matrix effects ... 

Fig. 13.7 Post-column infusion study of a ballistic gradient. The matrix effects can be seen at the early part of the chromatogram, but the later part of the chromatogram where the analytes should elute did not show matrix effects. Adapted from [99], with permission from John Wiley and Sons.

Reference values of this approach are not different from those for other amino acid analyses. An example of a mass chromatogram, representing the plasma of a PKU patient, is shown in Fig. 2.1.1. When evaluating the results of MS/MS amino acid analyses, one has to reahze that the hquid chromatographic separation is by far less efficient that the AAA separation. For this reason, any amino acid may (partly) coelute with other amino acid(s), which potentially interferes with its mass spectromet-ric behavior. This effect is known as quenching. In order to overcome this as much as possible, stable-isotope-labeled internal standards (as many as possible) should be used. However, this matrix effect of ion suppression is the major pitfall in the MS/MS analysis of amino acids. Consequently, the MS/MS analysis of amino acids cannot be regarded as a reference method, similar to all other amino acid analytical methods. 

The advantage to MHE is that sample matrix effects (which are mainly an issue only with solid samples) are eliminated since the entire amount of analyte is examined. This examination is done by performing consecutive analyses on the same sample vial. With the removal of each sample aliquot from the vial, the partition coefficient K will remain constant however, the total amount of analyte remaining in the sample will decline as each analysis is performed and more of the analyte is driven up into the vial headspace for removal and analysis. Chromatograms of each injection of sample show... 

The coupled-colurrm approach (c/ Ch. 1.4.6), where a particular peak of interest is heart-cut from the chromatogram developed on the first colurrm and sent to a second colurrm for a second stage of analysis, either via a sample loop or via a short trapping colurrm. Coupled-colurrm LC-MS was successfully applied as a tool in reducing matrix effects [84]. Sancho et al. [28, 89] reported the use of coupled-colurrm LC for biological monitoring of occupatiorral pesticide exposure (see Ch. 7.8). 

Figure 11.7 Typical results of a post-column infusion experiment. In the top chromatogram the separation of the parent drag, its metabolite, and an ANIS is shown. The bottom chromatogram shows the matrix effect on the response of the parent drag. The ion suppression and ion enhancement effects prevent the rehable determination of the target compounds. Reprinted from W.M.A. Niessen, J. Chromatogr. A, 1000 (2003) 413 with permissiom 2003, Elsevier Science BV.

A chromatogram is produced by developing a TLC/HPTLC plate, but it may be necessary to employ one of the reagents descnbed to make the positions, structures and sizes of the chromatogram zones apparent so that they can be recorded If the Rf values are the same a companson of the sizes of the zones of the sample and standard substances gives an indication for estimating the amounts If, as a result of matrix effects, the Rf values of sample and standard are not the same then their... 

Quantitative data were obtained by integration of selected ion chromatograms extracted from the total ion current. The ions used for quantification are presented in Table 1. For GC/MS-analyses of reference compounds the limit of quantitation (LOD) was 0.5 ng (signal to noise ratio 10 1). In Lippe river water samples concentrations of 10 ng/L resulted in similar signal to noise ratios due to matrix effects. Therefore these values were defined as limits of quantitation in the present study. 

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