Poly(ethylene glycol) quantitation by laser nephelometry

When poly(ethylene glycol) 3350 is estimated by the method of Skoog [(1979) Vox Sang. 37, 345-349], fine particles form. The particles are not attributable to residual protein but to a poly(ethylene glycol)/barium/iodine complex that can be quantitated by means of a laser nephelometer. The method is sensitive to at least 10 mg% poly(ethylene glycol) 3350 (4 micrograms in the cuvette) in 2500 mg% protein, and nephelometer response is approximately linear between 30 and 200 mg% of the polymer. The coefficient of variance is about 8%. Triton X-100, Pluronic F-68, Varonic 1000MS, and poly(ethylene glycol) of higher and lower molecular weight react well. Alkylated celluloses, dextrans, glycerol, glycine, and sodium dodecyl sulfate do not react significantly. Barium can be replaced with Mg, Ca, Ni, Fe, and other divalent cations in the reaction, but other than for Hg, light-scattering is most intense with Ba. The reaction goes to completion in about 5 min and is most intense when the barium is added before the iodine.