996 SHORT PAPERS Analyst, Vol. 105 Spectrophotometric Micro-determination of Silver( I ) and Iodide Ions Sudarsan Barua, B. S. Garg and R. P. Singh and lshwar Singh Depavtment of Chemistry, University of Delhi, Delhi-110007, India Department of Chemistry, Maharishi Dayanand Universaty, Rohtak-123001, India Keywords: S i l v e r ( I ) ; iodide; 4-(2-quinoZylazo)phenol This paper reports the analytical potential of 4-(2-quinolylazo)phenol (p-QAP), a new hetero- cyclic azo dye, as a sensitive chromogenic reagent in the spectrophotoinetric determination of silver(1). The silver(1) - (p-QAP) complex has also been used in the micro-determination of iodide ions. The principle involved is the ligand exchange reaction and the difference in absorbance between the silver(1) - (9-QAP) complex before and after the addition of iodide ions and the reagent blank is proportional to the concentration of iodide ions.The method is simple, rapid and the precision is high compared with some of the (other published methods.lJ Experimental Apparatus the spectra. Reagents p-QAP solution. 2-Hydrazinoquinoline (1.5 g, 0.01 mol) dissolved in the minimum volume of dilute hydrochloric acid or acetic acid was condensed with an ethanolic solution of p-benzoquinone (1.08 g, 0.01 mol). The resulting solution was neutralised with ammonia solution. The orange precipitate of p-QAP obtained was filtered, re-crystallised from ethanol and dried over phosphorus(V) oxide in a vacuum. The purity of the compound was checked by thin-layer chromatography and by elemental analysis (calculated values for C,,H,,N,O : A Unicam SP 600 spectrophotometer with matched 10-mm glass cells was used for recording A Beckman Expandomatic SS-2 pH meter was used for the pH measurements,October, 1980 SHORT PAPERS 997 C 72.28, H 4.42 and N 16.86%; the values found were C 72.00, H 4.48 and N 16.75%). A 5 x The solution is stable for several days.M solution of the reagent was prepared by dissolving 0.1245 g 1-1 in ethanol. 4-(2-Quinolylazo)phenol (p-QAP) Other reagents, standards and stock solutions. Standard solutions of silver(1) and iodide were prepared and standardised by conventional methods3; 0.05 M sodium tetraborate solution was prepared for adjusting the pH. All other chemicals used were of analytical-reagent grade. Recommended Procedure Determination of silver(I) To a suitable aliquot of sample containing 1.5-13.0 pg of silver(1) add 1.0 ml of 5 x lo-* M p-QAP solution followed by 1.0 ml of 0.05 M sodium tetraborate solution.Dilute to 10.0 ml with water and ethanol, giving a final ethanol concentration in the solution of 50%. Measure the absorbance of the solution a t 530 nm against a reagent blank. The amount of silver(1) in an unknown sample can be determined from a calibration graph prepared from known silver samples as described above. Determination of iodide ions using silver(I) - (p-QA P) M $-QAP solution followed by suitable aliquots of iodide solution containing up to 12.7 pg of iodide ions. Add 1.0 ml of 0.05 M sodium tetraborate solution, shake well and dilute to 10.0 ml with water giving a final ethanol concentration in the solution of 50%.Record the absorbance against a reagent blank. The difference in absorbance between the complex before and after the addition of iodide ions and the reagent blank is proportional to the concentration of iodide ions. To 1.0 ml of a 1 x M solution of silver(1) add 1.0 ml of 5 x Determination qf iodide ions by adding excess of silver(I) solution To an aliquot containing up to 15.0 pg of iodide add a known excess amount of silver(1). Allow to react for 1-2 min and then add 1.0 ml of 5 x M $-QAP solution followed by 1.0 ml of 0.05 M sodium tetraborate solution. Dilute to 10.0 ml with water and ethanol, again maintaining the ethanol concentration a t 50%, and record the absorbance against a reagent blank. The difference in absorbance between the complex before and after the addition of iodide ions and the reagent blank is proportional to the concentration of iodide ions, Results and Discussion Spectral Behaviour and Characteristics of the Silver (I) - (p-QAP) Complex An ethanolic solution of p-QAP forms a deep red coloured complex with silver(I), which has a maximum absorbance a t 530 nm in the pH range 8.1-11.2.The complex is stable in day- light. It decomposes when the ethanolic concentration is less than 30%; subsequent studies, therefore, were carried out in 50% ethanol solutions. Three moles of the reagent are required for full colour development. The composition of the complex, as determined by Job’s method of continuous variation and the molar ratio method, was found to be 1:2 (metal to ligand). Beer’s law is valid for up to 1.7 p.p.m.of silver. With the particular conditions adopted here 0.15-1.30 p.p.m. of silver can be determined accurately. The Sandell sensitivity of the colour system is 0.001 3 p g cm-2 of silver with a molar absorptivity, E , of 8.3 x lo4 1 mol-l cm-’ at 530 nm.998 SHORT PAPERS Analyst, V o l , 105 Studies in the Presence of Diverse Ions In the determination of 1.08 pg of silver(1) in solution, the results of the tolerance limits, in parts per million, of various ions in solution that caused a deviation smaller than 2% in absorbance are nitrite 800; sulphite 400; fluoride and tartrate 80; citrate and oxalate 60; chloride 20; bromide 15 ; lead( 11) 20; lanthanides(III), uranium(VI), cobalt (II), nickel( II), zinc(II), cadmium(I1) and iron(II1) 10.Iodide, sulphide, thiosulphate, thiocyanate, cyanide, EDTA, palladium(I1) and copper(I1) interfere. Determination of Iodide Ions The decomposition of the silver(1) - (9-QAP) complex in the presence of iodide ions was studied by taking varying amounts of silver(1) (0.15-1.30 pg ml-l). The amount of iodide ions determined was 0.09-1.5 pg ml-1 using the particular conditions adopted for the deter- mination of silver(1). The recovery results for iodide at ten known concentration levels (each repeated four times) of between 1.27 and 12.7 pg per 10 ml [1.08 pg ml-l of silver(I)] yielded coefficients of variation of less than 0.48y0. In each instance the difference between the measured and known concentration was less than 1.6%. The sensitivity of the method is 0.0015 pg cm-2 of iodide. Similar results were also obtained .when excess of silver(1) was allowed to react with iodide ions and unreacted silver(1) was determined following the recommended procedure. The effects of diverse ions upon the determination of 1.27 pg ml-l of iodide ions were also studied. Mercury(I1) interferes and other interferences were found to be of the same order as for the determination of silver(1). One of the authors (S.B.) is grateful to the University Grants Commission, New Delhi, India, for providing him with a Teacher Fellowship and Mr. Y. S. Varma for his helpful suggestions. References 1. 2. 3. Snell, F. D., “Photometric and Fluorometric Methods of Analysis, Metals, Part I,” John Wiley, New Marczenko, 2.. “Spectrophotometric Determination of Elements,” John Wiley, New York, 1976. Vogel, A. I., “A Text Book of Quantitative Inorganic Analysis,” Fourth Edition, Longmans, London, York, 1978. 1978. R.eceived Jafiuary 28th, 1980 Accepted May 29th, 1980