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.

Continue reading Tips for Improving Your Oil & Grease Recoveries

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!