AOX determination
multi X 2500
52
6
AOX determination
The samples for an AOX determination are prepared in accordance with column or
batch method stipulated in the respective standard. The loaded activated carbon is
combusted in the oxygen stream. During this process, the organically bound halogens
are transformed into hydrogen halides whose mass concentration is determined as
chloride.
The multi X 2500 can perform the AOX determination in both vertical and horizontal
operating mode. The default version in vertical operating mode is recommended. The
technical equipment for the standard version is simple, it requires little space and has
low operating costs. The duration of the analysis is relatively short.
Working in horizontal mode requires an extension kit and an automatic boat feeder
(ABD) or manual feed (MBD) for moving the quartz boats with the loaded activated
carbon into the combustion tube.
6.1
Sample preparation
6.1.1
Sample preparation for AOX determination from waters
Please observe the following:
The AOX method can be used to determine AOX contents of more than 10 µg/l
directly.
The DOC content should be smaller than 100 mg/l. Otherwise, the sample must be
diluted (especially if it contains alcohols, aromatics or carboxylic acids).
The content of inorganic chloride or bromide should be smaller than 1 g/l.
Otherwise, the sample must be diluted or replaced by a solid phase extraction for
preparing the sample (SPE-AOX method), for example.
If water samples (e.g. Cl
2
, I
2
or ClO
3
) are mixed with Na
2
SO
3
for sample
preparation, it is important to avoid an excess of Na
2
SO
3
.
If the sample contains living cells, the sample must rest for eight hours after
acidification before further analytic processing.
Samples must be examined as soon as possible. Where this is not possible, the
samples must be stored at 4 °C.
Preparing the nitrate stock solution:
WARNING
Concentrated nitric acid can cause severe chemical burns! Wear protective clothing
when preparing the nitrate stock solution! Observe all specifications in the safety data
sheet!
1.
Dilute 17 g of NaNO
3
in a 1-liter volumetric flask with water.
Basic Information
Sample preparation
