manual of methods of analysis of foods - Ministry of Health and ...

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METALS Stopper separator and shake vigorously for 1 min. All Hypochlorite should be reduced. Extract solution with 2 to 3 ml of CHCl 3 , drain off organic layer carefully and discard. Final aqueous solution should now be colourless. Now, to the solution in the third separator, add 3 ml of 30% HOAC and appropriate volume and concentration of dithizone solution as indicated in Table 3. Shake vigorously for 1 min and let layers separate. Insert cotton pledget into the stem of the separator and collect dithizone extract (discarding first ml) in test tube. Read absorbance ‘A’ of the extract at 490 nm. Convert ‘A’ to µg of Hg from working standard curve. Preparation of Standard Curve: Table 3 shown above is useful in preparing standard curve and for establishing approximate Hg range in sample. Prepare working standard curve of required range, starting with blank and extending to final standard of range with 4 intermediate increments. Add appropriate amounts of Hg to 50 ml of 0.1N HCl in separator. Add 5 ml H 2 NOH.HCl reagent (f) and 5 ml of CHCl 3 . Shake vigorously for 1 min let layers separate; drain off CHCl 3 and discard, being careful to remove as completely as possible all droplets of CHCl 3 . Add 3 ml of 30% HOAC and appropriate volume of dithizone solution. Shake vigorously for 1 min and let layers separate. Insert cotton pledged into stem of separator and collect dithizone extract (discarding first ml) in test tube and read absorbance at 400 nm. Plot ‘A’ against µg of Hg. 58
METALS Precautions: (i) Digestion must be almost complete. (ii) Oxidizing material in digest must also be destroyed. (iii) Careful heating of digest during preparation of sample is required. (iv) Acidity of final sample solution before extraction should be about 1N but not more than 1.2N. (v) Do not use silicone grease in stop cocks. ( Ref :- Manual Methods of Analysis for Adulterants and Contaminants in Foods, I.C. M.R 1990 , Page 156 ) 3.8 DETERMINATION OF TIN IN FOOD (Spectrophotometric Catechol Violet Method (IUPAC Method) Principle: The sample is wet digested with a mixture of nitric and sulphuric acids followed by subsequent treatment with perchloric acid and hydrogen peroxide and the residue is diluted with water to give an approximately 4.5M concentration of the acid. Potassium iodide is added Tin (IV) iodide is selectively extracted into cyclohexane. Tin (IV) is returned to aqueous solution by shaking organic layer with sodium hydroxide solution which is subsequently acidified. After removal of free iodine, Tin (IV) is determined spectrophotometrically as its coloured complex with catechol violet, the 59
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Lab. Manual 9 MANUAL OF METHODS OF
Page 3 and 4:
METALS MANUAL FOR ANALYSIS OF METAL
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METALS The edible portion of the sa
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METALS Procedure: Weigh accurately
Page 9 and 10: METALS (iii) Conc. HCl, HNO 3 , Bro
Page 11 and 12: METALS usually given by the manufac
Page 13 and 14: METALS 500 ºC. Ash at this tempera
Page 15 and 16: METALS (Ref:- A.O.A.C 17 th edn , 2
Page 17 and 18: 15 METALS
Page 19 and 20: METALS for about 1 hour. Remove hea
Page 21 and 22: METALS 2.2 DETERMINATION OF MERCURY
Page 23 and 24: METALS Determination: Take a suitab
Page 25 and 26: METALS remoisten it as mentioned ab
Page 27 and 28: METALS Reagents: (a) (b) (c) (d) (e
Page 29 and 30: METALS excessive. When reaction had
Page 31 and 32: METALS 3.2 DETERMINATION OF ARSENIC
Page 33 and 34: METALS with dil. HCl solution leavi
Page 35 and 36: METALS approximately 8.8 by adding
Page 37 and 38: METALS 3.4 DETERMINATION OF COPPER
Page 39 and 40: METALS Determination: Pipette suita
Page 41 and 42: METALS (d) (e) (f) Acetate buffer s
Page 43 and 44: METALS Calculations: Iron content o
Page 45 and 46: METALS (f) (g) Potassium cyanide so
Page 47 and 48: METALS (ii) Make slightly alkaline
Page 49 and 50: METALS ____________________________
Page 51 and 52: METALS 3.7 DETERMINATION OF MERCURY
Page 53 and 54: 51 METALS
Page 55 and 56: METALS volumetric flask and dilute
Page 57 and 58: METALS Slowly add 20 ml cool HNO 3
Page 59: METALS If first extraction indicate
Page 63 and 64: METALS (k) Sodium acetate solution:
Page 65 and 66: METALS Determination: (1) Quantitat
Page 67 and 68: METALS µg of Sn present in test so
Page 69 and 70: METALS (c) Dimethyl glyoxime soluti
Page 71 and 72: METALS dish and filter with several
Page 73 and 74: METALS sample as given above) and s
Page 75 and 76: METALS When clean ash is obtained,
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