Page 10 - 6_TOC in daily practice

SCA-130-604

Numerous status and alarm signals simplify whereby the inorganic carbon content
detection of exceeded limit levels and (carbonates and hydrogen carbonates) is
indicate the need for maintenance. A removed prior to the actual analysis. For this
Modbus communication channel purpose, the sample is drawn from the
complements the conventional continuous sample stream into a syringe and
communication modes. An optional web automatically acidified via the 8-port valve
browser gives access to the instrument from (pH 2).
any networked computer. Using the sparging gas connection, the CO 2
formed (from the carbonates and hydrogen
■ Sampling carbonates) is purged from the sample. The
For the 4200 series, various sample remaining solution containing the organic
preparation systems are available, which can components is subsequently injected
be optimally tuned to the individual (septum-free) into the oxidation unit using the
application area. As condensates are sliding valve technique. The syringe and 8-
homogeneous samples (in contrast to port valve allows automatic dilution and
wastewater), an extra sample preparation creation of calibration curves.
step is not necessary. Two sampling systems
are, therefore, suitable: ■ TOC measurement in the condensate
 an overflow tube, from which the sample The system is calibrated using a 2-point
is automatically drawn. calibration curve, blank water and 2 mg/L.
 filling the sampling chamber through a This is realized using a standard catalyst and
strainer (50 Mesh), in case the sample an injection volume of 200 µL. Typical
does contain particles that need to be measuring values are around 0.2 mg/L.
removed prior to measurement. The measuring values of 275 consecutive
Compressed air empties the chamber and measurements of a condensate monitoring
cleans the strainer. are presented in the Figure below:

The mean value is 0.208 mg/L with a
standard deviation of 0.006 mg/L. The results
show that the required detection limit of 0.05
mg/L presents no problem.
Fig. Sampling
■ Recommended analyzer / Configuration
■ TOC measuring method
TOC determination is often carried out via the TOC-4200
NPOC method, Backwash Strainer Sampling unit