Development of chloroform: Methyl red dosimeter for blood irradiation dosimetry :Sandip Mondal, SH Shinde, MS Kulkarni, S Adhikari, Radiation Protection and Environment

ORIGINAL ARTICLE
Year : 2016 | Volume : 39 | Issue : 4 | Page : 199--203

Development of chloroform: Methyl red dosimeter for blood irradiation dosimetry

Sandip Mondal¹, SH Shinde¹, MS Kulkarni¹, S Adhikari²,
¹ Radiation Safety Systems Division, Bhabha Atomic Research Centre, Trombay, Mumbai, Maharashtra, India
² Radiation and Photochemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai, Maharashtra, India

Correspondence Address:
Sandip Mondal
1-130 H, MOD Labs, Radiation Standards Section, Radiation Safety Systems Division, Bhabha Atomic Research Centre, Trombay, Mumbai - 400 085, Maharashtra
India

Abstract

The use of chloroform (CHCl₃) solution containing methyl red (CMR) was investigated for the dosimetric application. This is based on the radiolytic formation of hydrochloric acid from CHCl₃, which protonates a pH indicator, namely, methyl red, and leads to a visual change in color. The optimum concentration of methyl red and wavelength for absorption maxima for the dosimeter were established at 2 × 10⁻⁴ mol/dm ³ and 550 nm, respectively. The useful dose range for the dosimeter is 5–50 Gy. The reproducibility of the system is found to be within ±5%. Pre- and post-irradiation stability of the dosimeter solution was also investigated for 1 month and 24 h, respectively. The importance of a chemical dosimeter in the dose range of 5–50 Gy prominently lies in applications such as blood irradiation. Thus, dose mapping of the Blood Irradiator-2000 was carried out using CMR dosimeter. These dose values were further confirmed using a reference standard Fricke dosimeter.

How to cite this article:
Mondal S, Shinde S H, Kulkarni M S, Adhikari S. Development of chloroform: Methyl red dosimeter for blood irradiation dosimetry.Radiat Prot Environ 2016;39:199-203

How to cite this URL:
Mondal S, Shinde S H, Kulkarni M S, Adhikari S. Development of chloroform: Methyl red dosimeter for blood irradiation dosimetry. Radiat Prot Environ [serial online] 2016 [cited 2023 Mar 24 ];39:199-203
Available from: https://www.rpe.org.in/text.asp?2016/39/4/199/199978

Full Text

Introduction

Accurate measurement of the dose is very important in radiation biology and related areas. Ferrous sulfate, benzoic acid, and xylenol orange dosimetry system [1] is being widely used for measurement of low-dose gamma radiation because of its reproducibility and precision. However, due to low pre-irradiation stability and cumbersome preparation procedure makes it inconvenient as a ready to use dosimeter. Ferrous sulfate, sorbitol, and xylenol orange dosimeter [2] can also measure low doses but had dose range only up to 12 Gy. Alanine ESR dosimeter,[3] which has wide dose ranging from 1 to 105 Gy, appropriate for measuring low as well as high level of radiation doses and is used widely for dose intercomparison exercises. However, high cost restricts its use as a dosimeter for routine purposes. Other dosimetric systems for low doses, such as ionization chamber, Gafchromic film, and radiochromic dosimeter, have their own limitations for use in radiation biology and related areas.

In the present work, we have attempted to develop a chemical dosimeter for use in radiation biology, based on the principle of radiolytic formation of hydrochloric acid (HCl) from organic halogen compounds. Chloroform (CHCl3), when irradiated produces HCl,[4] which then protonates a pH indicator, namely, methyl red, and leads to a visual change in color from yellow to red. Thus, a new chemical dosimeter is being developed using a CHCl3 solution containing methyl red (CMR). The preliminary dose-response study indicates its usefulness for dosimetric application in the dose range of 5–50 Gy, which can be useful to ensure accurate dose delivery to the blood samples. Blood and blood components are irradiated to doses in the range of 15–50 Gy to prevent graft-versus-host disease by decreasing the number of viable T lymphocyte.[5]

Experimental

Reagents

CHCl3 from SD Fine-Chem Ltd., India, and methyl red from Fluka, Germany, were used without further purification. Ferrous ammonium sulfate and sulfuric acid were of analytical reagent grade.

Spectrophotometric measurement

A Jasco V-530 UV/VIS double beam spectrophotometer was used for recording absorbance spectra and for measurements of the absorbance at a fixed wavelength. The absorbance of irradiated and unirradiated CMR solutions was measured 45 min after dissolution against air as reference. Further, the difference between the two absorbance values, i.e., the net absorbance value was calculated.

Reaction mechanism

The radiolytic formation of HCl from CHCl3 is well established and the radiolysis mechanism of CHCl3 includes the following probable reactions.[6]

CHCl3^^^^^-> *CHCl3, CHCl3+, e −e − + CHCl3 → CHCl3− →• CHCl2 + Cl −CHCl3+ → CHCl2+ + ClCHCl3+ + Cl − → CHCl3 + ClCHCl2+ + Cl – →• CHCl2 + Cl*CHCl3→• CHCl2 + Cl

Which then followed by radical reactions, leading to major products,

CHCl3 + Cl →• CCl3 + HCl• CHCl2 + CHCl3 → CH2 Cl2+• CCl3• CHCl2+• CCl3 → C2 HCl52• CHCl2 → CHCl2 CHCl22• CCl3 → CCl3 CCl3

Carbon tetrachloride is apparently formed by an ionic reaction, although this has not been identified, and tetrachloroethene by a nonionic molecular reaction.

CCl2 + CHCl3→ *C2 HCl5 → C2 HCl5 → C2 Cl4 + HCl

Sample preparation for irradiation

Dosimeter containers, glass wares were cleaned as per recommended procedure.[7] For establishing optimum composition of CMR dosimeter solution, a stock solution of 5 × 10−3 mol/dm 3 methyl red in CHCl3 was prepared. From this, 10 different solutions of varying methyl red concentration from 0.5 × 10−4 to 5 × 10−4 mol/dm 3 were prepared. Each solution was irradiated to 25 Gy dose and absorbance spectrum for each solution was recorded in the wavelength range from 350 to 650 nm. For dose-response calibration of CMR, polypropylene tubes with dimension, namely, 13 mm OD, 54 mm height, and 1 mm wall thickness were used as dosimeter containers. This was further provided with the required build-up (400 mg/cm 2) for attaining electronic equilibrium [8] during irradiation. For the development of CMR dosimeter, all the irradiations were done using Gamma Chamber-900 (GC-900), which is having around 1 kCi, cobalt-60 source. The center position of the irradiation volume of GC-900 was calibrated using Fricke [9] and alanine ESR dosimeter.[10] A specially designed jig as shown in [Figure 1] was used during irradiation for maintaining geometrical reproducibility. Irradiation chamber of GC-900 has dimensions of 100 mm diameter and 140 mm height.{Figure 1}

To establish a dose-response relationship, three numbers of dosimeters were irradiated for each dose point. Five dosimeters were kept unirradiated which are to act as a control. The absorbance of these dosimeters was then measured at 550 nm, and the net change in absorbance (ΔA) was evaluated as per the recommended procedure [7] using the difference in absorbance of irradiated (Ai) and unirradiated (A0) solutions. Reproducibility of the dose response in this dose range was studied by irradiating 10 numbers of dosimeters to the same dose of 6, 15, and 45 Gy.

For determination of pre-irradiation stability of the dosimeter solution, 250 ml stock solution was prepared and kept in the dark. The absorbance of the unirradiated stock solution was measured at different time intervals at 487 nm, i.e. the absorbance maxima for unirradiated solution, and at 550 nm, i.e. the absorbance maxima for net absorbance. The absorbance was found almost constant for 1 month, under laboratory storage condition.

For determination of post-irradiation stability, 10 sets of dosimeters were irradiated to five different doses. The absorbance of these dosimeters was then measured at different intervals from 5 min to 24 h.

For dose mapping within the irradiation volume, 18 polypropylene tubes filled with CMR dosimeter were arranged along the central plane of irradiation volume of Blood Irradiator-2000 (BI-2000) using a perspex jig to reproduce the geometry, as shown in [Figure 2]. Irradiation chamber of BI-2000 has dimensions of 120 mm diameter and 179 mm height. Similarly, Fricke dosimeters were also irradiated at the same position for the respective dose range. Proper build-up was provided to all the dosimeters during irradiation. As the working dose range of CMR and Fricke dosimeters were different, irradiation was done for different timings depending on the dose range of corresponding dosimeters.{Figure 2}

Results and Discussion

The optimum composition of CMR was determined by varying the concentrations of methyl red from 0.5 × 10−4 to 5 × 10−4 mol/dm 3. It was found that the response of the dosimeter was continuously increasing with the increasing concentration of methyl red as shown in [Figure 3]. This increase in response was found to be insignificant after the methyl red concentration of 2 × 10−4 mol/dm 3. Furthermore, an increase in methyl red concentration resulted in an increase of the absorbance of unirradiated solution, which may lead to more uncertainty in response. Hence, the most suitable concentration of methyl red was fixed at 2 × 10−4 mol/dm 3. The wavelength of maximum absorbance at 550 nm was established by recording the net absorption spectra in the wavelength range of 350–650 nm for five different dose values as shown in [Figure 4]. The dose-response relationship of this system in the dose range 5–65 Gy was found to be the second-order polynomial as shown in [Figure 5]. However, above 50 Gy, it shows saturation effect and, thus, it is recommended to use in the dose range of 5–50 Gy. Reproducibility of the dose response in this dose range was found to be within ±5% as represented by [Table 1]. It was also found that the unirradiated dosimeter solution was stable for at least 1 month. After irradiation, the net absorbance was initially increased rapidly up to around 45 min and became constant for 8 h as shown in [Figure 6]. After 8 h, the response again starts to increase slowly and became unstable. Hence, it is recommended that all the absorbance measurements of the dosimeter should be done between 45 min to 8 h from irradiation.{Figure 3}{Figure 4}{Figure 5}{Table 1}{Figure 6}

For dose mapping experiment, the average dose value of dosimeter number 9 and 10 was taken as 100%. The dose values of all other dosimeters in the plane were then normalized with respect to that average. Dose distribution variation of about 12% from top to the center, 10% from center to the bottom, and 20% from center to the periphery was observed as shown in [Figure 7]. This was further confirmed by Fricke dosimeter. The agreement between dose profiles measured by CMR and Fricke dosimeters was within ±5%.{Figure 7}

Conclusions

These studies indicate that CMR dosimeter can be conveniently used in the recommended dose range of 5–50 Gy and has the potential to be used as a chemical dosimeter for its applications such as blood irradiation and some radiation biology experiments.

Acknowledgments

The authors are extremely grateful to Dr. K. S. Pradeepkumar, Associate Director, Health Safety and Environment Group and Head, Radiation Safety Systems Division, Bhabha Atomic Research Centre for his encouragement and support in this work and Mr. S. G. Mhatre of Radiation Standards Section, Radiation Safety Systems Division for his warm-hearted help in the improvement of this manuscript.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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