Method development and validation for the GC–FID assay of p-cymene in tea tree oil formulation

This paper describes the development and validation of an isothermal gas chromatography–flame ionisation detection (GC–FID) method for the assay of pure tea tree oil. The chromatographic conditions of the method employ a 5% carbowax packed column (20 m × 0.25 mm), isothermal elution with hydrogen at a column flow of 36 ml/min, injector and detector temperature at 220 °C and oven temperature at 100 °C, and a 1.5 μl injection volume. Samples and standard were diluted in hexane. The calibration curve for p-cymene was linear ( r 2 = 0.9995) from 20 to 120% range of the analytical concentration of 100 μg/ml. The precision of this method was calculated as the relative standard deviation (R.S.D.) was 0.66% ( n = 6). The R.S.D. for intermediate precision study was 0.13 and recovery of the p-cymene ranged between 93.39 and 97.86%. The limits of detection and quantitation were determined to be 2.08 and 10.39 ng/ml, respectively.