At the completion of the extraction procedure, no sample clean-up procedures were performed and the extraction solvent was concentrated, unless gross oil contamination was observed, to a final volume of 1–2 ml using rotary evaporation and blow-down with nitrogen gas. The QC/MS was set up for detection limits of 1 ppb in sample extracts and was typically linear over four or five orders of magnitude.
If samples contained large amounts of oil, as seen by particularly dark color of the methylene chloride extracts, then they were diluted as appropriate to bring the amount injected into the calibration range. The samples were analyzed by GC/MS-SIM to quantify the target petrogenic hydrocarbons, including the normal and branched saturated hydrocarbons (from nC10 to nC35, pristane and phytane), the two- to six-ringed PAHs and their respective C1 to C3 or C4 alkyl click here homologs (Table 2). Ion chromatograms for the hopanes, steranes, and triaromatic steroids biomarker compounds were acquired using ions 191, 217, 218, and 231). All GC/MS-SIM analyses used a Agilent 7890A GC system configured with a 5% diphenyl/95%
dimethyl polysiloxane high-resolution capillary column (30 m, 0.25 mm ID, 0.25 μm film) directly interfaced to an Agilent 5975 inert XL MS detector system. The GC flow rates were optimized to provide the required degree of separation, with particular attention given to nC17 and pristane which should be near-baseline resolved. An Agilent 7683B series injector was used in splitless mode to inject 1 μL of sample into check details the GC/MS system. The GC injection temperature was set at 280 °C and only high-temperature,
low thermal-bleed septa were used in the GC inlet. The GC was operated in temperature program mode http://www.selleck.co.jp/products/tenofovir-alafenamide-gs-7340.html with an initial column temperature of 60 °C for 3 min, and then increased to 280 °C at a rate of 5 °C min−1 and held for 3 min. The oven was then heated from 280 °C to 300 °C at a rate of 1.5 °C min−1 and held at 300 °C for 2 min. The total run time was 65.33 min per sample. The interface to the MS was maintained at 300 °C. The MS was operated in the Selective Ion Monitoring (SIM) mode to ensure low level detection of the target constituents associated with crude oil in sediment samples. The MS was tuned to PFTBA (perfluorotributylamine) before each set of analyses. If any of the tune parameters (e.g., percent air/water, peak abundances and ratios) were significantly different from prior tune parameter values, then the instrument was checked for error-causing problems (e.g., air leaks, worn septum, dirty liner, etc.) and then returned to normal operating conditions. Internal standards were added to the sample extracts just before the GC/MS-SIM analysis. The internal standard mix included naphthalene-d8, acenaphthalene-d10, chrysene-d12, and perylene-d12 (AccuStandard, Inc., New Haven, CT).