Ionics Instruments 2004 Page 10-7 DLM 30007-08 Rev. A
measured TOC increases, then continue increasing the oxidizer flow rate until
a steady TOC value is obtained and gas bubbles are not seen in the
instrument outlet line.
DI Reservoir Too Low
If there is not enough water in the DI loop, erratic TOC readings can result.
Follow the procedures in the Maintenance chapter to check the level of DI
water in the reservoir and refill if necessary.
Gas Bubbles in Reagent Lines or Syringes
The presence of gas bubbles in the lines from the reagent containers to the
syringe pumps and from the syringe pumps to the stainless steel cross can
cause erratic TOC readings. Turn off the analyzer and disconnect the power
cord. Open the top panel of the analyzer and inspect the 1/16" Teflon tubing
from the syringes. If gas bubbles are observed in the lines or a large (greater
than 30µL) gas bubble is in the syringe, perform a syringe flush. Select the
REAGENT FLUSH option from the REAGENTS menu and flush both
syringes.
Since the analyzer calculates TOC from the difference between total carbon
and inorganic carbon, erratic readings or even negative values of TOC can be
observed in water samples containing high levels of inorganic carbon. This is
often the case for ground water samples, some municipal water supplies, and
permeate from reverse osmosis systems.
The analyzer monitors the TOC/IC ratio. If this ratio is < 0.1, WARNING 42
will be shown on the LCD display and written to the error stack. If the response
of the IC CO
2
sensor is greater than the response of the TC CO
2
sensor, the
analyzer will report a negative TOC value.
Because the accuracy of the TOC measurement is ±3% of the TC
measurement, the accuracy of TOC measurements will be less for water
samples containing high levels of inorganic carbon.
To eliminate the problems encountered in TOC measurements of water
samples containing high levels of IC, Ionics Instruments has an on-line IC
Removal Module. The module is installed on the analyzer and uses a
membrane-based system and vacuum to remove greater than 99% of the IC
from the sample.
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