Rapid screening of glycoalkaloids in Solanum scabrum and S. nigrum berries using ultra-high performance liquid chromatography with pathway-specified in-source fragmentation tandem mass spectrometry

Rationale: The safe consumption of Solanum scabrum and S. nigrum berries (SNBs) depends upon a reliable and rapid chemical screen for the testing of the fruit and/or final food and industrial products for the presence and level of toxic glycoalkaloids. Such a rapid and sensitive screen could also be used by those involved in food safety and forensics, industry, research labs and those in agriculture production, breeding and food processing. Significant variation in glycoalkaloids content and composition across SNBs has been reported. To facilitate high-throughput targeted analysis, this work overcame the slow scan speed of a traditional triple quadruple mass spectrometry (QqQ) method by development of a pseudo-MS³ method.

Methods: In-source fragmentation functioned as a pseudo-MS or pseudo-hydrolysis to trim down the structurally diverse and complex glycosides into five types of aglycone ions, which were then analyzed using multiple reaction monitoring (MRM). Characteristic product ions were selected based upon aglycone skeleton and substitution pattern and associated fragmentation pathway.

Results: A compact method with only 15 MRM transitions were developed for high-throughput screening of very diverse glycoalkaloids. Glycosides of the same aglycone type were readily identified in the same transition window without need for mass spectra interpretation. Validated using solamargine, the sole available standard, the accuracy was 99.7~101.3%, the intra- and inter-day precision was, respectively, 2.5~5.0% and 8.0~9.2%, and the lower limit of detection and quantification was, respectively, 3.1 and 10.2 ng/mL (with 1 μL injection volume).

Conclusions: The peudo-MS³ method allowed for high-throughput targeted analysis with compact MRMs to address a large number of glycoalkaloids with diverse structures. This method could serve to meet the most heavy-duty demand for rapid inspection of SNBs glycoalkaloids. This method can be adopted and used by those involved in food safety and forensics, in developing food and industrial products and in genetics and breeding.