Stability of γ-Hydroxybutyrate in Blood Samples from Impaired Drivers after Storage at 4°C and Comparison of GC–FID–GBL and LC–MS-MS Methods of Analysis
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Alan Wayne Jones, Sven-Åke Gladh, Charlotte Norup Windberg, Sys Stybe Johansen
The stability of γ-hydroxybutyrate (GHB) was determined in 50 blood samples from impaired drivers after storage at 4 °: C for up to 12 months. GHB was determined in whole blood by gas chromatography-flame ionization detector (GC-FID) after conversion into γ-butyrolactone (GBL) and results were compared with LC-MS-MS. Both analytical methods showed a linear response (R(2) > 0.99) to GHB concentrations from 2 to 250 mg/kg. The mean decrease in concentration after storage was 4.8 mg/kg, with extreme changes of +13 mg/kg or -29 mg/kg. Results by the GC-FID-GBL method (y-variate) and the LC-MS-MS method (x-variate) were highly correlated (R(2) = 0.974). The regression equation was y = 0.85x + 2.2 and residual standard deviation (SD) was 7.8 mg/kg. The y-intercept (2.2 mg/kg) was not significantly different from zero (P > 0.05), although the slope of the regression line (0.85) differed from unity (P < 0.001), indicating a proportional bias of 15%. The LC-MS-MS method tended to give higher results than the GC-FID-GBL method. The mean difference (bias) was 12 mg/kg (P < 0.001). The SD of individual differences was 11.3 mg/kg and 95% limits of agreement were -11 to +33 mg/kg. The results of this study show that concentrations of GHB in whole blood are stable during storage at 4 °: C for up to 6 months.
|Tidsskrift||Journal of Analytical Toxicology|
|Status||Udgivet - feb. 2015|