Matrix post-factor

Vitamin K is a component of the carboxylase enzyme that carboxylates the amino acid glutamate in proteins to form y-carboxyglutamate, which binds calcium ions i.e. it catalyses a post-transcriptional modification. Proteins so carboxylated include clotting factors (Factors 11, Vll, IX, and X) and two proteins in bone oesteocalcin (known as matrix-gln-protein) and bone gin protein (BGP). The... 

The quadratic model (Eq.3.3) allowed the generation of the 3-D response surface image (Fig. 3.5) for the main interaction between injection time and voltage. The quadratic terms in this equation models the curvature in the true response function. The shape and orientation of the curvature results from the eigenvalue decomposition of the matrix of second-order parameter estimates. After the parameters are estimated, critical values for the factors in the estimated surface can be found. For this study, a post hoc review of our model... 

Direct inlet probe FAB-MS is an important tool in the analysis of compounds that are thermolabile and/or lack volatility [102]. Lack of sensitivity was initially a limiting factor but detection limits have been enhanced 10-100 fold, because of reduced suppression effects [103], with the use of a dynamic system in which the HPLC effluent is passed continuously into the ion source of the MS [104,105]. In the case of a frit-FAB HPLC interface, which is available commercially, reverse phase HPLC mobile phase, containing 1% glycerol as a matrix, is introduced into the ion source via a steel frit. The sample and matrix are then ionised on the inner surface of the frit with a beam of accelerated xenon atoms (Fig. 9). The optimum rate at which the HPLC mobile phase can be introduced into the ion source is 5 p.1 min and this necessitates the use of a reliable splitter when a conventional 2-5 mm bore HPLC column is used. Although a commercial post-column splitter is available, it is of limited value in the analysis of traee quantities of compounds. 

The accuracy of protein mass measurement depends on a number of factors because many proteins are sufficiently massive that resolution is not achieved from additional species such as salts or matrix adducts. Under these conditions, such species cause peak broadening and result in a small shift in measured mass to higher values. Post-translational modifications such as glycosylation can often be resolved for the smaller proteins such as ribonuclease B (Figure 3) with a single glycosylation site, but larger compounds with multiple modifications often produce only broad peaks. 

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