Ionics Instruments 2004 Page 4-22 DLM 30007-08 Rev. A
If the TOC measurements at the higher oxidizer flow rate are more than 3% of
the TOC values at the lower flow rate, then complete oxidation is not
occurring. Increase the oxidizer flow rates. Increase the oxidizer flow rate by
another 0.5 to 1.0 µL/min. and make 3-5 TOC measurements under these
news conditions. Again, inspect the new TOC measurements and if the
values show more than a 3% increase, continue increasing the oxidizer flow
rate at 0.5 to 1.0 µL/min. increments until there is no increase or < 3%
difference in the TOC values. While performing these tests, look for gas
bubbles in the 1/16" Teflon analyzer outlet tube on the right hand side of the
analyzer. If you see gases bubbles in this line, too much oxidizer has been
added and therefore, decrease the oxidant flow rate. If increasing the oxidizer
flow rate gives a lower TOC reading, then decrease the oxidizer flow rate.
There is a small TOC background of ~1-2 ppb in the oxidizer reagent. The
increase observed in the TOC measurements with and without oxidizer may
be due to this background and not an increase in oxidation efficiency.
The upper range for the oxidizer flow rates listed in Table 2 are approximate
values. If the water samples contain difficult to oxidize organic compounds or
compounds with a high oxidant demand, it may be necessary to add more
oxidizer than the upper flow rate listed for a particular TOC range. The
important thing is not to add too much oxidizer if there is a presence of gas
bubbles in the analyzer’s outlet tube.
WARNING
Operation at oxidizer flow rates above 2 µL/min. with low TOC samples can
result in excessive bubble formation and damage to the analyzer. Do not use
oxidizer flow rate above 2 µL/min. for samples containing < 5 ppm TOC.
Solutions of persulfate are unstable and will decompose over time. As the
persulfate oxidizer reagent ages, increase the flow rate of oxidizer in order to
achieve complete oxidation.
The syringe-pump flow rates for the acid and oxidizer have been set at the
factory to 0.75 µL/min. for the acid and 0.50 µL/min. for the oxidizer (Raw
Water Preset flow rates). For most water samples, keep the acid flow rate set
to 0.75 µL/min. Basic samples will require a higher acid flow rate to ensure
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