pharmacopoeial assays for quality. oxygen flask method

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.

pharmacopoeial assays for quality. oxygen flask method

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