Loss of THCCOOH from urine specimens stored in polypropylene and polyethylene containers at different temperatures.

The loss of delta9-tetrahydrocannabinol (THCCOOH) from urine specimens stored in polypropylene and polyethylene containers at 4 degrees C and 25 degrees C was examined. All specimens were analyzed by GC-MS after sampling at various times over a one-week period. Data were analyzed by one-way analysis of variance and fitted with a first order kinetic equation. Rapid loss of THCCOOH was seen at 4 degrees C for both polypropylene (14% maximal loss, t(1/2) = 0.53 min) and polyethylene (17% maximal loss, t(1/2) = 5.77 min) bottles. At 25 degrees C, a small loss (< 5%) was observed in polypropylene and no significant loss was seen for urine in polyethylene. All losses stabilized within 1 h, and no further losses were seen over one week. The results indicate that THCCOOH binding may be due to decreased solubility of THCCOOH at lower temperatures and subsequent association of THCCOOH with the more lipophilic plastic. The results also indicate that polypropylene and polyethylene do not bind THCCOOH to such an extent as to compromise the integrity of specimens.