You can automate extraction to accelerate testing and save time.
Many types of oils and grease from cooking, maintenance and cleaning, and manufacturing enter wastewater. To maintain regulatory compliance, you must quantify and reduce these contaminants from wastewater before the water can be discharged back into the environment. Oil and grease can wreak havoc on the environment and biological life in our waterways. If you are working in this industry and need to test for oil and grease, know that it’s a time-consuming and a strictly defined testing method. There are two approved methods that can be used for this type of analysis; both require the use of hexane as the extraction solvent. And, you can automate your extraction process to save you time.
If you want to expedite your analysis, you can use an instrument like the Environmental Express SPE-Express 2 that automates the extraction process. A new version of the original SPE-Express automated extraction unit for oil and grease analysis is in development. The SPE-Express 2 is coming soon and will be available as single-place, modular units that can be linked together to meet sample throughput demands. The system is fully enclosed and doesn’t require its own fume hood. This unit is the only system to extract the sample and evaporate the n-hexane, eliminating the transfer step. It uses a fluid sensor to verify the sample vessel is empty which improves accuracy. Plus you will be able to run multiple samples simultaneously on up to six stations, increasing efficiency.
Learn more about oil and grease analysis
Only two approved methods are available to analyze oil and grease: (Environmental Protection Agency) EPA Method 1664 (A and B) and (Standard Method) SM5520 B/F.
Hexane is used to extract material (ideally just oil and grease) from an acidified aliquot of the sample stream. The hexane is evaporated, and the entire amount of residue left behind is defined as oil and grease.
While many materials are visually recognizable, as oil and grease will be recovered by this method, other materials which are not oil or grease will also be recovered. Anything that is soluble in hexane will be counted as oil and grease for the purpose of this testing. This includes some dyes, sulfur, and substituted hydrocarbons but does not include some heavier petroleum residuals. Therefore, the analysis is better termed as hexane extractable material (HEM).
Two main components of oil and grease are petroleum-based hydrocarbons (referred to as ‘nonpolar materials’) and fatty compounds of animal or vegetable origin. You can determine these as a whole or as the nonpolar material, with the animal/vegetable material being the difference between the two. The differentiation between the two is done by adding an extra step involving silica gel. Anything left over after silica gel treatment is a nonpolar material.
Method 1664 deals with a liquid-liquid extraction procedure. To adhere to this method, you need to transfer your sample into large separatory funnels and add 30 mL of hexane. Agitate the sample and solvent and allow the layers to separate. Then collect the hexane and repeat the extraction two more times. Because hexane is lighter than water, the entire sample volume must be drained from the funnel, usually back into the sample container, before you can collect the hexane. Carefully vent during the agitation to avoid potentially dangerous buildup of pressure from the fumes. Often during the agitation process an emulsion will form between the organic and aqueous layers. This can cause significant delays in the extraction process due to the time needed to separate the emulsion. The method does allow alternative extraction methods provided they adhere to the method definition. Solid-phase extraction (SPE) is the most widely known and used of these alternatives. SPE is accomplished by passing the sample through a material which retains the HEM components. The HEM is than extracted by rinsing with solvent to carry the HEM into a collection dish or flask. This method has the advantage of reduced solvent usage (often more than 50% less), no dangerous pressure buildup, and avoiding the formation of emulsions.
Because this is a method-defined parameter, you need to meet certain requirements to stay within that definition. The most important one is the solvent of choice. Whether you choose liquid-liquid, Soxhlet, or some sort of SPE method, you need to use n-hexane as the active solvent. There are certain Standard Methods that are not allowed because they use a mix of solvents in the procedure.
If you are using solid-phase extraction disks that require activation (typically with methanol) before the sample is filtered, you need to remove all traces of that solvent before the sample is introduced onto the disk. Another crucial step is the evaporation temperature. Standard Methods recommends 85°C while 1664A says 70°C ± 2°C. 1664B simply says to adjust the temperature as appropriate. We recommend using 40°C. The lower temperature lends itself to better standard recovery, as you have less of a chance of volatilizing some of the lighter weight organics. Still lower evaporation temperatures would allow for losing less material to volatilization at the expense of longer evaporating times.
When performing an analysis for HEM, you always must use whole volume samples. Because the HEM constituents are typically not water soluble, the sample is not homogenous with respect to the analyte of interest. Almost all components of HEM will be found either on the surface of the sample or adhering to the walls of the container. Pouring aliquots of sample out for analysis will not give you a representative sub-sampling in most cases.
One final step to keep in mind—always acidify your blanks and other standards. Failure to do so will result in incomplete recovery of your standards.
Need standards for your oil and grease analysis?