Occurrence matrix residual

In the residual occurrence matrix comprised solely of independent columns, if a row contains only one nonzero element, the stream corresponding to the column in which the nonzero element appears is the only stream that can be torn to break the loop corresponding to that row. The next step of the algorithm is (1) to remove the columns in which a lone nonzero element in a row appears and (2) to remove all of the rows that have nonzero elements in that column. Each column removed in this step corresponds to tearing the stream represented by the column, and all of the rows removed represent loops that are broken by the tear. 

In the stepwise synthesis of peptides using cross-linked polystyrene supports, the rate of incorporation of a particular amino acid residue has been found to decrease with increasing chain length in a number of instances 41 -43). These occurrences have been attributed to steric hindrance at the various functional sites on the heterogeneous network. Sheppard investigated the origin of this steric hindrance and its sudden and unpredictable onset on the reactivity and physicochemical characteristics in the case of the cross-linked polystyrene-bound peptides 44). These studies suggested that the physicochemical incompatibility of the polystyrene matrix with the attached peptides is the factor responsible for the undesired influences of the solid support on the synthetic manipulations 44 45>. 

By collecting residues from the curtain plate in a Sciex API source (Figure 5.6) and re-injection, it was demonstrated that nonvolatiles present in the liquid flow, originating from nonvolatile mobile-phase additives or sample constituents actually increase the amount of analyte found at the curtain plate. The nonvolatiles prevent the preformed analyte ions to desorb from the droplet into the gas phase. This study emphasizes the importance of removing nonvolatile sample constituents during sample pretreatment [76]. It was concluded that APCI is less prone to matrix effects than ESI, which is also confirmed by others, e.g., [77-79], but one should certainly not exclude the occurrence of matrix effects in APCI-MS. 

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