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Estimation of heavy metals in crude drugs
- 1. Estimation Of Heavy Metals In Crude Drugs Herbal And Cosmetic Analysis M. Pharmacy II-Sem Mehul H Jain Pharmaceutical Analysis
- 2. Biological/Toxicological parameter • Determination of pesticides. • Determination of arsenic and heavy metals. • Determination of radioactive contamination. • Determination of aflatoxins.
- 3. Determination of Arsenic and Heavy Metals Limit Test for Arsenic(As) • The limit for arsenic is indicated in the individual monographs in terms of ppm. All reagents used for the test should have a content of arsenic as low as possible. • The method uses N-N-diethylmethyldithiocarbamate in pyridine and it reacts with hydrogen arsenide by giving a red-purple complex. • The limit is expressed in terms of arsenic trioxide (As2O3). • The method used is colorimetry and does not use toxic mercuric bromide paper.
- 4. Preparation of Test Solution Example: ginseng, powdered ginseng and red ginseng. Test solution is prepared with 1.0 gm of pulverized ginseng. Method: Weigh the sample as per monograph in a crucible Add 10ml of Mg. nitrate hexahydrate in Ethanol (95%) Burn Ethanol and heat gradually and ignite Note: If carbonized material still remains, moisten with a small quantity of nitric acid and ignite. After cooling, add 3ml of HCl, heat in water bath and designate it as test solution
- 5. Standard Solution Absorbing solution for hydrogen arsenide Dissolve 500mg of N-N-Diethyldithiocarbamate in pyridine to make 100ml. Standard arsenic stock solution 100mg of As2O3 Dry at 105oC for 4 hours Add 5ml of NaOH Add 10ml dil. H2SO4 Add dil. H2SO4 to neutralize Make up to 1000ml with freshly boiled & cooled water Standard arsenic solution Pipette 10ml of std. stock solution Add 10ml of dil. H2SO4 Make up with 1000ml of fresh & cooled water Each ml contains 1µg of As2O3
- 6. Procedure Place test solution in generator bottle Add 1 drop of methyl orange TS Add 5ml of KI Add 5ml of HCl Neutralize with NH3 Stand for 2-3 mins Add 5ml of Tin chloride Keep aside for 10mins Add 2gm of zinc & connect to the exit tube Add water to make 40ml Keep the generator bottle in water bath at 25oC Disconnect absorber tube and pyridine to make 5ml Observe in color of the absorbing solution
- 7. Preparation of Standard Color 2ml of std. arsenic solution in generator bottle Add 5ml of dil. HCl + 5ml of KI TS Allow to stand for 2-3 mins Add 5ml of acidic Tin chloride TS and allow to stand at RT for 10mins The color produced corresponds to 2µg of As2O3 and is used as standard
- 8. Limit test for Cadmium(Cd) and Lead(Pb) Digestion mixture 2 parts by weight of nitric acid (~1000g/l) TS and 1 part by weight of perchloric acid (~1170g/l) TS Reference materials Olive leaves (Olea europaea) 1 and hay powder 2. Preparation of sample Clean glassware 200-250mg of sample in cleaned silica crucible Add 0.1ml digestion mixture, cover the crucible Place in oven with controlled temp. & time regulator
- 9. Heat at 100oC for 3 hours Heat to 120oC for 2 hours Raise the temp. slowly to 240oC (avoid losses due to possible violent reactions) especially in the temp. range of 160-200oC Maintain this temp. for 4 hours Dissolve the inorganic residue in 2.5ml of nitric acid Used for determining heavy metals Every sample should be tested in parallel with a blank. The contents of Pb and Cd can be determined by inverse voltammetry or by atomic absorption spectrophotometry.