Fast screening method for the analysis of total flavonoid content in plants and foodstuffs by high‐performance liquid chromatography/electrospray ionization time‐of‐flight mass spectrometry with polarity switching

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Abstract
A liquid chromatography/electrospray ionization mass spectrometry (LC/ESI‐MS) method based on time‐of‐flight (TOF) MS with polarity switching and continuous exact mass measurement using a LockSpray ion source was developed for fast evaluation of the total flavonoid content in plants and foodstuffs. No complicated sample preparation was needed, but only a dilution of the extracts. A fast generic gradient elution and wide mass range acquisition was used with good sensitivity. The total analysis time was only 23 min. The ion chromatograms for flavonoid compounds were automatically extracted, and the fragmentation patterns obtained using positive ion mode and exact mass data for both polarities were used for the tentative identification of compounds. Software‐based automated searching of molecular ions for flavonoids and their glycosides (xylosides/arabinosides, rhamnosides, glucosides/galactosides) from total ion chromatograms was used. The compounds were quantified using quercetin, quercitrin, rutin and kuromanine as external standards and dextromethorphan as an internal standard. The detection limits ranged from 0.01–0.04 μg/mL, while the quantitation ranges obtained were 0.2–10 μg/mL for anthocyanins and 0.2–4 μg/mL for the other flavonoids. The accuracies within these ranges varied between 80–120% and precision was in the range 0–14% (relative standard deviation). Flavonoid contents of two medicinal plants (Hypericum perforatum and Rhodiola rosea), two grape red wines, two orange juices and two green teas were evaluated using the method, and the results obtained were in good agreement with those published previously. Copyright © 2004 John Wiley & Sons, Ltd.