Chemical apparatus and process disinfecting – deodorizing – preser – Analyzer – structured indicator – or manipulative laboratory... – Sample mechanical transport means in or for automated...
Reexamination Certificate
1998-08-27
2001-02-20
Soderquist, Arlen (Department: 1743)
Chemical apparatus and process disinfecting, deodorizing, preser
Analyzer, structured indicator, or manipulative laboratory...
Sample mechanical transport means in or for automated...
C436S074000, C436S166000, C436S079000, C073S078000
Reexamination Certificate
active
06190611
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a novel hardness indicator for detecting a hardness in a water sample.
2. Description of Related Art
Generally, city water is unsuitable for use as boiler feed water or food processing water because city water contains various kinds of impurities (e.g., hardness components such as calcium and magnesium), even if the water is fit for drinking.
Direct use of such city water as boiler feed water may cause scale deposition and/or corrosion. Therefore, it is usual practice to employ a water softening apparatus, a water deionizing apparatus, or the like thereby to provide water free of such impurities. In such a softening apparatus, for example, a strong acid cation exchange resin of Na type is used whereby hardness components (Ca
2+
and Mg
2+
) of the raw water are replaced by Na
+
so that the water is changed into soft water. However, the apparatus poses a problem that due to degradation or insufficient regeneration of the ion exchange resin there may occur hardness leaks. Therefore, it is necessary to check treated water constantly to see that there are no hardness leaks.
In the case where the method employed for detecting such a leak is such that a hardness indicator is added to soft water, so that any such leak can be detected by a change in the color of the indicator, it is desirable that for facilitating visual detection of the change in color, such a color change appears in a reasonably pronounced way in reaction to the hardness leak, even when the leak is small.
In many cases, the main component of the hardness indicator is usually EBT (eriochrome black T), and an aqueous solution of the hardness indicator is colored blue within a pH range of from 8 to 10. However, the aqueous solution has a characteristic feature where it promptly turns red upon inclusion of Mg
2+
. This characteristic feature is utilized for checking to see whether or not Mg
2+
, i.e., a hardness component, is present in the soft water.
A hardness indicator of this type reacts on Ca
2+
to form a water-soluble compound. However, as compared with a compound formed through its reaction on Mg
2+
, this compound is unstable and the change in its color is rather dull.
When such a hardness indicator is allowed to stand in a high temperature environment of greater than 50° C. as in a boiler room, EBT is oxidized so that the hardness indicator degrades.
As described above, while EBT is highly reactive with Mg
2+
to exhibit a sharp change in its color, an change in its color as a reaction on Ca
2+
is dull. As such, the sensitivity of EBT differs on the order of over 10 times depending upon the conditions. Usually, however, the concentrations of Ca
2+
and Mg
2+
in the raw water are such that the concentration of Ca
2+
is far much greater than that of the other, say, on the order of from about 3 times to 10 times the concentration of Mg
2+
, though their respective concentrations differ from district to district. Therefore, the possibility of Ca
2+
leak into the soft water is far much higher than the possibility of Mg
2+
leak and this requires early detection of Ca
2+
hardness leaks. Further, a quick reaction B required on trace amounts of Ca
2+
.
Another problem is that, as already stated, a hardness indicator is liable to faster degradation under high-temperature conditions. Therefore, in order that the hardness indicator may maintain its performance quality, it is necessary to slow down the degradation of the hardness indicator.
SUMMARY OF THE INVENTION
This invention has been developed for solving above mentioned problems and provides, in a first aspect thereof, a hardness indicator comprising EBT, a pH buffer, and a masking agent as main components, and an admixture of Mg-EDTA. According to its second aspect, the invention provides a hardness indicator comprising EBT, a pH buffer, and a masking agent as main components, and an admixture of anhydrous Mg-EDTA. In a third aspect of the invention, there is provided a hardness indicator in accordance with the second aspect which further comprises an admixture of a reducing agent such as potassium sorbate. In its fourth aspect, the invention provides a hardness indicator comprising EBT, a pH buffer, and a masking agent as main components, and an admixture of Mg-EDTA and a reducing agent such as potassium sorbate. In its fifth aspect, the invention provides a hardness indicator comprising EBT, a pH buffer, and a masking agent as main components, and an admixture of a reducing agent such as potassium sorbate.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Preferred embodiments of the invention will now be described in detail. In the invention, EBT is used as a main component of the hardness indicator. To the EBT are added a masking agent and a non-aqueous triethanolamine as a pH buffer, and the mixture is dissolved in ethylene glycol, a non-aqueous solvent, whereby a base for the hardness indicator is obtained.
Then, a commercially available Mg-EDTA is added to the base for the hardness indicator, so that a hardness indicator which sensitively reacts on a trace amount of Ca
2+
can be obtained. The commercially available Mg-EDTA is in the form of a hydrate containing a water molecule. The water molecule reacts with EBT to cause hydrolysis to thereby degrade the hardness indicator. Under ambient temperature conditions of not more than 50° C., the reaction rate in such hydrolysis is very low. Materials such as triethanolamine and ethylene glycol are non-aqueous and do not involve the problem of EBT hydrolysis. Therefore, the hardness indicator is little liable to degradation and poses no problem from the viewpoint of practical use.
Under ambient temperature conditions of greater than 50° C., the reaction rate in the process of the aforesaid hydrolysis is comparatively high, so that the degradation of the hardness indicator accelerates. Therefore, water molecules are removed from the commercial Mg-EDTA, and the resulting anhydrous is added to the base for the hardness indicator. In this way, a hardness indicator can be obtained which is slow to degrade under ambient temperature conditions of greater than 50° C.
When the base for the hardness indicator is loaded with potassium sorbate as a reducing agent, a hardness indicator can be obtained which is slow to degrade under ambient temperature conditions of greater than 50° C.
The above described modes of carrying out the invention may be carried out simultaneously. In that case, a hardness indicator can be obtained which is slow to degrade and which sensitively reacts on a trace amount of Ca
2+
. That is, the desired hardness indicator can be obtained when the base for the hardness indicator is loaded with anhydrous Mg-EDTA commercially available Mg-EDTA hydrate, and with potassium sorbate.
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patent: 3240717 (1966-03-01), Johnson
patent: 3368969 (1968-02-01), Palen
patent: 3496113 (1970-02-01), Platte
patent: 3697224 (1972-10-01), Means
patent: 3895913 (1975-07-01), Bockowske et al.
patent: 4205953 (1980-06-01), Miller
patent: 4205955 (1980-06-01), Sloat
patent: 1125682 (1962-03-01), None
patent: 48-102694 (1973-12-01), None
patent: 51-150392 (1976-12-01), None
patent: 2-82160 (1990-03-01), None
R. L. McCullough et al. Chem. Abstr, Jan. 1970, 72, 18133s.
L. Wunsch Clin. Chim. Acta 1970, 30, 157-163.
Fukumura Takeshi
Isshiki Katsufumi
Nakajima Junichi
Tachino Kazuhiro
Takechi Sadatoshi
Birch Stewart Kolasch & Birch, LLP.
Miura Co., LTD.,
Soderquist Arlen
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