AP239A

AP239A - Process for the determination of the iodine content of drinking water.

Info

Publication number: AP239A
Application number: APAP/P/1990/000215A
Authority: AP
Inventors: Gerard Gernez
Original assignee: Rhone Poulenc Sante
Priority date: 1989-10-27
Filing date: 1990-10-25
Publication date: 1993-02-14
Also published as: FR2653887B1; EP0425385A1; NZ235833A; CA2028651A1; OA09320A; AP9000215A0; BR9005547A; JPH03154863A; IL96121A0; US5137690A; FR2653887A1; AU646819B2; AU6497490A

Abstract

Method for the determination of the iodine

Description

The present invention relates to a method for the determination of the iodine content of drinking water, and to apparatus for carrying out the determination.

In humans, a lack or deficiency in iodine leads to particularly important pathological disorders in particular, goitre and its complications (deglutition disorders, respiratory disorders, cancer formation, collateral circulation) and, hypothyroidism and its complications (cretinism, cerebral disorders, premature deliveries, miscarriages, congenital anomalies).

Even if iodine deficiency is no longer a problem in industrialized countries, this is not the case in developing countries such as Latin American countries along the cordillera of the Andes, and the non-coastal countries of Africa and Asia.

Of the different methods proposed for remedying this deficiency, the most effective one consists in adding iodine to the water for domestic use (drinking, washing, irrigation) which most frequently is made available by wells and drillings.

Many studies have shown that a daily supply of about 100 ug of iodine equivalent per day and per person would be sufficient for preventing the development of endemic goitre.

Since it is known that an individual takes up on average 2 litres of water per day, it is desirable that one litre of treated water should contain at least 50 gg per bad original $

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There are various systems which make the controlled release of iodine into well or drilling water possible, and it is of particular importance to be able to control the effective iodine content in water.

According to the present invention, a method has been found which enables people who have no particular scientific knowledge to evaluate on site in a few minutes, with a minimum of handling and in complete safety whether the iodine content of drinking water is greater than or equal to 50 μς per litre.

The present invention therefore provides a method for the determination of the iodine content in drinking water, comprising comparing the coloration of the water to be analyzed to that of an iodine reference solution in the presence of a fixed amount of cerium and arsenic. Generally the cerium is present as cerium (IV) e.g. a cerium IV salt and the arsenic as arsenic (III).

The method of to the invention is based on a colorimetric method originating from the implementation of the Sandell-Kolthoff reaction, the steps of which are as follows :

in > 2 Ce³ + + I₂

I₂ ---> 2 Ce³+ + 2I⁺

As³+---> I₂ + As⁵ + is known that the Ce⁴+ ion is yellow ³+ ion is colourless, the presence of

Ce⁴+ + 2 Ce⁴+ + 2 1* +

Since it solution and the Ce

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- 3 iodine in the medium catalyses the reduction of Ce⁴⁺ to Ce³⁺by As³⁺ and hence the loss of coloration of the initial solution containing the Ce⁴+ ions. In the presence of small amounts of iodine, the reaction kinetics show a first order dependence upon iodine. Thus, by comparing the rate of de-coloration of the water to be analyzed in the presence of cerium and arsenic to that of the reference solutions, or comprising the coloration after a certain period of time the iodine content of the analyzed water can be determined.

Preferably the water is contacted with the arsenic before the cerium so that any oxidised iodine, e.g. in the form of iodate, is reduced to iodide before reaction with cerium begins.

The invention further provides apparatus for the determination of the iodine content of water as hereinbefore described, comprising a tube having a first closed end, inside which is a fixed amount of a supported cerium derivative, and a second closeable open end, there being a piercable film disposed between the open end and the supported cerium derivative, and a supported arsenic derivative in the space between the film and the open end, at least a portion of the tube, at the closed end, being transparent or translucent.

In particular the apparatus may comprise first and second coaxial, colourless, transparent or transluscent, preferably transparent tubes, the first tube having an open and a closed end, and the second tube having an open end and bad original $

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- 4 a closeable open end; the open end of the first tube engaging the open end of the second tube, and the piercable film being disposed across the open end of the first or the second tube. The two tubes may be arranged with the first tube as an outer tube and the second tube as an inner tube having the piercable film across the end engaging the outer tube and a removable closure across its other end.

Figure 1 shows an apparatus suitable for use in the method of the present invention.

The apparatus shown in Figure 1 comprises two transparent, colourless coaxial tubes:

- an outer tube closed (10) at one end contains a support (silica) containing a fixed amount of a cerium derivative (18) (e.g. cerium (IV) ammonium sulphate hydrate),

- an inner tube (12) whose outer diameter corresponds to the inner diameter of the outer tube and which is partially engaged in the outer tube. The inner tube is closed at its end located in the inside of the outer tube by means of a pierceable film (14) and contains a support (silica) containing a fixed amount of an arsenic derivative (20) (e.g. arsenic (III) oxide). The outer portion of the inner tube is closed by means of a removable closing (16) system.

In general, the outer tube has a diameter of substantially 1 cm, and the thickness of the wall of the outer tube is substantially 1 mm. Generally the length of the outer tube between its closed end and the pierceable film is substantially 6 cm.

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- 5 The outer and inner tubes can for example be made of glass or of a transparent, rigid and colourless plastic material (e.g. polystyrene). It is imperative that the material of which the tubes are made be insensitive to the cerium and arsenic derivatives and to iodine.

The apparatus described above functions in the following manner:

The removable closure is taken off the inner tube, a fixed amount of water (1 cc) is introduced for testing by means of a rigid and pointed tube, the film is pierced, the removable closure is replaced and the apparatus is carefully shaken. After letting stand for several minutes, the coloration of the solution obtained is compared to that of a solution obtained in the same manner using an iodine reference solution which is added to a second set of apparatus at substantially the same time as the solution to be analysed is added to the first set of apparatus.

The support containing the cerium derivative can be prepared as follows:

a) Analytically pure cerium (IV) ammonium sulphate dihydrate (2.50 g) and 0.5M sulphuric acid (56 cc) are introduced into a 100 cc volumetric flask and made up to 100 cc with twicedeionized water.

b) Silica (TIXOSIL 38 A) (5 g) , ^fche solution prepared above (25 cc) and °.5M sulphuric acid (51 cc) are introduced into the flask of a rotary evaporator. The mixture is evaporated to dryness at 60°C under reduced pressure (17 mm Hg;

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- 6 2.26 kPa). The weight of the residue must be slightly less than 13 g. It is made up to 13 g by adding twice-deionized water, the powder obtained is then homogenized to obtain a uniformly impregnated supported cerium derivative and placed at the bottom of the outer tube.

The support containing the arsenic derivative can be prepared in the following manner:

a) Analytically pure arsenic (III) oxide (0.5 g) and analytically pure sodium chloride (0.8 g) are introduced into a 100 c^c volumetric flask. 10 c^c of IM sodium hydroxide solution are added, and the mixture is made up to 100 c^c.

b) Silica (TIXOSIL 38 A) (5 g) and the solution prepared above (25 cc) are introduced into the flask of a rotary evaporator. The mixture is evaporated to dryness at 60°C under reduced pressure (17 mm Hg; 2.26 kPa). The weight of the residue obtained is close to 12 g. The powder obtained is homogenized and placed in the inner tube.

In general, when it is desired to determine iodine concentrations close to 50 Mg per litre, the outer tube contains 100 mg of powder containing the cerium derivative and the inner tube contains 100 mg of powder containing the arsenic derivative.

The invention also provides, as a further feature, a further apparatus for carrying out the method of the present invention, which apparatus comprises 4 tubes each having an open and a closed end, and each of which is

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- 7 identified by a ring and a coloured stopper; the first tube containing a fixed amount of an arsenic derivative, the second tube containing a fixed amount of an iodine reference solution and the third and fourth tubes containing a fixed amount of a cerium derivative. Generally the tubes are made of glass or a transparent rigid and colourless plastic material (e.g. polystyrene). The apparatus may be used with a sampling tube, generally containing 2 cc.

The tubes may, for example, contain the following reactants,

- first tube: O.lcc of an arsenic reactant the preparation of which is described below

- second tube: 2cc of an iodine reference solution, the preparation of which is described below

- third and fourth tubes: 200mg of a silica support containing the cerium, the preparation of which has been described above.

The apparatus may be used as follows:

Water (2 cc) for testing is sampled by means of a sampling tube and placed in the tube containing the arsenic reactant. The tube is closed and carefully shaken by turning it over several times in succession. The contents of the first and second tubes are then transferred to the third and fourth tubes, respectively. The tubes are then stoppered and carefully shaken by turning them over several times in succession: the suspensions obtained are yellow. They are allowed to stand, and the discoloration of

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- 8 the suspensions present in the third and fourth tubes are then noted. If the suspension of the third tube (test) is discoloured more rapidly than that of the fourth tube (reference), the water to be analyzed contains more than 50 Mg/litre of iodine.

The arsenic reactant can be prepared as follows:

Analytically pure arsenic (III) oxide (5.0 g) and analytically pure sodium chloride (8.09 g) are introduced into a 100 cc volumetric flask. A 10M sodium hydroxide solution (100 cc) is added, and the mixture is made up to 100 cc with twice-deionized water.

The iodine reference solution can be prepared as follows:

^The arsenic reactant described above (5 cc) and a 1 mg/litre iodine reference solution (5 cc) are introduced into a 100 cc volumetric flask. The mixture is made up to 100 cc with deionized water.

The present invention also relates to a kit for determining the iodine content of drinking water.

The assay kit can comprises either: a) - two sets of apparatus each comprising a tube with a piercable film disposed in it as described above, a rigid and pointed tube graduated, such that it takes up a fixed amount of water to be analyzed or of iodine reference solution, and

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- 9 an ampoule or closed tube containing a stabilized aqueous iodine solution of known concentration: (one tube is used for analyzing the water to be analyzed, the second one is used for carrying out a reference test with the iodine solution of known concentration), or:

b) 4 tubes containing reactants as described above and a sampling tube.

The comparison of the colorations obtained and the rate of decolouration with the water to be analyzed and the reference solution make it. possible to determine whether the iodine concentration in the water to be analyzed is lower than, equal to or higher than the concentration of the reference solution.

Claims

1. A method for the determination of the iodine content of drinking water by observing the discoloration of an aqueous solution containing yellow Ce^tV) ions with iodine in the presence of arsenic characterized in that the coloration of the water to be analysed in the presence of a fixed amount of Ce(IV) and arsenic is compared with that of an iodine reference solution in the presence of a fixed amount of cerium (IV) and arsenic.·*

2. Apparatus for the determination of the iodine content of drinking water by a method as claimed in claim 1, comprising a tube having, a first closed end,

10 inside which is a fixed amount of a supported cerium derivative, and a second closeable open end, there being a piercable film disposed between the open end and the supported cerium derivative, and a supported arsenic derivative in the space between the film and the open end,

15 at least a portion of the tube, at the closed end, being transparent or translucent.

3. Apparatus according to claim 2, which comprises first and second coaxial, transparent, colourless tubes, the first tube having an open and a closed end, and

20 the second tube having an open and a closeable open end; the open end of the first tube engaging the open end of the second tube, and the piercable film being disposed across the open end of the first or the second tube.

4. Apparatus according to claim 3, wherein

25 the first tube is an outer tube, the second tube is an inner bad original

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- 11 tube closed at one end by a piercable film and having at its other end a removable closure.

5. Apparatus according to claim 4, in which the outer tube has a diameter of substantially 1 cm and the thickness of the outer tube wall is substantially 1 mm.

6. Apparatus according to claim 3, 4 or 5, in which the tubes are made of glass or of a transparent, rigid and colourless plastic material.

7. Apparatus according to any one of claims 2 to 6, in which the supported cerium derivative comprises silica impregnated with an acidified cerium (IV) ammonium sulphate dihydrate.

8. The apparatus according to any one of claims 2 to 7 in which the supported arsenic derivative comprises silica impregnated with arsenic (III) oxide.

9. An assay kit for the determination of the iodine content of drinking water, which comprises

- two sets of apparatus as claimed in any one of claims 2 to 8

- a rigid and pointed graduated tube, and

- an ampoule or tube containing an aqueous iodine solution of known concentration.

10. Apparatus for the determination of the iodine content of drinking water by a method as claimed in claim 1, which comprises 4 tubes, each of which has an open end and a closed end and is identified by a ring and a coloured stopper, the first tube containing a fixed amount bad original ' ,. ; - - i-’s · -^:>7 . ^; - ϊ^{: :} - ' JfQS*

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- 12 of an arsenic derivative, the second tube containing a fixed amount of an iodine reference solution and the third and fourth tubes containing a fixed amount of a cerium derivative.

11. Apparatus according to claim 10, in which the tubes have a diameter of substantially 1 cm and the thickness of the tube walls is substantially 1 mm.

12. Apparatus according to claim 10 or 11, in which the tubes are made of glass or of a transparent, rigid and colourless plastic material.

13. Apparatus according to claim 10, 11 or 12, in which the arsenic derivative is a basic solution of arsenic (III) oxide.

14. Apparatus according to any one of claims 10 to 13, in which the cerium derivative comprises silica impregnated with an acidified cerium (IV) ammonium sulphate dihydrate.

15. Apparatus according to any one of claims 10 to 14, in which the iodine reference solution comprises an arsenic reactant and an iodine reference solution.

16. An assay kit for the determination of the iodine content of drinking water, which comprises:

- an apparatus as claimed in claim 8, and

- a further sampling tube.