Colorimetric processes for the determination and control of the

Details Colorimetric processes for the determination and control of the Colorimetric processes for the determination and control of the

1991-10-01

1995-08-01

Czaja, Donald E.

Chemistry: analytical and immunological testing

Condition responsive control

436129, 436135, 436164, G01N 3508

Patent

active

054380022

DESCRIPTION:

BRIEF SUMMARY
The invention concerns the determination and control of the content of peracid in the presence of hydrogen peroxide in an oxidizing solution, for example a cleaning and/or disinfecting solution which may for example be used on an industrial scale.
For cleaning and/or disinfecting industrial installations, for example in dairies, there are generally used oxidizing solutions comprising a peracid, for example peracetic acid (PAA) and hydrogen peroxide, possibly in the presence of other compounds such as for example acetic acid and/or nitric acid.
These solutions are normally used in closed circuit, in a main network which is possibly part of the installation to be cleaned and/or disinfected.
They may be used in a system which includes recovery of the solution after use or in a system without recovery of the solution after use but in which the composition of the solution is verified, at more or less regular intervals, and is adjusted if necessary.
For example, when it is used for disinfecting, it is important to make sure that the composition of the solution which is utilized be such that it is active against the microorganisms to be destroyed. In this context, it is therefore recommended to control at least the concentration of the most active substance, such as the peracid, which more often is peracetic acid.
In the present industrial practice, the peracid is subject to a manual determination at the time of use. This determination enables one to determine the exact concentration of peracid (and also, if necessary, of hydrogen peroxide) but it is complicated and requires the assistance of specialized manpower, it cannot be automated and does not enable one to continuously adjust the amount of peracid.
Attempts have therefore been made to automate this determination by relying on a simple and inexpensive means which also enables one to adjust "in real time" the concentration of peracid, for example of peracetic acid.
To do this, a certain number of methods and devices which are described and commented briefly hereinafter have already been proposed.
Patent application FR 2 595 837 (HENKEL FRANCE S.A.) proposes a solution which is essentially based on a potentiometric analysis in a measuring cell containing an electrode for measuring the redox potential of the oxydizing solution, and an electrode for measuring the pH of this solution. To obtain a significant reading, i.e. measuring points which are always on the same concentration/oxido-reduction potential curve within a zone in which variation is rapid, to prevent the polarization of the measuring electrode and to operate at constant pH, the proposed solution utilizes a secondary circuit enabling one to dilute the flow by means of an "adaptation solution". In the case of a solution containing hydrogen peroxide and a peracid, the analysis essentially indicates the concentration of hydrogen peroxide and not that of the truly active compound, namely peracid, for example peracetic acid.
On the other hand, other methods used, namely pH-metry and conductimetry give an indication with respect to the acidity of the medium but does not directly give information with respect to the evolution of the essential oxydizing agent, namely the peracid.
To analyze the disinfecting power of the solutions of the type in question, it has also been proposed to rely on colorimetry which enables one to distinguish between hydrogen peroxide and a peracid.
Thus, patent application EP 0 150 123 (INTEROX CHEMICALS LIMITED) describes a process for the analysis and control of the content of a peroxidized compound, such as peracetic acid, in the presence of hydrogen peroxide, by relying on colorimetric methods. This process is based on the fact that it is known that hydrogen peroxide reacts with colored reactants at room temperature, while peroxidized compounds, in particular peracetic acid, do not react significantly with these colored reagents but require heating to a temperature of for example 90.degree. C. to completely develop a color. The process described therefore uses two measuring c

REFERENCES:
patent: 3485588 (1969-12-01), Fouts
patent: 4391755 (1983-07-01), Huber et al.
patent: 4874498 (1989-10-01), Freal-Saison
patent: 4900682 (1990-02-01), Fischer et al.
D. M. Davis et al.; "Determination of Peracids in the Presence of a Large Excess of Hydrogem Peroxide Using a Rapid and Convenient Spectrophotometric Method"; Analyst, vol. 113, Sep. 1988, pp. 1477-1479.

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