Novel Laser-Assisted Electrospray Ionization Mass Spectrometry (Laser-Assisted ESI-MS): A Sensitive Method for...

Efficient ionization is essential for sensitive mass spectrometry (MS) analysis. Herein, a novel laser-assisted electrospray ionization (laser-assisted ESI) source was developed to efficiently ionize low-polar and thermal unstable compounds. By irradiating the electrospray nozzle with a simple and low-cost laser probe (450 nm, 500 mW), the sample droplets were stimulated with a laser beam as well as the high voltage of the electrospray, which significantly enhanced the ionization efficiency. In positive ionization mode, by further utilizing the reaction of Ag⁺ and tetrabromobisphenol A bis(allyl ether) (TBBPA-BAE), the established laser-assisted ESI strategy was able to efficiently ionize the low-polar and thermal unstable TBBPA-BAE. Specifically, a limit of detection (LOD) of 14 ng L^-1, linear range of 0.1-10 μg L^-1 (R² > 0.99), and relative standard deviations (RSDs) of 2.5% (n = 7, intraday) and 6.2% (n = 3 per day for 5 days, interday) were achieved. In negative ionization mode, laser-assisted ESI also improved the detection sensitivity of tetrabromobisphenol A (TBBPA), achieving a LOD of 3.3 ng L^-1, linear range of 0.01-10 μg L^-1 (R² > 0.99), and RSDs of 4.7% (n = 7, intraday) and 7.3% (n = 3 per day for 5 days, interday). Compared to extractive electrospray ionization mass spectrometry (EESI-MS) and ESI-MS, the LODs achieved with laser-assisted ESI-MS were 54 and 16 times lower for the detection of TBBPA-BAE and TBBPA, respectively. Notably, deep purification and preconcentration were not required to accurately detect TBBPA and TBBPA-BAE in river water and wastewater treatment plant effluent. The spiked recoveries were between 88.0% and 106.0%, demonstrating the high reliability and practicality of this method.