Chemical Reference Standards; don’t just snap and pour

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).

                 

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.