Investigation of a flat sheet membrane desolvator for aqueous solvent removal with inductively coupled plasma atomic emission spectrometry

Results obtained from a preliminary investigation of the performance of a flat sheet membrane desolvator (FSMD) utilizing dual hydrophobic polypropylene membranes with an average pore size of 0.05 mu m and a 50 +/- 5 mu m thickness are reported. The membranes have a desolvation area of 241 cm(2). The volume-to-surface area ratio is 0.3 cm. Using the FSMD with an ultrasonic nebulizer (USN), aqueous solvent desolvation efficiencies of greater than 99.9% were obtained at all nebulizer gas flow rates investigated (0.8, 1.2, and 1.8 1 min(-1)). This efficient desolvation occurred when the countercurrent gas flow rate was equal to or slightly greater than the applied nebulizer gas flow rate. Under these conditions preconcentration factors of 18, 44, and 590 were observed with flows of 0.8, 1.2 and 1.8 1 min(-1), respectively. Operating with countercurrent gas flow rates much higher than the nebulizer gas flow rates leads to a significant reduction in analyte flux, thus increasing detection limits. Depending on the nebulizer and countercurrent gas flow rate conditions, the FSMD contributed between 10-40% to the overall analyte loss in the system. The lowest detection limit observed for aqueous copper with the USN-FSMD system is 0.4 ppb at nebulizer and countercurrent gas flow rates of 1.2 and 1.4 1 min(-1), respectively. At this nebulizer gas flow rate, replacing the FSMD in the system with a commercial tubular membrane desolvator, MDX100, gave a lowest Cu detection limit of 0.2 ppb at a countercurrent gas flow rate of 1.2 1 min(-1). These detection limits represents improvements over the 0.7 and 8 ppb obtained with USN and pneumatic nebulization, respectively. (C) 1997 Elsevier Science B.V.