Page 30 - Application Handbook - TOC
P. 30

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)
   25   26   27   28   29   30   31   32   33   34   35