Chemistry: analytical and immunological testing – Halogen containing – In aqueous solution
Reexamination Certificate
1999-09-08
2004-08-17
Soderquist, Arlen (Department: 1743)
Chemistry: analytical and immunological testing
Halogen containing
In aqueous solution
C436S124000, C436S166000
Reexamination Certificate
active
06777242
ABSTRACT:
1. BACKGROUND OF THE INVENTION
1.1 Technical Field
The present invention relates to a stable aqueous solution (A) comprising an azo dye, a borate buffer and one or more masking agents, wherein the azo dye changes its coloration or coloration intensity in the presence of chlorine dioxide. The present invention further relates to a process for manufacturing the stable aqueous azo-dye solution (A), and to its use for the determination of residual chlorine dioxide in water.
1.2 Background of Art
Since the discovery of the interactions between chlorine and the microorganisms present in untreated water and the resulting formation of toxic compounds, such as trihalomethanes, many studies have been carried out worldwide in order to find replacement solutions for disinfecting drinking water. Among the disinfectants proposed is chlorine dioxide. Accordingly, in recent decades, chlorine dioxide has been used in many countries to disinfect drinking waters and to condition industrial waters.
Since a certain amount of disinfectant must be present in the treated water to prevent it from being recontaminated, it is essential to determine accurately the residual amount of the disinfectant in the water.
Moreover, during the treatment of water and the period in the distribution network, chlorine dioxide participates in various oxidation reactions which lead to the formation of reduction/decomposition by-products, mainly consisting of chlorides, chlorates and chlorates. Thus, it is necessary to have a reliable method for determining the chlorine dioxide content in the treated water even in the presence of other oxidizing agents and chloro-compounds.
Lastly, the process for determining the chlorine dioxide content in water should comprise a limited number of operations and should be able to be carried out directly on site so as to avoid a loss of chlorine dioxide by degassing.
Although several methods have been proposed for determining chlorine dioxide, none of them satisfy all the above-mentioned criteria. Various methods, particularly colorimetric methods, available to date are listed in the thesis by J. D. Peak, Edmonton, Alberta, 1991. According to J. D. Peak, because of their virtually unselective natures, these colorimetric methods have been excluded from routine practices in industry.
Specifically, the method using DPD (N,N-diethyl-p-phenylenediamine sulphate), which is not sufficiently selective, often leads to erroneous results. Furthermore, it cannot determine the chlorine dioxide contents less than 0.1 mg/l.
Similarly, the method based on the decolorization of Alizarin Violet 3R (ACVK), developed by W. J. Masschelein (
Analytical Chemistry
, 38:1839, 1996) has a quantification threshold greater than 0.1 mg/l of chlorine dioxide.
To make the Chlorophenol Red (CPR) method selective, J. Fletcher and P. Hemmings (
Analyst
, 110:695, 1985) have proposed to use masking agents. This method, which involves several steps, consists of mixing the sample with a sodium cyclamate solution, adding immediately a buffer solution with stirring, followed by a chlorophenol red solution, and finally adding a thioacetamide solution. By measuring the absorbance of the final mixture at 520 nm using a UV-visible spectrophotometer, the residual content of chlorine dioxide in the sample can be determined.
However, the major drawback of this method is that it involves many steps of placing the sample in contact with a series of reagents and thus leads to a considerable and uncontrolled loss of chlorine dioxide by degassing (up to 30%).
2. SUMMARY OF THE INVENTION
The present invention by the applicants provides an aqueous solution (A) comprising an azo dye, a borate buffer and one or more masking agents, wherein the azo dye changes its coloration or coloration intensity in the presence of chlorine dioxide, and now makes it possible to determine accurately and selectively the residual content of chlorine dioxide in water, in particular, in drinking water.
The azo dye is advantageously chosen from amaranth (trisodium salt of 1-(4-sulfo-1-naphthylazo)-2-naphthol-3,6-disulfonic acid, C
20
H
11
N
2
Na
3
O
10
S
3
), C.I. 16185, and Evans blue (tetrasodium salt of 6,6′-[(3,3′-dimethyl[1,1′-biphenyl]-4,4′-diyl)bis(azo)]bis[4-amino-5-hydroxy-1,3-naphthalenedisulfonic acid, C
34
H
24
N
6
Na
4
O
14
S
4
], C.I. 23860.
The concentration of azo dye in solution (A) is generally between about 1×10
−6
and about 1×10
−3
M. It is preferably between about 2×10
−5
and about 8×10
−4
M. An amaranth concentration of about 2×10
−4
M has been found to be particularly advantageous. When the dye is Evans blue, a concentration of about 5×10
−5
M is advantageously chosen.
The borate ion is generally present in solution (A) in a proportion of from about 5×10
−3
to about 1×10
−1
M. A borate ion concentration of about 5×10
−2
M is preferred.
In this specification, the term “masking agent” means any compound capable of reacting with free chlorine: for example, glycine, cyclamate of alkali metal or alkaline earth metal, and aqueous ammonia. The amount of masking agent(s) used in solution (A) depends on its (their) nature. Preferably, aqueous ammonia is used, and in an amount advantageously between about 1 and about 4 g/l of solution (A).
The aqueous azo-dye solution according to the present invention can further comprise one or more metal-chelating agents such as EDTA (ethylenediaminetetra-acetic acid) salts. The amount of chelating agent(s) used varies depending on its (their) nature. In the case of the sodium salt of EDTA, the amount used per liter of solution (A) is generally between about 0.5 and about 2 g and preferably about 1 g. The solution (A) which is most particularly suitable contains, per liter, about 5×10
−2
mol of borate, about 1.5×10
−2
mol of aqueous ammonia, about 1 g of sodium salt of EDTA, and about 2×10
−4
mol of amaranth or about 5×10
−5
mol of Evans blue.
Another subject of the invention is a process for manufacturing a solution (A). In general, this process comprises following steps:
(a) a buffered aqueous azo-dye solution is prepared by introducing the azo dye, the masking agent(s) and the borate buffer solution into a container containing a sufficient amount of double-deionized water;
(b) the chelating agent dissolved in advance in double-deionized water is optionally added thereto, with stirring; and
(c) the solution is made up to the desired volume with double-deionized water.
A pH of the aqueous azo-dye solution prepared in step (a), should be preferably about 9.2.
More particularly, the process for manufacturing a solution (A) comprises the following successive steps:
(i) the azo dye is dissolved in double-deionized water in a container;
(ii) a borate buffer solution is then introduced therein, followed by a solution of masking agent(s);
(iii) double-deionized water is added thereto and the pH is measured;
(iv) the pH is adjusted to about 9.2, if necessary;
(v) the chelating agent is optionally dissolved, with stirring; and
(vi) the solution is made up to the desired volume with double-deionized water.
Advantageously, an aqueous ammonia solution is used to adjust the pH. A concentrated aqueous ammonia solution at about 28% by weight is particularly suitable to be used for pH adjustment and as a masking agent.
The aqueous azo-dye solution (A) thus prepared remains stable at room temperature for at least one month in a closed bottle.
Yet another subject of the present invention is a process for determining the residual chlorine dioxide content in an industrial water or drinking water after biocidal treatment or disinfection and in distribution circuits. This process consists of placing the water to be analyzed in contact with the aqueous solution (A) and then measuring the absorbance of the resultant solution (S) using a UV-visible spectrophotometer, at the specific wavelength for the azo dye chosen.
Gautier Jean-Pierre
Mantisi Frédérick
Atofina
Roland Thomas F.
Soderquist Arlen
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