Improper sealing caused by the Styrofoam integrity seals in leakproof plastic bottles lead to significant loss of ethanol in frozen evidentiary urine samples.

Evidentiary urine samples (n = 345) stored frozen at -20 degrees C in their original containers (leakproof 100 mL plastic bottles) upon retesting for ethanol resulted in concentrations that were significantly lower (average loss = approximately 30%) than those prior to their storage at -20 degrees C (p < or = 0.0001). The observed loss of ethanol was independent of the method of thawing or the concentration of ethanol in the samples, but was dependent on the sample volume in the container, i.e., the larger the volume of sample the larger the magnitude of ethanol loss. The loss of ethanol was determined to be due to improper sealing by a Styrofoam integrity seal attached to the mouth of the container. Accordingly, adopting leakproof plastic containers that do not contain Styrofoam integrity seals, but rather an outside and across the cap tape integrity seal for evidence collection and long-term storage, will prevent loss of ethanol due to evaporation.