In the world of environmental testing, many labs encounter extremely dirty samples. For example, EPA Method 1664B is the protocol for extracting oil and grease from wastewater samples. More often than not, these types of samples are really dirty, requiring loads of pre-filters, glass wool, and filter aid in order to get the entire liter of water through the disk. Well, there is! We know that laboratories are always looking for ways to speed up the extraction process and reducing the volume of the sample to be extracted is one of the best places to start.
For our “sample reduction study” we chose to follow along with EPA Method 1664B because this is the protocol for wastewater samples. They are usually the most difficult samples to extract an entire liter of, due to the nature of the different varieties of sample matrices from discharge locations. Per EPA Method 1664B section 184.108.40.206, you have the ability to reduce your sample volumes from one liter to something smaller. The method specifically outlines the use of 100 mL sample volumes. The idea of reducing your sample volumes to 100 mL is very appealing, especially for samples that have a hard time filtering through even with all the filter aid, but there were some issues with accuracy on the gravimetric side. When you are reducing your sample volumes 10-fold you need to make sure that you can compensate for that reduction on the gravimetric side with a balance capable of measuring 10x more accurately. View the table below, to see what I mean: