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A Practical Book of Pharmaceutical Inorganic Chemistry Limit Tests, , . ___ Experiment No. 07, , Aim: To perform the limit test for Heavy metals in the given sample., , The limit test for heavy metals is designed to determine the content of metallic impurities, that are coloured by hydrogen sulphide or sodium sulphide under the condition of the test., The heavy metals (metallic impurities) may be iron, copper, lead, nickel, cobalt, bismuth,, , antimony ate ro { o,Ky, , Principle:, , Methods (A), (B) and (C) are based upon the reaction of the heavy metal ion with \, , hydrogen sulphide (in methods (A) and (B)) or sodium sulphide (in method C) leading to the, formation of heavy metal sulphides. The metal sulphides remain distributed in a colloidal, state and give rise to a brownish colouration. The colour produced in the test solution is, compared with that of standard solution containing a definite amount of the lead., Heavy Metal (M) + H»S/Na,S ——» Heavy Metal sulphide (MS) + H2, , Method (D) is based upon the precipitation of relatively insoluble and characteristically, coloured sulphides of heavy metals when aqueous solutions are treated with alkali metal, sulphides (NaSH). NaSH is generated immediately before use by heating thioacetamide with, sodium hydroxide solution. In this test there is a formation of brown colour because of the, precipitation of meta! sulphides at about pH 3.5 in colloidal form which is stabilized by the, glycerine., Procedure:, , The Indian pharmacopoeia has adopted four methods [Methods (A), (B), (C), and (D)] for, the limit test for heavy metals., Method (A):, , It is used for the substance which gives clear colourless solution under the specific, condition., Requirements:, , (a) Glasswares: Nesslers’ cylinders, measuring cylinder, glass rod, dropper etc., , (b) Chemicals: Test sample, standard lead solution, hydrogen sulphide solution, dilute, , ammonia solution etc., , , , Reasons/Inference, , Test sample, , Standard compound, , , , 1. Solution is prepared as, per the monograph and, 25 ml is transferred in, Nessler's cylinder., , 1. Take 2 ml of standard lead, , solution and dilute to 25 ml, with water., , . Suspected, , sample is, taken which might have, an impurity of heavy, metal and make its, solution., , , , N, , Adjust the pH between, 3 to 4 by adding dilute, acetic acid ‘Sp’ or dilute, ammonia solution ‘Sp’., , , , . Adjust the pH between 3 to, , 4 by adding dilute acetic, acid ‘Sp’ or dilute ammonia, solution ‘Sp’., , . Maintain pH by using, , , , acid and base., , , , , , , , ... (Contd.), , , , W, , Scanned with CamScanner, , i

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A Practical Book of Pharmaceutical Inorganic Chemistry Limit 7,, + _Test sample | Standard compound | Reasons/Inferenc. 7, j 3. Ditste with water to | 3. Dilute with water to 35 mi 3. Dilution for comp). =, ia 35 mi | ionization 1%, i : oe oy a = |, & | 4. Add freshly prepared |4. Add freshly prepared 10 mi [4 H2S aa ¥ added., v 10 ml of hydrogen | of hydrogen sulphide (H,S) | — precipitatio, | sulphide (H2S) solution. solution r | 5. Dilute with water to 5. Dilute with water to 50 ml. |S. Make up the same voly,,, {50m upto 50 ml in both, fs Allow to stand for five |6. Allow to stand for five |6. Compare the intensity, i | minutes and view minutes and view downwards colour in both., ¢ downwards on a white ona white background., j [ __background, i Sp = Specially for ais :, } ¥, Conclusion: Pi Mere. Sugg, | If colour produced in the sa ple solution is less than the standard solution, the samp: x, | will pass the im test of heavy metals and vice versa. R, | Method (B):, | It is used for the substances which do not give clear colourless solution under the specif, condition. a OO, Requirements:, (a) Glasswares: Nesslers’ cylinders, measuring cylinder, glass rod, dropper etc., (b) Chemicals: Test sample, standard lead solution, conc. nitric acid, conc. hydrochlor, acid, dilute acetic acid, dilute ammonia solution etc., | Test sample Standard compound, IL. Weigh specific quantity of test substance, | 1. Take 2 ml of standard lead solution, moisten with sulphuric acid and ignite on and dilute to 25 ml with water., | a low flame till completely charred., (a) Add few drops of nitric acid and heat, to 500 °C. Allow to cool and add 4 ml, of hydrochloric acid and evaporate to, | dryness., | (b) Moisten the residue with 10 ml of, hydrochloric acid and digest for two, minutes., (c) Neutralize with dilute ammonia Sé, solution and make just acidic with Mv, \ dilute acetic acid., .. (Contd) St, 12, , ‘Scanned with CamScanner

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Dee, , , , A Practical Book of Pharmaceutical Inorganic Chemistry, , , , , , , , , , , , , , , , , , [ Test sample 7 | Standard compound at, iz Adjust the pH between 3 to 4 and filter if} 2. Adjust the pH between 3 to 4 by |, , necessary. | adding dilute acetic acid ‘Sp’ or dilute |, | ammonia solution ‘Sp’ _}, 3._ Dilute with water to 35 ml. 3._ Dilute with water to 35 mi. 7 al, 4. Add freshly prepared 10 ml of hydrogen | 4. Add freshly prepared 10 ml of, , sulphide solution hydrogen sulphide solution. — z, _5._ Dilute with water to 50 ml. 5. Dilute with water to 50 mi. |, | 6. Allow to stand for five minutes. 6. Allow to stand for five minutes. — "|, , , , Conclusion:, , If the colour produced in the sample solution is less than the standard solution, the, sample will pass the limit test of heavy metals and vice versa., , Method (C): ‘, , It is used for the substance which gives clear colourless solution in sodium hydroxide, solution. OO ———, Requirements:, , (a) Glasswares: Nesslers’ cylinders, measuring cylinder, glass rod, dropper etc., , (b) Chemicals: Test sample, standard lead solution, dilute sodium hydroxide solution,, , sodium sulphide solution., , Test sample Standard compound, 1. Solution is prepared as per the monograph |1. Take 2 ml of standard lead solution., and 25 ml is transferred in Nesslers’ cylinder, or weigh specific amount of substance and, dissolve in 20 ml of water and add 5 ml of, , dilute sodium hydroxide solution., , 2. Make up the volume to 50 ml with water. 2. Add 5 ml of dilute sodium, hydroxide solution and make up the, , volume to 50 ml with water., , 3. Add 5 drops of sodium sulphide solution. 3. Add 5 drops of sodium sulphide, , , , , , , , , , , , , , , , , , solution., , 4. Mix and set aside for 5 min. 4. Mix and set aside for 5 min., , 5. View downwards over a white surface. 5. View downwards over a white, surface., , , , , , Conclusion:, If the colour produced in the sample solution is less than the standard solution, the, sample will pass the limit test of heavy metals and vice versa., Method (D):, It is based upon the precipitation of relatively insoluble and characteristically coloured, sulphides of heavy metals. eT, 13, , , , , , Scanned with CamScanner

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—__Lmity, , A Practical Book of Pharmaceutical Inorganic Chemistry, , Reagent Preparations:, , e Standard solution:, , i or standard lead so),, Pipette out 10.0 ml of either standard lead solution (1 ppm Pb), , (2 ppm Pb) into a small Nesslers’ cylinder labelled as “Stan, , dard”. Add 2.0 ml ofthe, /, , solution and mix,, Test solution:, , i ml into a small Nes¢),,, Prepare as directed in the individual monograph and pipette 12 Sher,, , cylinder labelled as “Test”., , Preparation of standard lead solution (2 ppm Pb): ;, , i with water, Dilute 1 volume of standard lead solution (20 ppm Pb) to 10 volumes, , Preparation of thioacetamide reagent:, , i | of 1N Litin, , To 0.2 ml of 4% w/v thioacetamide solution, add 1 ml of a mixture of 15 ml of 1M sodiy,, , hydroxide, § ml of water and 20 mi of glycerine (85%). Heat on a water bath jy, 20 seconds, cool and use immediately., , Preparation of acetate buffer of pH 3.5:, , Dissolve 25 g of ammonium acetate in 25 ml of water and add 38 ml of 7M hydrochloric, acid. Adjust the pH to 3.5 by using 3 M hydrochloric acid or 6 M ammonia and dilute to, , 100 ml with water., , , , , , , , Procedure:, Test sample Standard compound Inference/Reasons, 1. Prepare an aqueous | 1. Take 10 ml of standard lead | 1. Suspected sample js|, solution of sample as solution in a Nessler's, , directed in monograph and, pipette out 12 ml, transfer, to Nesslers’ cylinder., , cylinder, add 2 mi of test, solution and mix well., , taken which might have, an impurity of heavy, metal and make its, solution., , , , 2. Add 2 mi of acetate buffer, of pH 3.5 and mix., , , , . Add 2 ml of acetate buffer, , of pH 3.5 and mix., , Maintain optimum pH, for limit test. |, , , , 3. Add 1.2 ml of, thioacetamide reagent and, allow to stand for, 2 minutes., , . Add 1.2 ml of thioacetamide, , reagent and allow to stand, for 2 minutes, brown, , coloured precipitates start, to appear., , w, , . Added for precipitation, , , , of metal sulphides., , , , , , 4. View downwards over a, , white surface., , , , » View downwards over a, , white surface., , , , =|, Compare intensity of, colour in both., , , , Conclusion:, , If the colour produced in the sample solution is less inte, the sample will pass the limit test of heavy metals and vice ve, , A A, 14, , nse than the standard solutio", rsa., , Scanned with CamScanner