Underwater mass spectrometry is characterized by excellent consistency, strong specificity, and the ability to simultaneously detect multiple substances, making it a valuable tool in research fields such as aquatic ecosystems, hydrothermal vents, and the global carbon cycle. Nevertheless, current underwater mass spectrometry encounters challenges stemming from the high-water vapor content, constituting proportions of nearly 90%. This results in issues such as peak overlap, interference with peak height, decreased ionization efficiency and, consequently, make it difficult to achieve low detection limits for extremely low concentrations of gases, such as methane, and impede the detection of background CH levels. In this study, we optimized the design of the sampling gas path and developed a high gas-tightness, high pressure-resistant membrane inlet system, coupled with a small-volume, low-power online water vapor removal system. This innovation efficiently eliminates water vapor while maintaining a high permeation flux of the target gases. By elevating the vacuum level to the order of 1E-6 Torr, the ionization efficiency and detection performance were improved. Based on this, we created an online water vapor removal membrane inlet mass spectrometer and conducted experimental research. Results indicated that the water removal efficiency approached 100%, and the vacuum level was elevated by more than 2 orders of magnitude. The detection limit for CH increased from over 600 nmol/L to 0.03 nmol/L, representing an improvement of over 4 orders of magnitude, and reaching the level of detecting background CH signals in deep-sea and lakes. Furthermore, the instrument exhibited excellent responsiveness and tracking capability to concentration changes on the second scale, enabling in situ analysis of rapidly changing concentration scenarios.

中文翻译：

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高灵敏度检测溶解甲烷的在线水蒸气去除膜入口质谱仪

水下质谱具有一致性好、特异性强、能够同时检测多种物质的特点，使其成为水生生态系统、热液喷口、全球碳循环等研究领域的宝贵工具。然而，目前的水下质谱分析面临着水蒸气含量高的挑战，水蒸气含量接近90%。这会导致峰重叠、峰高干扰、电离效率降低等问题，从而难以实现甲烷等极低浓度气体的低检测限，并阻碍背景 CH 水平的检测。在本研究中，我们优化了采样气路的设计，开发了高气密性、耐高压的膜进气系统，搭配小体积、低功耗的在线水蒸气去除系统。这项创新有效地消除了水蒸气，同时保持了目标气体的高渗透通量。通过将真空度提高到1E-6 Torr量级，电离效率和检测性能得到提高。在此基础上，我们创建了在线水蒸气去除膜入口质谱仪并进行了实验研究。结果表明，除水效率接近100%，真空度提高2个数量级以上。 CH的检出限从600 nmol/L以上提高到0.03 nmol/L，提高了4个以上数量级，达到了检测深海和湖泊背景CH信号的水平。此外，该仪器对第二尺度的浓度变化表现出出色的响应能力和跟踪能力，能够对快速变化的浓度场景进行原位分析。