Ionics Instruments 2004 Page 3-5 DLM 30007-08 Rev. A
The oxidizing reagent – ammonium persulfate – is inherently unstable, slowly
decomposing to form sulfate ion and oxygen. The reagent is stored in a micro-
porous Teflon bag container to permit the oxygen to diffuse from solution. The
decomposition of the persulfate limits the useful lifetime of this reagent to three
months, regardless of the volume of reagent consumed by operating the
analyzer. Although the volume for the phosphoric acid reagent is sufficient for
three months under typical operating conditions, the shelf life is one year.
The analyzer’s firmware keeps track of the volume of both reagents consumed
and the age of the persulfate solution. Warning messages indicate when new
reservoirs must be installed.
Chemical Reagent Syringe Pumps
The reagents are added to the sample stream using microprocessor-controlled
syringe pumps. The capacity of each syringe is 0.5 mL.
Typically, phosphoric acid is added at a flow rate of 0.2 – 1.5 µL/minute,
dependent upon initial sample pH and TOC concentration, to reduce the pH of
the sample stream to pH <2.
For water samples containing up to 5ppm TOC, 0.75µL/min is a suitable flow
rate for persulfate oxidizer. For samples containing higher levels of TOC (up
to 50 ppm), the oxidizer flow rate may be increased to 4.5 µL/min. or higher.
Stream Splitter
After the addition of the chemical reagents, the sample stream is split into two
equal flows. One stream passes through a delay coil and into a CO
2
sensor,
which measures the concentration of total inorganic carbon (TIC), or simply
“IC”. The other stream passes through the oxidation reactor that
photochemically oxidizes organic compounds to form CO
2
, and into a CO
2
sensor that measures the concentration of total carbon (TC). As total carbon is
the sum of organic and inorganic carbon, the concentration of total organic
carbon is computed as the difference between the total and inorganic carbon
(TOC = TC–TIC).
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