Comparison of the stability of stock solutions of drugs of abuse and other drugs stored in a freezer, refrigerator, and at ambient temperature for up to one year.

The aim of this study was to evaluate the stability of stock solutions of a variety of illegal and medicinal drugs, important in forensic analysis, when stored refrigerated or at ambient temperature compared to solutions stored in a freezer. Stock solutions in methanol, acetonitrile, or a mixture of acetonitrile/methanol were transferred to autosampler vials and analyzed after storage for one month, three months, six months, and one year at ambient temperature, in a refrigerator, and in a freezer. Some of the compounds investigated, such as morphine and amitriptyline, showed to be stable for at least one year when stored at ambient temperature, but others, such as prometazine and olanzapine, nearly vanished when stored at ambient temperature for one month.