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Chemical Reference Standards; don’t just snap and pour

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  • Alan Sensue
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I still remember the first time I tried to prepare a chemical standard (back in the 80’s).  I failed miserably.  It was my first laboratory job and I was asked to snap open recently purchased ampules and dilute them to some concentration (which I don’t remember) for our 8270 analysis.  Back in those days there were no MegaMix® solutions, so I probably had eight or more ampules to open and dilute.  I double-checked my calculations, filled-out our laboratory notebook, measured the methylene chloride I was going to dilute the ampuled solutions into, and began snapping and pouring.  About halfway through the procedure I had a co-worker stop me and ask what I was doing.  Was this a trick question?  I was focused on the task and making good time, so I told him to back off (which he did).

                 
refstd-mixes

Then the manager showed up to let me know why I was so rudely interrupted by my coworker.  He explained that just because the ampule listed 1mL on the label as the volume, chemical reference standard manufacturers actually put more than the listed volume into each ampule, so one needed to measure the volume removed and not assume the contents were exactly 1mL.  In summary, I learned that day that the proper process was to snap the ampule and precisely remove the volume of the solution needed for dilution.  The remaining contents should be immediately transferred into a screw-cap or crimp-cap vial and placed in storage according to the recommendations of the manufacturer.

So why did I write this post?  This week I spoke to two customers who were snapping and pouring.  I thought if they didn’t know the correct procedure, then maybe I should write a post to tell others who also may not know.

Safely Opening Reference Standard Ampuls with the Restek® Safe Cracker

 

コメント

金, 3 14, 2014

Hi Maria. First, I would like to thank you for reading my post. I reviewed 8260B and confirmed that although MTBE is listed in section in Section 1.3 (which I refer to as a secondary list), it is not listed in Section 1.1 (which I consider the primary list), so I figured that was the answer. http://www.epa.gov/osw/hazard/testmethods/sw846/pdfs/8260b.pdf I then reviewed 8260C and MTBE is listed in Section 1.1 (the primary list) of this version of the method. In summary, you have asked a very good question and I do not know the answer. As a result, I have passed it along to the Chemical Reference Standards group for review. http://www.epa.gov/osw/hazard/testmethods/pdfs/8260c.pdf

木, 3 13, 2014

Any reason the 8260 mega mix doe not contain mtbe? I noticed that the drinking water voa mega mix rev.4.1 does. Just curious.

金, 3 21, 2014

The 8260B contains the majority of the primary list, but not all. Different labs in different states have different target compound lists. Additionally, some compounds are less stable than others, so if they are included in the mix, the shelf life of the mix would be drastically reduced (I think acrolein is a good example of this). Volatility can contribute to stability issues as well; this is a good reason to keep the volatile gases in a separate spike mix. You can put together a fairly comprehensive 8260 spike mix using the following standards: 30042 - 502.2 calibration mix 1 (6 volatile gasses including vinyl chloride) 30633 - the 8260B MegaMix (76 components) 30626 - Gasoline oxygenate additives (TAEE TAME TBA DIPE ETBE MTBE) 30006 - VOA Calibration mix 1 (acetone MEK MIBK 2-hexanone)

火, 3 25, 2014

When the Mega Mix was developed not all states were interested in MTBE… California was testing for it like crazy in 1999 to 2004, but since MTBE has not been used in CA for 10 years interest in this compound has subsided in that state – 25 other states have legislation banning MTBE currently or in the near future…