Page 17 - 3_Chemical industry

Sum parameter – Total Organic Carbon

TOC – Determination in sodium nitrate

and sodium nitrite
SCA-130-308

Basic chemicals may contain organic
contaminants influencing the quality of Compound
products. Quality control procedures of the (Concen- Dilution Conz.
reactants are, therefore, necessary in order to tration) Weighted Sample
detect impurities. 5 g / 50 ml approx.
Sodium nitrate add. 1-2 drops 10%
For the determination of organic (>99,9%) Sulfuric acid until
contaminations in salts, solutions of these pH<7
salts can be prepared and subsequently Weighted Sample
5 g / 50 ml
measured using a TOC-L analyzer. add. 1-2 drops
Sodium nitrite Sulfuric acid until approx.
(>99,9%) pH<7 10%
Caution: Nitrogen
oxide gas is
released

Caution: Nitrite salts react to form of toxic
nitrous gases. Sample preparation should,
therefore, always be carried out under a
hood. The samples should only be removed
from the hood, when no more nitrous gases
escape.

Calibration of the TOC-L system was done
High salt concentrations generally present a applying the automatic dilution function in the
problem for TOC analysis. These salts can range of 0.5 mg/L to 10 mg/L.
crystallize in the combustion system and lead
to higher maintenance needs.

In the case described below, the NPOC
content of two salts was determined. The
difficulty was the required detection limit of 10
mg/kg.

■ Sample preparation
For sample preparation, 5 g of both salts
(sodium nitrite and sodium nitrate) were Fig. Multi-point calibration
weighed into a 50 mL volumetric flask and with dilution function
diluted with ultrapure water. During dilution,
the solutions were acidified with concentrated
sulfuric acid (25%).