Abstract
Sinomenine (7,8‐didehydro‐4‐hydroxy‐3,7‐dimethoxy‐17‐methylmorphinan‐6‐one) is a pure alkaloid extracted from the Chinese medical plant. In this report a liquid chromatography–electrospray mass spectrometry (LC–ESI‐MS) method with in vivo microdialysis for the pharmacokinetic study of free‐form sinomenine in rat skin has been developed. A microdialysis probe was surgically implanted into the subcutaneous tissue of the rats and an isotonic phosphate buffer (PBS) was used as the perfusion medium. Samples were collected and then analyzed off‐line by LC–ESI‐MS. The chromatographic separation was achieved within 4.2 min by using a narrow‐bore Xterra C~18~ column (2.1 × 150 mm, 5 µm) with acetonitrile–(10 mmol/L ammonium acetate buffer, 0.1% acetic acid) (15:85, v/v). Ion signal m/z 330.1 for sinomenine was measured in the positive mode. Linearity was established for the range of concentrations of 2.0–10000.0 ng/mL with a coefficient of determination (r) of 0__.__9989. The intra‐ and inter‐day reproducibility of the present method was better than 6%. The lower limit of quantification (LLOQ) was 1.0 ng/mL. The proposed method described provides more authentic information on pharmacokinetics and metabolism at the site of action by using the coupling of microdialysis to LC–ESI‐MS technique than the traditional sampling methods. Copyright © 2006 John Wiley & Sons, Ltd.