Quantification of a Botanical Negative Marker without an Identical Standard: Ginkgotoxin in <i>Ginkgo biloba</i>

Abstract

A new strategy for the analysis of natural products uses a combination of quantitative ¹H NMR (qHNMR) and adsorbent-free countercurrent separation (CS) methodology to establish a quantification method for ginkgotoxin (4′-<i>O</i>-methylpyridoxine) in <i>Ginkgo biloba</i> preparations. The target analyte was concentrated in a one-step CS process using the ChMWat +2 solvent system (CHCl₃–MeOH–H₂O, 10:5:5) and subsequently assayed by qHNMR. While commercial <i>G. biloba</i> seeds contained 59 μg of ginkgotoxin per seed, the compound was below the limit of detection (9 ppm) in a typical leaf extract. Due to the enrichment potential and loss-free operation of CS, the combination of CS and qHNMR is a generally suitable approach for threshold assays aimed at quantifying target compounds such as botanical negative markers at the low ppm level. As the proof of principle is demonstrated for relatively small CS capacities (20 mL, 1:40 loading) and modest NMR sensitivity (<i>n</i> = 16, 400 MHz, 5 mm RT probe), the approach can be adapted to quantification at the ppb level. The procedure enables the quantification of a botanical negative marker in the absence of identical reference material, which otherwise is a prerequisite for LC-based assays