The Nigerian Research Reactor-1 was employed in the analysis of iodine in local food samples at an operating flux of
Iodine is an essential component of the thyroid hormones: thyroxine (T4) and triiodothyronine (T3), comprising 65 and 59 percent of their respective weights [
Without sufficient iodine, the body is unable to synthesize the thyroid hormones, and because they regulate metabolism in every cell of the body and play a role in virtually all physiological functions, iodine deficiency can have a devastating impact on health and well-being summarily termed iodine deficiency disorders (IDD). IDD is a major cause of retardation in children and was one of the contributing factors to high infant mortality [
The Nigerian Research Reactor-1 (NIRR-1) is the first in the country and its primary objective is to uplift the socioeconomic life of Nigerian citizen through effective utilization and research activities. It is meant to serve all categories in need of nuclear analytical and other related services. Irradiation and counting regimes for over 30 elements in both biological and geological matrices, including the essential elements Fe, Cr, Co, Cu, Mn, and Zn have been standardized [
Accurate determination of iodine and in particular in biological matrix has always been difficult due to its low concentration and the inherent volatility of molecular iodine through sublimation at room temperature. However, iodine concentrations in biological matrix have been analyzed using a variety of techniques including spectroscopy [
The NIRR-1 is a low power nuclear reactor and is normally operated at 5.0 × 1011 ncm−2 s−1. Detailed descriptions of the reactor operation parameters are earlier reported [
About 0.5 g of dried and homogenized food sample was accurately weighted, and then the samples were digested with 7 mL ultrapure nitric acid in a closed system microwave oven at 1000 W for two minutes. After digestion, the system was cooled to room temperature and further cooled in ice-bath for one hour. The clear solution of digested sample was transferred into a beaker containing 1 g of hydrazine sulphate; the sample cup and its lid were washed with 3 portions of 5 mL aliquots of 5% hydrazine sulphate solution and deionized water. The digested sample and the washings are combined and diluted to 100 mL. The pH of the solution was adjusted between 2 and 3 with 10% ammonia solution. Iodine was coprecipitated with 1 mL each, of freshly prepared 0.05 M bismuth sulphate and 0.25 M thioacetamide. The precipitate was filtered by suction with 0.45
The digest was diluted to 25 cm3 and then analyzed for iodine with a UV/visible GBT Cintra 6 spectrophotometer at 420 nm.
A standard curve using potassium iodate solution containing 0.5 to 10 ppm iodine was prepared. The intensity of the developed color was measured at 420 nm. The iodine concentration in the samples was calculated from the standard curve.
Quality control for iodine was maintained by including five reagent blanks to monitor contamination and estimate detection limits. Validation of the analytical techniques with each batch of samples analyzed was tested with the help of certified reference materials.
Significant challenge arises from the utilization of NIRR-1 in analysis of iodine in biological matrix, primary due to the low flux and external position of the cadmium lined irradiation channel. As such, the EINAA yield no result for iodine. Iodine 128 peaks at 442.9 keV and 526 keV were absent from the EINAA spectra of NIST 1548a and NIST 1515. However, both peaks were observed from the same NIST SRM spectra by employing PCNAA. The presence of, in most biological materials, large concentrations of elements such as sodium, chorine, manganese, and in some cases aluminum inhibits the determination of iodine by NAA which is often of microconcentration. The EINAA annihilates the thermal neutrons that largely excite the interfering nuclides. However, due to the low concentration of iodine in the SRMs (and biological samples especially food) coupled with the fact that NIRR-1 is a low flux reactor with
It is observed from Table
Comparison of SRM certified values and this work.
SRMs | PCNAA (mg/Kg) | % SD |
|
S-K spectroscopy (mg/Kg) | % SD |
|
SRM certified value (mg/Kg) |
---|---|---|---|---|---|---|---|
NIST 1548a | 0.759 ± 0.06 | 0 | 1 | 0.751 ± 0.05 | 1.12 | 0.95 | 0.759 ± 0.103 |
NIST 1515 | 0.30 ± 0.07 | 0 | 0.286 ± 0.01 | 6.99 | 0.3 |
Based on the local economy, the food samples were grouped into low (L), medium (M), and high (H) priced. L: food cost is less than US $1.5, M: food cost is between US $1.5 and US $3.5, and H: food cost is more than US $3.5; the first numeral gives the identity of the sampling point, while the last numeral is 1 = breakfast, 2 = lunch, and 3 = dinner.
The food samples are whole meals served in restaurants and local eateries across Zaria, Nigeria. Tuwo is a typical Northern Nigerian food; it is a stiff paste made from numerous cereals: Shinkafa, rice, Masara, and corn, while Waina is a pan fry corn paste.
The foods analysed have sufficient iodine to furnish the recommended daily intake (Figure
Iodine content of some commonly consumed local foods.
S/N | SAMPLE | PCNAA | Percentage deviation | S-K method | |||
---|---|---|---|---|---|---|---|
Code | Food items | Iodine (mg/Kg) | Iodine in food ( |
Iodine (mg/Kg) | Iodine in food ( | ||
1 | L 1-1 | Fried beans cake and pap | 0.30 ± 0.05 | 62.06 | 10.51 | 0.26 ± 0.02 | 55.54 |
2 | L 1-2 | Rice and beans meat, stew | 1.89 ± 0.08 | 118.41 | 36.83 | 1.19 ± 0.03 | 74.80 |
3 | L 1-3 | Tuwo Masara, dry okra sauce | 9.60 ± 0.16 | 2056.23 | 18.01 | 7.94 ± 0.29 | 1685.98 |
4 | L 2-1 | Fried sweet potato and gruel | 0.75 ± 0.06 | 157.07 | 15.01 | 0.63 ± 0.11 | 133.49 |
5 | L 2-2 | Rice, spaghetti, and vegetables | 1.34 ± 0.08 | 307.64 | 6.35 | 1.25 ± 0.06 | 288.11 |
6 | L 2-3 | Tuwo Masara, vegetable soup | BDL | 0.00 | BDL | BDL | |
7 | L 3-1 | Moi-Moi | 0.81 ± 0.10 | 125.75 | 3.85 | 0.78 ± 0.02 | 120.92 |
8 | L 3-2 | Jellop rice and beans | 1.16 ± 0.08 | 261.82 | 3.78 | 1.12 ± 0.02 | 251.92 |
9 | L 3-3 | Tuwo Masara, dry okra sauce | 0.78 ± 0.06 | 171.40 | 36.16 | 1.09 ± 0.02 | 233.38 |
10 | M 1-1 | Potato chips, eggs, liver sauce | 1.36 ± 0.07 | 341.66 | 15.11 | 1.16 ± 0.03 | 290.03 |
11 | M 1-2 | Fried rice, pea, carrot, cabbage | 1.61 ± 0.08 | 270.26 | 3.78 | 1.55 ± 0.02 | 260.04 |
12 | M 1-3 | Pounded yam, vegetables soup | 1.40 ± 0.07 | 463.20 | 11.76 | 1.22 ± 0.02 | 408.73 |
13 | M 2-1 | Waina da Taushe | 1.29 ± 0.07 | 332.48 | 4.41 | 1.24 ± 0.02 | 317.83 |
14 | M 2-2 | White rice,vegetables salad | 0.89 ± 0.09 | 168.39 | 5.38 | 0.94 ± 0.03 | 177.44 |
15 | M 2-3 | Tuwo Shinkafa, Egusi soup | 1.13 ± 0.22 | 155.57 | 2.58 | 1.16 ± 0.02 | 159.57 |
16 | M 3-1 | Potato chips, eggs, beef sauce | 0.55 ± 0.07 | 141.17 | 18.84 | 0.45 ± 0.03 | 114.58 |
17 | M 3-2 | Fried rice, pea, onion, beef | 1.31 ± 0.06 | 167.12 | 2.44 | 1.28 ± 0.01 | 163.05 |
18 | M 3-3 | Tuwo Shinkafa, Egusi soup | 2.96 ± 0.09 | 425.26 | 7.94 | 2.73 ± 0.15 | 391.50 |
19 | H 1-1 | French fries, eggs, liver sauce | 1.18 ± 0.07 | 191.96 | 2.89 | 1.14 ± 0.09 | 186.41 |
20 | H 1-2 | Savory rice, vegetables, chicken | 0.42 ± 0.04 | 110.63 | 34.53 | 0.27 ± 0.02 | 72.42 |
21 | H 1-3 | Semovita, vegetables soup | 2.09 ± 0.08 | 561.88 | 7.89 | 1.93 ± 0.04 | 517.52 |
22 | H 2-2 | Fried rice and salad, chicken | 2.44 ± 0.08 | 453.13 | 0.04 | 2.44 ± 0.03 | 452.95 |
23 | H 2-3 | Pounded yam, vegetables soup | 1.27 ± 0.04 | 372.79 | 1.41 | 1.26 ± 0.02 | 367.52 |
Iodine daily intake.
Iodine analysis reported considerable deviation between the two methods in some sample (Table
Comparison between PCNAA and spectroscopy.
The PCNAA result ranges from 0.295 to 2.960 mg/Kg, while that of spectroscopy is from 0.264 to 2.725 mg/Kg. However, sample L 1-3 at Table
In most cases, the PCNAA concentrations from Table
Samples L 1-3 and L 3-3 (Table
The determination of iodine content of commonly consumed foods in Zaria metropolis by preconcentration neutron activation analysis and Sandell-Kolthoff spectroscopy report results ranging from 0.295 to 2.960 mg/Kg and 0.264 to 2.725 mg/Kg, respectively.
While the spectroscopy is cheap with little labour, the accuracy of its result is not as excellent as that of the neutron activation analysis.
The foods analyzed supplied the recommended daily allowance for iodine and in some cases approaching the upper tolerable limit.
Iodine consumption by different income group is not significantly different since the major avenue for iodination for foods is iodized salt and is accessible to all at low cost.
The authors declare that there is no conflict of interests regarding the publication of this paper.
The authors appreciate and commend the effort of the management and staff of the Center for Energy Research and Training, Ahamdu Bello University, Zaria, especially those of Nuclear Science and Technology Section, for their assistance in various capacities in making this work possible.