Estimation of iodine in salt fortified with iodine _ iron by maclaren1

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									Indian J Med Res 123, April 2006, pp 531-540




Estimation of iodine in salt fortified with iodine & iron

S. Ranganathan & M.G. Karmarkar*


National Institute of Nutrition (ICMR), Hyderabad & *International Council for Control
of Iodine Deficiency Disorders, All India Institute of Medical Sciences, New Delhi, India


Received December 24, 2004


            Background & objectives: The National Institute of Nutrition (NIN), Hyderabad has developed
            double fortified salt (DFS) containing both iodine and iron to control the twin problems of iodine
            deficiency disorders (IDD) and iron deficiency anaemia (IDA). When the iodine content of DFS
            was estimated by the conventional iodometric titration using sulphuric acid (H2SO 4), problems
            such as wide variation between duplicate analysis and under/overestimations of iodine content
            were encountered, which led to inconsistent results. This study was undertaken to develop a modified
            method for the estimation of iodine in DFS so as to get reliable iodine content of DFS.

            Methods: A modified method was developed using orthophosphoric acid (H3PO4) and the sensitivity
            of the method was confirmed by estimating the iodine content of potassium iodate (KIO3) standard
            at different concentrations of iodine (0 to 100 ppm). The iodine content of DFS and iodized salt
            (IS) from local market and factory was estimated by the modified method as well as the conventional
            iodometric titration and the results were compared.

            Results: The pH of DFS was acidic. The time gap between the additions of acid and potassium
            iodide (KI) played a crucial role in getting the actual iodine content of DFS. The H2SO4 and ferrous
            sulphate (FeSO 4) interfered with the estimation of iodine in DFS resulting in underestimation or
            overestimation of iodine. Modified method (H 3PO4) produced consistent and reliable iodine content
            of DFS. Both H2SO4 and H3PO4 gave same results when tested with KIO3 standard, Reference salt
            and IS (both experimental and purchased from local market). Actually 0.50 ml of 1 per cent KI
            was sufficient to estimate the iodine content of DFS or IS.

            Interpretation & conclusion: The results of the present study showed that the conventional method
            using H2SO 4 was not suitable for the estimation of iodine in DFS. The modified method using
            H2PO 4 was ideally suited for the estimation of iodine in DFS. Also, iron from DFS did not interfere
            during estimation of iodine by this method. As both the conventional and the modified methods
            gave the same results for the iodine content of IS, it is practically prudent to use the modified
            method (H2PO4) for both DFS and IS instead of following one method (H3PO4) for DFS and another
            (H2SO4) for IS. The quantity of KI is also reduced and the order of additions of reagents is changed
            in the modified procedure.


Key words Double fortified salt (DFS) - iodine loss - iodized salt (IS) - iodometric titration - persulphate -
          phosphoric acid - sulphuric acid
                                                            531
532                                            INDIAN J MED RES, APRIL 2006


   Iodine deficiency disorders (IDD) and iron                       iodometric titration, several problems were
deficiency anaemia (IDA) are widely prevalent and                   encountered. There was a wide variation in the iodine
often coexist in the country 1,2. As part of dietary                content of duplicate analyses of the same samples of
diversification, fortification of food with iodine and              DFS and low iodine values were also observed in
iron is recommended to prevent and control nutritional              freshly prepared DFS (Table I), although the expected
deficiencies. To tackle the two deficiencies, the                   iodine content was about 40 µg/g of DFS. There was
National Institute of Nutrition (NIN), Hyderabad,                   a lack of consistency in the iodine content of DFS
India, developed double fortified salt (DFS), which                 when estimated over a period of time (Table II). In
contains refined common salt (100%), potassium                      some batches, very high iodine content was also
iodate, KIO 3 (0.0067%), ferrous sulphate hepta                     obtained (50 - 70 ppm) for the same samples of DFS
hydrate, FeSO4 .7H2O (0.508%) and sodium hexa meta                  (Table III). However, none of these problems were
phosphate (1%) so as to provide simultaneously                      encountered when the iodine content of IS was
40 µg iodine and 1000 µg iron per gram of DFS 3,4.                  estimated by the same method (Table II). Lack of
                                                                    consistency in the iodine content of DFS created a
    Generally the iodine content of iodized salt (IS)               lot of confusion regarding the stability of iodine in
is estimated by the conventional iodometric titration               the multicentric study on DFS6. Therefore, there was
using sulphuric acid reagent 5 . When the iodine                    a need to overcome the problems faced in order to
content of DFS was estimated by the conventional                    get consistency in the iodine content of DFS.


            Table I. Iodine content of double fortified salt (DFS), estimated by the conventional iodometric titration
       Sample no.                      Iodine (ppm)*                   Sample no.                    Iodine (ppm)*
                                Mean                   SD                                    Mean                    SD
            1                   14.1                   1.2                 21                 14.6                   4.8
            2                   31.4                   25.8                22                 15.4                   6.7
            3                    8.8                   5.6                 23                 18.6                   0.9
            4                   14.3                   2.3                 24                 16.4                   6.8
            5                   29.1                   15.7                25                 13.0                   3.3
            6                   23.0                   13.8                26                 10.6                   3.0
            7                   17.5                   6.7                 27                 20.4                   11.6
            8                   27.2                   4.9                 28                 12.5                   4.9
            9                   23.5                   2.6                 29                 15.1                   5.6
           10                   18.3                   11.6                30                 13.0                   2.6
           11                   16.4                   6.8                 31                 15.6                   1.1
           12                   35.4                   19.9                32                 22.3                   7.5
           13                   27.5                   5.2                 33                 18.7                   9.9
           14                   14.2                   2.7                 34                 21.4                   2.6
           15                   18.8                   4.8                 35                 18.0                   1.4
           16                   22.7                   17.2                36                 10.5                   7.3
           17                   10.6                   5.2                 37                 11.5                   4.0
           18                   18.0                   3.0                 38                 14.4                   5.4
           19                   12.3                   5.4                 39                 10.5                   5.9
           20                   20.2                   7.4                 40                 11.0                   5.0

*Average of duplicates done twice. ppm, part per million
                   RANGANATHAN & KARMARKAR: IODINE ESTIMATION IN DOUBLE FORTIFIED SALT                                                        533

   Thus, the objective of the present study was to                           packed in 0.5 kg low-density polyethylene (LDPE)
estimate iodine in DFS by modifying the                                      pouches with appropriate labelling. Twenty five
conventional iodometric titration so as to get reliable                      pouches of each type of salt were further packed in a
values of the iodine content.                                                double lined high-density polyethylene (HDPE) sac
                                                                             of respective label and 20 such bags each of DFS
                    Material & Methods                                       and IS were transported to NIN and the laboratory
                                                                             of the International Council for Control of Iodine
   In the conventional iodometric titration5 used for                        Deficiency Disorders (ICCIDD) at New Delhi. Thus,
the estimation of iodine in IS, 10 g of iodized salt                         both laboratories received 500 pouches, each
was dissolved in 50 ml of distilled water and 1 ml of                        belonging to different batches of DFS and IS. The
2 N sulphuric acid (H2SO4) was added followed by                             salt samples were tested over a period of six months
the addition of 5 ml of 10 per cent potassium iodide                         in the two laboratories for iodine content. In addition,
(KI). The reaction mixture was kept in the dark for                          the iodine content of IS purchased from the local
ten minutes and the liberated iodine was estimated                           market was tested by the two methods.
by titration with 0.005 M sodium thiosulphate
(Na2S2O3) using starch indicator near the end point                          Quality control: In order to ensure the reliability of
of titration.                                                                the results obtained by the methods used, both
                                                                             internal quality control and external quality control
   Modified method using orthophosphoric acid in                             measures were strictly adhered to in the two
place of sulphuric acid was also used to estimate                            laboratories. For internal quality control, multiple
iodine in DFS and IS during the study.                                       analyses (20 times) for iodine content of KIO 3
                                                                             standard (in 10 g of plain non iodized salt) and a
Source of DFS and IS: DFS and IS (500 kg each) were                          known Reference salt were performed. The 95 per
produced in the salt factory of M/s Prince                                   cent confidence interval (CI) of mean iodine values
International, Bhubaneswar by batch mixing process                           was calculated along with the operating control range
in different batches using dry mixing technique4,7 at                        (mean ± 2 SD) for preparing the quality control
an iodine level of 40 µg/g. Both DFS and IS were                             charts. Reference salt and KIO3 standard were also


                        Table II. Iodine content of DFS and IS, estimated by the conventional iodometric titration
                                                              Iodine content (ppm)*
      Month                     Double fortified salt (DFS)                                        Iodized salt (IS)
                        Mean                 SD               Range                  Mean                SD                Range
          1              17.5                3.9          11.4 - 22.6                46.6                2.8             43.5 - 50.2
          3              17.1                5.8          10.7 – 25.6                48.3                3.6             44.0 – 52.5
          6              15.4                3.5          10.1 - 19.5                47.6                3.2             44.7 - 53.7

*Mean + SD, n=40 samples/salt/each time

              Table III. Iodine content of DFS, when estimated number of times by the conventional iodometric titration
                                                           Iodine content (ppm)*
                                                              No. of times tested
                   1            2      3            4         5         6        7           8            9        10        11        12
   Mean          38.1       49.6      51.0         46.3   53.5        62.0      44.5        57.2        66.6      49.7      57.8       53.3
     SD          15.5       11.4      5.5          12.4    2.2        3.6       2.9         3.0          3.0       2.9       7.9       8.1
                                              Overall: Mean = 52.5; SD = 7.8; Range = 19 - 69
*Mean + SD, n=20 samples/each time
534                                       INDIAN J MED RES, APRIL 2006


analysed, whenever the iodine content of DFS and           the loss of iodine by volatilization. This is
IS were estimated in the two laboratories. For the         accomplished by adding iodide before the addition
external quality control, 10 samples each of DFS and       of acid. Therefore, we changed the sequence of
IS at NIN were drawn randomly and were sent to the         addition of reagents by adding 5 ml of 10 per cent
ICCIDD laboratory. There the samples were analyzed         KI to DFS followed by distilled water (50 ml), 1 ml
in duplicate simultaneously by the investigators from      of 2 N H 2 SO 4 and completed the titration steps
both the centers using the same reagents.                  (Method 2).

pH of DFS and IS: As 10 g salt dissolved in 50 ml              Kolthoff & Belcher9 also recommended the use of
distilled water (20% solution) is used for the             orthophosphoric acid (H3PO4) in place of H2SO4 for
estimation of iodine, the pH of 20 per cent aqueous        iodine estimation in the presence of iron. We
solutions of DFS as well as IS were determined using       therefore, used H3PO4 in the procedure and modified
a sensitive microprocessor-controlled digital pH           the method by adding 5 ml of 10 per cent KI first to
meter (Model 420Aplus, Thermo Orion, 500                   10g DFS followed by 50 ml distilled water, 5 ml of
Cummings Center, Beverly, MA 01915-6199 USA)               4N H3PO4 and completed the titration (Method 3). We
with pH auto calibration.                                  estimated the iodine content of the same samples of
                                                           freshly prepared DFS from the same batch by the
Iodine estimation: All reagents used were of               above three methods simultaneously. We also
analytical grade and distilled water (conductivity: 39-    estimated the iodine content of several samples of DFS
40 mho) was used in the preparation of reagents as         from different batches by using H2SO4 and H3PO4.
well as for iodine estimation. Iodine content of
DFS/IS was estimated by testing two aliquots of the        Sensitivity of the modified method: The iodine content
same sample simultaneously. Also, DFS and IS               of KIO 3 standard (1mg of iodine/ml) at different
samples from the same batch were tested for their          iodine concentrations (0, 10, 20, 30, 40, 50, 60, 70,
iodine content over a period of six months. Further,       80, 90, 100 ppm) was determined by both the
KI was added at different time intervals after             modified method using H3PO4 and the conventional
dissolving DFS in distilled water so as to find out        method using H 2 SO 4 in order to compare the
iodine loss, if any with time.                             sensitivity of the modified method with the
                                                           conventional method.
Interference of persulphate: Ferrous sulphate
(FeSO 4.7H 2O) in solution ionizes to give ferrous ion     Iodine estimation of IS by the modified method:
(Fe ++) and sulphate ion (SO 4- -). Similarly, dilute      Finally, we estimated the iodine content of refined
H2SO 4 in water gives hydrogen ion (H+) and sulphate       and ordinary IS, purchased from the local market,
ion (SO 4- -). These free sulphate ions combine to         by the modified procedure (Method 3) using H3PO4
form persulphate (S 2O8- -) ion. The persulphate ion       reagent to study the feasibility of this method for
is a strong oxidizing agent, which can liberate iodine     commercial IS also.
from KI that is normally added to solubilise the
liberated iodine. In order to test this hypothesis, we     Statistical analysis: Mean, standard deviation (SD)
used 7 per cent potassium persulphate in the               and coefficient of variation (CV) were calculated
conventional iodometric titration 5 without adding         wherever necessary and correlation coefficient was
any salt (DFS or IS) and studied the effect of             calculated for the comparison of methods.
persulphate.
                                                                                 Results
Comparison of methods: The iodine content of DFS
was estimated by the conventional iodometric               Quality control: The results of the internal quality
titration 5 (Method 1). According to Kolthoff &            control carried out at the two laboratories are shown
Belcher 8 , iodine should be liberated only after          in Figs 1 & 2. The operating range of iodine content
sufficient iodide is present in the solution to minimize   (mean ± 2SD) for KIO3 standard was 49.9 to 50.3
              RANGANATHAN & KARMARKAR: IODINE ESTIMATION IN DOUBLE FORTIFIED SALT                                     535




                First            Second               Third               Fourth             Fifth         Sixth
                                                                (Month)
                                     Fig. 1. Internal quality control chart of KIO3 standard.




                   First              Second              Third               Fourth              Fifth       Sixth
                                                                   (Month)
                                     Fig. 2. Internal quality control chart of Reference salt.




                  CV (%)   Month 1       Month 2      Month 3       Month 4        Month 5       Month 6
                   DFS       26            38           21            23             40            23
                    IS      5.6           11.1         7.7           5.8            8.2           6.0
                                                   Mean ± SD, n = 40/month
Fig. 3. Iodine content of double fortified salt (DFS) and iodized salt (IS) with time, estimated by the conventional
iodometric titration.
536                                             INDIAN J MED RES, APRIL 2006


Table IV. Iodine loss due to time interval between distilled water and KI additions in the estimation of iodine in DFS by the
conventional iodometric titration
Addition of KI                                     Iodine (ppm)                        CV (%)               Iodine loss (%)
                                         Mean                      SD
Immediately                              46.6                      3.0
                                         41.3                      7.5
                                         47.6                      3.0
                                         44.4                      6.0
                                         42.3                      5.9
                                         48.7                      4.5
                         Pooled value    45.2                      3.0                    11                       0
After one hour                           39.1                      3.0
                                         30.7                      5.9
                                         37.0                      7.5
                                         34.9                      4.5
                                         38.1                      7.5
                                         32.8                      5.9
                         Pooled value    35.4                      3.2                    16                      22
After 2 h                                34.3                      3.7
                                         24.3                      3.0
                                         23.8                      2.3
                                         40.2                      5.9
                                         38.1                      4.5
                                         39.2                      4.4
                         Pooled value    33.3                      7.5                    12                      26
After 5 h                                19.6                      9.7
                                         20.1                      5.9
                                         18.5                      9.7
                                         17.5                      5.2
                                         21.7                      2.3
                                         15.9                      6.0
                         Pooled value    18.9                      2.0                    34                      52
After overnight                          11.8                      4.2
                                         12.7                      4.5
                                         18.0                      2.9
                                         14.8                      4.5
                                         15.9                      4.4
                                         10.6                      4.5
                         Pooled value    14.0                      2.8                    31                      69
Average value of duplicate done twice.
n = 6/samples/each time


ppm and 45.2 to 45.6 ppm for Reference salt. The                  ± 2.84 ppm for ICCIDD. The intra-class correlation
day-to-day results were well within the acceptable                was very close to the unity (0.97).
operating range throughout the study period and the
coefficient of variation was low (0.18 to 0.26%).                 The pH of fortified salts: The pH of 10 g salt in 50 ml
Thus, effective internal quality control was ensured              of distilled water was 2.0 for DFS, 8.0 for refined IS
in the two laboratories. The external quality control             and 6.8 for ordinary IS. Thus, the pH of DFS was acidic
revealed good agreement between the duplicate                     and that of IS was alkaline. However, the pH at the
values within the laboratories and between the                    final stage of the reaction mixture after the addition
laboratories irrespective of DFS or IS. The iodine                of H2SO4 or H3PO4 was 0.9 regardless of whether DFS
content (mean ± SD) of DFS was 42.0 ± 2.94 ppm                    or IS or iodized salt from market (refined or ordinary)
for NIN, 42.1 ± 2.95 ppm for ICCIDD and in the                    was used. Also, the colour of the starch-iodine
case of IS, it was 46.1 ± 2.81 ppm for NIN and 46.0               complex was blue both with H2SO4 and H3PO4.
                 RANGANATHAN & KARMARKAR: IODINE ESTIMATION IN DOUBLE FORTIFIED SALT                                            537


  Table V. Interference of persulphate in the conventional iodometric titration with potassium iodate (KIO 3) as internal standard
Serial            Persulphate(ml)                             Iodine content (ppm)                            Recovery (%)
no.                                         Total*(T)       From persulphate**       From KIO 3Standard + R = (K ÷ 49.7) x 100
                                                                   (P)                   K = (T-P)
   1                       0                   49.7                      0                     49.7                  100
   2                     0.5                   76.2                   26.5                     49.7                   100
   3                     1.0                  102.0                   52.9                     49.1                  98.8
   4                     1.5                  127.8                   78.3                     49.5                  99.6
   5                     2.0                  149.7                  101.0                     48.7                  99.0
   6                     3.0                  204.6                  153.4                     51.2                   103
50 ml distilled water + 0.5 ml of KIO 3 standard + persulphate +1 ml 2N H 2SO 4 + 5 ml 10% KI.             Mean = 100.1
Kept in the dark for 10 min. Then titrated with 0.005M thiosulphate.
*Actually determined; **As observed earlier (Fig. 4)
Actually recovered from KIO3; Actual iodine content in the KIO 3 used


Iodine estimation by conventional iodometric titration:              persulphate liberated iodine only from KI by
When the iodine content of DFS was estimated by the                  oxidation as no IS or DFS was used. Also, the release
conventional iodometric titration, we observed a wide                of iodine from KI due to persulphate increased
variation between the duplicates (Fig. 3). There was                 proportionately with the concentration of persulphate
no consistency in the iodine content when estimated                  (Fig. 4). It should be noted that conventionally KI is
over a period of time and the coefficient of variation               added to help solubilise the iodine liberated from
of the determination was higher than the permitted                   KIO3 and does not by itself contribute to the estimated
level of 15 per cent for DFS while it was well below                 iodine content of the salt sample. Indeed, the
the permitted level for IS. Indeed the iodine content                interference of the persulphate was confirmed from
of IS, estimated by the conventional iodometric                      the recovery study when KIO3 standard was added
titration, showed consistency, reproducibility and also              as internal standard (Table V).
good agreement between the duplicate samples
(Fig. 3). These results suggested that the conventional              Iodine content of DFS by Methods 1, 2, and 3: The
iodometric titration was suitable only for IS and not                results of duplicate analysis of freshly prepared DFS
for DFS. However, this has not ruled out the                         when estimated simultaneously by the three methods
possibility that the observed discrepancy in the iodine              (n = 20 per method) showed that the iodine content
content of DFS could be due to the disturbed stability               (mean ± SD) was 80.8 ± 15.0 ppm for Method 1,
of iodine in DFS. To ascertain the facts, we followed                65.6 ± 7.6 ppm for Method 2 and 40.1 ± 3.9 ppm for
the modified method using H3PO4 for DFS.                             Method 3. The Methods 1 and 2, in which H2SO4 was
                                                                     used, gave higher levels of iodine than the level of
Iodine loss with time: It was found that the time of                 fortification (40 ppm). Method 2 showed slight
addition of KI, after dissolving DFS in distilled water,             advantage over Method 1 with respect to the
played a crucial role in determining the iodine levels               coefficient of variation, which was within the
of DFS (Table IV). The extent of iodine loss (20-                    permitted level of 15 per cent, but the estimated
70%) depended upon the time of addition of KI.                       iodine values were significantly higher than the
Further, the coefficient of variation was not                        expected range, perhaps due to the interference of
consistent with time, indicating that with an increase               persulphate. However, Method 3 (Modified method)
in the time gap the differences between the duplicate                showed that the iodine content was well within the
samples increased further (Table IV).                                expected range, indicating the non interference of
                                                                     iron or persulplate in the estimation of iodine when
Interference of persulphate: The reaction mixture                    H3PO 4 was used. That Method 3 is superior to the
turned yellow immediately after adding persulphate                   other two methods was confirmed when we estimated
indicating the liberation of iodine and confirmed that               the iodine content of more than 100 samples of DFS
538                                              INDIAN J MED RES, APRIL 2006




                             Fig. 4. Interference of persulphate in the conventional iodometric titration.




                              Fig. 5. Precision of the modified method (H3PO4) in iodometric titration.




Table VI. Iodine content of DFS and IS with time, estimated           using both H2SO4 and H3PO4 reagents, in that H2SO4
by the modified method                                                method overestimated the iodine content (68.1 ± 8.1
Month                   Iodine content (ppm)*
                                                                      ppm) but not H3PO4 method (40.5 ± 3.8 ppm).
        Double fortified salt (DFS) Iodized salt (IS)
                                                                      Precision of the modified method: When the iodine
         Mean      SD     CV (%) Mean      SD      CV (%)
                                                                      content of KIO3 standard was estimated at different
1        40.1     3.9        9.7      41.2      2.3      5.6          concentrations of iodine by the conventional
2        42.1     4.3       10.2      43.8      4.9      11.1         iodometric titration using H2SO 4 and the modified
3        42.3     4.2        9.9      43.1      3.3      7.7          method using H3PO4 reagents, very good agreement
4        42.4     3.6        8.5      42.9      2.5      5.8          was observed between the two methods at all
5        41.4     3.0        7.2      41.3      3.4      8.2          concentrations of KIO3 (Fig. 5). Also, the correlation
6        40.4     2.0        4.9      41.6      2.54     6.0          coefficient between the two methods was nearly unity
                                                                      (r = 0.9999). Therefore, the precision of the modified
*Mean + SD, n = 40 samples/salt/each time
                                                                      method using H3PO4 was as good as the conventional
              RANGANATHAN & KARMARKAR: IODINE ESTIMATION IN DOUBLE FORTIFIED SALT                                    539


                                                    H2 SO 4                 H3PO 4




                                   Mean + SD value of replicate analysis (n = 6 for each salt)

                Fig. 6. Iodine content of iodized salt purchased from local market: Comparison of methods.


method using H2SO4. It was further confirmed by the                added in the conventional iodometric titration5 for
iodine content of IS from factory or market when                   the estimation of iodine in IS or DFS is very high
tested by the two methods.                                         (500 mg of KI), to the tune of nearly 100 times
                                                                   more than the quantity that is actually required
Iodine content of DFS/IS with time (Modified                       (about 5 mg of KI), which is provided by 0.50 ml
method): The results of the stability of iodine in DFS             of 1 per cent KI. Therefore, the modified procedure
and IS using the modified method showed very good                  for the estimation of iodine was to add 0.50 ml of
consistency over a period of six months (Table VI).                1 per cent KI to 10g IS or DFS followed by 50 ml
The coefficient of variation for DFS as well IS was                of distilled water, 5 ml of 4N H3PO 4 and titration
well below the permitted level at every month,                     with 0.005M Na 2S 2O 3 after keeping in dark for
indicating good agreement between duplicate sample                 10 min.
analyses.
                                                                                                 Discussion
Iodine content of IS from local market: We estimated
the iodine content of different IS purchased from the                  Potassium iodate is used to produce IS in the
local market (ordinary: 10 and refined: 10) by both                country. The pH of 10 g IS in 50 ml of distilled
conventional iodometric titration using H 2SO 4 and                water is alkaline and therefore, iodine is stable in
the modified method using H 3PO 4. The results of                  IS. The pH of 10 g DFS in 50 ml of distilled water
replicate analysis (n = 6 for each salt) showed that               is acidic and hence iodine is unstable at this acidic
there was no difference between the two methods for                condition. Therefore, as soon as distilled water is
the iodine content obtained for the same sample                    added to DFS, iodine is slowly released and partly
(Fig. 6). The iodine content of refined IS ranged from             lost before the addition of KI in the conventional
41 to 50 ppm and that of ordinary IS ranged from 24                iodometric titration. Only when 5 ml of 10 per cent
to 33 ppm. The coefficient of variation was low.                   KI is added, whatever iodine is remaining is
These results indicated that the modified method                   solubilised. Further, considerable time is taken
using H 3 PO 4 was as sensitive and reliable as the                usually to dissolve the DFS in distilled water. When
conventional method using H2SO4 for the estimation                 the time gap increased between the additions of
of iodine in market IS whether it is iodized refined               distilled water and KI, DFS is kept in distilled water
salt or iodized ordinary salt.                                     without KI for a long time, which leads to more
                                                                   iodine loss. This might have contributed to the
Adequate amount of KI for iodine estimation:                       discrepancies observed with regard to iodine
Further studies revealed that the amount of KI                     stability of DFS in the multicentric study6.
540                                             INDIAN J MED RES, APRIL 2006


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handling one acid for DFS and another for IS. The                     Micronutrient Initiative (MI), The International Council for
precision of the modified method is as good as the                    Control of Iodine Deficiency Disorders (ICCIDD), The
conventional method, which was revealed by the                        World Health Organization (WHO). Sullivan KM, Houston
iodine content of KIO3 standard, Reference salt and                   R, Gorstein J, Cervinskas J, editors. Titration methods for
                                                                      salt iodine analysis. Chapter 11. PAMM/MI/ICCIDD,
IS from factory or market.
                                                                      Atlanta, USA; 1995 p. 86-9.

   Thus, the hurdles faced in the estimation of iodine             6. Operational evaluation of the stability of iodine in double
in DFS were resolved by the modified method using                     fortified salt: A multicentric study. Interim Report. National
H3PO4 in place of H2SO4, reducing the quantity of                     Institute of Nutrition, ICMR, Hyderabad, India, January
                                                                      2003.
KI and changing the order of addition of reagents.
From the results obtained by these modifications, it               7. Ranganathan S, Sundaresan S, Raghavendra I, Kalyani S.
is clear that the inconsistent stability of iodine                    Dry mixing technique for the large-scale production of
observed earlier in the DFS multicentric study6 was                   iodine fortified salt. Asia Pacific J Clin Nutr 1997; 6 : 92-4.
due to methodological problem and not an inherent
problem of DFS.                                                    8. Kolthoff IM, Belcher R. Volumetric analysis, Vol. III,
                                                                      Titration Methods: Oxidation-Reduction Reactions.
                                                                      INTERSCIENCE Publishers, Inc. New York; 1957 p. 235.
                    Acknowledgment
                                                                   9. Kolthoff IM, Belcher R. Volumetric Analysis, Vol. III,
   Authors acknowledge Prof. N. K. Ganguly, Director-                 Titration Methods: Oxidation-Reduction Reactions.
General, Indian Council of Medical Research, New Delhi, India,        INTERSCIENCE Publishers, Inc. New York; 1957 p. 247.
Dr B. Sivakumar, Director, National Institute of Nutrition
(ICMR), Hyderabad, India and Dr K. Vijayaraghavan, ICMR            10. The properties of persulphates. In: Parkes GD, editor.
Emeritus Medical Scientist for their keen interest in this study       Mellor’s modern inorganic chemistry, Longmans, London:
and thank Shri M. Krupadanam for technical assistance.                 New Impression; 1959 p. 477.


Reprint requests: Dr S. Ranganathan, Head, Isotope Unit, National Institute of Nutrition (ICMR)
                  Jamai Osmania, Hyderabad 500007, India
                  e-mail: drrangan@rediffmail.com

								
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