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Development of a simple field kit for monitoring iron in fortified salt

S. Ranganathan and B. S. Narasinga Rao



One practical way to control iron-deficiency anaemia is to fortify edible salt with iron. Effective implementation of a programme for producing and distributing iron-fortified salt requires regular monitoring of edible salt for iron, particularly at the retail sales and household levels. A simple, inexpensive (10 rupees) field kit was developed for this purpose. No glassware has to be carried, and reagents are supplied in the form of tablets. It is possible to detect iron fevers as low as 50 parts per million (ppm) and as high as 1,000 ppm. One kit can be used to test 200 salt samples.



Iron deficiency leading to anaemia continues to be widespread, especially in developing countries. The prevalence of iron-deficiency anaemia (IDA) is high at all ages in southern Asia, and it is a major public health problem in India. Severe anaemia during pregnancy is associated with increased risk of maternal mortality, premature delivery, and low birth weight. Iron-deficiency anaemia can impair the intellectual development and immune response in children and limit capacity for physical activity [1-4].

One of the practical ways of controlling IDA is to provide iron through the fortification of widely consumed dietary items such as common salt. The efficacy of such practice has been established by multicentric field studies [5]. Suitable technology to fortify edible salt with iron has been developed in India [6, 7].

We hope to produce and distribute iron-fortified salt (IFS) to control IDA. Effective implementation of this programme requires regular monitoring of IFS in the community, particularly at the retail sales and consumer levels. Anybody, including those without a chemistry background, must be able to use the system. Therefore, a simple field kit was developed to detect the level of iron in salt.


Materials and method


As illustrated in figure 1, the kit consists of two tablets, W and Y, with corresponding plastic dropper bottles, a white plastic plate with depressions, a plastic spoon, a colour gradation card to determine colour intensity, and an instruction card. Its cost is 10 rupees in India.

Tablet W contains an oxidizing agent and an acidifying agent. Tablet Y contains a material that produces colour in the presence of the ferric form of iron. Their chemical compositions are given in table 1. Distilled water is used to dissolve the tablets and make the reagents.

The principle involved in the test is that the ferrous form of iron present in IFS is oxidized to the ferric form in an acidic medium. The ferric form of iron reacts with ferrocyanide to give a blue colour. It is possible to estimate the level of iron in a given sample of IFS since the test produces distinguishable gradations of blue colour, reflecting differences in the amount of iron.


One of the reagent tablets is placed into each of the plastic dropper bottles, distilled water is added up to the mark, and the tablets are dissolved. At this point the reagents are ready for use and will remain stable for several months.

A small quantity of IFS to be tested is placed in the depression of the white plastic plate. One drop of reagent W is added to the salt, followed by a drop of reagent Y. Immediately the IFS turns blue (Prussian blue) and the colour remains for a long time. The intensity of the colour is compared with the colour gradation card, and a rough estimate of the iron content of the sample is made.

TABLE 1. Composition of the tablets used in the field kit for detecting iron-fortified salt.

Tablet Chemicals Quantity (mg)
W oxalic acida 1,000
potassium persulphate 135
Y potassium ferrocyanide 1,000

a. Citric acid or sodium acid sulphate can also be used at the same level.


Results and discussion

Our experience in the laboratory and field has shown that it is possible to detect iron levels as low as 50 parts per million (ppm) and as high as 1,000 ppm in salt containing iron (ferrous as well as ferric). The Prussian blue colour can differentiate iron levels of 50, 100, 500, 800, and 1,000 ppm. Good correlation was observed (p < .001) when iron levels obtained by the kit were compared with values obtained by actual chemical analysis of IFS.

One pair of tablets W and Y can be used to test about 200 salt samples. When the reagents are exhausted, one can reuse the kit by dissolving another pair of tablets.

In the field one may use distilled water available in ampoules from any medical shop. If distilled water is not available, one may use boiled, cooled, and filtered tap or well water.

A successful process has been developed at the National Institute of Nutrition, Hyderabad, for the simultaneous double fortification of edible salt with iron and iodine [8]. The kit can also be used to measure the iron content of the double-fortified salt, and the iodine levels can be assessed by using the iodized salt kit reported earlier [9].



This is an easy method for estimating the iron content of IFS at the community level. Only plastic materials are used, so the difficulty of carrying elaborate glassware is avoided. The expenditure involved is small. This kit may become an integral part of the IFS programme.



The authors thank Dr. Vinodini Reddy, Director of the National Institute of Nutrition, Hyderabad, for her keen interest in the work. The excellent art work done by Mr. Seshagiri Rao in the preparation of the colour gradation card is appreciated.



  1. WHO. Diet. nutrition and the prevention of chronic diseases: iron deficiency. Report of a WHO study group. Technical Report 797. Geneva: World Health Organization. 1990:23-25.
  2. Raman L. Anaemia in pregnancy. In: Menon MKK, Devi PK, Bhaskar Rao K, eds. Postgraduate obstetrics and gynaecology. 4th ed. Madras, India: Orient Longman, 1989:60-68.
  3. Srikantia SG, Siva Prasad J, Bhaskaram C, Krishnamachari KAVR. Anaemia and immune response. Lancet 1976;1:1307-09.
  4. Anderson HT, Barkve H. Iron deficiency and muscular work performance. Scand J Clin Lab Invest 1970; 114(suppl): 1-25.
  5. Working Group on Fortification of Common Salt with Iron. Report. Am J Clin Nutr 1982;35:1442-51.
  6. Narasinga Rao BS, Vijayasarathy C. Fortification of common salt with iron: effect of chemical additives on stability and bioavailability. Am J Clin Nutr 1975; 28:1395-1401.
  7. NIN. Modified formula for iron fortified salt. In: Annual report, 1989-90. Hyderabad: National Institute of Nutrition, 1990:56.
  8. NIN. Fortification of salt with iron and iodine. In: Annual report, 1984-85; Annual report, 1985-86. Hyderabad: National Institute of Nutrition, 1985:22-23; 1986:69-70.
  9. Narasinga Rao BS, Ranganathan S. A simple field kit for testing iodine in salt. Food Nutr Bull 1985;7(4):70-72.

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