Emulsion breakingtechniques for oil in water solvent extractions


Courtesy of Spectro Scientific

Certain types of samples, such as those containing detergent, may form emulsions when doing an oil in water extraction into a solvent. The boundary between the solvent and the sample will have an emulsion layer that lias a cloudy or milky appearance as shown in tlris photo. According to U.S. EPA Method 1664, 'if the emulsion is greater than one-third the volume of the solvent layer. Hie laboratory must employ emulsion-breaking techniques to complete the phase separation'. Tins is relevant to all oil in water measurements that use liquid-liquid extraction whether the analysis is done by infrared, gravimetric or UV. If such an emulsion cannot be broken by any attempted means, the test method may not give representative results for the problem sample.  The best way to break or reduce (lie emulsion depends on the sample matrix.

The following list includes some options that may be useful for reducing the emulsion enough to be able to take a valid measurement.

1. Let die sample sit. The easiest is to allow the sample to sit for tip to an hour and see if the emulsion decreases. Make sure the sample is covered to reduce any evaporation of tlie solvent. Gently taping the side of the container or stirring the solvent and emulsion layer with a stir bar can help to speed tip the separation.

2.Acidify the sample. If the emulsion is due to an alkali soap, detergent or surfactant then lower the pH to 2 with sulfuric acid, H2SO4, or hydrochloric acid, HC1, (as recommended in die oil and grease methods, mainly for preservation of die sample) will modify the surfactant's charge so that is no longer acts as an emulsifier.

3.Add table salt (NaCl). If you know that your sample forms emulsions,you can add the salt to the sample prior to shaking with the solvent. If you are trying to break an already formed emulsion, you can shake the salt into the sample. Hopefully, you will see the salt (hopping to the bottom as the droplets from the emulsion coalesce and the emulsion disappears in to cleanly partitioned layers. Sodium sulfate can also be sprinkled into the sample as described above or a more aggressive approach for sodium sulfate is described next.

4.  Filter through sodium sulfate. Pipette as much solvent/extract as possible into a clean container without taking the water layer. Add 1 or more grams of anhydrous sodium sulfate, Na2.S04 and stir with glass sailing rod. The extract should be non-turbid but may-have coloration Put an 11 cm No.40 Whatman filter paper into a glass funnel and filter to remove sodium sulfate from the solvent Alternately, you may be able to skip the stirring step and just pour the solvent and emulsion thought the filter paper with the sodium sulfate.  In this case, the sodium sulfate binds the water leaving the solvent behind so it coalesces into the solvent layer.

5.Centrifugation. A centrifuge is the sure fire way to break the emulsion but not all labs or especially on-site facilities one available.

6.Ultrasonic bath. Put the solvent/emulsion extract into an ultrasonic bath with ice.
All of die above emulsion-breaking methods are usable with portable infrared analyzers, such as the LifraCal TOG/TPH Analyzers, for virtually any type of oil in water measurements, including fat, oil and grease (FOG) wastewater discharges.

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