Rapid Differentiation of Angelica sinensis and Levisticum officinale by Ultrasonic Extraction and Nebulization in Real-Time/Carbon Fiber Ionization Mass Spectrometry

The rapid and accurate differentiation of Angelica sinensis and Levisticum officinale is a significant challenge in the quality control of traditional Chinese medicine. Angelica sinensis and Levisticum officinale are different genera of the same family. Due to their similar appearances and partially shared chemical components, unscrupulous traders often sell counterfeit Levisticum officinale as Angelica sinensis to make exorbitant profits. In this study, a fast and easy method of ultrasonic extraction and nebulization in real-time/carbon fiber ionization mass spectrometry (UENRT/CFI-MS) was introduced for the swift discrimination of these two easily confused traditional Chinese medicines. UENRT/CFI-MS primarily consists of an online extraction and nebulization unit, an ionization unit. The online extraction and nebulization unit employ an ultrasonic nebulizer chip for real-time sample extraction and nebulization. The ionization unit comprises a 10 mm long carbon fiber rod nested in a metal tube, achieving ionization through the application of a 3 kV high voltage, and the auxiliary solvent (methanol) is continuously supplied to the carbon fiber at a rate of 5 μL/min. Slices of Angelica sinensis and Levisticum officinale from different origins with similar size, appearance, and quality (diameter less than 16 mm, thickness not exceeding 0.5 cm) were selected and placed directly on the nebulizer chip. For each analysis, 200 μL methanol was continuously added using a pipette. When the nebulizer was activated, the lower end of the nebulizer chip generated a continuous spray of tiny droplets towards the carbon fiber tip for several seconds, which were then ionized before entering the mass spectrometer for detection. This device integrates online ultrasonic extraction, nebulization, and carbon fiber ionization technologies, enabling real-time analysis of complex samples without cumbersome pretreatment. By applying this technique, a characteristic ion peak of m/z 496 is uniquely identified in Levisticum officinale, serving as a distinctive marker for differentiation of Angelica sinensis and Levisticum officinale. Subsequently, comparative analysis was conducted using sample extracts on electrospray ionization mass spectrometry (ESI-MS) and carbon fiber ionization mass spectrometry (CFI-MS). These experimental results showed that CFI-MS exhibits superior selectivity and efficiency in detecting the m/z 496 characteristic peak, which is not observable in ESI-MS analysis. This finding highlights the unique ability of carbon fiber ionization to selectively detect certain compounds. The UENRT/CFI-MS technique was applied for the direct analysis of Angelica sinensis and Levisticum officinale, and can obtain the analysis results in just a few seconds. A distinctive ion of m/z 496 is detected in Levisticum officinale, facilitating swift discrimination between Angelica sinensis and Levisticum officinale. However, further research is needed to elucidate the structure of the m/z 496 characteristic peak. Additionally, the method’s applicability to a wider range of herbal medicines and its performance in more complex matrices should be investigated. This method is expected to play a role in traditional Chinese medicine identification.