Supercritical CO2 and Subcritical H2O Analysis (SCHAN) Instru-ment: Automated Lipid Analysis for in-situ Planetary Life Detection

The search for extraterrestrial extant or extinct life in our Solar System will require more capable instrumentation and methods for detecting low abundances of biosignatures. This paper introduces the Supercritical CO2 and Subcritical H2O Analysis (SCHAN) instrument, a portable and automated system that integrates supercritical fluid extraction (SFE), supercritical fluid chromatog-raphy (SFC), and subcritical water extraction coupled with liquid chromatography. The instrument is compact, weighing 6.2 kg, making it suitable for spaceflight missions to planetary bodies. Traditional techniques, such as gas chromatography–mass spec-trometry (MS), face challenges with involatile and thermally labile analytes, necessitating derivatization. The SCHAN instrument, however, eliminates the need for derivatization and co-solvents by utilizing neat supercritical CO2 with water as an additive. This SFE-SFC-MS method gives efficient lipid biosignature separations with median detection limits of 10 pg/g (ppt) for fatty acids and 50 pg/g (ppt) for sterols. Several free fatty acids and cholesterol were detected in biologically lean samples from the Atacama Desert, demonstrating the instrument's potential for in-situ life detection missions. The SCHAN instrument addresses the chal-lenges of conventional systems, offering a compact, portable, and spaceflight-compatible tool for the analysis of biosignatures such as lipids.在太阳系内搜寻地外现存或已灭绝生命，需要更先进的仪器与检测方法，以实现低丰度生物标志物（biosignatures）的检出。本文介绍了超临界CO₂与亚临界H₂O分析（Supercritical CO2 and Subcritical H2O Analysis, SCHAN）仪器——一款集成超临界流体萃取（supercritical fluid extraction, SFE）、超临界流体色谱（supercritical fluid chromatography, SFC）以及亚临界水萃取-液相色谱联用技术的便携自动化系统。该仪器结构紧凑，重量仅6.2 kg，适用于行星天体的航天探测任务。传统分析技术（如气相色谱-质谱联用法（gas chromatography–mass spectrometry, GC-MS））在处理非挥发性与热不稳定分析物时存在局限，需进行衍生化预处理。而SCHAN仪器无需衍生化步骤与助溶剂，仅需使用以水作为添加剂的纯超临界CO₂即可完成分析。该SFE-SFC-MS方法可实现高效的脂质生物标志物分离，对脂肪酸的检出限中位数为10 pg/g（ppt），对固醇的检出限中位数为50 pg/g（ppt）。研究团队在阿塔卡马沙漠的贫生物样本中检测到多种游离脂肪酸与胆固醇，证实了该仪器可用于原位生命探测任务。SCHAN仪器解决了传统系统的技术瓶颈，为脂质等生物标志物的分析提供了一款紧凑便携、适配航天任务的专用分析工具。