Determination of Menthol in Plasma and Urine by Gas Chromatography/Mass Spectrometry (GC/MS).

Menthol, a monoterpene, is a principal component of peppermint oil and is used extensively in consumer products as a flavoring aid. It is also commonly used medicinally as a topical skin coolant; to treat inflammation of the mucous membranes, digestive problems, and irritable bowel syndrome (IBS); and in preventing spasms during endoscopy and for its spasmolytic effect on the smooth muscle of the gastrointestinal tract. Menthol has a half life of 3-6 h and is rapidly metabolized to menthol glucuronide which is detectable in urine and serum following menthol use. We describe a method for the determination of total menthol in human plasma and urine using liquid/liquid extraction, gas chromatography/mass spectrometry (GC/MS) in selected ion monitoring mode and menthol-d4 as the internal standard. Controls are prepared with menthol glucuronide and all samples undergo enzymatic hydrolysis for the quantification of total menthol. The method has a linear range of 5-1000 ng/mL, and coefficient of variation <10%.

Pharmacokinetic study of borneol and menthol in rats after oral administration of qingyan drop pills.

Both borneol and menthol are bioactive substances derived from Chinese herbal medicines. In order to understand the pharmacokinetics of borneol and menthol in Qingyan drop pills, a rapid, sensitive, and simple gas chromatographic (GC) method with flame ionization detection (FID) was developed for the simultaneous determination of borneol and menthol in rat plasma. Sample preparations were carried out by liquid-liquid extraction (LLE) with an internal standard solution of naphthalene. The analytes and internal standard (IS, naphthalene) were separated well on an HP-1 capillary column. The pharmacokinetic parameters were estimated by a compartmental method using the Phoenix WinNonlin software program (Version 6.0). The standard curves were linear over a wide concentration range of 2.5-50.0 ng/µL ( R = 0.9963), 8.7-62.2 ng/µL ( R = 0.9994) for both borneol and menthol in plasma, respectively. The limits of quantification (LOQ) of borneol and menthol in plasma were 2.4 ng/µL and 5.0 ng/µL, respectively. The intra-day precisions for borneol and menthol were < or = 10.0 % R. S. D. at the LOQ and < or = 6.0 % at higher concentrations. The average value of CMAX was 18.97 ± 2.71 ng/µL with a TMAX at 20.00 ± 0.00 min for borneol after oral administration of the drop pills; for menthol, the average value of CMAX was 79.02 ± 11.40 ng/µL with a TMAX at 25.00 ± 4.40 min. This validated assay method was successfully applied to a pharmacokinetic study of borneol and menthol after oral administration of Qingyan drop pills in rat. The results showed that the kinetics of borneol and menthol can be described by an open one-compartment model. The pharmacokinetic parameters provide some information for clinical administration of Qingyan drop pills.