Solid-Liquid Extraction

1. Extraction of Adsorbed Organics from Soil

1. Place 20 g of soil in a clean, dry wide-mouth Pyrex dish in a 50 °C oven and dry for a minimum of 12 h. After drying, remove the soil from the Pyrex dish and grind to a uniform powder using a mortar and pestle. Weigh 5.00 g of the soil and place it into a clean, dry round-bottom flask (100 mL in size). To the flask, add 15 mL of n-hexane. Place flask in an ultrasonic bath, and sonicate for 60 min.

2. Separation of Extract and Soil

1. Prepare a Büchner funnel with analytical filter paper. Wet the filter paper with 1 mL of n-hexanes and begin vacuum filtration. Slowly pour the contents of the round-bottom flask over the filter paper. The Büchner flask now contains the n-hexanes with the organics extracted from the soil. The filter retains the stripped soil solids.

3. Clean up and Pre-concentration

1. If the n-hexane solution is cloudy, there is residual water. To dry the n-hexane solution, add one small spatula of CaCl₂. Swirl the solution and observe for a minimum of 15 min. If the solution is still cloudy and/or all of the CaCl₂ is clumped, there is still water remaining, and step 3.1 should be repeated. If the solution is translucent and the CaCl₂ is free flowing, then do not repeat step 3.1. Once a clear solution has been achieved, separate the hexanes from CaCl₂ using gravity filtration. If the extract concentration is sufficient for detection, the filtered hexanes may be transferred to a clean, dry flask for storage and later analysis. If extract concentration is low relative to the limit of detection, transfer the filtered hexanes into a clean, dry three-necked round-bottom flask, 100 mL in size. Place a rubber stopper into the center neck of the flask, and a rubber septum over one of the other necks. Leave the third neck open. Pierce the rubber septum and introduce a nitrogen flow through the flask. The nitrogen should be flowing in the space above the solution, not bubbling through the solution. The extract can now be pre-concentrated by flowing nitrogen to evaporate excess solvent. The sample is now ready for analysis.