Indian Journal of Chemical Technology Vol. 9, March 2002, pp. 127-129 Complexometric determination of palladium(II) using 2-mercapto propionyl glycine as demasking agent Prakash Shetty"*, A Nityananda Shett/ & R V Gadagb "Department of Chemistry, M.I.T. Manipal 576 119, India bDepartment of Chemistry, Karnataka Regional Engineering College, Surathkal, Srinivasnagar 574 157, India Received 12 January 2001; re vised 12 December 2001; accepted 24 December 2001 A simple, rapid and accurate compl exo metric method for the determination of palladium(ll) is proposed, based on the selective demasking property of 2-mercapto propionyl glycine (MPGH 2 ) towards palladium(II). In the presence of diverse metal ions, palladium(II) is complexed with excess of EDT A and the surplus EDT A is back titrated at pH 5-5.5 (acetic acid- acetate buffer) with standard zinc sulphate solution using xylenol orange as indicator. An excess of a 0.2% aqueous solution of MPGH2 is then added to di spl ace EDTA from Pd(II)-EDTA complex. The released EDTA is titrated with the same standard zinc sulphate solution as before. Reproducible and accurate results are obtained in the concentration range 2-22 mg of palladium with relative error of ±0.36% and coefficient of variation (n=6) not exceeding 0.31 %. The effect of diverse ions are studied. The method is used for the determination of palladium in its complexes, catalysts and synthetic alloy mixture s. A complexometric method for the determination of palladium(II) in the presence of diverse metal ions using selective demasking agent is very useful in the rapid analysis of palladium alloys. The Pd-EDT A complex can be selectively decomposed using demasking agents such as dimethylglyoxime 1 and I ,2,3-benzotriazole 2 • These methods are not rapid as they involve heating and extraction of Pd-reagent complex using chloroform. The I, I 0-phenanthroline method 3 does not work for Pd(II) in the presence of common metal ions. Thiourea 4 is free from these limitations. The quantitative release of EDT A by pyridine 5 requires heating of the solution to 60°C for I 0 min and the reagent is unpleasant to use because of its smell. Many metals interfere in thiosemicarbazide method 6 . Other reported reagents such as 4-amino-5- mercapto-3-propyl-l ,2,4-triazole 7 , thiocyanate 8 , thiosulphate 9 , 4-amino-3-mercapto-l ,2,4-triazine( 4H)- 5-one10, hydroxylamine hydrochloride'' , N-(2- pyridyl)thiourea 12, DL-methionine 13 and 3-mercapto propane-] ,2-diol 14 were found to be reliable besides being convenient. Howeve r, some of the reagents require tedious and time-consuming preparation method s. In this paper, the application of MPGH 2 as a selective demasking reagent in th e complexometric determina-tion of Pd(II) has been reported. *For correspondence Experimental Procedure All chemicals used were of A.R. or chemically pure grade. Palladium(II) chloride solution was prepared by dissolving PdC)z in minimum amount of cone. HCI and making up to a known volume with distilled water. The stock solution was standardised gravimetrically as palladium dimethylglyoximate 15 . Zinc sulphate solution (O.OIM) was prepared in distilled water and standardised gravimetrically as zinc oxinate 15 . EDTA solution (- O.OIM) was prepared from the disodium salt by dissolving in distilled water. A freshly prepared 0.2% aqueous solution of 2-mercapto propionyl glycine (MPGH 2 ) (kindly supplied by Santen, Japan) in distilled water was used. A freshly prepared 0. 5% aqueous solution of xylenol orange indicator was used. To an aliquot of solution containing 2-22 mg of palladium(II) and varying amounts of diverse metal ions, an excess of -0 .0 I M EDT A solution was added and diluted with 20 mL of distilled water. The pH of the solution was initially adjusted between 4 and 5 by the dropwise addition of dilute sodium hydroxide solution and finally to 5-5.5 by adding acetic acid- sodium acetate buffer. The uncomplexed EDTA was backtitrated with standard zinc sulphate solution using xylenol orange as indicator to the sharp colour change from yellow to red. To this, a freshly prepared 0.2% solution of MPGH 2 was added in required amounts and the contents were mixed well. The liberated EDT A was again titrated with the same standard zinc