RATIONALE Monitoring of isomeric analytes using mass spectrometry usually requires a time-consuming chromatographic separation of the analytes before analysis. Selected ion flow tube mass spectrometry (SIFT-MS) can provide rapid direct analysis of ethylbenzene and xylene by utilizing the different reaction chemistry of the isomers. O2 + yields the same product ions from each isomer but in different ratios. OH- yields different product ions. METHODS The reaction chemistry of C8 H10 with the reagent ion OH- generated from a microwave discharge of moist air in a commercial SIFT-MS instrument was utilized in this study. The product ion from OH- yielded ions at different masses for each isomer. To gain an understanding of how the product ion from ethylbenzene of HO2 - was generated, a theoretical study of the potential reaction surface was undertaken that accounted for the experimental observations. RESULTS Measurements of OH- with ethylbenzene showed the product ion to be HO2 - at m/z 33. The reaction of OH- with xylene yielded the major product ion at m/z 105, C8 H9 - . HO2 - also underwent a slow secondary reaction with CO2 and O2 present from air in the samples. These findings were supported by calculations of the potential energy surface for the reactions. Measurements made on a certified gas mixture of ethylbenzene and xylene in the concentration range up to 5000 ppbv gave a linear response for each analyte. CONCLUSIONS A fast, efficient method was developed for monitoring xylene and ethylbenzene in a mixture without the need for chromatographic separation before analysis using SIFT-MS.

中文翻译：

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使用选定的离子流管质谱仪实时区分乙苯和二甲苯。

理由使用质谱监测异构分析物通常需要在分析之前进行费时的色谱分离。通过利用异构体的不同反应化学，选定的离子流管质谱（SIFT-MS）可以提供乙苯和二甲苯的快速直接分析。O2 +从每个异构体产生相同的产物离子，但比率不同。OH-产生不同的产物离子。方法本研究利用C8 H10与在商用SIFT-MS仪器中从潮湿空气的微波排放中产生的试剂离子OH-的反应化学。对于每种异构体，由OH生成的离子以不同的质量产生离子。为了了解如何生成HO2的乙苯产物离子，进行了对潜在反应表面的理论研究，该理论解释了实验观察结果。结果OH-与乙苯的测量结果表明，产物离子在m / z 33处为HO2-。OH-与二甲苯的反应在m / z 105处生成了主要的产物离子C8 H9-。HO2-还与样品中空气中存在的CO2和O2进行了缓慢的次级反应。这些发现得到了反应势能面的计算的支持。在浓度范围高达5000 ppbv的乙苯和二甲苯的认证气体混合物上进行的测量给出了每种分析物的线性响应。结论开发了一种快速，有效的方法，用于监测混合物中的二甲苯和乙苯，而无需使用SIFT-MS进行色谱分离。