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Incomplete digestions usually result from the fact that either the digestion temperature was too low, the digestion time too short or an unsuitable acid mixture was selected. In the case of partial digestion, residues of the actual sample can often still be found in the digestion vessel. In the case of organic samples that have not been completely digested, the solution is often clearly turbid. In the case of fats and oils, in the worst case a layer of fat can be seen floating on the surface. Such residues must be purified to obtain the best results in subsequent digestions.
Use of hydrogen peroxide
Hydrogen peroxide increases the oxidation potential by forming oxygen and thus improves the digestion quality. Since it thus only has a supporting effect, the addition of 1-2mL to the reagent mixture is sufficient. The use of large volumes leads to a strong pressure increase which can result in a pressure overload of the vessel.
Mechanical cleaning of solid residues
In some cases it is sufficient to remove the residues mechanically with a soft brush or cloths. This helps especially when solid residues are found in the vessel. In the case of the fats/oils described above, blind digestion is generally recommended to rid the pressure vessel of undigested residues.
Storage of vessels
Storage of vessels in dilute acid (10% HNO3) is recommended. This not only prevents contamination of the vessels, but also conditions them at the same time. This allows the service life of the vessels to be increased.