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Portable, Solid-Phase Microextraction Low Temperature Plasma Ionization Source for Mass Spectrometry

机译：用于质谱的便携式固相微萃取低温等离子体电离源

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Mass spectrometry (MS) is an important analytical technique with high sensitivity and selectivity. However, all known MS ionization methods are significantly hindered by ion suppression that is caused by the competition for charge between analytes of interest and other species present in the sample matrix. To approach this key problem without using chromatography and/or sample preparation which can be tedious and time consuming, a portable ionization source was developed by (i) integrating solid phase microextraction with low temperature plasma MS, (ii) characterizing the extent of internal energy deposition during the ionization using novel thermometer ions, and (c) miniaturizing the plasma power source. Solid phase microextraction is directly integrated with plasma. The SPME fiber serves: (i) to extract molecules (e.g., toxins) from their native environment (e.g., urine) and (ii) as the ionization electrode that is used to desorb and ionize molecules. The SPME fiber consists of stainless steel coated with zeolitic material. Using this method, chemical warfare agent analogues can be detected at less than 100 ppb directly in water and urine in ≤ 2 min. Due to surface polarity differences, Linde Type A coating significantly outperformed the high alumina ZSM-5 coating of comparable thickness. Conversely, by conditioning the Linde Type A coated probe with aqueous CuSO4, the ion abundances can be significantly increased and sample recoveries of near 100 % were obtained. The internal energy deposition upon ion formation using three different ionization, techniques, low temperature plasma (LTP), atmospheric pressure chemical ionization (APCI), and direct analysis in real time (DART), was investigated by use of benzylammonium thermometer ions. Varying the DART ion source parameters, such as the distance between the plasma ionization region and the capillary entrance to the mass spectrometer and the DART temperature, had a minimal impact on the “softness” of the DART ion source under these conditions. Overall, LTP can be a significantly “softer” ion source than two of the most widely used plasma based ion sources that are commercially available. The key advantage of this innovation is that analyte of interest can be directly and rapidly sampled from complex mixtures, including urine, without sample preparation or chromatography for detection by MS. This ion source should prove beneficial for portable MS applications because relatively low detection limits can be obtained without the use of additional gadgets and importantly, has softer ionization. Besides, this ion source, when square-wave alternating current is utilised, generates homogeneous microdischarge, consumes 100× less power, and offers high ionization efficiency. Importantly, it was miniaturized using an H-bridge circuit, and when coupled with optimized transformer, it can be continuously powered for ~50 h by 9 V-battery (PP3).
机译：质谱（MS）是一种重要的分析技术，具有很高的灵敏度和选择性。但是，所有已知的MS电离方法都受到离子抑制的严重阻碍，离子抑制是由目标分析物与样品基质中存在的其他物质之间的电荷竞争引起的。为了不使用繁琐且费时的色谱和/或样品前处理来解决此关键问题，开发了一种便携式电离源，方法是：（i）将固相微萃取与低温等离子体MS集成在一起，（ii）表征内部能量的程度使用新型温度计离子在电离过程中进行沉积，以及（c）缩小等离子体电源的体积。固相微萃取与血浆直接整合。 SPME纤维的作用是：（i）从其自然环境（例如尿液）中提取分子（例如毒素），以及（ii）作为用于解吸和离子化分子的电离电极。 SPME纤维由涂有沸石材料的不锈钢组成。使用这种方法，可以在≤2分钟内直接在水和尿液中检测到小于100 ppb的化学战剂类似物。由于表面极性的差异，林德A型涂层明显优于具有相当厚度的高氧化铝ZSM-5涂层。相反，通过用CuSO4水溶液处理Linde A型涂层探针，可以显着提高离子丰度，并获得接近100％的样品回收率。通过使用苄基铵温度计离子，研究了使用三种不同电离技术，低温等离子体（LTP），大气压化学电离（APCI）和实时直接分析（DART）形成离子时的内部能量沉积。在这些条件下，改变DART离子源参数（例如，等离子体电离区域与质谱仪的毛细管入口之间的距离以及DART温度）对DART离子源的“柔软度”影响最小。总体而言，与市售的两种最广泛使用的基于等离子体的离子源相比，LTP可以是一种明显“更软”的离子源。这项创新的关键优势在于，可以从复杂的混合物（包括尿液）中直接，快速地对目标分析物进行采样，而无需进行样品制备或色谱法进行MS检测。这种离子源应被证明对便携式MS应用有利，因为无需使用其他小工具即可获得相对较低的检测限，而且重要的是，其离子化较软。此外，该离子源在利用方波交流电时产生均匀的微放电，消耗的功率减少了100倍，并且电离效率高。重要的是，它使用H桥电路进行了小型化，并且与优化的变压器配合使用时，可以通过9 V电池（PP3）连续供电约50小时。

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