Application of miniaturized open-column chromatography in geochemical characterization of crude oil

Between January 2025 and February 2026, 53,854 incidents were reported in Brazil across the oil and gas sector¹. In this context, traditional analytical strategies can become challenging due to the limited availability of samples, especially when considering affected animals². Moreover, environmental exposure promotes oil weathering processes that can further complicate geochemical characterization and forensic investigations. To address these limitations, this study proposes a miniaturized chromatographic method aimed at maintaining analytical performance while significantly reducing sample requirements. The study was conducted using a pre-salt oil, collected from a platform in Campos Basin, provided by the Brazilian Institute of Environment and Renewable Natural Resources (IBAMA), through a collaboration agreement. Initially, maltenes were obtained from the oil by extraction with hexane and a 5-minute centrifugation at 2000 rpm. The method was developed in triplicate using a Pasteur pipette filled with 1 g of silica gel, in which 25 and 10 mg of maltene with 11 surrogate standards were eluted with volumes of 2 mL and 3 mL of extraction solvents. The fractions of saturated and aromatic compounds were analyzed using gas chromatography-tandem mass spectrometry system TSQ 9010 (ThermoFisher Scientific). The column was a TG5-MS (30 m x 0.25 mm x 0.25 µm), and the oven was programmed at 70 °C, ramped at 20 °C min^-1 to 170 °C and at 2 °C min^-1 to 310 °C and held for 10 min. The analyses were conducted in scan mode and data treatment was performed with the software Xcalibur. Tetracyclic terpenes (m/z 191), steranes (m/z 217, 218, 257), diasteranes (m/z 259), and hopanes (m/z 191, 205, 369) were detected in saturated fraction; and benzohopanes (m/z 191), triaromatic steroids (m/z 231, 245) in aromatic fraction. Parameters of biodegradation, such as the geochemical ratio between 25,28,30-tris-norhopane (25,28,30-TNH) and 29-hopane (H29) indicated a non-biodegraded oil. Ratios among steranes, such as C29/(C27+ C28) and among hopanes, like 18α(H)-22,29,30-trisnorneohopane (Ts)/ Ts + 17α(H)-22,29,30-trisnorhopane (Tm), suggest low thermal maturity in the analyzed oil. The origin parameters, related to terpanes, hopanes, and diasteranes, including the ratio between C30 tetracyclic polyprenoid (TPP) and C27 (R+S) sterane, indicate a saline lacustrine depositional environment. The proposed miniaturized method enabled the detection and identification of all target biomarkers and yielded the same geochemical parameters as the traditional method, which uses 50 mg of maltene³. Miniaturization reduced sample preparation time by about 70 % and elution solvent consumption by 80 %. Therefore, the proposed method represents a more resource-efficient alternative, reducing solvent consumption and sample requirements in alignment with the principles of green analytical chemistry, without compromising the geochemical information obtained from conventional procedures.