Spectrophotometric determination of iodine species in table salt and pharmaceutical preparations

Article abstract of DOI:10.1248/cpb.56.888

A sensitive spectrophotometric method for the determination of iodine species like iodide, iodine, iodate and periodate is described. The method involves the oxidation of iodide to ICl^-₂ in the presence of iodate and chloride in acidic medium. The formed ICl^-₂ bleaches the dye methyl red. The decrease in the intensity of the colour of the dye is measured at 520 nm. Beer's law is obeyed in the concentration range 0-3.5 μg of iodide in an overall volume of 10 ml. The molar absorptivity of the colour system is 1.73×10⁵lmol^-1cm^-1 with a correlation coefficient of -0.9997. The relative standard deviation is 3.6% (n=10) at 2 μg of iodide. The developed method can be applied to samples containing iodine, iodate and periodate by prereduction to iodide using Zn/H⁺ or NH₂NH₂/H⁺. The effect of interfering ions on the determination is described. The proposed method has been successfully applied for the determination of iodide and iodate in salt samples and iodine in pharmaceutical preparations.

Full text of DOI:10.1248/cpb.56.888

888
Chem. Pharm. Bull. 56(7) 888—893 (2008)
Vol. 56, No. 7
Spectrophotometric Determination of Iodine Species in Table Salt and
Pharmaceutical Preparations
George MARY,a Natesan BALASUBRAMANIAN,b and Karachalacherevu Seetharamiah NAGARAJA*,a
a Department of Chemistry, Loyola Institute of Frontier Energy (LIFE), Loyola College; Chennai 600 034, India: and
b Department of Chemistry, Indian Institute of Technology; Madras Chennai 600 036, India.
Received November 21, 2007; accepted March 30, 2008; published online April 14, 2008
A sensitive spectrophotometric method for the determination of iodine species like iodide, iodine, iodate and
periodate is described. The method involves the oxidation of iodide to ICl2ꢀ in the presence of iodate and chloride
in acidic medium. The formed ICl2ꢀ bleaches the dye methyl red. The decrease in the intensity of the colour of the
dye is measured at 520 nm. Beer’s law is obeyed in the concentration range 0—3.5 mg of iodide in an overall vol-
ume of 10 ml. The molar absorptivity of the colour system is 1.73ꢁ105 l molꢀ1 cmꢀ1 with a correlation coefficient
of ꢀ0.9997. The relative standard deviation is 3.6% (nꢂ10) at 2 mg of iodide. The developed method can be ap-
plied to samples containing iodine, iodate and periodate by prereduction to iodide using Zn/Hꢃ or NH2NH2/Hꢃ.
The effect of interfering ions on the determination is described. The proposed method has been successfully ap-
plied for the determination of iodide and iodate in salt samples and iodine in pharmaceutical preparations.
Key words spectrophotometry; iodine species; ICl2ꢀ; methyl red
Iodine is an essential micronutrient in human growth and There is a need for the determination of iodine species in
is very important for iodine supplementation metabolism. table salts and pharmaceutical samples. The developed
Deficiency of iodine causes serious delay in neurological de- method should be sensitive, simple and reliable.
velopment, goiter and hypothyroidism.1) Table salts are
This paper describes a spectrophotometric method for the
iodized with iodate or iodide to serve as a source of iodine. determination of iodine species like iodide, iodine, iodate
The iodized salt is recognized as the method of choice and and periodate. The method involves the oxidation of iodide
the most successful strategy for the prevention of iodine defi- to ICl2ꢀ in the presence of iodate and chloride in acidic
ciency disorders. The recommended concentration of iodate medium.22) The formed ICl2ꢀ bleaches the dye methyl red.
in salts is 40 ppm.2) Iodine is an effective germicide for a The decrease in the intensity of the colour of the dye is meas-
wide range of microorganisms. Iodine is often used in con- ured at 520 nm. The system obeys Beer’s law in the concen-
junction with complexing nonionic surfactants or polymers tration range 0—3.5 mg of iodide in an overall volume of
(iodophors) in disinfectants that are used in dairies, laborato- 10 ml. The developed method can be applied directly to sam-
ries and food processing plants. In addition to this iodine ples containing iodide and iodine and after prereduction of
finds applications as dietary supplements, catalysts, pharma- iodate and periodate to iodide using Zn/Hꢁ or NH2NH2/Hꢁ.
ceutical preparations, stabilizers and in photography. Iodine The proposed method has been successfully applied to the
is also used in the production of motor fuels, high purity determination of iodide and iodate in salt samples and iodine
metals and in cloud seeding. The varied applications of io- in pharmaceutical preparations.
dine have made the determination of iodine very important.
Several methods of iodine determination have been pro-
posed, including selective electrodes,3) X-ray fluorescence
(XRF),4) inductively coupled plasma mass spectrometry
(ICP-MS).5,6) Trace levels of iodide have been determined by
the catalytic effect usually on the cerium(IV)–arsenic(III) re-
action.7,8) Other reactions catalyzed or inhibited by iodide
have also been described.9,10) Precipitation as silver iodide,
dissolution in potassium cyanide, and determination of silver
in the complex by atomic absorption spectrometry has been
used for the indirect determination of iodide in a flow sys-
tem.11) Sensitive extraction photometric methods based on
ion-pair formation with methylene blue,12) or with brilliant
green13) are well known. Recently methods based on the oxi-
dation of leuco xylene cyanol FF14) or thionin15) with iodate
are reported. Several spectrophotometric methods have been
Experimental
Apparatus All absorbance measurements were made using Elico SL
177 scanning spectrophotometer with 1 cm glass cells.
Reagents All reagents were of analytical reagent grade and distilled
water was used for preparing all solutions.
A stock solution of iodide (1000 ppm) was prepared by dissolving
0.1307 g of potassium iodide in distilled water and made upto 100 ml in a
standard flask. A working solution of 1 mg mlꢀ1 was prepared by suitable di-
lution. A stock solution of iodate (1000 ppm) was prepared by dissolving
0.1223 g of potassium iodate in distilled water and made upto 100 ml in a
standard flask. A working solution of 69 mg mlꢀ1 was prepared by suitable
dilution. A stock solution of periodate (1000 ppm) was prepared by dissolv-
ing 0.1205 g of potassium periodate in distilled water and made upto 100 ml
in a standard flask. A working solution of 75 mg mlꢀ1 was prepared on dilu-
tion. Iodate solution (0.04%) was prepared by dissolving 0.040 g of potas-
sium iodate in 100 ml of distilled water. Sodium chloride solution (22%) was
prepared by dissolving 22 g of sodium chloride in 100 ml of distilled water.
Sulphuric acid (6 M) was prepared by the addition of 166.7 ml of concen-
reported for the determination of periodate and iodate.16—20) trated sulphuric acid (Sp. Gravity 1.84) to 200 ml of distilled water, cooled
El-Shahawi21) used the ion-associate of periodate with
amiloride hydrochloride for simultaneous spectrophotometric
determination of periodate and iodate by liquid–liquid ex-
and diluted to 500 ml. Methyl red solution (0.003%) was prepared by dis-
solving 0.1 g of methyl red dye in 1 ml of 4.5 N sodium hydroxide and dilut-
ing to 100 ml. Ten milliliters of this solution was diluted to 100 ml after
acidifying it by adding 0.5 ml of 6 M sulphuric acid. Thirty milliliters of this
traction. Most of the reported methods are not sensitive
enough or require complicated and expensive instruments.
solution was diluted to 100 ml to obtain 0.003% methyl red. Hydrazine solu-
tion (400 ppm) was prepared by dissolving 0.1626 g of hydrazinium sulphate
∗ To whom correspondence should be addressed. e-mail: ksnagi@vsnl.net; dr.ksnagaraja@gmail.com
© 2008 Pharmaceutical Society of Japan

July 2008
889
concentration of iodate in 50 mlꢂconcentration of iodideꢃ1.378ꢃ50/3
in 100 ml of water. Formaldehyde solution (7600 ppm) was prepared by di-
luting 2 ml of formaldehyde (38%) to 100 ml with water. Suitable aliquot of
this solution was diluted to obtain 1000 ppm solution. p-Phenylenediamine
solution (0.5%) was prepared by dissolving 0.50 g of p-phenylenediamine in
5 ml of 6 M sulphuric acid and diluting to 100 ml with distilled water.
Bromine solution (600 ppm) was prepared by dissolving 0.2143 g of potas-
sium bromate and 2.143 g of potassium bromide and diluting to 1 l with
water. Fifty milliliters of this stock solution was transferred into a 100 ml
calibrated flask containing 40 ml of 4.25 M sulphuric acid and diluting to
100 ml with water (300 ppm). This solution was prepared on the day of use.
Sulphuric acid (4.25 M) was prepared by adding 59 ml of concentrated sul-
phuric acid (Sp. Gravity 1.84) to 150 ml of water, cooled and then diluting to
250 ml. Sulphamic acid solution (1000 ppm) was prepared by dissolving
0.1 g of sulphamic acid in 100 ml of water.
Procedure. Calibration Graph To a series of 10 ml calibrated flasks,
3 ml aliquot of the sample containing 0—3.5 mg of iodide, 2 ml of 0.04% io-
date, 1 ml of 22% sodium chloride and 1 ml of 6 M sulphuric acid were
added. The solutions were mixed well and kept aside for 10 min. One milli-
liter of 0.003% methyl red was added before diluting to 10 ml with distilled
water. The absorbance of the solution was measured at 520 nm against water.
The plot of absorbance versus concentration of iodine is a straight line with
negative slope.
Determination of Iodide in Salt Samples Dissolve 5—10 g of salt
sample in 70—80 ml of water taken in a beaker. Filter the sample and dilute
it to 100 ml in a calibrated flask. Dilute the sample suitably to get a solution
containing 1 mg mlꢀ1 of iodide. Three milliliters of the sample containing
not more than 3.5 mg of iodide is treated with 2 ml of 0.04% iodate, 1 ml of
22% sodium chloride and 1 ml of 6 M sulphuric acid. The solutions were
mixed well and kept aside for 10 min. One milliliter of 0.003% methyl red
was added before diluting to 10 ml with distilled water in a calibrated flask.
The absorbance of the solution was measured at 520 nm against water. The
concentration of iodide is established from the calibration graph.
Determination of Iodate and Periodate Method 1: Reduction of Io-
date and Periodate to Iodide Using Zn/Hꢁ: One milliliter of 69 mg mlꢀ1 of
iodate or 75 mg mlꢀ1 of periodate is added to 25 ml of water taken in a 50 ml
beaker. To this 0.2—0.25 g of zinc metal and 1 ml of 6 M sulphuric acid were
added and the contents were mixed well and kept aside till the dissolution of
zinc. The solution was made upto 50 ml. Each milliliter is equivalent to 1 mg
of iodide (Chart 1).
concentration of periodate in 50 mlꢂconcentration of iodideꢃ1.5ꢃ50/3
Method 2: Reduction of Iodate and Periodate to Iodide Using Hydrazine
and Acid: One milliliter of 69 mg mlꢀ1 of iodate or 75 mg mlꢀ1 of periodate
is added to 25 ml of water taken in a 50 calibrated flask. To this 1 ml of
400 ppm hydrazine and 1 ml of 6 M sulphuric acid were added and the con-
tents were mixed well and kept aside for 10 min. One milliliter of 1000 ppm
formaldehyde was added mixed well and diluted to 50 ml. Each milliliter is
equivalent to 1 mg of iodide (Chart 1).
Determination of Iodate in Salt Samples Twenty to twenty-five grams
of salt samples containing iodate were dissolved in 70—80 ml water taken in
a beaker. Filter the sample and dilute the sample to 100 ml in a calibrated
flask. Ten milliliters of the salt solution is added to 15 ml of water taken in a
50 ml calibrated flask. To this 1 ml of 400 ppm hydrazine and 1 ml of 6 M sul-
phuric acid were added and the contents were mixed well and kept aside for
10 min. One milliliter of 1000 ppm formaldehyde was added mixed well and
diluted to 50 ml. To 3 ml of this solution, 2 ml of 0.04% iodate, 1 ml of 22%
sodium chloride and 1 ml of 6 M sulphuric acid were added. The contents
were mixed well and kept aside for 10 min. One milliliter of 0.003% methyl
red was added before diluting to 10 ml with distilled water in a calibrated
flask. The absorbance of the solution was measured at 520 nm against dis-
tilled water. The concentration of iodide is established from the calibration
graph. The concentration of iodate is calculated.
concentration of iodate in 50 mlꢂconcentration of iodideꢃ1.378ꢃ50/3
concentration of periodate in 50 mlꢂconcentration of iodideꢃ1.5ꢃ50/3
Determination of Iodine in Pharmaceutical Samples Dissolve 0.5 g
of iodine containing ointment or dilute 1 ml of iodine containing pharmaceu-
tical preparation to 50 ml. Take 1 ml of the diluted solution and further dilute
it to 50 ml in a calibrated flask. Take 3 ml of sample containing not more
than 3.5 mg of iodine and analyse it following the procedure recommended
under calibration graph. Calculate the concentration of iodine in the sample.
Following the above recommended procedures, analysis of 5 samples con-
taining iodine species can be completed in 60 min.
Results and Discussion
Quantitative bleaching of azo dyes by halogens like chlo-
rine or bromine is widely used for their spectrophotometric
determinations.23) The present method involves the oxidation
of iodide to ICl and stabilization as ICl2 (IClꢁCl ←ICl2 ) in
the presence of iodate and chloride in acid medium. The
formed ICl2ꢀ bleaches the dye methyl red and the decrease in
the intensity of the colour is a measure of iodide concentra-
tion.
Methyl red, an azodye, shows two absorption bands at
520 nm and 315 nm. The intensity of the band at 315 nm is
very weak compared with the band at 520 nm (Fig. 1).
It was observed that with increasing ICl2ꢀ concentration,
absorption decreases for the band at 520 nm whereas it in-
Determination of Iodate in Salt Samples Twenty to twenty-five grams
of salt samples containing iodate were dissolved in 70—80 ml water taken in
a beaker. Filter the sample and dilute the sample to 100 ml in a calibrated
flask. Ten milliliters of the salt solution is added to 15 ml of water taken in a
50 ml beaker. To this 0.2—0.25 g of zinc metal and 1 ml of 6 M sulphuric
acid were added and the contents were mixed and kept aside for dissolution
of zinc. The solution was made upto 50 ml. To 3 ml of this solution, 2 ml of
0.04% iodate, 1 ml of 22% sodium chloride and 1 ml of 6 M sulphuric acid
were added. The contents were mixed well and kept aside for 10 min. One
milliliter of 0.003% methyl red was added before diluting to 10 ml with dis-
tilled water in a calibrated flask. The absorbance of the solution was meas-
ured at 520 nm against distilled water. The concentration of iodide is estab-
lished from the calibration graph. Concentration of iodate is calculated.
ꢀ
ꢀ
→
ꢀ
Fig. 1. Absorption Spectra of Methyl Red Measured against Water
A, blank; B, 0.5 mg of iodide; C, 1.5 mg of iodide; D, 2.5 mg of iodide; E, 3.5 mg of
iodide.
Chart 1. Reaction Scheme

890
Vol. 56, No. 7
creased for the band at 315 nm (Fig. 1). The reaction of ICl2ꢀ
with methyl red involves competition between aromatic ring
substitution and azo link cleavage resulting in the bleaching
of colour at 520 nm. The bleaching of the colour of methyl
red by strong oxidizing agents like MnO4ꢀ, Ce4ꢁ and Cr2O72ꢀ
is by oxidative destruction of azo linkage. The proposed
scheme of bleaching of methyl red by ICl is similar to the
bleaching of colour of methyl orange by chlorine or
bromine.23) In the case of chlorine (stronger oxidizing agent
compared to bromine) the bleaching is carried upto 70% by
oxidation of azo linkage and 30% by aromatic ring substitu-
tion.
In the case of bromine the bleaching of methyl orange is
greater than 95% by aromatic ring substitution. This was
clearly established by the synthesis and spectral characteriza-
tion of relevant compounds.23) ICl is a good iodinating agent
compared to iodine.24) Iodination of dyes like dichlorofluo-
rescein and thymol blue with ICl were used for the spec-
trophotometric determination of ascorbic acid25) and sulphur
dioxide.26) Based on this, the major pathway of bleaching of
methyl red by ICl is by aromatic ring substitution by iodine
(Chart 1). The system obeys Beer’s law in the concentration
range of 0—3.5 mg of iodide in an overall volume of 10 ml.
Experimental conditions were optimized for the formation
of ICl using 2 mg of iodide. The effect of variation of iodate
was studied. It was established that a minimum of 1 ml of
Table 1. Effect of Some Interfering Species in the Iodide Determination
(Iodideꢂ2 mg)
Species
Amount tolerated (mg)
Phosphate, oxalate, citrate,
tartrate, borate, carbonate, bicarbonate,
fluoride, oxalate, sulphate
Brꢀ
1000
2
Ba(II), Pb(II), Mg(II), Co(II),
Cd(II), Bi(III), Ni(II), Li(I), Mn(II),
1000
ꢁ
Sr(II), Cr(III), NH4
NO3ꢀ
100
10
100
1000
1
1
1
400
400
1000
10
NO2ꢀ
NO2ꢀ a)
Sulphamic acid
SO32ꢀ, S2O32ꢀ
Hydrazine
Hydroxylamine
Hydrazineb)
Hydroxylamineb)
HCHO
Fe(II)
Fe(III)
2
Hg(II), Cu(II)
Glucose, acetone
5
100
a) Treated with 1 ml of 1000 ppm sulphamic acid solution prior to the addition of io-
date to form ICl2ꢀ. b) Treated with 1 ml of 1000 ppm HCHO solution prior to the ad-
dition of iodate to form ICl2ꢀ.
0.04% iodate was required for the formation of ICl. Further concentration range 0—3.5 mg of iodide. The detection limit
addition upto 1 ml of 0.12% of iodate showed no change in of iodide (3s) is 0.22 mg in an overall volume of 10 ml. The
the formation of ICl for a given concentration of iodide. molar absorptivity of the system was found to be 1.73ꢃ
Hence 2 ml of 0.04% is recommended as optimum concen- 105 l molꢀ1 cmꢀ1. A calibration graph was obtained with a
tration.
negative slope and the equation being Yꢂꢀ0.1342Xꢁ0.5718
The amount of chloride required for the reaction was stud- where Y is the absorbance and X (mg) is the concentration of
ied. It was found that a minimum of 1 ml of 15% sodium iodide. The correlation coefficient was ꢀ0.9997 and the rela-
chloride is sufficient for the formation of ICl and stabiliza- tive standard deviation was 3.6% (nꢂ10) for 2 mg of iodide.
tion as ICl2ꢀ. Addition upto 1 ml of 30% sodium chloride
Interferences The interfering effect of anions and
showed no change in the formation of ICl with 2 mg of io- cations, which may co-exist with iodide were studied. Any
dide. Hence the use of 1 ml of 22% sodium chloride is rec- deviation in the absorbance value of ꢄ0.01 to that obtained
ommended.
in the absence of other interfering ions in iodide determina-
The effect of variation of acidity required for the reaction tion was taken as a sign of interference. Varying concentra-
was studied. It was established that a minimum of 1 ml of 4 M tion of interfering species were introduced along with 2 mg of
sulphuric acid is sufficient for the formation of ICl and its iodide and the absorbance values were compared to that in
stabilization as ICl2ꢀ. Further addition upto 1 ml of 7 M sul- the absence of interference. Tolerance limit of various ions
phuric acid showed no change in the formation of ICl. Hence studied in iodide determination are summarized in Table 1.
1 ml of 6 M sulphuric acid is recommended as the optimum
concentration of sulphuric acid.
Hydrazine and hydroxylamine were tolerated upto
400 ppm by the addition of 1000 ppm HCHO prior to the ad-
The effect of methyl red concentration required for bleach- dition of iodate to form ICl2ꢀ. Nitrite was tolerated upto
ing by ICl2ꢀ was studied. One milliliter of 0.003% methyl red 100 ppm by treating with 1 ml of 1000 ppm sulphamic acid
solution is recommended as optimum concentration to have prior to the addition of iodate to form ICl2ꢀ.
maximum absorbance at 520 nm in an overall volume of
10 ml.
Applications In order to evaluate the analytical applica-
bility of the proposed method sample of table salts contain-
Samples containing iodate or periodate require reduction ing iodide or iodate and pharmaceutical preparations contain-
to iodide in acidic medium prior to determination. This was ing iodine were analysed. The salt samples from the local
achieved by using zinc and acid or with hydrazine solution. market, U.S.A., U.K. and Germany were analyzed. p-
The unreacted hydrazine should be removed prior to the con- Phenylenediamine method2) was used as reference method to
version of iodide to ICl with iodate. The effect of excess hy- compare results. The method is based on the oxidation of p-
drazine was masked by the addition of 1 ml of 1000 ppm phenylenediamine with iodate in acid medium. Tables 2 and
formaldehyde solution. Reduction of iodate or periodate to 2A show the results obtained for the analysis of iodate in
iodide by both methods gave excellent results. Samples con- iodized salt from India and Germany by both the proposed
taining iodine can be directly used for its determination like and reference method.2) In the reference method, a 10 ml
iodide without the reduction step.
aliquot of sodium chloride solution (25%), 0—5 ml of
Under these conditions the system obeys Beer’s law in the 80 ppm iodate, 4 ml of 0.5% p-phenylenediamine (ppda) in

July 2008
891
Table 2. Determination of Iodate in Iodized Salt
Amount of iodate
present (ppm)
Amount of iodate
present (ppm)
p-Phenylene
diamine
Amount of iodate
present (ppm)
BIS methodc)
Salt sample (Manufacturer)
Manufacturer’s claim
Developed methoda)
methodb)
Zn/Hꢁ
NH2NH2/Hꢁ
Annapurna (Hindustan Lever Ltd.,
Mumbai, India)
Minimum 30 ppm of iodine
ꢀiodate 41.34 ppm
41.34
39.62
38.47
39.81d)
37.34
41.34
41.34
40.01d)
40.19
39.04
39.91
39.71d)
41.05
40.19
40.77
40.67d)
40.19
39.62
40.38
40.07d)
39.62
39.62
39.04
39.43d)
39.62
42.20
40.19
40.67d)
39.62
39.62
40.19
39.81d)
41.34
40.48
40.19
40.67d)
40.19
40.19
40.19
40.19d)
38.40
41.60
40.00
40.00d)
41.60
41.60
40.00
41.07d)
41.60
40.00
40.00
40.53d)
40.00
38.40
40.00
39.47d)
41.60
38.40
40.00
40.00d)
39.66
39.13
40.19
39.66d)
40.72
40.72
39.66
40.37d)
39.66
38.60
40.72
39.66d)
40.77
40.72
39.66
40.72d)
42.30
40.72
40.72
41.25d)
Aashirvaad (ITC Ltd.,
Kolkata, India)
Minimum 30 ppm of iodine
ꢀiodate 41.34 ppm
Udhayam (GHCL Ltd.,
Thirupporor, Tamilnadu, India)
Minimum 30 ppm of iodine
ꢀiodate 41.34 ppm
Tata iodized salt (Tata Chemicals
Ltd., Mumbai, India)
Greater than 15 ppm of iodine
ꢀiodate greater than 20.67 ppm
i-shakti crystal (Tata Chemicals
Ltd., Mumbai, India)
Greater than 15 ppm of iodine
ꢀiodate greater than 20.67 ppm
a) 1 g of the salt sample dissolved in 25 ml of water was subjected to reduction by Zn/Hꢁ or NH2NH2/Hꢁ. Volume was made upto 50 ml. 3 ml of this solution was used for the
analyses by the proposed method. b) Volume of salt sample used: 10 ml of 25% salt solution. c) 20 g of the salt sample was dissolved in 100 ml. To this solution 10 ml of 10%
KI and 5 ml of 2 N sulphuric acid were added. The contents were titrated against 0.05 N sodium thiosulphate solution using starch as indicator. d) Average of three determinations.
Table 2A. Determination of Iodate in Iodized Salt
Amount of iodate
present (ppm)
Amount of iodate
present (ppm)
p-Phenylene
diamine
Amount of iodate
present (ppm)
BIS methodc)
Salt sample (Manufacturer)
Manufacturer’s claim
Developed methoda)
methodb)
Zn/Hꢁ
NH2NH2/Hꢁ
Marken Jodsalzd) Reines
Alpensalz aus NatursoleꢁFluoridꢁ
Folsaure (Sudsalz Gmbh, Ridlerstr.
75, 80339 Munchen)
Iodate 20.4 mg
21.19
21.01
21.19
21.19
21.67
21.67
21.86
20.40
21.01
21.01
22.50
21.86
21.07f)
0.00257%
21.13f)
0.00258%
21.95f)
0.00268%
21.37f)
0.00261%
ꢀpotassium iodate 0.0025%
Iodate 20.4—32.5 mg
Altlandere) Jodsalz mit Fluor
(Akzo Nobel Salt bv,
Den Niederlanden)
21.70
21.53
21.70
21.53
20.83
20.00
21.87
21.13
21.53
21.53
20.00
20.40
21.59f)
0.00264%
21.59f)
0.00264%
20.28f)
0.00248%
21.13f)
0.00258%
ꢀpotassium iodate 0.0025—0.0042%
a) 2.5 g of the salt sample dissolved in 25 ml of water was subjected to reduction by Zn/Hꢁ or NH2NH2/Hꢁ. Volume was made upto 50 ml. 3 ml of this solution was used for
the analyses by the proposed method. b) Volume of salt sample used: 16 ml of a 30% salt solution. c) 20 g of the salt sample was dissolved in 100 ml. To this solution 10 ml of
10% KI and 5 ml of 2 N sulphuric acid were added. The contents were titrated against 0.05 N sodium thiosulphate solution using starch as indicator. d) Marken Jodsalz contain in-
gredients such as calcium carbonate, magnesium carbonate, sodium fluoride 0.047—0.064% as additives in addition to iodate. e) Altander Jodsalz contain ingredients such as
potassium fluoride 0.065—0.087%, sodium hexacyanoferrate(II)[E535] and silicon dioxide[E551] as additives in addition to iodate. f) Average of three determinations.
sulphuric acid were added. The contents were mixed well and iodide or iodine were converted to iodate using bromine
the volume made upto 25 ml with water. The colour devel- water and removing excess bromine with formic acid.27)
oped was measured at 525 nm. A calibration graph was ob- The formed iodate was determined by p-phenylenediamine
tained by plotting absorbance versus amount of iodate. Salt (ppda) method.
samples were analysed by the p-phenylenediamine (ppda)
Table 3 shows the results obtained for the analysis of io-
method by taking 10 ml of 25% salt solution, 6 ml of water, dide in iodized salt from U.K. and U.S.A. There is a good
4 ml of 0.5% ppda solution in sulphuric acid in a 25 ml cali- agreement between the results obtained by the proposed and
brated flask. The contents were mixed well and the volume reference method.2) Iodophore is a weak complex of iodine
was made upto 25 ml. The colour developed was measured at and carrier polymer. It has a prolonged microbial action and
525 nm. The amount of iodate present in the salt sample was used as an antiseptic and disinfectant. It is mainly used for
established from the calibration graph. Samples containing cleaning the contaminated wounds, preoperative skin and

892
Vol. 56, No. 7
disinfection of equipments. Pharmaceutical preparations con- were filtered before diluting to known volume. One gram of
taining iodine were purchased from the local market and ana- salt sample from local market and 2.5 g of salt sample from
lyzed for iodine content by the proposed and p-phenylenedi- Germany were used for the reduction of iodate to iodide with
amine (ppda) method. Table 4 shows the results obtained for Zn/Hꢁ or NH2NH2/Hꢁ. A 3 ml aliquot containing not more
the analysis of iodine in pharmaceutical preparations.
than 3.5 mg of iodide was used for the analysis by the pro-
1. Determination of Iodate in Iodized Salt: a) Salt samples posed method. The results were also compared with the ref-
containing iodate from the local market and Germany were erence method2) and BIS (Bureau of Indian Standards-IS
analysed by Zn/Hꢁ and NH2NH2/Hꢁ reduction methods. Salt 7224: 1985) method.28) In the BIS method, 20 g of salt sam-
samples were dissolved in water and made up to known vol- ple was dissolved in 100 ml of water, to this 10 ml of 10%
ume. Salt solutions containing insoluble additives such as potassium iodide solution and 5 ml of 2 N sulphuric acid were
magnesium carbonate, calcium carbonate and silicon dioxide added. The liberated iodine was titrated against 0.05 N
sodium thiosulphate solution, adding 1 ml of 1% starch solu-
tion near the end of titration. The results are summarized in
Tables 2 and 2A.
Table 3. Determination of Iodide in Iodized Salt
b) Salt samples containing iodide one each from U.K. and
Amount of
iodide present
(mg)/g
Developed
methoda)
Amount of
iodide present (mg)/g
p-Phenylene
diamine
U.S.A. was analyzed. Ten grams of the salt sample (Cerebos
Extra fine iodized salt from U.K.) and 5 g of the salt sample
(Diamond Crystal iodized salt from U.S.A.) were dissolved
in 100 ml of water. Suitable aliquot of the salt solution con-
taining not more than 3.5 mg was used to determine the
amount of iodide by the proposed method. The results (Table
3) were compared with the p-phenylenediamine (ppda)
method after oxidation of iodide to iodate with 2 ml of
300 ppm bromine solution. The excess bromine was de-
stroyed by the addition of 1 ml of 85% formic acid.
Salt sample
Manufacturer’s
claim
(Manufacturer)
methodb)
Cerebos Extra fine
iodized table
Iodide 8.8 mg/g
8.375
8.625
8.500
8.500e)
8.063
8.868
8.868
8.600e)
saltc) (Cerebos,
Middlewich, Chechire,
England)
ꢀ(Potassium Iodide
1150 mg/100 g)
(1111 mg/100 g)e)
(1127 mg/100 g)e)
2. Determination of Iodine in Pharmaceutical Prepara-
tions: a) Wokadine ointment: About 0.5 g of the Wokadine
ointment was dissolved in 50 ml of water. One milliliter of
this solution was diluted to 50 ml. A suitable aliquot contain-
ing not more than 3.5 mg of iodine was withdrawn from this
solution and analyzed to determine the amount of iodine by
the proposed method. The results were compared with the p-
phenylenediamine (ppda) method after oxidation of iodine to
iodate with 2 ml of 300 ppm bromine solution. The excess
bromine was destroyed by the addition of 1 ml of 85% formic
acid. The results are shown in Table 4.
Diamond Crystal
iodized saltd)
Iodide 49 mg/g
49.000
51.001
48.500
49.500e)
49.930
48.770
49.930
49.540e)
(Cargill Incorporaed,
Minneapolis,
MN-55440)
ꢀ(Potassium Iodide
0.0064%)
(0.00649%)e)
(0.00649%)e)
a) Volume of sample used: Cerebos salt, 2 ml of 10% salt solution; Diamond Crystal
salt, 1 ml of 5% salt solution. b) Volume of sample used: Cerebos salt, 12 ml of 30%
salt solution; Diamond Crystal salt, 10 ml of 25% salt solution. c) Cerebos Iodized
salt contain ingredients such as magnesium carbonate, sodium hexacyanoferrate(II) as
anticaking agents in addition to iodide. d) Diamond Crystal iodizd salt contain ingre-
dients such as silicon dioxide, tricalcium phosphate, dextrose and sodium bicarbonate
as additives in addition to iodide. e) Average of three determinations.
Table 4. Determination of Iodine in Pharmaceuticals
Developed methoda)
p-Phenylenediamine methodb)
Concentration of
Sample (Manufacturer)
Manufacturer’s claim
Concentration
of iodine in
sample (mg)
% of iodine in
sample
% of iodine in
iodine in
sample
sample (mg)
Wokadine ointment
(Wockhardt Ltd.,
New Delhi, India)
Available iodine
0.5% w/w
2.975
2.950
3.000
0.496
0.492
98.694
101.597
98.694
0.494
0.508
0.500
0.494
0.496c)
0.498c)
Betadine solution (G.S.
Pharmbutor Pvt. Ltd.,
Uttarakhand, India)
Available iodine
0.5% w/v
2.975
2.975
2.950
0.494
0.496
101.597
101.597
98.694
0.508
0.508
0.492
0.494
0.494c)
0.503c)
Betadine ointment (G.S.
Pharmbutor Pvt. Ltd.,
Rajasthan, India)
Available iodine
0.5% w/w
2.950
2.950
2.975
0.492
0.492
98.694
101.597
98.694
0.494
0.508
0.496
0.494
0.493c)
0.498c)
Collosol iodine
Available iodine
8 mg/5 ml
2.425
2.475
2.475
8.082 mg/5 ml
8.250 mg/5 ml
8.250 mg/5 ml
8.195 mg/5 mlc)
98.694
95.791
95.791
8.225 mg/5 ml
7.983 mg/5 ml
7.983 mg/5 ml
8.063 mg/5 mlc)
oral solution (Solvay
Pharma India Limited,
Ahmedabad, India)
a) Wokadine and Betadine ointment (0.5 g of ointment dissolved in 50 ml water, 1 ml of this solution was diluted to 50 ml, 3 ml of this solution was used), Betadine solution
(0.5 ml dissolved in 50 ml, 1 ml of this solution diluted to 50 ml, 3 ml of this solution was used.), Collosol iodine oral solution (2.5 ml dissolved in 100 ml of water, 1 ml of this solu-
tion was diluted to 50 ml, 3 ml of this solution was used.) b) Wokadine and Betadine ointment (0.5 g of ointment dissolved in 250 ml water, 10 ml of this solution was used), Be-
tadine solution (1 ml dissolved in 250 ml water, 5 ml of this solution was used), Collosol iodine oral solution (2.5 ml dissolved in 250 ml of water, 6 ml of this solution was used).
c) Average of three determinations.

July 2008
893
b) Betadine ointment: About 0.5 g of the Betadine oint- ples and iodine in pharmaceutical preparations demonstrate
ment was dissolved in 50 ml of water. One milliliter of this the utility of the method to serve as alternate to the existing
solution was diluted to 50 ml. A suitable aliquot containing methods.
not more than 3.5 mg of iodine was withdrawn from this solu-
Acknowledgement One of the authors (MG) sincerely acknowledges
the encouragement and support from Dr. Sr. Annamma Philip, Principal,
Stella Maris College, Chennai, UGC (New Delhi) and DCE (TamilNadu
Government) for the leave granted on FIP scheme for the Doctoral pro-
tion and analyzed to determine the amount of iodine by the
proposed method. The results were compared with the p-
phenylenediamine (ppda) method after oxidation of iodine to
iodate with 2 ml of 300 ppm bromine solution. The excess
bromine was destroyed by the addition of 1 ml of 85% formic
acid. The results are tabulated in Table 4.
gramme.
References
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logical Basis of Therapeutics,” 7th ed., Macmillan, New York, 1985, p.
964.
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c) Betadine solution: One milliliter of Betadine solution
was diluted with 50 ml of water. One milliliter of this solu-
tion was diluted to 50 ml. A suitable aliquot of iodine con-
taining not more than 3.5 mg was withdrawn from this solu-
tion and analyzed to determine iodine by the proposed
method. The results were compared with the p-phenylenedi-
amine (ppda) method after oxidation of iodine to iodate with
2 ml of 300 ppm bromine solution. The excess bromine was
destroyed by the addition of 1 ml of 85% formic acid. The re-
sults are shown in Table 4.
d) Collosol: Collosol solution 2.5 ml was diluted with
100 ml of water. One milliliter of this solution was diluted to
50 ml. A suitable aliquot containing not more than 3.5 mg of
iodine was withdrawn from this solution and analyzed to de-
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175—180 (1989).
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compared with the p-phenylenediamine (ppda) method after
oxidation of iodine to iodate with 2 ml of 300 ppm bromine
solution. The excess bromine was destroyed by the addition
of 1 ml of 85% formic acid. The results are shown in Table 4.
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Conclusion
The developed method is simple, precise and sensitive for
the determination of iodine species like iodide, iodine, iodate
or periodate. The system obeys Beer’s law in the concentra-
tion range of 0—3.5 mg of iodide in an overall volume of
10 ml with the molar absorptivity of 1.73ꢃ105 l molꢀ1 cmꢀ1.
The developed method is more sensitive compared to the
spectrophotometric methods based on the oxidation of
leuco xylene cyanol FF14) (eꢂ1.7ꢃ104 l molꢀ1 cmꢀ1) and
thionin15) (eꢂ2.7ꢃ104 l molꢀ1 cmꢀ1) with iodate. The molar
absorptivity of the developed method is comparable to the
extraction method based on the ion pair with brilliant
green13) (eꢂ3.0ꢃ105 l molꢀ1 cmꢀ1) or methylene blue12)
(eꢂ3.1ꢃ104 l molꢀ1 cmꢀ1). The application of proposed
method to the determination of iodide and iodate in salt sam-
26) Gayathri N., Balasubramanian N., J. AOAC Int., 84, 1065—1069
(2001).
27) Bhatty M. K., Townshend A., Anal. Chim. Acta, 56, 55—60 (1971).
28) Indian Standard Specification for Iodized Salt IS 7224: Bureau of In-
dian Standards, New Delhi, 1985, pp. 986, 987.