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behr InKjel P
142109
Avoid bumping!
With liquid samples, bumping may occur so that liquid
will splash out of the sample. With liquid samples, add
some boiling chips. Boiling chips do not contain nitro-
gen. Nevertheless, treat the blank in the same way as
the samples.
When digesting liquids like water or milk, the water con-
tained in them must be evaporated before digesxtion
really starts. During this time, heating must be adjusted
in such a way that the sample is boiling steadily but
does not boil over.
Foaming
Some kinds of samples will develop a foam when react-
ing with concentrated sulfuric acid, which will rise up in
the vessels, creep over the rims or even rise into the
suction nozzles. Textbooks have various advices what
to do against foam – but it will depend on the kind of
sample which technique will work.
Heating slowly so the foam won’t rise so fast, maybe
even preparing the sample in the evening and letting
it rest overnight before starting the digestion. That
will sometimes work, but it won’t always work. Some
sample materials will start reacting with the sulfuric
acid in the cold, and the longer it takes the sample to
reach digestion temperature, the higher the foam will
rise.
In these cases it is better to have the sample come
to digestion temperature as quick as possible so the
foam will collapse soon. Which means: preheat the
block and prepare the sample immediately before
starting the digestion.
An anti-foam agent can neutralize the foaming com-
ponents of the sample. Add some drops of paraffine
oil or silicone oil to the sample. Make sure to treat
the blank in the same way as the samples.
If you have an infrared digestion device (e. g. behr
InKjel) too, the easiest way to digest high-protein
samples will be the infrared digestion. In an infrared
digestion, the samples reach digestion temperature
very quickly so the foam will collapse soon.
For liquid samples,
use boiling chips