2.4. Analytical procedure
The samples, controls and calibrators were prepared using the procedure described by several authors for the determination of ethanol [18,21–24]. When aqueous ethanol solutions are used for instrument calibration involving a HS GC technique to quantify this substance, it is necessary to eliminate the matrix effects. Prior to analysis by gas chromatography, all samples, including the calibrators, were diluted: 100 mL of urine, vitreous humor or whole blood were diluted with 1 mL aqueous solution of n-propanol (100 mg/L), used as internal standard. No inorganic salt was used.
Before starting the analytical procedure, all samples, controls and calibrators (with the exception of chloroform) reached room temperature. Taking into account the characteristics of the substances involved, in terms of their volatility, the vials were sealed immediately after preparation.