Mass Spectrometric Detection of Lysine and Royal Demolition Explosive on Large Surfaces

Ambient ionization mass spectrometry has significantly improved the efficiency of analysis complex matrix sample due to its high sensitivity, selectivity and throughput. At present, direct ionization sources coupled with mass spectrometer including desorption electrospray ionization (DESI), real time online (DART), matrix assisted laser desorption ionization (MALDI), laser ablation electrospray ionization (LAESI), desorption atmospheric pressure chemical ionization (DAPCI), extractive electrospray ionization (EESI) etc. are applied for the direct ionization targeting molecular followed by mass spectrometer characterization. A famous ionization technique namely DESI is the most representative ambient source, which can ionization the polar compounds with bulk solid surface focused on a large number of studies on the detection methods of explosives. However, DESI in the ionization of solid explosives is needed continuous scanning and a single sampling area can not exceeding 1 cm², resulting in time consuming and inaccurate enough results. In order to further improve the analysis rate of the large surface sample and decrease the number of scanning for a given sample surface, a novel mass spectrometry method with a single scan was established for detecting trace substance distributed in large sample surface of any position. Using artificial leather surface (length of a side: 4 cm×4 cm) added lysine and royal demolition explosive (RDX) as representative detection object, the triangular metal copper electrode (length of a side: 8.6 cm) which was applied the ionization regent with methanol-water (3∶7, V/V) was closed to the sample surface, making the tip of the triangle metal copper electrode on the mass spectrometer entrance. The trace substance form into ions in triangle electrode tip towards mass spectrometry when applying +5.8 kV high voltage on the metal copper electrode. This experimental results show that the novel method with a single scan can detect randomly and non-uniform distributed on the surface of the leather sample of lysine and/or RDX at any position, providing the speed for a single sample analysis within 2 s, the limit of detection (LOD) of 6.2×10^-7 μg/cm². compared with analyzing speeding on desorption electrospray ionization mass spectrometry (single sampling area less than 1 cm²), the analyzing speed of the established method is 1000 times than DESI. Overall, this method can provide a promising analytical tool for advanced studies on monitoring of trace explosive, the identification of the food quality and the products in the import and export trade, and the pharmacokinetics of drug metabolism in vivo.