On the pH dependence of polymerization efficiency, as investigated by capillary zone electrophoresis

The conversion efficiency of 5 different catalyst systems for polyacrylamide gel polymerization has been assessed as a function of pH of the gelling solution, in the pH 4.0-10.0 range. The system of persulfate-N,N,N',N'-tetramethylethylene-diamine (TEMED) gives optimal incorporation of monomers only in the pH 7.0-10.0 range; at progressively acidic pH values, the conversion drops markedly until, at pH 4.0, no gelation occurs. In the system of riboflavin-TEMED, the opposite behavior is observed: good conversions in the pH 4.0-7.0 interval (with a peak at pH 6.2), followed by progressive worsening at alkaline pH values until, at pH 10.0, no gelation occurs. An excellent catalyst system appears to be the complex comprising methylene blue, toluene-4-sulfinic acid and diphenyliodonium chloride, which is able to guarantee > 95% conversion in the pH 4.0-8.0 range. Lower efficiencies are obtained at pH 9.0 and 10.0 (down to 81% conversion) but gelation still occurs in the entire pH range. Two other systems (ascorbic acid, ferrous sulfate and hydrogen peroxide in one case, and persulfate, TEMED and hydrosulfite, in another case) have been investigated. The former has some efficiency only at pH 4 (81% conversion), with a rapid drop as pH increases (only 48% incorporation at pH 6). The latter exhibits the opposite behavior: 70% efficiency at pH 4.0, increasing to 92% conversion at pH 6.0.