Knochenmuss R, McCombie G, Faderl M
Novartis Institutes of Biomedical Research, 4002 Basel, Switzerland.
J Phys Chem A. 2006 Nov 30;110(47):12728-33. doi: 10.1021/jp064760t.
Thin MALDI samples can perform differently than thicker samples, on metal substrates. Divergent results and models for the effect have been presented. Positive and negative yields are investigated here for three matrixes (2,5-dihydroxybenzoic acid (DHB), sinapinic acid, and alpha-cyano 4-hydroxycinnamic acid) on stainless steel and gold substrates. Samples were electrosprayed for uniformity and thickness control and imaged across a metal-metal boundary. Thin sample enhancement is found in both polarities for all three matrixes on a steel substrate. On gold, only alpha-cyano-4-hydroxycinnamic acid shows enhancement. These and earlier data are used to evaluate two models. The first is based on one-photon photoelectron emission from the metal; the second one, on two-photon matrix ionization at the metal interface. The surface-enhanced matrix photoionization model best fits the evidence, including the fluence dependence of electron emission from DHB on steel.
在金属基底上，薄的基质辅助激光解吸电离（MALDI）样品与较厚的样品表现可能不同。关于这种效应已经有不同的结果和模型。本文研究了三种基质（2,5 - 二羟基苯甲酸（DHB）、芥子酸和α - 氰基 - 4 - 羟基肉桂酸）在不锈钢和金基底上的正离子和负离子产率。通过电喷雾使样品均匀并控制厚度，然后在金属 - 金属边界上成像。在钢基底上，所有三种基质在两种极性下均发现薄样品增强现象。在金基底上，只有α - 氰基 - 4 - 羟基肉桂酸表现出增强。利用这些以及早期的数据来评估两种模型。第一种基于金属的单光子光电子发射；第二种基于金属界面处的双光子基质电离。表面增强基质光电离模型最符合现有证据，包括DHB在钢上电子发射的fluence依赖性。
