Sensitivity improvement of ambient mass spectrometry using a continuous wave infrared laser

Due to its easy operation and deployment by removing a vacuum system, ambient mass spectrometry has gradually drawn more and more attention. However, the convenience also results in a considerable sensitivity downgrade. To improve sensitivity of the ambient mass spectrometry, a laser-assisted direct-analysis-in-real-time (DART) time-of-flight mass spectrometer (LA-DART-MS) was developed by integrating a continuous wave (CW) infrared (IR) laser into a conventional DART-MS in this work. The CW IR laser (with central wavelength of 1070 nm) was used to assist the desorption of analytes and promote the reactivity of protonated water from the DART ion source. Using the LA-DART-MS, signal-to-noise ratios (SNRs) of Rhodamine 6G (R6G) and its major fragmentation by losing a C₂H₄ moiety are enhanced by factors of 4 and 6.7, respectively, compared with those from a conventional DART-MS. To demonstrate the capability of the LA-DART-MS technique, urine and testosterone are investigated and the SNRs are enhanced by factors of 10.7 and 4.3, respectively. The experimental results show that the sensitivity enhancement is ascribed to the increased analyte concentration in air and activated protonated water induced by the IR laser irradiation through OH bending vibration.