Myth Busters: Smaller Sample Volumes

EPA Method 1664B

Have you ever had days of extracting oil and grease samples and thought to yourself “there must be an easier way to work with wastewater samples”? Whether you run oil and grease samples by liquid-liquid extraction (LLE) or by solid-phase extraction (SPE) it can be challenging at times to efficiently extract 1-liter samples due to the sample matrix. Wastewater is challenging and can be very complicated and contain many types of particulates and or detergents. The makeup of the sample not only interferes with efficient extractions due to matrix issues (such as emulsions) but can also cause slow flow rates.

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EPA Methods and the Use of Drying Techniques

Do you ever tire of using sodium sulfate to dry your extracts?  I know I do.  That is why, whenever I get the chance to avoid using it, I do.  The worst experience when using sodium sulfate is when you do not use enough of it, and the sodium sulfate reaches its maximum capacity leading to water breakthrough into your ‘what was supposed to be a dried extract.’  Then, you must dry the extract again with more sodium sulfate.  When you are a high throughput lab, redoing steps is not ideal.  Unfortunately, EPA Methods 525.2 and 525.3 require sodium sulfate drying as the drying technique, to name a couple, but not all EPA methods require sodium sulfate for drying.  That is why when there is an alternative technique available and you are permitted to use it, why not use it?!

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Tips for Improving Your Oil & Grease Recoveries

On the surface, EPA Method 1664B seems pretty straightforward – use n-hexane to extract compounds (commonly referred to as “oil and grease”) from an acidified water sample.  Evaporate the hexane from the extract, weigh the residue that gets left behind, and report that weight in terms of a concentration (often as mg/L of HEM).  Yet many laboratories have found themselves looking at data which indicates that their spikes aren’t being recovered at levels that are compliant with the method.  Unfortunately, there are a few details in the method that can cause trouble, regardless of whether you are extracting your samples using liquid-liquid extraction (LLE) or solid phase extraction (SPE).  Keep reading for some tips to improve your analyte recoveries when doing oil and grease extractions.

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Reducing the Headache of Challenging Emulsions

Have you ever opened a jar of olives and noticed the shimmering liquid floating on the surface?  Believe it or not, that liquid is actually residual oil that is given off by the olives themselves.  Since the oil is less dense than the aqueous solution that the olives are stored in (olive brine), it floats to the top of the jar.  This may not seem like a big concern to the typical olive consumer, however, olive manufacturers believe that too much oil in a jar is something that negatively affects the final product.  For this reason, olive companies are putting effort and resource into finding a way to quantify the amount of oil in their final product.

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Tuesday Trivia Answer for September 11, 2018

On the eve of World Water Monitoring Day, we thought we would post last Tuesday’s response a day earlier! Celebrations for tomorrow’s epic event might otherwise interfere.

Just a reminder of last week’s post:

According to EPA Method 1664 A/B, n-hexane is used as an extraction solvent and must have a minimum purity level of…

Answer: 85%

EPA Method 1664 B outlines the use of n-hexane as an extraction solvent and Section 1.7.2 specifies a minimum purity level of 85% (Method 1664 A has the same requirement).

Believe it or not, hexane solutions typically contain a mixture of 5 structural isomers (i.e. same molecular formula, different arrangement of atoms). N-hexane is the longest (least branched) of the 5 isomers, which gives it the highest boiling point and lowest vapor pressure. Therefore, specifying a minimum purity level of 85% means you’re dictating that at least 85% of the solution must contain the x-hexane isomer.

Join us next week to Expand Your Horizon!

Fats, Oils and Grease, Oh My!

If you are unfamiliar with terms like “fatberg” and “FOG,” you might not realize the significance and environmental ramifications of this phenomenon. Your perspective will change if you look through recent news articles where fatbergs have blocked and damaged sewer systems in major cities.

Photo credit: Thames Water

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