Method Development and Quality Assurance for the Analysis of Hydrocarbons In Environmental Samples

Abstract

Extraction procedures for the analysis of hydrocarbons at the trace level in marine sediment samples were compared in terms of trueness and precision. Three extraction techniques—ultrasonic bath, mechanical shaker and Soxhlet—and three solvents—hexane, 1,1.2 trichloro-trifluoroethane (Freon-113) and dichloromethane (CH₂Cl₂)—were used. Extracts were analyzed by synchronous scanning fluorescence spectrography (SSFS); high-performance liquid chromatography (HPLC) on NH₂ normal-phase columns with UV and fluorescence detectors, gas chromatography on fused-silica capillary columns (GC) with flame ionization detector (FID), and high-resolution molecular spectrofluorimetry in Shpol'skii matrix at 10 K (HRMSS). The more effective parameter for recovery efficiency proved to be the solvent selection. Hexane and freon-113 were found of very low efficiency for sediment samples. Soxhlet washing and mechanical shaking with CH₂Cl₂ on freeze-dried sediment gave the best recoveries. Precisions (repeatability and reproducibility) found for total hydrocarbon determination after both extraction methods varied from 2% up to 18%, mostly depending on the proficiency of the analyst. Mechanical extraction after acidic treatment of the freeze-dried sediment gave the more accurate GC-FID profiles. Repeatabilities of this technique as determined on the total saturated and aromatic fractions by GC-FID and HPLC-fluorescence measurements were 7% and 12% respectively. This was selected as the more convenient method. A biota sample (oysters) was extracted by mechanical extraction while using a CH₃OH:CH₂Cl₂ (2:3) solvent mixture; GC-FID and HPLC-fluorescence measurements showed good precision, 8% and 6% for the total saturated and aromatic fractions respectively. A standard research material (SRM-1649—urban dust/organics) was analyzed by HRMSS and HPLC after mechanical extraction, and results were in good agreement with certified values.

Key Words:

• Extraction
• marine sediments
• oysters
• hydrocarbons
• quality assurance