Protein precipitation by acetone for the analysis of polyethylene glycol in intestinal perfusion fluid

Canine ileal segments were luminally perfused with known amounts of polyethylene glycol (PEG), and samples obtained were freed of protein by a cold acetone (CA) method and assayed for PEG by trichloroacetic acid in the presence of calcium cations. This procedure was compared to the Barium salt (BaS) protein precipitation method of Hyden (Ann R Agric Coll Sweden 22:411-424, 1955). The CA method saved specimen volume and time in handling, whereas its stability, linearity, and reproducibility were equivalent to the more complex BaS method. In vitro studies disclosed no appreciable differences when PEG specimens were bile stained or dissolved in various solvents. A small modification of the CA method improved accuracy in measurement of small PEG concentrations.