My First Acid Digestion.

When looking at archaeological material, we sometimes need to use a destructive analysis to get a better idea of the chemistry of the object. So, we've been allowed to take a small sample of the object, what do we do next?

This week, I've been learning how to do acid digestion. This is a way to dissolve your sample into a liquid. The idea is that the if the sample is in a liquid form, it is more homogeneous (the same composition throughout the sample). This means that an analysis is more reliable because the chemical signature we see is representative of the whole sample, rather than just a small area of the sample.

How do we dissolve our sample? First we have to crush and powder the material (the finer the better). This already starts to homogenise the mix. Then we weigh out a very small, precise, amount (our scales are accurate to 5 decimal places). We put this powder in a special tube and add a very precise measure of nitric acid. We then seal the tube and place it in a microwave (similar to the one in the picture). After 20 mins we allow the samples to cool in the microwave, then (under a fume hood because of the gases produced) we open the tubes and filter the solutions into special flasks. We then add deionised water to make the solution to a set volume. We mix thoroughly with a really good shake, and then our sample, in solution form, is ready to be analysed.

I tried this method of preparation for the first time, and I'll be honest, I was a little nervous. But, there was really nothing to worry about. The hardest part is making sure you have exactly the right amount of each ingredient. There is something satisfying about taking the tops off the tubes and watching the swirling, orange/yellow, gas escape into the fume hood. However, you do have to remember that you are working with acid and safety goggles, gloves, and a lab coat are essential!