assays by oxygen flask combustion

7/27/2019 Assays by Oxygen Flask Combustion

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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.

-In case of iodo-compound, a mixture of iodine & iodate are formed.

-Oxidation is carried out with bromine.

-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.

-The method is adapted to determine elemental sulphur.

-Sulphur is oxidised to sulphur trioxide absorbed in water. S→SO3

-To ensure the complete oxidation, hydrogen peroxide is also added in the water.-Then sulphur is determined by titrating with barium perchlorate solution using indicator

alizarin red S or thoron/methylene blue as appropriate.

- The method is applicable in the determination organo-mercury compounds as well.

Apparatus:

i)Iodine flask(500ml) as per British standard specification (BS 2735:1956).

ii)To the stopper platinum wire is fused.

iii)To the wire a platinum gauze of specified dimension is attached.

iv)The gauze complies to dimension of No.36 sieve.



Propyliodone: Determination of the percentage of

C10H11I2 NO3

3I2 + 6NaOH → 5NaIO3+ 3H2O

5[NaI+3Br 2 +3H2O → NaIO3 +6HBr]6[NaIO3 +5KI +6HBr → 3I2 +NaBr+5KBr]

I2+ 2Na2S2O3 → 2NaI +Na2S4O6

3X447g C10H11I2 NO3 ≡6I ≡NaIO3 ≡36I ≡36000ml M

0.7450mg C10H11I2 NO3 ≡ 1ml 0.02M Na2S4O6



-Accurately weighed sample is folded in an ashles- filter paper.

-The folded paper is placed in the platinum gauze cup.

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

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

-The flask is swirled to saturate the solution with O2

-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.

-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 for two minutes.-Iodide is oxidised to iodate by bromine in potassium acetate-acetic acid buffer solution.

-Excess bromine(reduction to HBr) is removed by addition of formic acid,

-Trace of bromine is swept out by current of air

-Potassium iodide is added & titrated with sodium thiosulpahte(V.S.) using starch mucilage as

indicator.

Cognate determination:

Iophendylate injection,

Liothyronine sodium

Propyliodone suspension,

Proppyliodone oily suspension,

Thyroxine sodium,

Nitroxynil

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 fluorine

blue & cerous nitrate in an acetate buffer.



-Standard used is sodium fluoride.

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.

assays by oxygen flask combustion

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