Delineation of background laboratory contamination in the analysis of trace concentrations of extractable organic materials in crystalline rocks by Soxhlet extraction, column chromotography, and gas chromatography

Abstract

Contamination checks were carried out for sample preparation, Soxhlet extraction and the subsequent analyses of extracted bitumen, from high-grade metamorphic and igneous rocks, carbonaceous rocks from ore deposits, and other crystalline rocks. We examined possible contamination from solvents, laboratory apparatus, and from most of the analytical steps of the total procedure. The results of our examination were as follows: Once-distilled dichloromethane, twice distilled hexane, twice distilled benzene, and HPLC-grade methanol were pure enough to be used as solvents. No contaminants were leached from the septa of the cone vials used for the automated sampler on our gas chromatograph by hexane, benzene, or dichloromethane. Activated copper strips (used to remove sulfur during extraction) did not produce organic contamination by reacting with dichloromethane. However, new copper strips had to be rinsed with dichloromethane before their use, because the copper strips had a surficial wax coating from their manufacture. Saturated and aromatic hydrocarbon (HC) fractions from blank alumina/silica-gel column chromatography had only negligible peaks. Glass bottles with foil-lined caps should always be used for sample storage, because of possible wax contamination from cardboard products. Obviously, if samples are to be cut with a saw, it should be done in a pre-cleaned water-based system.We compared the saturated-and aromatic-HC and resin gas chromatograms from a mantle xenolith to those from a blank procedural check, to determine indigenous organic materials in the mantle xenolith. This comparison demonstrated that we can quantitatively and qualitatively analyze organic materials at very low concentrations (0.1 to 0.5 ppm total bitumen by weight). This comparison also demonstrated that the contaminates in the saturated-and aromatic-HC fractions are negligible. Thus, as demonstrated by the results herein, our Soxhlet extraction procedure has been optimized for analysis of small concentrations of exotic indigenous organic compounds in very high-rank crystalline rocks.

Sulfur Species in Source Rock Bitumen before and after Hydrous Pyrolysis Determined by X-ray Absorption Near-Edge Structure

“…Upon passing the leak check, helium pressure was reduced to approximately 25 psia and the reactors were weighed and placed in an electric heater. The loaded reactors were heated from room temperature (∼20 °C) to 360 °C within 1 h (heating rate of ∼6 °C/min) and held at that temperature for 72 h. This treatment typically results in thermal maturities consistent with maximum oil generation . Afterward, the reactors were removed from their heaters and allowed to cool to room temperature overnight.…”

“…The loaded reactors were heated from room temperature (∼20 °C) to 360 °C within 1 h (heating rate of ∼6 °C/min) and held at that temperature for 72 h. This treatment typically results in thermal maturities consistent with maximum oil generation. 24 Afterward, the reactors were removed from their heaters and allowed to cool to room temperature overnight. Once cooled, the reactors were weighed to determine mass loss (a small decrease in mass of approximately 0.3 g is expected as a result of burn off of an anti-seize compound used on the compression bolts), reactor temperature and pressure were measured, and gas samples were collected using Swagelok stainless-steel cylinders.…”