Journal of Radioanalytical and Nuclear Chemistry

, Volume 297, Issue 1, pp 107–113

Portable automated separation system for routine purification and/or pre-concentration of radionuclides based on column chromatography

Authors

    • Safety and Radiation Protection, Forschungszentrum Jülich
  • R. Flucht
    • Safety and Radiation Protection, Forschungszentrum Jülich
  • M. Burow
    • Safety and Radiation Protection, Forschungszentrum Jülich
Article

DOI: 10.1007/s10967-012-2315-8

Cite this article as:
Zoriy, M.V., Flucht, R. & Burow, M. J Radioanal Nucl Chem (2013) 297: 107. doi:10.1007/s10967-012-2315-8

Abstract

In recent years the purification and/or pre-concentration of radionuclides before the measurement has grown increasing interest in analytical chemistry. In this study, a new compact and portable stand-alone equipment permitting automatisation of various separation tasks is developed. The new system allows performing quick and reliable automated separation of the selected radionuclide. Since there is no need for permanent manual control of the separation procedures (automatic loading of the sample, washing and stripping solution on the column are controlled via a computer program) the system can be operated overnight. The new system posses the possibility of more variable control for the separation process via new developed user-friendly software, is shielded against the chemical vapors and could be universally equipped with any available chromatographic column. For the automated separation of U, Pu and Am isotopes (achieved recoveries were in the range of 65–95 %, depending on the element separated. The data, presented, show that the application of the module should be also straightforward for other elements: simply by changing the chromatographic columns with the resin having high chemical selectivity for the target ion. The developed separation column module, software and hardware can be readily adapted in any laboratory to meet defined analytical requirements.

Keywords

Automated separationExtraction chromatographyRadionuclides

Introduction

During the past few decades releases of man-made radionuclides into the biosphere have created environmental contamination that provoked public concern [18]. On the other hand, presence of primordial radionuclides (as for example, 238U, 235U, 234U, 226Ra, 222Rn etc.) should be also carefully examined in order to truly evaluate the effective dose coming from natural radioactivity [914]. All this has raised the needs of a reliable, accurate and rapid analysis of radionuclides in order to access their potential impact on public health.

Nowadays many analytical methods are applied for the determination of long-lived radionuclides [1, 1518]. Conventional alpha spectrometry has been used for a long time as a reliable method for the determination of alpha nuclides in mBq activity level. In order to overcome self-absorption of α-radiation during the measurements the method includes the separation of the radionuclides of interest from the sample matrix following by the deposition on the suitable substrate for the alpha counting.

In the resent years, because of its high sensitivity, short analysis time and relatively easy operation, mass spectrometric methods (i.e. TIMS, ICP-MS or MC-ICP-MS) are increasingly applied for determination of isotopes of uranium, thorium, plutonium, 90Sr, 99Tc, 129I, 210Pb, 226Ra, 237Np, 241Am, 244Cm etc. in environmental, bio-assays and waste samples [1921]. However, due to the formation of possible interferences on the m/z of the analyte as well as for pre-concentration purposes, selective separation/purification of radionuclide of interest prior to the measurements is also required.

Most of the conventional methods for actinide separation include ion exchange, liquid–liquid extraction, chromatographic extraction and ion chromatography, or a combination of these techniques. In recent years, column chromatographic methods such as ion chromatography and extraction chromatography (i.e. UTEVA, TRU, Sr-spec. resins (TrisKem Int.)) have become the dominant methods of choice [2224]. These resins are currently used in routine procedures that significantly improve the separation processes of actinides and other radioisotopes. However, all of these methods involve a great consumption of reagents and time. In addition, continuous contact with aggressive reagents and potentially hazardous (radioactive) samples must be considered an important risk factor for the analyst. Furthermore, analytic pre-concentration and sample matrix elimination may be advantageous to improve analysis sensitivity and detection limits.

A literature review [2528] of the separation technologies employed for the separation of radionuclides reveal that the recent advances in separation science (i.e. materials with greater chemical inertness, simplified processing, reducing processing time and costs) have not been widely implemented despite ongoing research in metal ion separation chemistry. In all the cited work, commercially available separation systems were adapted to planned tasks that do not always fit the claimed requirements and desired sample throughput. They are usually relatively expensive and complex to operate.

Recently we reported a development of a simple separation arrangement for separation of radionuclides by means of extraction chromatography [29]. In this arrangement the solution being separated was pumped through the set of equal chromatographic columns via peristaltic pump. The sequence of passed solutions was automated and was controlled using a simple serial port utility that send a sequence of text strings at timed intervals to the valve in order to control the algorithm of the separation procedure.

In the current work we significantly improved the previous arrangement and developed a stand-alone separation column equipment TSM (germanTrennsäulenmodul”) for the very simple, quick and reliable automated purification and/or pre-concentration of radionuclides. The new system is an independent device that posses the possibility of more variable control for the separation process via a new developed “user-friend” software, is shielded against the chemical vapors and could be universally equipped with any available chromatographic column of appropriated size.

Experimental

Reagents and sample solutions

All acids and reagents used for the testing of developed TSM system were of analytical grade or better: HNO3 65 % (Suprapur, Merck); HCl 37 % (Suprapur, Merck); 0.1 mol/l ammonium hydrogen oxalate (obtained from 6.31 g of oxalic acid (H2C2O4·2H2O) + 7.11 g of ammonium oxalate [(NH4)2C2O4·H2O] in distilled water made up to 1 l of solution); ascorbic acid (Merck, Germany); NaNO2 (Merck, Germany); Al(NO3)3·9H2O (Merck, Germany). Standards of 232U, 233U, 242Pu or 243Am certified by the Physikalisch-Technische Bundesanstalt (national metrology institute, Germany) were used as tracers. All the solutions were diluted with high quality water from Millipore (18.2 MΩ cm).

For all experiments in this work, two types of samples were used: water and urine. The water was a conventional tap water; urine samples taken from the pooled urine, collected from individuals not professionally exposed to radiation. Before the analysis water or urine samples were spiked with known amounts of the standards of 233U, 242Pu or 243Am in accordance with the separation procedure. Then, samples were digested in furnace oven in order to destroy the organic matrix, for instance, in urine samples. Depending on the method used, all samples were diluted to the final solutions of 0.1 mol/l ascorbic acid + 5 mol/l HNO3, 2 mol/l HNO3 or 1 mol/l HCl for the separation of Pu and Am, and U, respectively.

Chromatographic resins and column preparation

Automated module TSM was tested on three different resins UTEVA, DGA-normal and DGA-branched (TrisKem Int., Bruz, France). The resins were used for the purification and/or pre-concentration of Uranium, Plutonium and Americium. Chromatographic columns (from Quartzglass, 8 mm i.d. × 100 mm long) were filled with approximately 0.7–1 g of the corresponding resins and installed in the TSM automated system. All conditioning and separation algorithms used for the testing are described elsewhere [29].

Instrumentation

The schematic arrangement of the automated separation system TSM is presented in Fig. 1a. The system consists of two multi-position microelectric valve actuators (Model EMHCA-CE, Valco Instruments Co. Inc.) with all the required connections to the computer; Low Flow Ratio:Matic® Duplex Stepper Pump (Fluid Metering, Inc., USA) and chromatographic column containing resin hawing high chemical selectivity for the target ions. All component are connected with polytetrafluorethylene (PTFE) tubing (1/16 AD × 1 mm i.d., Chromatography Service GmbH).
https://static-content.springer.com/image/art%3A10.1007%2Fs10967-012-2315-8/MediaObjects/10967_2012_2315_Fig1_HTML.gif
Fig. 1

a) Schematic arrangement of the automated separation system TSM; b) picture of the automated TSM (front view)

The measurements after separation process were performed using MC-IPC-MS (Neptune/Plus, Thermo Scientific) and alpha spectrometric system (Analyst, Canberra GmbH).

Results and discussions

Improvements of separation column equipment TSM

A picture of the TSM system is shown on see Fig. 1b. It is an independent device for the very simple, quick and reliable automated purification and/or pre-concentration of radionuclides. One of the improvements of our previous work was the development the protective housing in order to seal all the sensitive components from the aggressive acid vapours. On the right side of the TSM two connectors for the one single column are located, where the prepared column could be easy attached. The advantage of this one-column arrangement in comparison to the system with the multiple columns is that in case of any technical fault it could be separately fixed without influence on the separation of other samples.

The TSM system is controlled via communication interface between the device and operation program written in LabVIEW (System Design Software, National Instruments). The screenshot of the user interface is presented in Fig. 2. Using this user-friendly software it is possible with only few mouse clicks establish a separation procedure for the automated separation of the selected radionuclides. The programmed separation sequences could be saved on the internal memory of the device (up to 4 sequences) and loaded later on demand.
https://static-content.springer.com/image/art%3A10.1007%2Fs10967-012-2315-8/MediaObjects/10967_2012_2315_Fig2_HTML.gif
Fig. 2

Screenshot of the software operation software menu written in LabVIEW and used to control the developed automated TSM

All the needed parameters (i.e. program name, flow-rate, time, separation steps, etc.) are continuously displayed during the separation on the implemented display. All commonly encountered functionalities have been designed to appear familiar to the laboratory technician.

A further improvement in current automated TSM was the application of Low Flow Stepper Pump to transfer the solutions through the appropriated column. The advantage of this pump compared to the peristaltic one is the fact that the Stepper Pump could be operated at a much higher pressure (up to 7.9 bars). This results in a more stable flow-rate of the solution in a case high viscous liquids or partial clogging of the packed column. In addition, in contrast to the peristaltic pump, Stepper Pump posses a superior chemical resistance to handle as many chemicals as possible; all wet end parts are exclusively manufactured of high resistant materials (SiC, PTFE & SCS14).

Validation of separation column equipment TSM

Flow-rate stability

The stability of the flow-rate by developed automated separation column equipment TSM was studied using seven different viscous liquids: MilliQ water, 1M HNO3, 2M HNO3, 5M HNO3, 0.025M HCl, 1M HCl, 5M HCl. The samples were pumped with the three different flow rates 1, 1.5 and 2 ml/min through the columns packed with UTEVA, DGA-normal und DGA-branched resins. The results, summarised in a Table 1, show a relatively good correlation between the reference flow-rate (adjusted using the tuning program (see Fig. 2)) and the flow rate measured through the tested separation columns. The average accuracies of 2.3, 1.1 and 1.0 % for the flow rates of 1, 1.5 and 2 ml/min, respectively, were observed.
Table 1

Flow-rates (presented in ml/min) of the solutions passed through the packed with different columns resin and measured for the reference pumps rates of 1, 1.5 and 2 ml/min, respectively

Resin

Reference flow-rate (ml/min)

Water

1M HNO3

2M HNO3

5M HNO3

0.025M HCl

1M HCl

5M HCl

UTEVA

1

1.01

1.05

1.02

1.01

1.02

1.05

1.05

1.5

1.50

1.52

1.50

1.55

1.51

1.50

1.50

2

2.03

2.01

2.0

2.03

2.02

2.01

2.03

DGA-normal

1

1.02

1.03

1.05

1.03

1.01

1.02

1.03

1.5

1.51

1.52

1.52

1.50

1.52

1.51

1.53

2

2.01

2.02

2.01

2.03

2.02

2.03

2.03

DGA-branched

1

0.99

1.01

1.02

1.05

1.03

1.0

0.99

1.5

1.51

1.53

1.53

1.51

1.52

1.52

1.53

2

2.01

2.01

2.03

2.03

2.03

2.02

2.02

Recovery studies

To study the recoveries three water and three urine samples, spiked with know amount of 233U, 242Pu and 243Am tracers, were subjected for the corresponding separation procedures using developed automated TSMs. After the separation all uranium determinations were performed using MC-ICP-MS, while the plutonium and americium measurements with alpha-spectrometry. All the data are summarised in Table 2. The results show that relatively good and reproducible recoveries were achieved. Observed recoveries were in the range of 65–72 % for 233U and in the range of 68–75 and 86–95 % for 242Pu and 243Am, respectively. The recoveries were also comparable with those were found for the manual separation procedure; however the reproducibility was better when the automated separation protocol was used.
Table 2

Observed recoveries of 233U, 242Pu and 243Am, separated from the three water and three urine matrixes using developed automated column equipment TSM

Sample

Recoveries (%)

233U

242Pu

243Am

Water-1

71

74

91

Water-2

68

72

93

Water-3

70

74

95

Urine-4

67

75

86

Urine-5

65

71

89

Urine-6

72

68

90

Urine-7 (manual separation)

65

70

80

The last row presents the typical recoveries observed by manual separation using the same separation procedure

Additional advantages of the TSM system in comparison to the manual separation are comprised in Table 3. The separation time for all elements using the automated system was found to be lower up to 35 % in comparison with manual introduction. Some important advantages using automated introduction, such as avoiding bubbles and clogging in the column or the same procedures for different samples, make the separation of the element more accurate and precise. Overnight operation, no need to permanently check the separation procedures and enhanced speed of introduction are important factors for relatively cheaper and easier separation.
Table 3

Comparison of manual and automated by TSM separations of selected radionuclides

 

Separation

Manual

By means of TSM

Time separation of U for 1 sample, min

80

60

Time separation of Am for 1 sample, min

140

100

Time separation of Pu for 1 sample, min

110

80

Operation overnight

No

Yes

Work with harmful acids

No

Yes

Changed speed of introduction solution

No

Yes

Avoiding bubbles and clogging in column

No

Yes

Permanent manual controlling of separation procedures

Yes

No

Separation chromatogram

A more rigorous examination of the instrument operation was obtained using the analytical method of separation fractions. During the separation protocol relatively small volume fraction (each 2 ml) were collected for each separation step to build a whole separation chromatogram. As a sample one of the “pool-urine” samples was spiked with a known amount of 233U tracer and was separated. The resulted chromatograms for separation of natural uranium as well as the tracer chromatogram are presented in Fig. 3a and b, respectively. As shown on the Fig. 3a an acceptable separation profile of the uranium from the matrix could be achieved. The chromatogram shows a profile as typically obtained by conventional manual operation. No significant quantities of uranium were detected neither during the sample loading procedure not with the rinsing afterwards with 50 ml of 3 M HNO3. The uranium was stripped, as it was expected, <93 % with 7 Bed Volumes of 0.025M HCl. At the end of separation process clear background level was reached.
https://static-content.springer.com/image/art%3A10.1007%2Fs10967-012-2315-8/MediaObjects/10967_2012_2315_Fig3_HTML.gif
Fig. 3

Separation chromatogram showing the purification/pre-concentration of a U (nat) and b233U (as a tracer) performed using developed automated separation column equipment TSM

The separation chromatogram of 233U tracer, presented in Fig. 3b, shows the identical profile to the U (nat) one. This confirms the possibility of successful application of 233U as an internal standard for the recovery assessment during uranium separation via developed automated TSM.

Conclusion

In this work robust automated separation column module TSM was developed and successfully applied in order to simplify the separation task. This was achieved due to the significant improvement of the design and required hardware of the instrument. Installing internal memory and optimising operation software allow to work with the developed TSM independently, as stand-alone equipment; up to 4 different separation protocols could be loaded into the device and be used afterwards on the demand.

Since there is no need for permanent manual control of the separation procedures (automatic loading of the sample, washing and stripping solution on the column are controlled via a programmed sequences) the system can be operated overnight.

The studies on the recoveries show acceptable results for the automated separation of U, Pu and Am isotopes (achieved recoveries were in the range of 65–95 %, and were depended on the element separated) and suggest the possibilities to its application for other elements: simply by changing the chromatographic columns with the resin having high chemical selectivity for the target ion and loading corresponded separation program.

The developed separation column equipment TSM, software and hardware can be readily adapted in any labour to meet defined analytical requirements.

Acknowledgments

The authors would like to thank Mr. G. Henschke for the technical realisation of the automated separation column module TSM. The assistance of the staff of the Radioanalytical Laboratory in performing and testing the module is very much appreciated.

Copyright information

© Akadémiai Kiadó, Budapest, Hungary 2012