How to make a 500 mM EDTA solution

Getting EDTA into solution is easier said than done. I just needed 50 ml of a 500 mM EDTA stock, but it really does not dissolve well. Buying it was not an option since I couldn't find any solution that was not buffered, and I wanted it as pure as possible. So I prepared it myself.

First Try
In the beginning I made the mistake of starting with the pure acid which has to be completely deprotonated before it goes into solution, and that is a long way to go. A nasty surprise was that such a solution goes up to a pH of 8 when a NaOH solution is added, but then decreases to 7.8 within a few minutes without any visible effect of dissolving the salt. I had to discard this failure because I exceeded the 50 ml maximum volume.

Second Try
Next time I tried to use water and pure NaOH tablets, again starting with the EDTA acid. This resulted in a white sludge (I did not keep a proper record on the number of NaOH tablets added after various waiting times) which spilled out of a not properly closed Falcon tube. In the end I got it into solution, but because of the leak I did not trust the concentrations anymore and dumped it.
I finally got the idea that starting with an acid and taking it's pH up is not the best thing to do if there is already a disodium salt available.

Third Try
Eventually I managed to do it like this (for 50 ml of 500 mM EDTA with a pH of ~9):

• 9.3 g EDTA disodium salt dihydrate (the stuff we had on the shelf, 372.24 g/mol) in 50-ml-Falcon tube. Watch out, that stuff is charged and reacts to static electricity!
• Add 40 ml water. Mix and watch the precipitating EDTA settling down.
• Add 10 tablets of pure NaOH. Mix and wait for 1 hour. Feel the warmth spreading through the tube.
• Add another 10 tablets of pure NaOH. Mix and wait for 1 hour.
• The solution was now clear. A pH check gave me 9.71, which was good enough since this was a stock solution to be added to some buffer. Next time I will be more careful about the second lot of NaOH tablets.
• Fill up to 50 ml and filter with 0.2 µm syringe filter (just to have done it).

This is probably more than I will ever need.

A nice Sunday walk in the mud

I don't have much time for walking these days, but I try to get at least twice a week out there for some fresh air and some dirt on my boots.

The walk two weeks ago gave me the opportunity to test the camera of my new phone, the Samsung Galaxy Nexus. It was holding out quite well when compared to that of my old HTC Desire. The built-in panorama function is working great! Just point the camera at the landscape, and the phone does the rest. Just don't go too fast: That led to the  aberrations on the right side of the image. 

Panorama view somewhere north of Cardiff

There are some alternatives out there, but unfortunately I hadn't thought to compare them on the spot. The app Pano does not take the images automatically, but the user has to take them one by one (with some help from the app). And one has to be careful to not twist the camera which leads to a distorted stitched image.
An alternative I used with my proper cameras is Microsoft ICE which allows me to stitch the images together after I got them off the camera. This works quite well, and one can create stitches in more than one dimension, i.e. take pictures in a grid and then create a composite. I will add some examples later.

Other than a testing ground for the phone camera the walk was quite muddy, and it was worse than these images suggest:

Left foot

Right foot

Usually the ground is quite easy to walk in that area north of Cardiff, but the recent rain and the heavy use by horses turned some of the horse paths we ended up walking on turned them into shallow bogs. But at least the first daffodils were out, although we are not sure if they will make it through the spring: 

The first daffodils

One of the surprises we found is this sign of some hiking path leading into nowhere. It seems no one has been using that path for a long time, and nature claimed it back. Not sure if the owner of the land would actually care ...

A path to nowhere

... since the house just across the fence is derelict:

Anyone home?