Measurement of polyethylene glycol 4000: Effect of storage and freeze thawing in biological fluids

Summary The effects of storage and freeze-thawing on polyethylene glycol 4000 (PEG 4000) and¹⁴C PEG 4000 in a solution of NaCl (150 mmoles/l) containing varying amounts of human albumin were studied. Results showed that the analysis of both PEG 4000 and¹⁴C PEG 4000 is likely to be inaccurate in these fluids if the specimens have been freeze-stored, thawed and refrozen several times during a period of several weeks. This seems to be due to the freeze-thawing process itself rather than the actual storage. The amount of protein in the samples may increase the fall in estimated levels of polyethylene glycol observed.