Transport processes through track-etch membrane filters in a reagent delivery cell

A reagent delivery cell with a track-etch membrane filter for on-line dilution of concentrated salt solutions is described. The influence of several system parameters such as concentration of the stock solution, temperature. transmembrane pressure and the dependence on the diffusion coefficients of several salt components on the dilution was evaluated. As an application example, the use of the reagent delivery cell for on-line calibration of an atomic absorption spectrometer was studied. Fluxes through the membrane filter of 10 to 50 nL mm(-2) min(-1) with relative standard deviations of 0.8% within a day and 1.9% from day to day were achieved. The permeation experiments with the track-etch membrane filter for the dilution of aqueous solutions of several chlorides and sodium salts confirm a diffusion process. Flux rates can be estimated mathematically using Fick's first law with an agreement between measured and calculated dilution factors within 86 to 113%.