QUANTITATIVE-DETERMINATION OF POLYETHYLENE-GLYCOL BASED UPON ITS SALTING-OUT AND PARTITIONING OF A DYE INTO THE RESULTING AQUEOUS 2-PHASE SYSTEM

A method is described that allows quantitative determination of polyet hylene glycol (PEG) concentrations by spectrophotometric measurement o f fluorescein dye absorbance after its partitioning into an aqueous tw o-phase system containing mPEG (M(r) 5 kDa) in the upper phase and amm onium sulfate in the lower phase. The absorbance decrease of fluoresce in in the lower phase is directly proportional to the mPEG concentrati on, with two proportionality constants equal to 4.42 x 10(5) and 2.84 x 10(5) M(-1) cm(-1) in the range of 0-0.4 and 0.4-1 mu M, respectivel y. This experimental technique can be extended to PEGs of other molecu lar weights by means of calibration curves that give for each size of PEG the adequate proportionality constants. The results indicate that the quantitative determination is not affected by the presence of many substances such as proteins, reducing agents, and salts, at the usual concentrations. (C) 1995 Academic Press, Inc.