ASSAY FOR COMPOUNDS WHICH ARE, OR CAN BE CONVERTED TO, ALDEHYDES

Abstract: An aqueous sample containing methylenebisthiocyanate or another compound capable of releasing an aldehyde is assayed by determining the amount of aldehyde released by conversion, e.g. with respect to a sample from which existing aldehydes have been separated. An aqueous sample containing glutaraldehyde or another aldehyde having at least 2 C atoms is assayed by adding an agent which gives a water-insoluble complex, and determining the amount of complex or, after regeneration, the aldehyde.

Description: Assay for compounds which are, or can be converted to, aldehydes This invention relates to an assay for compounds which are, or can be converted to, aldehydes. Known aldehyde tests include the Sawicki and Purpald reactions. Both these known reactions, and especially the latter, are good for assaying formaldehyde. They are less sensitive, to varying degrees, to other aldehydes. Moreover, the Purpald reaction requires alkali, and may therefore be experimentally-undesirable. Known biocides include glutaraldehyde and methylene- bisthiocyanate (MBTC) . They are used in cooling towers, in order to control organisms such as Leσionella. in paper- making and in other aqueous environments. It is an object behind this invention to monitor the level ' of such compounds in the water. The invention is based, at least in part, on the realisation that MBTC releases formaldehyde under alkaline conditions such as those that prevail in cooling towers. The Purpald reaction is clearly unsuitable in these circumstances, since it cannot distinguish between MBTC and any free formaldehyde with which such a compound may be in equilibrium or with any formaldehyde from another source. According to the present invention, a compound capable of releasing an aldehyde under alkaline or other given conditions (described herein as an aldehyde-releaser) , and free aldehyde in an aqueous sample are distinguished. One aspect of the invention is a method which comprises: in a first sample, converting the aldehyde-releaser to aldehyde; in a second sample, separating the aldehyde-releaser and aldehyde; and determining the difference between the respective amounts of aldehyde obtained from the first and second samples. In this method, the amount of aldehyde obtained from the first sample corresponds to the total amount of aldehyde-releaser and free aldehyde (which may include any aldehyde already present in the sample) . The amount of aldehyde obtained from the second sample corresponds to free aldehyde only, and the difference between the two amounts therefore corresponds to the amount of aldehyde- releaser. A second aspect of the invention is a method which comprises: separating the aldehyde-releaser and aldehyde; converting the aldehyde-free aldehyde-releaser to aldehyde; and determining the amount of aldehyde obtained by conversion. If the aldehyde is formaldehyde, it can be determined by the Purpald or Sawicki reaction. This is less satisfactory for an aldehyde having at least 2, 3 or more carbon atoms, e.g. glutaraldehyde. According to a further aspect of the invention, such an aldehyde is assayed by reacting an aqueous sample containing the aldehyde with an agent with which the aldehyde reacts to form a water- insoluble complex, adding a reagent that gives a colour on reaction with the complex, and determining the colour. The use of such a complexing agent provides one means of separating aldehyde from aldehyde-releaser. Alternatively, they may be separated by contacting the appropriate sample with an anion-exchange resin, bisulphite or other immobilised medium that retards either the aldehyde or the aldehyde-releaser; if it is then necessary or desired to assay the bound aldehyde or bound aldehyde- releaser, the bound species may be eluted. If a complexing agent is used, it should be added in an amount sufficient to precipitate all free aldehyde, e.g. free formaldehyde (or glutaraldehyde, acetaldehyde, propionaldehyde or other aldehyde) . Then it may be necessary to remove excess complexing agent in the system, e.g. to use a filtrate obtained by removing the excess complexing agent. This can be achieved by adjusting the conditions so that the excess reagent becomes insoluble. The filtrate thus obtained can be subjected to alkaline hydrolysis or any other reaction that releases the aldehyde and allows determination of the releaser. In one embodiment, the utility of the novel method is based on the realisation that the aldehyde, but not the releaser, will form a water-insoluble complex with compounds such as substituted 1,2-diaminoethaneε which themselves are readily assayed by reaction with a suitable reagent, specifically a diazo compound, to give a characteristic colour. Specific complexing agents that can be used are 1,2-dianilino-l,2-diphenylethane and 1,2- dianilinoethane (Wanzlick's reagent). In this case, the assay can suitably be conducted by - forming the complex, filtering the system, e.g. through a syringe filter, washing the complex residue, solubilising the complex, and adding a suitable diazo compound (of which many are known) . Thorough washing of the residue is desirable; it is preferred to use dilute acetic acid. The solubilising agent may be IM HC1, optionally in admixture with methanol. The formation/physical properties of the complex may be enhanced by salting out or another procedure such as adding a polymer that reduces its adherent tendencies, thus facilitating precipitation and recovery. The complexing agent serves to concentrate aldehyde in the sample under test. An aldehyde that would give a reaction of low sensitivity to, say, Purpald reagent in the original sample may, after concentration, be so assayed. The most preferred procedure is to separate the aldehyde-releaser and the aldehyde by bringing the sample into contact with a suitably immobilised reagent, e.g. an anion-exchange resin which binds/retards the aldehyde- releaser. The bound species can subsequently be released by elution: for example, aqueous NaCl will serve to elute MBTC from an anion-exchange resin. The releaser can then be assayed. Alternatively, the aldehyde that is not immobilised may be compared with total aldehyde that can be generated by the sample. Formaldehyde that is released can of course be assayed by the Sawicki or Purpald reaction. The following Examples illustrate the respective aspects of the invention. Example 1 (Glutaraldehyde Assay) The following steps were conducted (Polymer is Synperonic) : STEP 1. Close syringe and filter by means of the 3 way tap and pipette into syringe 6ml water to be tested for its glutaraldehyde content (or 6ml RO water to which appropriate quantities of glutaraldehyde have been added) . STEP 2. Add 0.4ml Wanzlick's reagent (22 g/ml 4M acetic acid) . Mix well, wait 20 minutes. STEP 3. Add 1ml 3M NaCl solution, mix well, wait 30 seconds. STEP 4. Open tap on bottom of syringe and allow liquid to pass through the Whatman O.lum Puradisc filter in the filter unit; discard filtrate. STEP 5. Wash precipitate (glutaraldehyde-Wanzlick's complex) on the filter disc with 7.5ml 0.25M acetic acid. Discard filtrate. STEP 6. Repeat step 5. Close tap on bottom of syringe. STEP 7. Add 3 ml IM HCl to the syringe and shake for 1 minute to dissolve any of the complex stuck to the wall of the syringe. Open the tap. The acid is then pushed slowly through the filter. The crystalline glutaraldehyde-Wanzlick's complex on the filter dissolves. Collect the filtrate in a test tube. STEP 8. Adjust pH of filtrate to pH 3.5 by titration with 3.75M NaOH. STEP 9. Add 0.4ml 4M acetic acid and mix. STEP 10. Add 0.15ml Polymer (0.1% in RO water). Mix. STEP 11. Add 0.2ml Fast Scarlet GG solution (lOmg/ml in RO water) :mix and wait for 5 minutes. STEP 12. Take out 1.5ml into test tube. STEP 13. Add 1.5ml cone. HCl;mix;wait for 2 minutes. STEP 14. Read light absorption in colorimeter at 490nm. In this report, except where stated, optical densities are reported in comparison with water so that the O.D. of reagent blanks can be compared with the values obtained with the substance under consideration. Example 2 (MBTC Assay) 1. REAGENTS SUBSTI TUTESHEET Purpald reagent (4-amino-3-hydrazino-5-mercapto-l,2,4- triazole) : available from Aldrich Chemical Co. Ltd. and Sigma Chemical Co. Ltd. Solutions were prepared in 0.5 M HC1 (warm, to dissolve completely; such solutions appear to be stable for about 1 month. (In some experiments, Purpald dissolved in a 2 M NaOH solution was used) . Sodium Hydroxide. Analar grade; prepare a 5 M solution in water (dissolve lOg NaOH in 50 ml water) . Sodium periodate: Analar grade; prepare a 0.1 M solution in water (21.4 mg/ml) ; this solution is stable for about 1 month. Formaldehyde: Analar grade; B.D.H.; 37-41 w/v. 2. APPARATUS Colorimeter: WPA CO 210, or equivalent, with cuvettes (Polystyrene or silica) . Pipettes: Gilson Pipetman: P100, P200, P1000, P500020-100 μl, 50-200 μl, 100-1000 μl, 1000-5000 μl. Test tubes, plastic, 8 ml; obtainable from Sarsted, West Germany. Timer. Volumetric flasks, glass; 10 ml; 100 ml. 3. PROPOSED METHOD OF ANALYSIS Step 1: pipette into plastic test tube de-ionised water followed by the required volume of MBTC "working solution"; final volume: 1ml. (If a test on a water sample is to be carried out, use 1 ml of the water to be tested for its MBTC content) . Step 2: add 1 ml of 5 M NaOH, mix well by flicking the tube with finger and thumb (or shaking) and wait 5 in. Step 3: add 0.5 ml Purpald reagent (10 mg/ml in 0.5 M HC1) , mix and allow 5 min for the formation of the first purple colour complex (see BASIS OF REACTION FOR ANALYSIS) . SUBSTITUTESHEET Step 4 : add 0.3 ml of NaI0 4 solution (21.4 mg/ml water) ; mix, wait 1-5 min. Step 5: read optical density (O.D.) of the deep purple solution at 550 nm in a colorimeter; use silica or polystyrene cuvettes. Fig. I shows the absorption spectrum of the colour complex formed by different amounts of MBTC with the Purpald reagent after oxidation with NaI0 4 . Linearity of response of the proposed method for the estimation of MBTC in water: Table 1. and Fig. II. show values for a typical calibration curve for MBTC obtained by the above method. Table 1. MBTC μg/sample 1 2 3 4 5 6 8 10 SUBSTITUTESHEET

Claims: CLAIMS 1. A method of assaying, in an aqueous sample, a compound capable of releasing an aldehyde under given conditions, which comprises: in a first sample, converting the compound to aldehyde; in a second sample, separating the compound and aldehyde; and determining the difference between the respective amounts of aldehyde obtained from the first and second samples. 2. A method of assaying, in an aqueous sample, a compound capable of releasing an aldehyde under given conditions, ,which comprises: separating the compound and aldehyde; converting the aldehyde-free compound to aldehyde; and determining the amount of aldehyde obtained by conversion. 3. A method according to claim 1 or claim 2, wherein the compound is separated from aldehyde by contacting the sample with an insolubilised medium that retards the compound; and, if necessary, or desired, eluting the bound compound. 4. A method according to claim 3, wherein the insolubilised medium is an anion-exchange resin. 5. A method according to claim 1 or claim 2, wherein the compound and aldehyde are separated by adding to the sample an agent with which the aldehyde reacts to form a water- insoluble complex. 6. A method according to claim 5, which comprises: if necessary or desired, removing excess complexing agent; regenerating the aldehyde from the complex; and determining the amount of the regenerated aldehyde. 7. A method according to claim 5, which comprises determining the amount of the complex. 8. A method according to any of claims 5 to 7, wherein the complex or the complexing agent gives a colour on reaction with a suitable reagent. 9. A method according to claim 8, wherein the reagent is a diazo compound. 10. A method according to claim 9, wherein the complexing agent is Wanzlick's reagent or an analogue thereof. 11. A method according to any preceding claim, wherein the aldehyde is formaldehyde. 12. A method according to claim 11, wherein the formaldehyde is determined by the Purpald or Sawicki reaction. 13. A method according to any preceding claim, wherein the compound releases aldehyde under alkaline conditions. 14. A method according to claim 13, wherein the compound is methylenebisthiocyanate. 15. A method of assaying, in an aqueous sample, an aldehyde having at least 2 C atoms, which comprises adding to the sample an agent with which the aldehyde reacts to form a water-insoluble complex, adding a reagent that gives a colour on reaction with the complex or with the complexing agent, and determining the colour. 16. A method of assaying, in an aqueous sample, an aldehyde having at least 2 C atoms, which comprises adding to a sample an agent with which the aldehyde reacts to form a water-insoluble complex; regenerating the aldehyde from the complex; and determining the amount of the regenerated aldehyde. 17. A method according to claim 15, wherein the reagent is a diazo compound. 18. A method according to any of claims 1 to 4, wherein the aldehyde has at least 2 C atoms and is determined by a method according to any of claims 15 to 17. 19. A method according to any of claims 15 to 18, wherein the agent is Wanzlick's reagent or an analogue thereof. 20. A method according to any of claims 15 to 19, wherein the aldehyde is glutaraldehyde.

Inventors: HILL MARTYN WILLIAM, SHARMAN DENNIS FRANK, HILL, MARTYN, WILLIAM, SHARMAN, DENNIS, FRANK
Applicants: CAMBRIDGE TECHNOLOGY & SCIENCE, CAMBRIDGE TECHNOLOGY & SCIENCE PLC
Application year: 1991
Main classification: G01N31
IPC codes: G01N31