Pressurized Liquid Extraction of Soil Samples for the Analysis of Diesel Range Organics by GC–FID

Diesel range organics or DRO is the cumulative analysis of extractable alkanes between the ranges C10 through C28 as measured on a flame ionization detector. Within this range, specific fuel oil identifications are possible through pattern or "finger print" matching. Not regulated under RCRA, various individual US state methods exist, many expanding analysis to the oil range organics (ORO) or C25–C35.

The following application note focuses on the DRO constituents which due to their increased volatility, can pose greater analytical difficulties than the OROs. The approach of pressurize liquid extraction paired with a gentle evaporation at low temperatures was chosen for optimal recoveries.

Equipment

• FMS, Inc. PLE system

• FMS, Inc. SuperVap® Concentrator

• FMS, Inc. concentrator tubes

• Agilent 7890 GC with FID detector

Consumables

• Fisher Optima* Methylene Chloride

• Agilent Hydromatrix®

• Restek Ottawa Sand

• Aliphatic HC standard (1000 μg/mL)

• O-Terphenyl Standard (2000 μg/mL)

• Diesel Reference Material

Sample Prep

1. 9 × 10 g samples were weighed out of both Ottawa sand and soil matrices

2. All samples spiked with O-terphenyl surrogate solution.

3. 5 replicates of each matrix were spiked with Aliphatic HC solution.

4. 3 replicates of each matrix were spiked with diesel reference material.

5. Samples mixed with Hydromatrix® and transferred to 40 mL extraction cells.

Figure 1: FMS Inc. PLE w/SuperVap®.

PLE Procedure

Cells loaded onto PLE extraction system and DRO program initiated.

Solvent: Methylene Chloride

Extraction Temp.: 150 °C

Extraction Time 15 min

Flush volume: 2 × cell volume

N₂ Purge: 1 min

SuperVap

1. Preheat temp: 10 min at 35 °C

2. Evap. mode w/sensor temp: 35 °C

3. Nitrogen Pressure: 5 psi

4. Samples reduced to 1 mL

5. Samples reduced to 1 mL final volume

Results

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Conclusions

Analysis of aliphatic hydrocarbon spikes showed good DRO range recoveries for both sand and soil matrices, with all individual alkanes in the C10–C28 range recovering within 70–130%. Blank analysis not only yielded good recovery for OTP, but no detectable DRO range was measured. Lastly the analysis of a diesel reference material resulted in calculated concentrations very close to the known reference amount (within 20% for both matrices).

FMS, Inc.
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Website: www.fms-inc.com