Approaches for Improving the Precision and Sensitivity of Continuous pervaporation Processes

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Abstract
Simple approaches aimed at enhancing both the sensitivity (by improving the mass transfer both from the liquid to the gas phase and through the membrane) and the precision of pervaporation processes are proposed. A conventional method based on formation of ethylene blue was used for the determination of sulfide after pervaporation. The use of a 280-cm waste tubing instead of the usual 20–30 cm length dramatically improved the sensitivity [slope of the calibration curve from 0.015 to 0.154 AU/(μg/mL of sulfide) for the sample injection mode, with detection limits from 0.68 to 0.07 μg/mL; and from 0.018 to 0.088 AU/(μg/mL) for the continuous sample introduction mode, with detection limits from 0.42 to 0.07 μg/mL], and the precision (r.s.d. % from 5.46 to 2.86 for the sample injection mode, and from 7.03 to 1.61 for the continuous sample introduction mode). Halting the flow during 5 min enhanced both the sensitivity [slope 0.123 vs 0.015 AU/(μg/mL)], and the precision (r.s.d. % 1.61 vs 7.03) but was detrimental to the sampling frequency.