Pervaporation, analytical derivatization reactions

Fig. 4.18. Continuous iscrete approach to implementing analytical pervaporation of solid samples. The dotted line corresponds to a potential derivatization reaction of the pervaporated species and the dashed lines represent the continuous manifold used for automatic insertion of liquid samples. P peristaltic pump, AS acceptor stream, IV injection valve, SV switching valve for changing between continuous and discrete insertion of sample into the pervaporator, R reagent, DS donor-sample stream, S sample, RC reaction coil, PM pervaporation module, M membrane, D detector, W waste.

Fig. 4.19. Simplified scheme of a hydrodynamic manifold for evaluation of pervaporation efficiency. Note that, when a derivatization reaction is required prior to or after analyte separation, one or more additional channels for the reagent solution(s) must be included in the donor and acceptor stream, respectively. AIV auxiliary injection valve, MIV main injection valve, PM pervaporation module, m membrane, a merging point, D detector, W waste, AUX auxiliary channel containing acceptor solution, S sample, AS acceptor solution, DS donor solution. (Reproduced with permission of Wiley Sons.)...

When the concentrations of the target analytes in the sample exceed the upper limit of the linear range of the calibration curve, a dilution or pseudodilution step is mandatory in order to fit the vmknown concentration to this portion of the calibration curve, and hence to increase the precision of the measurements. A series of alternatives to the usual previous dilution of the sample have been developed in order to avoid the errors involved in a dilution step or in the weighing of small amounts of a solid. These alternatives are (1) using of a lower pervaporation temperature (2) changing the chemical conditions to a less favorable situation if a derivatization reaction is required, in order to reduce the yield of the monitored species (3) enlarging the air gap between the... 

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