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 (r2 = 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.