Improved detection sensitivity of elements in solids via laser postionization in laser desorption time-of-flight mass spectrometry.

A newly constructed laser desorption (532 nm, 5 ns) and laser postionization (266 nm, 5 ns) time-of-flight mass spectrometer (LD-LPI-TOFMS) has been applied for improving the detection sensitivity of elements in solid samples. This method affords to acquire the information of the elemental impurities in solid standards as well as limit of detection (LOD) down to 10-8  g/g for some elements. Neutral atoms of solids are generated by low-irradiance laser desorption (< 108  W/cm2 ), followed by high-irradiance laser postionization (~ 109  W/cm2 ) of the desorbed atoms, facilitating to decouple the desorption and ionization processes in spatial and temporal domain. This non-interacting feature overcomes the discrimination between deteriorating spectral resolution at high irradiance (109 -1011  W/cm2 ) and limited detectable elemental species and high LOD at low or medium irradiance (below 109  W/cm2 ). The utilization of originally "wasted" neutral atoms by laser postionization will help improve atom utilization and instrumental sensitivity. In this work, getting the utmost out of the consumed neutral atoms instead of an increment in sampling amounts is given attention with high priority for achieving high sensitivity and low LOD, which is especially useful on the occasions where very low sample consumption is desired.