IKA AOD 1 - Manual (Page 54)

IKA  -WERKE AOD 1 Ver. 01 01.03
Page 6-1
6 Carrying Out Decomposition Tests
The prerequisites for reproducible and accurate testing are cleanliness when han-
dling the decomposition vessel, purity of the chemicals used, and meticulously fol-
lowing the chosen procedure. Always observe the hints and instructions in Section 1
"For Your Safety" and the following sections; they are there to ensure safe opera-
tion.
6.1 Recommendations for the Sample
Samples to be analysed must be homogenised or, if necessary, ground before they
are weighed. Samples that readily generate dust are easier to handle if they are first
pressed into pellets. This also helps achieve more uniform combustion.
Please also read the safety notes for Decomposition Vessel AOD 1.1.
Normally, solid fuels can be burnt directly in powder form. Fast-burning substances
(e.g. benzoic acid) must not be burnt in a loose form.
Fast-burning substances tend to spluttering combustion. Complete combus-
tion is then no longer certain. In addition, the inner wall of the decomposition
vessel may be damaged. Such substances must be pressed to form pellets
before they are burnt.
The IKA  C 21 Pelleting Press is suitable for this task (accessory).
Most liquids can be weighed directly into the crucible. Liquids that are cloudy or with
separable water must be dried or homogenised before weighing. For solvents with
different phases, each phase should be tested separately.
Loss due to evaporation, dusting, and environmental factors can be minimised by
weighing the sample in acetobutyrate C 10 or gelatine capsule C 9 (see Accesso-
ries). These capsules also act as a combustion aid.
For a low-flammability substance, a combustion aid should be weighed into the cru-
cible together with the sample.
Low-calorific-value samples may also require an aid to combustion such as paraffin
or benzoic acid for thorough burning. Paraffin can also be used to treat samples that
tend to produce dust, acting as a binding agent and improving combustion. Besides
the capsules mentioned above, polyethylene combustion bags C 12 and C 12A or
combustible crucible C 14 (accessories) can also be used.
At low detection levels, it is better to avoid using a cotton thread as an ignition aid,
and to use a paraffin strip C 15 instead. In this way, the effects of impurities in the
cotton, which adversely affect the lower limits of detection, can be minimised. We
strongly carrying out blind determinations to establish whether impurities are likely to
be present.
Liquids
Highly-volatile
substances
Combustion
aids
Solids