Stability studies in biological fluids during post-analysis custody. Opiate compounds derived from heroin consumption.

In Forensic Toxicology, the evidences have to be maintained under custody for, at least, one year. Depending on the conditions and duration of storage, drug concentrations might have changed considerably since the first analysis. The aim of this study is to evaluate in vitro stability of opiate compounds, derived from heroin consumption, 6-acetylmorphine (6-MAM), morphine (MOR) and codeine (COD), in blood and urine, during post-analysis custody. Parameters evaluated were: time of custody, temperature, addition of preservative (blood) and pH (urine). Blood and urine samples were spiked with the three analytes to give a final concentration of 1000 ng/mL. The prepared samples were divided into 2 groups and stored at two temperatures (4 °C and -20 °C). Each one of these groups was subsequently divided in other two groups: with and without preservative (1%NaF) for blood, and pH 4 and 8 in the case of urine. 6-MAM, MOR and COD were analyzed by GCMS after SPE and derivatization with BSTFA. Analyses were performed in triplicate every two weeks for a year. In blood samples 6-MAM is the only compound that degrades. The best storage conditions were at -20 °C with NaF, with 6-MAM recoveries, after one year of custody, of 47.1 ± 1.5%; while in the other conditions 6-MAM disappeared after 215 days (at 4 °C with NaF), 45 days (at -20 °C without NaF) and 15 days (at 4 °C without preservative). COD does not degrade, with recoveries higher than 90%, in all of the conditions. They ranged from 89.7 ± 3.6% in samples maintained at -20 °C without NaF to 95.9 ± 2.0% in those maintained at 4 °C with NaF. MOR recoveries were lower than those of COD. They ranged from 66.9 ± 3.6%, in frozen samples added with NaF, to 78.6 ± 0.5% in refrigerated samples without preservative. In urine samples the three compounds were stable in all the studied conditions, with the exception of 6-MAM in samples at pH 8 and stored at 4 °C. In these conditions, 6-MAM disappeared after 135 days of custody; while recoveries in the other conditions ranged from 93.7 ± 6.4%, at 4 °C and pH 4, to 85.1 ± 2.0% at -20 °C and pH 8. MOR and COD recoveries were similar in the four conditions. In the case of MOR, they ranged from 82.1 ± 1.2% at 4 °C and pH 4 to 89.5 ± 6.0% at -20 °C and pH 8. As far as COD is concerned, recoveries ranged from 111.6 ± 5.8% at 4 °C and pH 8 to 102.6 ± 1.2% at 4 °C and pH 4. In conclusion, the study showed that the most labile opiate compound is 6-MAM. Its stability mainly depends on urine pH or the addition of preservative, in blood samples. The best storage conditions for samples from heroin consumers are in the freezer, at -20 °C. In addition, blood samples must be added with 1%NaF and urine samples must be buffered at pH 4.