Rapid Analysis of Glucosinolates Using Direct-Infusion Mass Spectrometry

Abstract

We developed a rapid, accurate, and quantitative method for analyzing glucosinolates (GSLs) by combining column-free liquid chromatography (LC) with direct-infusion mass spectrometry (MS). Conventional methods for analyzing GSLs take a long time (20-50 min per sample) to perform compound separation on an LC column. We achieved a shortened analysis time of 30 seconds per sample using a direct-infusion method. Samples were continuously injected by a pump and autosampler on an LC system directly into the MS. Orbitrap MS detected 11 types of GSLs in the extracts of turnip hypocotyls. The calibration curve of a GSL standard showed a linear response over a 6-digit concentration range from 1 nM to 1 mM. In addition, no decrease in the detected intensity of GSL ions in 100 continuous analyses of turnip extracts was observed. This method may be applied for rapid analysis of GSLs and other health-functional or bioactive compounds.

Keywords: orbitrap MS; solid phase extraction; turnip.

Fig. 1. Mass spectra of BZG and SNG. BZG, benzylglucosinolate; SNG, sinigrin.

Fig. 2. Chromatograms of BZG and SNG in different flow rates. The vertical axis indicates the relative ion intensity to the maximum. RT, retention time; AA, auto-integrated area; AH, auto-integrated height; SN, signal-to-noise ratio; BZG, benzylglucosinolate; SNG, sinigrin.

Fig. 3. Isotope GNT peaks. The left figure shows the mass spectrum of GNT in the mass range from 421 to 425. The right figure shows an enlarged view of the mass spectrum near 424. GNT, gluconasturtiin.

Fig. 4. Relative area values at different concentrations of GNP (left figure). The right figure is an enlarged view from 1 nM to 1 mM, where the relative area value showed linearity with respect to concentration. The approximate curve formula and R-squared values are shown in the figure. The axes in the left and right figures are expressed in logarithms and absolute numbers, respectively. GNP, gluconapin.

Fig. 5. Changes in the ion intensity of GSLs detected from turnip seedlings in 100 consecutive analyses. The horizontal axis shows the number of analyses, and the vertical axis shows the detected ion intensity. GSLs, glucosinolates.