Online supercritical fluid extraction and chromatography of biomarkers analysis in aqueous samples for in situ planetary applications.

Sensitive and robust in situ chemical analysis of organic biomarkers is essential in the endeavor of finding chemical signatures of life either extinct or extant on our solar system bodies such as Europa, Enceladus, or Titan. Development of new analytical instruments and accompanying methodologies are needed, especially those that are compatible with unknown and diverse samples potentially found on solar system targets and that avoid complexities involved with other wet chemistry techniques (desalting, derivatization and contamination issues, etc.). In this study, we demonstrate that online supercritical fluid extraction and supercritical fluid chromatography with water-saturated CO2 can extract and separate nonpolar analytes of astrobiological interest, such as free fatty acids, polycyclic aromatic hydrocarbons, and polycyclic aromatic compounds containing nitrogen or sulfur. Silica was used as a support material to immobilize aqueous samples during extraction. A C18 stationary phase with an embedded polar functional group and efficient end-capping in combination with water in the mobile phase allowed efficient separation of both free fatty acids and basic compounds. The total analysis time was 30 min, including extraction, equilibration, and separation. Detection was performed with a UV detector and a quadrupole mass spectrometer equipped with electrospray ionization. The method was validated in terms of lower detection limits (0.02-40 μg/L), precision (repeatability 3-13%), relative standard deviation (RSD), intermediate precision 4-26% (RSD), trueness (bias ranging from - 48 to 9%), and retention time shifts (< 2% RSD) for 16 analytes in sample matrices with sodium chloride and magnesium sulfate that may be present in ocean worlds such as Europa or Enceladus. Graphical Abstract.