Additional Linked Scan Functions

Whereas TOF instruments solely allow for the detection of product ions of a selected precursor, sector instruments offer additional modes of operation i) to exclusively identify product ions of a particular precursor ion, so-called precursor ion seems [70,71], or ii) to detect only ions formed by loss of a specific neutral mass, so-called constant neutral loss (CNL) scan [72]. This can be achieved by some technically more demanding linked scans (Table 9.2) [73-76]. 

Example The B E = const, linked scan [71] has been enployed to quantify the caffeine content of coffee, black tea, and caffeinated soft nks [77]. Caffeine, M = 194, was determined by spiking the sample with a known conemtration of [D3]caffeine, M = 197, as internal standard. Both molecular ions dissociate to form a fragment ion at m/z 109 which was selected as m2 Then, the precursor ion scan showed both molecular ion, m/ and [D3]m/, as precursor of the ion at m/z 109. The ratio of peak intensities was taken as a measure for the relative concen- 

Selected mass Scan law KER from peak width Analyzer andFFR Properties 

Note Precursor ion scanning suggests some sort of measuring into the past. One should be aware that also in precursor ion scans the product ions are detected, but this is accomplished in a way that only fragments of a selected precursor ion mass can reach the detector, hence the term. 

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Cysteine-scanning mutagenesis, involving more than 100 mutations, has been systematically carried out through Cl—C3, the cytoplasmic terminations of TM1-TM7, H8, and the C-terminal tail. In addition, more than 40 pairs of cysteines have been introduced at the cytoplasmic face. With these mutants as a basis set, three classes of experiments have been carried out, namely SDSL, sulfhydryl reactivity, and disulfide cross-linking kinetics. A global comparison of the results provides a unique view of the solution state, its dynamics, and its correlation with the crystal structure. By solution state is meant, in all cases, rhodopsin solubilized in dodecyl maltoside (DM) micelles. The measured functional properties of rhodopsin, namely transducin activation (Resek et al., 1993) and phosphorylation by the rhodopsin kinase (Thurmond et al., 1997), are conserved in this detergent, and it is presumed to be a reasonable approximation to the bilayer environment. 

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