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Analyzing for (4-Methylcyclohexyl)methanol (MCHM) in Source and Finished Drinking Waters

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  • Chris Rattray
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I got my hands on the new MCHM custom standard Chas blogged about Tuesday and performed some test runs yesterday. There are 2 isomers of the compound in the standard (cis and trans), referred to as isomer I and isomer II below because I don't know the elution order.

After injecting the 1 PPM standard at a 30:1 split to determine the retention time, I attempted a 5 mL ambient temperature purge and trap run of a sample spiked at 25 µg/L. Because of the hydroxyl group I did not expect a high purge efficiency, but was surprised by the apparent total lack of response at 25 ppb.


After the lack of response on the ambient purge and trap run, I had little hope for the 45°C heated purge and trap run. However, the 25 ppb sample showed a slight response for both MCHM isomers.


Together the heated and ambient purge and trap runs confirmed my fears that purge and trap (and consequently EPA 524) would not be appropriate. I considered trying the activated charcoal  EPA 521 & 522 method specific SPE tube, but after talking it over with Jack we decided that a micro extraction would be the fastest way to go, with the added benefit of using very little solvent or lab glassware and avoiding evaporative loss because there is no extract concentration step. I decided to use EPA Method 3511 (with slight modification) for my extraction procedure.


For my GC-MS analysis, I used a 30 m x 0.25 mm ID x 0.25 µm df Rxi-5ms because it was already installed in another 7890-5975C for some semivolatiles work I've been doing. Starting at 35°C, I used a 1 µL pulsed splitless injection (0.6 min) and optimal flow (1.44 mL/min) and heating rate (11.9) to 200°C.

blog-analyzing-for-4-methylcyclohexylme-drinking-waters-slide4.png

As you can see above, the micro extraction combined with a 1 µL pulsed splitless injection provides a good starting point for a MCHM trace analysis method. The peak areas of the two MCHM isomers relative to the 12.5 PPB internal standards and surrogates indicate that a very high percent recovery is possible.

If I was setting up a method to regularly test for this compound, I would make a couple changes to the procedures outlined above. I would salt out the sample using the 12g of sodium chloride as described in EPA Method 3511, and I would I would use a thick film VMS column (Cat# 19915) for the GC analysis to improve focusing (the internal standards and surrogates are tailing in the thin film 5ms run above).

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Comments

Wed, Apr 09, 2014

Hello, I have analyzed 4-MCHM by 524.3 Method with Restek Column (30m X 0.25mm X 1.4um) and Purge and Trap (Tekmar Stratum Concentrator and AquaTek Autosampler). It worked perfectly without any problem. The lowest concentration was 5ppb. You don't have to do any sample preparation. Just follow EPA Method 524.3.