Stability of Cocaine, Opiates, and Metabolites in Dried Saliva Spots

Abstract

Drug abuse still represents a global problem, and it is associated with an increased risk of diseases, injuries, and deaths. Cocaine (COC) and opiates are the most abused drugs and account for a significant number of fatalities. Therefore, it is important to develop methods capable of effectively identifying and quantifying these substances. The present study aims to evaluate the long-term stability of COC, ecgonine methylester (EME), benzoylecgonine (BEG), cocaethylene (COET), norcocaine (NCOC), morphine (MOR), codeine (COD) and 6-monoacetylmorphine (6-MAM) in oral fluid samples. The analytes of interest were isolated from the matrix (50 µL) using the dried saliva spots (DSS) sampling approach and were subsequently analyzed by gas chromatography coupled with tandem mass spectrometry (GC-MS/MS). The parameters that could influence the stability of the target compounds were studied, and these were storage temperature, light, use of preservatives (and respective concentrations), and time. The effects of each parameter were evaluated using the design of experiments (DOE) approach. The stability of the target analytes was improved when the DSS were stored at room temperature, in the presence of light and using 1% sodium fluoride. The best conditions were then adopted for the DSS storage and long-term stability was assessed. COD was only stable for 1 day, EME was stable for 3 days, COC, COET, NCOC and 6-MAM were stable for 7 days, MOR for 14 days and BEG remained stable throughout the study (136 days). This is the first study that evaluates the stability of these compounds in oral fluid samples after application in DSS cards, and optimizes the conditions in order to improve their stability.

Keywords: GC–MS/MS; cocaine; dried saliva spots; opiates; oral fluid; stability.

Figure 1

Pareto diagrams of the compounds under study, obtained when ascorbic acid was used as the preservative. The blue bars represent the effects of factors or a combination of factors: A—Temperature, B—Light, C—Preservative, and D—Time.

Figure 2

Main effects plots of the compounds when ascorbic acid was used as the preservative; The slope of the lines represents the effect of the response for the factors under study: temperature (room or refrigerator (4 °C)), light (presence or absence), preservative concentration level (low or high), and storage time (1 or 7 days).

Figure 3

Pareto diagrams of the compounds under study, obtained when sodium fluoride was used as the preservative. The blue bars represent the effects of factors or a combination of factors: A—Temperature, B—Light, C—Preservative, and D—Time.

Figure 4

Main effects plots of the compounds when sodium fluoride was used as the preservative; The slope of the lines represents the effect of the response for the factors under study: temperature (room or refrigerator (4 °C)), light (presence or absence), preservative concentration level (low or high), and storage time (1 or 7 days).

Figure 5

Chromatograms obtained for EME (A) and COET (B) for refrigerator temperature, absence of light, high concentration of preservative, day 1 (1A and 2A), and day 7 (1B and 2B) using sodium azide.

Figure 6

Long-term stability of analytes under study. The graphs represent the percentage of the compounds in the DSS samples as a function of time.