WO1992003727A1

WO1992003727A1 - Assay for isothiazolones

Info

Publication number: WO1992003727A1
Application number: PCT/GB1991/001389
Authority: WO
Inventors: Martyn William Hill; Dennis Frank Sharman
Original assignee: Cts Biocides Ltd.
Priority date: 1990-08-15
Filing date: 1991-08-15
Publication date: 1992-03-05
Also published as: GB9017880D0; AU8421491A

Abstract

A process for determining the presence of an isothiazolone in a sample, comprises treating the sample with base and then with a phosphomolybdtungstic acid reagent, and observing and, if desired, measuring, the colour thus generated. The reagent may be Folin and Ciocalteu's reagents.

Description

ASSAY FOR ISOTHIAZOLONES Field of the Invention

This invention relates to an assay for isothiazolones. Background of the Invention Isothiazolones, such as those marketed by Rohm and Haas Company under the registered Trade Mark Kathon, are antibacterial agents or biocides which are widely used in a variety of aqueous and non-aqueous systems. For example, isothiazolones are useful as algicides in swimming pools and as sli icides in cooling-tower water. There is a need for a sensitive assay for isothiazolones.

A definition of isolthiazolones and a review of the prior art relating to assays for these compounds is given in US-A-4652530. The process claimed in that specification comprises a number of steps, including adsorption/desorption, and treating the ring-broken system with FeCl₃ and K₃Fe(CN)₆, in addition to base-catalysed ring breakage and colorimetric determination.

Folin and Ciocalteu's phenol reagent (hereinafter "F & C reagent") is a hygroscopic yellow liquid that is used in Lowry analysis. For the reaction with protein, the sample must be left in the dark, and the pH must be varied. These steps are only part of a time-consuming analysis. Summary of the Invention An assay according to the present invention, for any isothiazolone of the type defined in US-A-4652530, comprises only treatment with base and a colorimetric reaction, since it has surprisingly been found that a phosphomolybdotungstic acid, and specifically F & C reagent, provides a quantitative blue colouration. The novel assay is therefore much cheaper and simpler than the prior art. Further, the reaction is substantially unaffected by a range of potentially interfering materials, to an unexpectedly advantageous extent with respect to the results shown in US-A-4652530. Description of the Invention

By way of example only, the invention will now be described with reference to the determination of 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one which are apparently components of the biocide commercially available as Kathon WT. In operation of the invention, an aqueous sample containing Kathon is treated with sodium hydroxide to split the ring and form an oxidisable group. After one minute, F & C reagent is added. This produces a blue colour for measurement. F & C reagent measures reducing power.

In a particular case, samples containing varying concentrations of Kathon were reacted with 150 μl of 5M NaOH and 50 μl of F & C Reagent; the Optical Density was read at 700 nm.

The results showed a substantially linear relationship between absorbance (0-0.3) and Kathon concentration (0-20 mg/ml) . On further testing, maximum absorbance was found at 680 nm. In a further experiment, a 3 ml water sample containing 11.3 μg/ml Kathon was mixed with a a total of 300 μl of NaOH and/or water. After one minute, 50 μl F & C reagent was added.

The highest O.D. at 700 nm was obtained with Kathon and 100 μl of 5M NaOH. It was also found that, in order to maximise the difference between Kathon and Dithiol under the same conditions, over a wide range, it is preferable to use 150 μl NaOH.

A stronger colour reaction is produced between Kathon and F & C reagent than between Dithiol and F & C reagent. Using small amounts of F & C reagent results in minimal colour development wi Dithiol and maximum O.D. reading for Kathon. 25 μl of F & C reagent generates optimum colour development. A confirmatory experiment was conducted, using a 3 ml sample, adding 150 μl 5M NaOH, adding 25 ml F & C reagent after 1 min, and reading after 30 sec. at 700 nm. The results were:

Sample O.D. at 700 nm Water blank 0.01 11 μg/ml Kathon 0.24 11 μg/ml Dithiol 0.03

The colour development with Kathon was stable after 15 sec, and remains stable for at least 25 min. 10 μl 3M HCl (pH changed to 1) , and different temperatures (6°C, 23°C and 39°C), had no effect on the effect of the assay.

The effect of potentially interfering materials has been tested. Other than the raising of O.D. values in some cases, no effect was observed in the presence of up to 300 ppm of any of

Polymate 942 (alkaline solution of organic phosphate, synthetic organic polymer and organic heterocyclic compounds) ,

Polymate 943 (aqueous blend of organic and inorganic phosphates, organic polymer and organic heterocyclics) ,

Polymate 945 (blend of zinc salts and phosphonates highly acidic) ,

Polymate 947 (aqueous blend of sodium nitrite, organic phosphonates and organic polymers) ,

Polymate 967 (aqueous blend of zinc salt and organic phosphonate) ,

Polymate 5622 (aqueous blend of zinc salt and organic phosphonate, with polymer) ,

Flomate 5805 (aqueous alkaline solution of organic and inorganic corrosion inhibitors and a synthetic organic polymer; contains heterocyclic amine and molybdate) ,

Polymate 5832 (contains phosphonates, polymer and azole)

Polymate 5835 (contains phosphonates, polymer and azole) Polymate 5840 (aqueous solution of phosphonates, polymer, inorganic acid and azole) , and D8374 (aqueous solution of synthetic organic polymer) .

Next, a 1 μg/ml sample of Kathon was tested in the presence of 0.2 tg/ml and 5 μg/ml of other biocides. No significant interference was found within the limits of the tests, for the biocides Aqucar, Dithiol, Bellacide 350, MBTC, DBNPA, Bronopol and Hyamine 3500. Interference was observed, at the 5 μg/ml concentration, with Fenticlor.

US-A-4652530 discloses that interference with Dequest 2000 and Dequest 2010 is observed at levels of about 20 ppm. By contrast, the process of the present invention is unaffected by the presence of such products at levels up to a factor of 20 greater.

Claims

1. A process for determining the presence of an isothiazolone in a sample, which comprises treating the sample with base and then with a phosphomolybdtungstic acid reagent, and observing and, if desired, measuring, the colour thus generated.

2. A process according to claim 1, wherein the treatment with base is to a pH of about 10.

3. A process according to either preceding claim, wherein the reagent is Folin and Ciocalteu's reagent.

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