Abstract
BackgroundPlant extracts are a reservoir of pharmacologically active substances; however, conventional analytical methods can analyze only a small portion of an extract. Here, we report a high-throughput analytical method capable of determining most phytochemicals in a plant extract and of providing their molecular formulae from a single experiment using ultra-high-resolution electrospray ionization mass spectrometry (UHR ESI MS). UHR mass profiling was used to analyze natural compounds in a 70% ethanol ginseng extract, which was directly infused into a 15 T Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer for less than 10 min without a separation process.ResultsThe UHR FT-ICR MS yielded a mass accuracy of 0.5 ppm and a mass resolving power (m/Δm) of 1,000,000–270,000 for the range m/z 290–1,100. The mass resolution was sufficient to resolve the isotopic fine structure (IFS) of many compounds in the extract. After noise removal from 1,552 peaks, 405 compounds were detected. The molecular formulae of 123 compounds, including 33 ginsenosides, were determined using the observed IFS, exact monoisotopic mass, and exact mass difference. Liquid chromatography (LC)/FT-ICR MS of the extract was performed to compare the high-throughput performance of UHR ESI FT-ICR MS. The LC/FT-ICR MS detected only 129 compounds, including 19 ginsenosides. The result showed that UHR ESI FT-ICR MS identified three times more compounds than LC/FT-ICR MS and in a relatively shorter time. The molecular formula determination by UHR FT-ICR MS was validated by LC and tandem MS analyses of three known ginsenosides.ConclusionsUHR mass profiling of a plant extract by 15 T FT-ICR MS showed that multiple compounds were simultaneously detected and their molecular formulae were decisively determined by a single experiment with ultra-high mass resolution and mass accuracy. Simultaneous molecular determination of multiple natural products by UHR ESI FT-ICR MS would be a powerful method to profile a wide range of natural compounds.
Highlights
Plant extracts are a reservoir of pharmacologically active substances; conventional analytical methods can analyze only a small portion of an extract
The assignment of a molecular formula to a peak was enabled by the high mass accuracy and the isotopic fine structure (IFS) revealed in the ultra-high resolution (UHR) mass spectrum as described later
The number of ginseng compounds detected by UHR electrospray ionization (ESI)/Fourier transform ion cyclotron resonance (FT-ICR) Highresolution mass spectrometry (MS) was 405, which was more than three times the number detected by Liquid chromatography (LC)/FT-ICR MS
Summary
Plant extracts are a reservoir of pharmacologically active substances; conventional analytical methods can analyze only a small portion of an extract. Most analytical methods for plant extracts employ a combination of bioactivity assays and separation steps to isolate a few target compounds from a pool of numerous components. These traditional methods have been useful, there are disadvantages such as the high cost in time and labor, the blindness of molecular information, the possible loss of target compounds during the separation stage, and the disregarding of many active compounds not screened by the bio-assays used [3]. Reversed-phase high-performance liquid chromatography (HPLC) employs hydrophobicity and seldom detects extremely hydrophilic or hydrophobic compounds such as petroleum and natural products, which can be analyzed by direct infusion into a mass spectrometer [4,5]. Multi-dimensional liquid chromatography [6,7] and high-resolution mass spectrometry (HR MS) [8,9] have been optimized in this fashion
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