From various contributions, I now realised that any good spectrophotometer can be employed to determine Cd. The only condition to good results is the digestion strength of extractants. I have been using Nitric-perchloric acid method; is this method good or there are better ones?
We tested a method for Cd (and Pb) in "chorume". We did digestion with HNO3+HCl (3:1). It is important that the digestion is in a closed system to do not lost material.
Cd can form volatile species and might be lost during open beaker digestion. I would be very careful when using perchloric acid. If you do not have dedicated fume hoods that are able to wash out perchloric acids fumes you will accumulate explosives over time. A question would be if Cd is bound to silicates, if so you would need to apply HF but again this acid is also very dangerous and should be avoided. What is left over: as already mentioned by Marco, you can try aqua regia with a microwave oven or on a hot plate in closed vials and hope that your extaction efficiency is high enough.
If I were you, I would go for microwave digestion using aqua-regia. The results is quite close with desired extraction level.
why to extract if the total digestion of the soil applying the EPA 3052 procedure ( digestion assisted by a microwave digestor employing nitric and hydrofluoric acid) is simple and quick?
The choice of the digestion procedure is pretty much associated to the type of matrix (soi, sediment, plant, animal) and type of analytical device that will be employed. Besides these two factors the ensure the efficiency and accuracy of your digestion it is imperative that you run also a digestion of an appropriate certified reference material (from the same type of your sample) toghether with your samples.For all cases i recommend the use of hermetical teflon vessels to carry out the digestion safely and without losses by volatilization.
If you want to measure the total content of Cd in a soil, microwave digestion with aqua regia is a good solution. Hydrofluoric acid is a very dangerous product. Lots of laboratories don't use this product anymore. Nevertheless, the total content of Cd does not help to know the soil solid phases associated to Cd and is a poor information for the evaluation of potential mobility or bioavailability of metals like Cd.
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