Page 30 - Application Handbook - TOC

Sum parameter – Total Organic Carbon

TOC – Determination in nitric acid

SCA-130-302

Organic contaminants present in basic Calibration of the TOC-L system was carried
chemicals may constitute the impurities in out using the automatic dilution function in the
products. This is why quality control of the range of 0.5 mg/L to 10 mg/L.
reactants is indispensable.

Fig. Multi-point calibration
with dilution function

To protect the NDIR detector, the B-type

scrubber was used together with the halogen
The determination of organic contaminations scrubber.
in concentrated nitric acid (69%) becomes a
challenge when the required detection limit ■ Matrix interferences
does not allow large dilution steps. In addition to CO 2, various nitrogen oxides
are formed from the organic components
An example is the TOC determination in a during the combustion of nitric acid.
69% HNO 3 solution with a detection limit of < Excessively high levels of NO 3 can lead to
10 mg/L. significant amounts of N 2O (nitrous oxide).
Nitrous oxide exhibits absorption bands in the
■ Sample preparation same IR detection range as CO 2 and can,
For sample preparation, the 69% HNO 3 therefore, be misinterpreted for CO 2. In
solution was diluted to a ratio of 1:10 with addition, nitrous oxide can cause tailing and
ultrapure water. can affect the peak symmetry.
Compound Due to the high solubility of N 2O in water, the
(concen- Dilution Conz. [%]
tration) gas is dissolved in the B-type scrubber and
1 : 10 diluted with will not reach the detector.
Nitric Acid water Ca. 7%
(69%)
(5ml / 50ml)