Saturday, May 17, 2008

Sometimes you need to slow down.

Originally uploaded by desireux

I seldom write about science, but this is special. I'm writing about the most annoying buffer to make: 5x Maleic Acid Buffer (MAB). Hopefully, these tips will spare some other graduate student some grief.

The thing about MAB buffer is that it starts of with a very low pH and you have to add sodium hydroxide (NaOH) to bring it up to around 7.5. This takes quite a lot of NaOH, but, once it reaches a certain point, the pH will increase very drastically. So yesterday, I was at around pH 7.0 and up to that point, adding about 5 pellets of NaOH would increase the pH by about 0.2. However, I found out the hard way that adding 5 pellets of NaOH to the solution when it was at 7.0 brought it up to 8.45!

This was not the first time though :) It has happened before, but MAB lasts quite long so each time I make it, I forget my "mistake" and repeat it. This time I made BIG BOLD notes beside my recipe. It will not happen again.

However, if this happens to you, fear not, just calculate the reagents needed for an extra 0.2 L and proceed with the pHing process as usual.

And here are some observations when I did mine:

The solution will be warm and cloudy. It will clear up at around pH 6.0. At this stage, the pH is still quite stable. From around 6.7, addition of 1 pellet of NaOH will bring the pH up 0.1.

At around pH 7.0, go VERY slowly, because the pH increases drastically at this point. It took just one pellet to go from 7.0 to 7.17 and another pellet to go to 7.4.

*Also, I've noticed that MAB can go bad easily if contaminated so I always aliquot it into a small bottle which I use from*

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