Influence of pre-analytical conditions on the interpretation of zopiclone concentrations in whole blood

Exploring Enzymatic Hydrolysis of Urine Samples for Investigation of Drugs Associated with Drug-Facilitated Sexual Assault

“…Cathinones in urine have been shown to be pH- and temperature-dependent with elevated temperatures causing more alkaline urine and thus more instability [ 23 , 24 , 25 ]. Additionally, the instability of zopiclone is well-documented in blood and in urine, as well as its degradation into ACP [ 26 , 27 , 28 , 29 , 30 ]. The pH of urine typically increases with increasing storage temperature due to microbial growth [ 23 , 24 , 25 ], but preservation with sodium fluoride, storage in a freezer and the addition of a buffer during pretreatment should typically keep the pH of the urine samples stable.…”

Zopiclone concentrations in oral fluid and blood after, administration of therapeutic doses of zopiclone

“…Zopiclone is well known as a notoriously unstable analyte in biological matrices, and analytical results might therefore depend on pre-analytical factors, such as storage time and temperature (39,40,191,192). A stability study of zopiclone in blood showed that zopiclone was stable less than 1 day at 20 °C, less than 2 weeks at 5 °C but stable for 3 months at -20 °C (193). Due to the known instability of zopiclone (39,194) the pre-analytical conditions from sampling to analysis were thoroughly controlled.…”

“…The main difference between the two devices used in our studies is that the OF collection pad of the Some of the OF samples were stored in a freezer and analyzed some weeks later according to the analytical capacity in the laboratory. The instability of zopiclone in biological matrices is well known (193,245) and it can be questioned whether the mean higher ratio for the Intercept device was due to larger instability in the Statsure device. This was investigated by performing stability studies of two separate OF sample pools made by mixing large numbers of OF samples collected from drug users by using the Intercept device or the Statsure device (191).…”

Issues Affecting Interpretation: Stability and Artefacts

“…Even when stored at -20°C for a time period of 1 year, a decrease between 10% and 20% of the starting concentration could be observed for five benzodiazepine-type drugs (El Mahjoub and Staub 2000). Zopiclone is a very labile compound; similar to flunitrazepam, its stability is less than 1 day in blood stored at ambient temperature and about 3 months at -20°C (Nilsson et al 2011). This study is also worth noting in that instability did not differ between authentic and spiked at 4°C.…”