Stability Study of Propoxur (Baygon) in Whole Blood and Urine Stored at Varying Temperature Conditions

A stability study has been initiated for propoxur (Baygon) in whole blood and urine samples stored over a period of 60 days at four different temperature conditions (room temperature, 4°C, −20°C, and −80°C). Stability data was established on day 0, 1, 7, 14, 28, 42, and 60. Sample purification was done by solid-phase extraction using a weak cation exchange cartridge (Isolute® CBA), and quantitation was carried out by a validated high-performance liquid chromatographic method with a photodiode-array UV detector. Propoxur was spiked at two different concentration levels in both blood and urine samples [low concentration (10 µg/L) and high concentration (100 µg/L)]. Isopropoxy phenol was observed as the major degradation product in blood and urine samples and confirmed by liquid chromatography-electrospray ionization-mass spectrometry. At room temperature, a substantial decrease in concentration of about 95% was observed at the end of the stability study in both blood and urine samples. However, at 4°C, the concentration of propoxur observed after 60 days was around 60% in both samples. A decrease in temperature reduced the degradation, and finally propoxur was found to be stable at −80°C and −20°C for the whole observation period (60 days). The data collected suggests that knowledge about time-dependent decrease of propoxur in urine and blood samples is of considerable significance in forensic toxicology, and, therefore, forensic cases should be interpreted with caution.