Gamma Radiation Effects on UO2 (II), Fe (II) and Fe (III) Complexes with Ferron and Tiron in Solutions
M. F. Barakat(1) and M. El-Banna(2)
(1) Nuclear and Radiological Regulatory Authority,
(2) National Center of Radiation Research and Technology,
Atomic Energy Authority, Nasr City, Post Code 11762, P.O. Box 7551, Cairo, Egypt Fax: 2287603
ABSTRACT
UO2 (II) – ferron complex solution in ethanol and also Fe (II) – ferron or tiron complexes, and Fe (III) – ferron or tiron complexes in aqueous solutions were prepared and their composition was determined by the molar ratio method. The complex solutions formed were found to obey Beer`s law within certain concentration ranges. The color bleaching of these complex solutions upon gamma irradiation was followed spectrophotometrically. The % color bleaching occurring in different complex solutions on using different gamma irradiation doses was calculated and plotted against the applied irradiation doses and the results obtained showed the existence of good linear relationships. The linear sections were used as calibration curves for evaluating unknown gamma irradiation doses. From the obtained results, it was concluded that UO2 (II) – ferron in ethanol, Fe (II) – ferron in water and Fe (III) – tiron in water could be used for dose evaluation within the dose ranges 0-600 kGy for UO2 (II) – ferron complex in ethanol, 0 – 25 kGy for Fe (II) – ferron complex in water and 0 – 10 kGy for Fe (III) – tiron in water.
Key words: Gamma irradiation/ Ferron / Tiron / Complex / spectrophotometry.
INTRODUCTION
The possibility of using non-aqueous and aqueous organic dyes solutions in dose evaluation, have been reported (1-3). Recently, the radiation induced color bleaching of Titan yellow dye (TY) in different solvents has been studied. It was found that the dye in pure ethanol or ethanol-water mixtures could be reliably used for gamma irradiation dose evaluation, which is not the case on using that dye in pure DMF, methanol or water (4).
On the other hand, many studies on the radiolysis of metal ion complexes in aqueous solutions have been reported (5-6). Dawood and Mahmoud studied the radiolysis of solid cobalt (II), nickel (II) and copper (II) complexes in aqueous systems containing mixed ligands (7-9). The results showed that some complexes decomposed by gamma irradiation while other complexes, were not. The color bleaching of metal-complexes in aqueous solutions is interesting due to the fact that there are two reactive sites, the metal and the ligand which could be susceptible to interaction with the active water radiolysis products i.e. OH, H, e-aq… etc. (10).
Sorenson studied some systems involving reducing free radicals. It has been reported that hydrated electrons (eaq) and hydrogen atoms (H) are capable of reducing the central metal ions in a complex compound (11).
Gamma radiolysis of aqueous solutions of α- Cobalt (III) Nitrilotriacetate was studied by Bhattacharyya and Srisankar (12). During radiolysis, Co (III) is reduced to Co (II) under various experimental conditions. And also gamma radiolysis of aqueous solutions of iron-salicylate complex was studied by Barakat and El Banna (13). They were observed that this iron-salicylate complex could be applied in dosimetry within the dose range between 0-2 kGy and between 2-6 kGy.
In the present work, the nature of color bleaching upon gamma irradiation of iron and uranium-complexes with ferron and tiron in aqueous solutions has been studied. The possibility of using the color bleaching of these solutions in unknown dose evaluation has been investigated in a trial to use these systems for evaluation of low gamma irradiation doses.
EXPERIMENTAL
A – Materials
a- Uranyl acetate UO2 (CH3COO)2 .2H2O was obtained from BDH Chemicals LTd Poole, England, (M.W. 424.15).
b- Ferrous sulphate Fe SO4. .7H2O was obtained from El Nasr Pharmaceutical Company, Egypt, (M.W. 278.02).
c- Ferric sulphate Fe2 (SO4)3. 5H2O was obtained from El Nasr Pharmaceutical Company, Egypt, (M.W. 489.96).
d- Ferron, analitycal grade reagent (8-hydroxy 7-iodoquinoline 5-sulphonic acid) was obtained from the British Drug Houses LTD. (BDH), England, (M.W. 351.12) m.p. 260 ~ 270 °C.
e- Tiron, analitycal grade reagent (4,5-dihydroxy -1,3-benzene disulphonic acid, disodium salt monohydrate.H2O) was obtained from Riedel-De Haen AG Seelze-Hannover, Germany, (M.W. 332.22), m.p. > 300°C.
f- Double distilled water was used allover the work.
B – Methods
a- Formation of UO2 (П) Ferron complex.
Aliquots of 1 ml of 11 × 10-3M UO2 (П) solutions in alcohol were mixed with increasing amounts of 2 ×10-3M ferron solutions in alcohol, and the mixtures obtained were completed to the mark with alcohol in 5ml volumetric flasks. The optical density of the resultant colored orange solutions was measured spectrophotometrically and the results obtained are shown in figure 1.
Alternatively, 2 ml aliquots of 2 ×10-3M ferron solutions in alcohol were mixed with increasing amounts of 11×10-3M UO2 (П) solutions in alcohol, and the mixtures obtained were completed to the mark with alcohol in 5 ml volumetric flasks. The optical density of the resultant orange solutions was measured spectrophotometrically and the results obtained are shown in figure 2.
b- Formation of Ferron and Tiron complexes with Fe (П):
2 ml aliquots of aqueous 10-3M ferron solution were mixed with increasing amounts of ammonium ferrous sulphate Fe (II) solutions, and the mixtures obtained were completed to the mark with water in 5 ml volumetric flasks. The optical density of the resultant green solutions was measured spectrophotometrically and the results obtained are shown in figure 6 a.
0.5 ml aliquots of aqueous 10-2 M tiron solution were mixed with increasing amounts of Fe (II) solution, and the mixtures obtained were completed to the mark with water in 5 ml volumetric flasks. The optical density of the resultant blue solutions was measured spectrophotometrically and the results obtained are shown in figure 6 b.
c- Formation of Ferron and Tiron complexes with Fe (III):
0.5, 1 and 1.5 ml aliquots of 10-3M Fe (III) solution were mixed with increasing amounts of ferron and the resultant green solution was completed to the mark in 5 ml volumetric flasks and the optical density of the complex solutions was measured. Figure 9 shows the results obtained.
0.5, 1, 1.5 and 2 ml aliquots of 10-3M aqueous Fe (III) solutions were mixed with increasing amounts of tiron solution, and the resultant blue solutions were completed to the mark in 5 ml volumetric flasks with water and the optical density of the complex solutions was measured spectrophotometrically. Figure 11 shows the results obtained.
Applicability of Beer’s law.
By appropriate dilutions, samples containing increasing concentrations of the complex were prepared. For testing the applicability of Beer’s law, the optical density of the solutions was measured and the values obtained were plotted against the corresponding concentrations of the used solutions. The results are given in figure 3, for UO2 (II), in figure 7 and 11, for Fe (II) and Fe (III) complexes.
Preparation and irradiation of samples
Complex solutions with concentrations corresponding to the upper end of the Beer’s law applicability line were used (10-3M).
3 ml aliquots of the complex solutions were placed in well stoppered glass vials (1.5 cm in diameter and 5 cm in length), and were irradiated in the gamma cell in presence of air.
Irradiation of samples was carried out using the Canadian Co-60-gamma cell with a dose rate 3.33 – 3.19 kGy/h at the National Center of Radiation Research and Technology, Cairo, Egypt. The operator used a Reference Alanine Dosimeter supplied by the National Physical Laboratory, UK, to determine the irradiator’s dose every 12 months. The dose applied was determined daily by calculation.
Apparatus
Spectrophotometric measurements were carried out using a single beam T60 UV-VIS spectrophotometer, using glass cells with optical path length of 1 cm. Absorbance of the dye solutions was measured against the appropriate blanks ferron or tiron. All measurements of optical density were carried out immediately after irradiation.
Color bleaching measurements:-
Color bleaching was observed upon subjecting the dye samples to increasing gamma-radiation doses. The % color bleaching was determined using the following equation:
% Color bleaching = ×100 (1)
Where A0 and Ax are the absorbance of the dye samples before irradiation and after being subjected to a gamma dose x, respectively (1).
RESULTS AND DISCUSSIONS
The molecular formula of ferron and tiron are as follows:
C9H6INO4S C6H6Na2O9S2
Ferron Tiron
1-Uranyl-ferron complex
UO2 (II) ions form with ferron in ethanol solution a deep orange colored complex. The spectrum of the complex shows a single absorption band at 400 nm. In order to determine the composition of that complex, increasing amounts of ferron were added to a certain concentrations of UO2 (II) ions in ethanol and the absorbance of the resultant solutions were measured. Figure 1 shows the relationship between the absorbance at λmax. at different concentrations of ferron used. From these data, it could be observed that the formed complex involves the formation of 1: 0.5 uranyl – ferron complex.
Fig.1: Absorbance change of complex solution on using increasing concentrations of ferron in presence of (2.2 ×10-3M) UO2 (II).
Again, the absorbance of the solutions formed by adding increasing amounts of UO2 (II) ions to 0.8 × 10-3 M ferron solutions was determined and plotted against UO2 (II) concentrations. The results are shown in figure 2. From which it could be deduced that the structure of the formed complex involves the formation of 1: 0.4, uranyl – ferron complex.
Fig.2: Absorbance change of complex solution on using increasing concentrations of UO2 (II) in presence of (0.8 ×10-3M) ferron.
In order to test the applicability of Beer`s law, a stock solution of uranyl-ferron complex was prepared and the change of the absorbance of the solutions at λmax. on changing the concentration of the complex was studied. A good linear relationship was obtained within the concentration range 0 – 1.11×10-3 M, as shown in figure 3. The correlation coefficient determined by linear regression analysis of the data obtained was 0.9709. The molar absorption coefficient of the complex solutions was 2660 mol-1 dm-3 cm-1. From these results ~ 1×10-3M complex solution was used in irradiation experiments.
Fig. 3: Absorbance-concentration relationship of UO2 (II) – ferron complex.
Effect of irradiation on UO2 (II) – ferron complex.
The effect of gamma irradiation on the color bleaching of uranyl-ferron complex solution 1×10-3 M was followed spectrophotometrically; the results are given in figure 4a. Gradual color bleaching occurred on increasing the irradiation dose up to ≈ 600 kGys. The percent color bleaching of the complex solutions at different absorbed doses were calculated and plotted against the corresponding irradiation doses used. The results are also represented in figure 4b. A good linear response relationship was obtained. It has been shown before that it is possible to use this linear relationship as a calibration curve for determining the irradiation dose to which a sample of uranyl- ferron complex in solution has been exposed.
Fig. 4: a-Change of the absorbance of UO2 (II) complex compounds with ferron upon gamma irradiation.
b-Change of the percent color bleaching of UO2 (II) complex compounds with ferron upon gamma irradiation.
For testing that possibility and the accuracy and precision of unknown dose evaluation process, some test samples of UO2 (II) – ferron complex were subjected to different unknown gamma irradiation doses, as determined by the operator of the gamma source. After irradiation, the optical density of the irradiated solutions was measured. The % color bleaching occurring in the irradiated samples at different applied doses, were calculated. By using the % color bleaching – dose curve (figure 4b), the applied unknown irradiation doses of the test samples were determined and the results are given in table (1).
Table 1: Unknown dose evaluation using alcoholic solution of UO2 (II) complex with ferron.
Applied doses, kGy / Dose found / Standard deviation / Mean deviation / % Difference from calculated doseNo. of determinations / Mean dose , kGy
50 / 6 / 67 / 27.1 / 17.4 / 34.8
100 / 6 / 106 / 16.7 / 6.4 / 6.4
150 / 13 / 136 / 18.0 / -9.3 / -13.9
200 / 5 / 215 / 62.4 / 14.7 / 7.5
250 / 5 / 251 / 16.5 / 13.3 / 0.4
300 / 2 / 309 / 31.6 / 18.9 / 3.2
400 / 10 / 416 / 31.5 / 16.3 / 4.1
500 / 3 / 508 / 37.6 / 8.1 / 1.6
600 / 8 / --- / --- / --- / ---
From these results it is possible to observe a rather good concordance of the values of the determined doses with the magnitude of the actual applied doses.
The post-irradiation change of the absorbance of the uranyl- ferron complex solution was studied. Thus, the absorbance of irradiated complex solutions was measured at intervals after irradiation. The results are shown in figure 5. From these data it is clear that while the unirradiated UO2 (II) – ferron complex is stable for a long time, most of the irradiated samples were found to show a post irradiation effect. Therefore, although that effect is not greatly significant, the absorbance of the irradiated samples was measured directly after irradiation.
Fig. 5 : Absorbance-time relationship of irradiated samples of UO2 (II) – ferron complex.
a- unirradiated b- 50 kGy c- 100 kGy d- 350kGy e- 600 kGy
2- Iron (II) – ferron and tiron complexes.
Fe (II) ions form with ferron in aqueous solutions a green complex. The spectrum of that complex shows two absorption maxima at 450 nm and 610 nm. With tiron, Fe (II) ions in aqueous solution form a blue complex. The spectrum of that complex shows a single absorption band at 670 nm.
The structure of Fe (II) – ferron and Fe (II) – tiron complexes were studied by the molar ratio method. Thus, increasing amounts of Fe (II) ions were added to a given concentration of ferron or tiron aqueous solutions. The absorbance of the formed complex solutions was measured. Figure 6 shows the relationship between the absorbance at λmax.. of the complex solutions and the concentrations of the Fe (II) ions in solution in case of ferron (figure 6a) and tiron (figure 6b). It could be observed that a Fe (II) – ferron as well as Fe (II) – tiron complexes are 1:1 complexes.