Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, 10617, Taiwan.
Chem Asian J. 2011 Nov 4;6(11):2986-91. doi: 10.1002/asia.201100445. Epub 2011 Aug 31.
High-resolution angular and velocity distributions for neutral analytes (tryptophan and poly-tryptophan) and matrix (2,4,6-trihydroxyacetophenon, THAP) are measured by using 355 nm laser desorption. The information suggests that two separate mechanisms dominate the angular and velocity distributions at the beginning and before the end of desorption. A molecular jet-like isentropic expansion dominates the plume expansion at the beginning of desorption. This only occurs at high surface temperature, thus resulting in a large velocity normal to the surface and a very narrow angular distribution. Most of the analytes are produced under these conditions. Before the end of desorption, the surface temperature decreases and the mechanism of thermal desorption at low vapor pressure takes over. The velocities become small and the angular distribution is close to cosθ. Only a very small amount of analytes are generated under these conditions. Compared to tryptophan, poly-tryptophan has a much narrower angular distribution, thereby suggesting that it is only produced at the higher surface temperatures.
利用 355nm 激光解吸技术，测量中性分析物（色氨酸和聚色氨酸）和基质（2,4,6-三羟基苯乙酮，THAP）的高分辨率角分布和速度分布。信息表明，在解吸开始和结束前，两种不同的机制主导着角分布和速度分布。分子射流状等熵膨胀在解吸开始时主导着羽流的膨胀。这种情况仅在表面温度较高时发生，从而导致垂直于表面的速度较大，角分布非常狭窄。大多数分析物在这些条件下生成。在解吸结束前，表面温度降低，低蒸气压下的热解吸机制开始发挥作用。速度变小，角分布接近 cosθ。在这些条件下仅生成很少量的分析物。与色氨酸相比，聚色氨酸的角分布要窄得多，这表明它仅在较高的表面温度下生成。
