Determination of Epigoitrin in Radix Isatidis by Solid Phase Extraction-Quantitative Nuclear Magnetic Resonance Spectroscopy

Abstract

A method of quantitative nuclear magnetic resonance spectroscopy (qNMR) for the determination of epigoitrin in Radix Isatidis decoction pieces was established based on solid phase extraction (SPE). The twice ultrasonic extraction method using pure water was used for fully extracting epigoitrin in sample, and then the extraction was enriched and concentrated by poly-Sery MCX SPE cartridge. The qNMR analysis was carried out under the optimum experimental conditions including deuterated DMSO as solvent, calibrated 2,3,5-triiodobenzoate acid as internal standard, P1 (pulse width) = 14.1 μs, d1 (pulse delay time) = 5 s, and NS (number of scan) = 256. The 1H-NMR peaks of δ 5.365–5.399 (H-7b, d, 1H) of epigoitrin was chosen as the quantitative peaks. Method validation was performed including precision (the intra-day precision RSD was 0.5%, and the inter-day precision was 0.8%); linearity (correlation coefficient r > 0.9991), LOD (0.05 mg g−1, standard curve method) and LOQ (0.19 mg g−1, S/N ≥ 150). The recovery of the SPE-qNMR was 97.4%–101.7%. The result showed that the method was stable, accurate and reliable. With this method, the epigoitrin in real samples of Radix isatidis decoction pieces was determined to be 0.19–1.26 mg g−1. The result suggested that SPE was suitable as extender for qNMR determination of low-content composition in complex samples.