|Year : 2010 | Volume
| Issue : 4 | Page : 219-221
Conceptual design for comprehensive automation in radiochemical analysis of bioassay samples
PD Sawant1, SP Prabhu1, SS Raj1, S Bhati1, PK Sarkar1, HS Kushwaha2, S Rajendran3, C Dey3, AP Das3, V Shiwalkar3, Manjit Singh3
1 Health Physics Division, Bhabha Atomic Research Centre, Trombay, Mumbai, India
2 Health Safety & Environmental Group, Bhabha Atomic Research Centre, Trombay, Mumbai, India
3 Division of Remote Handling and Robotics, Bhabha Atomic Research Centre, Trombay, Mumbai, India
|Date of Web Publication||1-Dec-2011|
P D Sawant
Health Physics Division, Bhabha Atomic Research Centre, Trombay, Mumbai
Source of Support: None, Conflict of Interest: None
Bioassay Laboratory of Health Physics Division is entrusted with the task of carrying out the bioassay monitoring of occupational workers from various plants / divisions of BARC e.g. FRD, FCD, RCD, WMD, UED etc. for various radionuclides like Pu, U, Th, 90 Sr, 3 H etc. On the average, about 1400-1500 analyses are performed on 700-800 urine samples collected annually from radiation workers. The number of samples has increased in the recent years and is expected to increase further. Hence, it is planned to carry out automation in various stages of sample handling and processing to cope up with the expected increase in workload. The present paper describes the conceptual design for fabrication of comprehensive automated system for radiochemical analysis of bioassay samples.
Keywords: Automation, bioassay laboratory, radiochemical analysis
|How to cite this article:|
Sawant P D, Prabhu S P, Raj S S, Bhati S, Sarkar P K, Kushwaha H S, Rajendran S, Dey C, Das A P, Shiwalkar V, Singh M. Conceptual design for comprehensive automation in radiochemical analysis of bioassay samples. Radiat Prot Environ 2010;33:219-21
|How to cite this URL:|
Sawant P D, Prabhu S P, Raj S S, Bhati S, Sarkar P K, Kushwaha H S, Rajendran S, Dey C, Das A P, Shiwalkar V, Singh M. Conceptual design for comprehensive automation in radiochemical analysis of bioassay samples. Radiat Prot Environ [serial online] 2010 [cited 2021 Aug 3];33:219-21. Available from: https://www.rpe.org.in/text.asp?2010/33/4/219/90479
| 1. Introduction|| |
Annually 1400 - 1500 analyses are preformed on 700 - 800 bioassay samples collected from occupational workers working in different nuclear facilities of BARC. The workload has increased by 1.5 to 2.0 times in recent past and is expected to increase further by a factor of two over the existing workload due to expanding nuclear programmes of the department. An increase in workload and reduction in man power has necessitated automation of the bioassay procedures. Therefore, it was planned to carry out automation in various stages of bioassay sample handling, processing and analysis under the XI plan programme of the division. Since it is a specialized project being carried out for the first time in India, it required proper planning for finalization of the design layout of the automation system as well as preparation of detailed technical specifications for procuring various parts of the system. Automation work in Bioassay Lab. Is planned to be taken - up in three stages namely, automation in initial processing of i) urine samples, ii) fecal samples and iii) automation in radiochemical analysis of bioassay samples. In the initial phase, automation in radiochemical analysis of bioassay samples has been taken up. The various features incorporated into the design of the automation system are described in the paper.
| 2. The Radiochemical Procedure|| |
The radiochemical procedure presently followed at Trombay's Bioassay Laboratory is described briefly as follows:
2.1 Initial processing of urine samples
Upon the receipt of urine sample from the worker in the Laboratory, the total volume of the sample is measured and it is assigned a sample identification number. The sample is transferred to glass beaker, conc. nitric acid, hydroxylamine hydrochloride (5%) and hydrogen peroxide are added to the sample and heated on hot plate. After wet digestion sample is cooled, calcium phosphate precipitated by addition of liquid ammonia and kept for overnight settling. Next day the supernatant is discarded and precipitate centrifuged, washed with water and dissolved in conc. HNO 3 to destroy any traces of organic matter left behind. The solution is evaporated to dryness to obtain a white residue.
2.2 Radiochemical separation
Radiochemical separation of radionuclides in bioassay samples is done using ion exchange technique. For this purpose, anion exchange resin (Dowex - 1 * 8, 100 - 200 mesh, 1.5g) is used. The resin columns are regenerated and brought in chloride form by passing 8M HCl (20 ml) before using them for radionuclide separation. After passing 8M HCl the resin columns are washed with distilled water to make them free of any traces of acid. This is presently tested manually by placing a small piece of pH indicator paper (E. Merck make, 1 - 14 pH) under the column. Droplets from the column are made to fall on the pH paper and from the change in colour of the pH-paper; it can be decided if the column is acid free or needs more water washings. Once it is free of any acid the column is used for sequential separation of radionuclides in bioassay samples.
Each resin column is preconditioned with 8M HNO 3 (20 ml) before loading the sample. 5 ml of 8M HNO 3 is added at a time and the next aliquot of 5 ml is added only after the first aliquot has passed through the column. The white residue of the sample obtained on complete evaporation is dissolved in 8M HNO 3 with a pinch of sodium nitrite and loaded onto anion exchange resin. Column is sequentially washed with 20 ml of 8M HNO 3 and 8M HCl. Uranium does not get adsorbed in 8M HNO 3 medium and is thus eluted. Thorium gets eluted with the 8M HCl. Pu adsorbed on the column was eluted with 25 ml of 1.5 M Hydroxylamine Hydrochloride in 1 M HCl. These Th, U and Pu fractions are collected in separate beakers, evaporated to dryness and are then taken-up for source preparation.
It is planned that the radiochemical separation of radionuclides mentioned above will be automated in the initial phase I under the XI Plan Programme of the Division. The basic design description of the proposed automation system for the radiochemical separation of radionuclides is given below
2.3 Important features of the automated system
General assembly drawing for the automation system is given in [Figure 1] and its side view showing the 3 axis robot, pH paper handling robot and beaker handling mechanism is illustrated in [Figure 2].
|Figure 1: General assembly drawing for the automation system illustrating front view|
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|Figure 2: Side view of the automation system showing the 3 axis robot, pH paper handling robot, beaker handling mechanism|
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2.4 Automation in regeneration of resin column
It is planned to automate the regeneration of resin column in chloride form as well as the testing of whether the resin column is acid free by using a colour camera system with pH paper handling robot. 8M HCl will be added to the column in 5 ml aliquots by a 3-axis Robot, located above the resin columns. The same robot will then add water for washing the resin column to make free of any traces of acid. The neutrality testing of the column will be done by another pH paper handling robot. This robot will pick up a pH-paper from a tray and position it under the column to be tested, for collection of a few drops on the paper. It will then be brought under the camera to match the colour with that of the stored value. If it does not match, the column would be cleaned with some more distilled water and the procedure would be repeated after certain period of time. If the colour matches with the set value then the sample would be transferred to the column for radiochemical analysis.
2.5 Automation in radiochemical separation
In the proposed automation, it is planned to have 12 resin columns fixed on horizontal bars with quick release type clamps. The condition during ion exchange separation is that the column should not go dry at any stage during the entire operation as it can adversely affect radiochemical recovery of the process. Therefore, in the automated system, level sensors will be mounted on the each resin columns to sense the level of liquid in the columns. If the reagent level in the column falls below the set value, the level sensor will give feedback to start the next sequential operation of the chemical procedure within the available time period.
In the initial set-up, the beakers containing the bioassay samples ready to be loaded onto the resin columns (12 nos.) would be placed manually behind each column. Transferring the samples from the beakers to the column will be done by a 3-axis Robot, located above the resin columns. This robot arm will carry a set of 7 transfer tips. A tip with vertical motion is used for collecting sample from a beaker and dispensing it into the resin column and the remaining 6 tips will be used to dispense various reagents. The central tip is connected to a valveless pump which can aspirate as well as dispense the sample depending on its direction of rotation. Special tip storage and pick - up station is also planned so that after each sample transfer the tip is discarded and a new tip is picked - up for the next sample transfer. Once the process of sample transfer is completed, a known amount of reagent aliquots will be added by other tips present on the XYZ robot. The X and Y motion of the robot is controlled by servo modules of the Programmable Logic Controller (PLC). There will be 7 valvlesss ceramic pumps and 6 reservoirs used in the system. One pump is connected to the sample tip and the rest are connected between the reagent disposal tips and the reservior. The pumps and reservoirs will be mounted on a trolley, which can be located in the bottom chamber of the Fume Hood. Hoses will be routed through the holes in the walls of the Fume Hood and sealed properly.
2.6 Beaker handling mechanism
To collect each reagent fraction separately, 3-beakers will be positioned under each column on a motorized slide. Depending on the reagent used for radiochemical procedure, the corresponding beaker would be positioned under the column for collection. Proximity sensors will be fixed (2 nos.) to sense position of beakers and the home position.
2.7 Control system for operation of the automated system
The complete operations of the automated system will be controlled by a PLC and supervised with a personal computer (PC). The front end of controls will be the PC monitor, which will display status of the operations, error messages and will also used to select processes, set parameters, test elements on manual mode. All the liquid lines and electrical cables will routed through penetration on the wall of the fume hood and sealed properly.
2.8 Protection against corrosion by acid fumes
Analysis of bioassay samples involves use of large quantity of nitric as well as hydrochloric acids which generate a lot of acid fumes. These acid fumes leak out from the fume hood into the working environment when the fume hoods are shut down in the evening. Thus, there is always a danger of material getting attacked by acid fumes. Care has been taken in the design for selecting material for the fume hoods and the components of the automation system. Load bearing components of the automation system would be of stainless steel, grade 316, coated with Teflon for protection against corrosion. Linear motion (LM) guides will be made of Hastelloy. All LM bearings will be of polymer IGUDUR brand from IGUS. The various electrical motors and the camera will be encased in an acrylic enclosure. The ball bearings and shafts used to transmit motion of enclosed motors will be protected by Labyrinth seals. The sensors will have plastic body with no exposed metalic terminals.
2.9 Manual override for X, Y & Z gantry motion
In case the motors in any part of the automation system fail to move due to power failure / motor failure, provision is being made to move these to the extreme end to continue the manual mode operation. Emergency stop button is provided in front of the fumehood to stop the operation in case of any malfunction.
| Conclusions|| |
This paper has presented a comprehensive design for the automation in radiochemical analysis of bioassay samples. The design incorporates features for the automation in regeneration of resin column, radiochemical separation, sample beaker handling, control system for operation etc. When developed the system will be commissioned at Trombay's Bioassay Laboratory and used for routine monitoring of occupational workers in BARC. Completion of the automation work will help in coping up with the expected increase in workload. There are potential users of this system at various DAE Environmental Survey and Bioassay laboratories in India.
[Figure 1], [Figure 2]