Chemistry Reference
In-Depth Information
Amperometric determination of hydrogen peroxide in the
presence of additives
An important question is whether the above-mentioned influence of addi-
tives on the pseudo-limiting-current could jeopardise the use of the
prewave of the oxidation of hydrogen peroxide with glassy carbon for ana-
lytical purposes. To investigate this, a number of experiments with varying
hydrogen peroxide concentrations and pH, which have already been per-
formed in the absence of additives, were carried out again in their presence.
The results indicated that the reaction orders of the reagents involved and
the oxidation mechanism in the prewave remained the same as in the
absence of additives. This is an additional argument in favour of the hypoth-
esis that the drastic decrease in current in the presence of additives is due
to the decrease of the active surface of the working electrode. In Equation
5.2, the presence of additives is manifested in the decrease of the value of
parameter
G
.
In practice, the effect of the additives could easily be overcome by cali-
brating the sensor in the presence of the additives. This means that the
sensor needs to be calibrated in the bleaching solution of the process, which
is favourable from an industrial point of view since it is not necessary to
remove the sensor from its working environment and no standard solutions
need to be made or bought. In the next part, it is explained how this cali-
bration needs to be done.
5.3.2
Calibration of the sensor electrode
To be able to use a sensor in practice, it must always be calibrated. All vari-
able parameters should be known at the time of calibration (in this case,
current signal, pH, temperature and hydrogen peroxide concentration) and
hence should be measured. The current signal is measured by means of the
amperometrical circuit, the pH by means of the glass electrode and the tem-
perature by means of a PT100 thermometer. The hydrogen peroxide con-
centration needs to be determined by means of an independent method,
e.g. titration of a sample of the bleaching solution on potassium perman-
ganate in an acidic medium. In the event that the mutual relations between
these variable parameters are known (which is the case in this system and
is translated in Equation 5.2), it is possible for every other sample to calcu-
late the unknown hydrogen peroxide concentration after measurement of
the amperometrical current, temperature and pH. Based on Equation 5.2,
formulated for the conditions where the calibration (Equation 5.3) and the
measurement (Equation 5.4) occur, respectively, a general deduction can be
made for the measurement of the hydrogen peroxide concentration, repre-
sented in Equation 5.5:
