Gas Chromatography Determination of the Concentration of Ethanol in the Iodine Tincture Using Direct Injection and Head-Space Injection

OBJECTIVE To establish and compare methods for detection of the ethanol in the iodine tincture by GC using direct injection and head-space injection. METHODS The ethanol in the iodine tincture was determined by GC with Agilent DB-ALC1 capillary column(30 m×0.53 mm, 3.0 μm) and FID detector, using nitrogen as the carries gas. The injector temperature was 200℃; the detector temperature was 250℃; the column temperature was 80℃. The flow rate of N₂ was 5 mL·min^-1, and the auxiliary heating temperature was 115℃. Tertbutyl alcohol was used as the internal standard, 1.0 mL sample was injected by headspace injector and 1.0 μL by direct injection. RESULTS With head-space injection, the calibration curves of ethanol had good linear relationship within 15.78-63.12 mg·mL^-1, Y=3.558 9X-0.341 3 (R²=0.998 9); the recovery was ≥ 96.55%; RSD was ≤ 4.30%; the within-day precision was ≤ 3.86%. The calibration curves of ethanol between concentration of 15.78-63.12 mg·mL^-1 by direct injection was Y=0.015X-0.006(R²=0.999 5), the recovery was ≥ 97.8%(RSD ≤ 3.22%); the within-day precision was ≤ 3.85%. CONCLUSION Both two methods are accurate and reliable, and can be used for the determination of the concentration of ethanol in the iodine tincture, and the method using head-space injection has more sensitive, less disturb and long analysis time than direct injection.