Sievers TOC 800, Руководство по эксплуатации и обслуживанию

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Ionics Instruments

2004 Page 4-21 DLM 30007-08 Rev. A
Selecting Oxidizer and Acid Flow Rates
The analyzer can use the oxidizer to ensure complete oxidation of the organic
compounds in the water samples. For most samples, the Preset Flow Rates or
the flow rates listed in Table 2 can be selected to provide sufficient oxidizer for
different TOC concentrations. However, investigate the optimum oxidizer flow
rate for the particular water samples. A few guidelines are listed below that can
be of assistance in selecting the best oxidizer flow rate.
For most water samples containing < 1 ppm TOC, only minimal oxidizer is
required (flow rate =0.01
µ
L/min). Direct UV oxidation will convert the organic
compounds to carbon dioxide. However, a small amount of acid (up to 0.75
µL/min.) must be added to any water sample, including low TOC deionized
water. For basic samples, add sufficient acid to ensure that the pH of the
waste stream is <2.
For water samples containing > 1 ppm TOC, the flow rate of persulfate
oxidizer needs to be large enough to ensure complete oxidation, but problems
may be encountered if the oxidizer flow rate is too high. When organic
compounds are present in a water sample, the oxidizer will be consumed by
the oxidation reactions. However, if a large excess of persulfate oxidizer is
present, UV-promoted decomposition of persulfate will produce oxygen. The
oxygen will collect as gas bubbles that can cause problems in the
measurement. These problems may include “TOC spikes”, poor
reproducibility, low, and possibly negative, TOC readings, and, in the worst
case, enough gas bubbles may form to prevent sample from flowing through
one or both measurement channels. One method for evaluating the effects of
different oxidizer flow rates on the accuracy of the TOC measurements is to
start with the Preset Oxidizer Flow representative of the water sample (Raw
Water, Post GAC/RO, etc.) discussed later in this chapter, or the lowest flow
rate listed in Table 2 and make 3-5 TOC measurements under these
conditions. Increase the oxidizer flow rate by 0.5 to 1.0 µL/min. and make 3-5
TOC measurements under these conditions. If there is no change or a < 3%
difference in the TOC measurements at the higher flow rates is being
observed, then sufficient oxidizer was being added initially for complete
oxidation of the organic compounds in the water sample.