| |
|
National Iodine Deficiency
Disorders Control Program (NIDDCP)
|
| |
|
Estimation of
Iodine Content in Iodised Salt by Iodometric Titration |
|
Principle |
|
The principle is that iodine is
liberated by adding sulphuric acid to a solution of iodised salt.
Potassium iodide solution is added to keep the iodine in the dissolved
state. Iodine liberated is titrated with sodium thiosulphate solution
to form sodium iodide and sodium tetrathionate. Starch is used as an
external indicator.
KIO3 + 5KI + 3H2SO4
-----> 3K2So4 + 3I2 +
3H2O
KI + I2 ------> KI3
2Na2S2O3 + I2
-------> 2NaI + Na2S4O6
|
|
Equipment and Chemicals
|
|
Equipment |
 |
Chemical
balance/Electronic balance/Electrical balance
|
|
|
Gas burner
|
|
|
Reagent bottles
with stoppers à
250 ml, 500 ml & 1000 ml
|
|
|
Measuring cylinder
with stopper, 50 ml
|
|
|
Wash bottle, 500
ml
|
|
|
Glass stirring rod
|
|
|
Conical flask with
stopper, 100 ml
|
|
|
Glass or plastic
funnel
|
|
|
Burette, 50 ml
|
|
|
Burette, stand
|
|
|
Pipette – 25 ml
|
|
|
A closed box,
cupboard or drawer to keep the conical flask
|
|
|
Physical balance
(capacity 50 – 100 gms)
|
|
|
Chemicals |
|
|
Sodium
thiosulphate, (2Na2 S2 03 5H2O)
|
|
|
Concentrated
sulfuric acid, (H2SO4)
|
|
|
Potassium iodide (KI)
|
|
|
Soluble chemical starch
|
|
|
Potassium Iodate
|
|
|
All the chemicals
should be analytical grade and double distilled water to be used which
should be free of iodine and other contaminants. |
|
Preparation of
Standard solutions and reagents |
|
Sodium
thiosulphate (0.005 M) |
|
Dissolve 1.24 g
sodium thiosulphate in 1 litre hot double distilled water. This volume
will be sufficient for testing 200 salt samples. The solution should be
stored in a cool, dark place. |
|
Sulfuric acid (2N
H2SO4) |
|
Add 5.56 ml
concentrated sulfuric acid drop wise into a 90 ml of chilled double
distilled water and make the final volume upto 100 ml with double
distilled water. This volume will be sufficient for testing 50 salt
samples. CAUTION: To avoid violent and dangerous reaction,
always add acid to water, never water to acid. |
|
Potassium iodide
(KI) |
|
Dissolve 100 g
potassium iodide in 1000 ml double distilled water. This volume will be
sufficient for testing 200 salt samples. This should be stored in a
refrigerator. |
|
Saturated Salt
Solution |
Take 100 ml double
distilled water in a conical flask and add sodium chloride until the
salt is insoluble. Heat the solution till the NaCI crystals are formed
on the sides of the vessels.
After cooling down the saturated salt solution at room temperature
transfer the supernatant to a clean bottle. |
|
Starch(1%) |
|
Take 1 g of starch
and prepare a slurry in 50 ml water. Add this slurry slowly to 50ml of
boiling water. |
|
Standardistaion
of Sodium Thiosulphate solution |
The sodium
Thiosulphate solution is to be standardized with Standard Potassium
iodate solution to determine its exact normality. Take 0.005 N
thiosulphate solution in a burette. Pipette out 25 ml of 0.005 N
standard potassium iodate solution in a conical flask. Add 2 ml of 2N H2
So4 and 5 ml of 10% KI solution. Titrate the solution against
sodium thiosulphate till the solution becomes pale yellow in colour.
To this, add 1 ml starch. The solution turns deep purple. Add
thiosulphate sulphate solution drop by drop from the burette till the
purple colour completely disappears.
Normality of Thiosulphate is calculated as follows :
Volume of KIO3
(V1) x Normality of KIO3 (N1)
= Volume of Na2S2O3 (V2)
x Normality of Na2S2O3
(N2)
Normality of Sodium
Thiosulphate = V1 x N1
V2
|
|
Procedure
|
|
Dissolve 10 g of salt in 50 ml double
distilled water. Then add 1 to 2 ml of 2 N sulfuric acid and 5 ml of
10% potassium iodide to it. On shaking, the solution will turn to a
yellow colour. Close the flask with stopper and keep the flask in the
dark for about 10 minutes. Remove the samples from the dark and titrate
against the sodium thiosulphate solution until it turns into a very
light yellow colour (pale yellow). Subsequently, add a few drops (1-5
ml) of 1 % starch solution. The solution will turn into a deep purple colour. Add thiosulphate drop by drop from the burette until the
solution becomes colourless and note the final reading.
.jpg)
The iodine content of the sample in parts per million is calculated by
the formula:-
Iodine Content (ppm) = R x 100 x 103 x 0.127 x N
6
where R - The Volume of Thiosulphate used (burette
reading)
100 - For converting burette
reading for 1000gm of salt
103 - For converting
gms of iodine to milligrams
0.127 - The weight of Iodine
equivalent to 1ml of normal sodium thiosulphate solution
N - Normality of
sodium thiosulphate solution
6 - To arrive at the
value of 1 atom of iodine liberated
|
|
|
|
Precautions |
|
|
The reaction mixture should be kept in
the dark for 10 minutes before titration because light accelerates a
side reaction in which iodide ionsare oxidized to iodine by atmospheric
oxygen.
|
|
|
USE OF SPOT
TESTING KIT
|
|
A simple kit has been
developed for on the spot estimation of iodine content. In the spot
testing method, estimation of iodine content in salt is done with the
help of a standard starch solution provided in the Spot Testing Kit (STK).
The STK has been advocated as a method for semi-quantitative estimation
of iodine in salt. The STK consists of a test solution (A), and a
recheck solution (B). One drop of test solution (A) will be added to a
pinch of salt sample. The change in colour of salt sample will range
from white to dark violet depending on the iodine content of salt, i.e. Nil, less than 15ppm, and 15 ppm and above, which will be
compared to the standard colour chart provided with the kit. If on
addition of test solution (A), no change in colour of salt is observed,
the recheck solution (B) will be added. This will be done to make the
salt medium acidic, in case the salt has alkaline constituents, then the
test solution (A) will be added again. The intensity of the blue colour
will be directly proportionate to the iodine content of salt
|
|
Procedure for
use of Spot Testing Kit |
|
|
Take a spoonful of iodated salt to be checked and
spread it flat.
|
|
|
Open the seal of the ampule (white cap) by making a
pin hole.
|
|
|
Discharge a drop
of the test solution on the surface of the salt by gently pressing
the ampule.
|
|
|
The salt will turn
light blue to dark violet depending on the iodine content of the
salt.
|
|
|
Use the colour
chart given on plastic box to compare and determine the iodine range
in the iodated salt.
|
|
|
IF THE SALT IS
ALKALINE OR MIXED WITH ALKALINE FREE FLOW AGENTS, A DROP OF TEST
SOLUTION WILL NOT DEVELOP ANY COLOUR EVEN IF IODINE IS PRESENT, WHENEVER
ONE GETS NO COLOUR INDICATION PLEASE ADOPT PROCEDURE GIVEN BELOW:
|
|
|
Take a spoon of
salt on plate and level it
|
|
|
Add one drop of
Recheck solution (Red cap)
|
|
|
Over the same
spot, put one drop of test solution (white cap)
|
|
|
If iodine is present colour will
develop. If Iodine is not present no colour indication will be there.
|
Note: Shelf
life of spot testing kit is 18 months.
|
|
EXTERNAL EVALUATION OF NIDDCP:
|
|
An Evaluation of
the status of NIDDCP in India was carried out during 1996 by the
Canadian International Development Agency (CIDA) which felt that the
story of USI in India was one of the remarkable achievements as it has
made spectacular progress towards the goal of USI. The study revealed
that the Salt Department has been successful in ensuring the supply of
good quality iodised salt for human consumption and cited that the Role
of the Salt Department is one of the seven issues that has an important
bearing on the future sustainability of Universal Salt Iodisation. The
study also commended India for offering two technologies : iodizing
machinery and the spot testing kit which are important tools for
producing good quality iodised salt. |
|
INTERNAL EVALUATION OF NIDDCP:
|
|
The Government of
India, Ministry of Industry with support of UNICEF carried out an
Internal evaluation of the USI component of the programme during
1997-98. The study carried out by the Indian Institute of Health
Management & Research, Jaipur, concluded that not only has the capacity
and production of iodised salt in the country increased considerably,
but the movement and distribution also have been streamlined. Further,
the consumption of iodised salt at the household levels in urban and
rural areas has also showed Improvement. Nevertheless, to maintain the
significant achievements in universal accessibility and availability of
iodised salt, the study concluded that efforts are needed to consolidate
the gains, bridge the existing gaps and deficiencies, and strengthen the
programme efforts to sustain the production and consumption of iodised
salt. It also commended that the Salt Department has made a significant
contribution towards the universal iodisation of salt and has played a
crucial role in increasing the production of iodised salt and its
distribution throughout the country. |
|
NATIONAL BAN ON SALE OF NON-IODISED
SALT FOR EDIBLE USE:
|
Ban Notifications
on sale of non-iodised salt for edible use were issued by various State
Governments/Union Territories under provisions of PFA Act, 1954 in the
interest of public health so that iodised salt is only made available
for consumption by masses to eliminate Iodine Deficiency Disorders. All
the State Governments/Union Territories except Gujarat, Kerala,
Arunachal Pradesh and Maharashtra had issued such ban notifications. In
Maharashtra ban orders were issued covering 19 districts of the State.
The non-existence of ban orders in some States was found as a bottleneck
in implementation of NIDDCP. Arunchal Pradesh withdrew its State Ban
Notification consequent on Supreme Court ruling in Pan Masala Case that
State Governments are not vested with powers under PFA Act, 1954 to
issue such ban notification. In view of the above, Government of India,
Ministry of Health & Family Welfare, vide its Notification No.GSR 670(E)
dt.17th November, 2005 has banned sale of non-iodised salt
for direct human consumption throughout the country with effect from 17th
May, 2006. This would give the much needed fillip for effective
implementation of National Iodine Deficiency Disroders Control Programme
in the country. |
|
TENTH FIVE YEAR
PLAN GOALS: |
Iodine Deficiency Disorders (IDD)
elimination is included under Tenth Five-Year Plan 2002-2007. The Tenth
Plan goals are to
|
|
Achieve Universal
access to iodised salt |
|
|
Generate district-wise data on
iodised salt consumption |
|
|
Reduction in the
prevalence of Iodine Deficiency Disorders in the country to less than 10
per cent by 201 |
|
|
BRIDGING THE GAP:
|
|
|
It is imperative to not only achieve
the Goal of Universal Salt iodisation but also take concerted steps for
sustaining the progress made on USI. Our strategy for bridging the gap
would be |
|
|
Supply of iodised salt under
PDS to BPL population throughout the country to increase the consumption
of iodised salt |
|
|
Enforcement of National ban
orders on sale of non-iodised salt for edible purpose |
|
|
Support to small scale salt
manufacturers to join the mainstream salt iodisation program and
contribute actively |
|
|
Strengthening Information,
Education & Communication (IEC) Campaigns for creating awareness on IDD
and benefits of consuming Iodised salt |
|
|
Strengthening
Monitoring of quality of iodised salt at production and consuming level
to ensure production and supply of adequately iodised salt to the masses |
|
|
**********
|