APPI-MS: Effects of mobile phases and VUV lamps on the detection of PAH compounds
APPI-MS: Effects of mobile phases and VUV lamps on the detection of PAH compounds
复制标题
DOI：
10.1016/j.jasms.2006.11.004
复制
发表时间：
2007-04-01
影响因子：
3.2
通讯作者：
Syage, Jack A.
中科院分区：
文献类型：
--
作者：
Short, Luke Chandler;Cai, Sheng-Suan;Syage, Jack A.
与电喷雾电离（ESI）和常压化学电离（APCI）技术相比，常压光电离（APPI）技术具有非极性或低电荷亲和化合物的高效电离、对离子抑制的敏感性低、灵敏度高、线性动态范围大等优点。这些好处在低流速（即< 100 μ L/min）下最大，而在高流速下，光子吸收和离子-分子反应变得显著。在某些情况下，APPI信号和S/N在高流量下表现优异，这可能是由于非光离机制。为了更好地了解高流速下的APPI，我们选择了三种灯（Xe， Kr和Ar）和四种典型的反相高压液相色谱流动相：乙腈，甲醇，（1:1）乙腈：水和（1:1）甲醇：水。以苯并[a]芘、茚并[1,2,3-c， d]芘和苯并[a]蒽为试验化合物进行了研究。我们发现溶剂光吸收截面不是解释相对信号强度的唯一参数，溶剂光离子化学也可以发挥重要作用。本研究的三个结论是：(1)甲醇光电离导致质子化的甲醇团簇，可以导致分析物分子的化学电离；(2)使用Ar灯往往会产生更大的信号和信噪比；(3)乙腈光电离效率较低，产生的团簇结合太强，无法有效地化学电离分析物，因此分析物离子的形成主要是直接光电离。
The technique of atmospheric pressure photoionization (APPI) has several advantages over electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI), including efficient ionization of nonpolar or low charge affinity compounds, reduced susceptibility to ion suppression, high sensitivity, and large linear dynamic range. These benefits are greatest at low flow rates (i.e.,< 100 mu L/min), while at a higher flow, photon absorption and ion-molecule reactions become significant. Under certain circumstances, APPI signal and S/N have been observed to excel at higher flow, which may be due to a nonphotoionzation mechanism. To better understand APPI at higher flow rates, we have selected three lamps (Xe, Kr, and Ar) and four mobile phases typical for reverse-phase, high-pressure liquid chromatography: acetonitrile, methanol, (1:1) acetonitrile:water and (1:1) methanol:water. As test compounds, three polyaromatic hydrocarbons are studied: benzo[a]pyrene, indeno[1,2,3-c, d]pyrene and benz[a]anthracene. We find that solvent photoabsorption cross-section is not the only parameter in explaining relative signal intensity, but that solvent photo-ion chemistry can also play a significant role. Three conclusions from this investigation are: (1) methanol photoionization leads to protonated methanol clusters that can result in chemical ionization of analyte molecule; (2) use of the Ar lamp often results in greater signal and S/N; (3) acetonitrile photoionization is less efficient and resulting clusters are too strongly bound to chemically ionize the analyte efficiently, so that analyte ion formation is dominated by direct photoionization.