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Se ee, , Experiment No. 06 , Aim: To perform the limit test of Lead in the given unknown sample., Requirements: , kere, (a) Glassware: Separating funnel, measuring cylinder, glass haat :, (b) Chemicals: Test sample, standard lead nitrate solution, — i aaeaia a, - dithizone standard solution, ammonium citrate, potassium 8 ate venine, hydrochloride, phenol red, ammonia solution, ammonium cyanide, dil. nitric - u yh a, Lead is a most undesirable impurity in medical compounds and comes Use of, sulphuric acid, lead lined apparatus and glass bottles use for storage of chemicals., Common sources of lead impurities are:, 1. Equipment used for manufacturing., 2. Storage container., 3. From packaging material., Principle:, , Limit test of lead is based on the reaction of lead and di henylthiocarbazone eaten, in alkaline solution which leads to the formation of lead dithizone complex which is violet in, , colour. ; ~ cen, NHNHCeH, f es NN, \, Ne NSN.CgH, CH HN.HN, N.CHs, , Vided - ves, Lead ion Dithizone Lead dithizonate, , , , 8, , ‘Scanned with CamScanner

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vale, A Praotloal Book of Pharmnaceuttoat Inorgante Chemlaty Limit Tee, , In (his test, Nesslers’ cylinders are nol used, Instead itis performed by extracton with the, help of a separating tunnel, The original colour of dithivone in chloroform. te green while the lead dithizanate, complex is violet in colour, The Intensity of the violet Colour of the complex depends upon, the quantity of lead Present in the solution which te compared with that of the standard, colour produced by treating standard solution containing definite amount of lead in the, similar manner,, Intensity of this violet colour fs compared in both the test and standard solution ina, chloroform solvent medium dae hen, Reagent Preparations:, * Preparation of standard lead solution (1 ppm Pb):, » Dissolve 0.400 g of lead nitrate in water containing 2 mbof dilute nitric acid and add, sufficient water to produce 250.0 ml, This gives standard lead solution (1% Pb)., » Standard lead solution (1 ppm Pb) Is prepared by diluting 1 volume of standard lead, solution (19% Pb) to L000 volumes with water,, * Preparation of dithizone extraction solution:, , Dissolve 30 mg of dithizone in 1000 ml of chloroform and add 5 ml of ethanol (95%). The, solution is stored in a refrigerator, Before use, the solution is shaken with about half of its, , volume of 1% v/v nitric acid solution and the acid is discarded,, * Preparation of dithizone standard solution:, Dissolve 10 mg of dithizone in 1000 ml of chloroform., , , , , , , , , , , , , , , , , , , , , , Procedure:, Test sample Standard compound Inference/ Reasons, 1. A known quantity of 1. Astandard lead solution is | 1, Suspected sample is, sample solution is prepared equivalent to the taken which might, transferred in a separating amount of lead permitted have an impurity of, funnel. in the sample under lead., examination,, 2. Add 6 ml of ammonium 2. Add 6 ml of ammonium 2, Ammonium citrate is, citrate. citrate, added to maintain, optimum pH and to, prevent the formation, of undesired, 0 precipitates., —_ ... (Contd,, = ee” \ ( ), 9, , er NG TE, , Scanned with CamScanner

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A, Practical Book of Pharmaceutical inorganic Chemistry, , , , Test sample, , Standard compound, , Inference/ Reason., , , , 3. ie ml of potassium, cyanide and 2 ml of, hydroxylamine, hydrochloride,, , w, , Add 2 ml of potassium, cyanide and 2 ml of, hydroxylamine, hydrochloride., , 3. Cyanide forms, complexes with all the, interfering metals in, the solution., , , , Add 2 drops of phenol red, indicator,, , Add 2 drops of phenol red, indicator., , 4. It is used as an, indicator to develop, colour at the end of, , = |, the process. |, , , , , , 5. Make solution alkaline by, adding ammonia solution,, , Make solution alkaline by, adding ammonia solution., , 5. Ammonia provides, basic conditions to, develop red colour,, , , , =—=——— |, , , , 6. Extract with 5 ml of, , dithizone until it becomes, green. , Extract with 5 ml of, dithizone until it becomes, green., , 6. Atleast 2-3 extractions ,, are done in separating, funnel and mix all the |, extracts in the end. |, , , , 7, Combined dithizone, extracts are shaken for, 30_min. with 30 ml of nitric, acid and the chloroform, layer is discarded., , Combined dithizone, extracts are shaken for, , 30 min. with 30 ml of nitric, acid and the chloroform, layer is discarded., , 7. Acidic layer (contains, free lead Pb?’) is, separated from, chloroform. Nitric acid |, , make lead free from |, , chloroform layer., , , , 8. To the acid solution, add, 5 ml of standard dithizone, solution., , To the acid solution, add, 5 ml of standard dithizone, solution., , 8. Violet colour appears, due to complex lead, dithizonate., , , , 9. Add 4 ml of ammonium, cyanide., , Add 4 ml of ammonium, cyanide., , 9. Maintain optimum pH., , , , 10. Shake for 30 min. and, observe the colour., , , , , , . Shake for 30 min. and, , observe the colour., , , , 10. Comparisan of colour., , , , Conclusion:, , If the colour produced in the samp'2 solution is less than the standard solution, the, , sample will pass the limit test of lead and vice versa., , AAA, , , , , , 10, , Scanned with CamScanner