Principles of gas diffusion and its numerous applications have recently been thoroughly
reviewed (Luque de Castro 2008). In conventional SI format, attachment of a ga diffusion unit to adjacent ports of an eight position valve is a logical approach. Such a system was used for colorimetric assay of chlorine, in water and bleach samples. The assay sequence starts by acidification of sample with HCl and subsequent diffusion of liberated chlorine into an acceptor stream of NaOH, which is later mixed with color forming reagent (diadisidine in acetic acid). Finally, the measurement is carried out spectrophotometrically at 453nm (Mesquita and Rangel 2005).
Gas Diffusion in Conventional SI Format
2.3.27.
While simple in construction, there are several sections of this configuration where carryover and cross contamination can occur. First, conduits between sample containers and valve ports must be flushed between subsequent samples. Next, the groove in the rotor which is used to transport donor and acceptor solution in sequence must be washed out. While careful flow programming and thorough flushing will avoid these potential problems, the use of a single pump to carry out all the necessary operations results in a low sampling frequency and elevated reagent consumption. Therefore a two-pump system is preferable
M.D. Luque de Castro, Membrane Based Separation Techniques: Dialysis, Gas Diffusion and Pervaporation, Ch 8 in
