If you were ever a fan of the show MythBusters, you can appreciate the hours I spent watching myths being confirmed or busted in the most entertaining ways. For me, this show was appealing because the scientific theory was used to design and test experiments to produce facts about interesting phenomena such as: humans use only 10% of their brains, a household vacuum cleaner can generate enough suction to lift a car into the air, or a goldfish’s memory is only 3 seconds long.
Myths have been with us for thousands of years and play a significant role in our recorded history; however, they can be troublesome when they spread fiction and falsehood. This is particularly significant when myth and folklore start to replace scientific facts, methods and processes.
With that in mind, I wanted to take an opportunity to dispel 5 relatively common myths that are related to oil and grease measurements in accordance with EPA Method 1664.
Myth 1: You can use Freon (or tetrachloromethane) as your extraction solvent, as long as you demonstrate equivalency
BUSTED – Freon was phased out of EPA Method 1664 (both A and B) in the early 1990s. The extraction solvent must be n-hexane
Myth 2: The use of co-solvents is not allowed, even if you are using an extraction technique which employs co-solvents
BUSTED – if you are performing your extractions using a technique which uses a polar solvent to remove residual water (such as solid phase extraction), the use of a co-solvent is allowed as long as you can demonstrate that the polar solvent is not ending up in the final hexane extract
Myth 3: To save money, you can use 47 mm SPE disks on your QC standards and cleaner samples, then switch to the 90 mm SPE disks for your dirtier samples
BUSTED – the method requires you to use the same SPE disks (same manufacturer, same size) for all standard and sample processing in the same analytical batch
Myth 4: If you use prefilters for any of your samples, the same type and number of prefilters must be used for all samples, to ensure a consistent approach to the extractions
BUSTED – Prefilters may be used for only those samples which require them (i.e. prefilters do not have to be used for the entire batch)
Myth 5: When drying your extracts, you should use sodium sulfate – it’s relatively inexpensive and a well-established technique
BUSTED – The method allows a wide range of extract drying approaches (sodium sulfate, separation paper, PTFE membranes, manual separation using a separation funnel); the only approach that is NOT allowed is to carefully pipette or drain one immiscible layer from another
These myths (and others!) are explained in detail in this Oil & Grease Best Practices webcast, so check it out if you get the chance.