RESULTS - SR97

SR97_05
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Ion chromatography with conductivity detection

Instrument: Dionex ion chromatograph

Column: PAX-500

Solvent: A = 200 mM NaOH; B = 0.6 mM NaOH; C = 5% methanol

Gradient: T = 0 to 10 min: 0/25/75 (A/B/C)

T = 10 to 15 min: 10/65/25

T = 15 to 30 min: 30/45/25

T = 30 to 40 min: 30/45/25

T = 40 to 45 min: 0/75/25

Flow rate: 1.0 mL/min

Anion suppressor: 27 mM H2SO4

Hydroxyl radical oxidations

Hydroxyl radicals were generated using Fenton's system, where Fe+2 is oxidized to Fe+3 in the

presence of hydrogen peroxide to generate hydroxyl radical as shown below.

Fe+2 + H2O2 --------> Fe+3 + HO + OH

In this system, hydrogen peroxide is incrementally added in the dark to freshly prepared 0.88 M

Fe(ClO4)2 solution containing the ADNT and p-nitroacetophenone (PNAP, internal reference chem-

ical). The solution was stirred for 20 min and the ADNT and PNAP were analyzed directly by

HPLC.

Peroxone treatment system oxidations

The efficiency of peroxone oxidations compared to oxidations by other potential oxidants in the

peroxone system was determined in three experiments: one with ozone and 1.9 mM t-butyl alcohol

as a HO scavenger; one using ozone alone; and one using ozone with 117 M hydrogen peroxide.

In each of these experiments, ozone was added at 0, 39, 82, or 182 M to stirred solutions of the

ADNT. After each ozone addition, samples were removed for analysis of the ADNT by HPLC and

remaining hydrogen peroxide by the titanium sulfate method (Setterfield and Bonnel 1955).

RESULTS

Direct ozonation rate constant (kO )

Two reference chemicals, resorcinol and nitrite ion, with reported rate constants of 9.4 104

M1 s1 and 3.5 105 M1 s1, respectively (Buxton and Greenstoch 1988), were selected for compet-

itive kinetic studies with 2-ADNT and 4-ADNT. Both ADNTs disappeared in the presence of ozone;

the data appear in Table 1.

First-order plots of 2-ADNT and 4-ADNT loss and reference compound loss (nitrite) appear in

Figure 1. From eq 4 the rate constant for 2-ADNT loss was calculated to be 1.4 105 M1 s1 with

resorcinol as a reference and 5.3 105 M1 s1 with nitrite as a reference. For 4-ADNT, the rate con-

stants were 1.5 105 M1 s1 and 1.9 105 M1 s1.

Because the reaction of ozone with the ADNTs could generate hydroxyl radical, identical exper-

iments were performed in the presence of twentyfold excess t-butyl alcohol as a hydroxyl radical

scavenger. The loss of ADNTs was not affected (see "Oxidation in peroxone oxidizing system,"