pharmacopoeial assays for quality. oxygen flask method

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  • 7/29/2019 Pharmacopoeial Assays for Quality. Oxygen Flask Method

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    Assays by oxygen flask combustion

    -Developed by Schoniger(1955).

    -Rapid assay method for organically combined

    halogens.

    -Halogen is released following the complete

    combustion of organic matter by oxygen.

    -Halogen is absorbed by caustic soda solution.

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    -In case ofiodo-compound, a mixture ofiodine &

    iodate are formed.

    -Oxidation is carried out withbromine.

    -After acidification in the presence of iodide, six

    fold yield of iodine is generated.

    -The iodine is titrated against sodium thiosulphate.

    -The method is useful for expensive materials &

    product in which the halogen-containing material is

    present at low dosage.

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    -The method is adapted to determine elemental

    sulphur.

    -Sulphur is oxidised to sulphur trioxide absorbed in

    water.

    -To ensure the complete oxidation, hydrogenperoxide is also added in the water.

    -Then sulphur is determined by titrating withbarium perchlorate solution using indicator

    alizarin red S or thoron/methylene blue as

    appropriate.

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    - The method is applicable in the determination

    organo-mercury compounds as well.

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    Apparatus:

    i)Iodine flask(500ml) as per British standard

    specification (BS 2735:1956).

    ii)To the stopper platinum wire isfused.

    iii)To the wire a platinum gauze of specified

    dimension is attached.

    iv)The gauze complies to dimension ofNo.36 sieve.

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    Propyliodone: Determination of the percentage of

    C10H11I2NO3

    C10H11I2NO3

    3I2+ 6NaOH 5NaIO3+ 3H2O

    5[NaI+3Br2 +3H2O NaIO3 +6HBr]6[NaIO3+5KI +6HBr 3I2 +NaBr+5KBr]

    I2+ 2Na2S2O3 2NaI +Na2S4O6

    3X447g C10

    H11

    I2NO

    36I NaIO

    336I 36000ml M

    0.7450mg C10H11I2NO3 1ml 0.02M Na2S4O6

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    -Accurately weighed sample is folded in an ashles-

    filter paper.

    -The folded paper is placed in the platinum gauzecup.

    -A narrow strip of filter paper is inserted in thefolded paper to act as a fuse.

    -Air is displaced from the flask with oxygen & theneck is moisten with water.

    -The flask is swirled to saturate the solution with O2

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    -Water & M sodium hydroxide are placed in the

    flask & was filled with oxygen .

    -End of the fuse is lit & the stopper is inserted

    immediately.

    -The flask is held firmly in place.

    -The flask is tilted in order to prevent incompletely

    burned material from falling into the liquid.

    -Upon completion of the combustion, the flask is

    shaken vigorously for 5 minutes.

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    -Few ml of water is placed in the cap, the stopper is

    carefully withdrawn.

    -The stopper & wire assembly are washed with

    water & excess of acetic bromine solution is

    added.

    -Then the solution is allow to stand fortwo minutes.

    -Iodide is oxidised to iodate by bromine in

    potassium acetate-acetic acid buffer solution.

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    -Excess bromine(reduction to HBr) is removed by

    addition offormic acid.

    -Potassium iodide is added & titrated with sodium

    thiosulpahte(V.S.) using starch mucilage as

    indicator.

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    Cognate determination:

    Iophendylate injection,Liothyronine sodium

    Propyliodone suspension,

    Proppyliodone oily suspension,Thyroxine sodium,

    Nitroxynil

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    Fluocinolone acetonide:

    -Borosilicate glass must be avoided as fluorine

    reacts with boron present in the hard glass.

    -Organically combined fluorine is converted to

    fluorine by combustion in oxygen in a silica or soda

    glass flask.

    -Absorbed fluorine in water is determined

    colourimetrically at 610nm using alizarin fluorineblue & cerous nitrate in an acetate buffer.

    -Standard used is sodium fluoride.

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    Other uses of oxygen flask method:

    -Determination of fluorine in cloxacillin sodium to

    supplement the assay.

    -To establish the presence of chlorine in diloxanide

    furoate & chlorthalidone.

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    Reference:

    IP2007.A.H. Beckett/J.B.Stenlake

    Practical pharmaceutical chemistry.