Multiple internal selection sampling

The software tools accompanying the QTRAP MS/MS allow set-up of multiple selected reaction monitoring (SRM) transitions for all likely metabolites after the major product ion transitions for the dosed compound are known. Because QTRAP MS/MS can monitor up to 100 SRM transitions during a single assay, the SRM transitions required for quantitation of the dosed compound and internal standard are obtained along with the possible metabolite transitions. During sample analysis, when a possible metabolite transition exceeds a preset threshold value, the QTRAP MS/MS performs an enhanced product ion (EPI) scan. When the assay is complete, the EPI scans can be used to determine whether the hits are metabolites, and if they are metabolites, what part of the molecule has changed. Thus, one analytical run provides both quantitative and metabolite information. 

N diffuses into the structural pores of clinoptilolite 10 to 10 times faster than does CH4. Thus internal surfaces are kinetically selective for adsorption. Some clino samples are more effective at N2/CH4 separation than others and this property was correlated with the zeolite surface cation population. An incompletely exchanged clino containing doubly charged cations appears to be the most selective for N2. Using a computer-controlled pressure swing adsorption apparatus, several process variables were studied in multiple cycle experiments. These included feed composition and rates, and adsorber temperature, pressure and regeneration conditions. N2 diffusive flux reverses after about 60 seconds, but CH4 adsorption continues. This causes a decay in the observed N2/CH4 separation. Therefore, optimum process conditions include rapid adsorber pressurization and short adsorption/desorp-tion/regeneration cycles. 

By specifically and selectively reconstructing the total ion peak observed after a loop flow injection to display only the m/z values of interest, the area count for that ion can be extracted from the composite total ion peak. The measured area count can then be used to estimate the quantity of specific alkaloid by comparison to a calibration curve. Thus, component compounds in a mixture are separated by mass, as opposed to chromatography, for quantitation. To normalize the variability of the API response, an internal reference standard is added to the sample prior to loop injection. Alkaloids for which standards are not available are reported as equivalents of a closely related and available standard used to generate the calibration curve, for example, deltaline and methyllycaconitine have been used as calibration standards to represent the non-MSAL and MSAL types of alkaloids, respectively, in the plant material. Calibration curves for these two compounds were linear (r > 0.990) and there appears to be no selective suppression of lower-level alkaloids (figure 13.21). Multiple analyses of Delphinium barbeyi samples returned a level ofprecision that was less than 10 % (relative standard deviation) for all components [56]. 

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