GE Sievers 900 Series, Operation And Maintenance Manual

Page: 211 / 236

GE Analytical Instruments ©2009 211 of 236 DLM 90488-01 Rev. A
Erratic Readings Due to High IC
The Analyzer calculates TOC from the difference between TC and IC, and erratic readings of TOC
can be observed in water samples containing high levels of IC, where the IC is greater than 10 times
the TOC value. This is often the case for ground water samples, some municipal water supplies, and
permeate from reverse osmosis systems.
To eliminate the problems encountered in TOC measurements of water samples containing high
levels of IC, GE Analytical Instruments offers an inline ICR accessory. The module is installed on the
Analyzer and uses a membrane-based system and vacuum to remove approximately 99% of the IC
is at concentrations up to 25 ppm. For more information on the ICR, contact GE Analytical
Instruments.
If sampling from a container, you can manually remove the IC from the sample as follows:
1. Add a few drops of acid (6 M H
3
PO
4
) to the sample.
2. Use an N
2
or He purge gas to remove CO
2
from the sample.
3. After purging for 5-10 minutes, analyze the sample.
Acidifying the sample and purging may introduce organic impurities into the sample, so treat a
sample of low-TOC DI water in the same manner as a blank.
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.
If the reading appears to have drifted by 5 ppb (or 10 ppb at the most), perform the TOC Autozero. If
the drift is greater than 10 ppb, check the TC and IC calibration before performing the TOC
Autozero. Follow the procedures in the section called “Perform a TOC Autozero” on page 140.
Negative Measurements
Many of the previous steps in this chapter will help troubleshoot negative measurements. If the
previous steps did not remedy the situation, you may need to perform a Conductivity Autozero; if IC
values continue to be high, you may need an ICR for your system.
Conductivity Autozero
1. Make sure the Analyzer is not taking measurements.