GE Analytical Instruments ©2009 96 of 236 DLM 90488-01 Rev. A
The acid flow rate is adjusted according to the IC concentration measurements made during those
analytical measurements — if the IC concentration increases from 49.9 ppm to 50.0 ppm during the
analytical measurements, the acid flow rate will increase from 1.0 to 2.0 mL/min. (The Analyzer
makes these adjustments using averages of the IC measurements so that a single measurement of
50.0 ppm IC will not result in an abrupt increase in acid flow.)
Following the preliminary measurement, the Analyzer adjusts the oxidizer flow rate as the TOC
concentration changes during the analytical measurements. To do this, the Analyzer calculates the
ratio:
This ratio is used to calculate the oxidizer flow rates to be used in the analytical measurements. The
Analyzer uses an average TOC concentration in this calculation to avoid abrupt changes to the
oxidizer flow rate caused by occasional higher or lower TOC measurements.
In the On-line mode, the preliminary measurement is repeated to allow the ratio of oxidizer flow
rate to TOC concentration to be updated. The frequency of performing the preliminary
measurement should be greater for sample streams that are expected to have more variable
compositions. Therefore, the frequency is adjustable, with every 12 hours being the most frequent
setting possible.
Persulfate is normally only added for TOC samples above 1 ppm. Below 1 ppm, the hydroxyl radicals
formed from the photolysis of water achieve sufficient oxidation and a low oxidizer flow rate (0.1 to
0.7 µL/min) is used.
Manual reagent mode should be selected for samples that are expected to be below 1 ppm. For
samples below 500 ppb, it is common to set the oxidizer flow rate to 0 or 0.1 µL/min. Between 500
ppb and 1 ppm, set flow rates manually between 0.1 and 0.7 µL/min. Once established, there
should not be a need to modify the flow rates.
Autoreagent mode is optimized for samples > 1ppm TOC where the TOC is unknown or highly
variable; it should not be used for samples below 1 ppm as oxidizer injected during the preliminary
measurement (used to determine the proper flow rates) can result in bubble formation if the
premeasurement sample is very low in TOC. It may take several minutes for the Analyzer to clear
these bubbles and return to a stable condition.
Selected Oxidizer Flow Rate, µL/min
TOC Measured During Prelim. Meas., ppb
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