Mochalski Paweł, Unterkofler Karl, Španěl Patrik, Smith David, Amann Anton
Breath Research Institute of the University of Innsbruck, Rathausplatz 4, A-6850, Dornbirn, Austria.
Rapid Commun Mass Spectrom. 2014 Aug 15;28(15):1683-90. doi: 10.1002/rcm.6947.
The reactions of NO(+) with volatile organic compounds (VOCs) in Selective Reagent Ionization Time-of-Flight Mass Spectrometry (SRI-TOF-MS) reactors are relatively poorly known, inhibiting their use for trace gas analysis. The rationale for this product ion distribution study was to identify the major product ions of the reactions of NO(+) ions with 13 organosulfur compounds and 2 organoselenium compounds in an SRI-TOF-MS instrument and thus to prepare the way for their analysis in exhaled breath, in skin emanations and in the headspace of urine, blood and cell and bacterial cultures.
Product ion distributions have been investigated by a SRI-TOF-MS instrument at an E/N in the drift tube reactor of 130 Td for both dry air and humid air (4.9% absolute humidity) used as the matrix gas. The investigated species were five monosulfides (dimethyl sulfide, ethyl methyl sulfide, methyl propyl sulfide, allyl methyl sulfide and methyl 5-methyl-2-furyl sulfide), dimethyl disulfide, dimethyl trisulfide, thiophene, 2-methylthiophene, 3-methylthiophene, methanethiol, allyl isothiocyanate, dimethyl sulfoxide, and two selenium compounds - dimethyl selenide and dimethyl diselenide.
Charge transfer was seen to be the dominant reaction mechanism in all reactions under study forming the M(+) cations. For methanethiol and allyl isothiocyanate significant fractions were also observed of the stable adduct ions NO(+) M, formed by ion-molecule association, and M-H ions, formed by hydride ion transfer. Several other minor product channels are seen for most reactions indicating that the nascent excited intermediate (NOM)(+) * adduct ions partially fragment along other channels, most commonly by the elimination of neutral CH3 , CH4 and/or C2 H4 species that are probably bound to an NO molecule. Humidity had little effect on the product ion distributions.
The findings of this study are of particular importance for data interpretation in studies of volatile organosulfur and volatile organoselenium compounds employing SRI-TOF-MS in the NO(+) mode.
在选择反应离子化飞行时间质谱（SRI-TOF-MS）反应器中，NO(+)与挥发性有机化合物（VOCs）的反应相对鲜为人知，这限制了它们在痕量气体分析中的应用。这项产物离子分布研究的目的是确定在SRI-TOF-MS仪器中NO(+)离子与13种有机硫化合物和2种有机硒化合物反应的主要产物离子，从而为在呼出气体、皮肤散发物以及尿液、血液、细胞和细菌培养物的顶空中对它们进行分析铺平道路。
使用SRI-TOF-MS仪器，在漂移管反应器中E/N为130 Td的条件下，以干燥空气和潮湿空气（绝对湿度4.9%）作为基质气体，研究了产物离子分布。所研究的物质包括五种单硫化物（二甲基硫醚、甲乙硫醚、甲丙硫醚、烯丙基甲硫醚和甲基5-甲基-2-呋喃基硫醚）、二甲基二硫醚、二甲基三硫醚、噻吩、2-甲基噻吩、3-甲基噻吩、甲硫醇、烯丙基异硫氰酸酯、二甲基亚砜，以及两种硒化合物——二甲基硒和二甲基二硒。
在所有研究的反应中，电荷转移被视为形成M(+)阳离子的主要反应机制。对于甲硫醇和烯丙基异硫氰酸酯，还观察到了相当一部分由离子-分子缔合形成的稳定加合离子NO(+) M，以及由氢负离子转移形成的M-H离子。大多数反应还出现了其他一些次要的产物通道，这表明新生的激发中间体（NOM）(+) *加合离子会沿着其他通道部分裂解，最常见的是通过消除可能与NO分子结合的中性CH3、CH4和/或C2 H4物种。湿度对产物离子分布影响不大。
本研究结果对于采用NO(+)模式的SRI-TOF-MS对挥发性有机硫和挥发性有机硒化合物进行研究的数据解释尤为重要。
