GB2218201A - Method and product for determining cationic compounds - Google Patents

Abstract

A product which may be used in determining cationic surface-active compounds, especially such compounds as cannot readily be measured by available test methods, comprises in combination a solid component containing dimidium bromide, disulphene blue and a water-soluble anionic compound, and a liquid component containing an aliphatic alcohol having from 6 to 10 carbon atoms in the molecule. The solid component may usefully be in the form of one or more tablets. The product may be used by contacting an aqueous solution of the cationic compound under test with the solid and liquid components, shaking the mixture, allowing the organic and aqueous phases to separate and comparing the colour of the organic phase with an appropriate colour standard.

Description

Method and Product for Determining Cationic Compounds.

The present invention is a novel product of value for determining concentrations of cationic surface-active compounds and also a novel test method using that product. They are of particular value in determinina cationic compounds which cannot readily be measured by available test methods.

Cationic surface-active compounds, and formulations based on such compounds, are extensively used as biocides and algicides in commercial applications. Typical uses include products for the control of slime and algae growth in cooling water systems, the control of bacteria and algae in swimming pool water, the sterilizing or sanitizing of utensils, equipment and plant in food processing establishments and in mechanical dish washing products used in canteens, restaurants and such establishments.

In such applications the availability of a single test method for the level of cationic surface-active agent in solution is desirable, if not essential, for effective control over use of the product.

For example it is essential to ensure that a sufficiently high level of the cationic compound is present to ensure rapid destruction of micro organisms, whilst at the same time excessive levels must obviously be avoided. For this purpose, a simple on-site test method is necessary. The precise levels of cationic compound to be maintained will depend on the requirements of individual applications.

In most cases, concentrations of cationic surface-active compounds can be easily measured by readily available colorimetric test procedures. The roost widely applied tests are those which involve the direct reaction in aqueous solution of the cationic compound with an indicator of the sulphonephthalein type. Typical examples of indicators used include brcmDcresol green, bratocresol purple and bromothymol blue. Differing concentrations of cationic compound react with a prescribed amount of indicator to produce a distinctive range of colours which can be compared against colour standards in the form of a printed colour strip or plastic or glass colour standards.

ver, some cationic compounds, and formulations thereof, cannot be tested by this simple method of determination. There are various reasons for this, notably where the cationic activity of the compound concerned is weak and will not thus form the desired colour complex with the indicator in aqueous solution; where a compound has adequate cationic activity but the colour complex is imuediately precipitated from solution by the coagulating and flocculating action of the compound; or in compounds where the nature of other chemical groups or ingredients acts to inhibit the normal colour-forming reaction.Three such cationic surface-active compounds which fall into this difficult-to-analyse category are the following: Poly (hydroxy ethylene (dLmethylirino) beta - hydroxypropvl (dimethylimino) - methylene - dichloride) Poly (2-hydroxyethylene (dimethylimino) ethylene (dlmethylimino) methylene dichloride) Poly (oxyethylene (dlmethylimino) ethylene (dimethylimino) ethylene dichloride) It is necessary in determining compounds of this type to use alternative test methods. Such methods are available as laboratory procedures and involve adding the solution of the cationic surface- active compound under test as a titrant to a two-phase mixture comprising an aqueous phase containing a standard amount of an anionic surface-active compound and an indicator system and a chloroform phase which extracts the indicator colour. The titration is carried out with repeated shaking of the reaction flask, the titration being considered complete when a colour change is observed in the chloroform layer.

While methods of this type provide an accurate and viable means for determining cat ionic surface-active compounds in the laboratory, for various reasons they are totally unsuitable for use for testing on site. For example, they require the use of standard chemical apparatus and are therefore suitable for use only by those practised in the art of chemistry and acquainted with the use of such apparatus moreover, they require a multiplicity of different reagents and the use of solutions prepared in three different solvents, for example water, ethanol and chloroform. The use of such solvents is inappropriate for a simple on-site test.Ethanol solutions are volatile and readily inflammable, and, rttre importantly, the use of chloroform is not acceptable on toxicity grounds. Moreover because of the chmical properties of chloroform it is necessary for the whole test to be carried out in glass apparatus. Conventional and readily available plastics materials are not suitable for use with chloroform mixtures.

A final objection to the use of chloroform as a solvent in, such tests is the fact that chloroform is heavier than water and thus florins a layer below that of the aqueous phase in the test flask. This does not create any problem when analysing clean aqueous solutions of standard cationic compounds in the laboratory.

However in on-site testing in typical situations, a heavier-than-water solvent has a nutter of disadvantages. These stem from the fact that cationic surface-active compounds are powerful coagulating aaents and will readily precipitate from solution any finelydivided particulate matter which may be present.In the practical use of surface-active compounds such as in cooling water treatment, swiming pool water treatment or in mechanical dish-washing applications, the test solution may be considerably oontarninated with particulate matter which can be readily coagulated by the action of the surfaceactive compound. In practice therefore when using chloroform as the non-aqueous solvent in the test procedure, the solution does not readily separate into two clean and distinct layers after the shaking period. The particulate matter collects at the bottam of the aqueous layer, i.e. at the interface between the aqueous and chloroform layers, making separation of the two layers indistinct and observation of the colour of the chloroform layer difficult.

In severe cases the chloroform can be completely absorbed onto the particulate matter to form a dirty scum at the bottom of the tube without any distinct separation between the two layers.

Thus there remains a need for a simple and reliable test method for cationic surface-active compounds, especially such compounds as are in the difficult-to-analyse category, which irthod is suitable for on-site use. Preferably the test uses a single reagent mixture of standardised composition and does not entail the use of a heavier-than-water or toxic solvent, and can be carried out in a single test tube using simple colorimetric evaluation.

The present invention aims to satisfy that need by the provision of a novel product and a test method which uses that product.

The product according to the present invention, for determining cationic surface-active ccmpounds, comprises in combination a solid component containing dimidium branide, disulphene blue and a watersoluble anionic compound, and a liquid component containing an aliphatic alcohol having from 6 to 10 carbon atoms in the molecule.

The novel test method according to the invention oamprises contacting an aqueous solution of the cationic surface-active compound under test with a solid component as aforesaid and with a liquid component as aforesaid, shaking the resulting mixture, allowing the organic and aqueous phases to separate and comparing the colour of the organic phase with one or more colour standards.

The solid component may be used in the form of a powder but preferably is in tablet form, in particular a tablet of predetermined composition equivalent in amount to a standard test measure or a sub-multiple of the standard measure. The component may contain an inert diluent and, when in tablet form, may also contain one or more lubricants, binders, fillers or other tableting aids.

The water-soluble anionic compound may be any such anionic surface-active compound as will react readily with cationic surface-active compounds and may, for example, be such compounds as are already used in the conventional colorimetric test methods for cationic surface-active compounds. A preferred and readily available anionic compound for this present purpose is sodium lauryl sulphate. Other suitable compounds include ammonium lauryl sulphate, triethanolamine lauryl sulphate, sodium lauryl ethoxylate sulphate, sodium o'eyl cetyl sulphate, sodium toluene sulphonate and sodium dodecyl benzene sulphonate.

The liquid component, which forms the organic phase in carrying out the test method, may comprise the aliphatic alcohol alone or forming a major part of a solvent mixture. Preferably the alcohol is used alone. Any aliphatic alcohol may be used which contains from 6 to 10 carbon atoms in the molecule. Aliphatic alcohols containing fewer or more carbon atoms than this are unsuitable. Thus the CX to C3 alcohols become completely miscible with the aqueous phase and do not form a separate organic layer.

The C4 and C5 alcohols form a separate organic layer, but completely extract the indicators into the organic phase and do not show the requisite colour change in the presence of cationic or anionic suface-active compounds within the aqueous phase. When higher aliphatic alcohols (i.e. C11 alcohols and over) are used, these form a separate organic layer but do not have sufficient miscibility with water to adequately dissolve the solid indicator compounds.

Thus aliphatic alcohols which may form the liquid component, alone or in admixture, of the present invention include hexanol, heptanol, 2-ethyl hexanol, iso-octanol and nonanol.

As already indicated, the test procedure is a simple one, readily applied "in the field" without recourse to laboratory equipment or facilities. In one form it comprises taking a prescribed volurre of the solution under test in a plastic test tube; adding a tablet of the solid reagent mixture and a prescribed volume of the aliphatic alcohol; shaking the mixture for a prescribed period (typically 30 seconds); allowing the coloured organic phase to separate as an upper layer in the test tube; and then comparing the colour of the organic phase with prepared printed or transparent colour standards.

The invention is further described and illustrated by means of the following Exfflmples:- Example 1.

A solid reagent powder was prepared by mixing the following ingredients: Dimidium bromide 0.2g Disulphene blue 0.2g Sodium lauryl sulphate 12.0g Boric acid 1988.0g A series of standard aqueous solutions were prepared from a concentrated solution of cationic surface-active compound containing 50% Poly (2-hydroxyethylene (dimethylimino) ethylene (dimethylimino) methylene dichloride). After dilution, the standard solutions corresponded to 12.5, 18.75, 25 and 31.25 mg/l of active cationic compound.

10 ml of each of the above standard solutions were taken in a series of plastic test tubes. To each tube was added 0.1 g of the powdered reagent mixture previously described, and 0.5 ml of iso-octanol. The tubes were then stoppered and shaken for 30 seconds and then allowed to stand for 30 seconds. At the end of the standing period a discreet, clear, coloured organic layer had separated at the top of the tube. The colour of the organic phase was noted as follows: Concentration of Active Colour of Organic Layer Cationic Compound (mg/l) 12.5 Pink 18.75 Pink 25.00 Purple 31.25 Blue This example has demanstrated the use of a solid powder reagent in conjunction with iso-octanol solvent for checking the level of cationic surface-active compound in solution. In the manner described the reagent and solvent mixture enable the solution to be checked to determine whether this corresponds to 25.00 mg/l (a typical use-concentration), or whether the concentration of solution is above or below this figure.

Example 2.

A series of standard solutions were prepared using a concentrated solution of cationic surface-active compound containing 50% Poly (oxyethylene (dimethylimino) ethylene (dfimethylimino) ethylene dichloride). After dilution the standard solutions corresponded to 25, 50 and 75 mg/l active cationic compound.

20 ml of each of the standard solutions were taken in a series of plastic tubes. To each tube was added 0.4 g of the powdered reagent mixture described in Example 1 and 2 ml nonanol.

The tubes were stoppered and shaken for a period of one minute and then left to stand for a period of 30 seconds. At the end of the standing period a discreet, clear-coloured organic layer had separated at the top of each tube. The observed colours of the organic layer were as follows: Concentration of Active Colour of Organic Layer Cationic Compound (ma/l) 25 Pink 50 Purple 75 Blue This example has further illustrated the use of the powdered reagent and solvent for the on-site testing of cationic surface-active compound at a control level of 50 mg/l active cationic content.

Example 3.

A tablet reagent was prepared by compressing together the following ingredients: Dimidirm bromide 6.0g Disulphene blue 6.5g Sodium lauryl sulphate 30g Boric acid 4000g Adipic acid 500g Microcrystalline cellulose 1800q Talc log Each tablet weighed 100 mg.

A series of standard solutions were prepared using a concentrated solution of cationic surface-active compound containing 50% Poly (hydroxy ethylene (dimethylimino) beta hydrocypropyl (dimethylimino) - ethylene - dichloride).

After dilution the solutions corresponded to 17.5, 18.75 and 20 mg/l active cationic compound.

10 ml of each standard solution was taken in a plastic test tube. To each tube was added one of the reagent tablets previously described and 0.5 ml of iso-octanol. The tubes were stoppered, shaken for 30 seconds and then allowed to stand for one minute, At the end of the shaking period a discreet, clear-coloured organic layer separated. The colours observed in the organic layer were as follows: Concentration of Active Colour of Organic layer Cationic Compound (mg/l) 17.5 Pink 18.75 Purple 20.00 Blue The example demonstrates the use of the tablet reagent in conjunction with iso-octanol as solvent as an accurate on-site control test for cationic surface-active compounds at a proposed use concentration of 18.75 mg/l active cationic compound.

Example 4.

The procedure described in Example 3 was repeated except that the solvent used in the test procedure was 1 ml of nonanol. The tubes containing the standard solution, tablet reagent anci nonanol were shaken for a period of 30 seconds and allowed to stand for 30 seconds. At the end of the standing period the observed colours were as follows : - Concentration of Active Colour of Organic Layer Cationic Compound (mg/l) 17.5 Pink 18.75 Purple 20.00 Blue This example further demonstrated the use of the tablet reagent, with nonanol as solvent, for the on-site testing for cationic surface-active compound at an optimum use concentration of 18.75 mg/l active cationic content.

Example 5.

A test kit suitable for on-site testing of cationic surface-active compounds was made up with the followinc contents: 30 of the test reagent tablets of Example 3; 30 ml of nonanol in a plastic bottle; A stoppered plastic test tube printed with two calibration marks corresponding to volumes of 10 ml and 11 ml respectively; and A printed colour chart showing pink, purple and blue colour standards corresponding to the different colours produced in the organic layer in use.

The kit was used for testing cationic surface-active compounds in the manner exemplified as follows: The graduated plastic test tube was filled to the 10 ml mark with the solution under test of the cationic surface-active compound used in EXample 3. Nonanol was added to make up the volume in the tube to the 1l ml mark (that is, 1 ml of nonanol was added). One test reagent tablet was added to the tube and the tube was stoppered and shaken for a period of 30 seconds and then allowed to stand for a period of 30 seconds. At the end of the standing period, the colour of the clear organic layer separating at the top of the tube was compared against the printed colour standards. The levels of cationic surface-active compound corresponding to each of the three colour standards were as follows : - CONCENTRATION OF ACTIVE COLOUR STANDARD CATIONIC COMPOUND (ng/l) Pink 17.5 or below Purple 18.75 Blue 20.00 and above In a second version of the test kit described above, designed for the on-site control of a cationic surface-active compound at an optimum use concentration of 18.75 mg/l, the three colour standards Pink, Purple and Blue were marked Too Low, Correct and Too High respectively.

Claims (10)

1. A product for use in determining concentrations of cationic surface-active compounds, comprising in combination a solid component containing dimidium bromide, disulphene blue and a water-soluble anionic compound, and a liquid component containing an aliphatic alcohol having from 6 to 10 carbon atoms in the molecule.

2. A product as claimed in claim 1, wherein the solid component contains an inert diluent.

3. A product as claimed in either of claims 1 and 2, wherein the solid component is in tablet form.

4. A product as claimed in claim 3, wherein the tablets of the solid component also contain one or rrore lubricants, binders, fillers or other tableting aids.

5. A product as claimed in any of the preceding claims, wherein the water-soluble anionic compound is sodium laurel sulphate.

6. A product as claimed in any of claims 1 to 4, wherein the water-soluble anionic compound is ammonium lauryl sulphate, triethabolamine lauryl sulphate, sodium lauryl ethoxylate sulphate, sodium oleyl cetyl sulphate, sodium toluene sulphonate or sodium dodecyl benzene sulphonate.

7. A product as claimed in any of the preceding claims, wherein the aliphatic alcohol is hexanol, heptanol, 2-ethyl hexanol, iso-octanol or nonanol.

8. A product as claimed in any of the preceding claims, substantially as hereinbefore described in any of the foregoing Examples.

9. A test method for determining the concentration of a cationic surface-active compound in an aqueous solution by means of the product claimed in any of the preceding claims, comprising contacting said solution with the solid component and with the liquid component of said product, shAing the resulting mixture, allowing the organic and aqueous phases to separate and comparing the colour of the organic phase ith one or morse colour standards.

10. A test method for determining the concentration of a cationic surface-active compound in an aqueous solution, which method is substantially as hpre nbefore described in an of the foregoing Examples.