Analysis of Samples from the Gulf of Mexico Oil Spill by GCxGC-TOFMS - Leco Corporation

Two petroleum samples from the Gulf of Mexico Oil Spill were obtained: a Well Head Source Oil sample and a sample of Red Mousse. The Well Head Source Oil sample was collected by a Remotely Operated Vehicle (ROV) at the initial leaks in the damaged riser pipe. The Red Mousse sample was collected on the surface in the offshore marine environment. It had not been exposed to the surf zone.
The samples provided had already been diluted in dichloromethane and had internal standards added prior to shipment to the lab for GCxGCTOFMS analysis.

This analysis took advantage of a new feature allowing the analyst to vary the modulation period and hot pulse duration during an acquisition. Leco would like to take this opportunity to thank Professor Ed Overton for providing the samples analysed in this project.

Instruments and Methods
In this study, measurements were made with a Leco Pegasus 4D GCxGC-TOFMS system. It was equipped with a Gerstel MPS2 rail-type auto sampler. Data collection and work-up were performed using ChromaTOF version 4.30.

For this study, the primary analytical column was a 30.0m x 0.25mm ID x 0.25μm df Rtx-5SilMS. The secondary column was a 1.50 m x 0.10mm ID x 0.10μm df BPX-50. The temperature program started at 45°C with a 3 minute hold, and then ramped at 5°C/min to 340°C with a final hold of 15 minutes. The column offset was +5°C with a +20°C modulator offset. Variable modulation period and hot pulse durations were utilised. From time 0 seconds to 1280 seconds, a 3 second modulation period with a 500ms hot pulse was utilised. From time 1280 seconds to 2044 seconds, a 4 seconds modulation period with a 600ms hot pulse was utilised. From time 2044 seconds to 2999 seconds, a 5 seconds modulation period with a 800ms hot pulse was utilised. From time 2999 seconds to the end of the analysis, a 5 seconds modulation period with a 1000 ms hot pulse was utilised.

Acquired data was saved for a range from 45 to 400 m/z at 200 spectra/seconds. Helium was used as the carrier gas at a corrected constant flow of 1.0mL/min. A split/splitless inlet, operated in split mode, was used for sample introduction. The inlet was maintained isothermally at 280°C. An injection size of 1.0μL was used for each analysis. The Well Head Source Oil was analysed with a split ratio of 200:1. The Red Mousse sample was analysed with a split ratio of 50:1.