水下质谱的特点是具有优良的一致性,特异性强,同时检测多种物质的能力,使其成为水生生态系统等研究领域的宝贵工具,热液喷口,和全球碳循环。然而,当前的水下质谱技术面临着来自高水蒸气含量的挑战,构成比例接近90%。这导致峰重叠等问题,干扰峰高,电离效率降低,因此,使其难以达到极低浓度气体的低检测限,比如甲烷,并阻碍背景CH4水平的检测。在这项研究中,我们优化了采样气路的设计,开发了高气密性,耐高压膜进气系统,再加上小体积,低功耗在线水蒸气去除系统。这种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。通过将真空度提升到1E-6Torr的量级,提高了电离效率和检测性能。基于此,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%,真空度提高了2个数量级以上。CH4的检出限从超过600nmol/L提高到0.03nmol/L,代表了超过4个数量级的改进,并达到在深海和湖泊中检测背景CH4信号的水平。此外,仪器在第二尺度上对浓度变化表现出优异的响应性和跟踪能力,能够对快速变化的浓度情景进行原位分析。
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 CH4 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 CH4 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 CH4 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.