Direct determination of the residual acrylamide concentration in inverse (water-in-oil) polyacrylamide emulsions following phase inversion: Size exclusion chromatography using a micellar mobile phase

Abstract

A rapid and low cost method has been developed for the direct analysis of the residual monomer concentration of acrylamide from inverse-emulsion reactions. Inverse-emulsion polymerizations involve the dispersion of a water soluble monomer in aqueous solution in a continuous organic phase. The addition of a low-medium hydrophilic-lypophilic balance (HLB) steric stabilizer and continuous agitation is required to maintain emulsification. This method consists in inverting the “inverse” (water-in-oil) emulsion by utilizing a high HLB surfactant, large amounts of water and rapid stirring to produce a “direct” (oil-in-water) emulsion. Once the residual acrylamide is in the continuous aqueous phase, aliquots of this inverted mixture are then injected into a liquid chromatograph where the polymer and the residual acrylamide are separated by size exclusion chromatography using an aqueous micellar mobile phase. The micellar mobile phase is used to solubilize the organic phase and emulsifier present in the original inverse-emulsion recipe. The organic phase present in the original water-in-oil emulsion is trapped inside the micelles of the mobile phase and these elute with a retention volume comparable to that of the polymer. The large pore volume of the column separates the polymers from the residual monomer and provides sharp and symmetric acrylamide peaks with a good plate count. This method results in linear calibration curves for the acrylamide monomer up to 100 ppm. Further, the elimination of an organic mobile phase reduces the analysis cost considerably. In addition, the sample preparation time is reduced from between 30 minutes to several days for the traditional methods to 15 minutes for the newly proposed method. Therefore, this inversion procedure is suitable for rapid data analysis from reaction mixtures obtained from inverse-emulsion polymerizations. © 1996 John Wiley & Sons, Inc.