Journal of Analytical Sciences, Methods and Instrumentation, 2011, 1, 1-8 1 doi:10.4236/jasmi.2011.11001 Published Online September 2011 (http://www.SciRP.org/journal/jasmi) Application of in-House Method for Determination of Radium Isotopes in Environmental Samples Using the Liquid Scintillation Counting Technique Nik Azlin Nik Ariffin1*, Zal Uyun Wan Mahmood2, Che Abd Rahim Mohamed3 1School of Environmental & Natural Resources Sciences, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, Bangi, Selangor, Malaysia; 2Radiochemistry and Environment Group, Malaysia Nuclear Agency, Bangi, Selangor, Malaysia; 3Marine Ecosystem Research Centre (EKOMAR), Universiti Kebangsaan Malaysia, Bangi, Selangor, Malaysia. Email: *[email protected]; [email protected] Received August 25th, 2011; revised September 19th, 2011; accepted September 28th, 2011. ABSTRACT A method for determination of 226Ra and 228Ra in environmental samples using the α-β coincidence liquid scintillation counting (LSC) has been developed. Radium were preconcentrated from environmental samples by coprecipitation with BaSO4, then purified from others radionuclide interferences using the cation column exchange (Bio-Rad AG 50 W-X4 resin with 200 - 400 mesh size and H+ form) and operating in warm temperature which is between 70˚C - 80˚C. Then, the Ba(Ra)SO4 precipitate was filtered through the Millipore filter paper, dried and weighed to calculate chemical yield. The activity concentration of radium isotopes in mixture of liquid scintillation cocktails were measured using LSC after being stored for over 21 days to allow the growth of the progeny nuclides. The method has been validated with a certi- fied reference material supplied by the International Atomic Energy Agency and reliable results were obtained. The radiochemical yields for radium were 59% - 90% and recovery was 97% and 80% for 226Ra and 228Ra, respectively. Sixteen seawater and fish flesh samples collected in Kapar coastal water have been analyzed with the developed method. The obtained radium activity concentrations in seawater were in the range of 2.08 ± 0.82 mBq/L to 3.69 ± 1.29 mBq/L for 226Ra and 6.01 ± 3.05 mBq/L to 17.07 ± 6.62 mBq/L for 228Ra. Meanwhile, the activity concentrations of 226Ra and 228Ra in fish flesh were in the range of 11.82 ± 5.23 - 16.53 ± 6.53 Bq/kg dry wt. and 43.52 ± 16.34 - 53.57 ± 19.86 Bq/kg dry wt., respectively. Keywords: 226Ra, 228Ra, Environmental Samples, Chemical Yield, Liquid Scintillation Counting 1. Introduction methods [20]. The radionuclides of 226Ra and 228Ra can be measured Radium is commonly measured using a various analyti- in environmental samples using a range of techniques cal procedures and equipments. The most common with offers a number of advantages such as time saving methods for determining radium isotopes are alpha spec- and simplicity [21]. Through LSC methods also, radium trometry [1,2], gamma spectrometry [3-5], Cerenkov in mineral waters [22], contaminated rivers [8] and counting [6] and liquid scintillation counting [7-14]. Al- phosphogypsum samples [23] can be measured. The aim pha spectrometry is the most sensitive technique and of the study is to develop a simple method for determina- allows simultaneous measurement of α-emitting radium tion of 226Ra and 228Ra in environmental samples using isotopes but it is difficult to isolate the radium from other the α-β coincidence LSC. The present method is applied alkaline earth metals [15-17]. Meanwhile γ-emission is to some environmental samples and certified reference relatively low due to low counting sensitively and liable material prepared by International Atomic Energy Agen- 235 to interference from U [17-19]. But the liquid scintilla- cy (IAEA) for procedure validation. tion counting (LSC) provides detection efficiency up to 100% for unquenched samples and intrinsically high 2. Experimental background count rate compared with other counting The complete procedure of isolation and determination of Copyright © 2011 SciRes. JASMI 2 Application of in-House Method for Determination of Radium Isotopes in Environmental Samples Using the Liquid Scintillation Counting Technique 226 228 Ra and Ra in natural samples was tested in the fol- digested with 10 ml of each HNO3, HClO4, HF concen- lowing IAEA reference materials: IAEA 300 (Radionu- trated acid and a few drops of H2O2 on hot plate until clides in Baltic Sea sediment) and IAEA-315 (Radionu- dryness. After digestion, samples were added with 5 mL clides in marine sediment). Then, this procedure with of concentrated HNO3 and a few drops of H2O2, then minor modification was used to determine activity con- dried on hot plate. The sample residue containing radium 226 228 centration of Ra and Ra in seawater and fish sam- isotopes was re-dissolved with 20 ml of 1% HClO4 and ples collected at Kapar coastal area which located at Str- kept warm on hot plate for 1 hour - 2 hours prior to pass aits of Malacca, Malaysia (Figure 1). through the column. 2.1. Chemicals and Reagents 2.3.2. Solution Sample (Seawater) About 12 L of seawater samples were collected using The cation exchanger Bio-Rad AG 50 W-X4 resin with Van Dorn water sampler and the in-situ parameters such size 200 - 400 mesh and H+ form was used to purify as salinity, conductivity, pH, DO were also measured 226Ra and 228Ra from other radionuclide interferences. All using the calibrated portable meter (Model: YSI-SCT reagents of analytical grade were used unless otherwise 6810). After that, seawater samples were filtered, trans- stated. High quality of instagel® XF and Ultimate™ Gold ferred into bucket and acidified with concentrated HNO AB supplied by Perkin Elmer also was used. 3 to pH 2. Then, 1 ml of barium and ferum carrier solutions 2.2. Instrumentation (25 mg/ml) and 10 g of Na2CO3 were added into the seawater samples. The samples were stirred vigorously A Perkin Elmer-Wallac 1414 α-β coincidence Liquid after added 20 ml of ammonia solution to reach pH 10. Scintillation Analyzer connected to compatible personal computer was used. High quality and performance of 20 Then, the samples were put aside for overnight to settle mL glass vials were used in this study. down the precipitate that appeared after a few minutes added with ammonia solution. The liquid was then 2.3. Analytical Procedure poured out and discarded. Meanwhile, the precipitate was 2.3.1. Solid Sample (Reference Materials and Fish siphoned out into cleaned beaker. The precipitate with Flesh) the rest of liquid was centrifuged for 10 minutes at 2500 All the solid samples were dried in an oven at 60˚C until rpm to separate both phase. The precipitate containing a constant weight prior to further analysis. Briefly, about radium isotopes was re-dissolved with 20 ml of 1% 0.5 g solid sample was weighed and 25 mg/ml of Ba2+ HClO4 and kept warm on hot plate for 1 hour - 2 hours carrier was added in the sample. Then, the samples were prior to pass through the column. Kapar Stn.2 Stn.8 Stn.4 Stn.7 Stn.1 Stn.6 Figure 1. Sampling sites of water samples at Kapar coastal area. Copyright © 2011 SciRes. JASMI Application of in-House Method for Determination of Radium Isotopes 3 in Environmental Samples Using the Liquid Scintillation Counting Technique 2.3.3. Radiochemical Separation Using Cation Ex- and kept cool for a while. About 20 ml of 0.5 M HCl and change Resin 1 ml of concentrated H2SO4 were continue added into the The above warmed solution samples were passed through residue for making white precipitate of Ba(Ra)SO4. The into the cation exchange column resin (35 ml of Bio-Rad precipitates were then filtered using 25 mm diameter of AG 50 W-X4; 200 - 400 mesh; H+ form) under warm 0.45 µm pore size Millipore filter paper, dried and condition at 70˚C which pre-conditioned with 1% HClO4 weighed for calculating chemical yield. The dried pre- prior to use. Then, all solution were collected in beaker cipitates together with the filter paper were then trans- and discarded. In the first stage, about 200 ml of 1 M ferred into a 20 ml glass vial followed by adding 8 ml of HCl were added into the column; the aqueous solutions distilled water, 4 ml of Instagel® XF and 8 ml of Ulti- were collected into new beaker and kept it at safe place mate™ Gold AB. After well mixing using ultrasonic for lead, uranium and others radionuclide analysis pur- cleaner, the vials were stored for over 21 days to allow poses. During second stage, the column were added with the growth of the progeny nuclides [9,10,12]. Finally the 200 ml of 2 M HCl and aqueous solution which con- vials were counting using the α-β coincidence liquid tained radium isotopes were collected into cleaned bea- scintillation counter (LSC) for one hour. The flowchart ker. of detail analytical procedure for separation of radium is The aqueous samples were evaporated nearly dryness illustrated in Figure 2. Figure 2. Flow chart of separation procedure and preparation for radium isotopes. Copyright © 2011 SciRes. JASMI 4 Application of in-House Method for Determination of Radium Isotopes in Environmental Samples Using the Liquid Scintillation Counting Technique 2.4. Preparation of Blank and Standard Solution 3.1. Quality Control A 8 ml of distilled water, 4 ml of Instagel® XF and 8 ml The use of certified reference materials containing the of Ultimate™ Gold AB were mixed into the vial and radionuclide at known concentration and composition is were measured using α-β coincidence liquid scintillation one of the most appropriate tests to validate methods and counter for one hour as a blank sample. Meanwhile, 1 ml the performance of the analysts.