Hadamard Transform Proton Transfer Reaction Mass Spectrometry for Real-Time Atmospheric VOC Measurements

用于实时大气 VOC 测量的 Hadamard 变换质子转移反应质谱法

• 批准号: NE/H025065/1
• 负责人: Andrew Michael Ellis
• 金额: $ 8.53万
• 依托单位: University of Leicester
• 依托单位国家: 英国
• 项目类别: Training Grant
• 财政年份: 2010
• 资助国家: 英国
• 起止时间: 2010 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FH025065%2F1
• 关键词: Hadamard; Transform; Proton; Transfer; Reaction

Trace gases in air are important indicators of the state of our environment. The ideal instrument for measuring these gases would offer high accuracy and precision, good temporal resolution, and high sensitivity. It should also be able to distinguish between the various components of a complex mixture. Proton transfer reaction mass spectrometry (PTR-MS) is a relatively new trace gas measurement technique which goes some way towards achieving the ideal qualities described above. The technique is based on chemical ionization in which a proton, usually from H3O+, is captured by a neutral molecule in the analyte gas to generate a protonated ion. Charge transfer takes place in a drift tube and the product ion(s) are subsequently detected by mass spectrometry. Only those molecules with proton affinities exceeding that of H2O can accept a proton from H3O+, a criterion that excludes the major components of air such as N2, O2 and CO2, but includes most volatile organic compounds (VOCs). This discrimination enables trace VOCs to be detected without complications from intense background signals and confers high sensitivity. A wide variety of applications of PTR-MS have already been demonstrated, including environmental gas monitoring, and the growing importance of this technique is reflected in the large and increasing number of research groups with access to PTR-MS instrumentation. Quadrupole mass spectrometry (QMS) is employed in most existing PTR-MS instruments but in the past five years several have been built that use time-of-flight mass spectrometry (TOF-MS), and indeed a commercial version has recently been marketed. TOF-MS offers several improvements over QMS, including a much higher mass resolution, a wider mass range, and the ability to collect data in all mass channels simultaneously, i.e. it is a multichannel device. However, the downside of TOF-MS is its limited duty-cycle, which arises because ions are injected into the flight tube in 'packets' which must reach the detector before the next 'packet' is injected. This gives typical duty-cycles of < 5%, which means that >95% of the potential signal is wasted. The aim of the work proposed here is to take PTR-MS to the next level, where all the advantages of TOF-MS as the mass detector are retained while solving the low duty-cycle problem. This will be achieved using a new form of TOF-MS that has been developed in the past decade, Hadamard transform TOF-MS. We will demonstrate, through laboratory-based studies and through field deployment, that a PTR-MS instrument utilising Hadamard transform TOF-MS offers important advantages over existing PTR-MS instruments for the detection of trace VOCs. The student employed on this project will adapt and refine an existing prototype instrument, will formally establish its capabilities, and will use its strengths to tackle a fundamental problem in trace gas measurement, namely to determine the extent and importance of rapid variations of VOC concentrations in the urban environment.

空气中的微量气体是我们环境状况的重要指标。测量这些气体的理想仪器应具有高准确度和精度、良好的时间分辨率和高灵敏度。它还应该能够区分复杂混合物的各种成分。质子转移反应质谱（PTR-MS）是一种相对较新的痕量气体测量技术，其在某种程度上实现了上述理想质量。该技术基于化学电离，其中质子（通常来自H3 O+）被分析物气体中的中性分子捕获以产生质子化离子。电荷转移发生在漂移管中，随后通过质谱法检测产物离子。只有那些质子亲和力超过H2O的分子才能接受来自H3 O+的质子，这一标准排除了空气中的主要成分，如N2，O2和CO2，但包括大多数挥发性有机化合物（VOC）。这种区分使痕量VOC能够被检测而不受强背景信号的影响，并赋予高灵敏度。PTR-MS的广泛应用已经得到证实，包括环境气体监测，并且这种技术日益增长的重要性反映在大量和越来越多的研究小组可以使用PTR-MS仪器。四极杆质谱（QMS）用于大多数现有的PTR-MS仪器，但在过去的五年中，已经建立了几个使用飞行时间质谱（TOF-MS）的仪器，实际上最近已经上市了商业版本。与QMS相比，TOF-MS提供了几项改进，包括更高的质量分辨率，更宽的质量范围，以及同时在所有质量通道中收集数据的能力，即它是一种多通道设备。然而，TOF-MS的缺点是其有限的占空比，这是因为离子以“包”的形式注入飞行管，这些离子必须在下一个“包”注入之前到达检测器。这给出了<5%的典型占空比，这意味着>95%的电位信号被浪费。这里提出的工作的目的是采取PTR-MS到一个新的水平，其中所有的优点TOF-MS作为质量检测器被保留，同时解决低占空比的问题。这将实现使用一种新形式的飞行时间-MS，已在过去的十年中，阿达玛变换飞行时间-MS。我们将证明，通过实验室为基础的研究和通过现场部署，一个PTR-MS仪器利用阿达玛变换飞行时间-MS提供了重要的优势，超过现有的PTR-MS仪器的痕量挥发性有机化合物的检测。该项目的学生将调整和改进现有的原型仪器，正式建立其能力，并将利用其优势来解决痕量气体测量中的一个基本问题，即确定城市环境中VOC浓度快速变化的程度和重要性。