INVESTIGATION OF A FLAT SHEET MEMBRANE DESOLVATOR FOR AQUEOUS SOLVENTREMOVAL WITH INDUCTIVELY-COUPLED PLASMA-ATOMIC EMISSION-SPECTROMETRY

Results obtained from a preliminary investigation of the performance o f a flat sheet membrane desolvator (FSMD) utilizing dual hydrophobic p olypropylene 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 a rea of 241 cm(2). The volume-to-surface area ratio is 0.3 cm. Using th e 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 obs erved with flows of 0.8, 1.2 and 1.8 1 min(-1), respectively. Operatin g with countercurrent gas flow rates much higher than the nebulizer ga s flow rates leads to a significant reduction in analyte flux, thus in creasing detection limits. Depending on the nebulizer and countercurre nt gas flow rate conditions, the FSMD contributed between 10-40% to th e overall analyte loss in the system. The lowest detection limit obser ved for aqueous copper with the USN-FSMD system is 0.4 ppb at nebulize r and countercurrent gas flow rates of 1.2 and 1.4 1 min(-1), respecti vely. At this nebulizer gas flow rate, replacing the FSMD in the syste m 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, respectivel y. (C) 1997 Elsevier Science B.V.