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United States Patent (19) 11) 4,065,363 Herrmann 45) Dec. 27, 1977

54) PROCESS FOR THE ELECTROMETRIC 3,615,737 10/1971 Schneble et al...... 106/1 MEASUREMENT OF CYANDE ONS IN 3,650,777 3/1972 Schneble et al...... 106/1 SOLUTIONS CONTAINING METALIONS OTHER PUBLICATIONS 75) Inventor: Gunther Herrmann, Furth, Germany “ Selective Electrodes', NBS Pub. 314, Nov. 1969, (73) Assignee: Photocircuits Division of Kollmorgen p. 371. Corporation, Hartford, Conn. "Analytical Chem.'', vol. 43, No. 12, Oct. 1971, pp. 1575-1581. (21) Appl. No.: 205,297 "Plating', July, 1971, pp. 686–693. 22 Fied: Dec. 6, 1971 Orion Instruction Manual, “ Activity Elec 30 Foreign Application Priority Data trode', 1967, pp. 1-16. Primary Examiner-T. Tung Dec. 17, 1970 Germany ...... 2064822 Attorney, Agent, or Firm-Morgan, Finnegan, Pine, (51) int. Cl’...... G01N 27/46 Foley & Lee (52) U.S. C...... 204/1 T; 204/195M; 427/437; 96/60 R 57 ABSTRACT 58) Field of Search ...... 106/1; 117/130 E; This invention is concerned with a novel process for the 204/1 T, 195 M, 195 L electrometric determination of the cyanide ion content 56 References Cited of solutions comprising cyanide ion, a strong and a metal ion. U.S. PATENT DOCUMENTS 3,337,350 8/1967 Hata et al...... 106/1. 1 Claim, No Drawings 4,065,363

PROCESS FOR THEELECTROMETRIC or, after rearrangement, MEASUREMENT OF CYANDE ONS IN SOLUTIONS CONTAINING METAL FONS E = E -- RT. n. F (ln 2L/B - lnay-) BACKGROUND OF THE INVENTION results. If the stirring velocity and the temperature are Process and specialized apparatus have been de kept constant, E and ln 2L . B-1 are constant and --RT scribed in the prior art which have been specially . 2-1 . F-1 can be set equal to a constant K1. adapted for the electrometric determination of the cya Thus, for - ; : . . . . ; nide ion content of solutions thereof. Heretofore, it has 10 not been possible, however, to apply this specialized E = E + RT. n-. F-1. In acy apparatus to solutions containing cyanide ion, a strong or for: AE = E - EE K in CCN reducing agent and a metalion. This was due to the fact results. Hence, it follows that the direct measurement of that the metal ion would be deposited on the electrode cyanide ion concentration at constant stirring velocity as the free metal and would eventually render the elec 15 and temperature is possible so far as no side reactions trode inoperative. Applicant has provided a solution for occur at the membrane in the solution to be measured. this problem which is a novel method for measuring the At the appearance of such side reactions, however, cyanide ion content of metalion containing solutions. the use of this measurement concept to determine cya SUMMARY OF THE INVENTION 20 nide ion concentration had hitherto proved unavailing The invention provides a method of electrometrically in solutions that contain a strong reducing agent. The measuring the cyanide content of solutions, containing reducing agent to the formation of a metal, here a cyanide ion, a metal ion such as or and a silver deposit on the membrane. strong reducing agent such as , According to the process of the invention, the forma It is an object of this invention to provide a method 25 tion of such a metal deposit is prevented by providing a for electrometrically measuring the cyanide ion content solution sample for use in the determination of the cya of solutions such as are customarily employed in the nide ion concentration which contains a complexing photographics, electroless plating and other industrial agent for the metal. processes. The complexing agent must be so chosen that it does not interfere with the test reaction. For example, trieth This and other objects will become apparent from the 30 ylenetetramine, ethylenediaminetetraacetic acid, detailed description. N',N',N,N-tetrakis-2(2-hydroxypropyl)ethylenedia DETAILED DESCRIPTION mine, , tartaric acid, 1,3-propanediamine, Ion selective electrodes for use in the determination diethylenetriaminepentaacetic acid, Rochelle , of the cyanide ion content of solutions are described in 35 mono-, di- and trisodium of n-hydroxy-ethylene the literature and are commercially available. The mem diaminetetraacetic acid, nitrilotriacetic acid and its salts, brane material of such special electrodes as a rule con triethanolamine, and cyclohexanediaminetetraacetic sists of AgCl, AgBr, Ags or AgCN. The system Ag acid have proved to be suitable. /AgCl in KCl of a specific molarity, e.g., 0.01M, or If metal which form complexes with the com Ag/AgBr in KBr, Ag/AgI for example, serves as the 40 plexing agent are present in the bath solution specified reference electrode. These type electrodes are also de for the concentration measurement, care must be taken, scribed in Ion Selective Electrodes, National Bureau of in accordance with the present invention that the com Standards Special Publication, 314, Issued November plexing agent is added in an amount that leads to an 1969, which is incorporated by reference. excess of that required to complex the metal ions. The ion selective electrodes may be used in connec If bath solutions are to be measured for example, tion with a device for measuring potential differences baths for autocatalytic metal deposition on sensitized such as an expanded scale pH meter or more preferably surfaces, already contain a complexing agent for the a specific ion meter of the type designed for use in mea metal ions along with a metal compound, care must be suring small differences in ion concentration. These taken in accordance with the invention that the com instruments are commerically available. 50 plexing agent be present in excess. If a separate com The measuring procedure depends on the slow dis plexing agent is added to such a solution, it is important solving of the active membrane constituent; the cyanide that the sum of the complexing agents present must ions present in the solution combine with the slightly result in an excess in order to permit the undisturbed soluble silver salts of the membrane surface for the determination of the cyanide ion concentration accord measurement. This reaction proceeds as follows: 55 ing to the invention. The following Examples are given by way of illustra AgX + 2 CN- Ag(CN), - + X tion and are in no way to be construed as limitations on the scope of the invention: The X- ions liberated in this reaction determine the activity of the silver ions at the membrane surface in EXAMPLE I accordance with the solubility product relation An electrode supplied by Orion Research Incorpo rated, Cambridge, Mass. which is described as the Ion A se L/B air alyzer cyanide ion activity electrode, Model #94-06-00 in which L is the solubility product of the silver salt, B was employed to monitor the cyanide ion activity of the the stirring velocity and ar- the activity of the Xions. 65 following electrodes copper bath: By substitution in the Nernst equation Copper sulfate 10. E = E + RT. n. F. n 2L/B acy Tetrasodium EDTA 4,065,363 3 4 -continued -continued Formaldehyde 37% 4.0 mM g/1 moles/1 25. mg/ yer qsad 1999 Gaflac RE 610 0.25 g/1 5 pH at 25' C 12.4 Further variations in the application of the process of the invention will be readily understood by those skilled The use of the excess of the tetrasodium EDTA made in the art, however, in each case it should be remem possible the monitoring of the cyanide concentration. 10 bered that an excess of complexer must be employed. What is claimed is: EXAMPLE II 1. A process for the determination of the cyanide ion content of a solution which comprises cyanide ions, a A cyanide ion content of the silver bath of the follow strong reducing agent, and a silver ion, said method ing formulation is also monitored by the technique of 5 comprising providing in said solution an amount of Example I: metal complexer in excess of that required to complex the silver ion; providing in contact with said solution a cyanide ion selective electrode that has connected g/l moles/1 thereto, direct reading potentiometric measurement Silver nitrate 1.7 0.010 20 means and, thereafter, determining from said direct Sodium potassium tartrate 4. 0.014 reading potentiometric measurement means the cyanide Sodium cyanide .8 0.04 ion concentration. Dimethylamine borane 0.8 0.013 s

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