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SCA-130-311




            ■ Measurement method and results                    ■ Further considerations
                                                                The oxidation products of H2O2 pose no harm
            Measurement type:   NPOC
                                                                to the liquid handling system, catalyst and de-
            Addition of acid:     1.5%
                                                                tectors of the TOC-L. The samples themselves
            Sparge time:          5 minutes
                                                                however  should  be  placed  in  septum-sealed
            Injection volume.:    50 μL
                                                                vials in the autosampler, to exclude accidental
                                                                spilling of the aggressive substance.
               40
                                                                The  injection  volume  for  both  TOC  and  TNb
               30
                                                                determination can be increased further to be
              Signal[mV]  20                                    able to measure in lower ranges.
               10
               0                                                Higher concentrated solutions (e.g. 55%) can
               -4
                0       2       4       6      8       10
                                  Time[min]                     be  measured  as  well.  Unstabilized  solutions

                   Fig.2: 3 NPOC Injections of 30% H2O2.        might tend to create foam when applying the
                                                                NPOC method. In such cases it is advised to
            Multiple injections of the untreated 30% hydro-
                                                                use  the  difference  method  (TOC=TC-IC)  to
            gen  peroxide  solution  were  conducted  suc-
                                                                prevent bad reproducibility.
            cessfully and with good reproducibility.

            To investigate matrix influences, a potassium
            hydrogen phthalate solution was subsequently
            added to increase the TOC content by 10 and
            20mg/L  respectively.  Concurrently,  a  mixed
            Potassium nitrate and Ammonium sulfate so-
            lution was added to increase the TNb by 1 and
            2mg/L (Figure 3).

                                 NPOC      TNb     RSD
                   Sample
                                  [mg/l]   [mg/l]   [%]
             H2O2 (30%)           19,4     2,76     1,0
             H2O2 (30%)           29,0     3,71     1,5
             (spiked  with  10mgC/l
             and 1mgN/l)
             H2O2 (30%)           38,9     4,71     0,5
             (spiked  with  20mgC/l
             and 2mgN/l)
                  Fig.3: Results of original and spiked H2O2

            The NPOC and TNb contents were found pre-           ■ Recommended analyzer / configuration
            cisely  according  to  the  added  amounts.  The    TOC-LCXH
            validity  and  efficiency  of  the  measurement     TNM-L for TNb determination
            method was thereby considered verified.             ASI-L with external sparge kit
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