Rapid determination of 90 Sr in seawater samples

Transcription

1 DOI /s Rapid determination of 90 Sr in seawater samples Sherrod L. Maxwell Brian K. Culligan Jay B. Hutchison Robin C. Utsey Daniel R. McAlister Received: 15 May 2014 Ó Akadémiai Kiadó, Budapest, Hungary 2014 Abstract A rapid method for 90 Sr in large seawater samples has been developed at the Savannah River National Laboratory (SRNL) to assay 90 Sr at very low levels. The new method employs novel pre-concentration steps to collect 90 Y quickly from up to 40 L of seawater to achieve a very low minimum detectable activity (MDA). An MDA for 90 Sr of *150 lbq L -1 may be obtained with this method using a 40 L seawater sample aliquot, counting 1,000 min with gas flow proportional counting. Following the pre-concentration of 90 Y from the seawater, DGA Resin is used to rapidly separate 90 Y from seawater samples and remove additional beta interferences. Gas flow proportional counting, liquid scintillation or Cerenkov counting may be used to count the purified 90 Y and determine 90 Sr present in the seawater sample. This new sample preparation method takes \8 h. Keyword Rapid Seawater Sr-90 Radiostrontium Fission products Ocean studies Introduction 90 Sr (t 1/2 = 28.9 years), is an artificial radionuclide added to the marine environment in the last several decades mainly as a result of atmospheric nuclear weapons testing in the 1950s and 1960s. In addition, there have been direct S. L. Maxwell (&) B. K. Culligan J. B. Hutchison R. C. Utsey Savannah River National Laboratory, Building 735-B, Aiken, SC 29808, USA sherrod.maxwell@srs.gov D. R. McAlister PG Research Foundation, Inc., Lisle, IL 60532, USA releases into the sea from nuclear reprocessing facilities. 90 Sr has a long environmental half-life and a high radiotoxicity, following calcium in the food chain into bones. Exposure to the 90 Sr beta particle (0.546 MeV) as well as exposure to 90 Y beta particles (2.2 MeV) resulting from the decay of its short-lived 90 Y daughter, make the presence of 90 Sr in the environment a significant health concern [1]. The nuclear accident at Fukushima Nuclear Power Plant in March, 2011 reemphasizes the need for rapid methods which can be applied to environmental samples resulting in high chemical yields and effective removal of interferences. Recently, there were questions about the measurement reliability of 90 Sr in seawater samples related to the Fukushima Daiichi release [2]. The use of rugged, reliable methods to ensure high quality measurements and to maintain the public trust is essential. Many seawater methods seem to use older, more tedious sample preparation steps or need improvements in chemical yield. Older methods which use very large cation exchange columns and/or multiple precipitations, for example, have a very low sample throughput [3, 4]. Other methods employ fuming nitric acid to precipitate Sr from seawater. Fuming nitric acid not only presents safety and handling difficulties but methods using Sr(NO 3 ) 2 precipitation can be very tedious and time-consuming [5]. An additional precipitation step to remove barium as barium chromate may also be required and chemical yields for Sr can be *40 60 %. Other methods collect 90 Sr from seawater, allow 90 Y ingrowth and then collect the 90 Y using cation resin or HDEHP [Di-(2-ethylhexyl) phosphoric acid] solvent extraction [3]. A new rapid method was reported recently from this laboratory to determine 89 Sr and 90 Sr in seawater samples [6]. The new method allows rapid pre-concentration and

2 separation of strontium and yttrium isotopes in seawater samples for measurement. The new method employs a preconcentration step that utilizes a blend of calcium phosphate with iron hydroxide to collect 89 Sr and 90 Sr rapidly from the seawater matrix with enhanced chemical yields. 89 Sr and 90 Sr can be precipitated from seawater samples up to 6 L and then purified using Sr Resin. A Minimum Detectable Activity (MDA) of 1 10 mbq L -1 for 89 Sr and 90 Sr can be achieved, depending on count times using gas flow proportional counting. However, the stable strontium content in seawater (*8 mgl -1 ) limits the sample aliquot size when Sr Resin is used. Another option to determine 89 Sr and 90 Sr, especially if high levels of 89 Sr are present is to rapidly measure the total 89 Sr? 90 Sr activity, wait 1 10 days for 90 Y ingrowth, and collect and purify 90 Y using DGA Resin to determine 90 Y, and thus 89 Sr and 90 Sr, respectively. This approach, unlike column re-pass methods using Sr Resin after 90 Y ingrowth, eliminates any risk of high levels of 89 Sr bleeding through Sr Resin into the 90 Y fraction. A 90 Sr only method using DGA Resin was also reported, with collection from 10 L of seawater. This method had high chemical yields ([90 %), but still used the calcium phosphate/iron hydroxide approach and utilized a combination of 2 L aliquots using a 2 ml DGA Resin cartridge with each 2 L aliquot to total 10 L. While the chemical yields were high and this pre-concentration approach collected the 90 Sr parent along with the 90 Y daughter, this method was limited to *10 L of seawater. There is a need to measure 90 Sr in seawater samples at levels lower than 1 mbq L -1.A 90 Sr ( 90 Y) method rapidly collecting 90 Y from larger aliquots is therefore still needed. Butkalyuk et al. [7] reported an approach in which 90 Y was collected from 1 L seawater samples using rare earth fluoride columns, with lead sulfide column being used to remove 210 Bi, followed by Cerenkov counting. The method seemed to be limited to 1 L seawater aliquots. Other methods precipitating Sr and Y from larger seawater aliquots utilize oxalate or other precipitation methods. For these types of methods, chemical yields may be *50 60 % and the methods are typically not very rapid. The seawater matrix offers significant sample matrix challenges due to the high salt content, in particular, the stable strontium (*8 mgl -1 ), calcium (*400 mg L -1 ) and magnesium (*1,300 mg L -1 ) ion content. A new rapid method for actinides in seawater was reported by this laboratory using iron/titanium hydroxide co-precipitation combined with lanthanum fluoride preconcentration steps to remove the seawater matrix and achieve high chemical yields [8]. This method allows the use of large amounts of iron and titanium ions to effectively control valence and collect actinides with high chemical yields. The method removes the iron and titanium with the lanthanum fluoride step, resulting in a very small precipitate containing the actinides to be processed further. A new method to rapidly collect and purify 90 Y was developed at SRNL for seawater aliquots up to 40 L to allow the determination of 90 Sr. In a similar way, 90 Yis rapidly co-precipitated from the seawater sample using an iron hydroxide co-precipitation step, followed by a lanthanum fluoride matrix removal step to remove the iron and other matrix components. DGA Resin is used to purify the 90 Y using rapid flow rates and vacuum box technology. DGA Resin has an extremely high affinity for 90 Y[9] and it has been used previously to effectively purify 90 Y[6]. The level of stable yttrium is typically very low (*9 ngl -1 seawater) but increases with ocean water depth [10]. This level of yttrium would not have a significant impact on the stable yttrium carrier added as a yield monitor. Although samples collected from deeper ocean waters will typically be higher in stable yttrium, an adverse impact on chemical yield is still not expected. An ICP-MS measurement of yttrium in the seawater samples, however, may easily be performed to confirm there is no significant impact on the yttrium tracer yield. Experimental Reagents DGA Resin (N,N,N 0,N 0 tetraoctyldiglycolamide) cartridges were obtained from Eichrom Technologies, Inc., (Lisle, Illinois, USA). Nitric, hydrochloric and hydrofluoric acids were prepared from reagent-grade acids (Fisher Scientific, Inc., Pittsburgh, PA, USA). All water was obtained from a Milli-Q2 TM water purification system. All other materials were ACS reagent grade and were used as received. The radiochemical isotope 90 Sr was obtained from Eckert & Ziegler Analytics, Inc. (Atlanta, GA, USA) and diluted to the appropriate level. Lanthanide solutions used in column elution and batch uptake studies were prepared from metal oxides ([99.9 %) purchased from Strem Chemicals (Newburyport, MA, USA). 241 Am, 244 Cm, 252 Cf and 147 Pm used in column elution and batch uptake studies were obtained from Isotope Product Laboratories (Valencia, CA, USA). Lanthanide elements were measured using microwave plasma atomic emission spectrometry (MP-AES, Agilent 4100). 241 Am was measured on a Packard Cobra Autogamma Sodium Iodide detector. 241 Am, 244 Cm, and 252 Cf were measured on a Packard Tricarb 2250 TR/AB liquid scintillation counter with Ultima Gold LLT scintillation cocktail.

3 Procedures Column preparation DGA Resin was obtained as cartridges containing 2 ml of each resin from Eichrom Technologies, Inc. Small particle size ( lm) resin was employed, along with a vacuum box extraction system (Eichrom Technologies). Apparatus Seawater Sample Acidify to ~ph 2 with 12M HCl (1 ml per L) Add stable Y carrier (1mg) Add 10 mg La to each aliquot. Add Fe (50 mg per L). Mix, add 14.5 M NH 4 OH (1.75mL per L), mix, allow to settle, pour off supernate to ~2-4L (ph= ) Transfer to four 500 ml centrifuge tubes Centrifuge 10 minutes, discard supernate. Rinse each ppt. with 100 ml water (ph ). Mix, centrifuge and discard supernate. Add 100 ml 1.5M HCl to one tube, redissolve and transfer to 2 nd tube, rinse first tube 2-3 times with 20 ml 1.5M HCl, Cap and mix Add 75 mg Ca and 50 ml 28M HF, mix, and allow to sit ~15 min. Centrifuge and discard supernate. Redissolve in 10 ml 3M HNO M Boric acid, 10 ml 15.8M HNO 3, 10 ml 2M Al(NO 3 ) 3 Column Load Solution Fig. 1 Rapid sample preparation method for 90 Sr in seawater Polycarbonate vacuum boxes with 24 positions and a rack to hold 50 ml plastic tubes were used. Two boxes were connected to a single vacuum source by using a T-connector and individual valves on the tubing to each box. A large volume vacuum box liner was used to collect rinses to eliminate having to change out 50 ml tubes during the load and rinse steps. Sample preparation Seawater samples were obtained from Isle of Palms, South Carolina, USA. In addition, synthetic seawater samples were prepared using CoraLife Marine mix [11]. This scientific grade salt mix is formulated to replicate natural seawater chemistry. Measurements with inductively-coupled plasma mass spectrometry (ICP-MS) confirmed that the Na, Mg, Ca and K levels in the synthetic seawater were approximately 6,835, 1,031, 415 and 356 mg L -1 respectively. Figure 1 shows the sample preparation to collect 90 Y from 10 to 40 L seawater aliquots. Yttrium carrier (1 mg) was added to determine chemical yield. 10 mg of lanthanum (La) was added to each sample aliquot regardless of aliquot volume. The addition of La enhances the recovery of yttrium during the ferric hydroxide precipitation and subsequently during co-precipitation with LaF 3. The addition of La, however, is limited to 10 mg so that separation of Y on DGA Resin is not adversely impacted. 50 mg of iron is added per liter of sample. After an initial iron hydroxide precipitation at ph * , the iron hydroxide precipitate was collected in four 500 ml centrifuge tubes, and each precipitate was rinsed with 100 ml of water (ph of ). The use an initial ph of * and a water rinse (ph ) facilitates removal of calcium. A 40 L aliquot of seawater is very high in calcium ions, containing approximately 16 g of calcium. After centrifuging again and pouring off the water rinse, the iron hydroxide precipitate in one of the tubes was dissolved in 100 ml 1.5 M HCl and transferred from tube to tube to combine into a single 500 ml centrifuge tube. Three volumes of 20 ml 1.5 M HCl were used to rinse each tube, so that the sample aliquot was moved quantitatively to the last tube. After the dissolved iron hydroxide was combined in a single centrifuge tube, 75 mg Ca and 50 ml HF were added to precipitate (Y/La) F 3. Ca was removed using ph control during the iron hydroxide precipitation. By adding back 75 mg Ca, the effectiveness of the LaF 3 co-precipitation was enhanced. The LaF 3 step removes the large amount of iron present, so that a very small precipitate is obtained. The LaF 3 precipitate was dissolved in 10 ml 3 M HNO M boric acid, 10 ml 15.8 M HNO 3 and 10 ml 2 M Al(NO 3 ) 3. The solution results in a column load solution of about 8 M total nitrate. The method assumes that the 90 Y daughter (t 1/2 = 64 h) is in equilibrium with 90 Sr in seawater. The point at which 90 Sr is removed and 90 Y is assumed to be unsupported is at the water rinse step of the iron hydroxide precipitate. Figure 2 shows the rapid DGA Resin separation using a 2 ml DGA Resin cartridge. The sample is loaded and 90 Y is collected on DGA Resin at *1 ml min -1 (1 drop

4 Fig. 2 Rapid column separation method for 90 Yin seawater sec -1 ). Ca, Sr, and Pb isotopes are removed further during the 8 M HNO 3 rinse step, while La carrier is removed using the 0.05 M HNO 3 rinse step. Bi isotopes are also removed using DGA Resin, as Bi isotopes are retained on the resin during the nitric acid rinses and also during the 0.25 M HCl elution of yttrium. U and Th isotopes are removed from DGA Resin using 3 M HNO M HF rinse steps, and Ca, La and Pb are also removed with the 3 M HCl rinse. The application of this method is not designed for use when significant amounts of fission products are present following a radiological accident, because of the interference of 91 Y. Figure 3 shows that DGA Resin has a very low k 0 for La in 0.05 M HNO 3.Thek 0 for Ce is higher than La in 0.05 M HNO 3, but is still relatively low. Cerium isotopes, such as the fission product 144 Ce (t 1/2 = days), might still be present even after 91 Y has decayed due to its longer halflife. Most of the Ce isotopes are removed along with La using the 0.05 M HNO 3 rinse on DGA Resin. The k 0 values were measured using the batch extraction procedure and calculations described in reference [9]. Figure 4 illustrates that if a more robust removal of cerium or other light rare earth isotopes are needed, an enhanced removal step using M HCl (instead of the 3 M HCl rinse) may be used prior to elution of yttrium. This rinse is not typically needed since the application of this method is for seawater samples where 91 Y would not be present from a fission event and interfere. This more

5 Fig. 3 Retention of rare earth elements on DGA resin 10 3 k' on DGA Resin vs HNO µm, 2 h, 21(1) o 3 C Gd Eu 10 3 k' on DGA Resin vs HCl µm, 2 h, 21(1) o C Sm 10 2 Pm Cm Am Nd 10 2 k' Pr k' Ce La Sc Y Sm Cm Pm Am Nd Pr Ce La [HNO 3 ], M [HCl], M Fig. 4 Elution of rare earth elements on DGA resin ppm or cpm La Pr Ce Elution on DGA Resin 2mL cartridge, µm, 21(1) o C, 2mL/min Nd 2.0M HCl Am La >99% Ce >99% Pr >99% Nd >99% Am 88% Pm 0.025M HCl Gd Eu Sm Pm 59% Sm 91% Eu >99% Gd >99% Am 12% Bed Volumes robust rinsing has been used, however, when 90 Sr is purified and 91 Y is removed immediately, and then 90 Y is collected and purified on DGA Resin after in-growth [6]. In that case, when isotopes such as 147 Nd, 141 Ce, 144 Ce might be present at high levels after a radiological event, these isotopes may be removed with 1.75 M HCl. The chromatogram in Fig. 4 is a composite of three separate elution curves on 2 ml DGA Resin cartridges loaded with 250 lg of La, Ce, Pr, Nd, Gd, Eu and Sm in 10 ml of 2 M HNO 3, rinsed with 20 ml of 2 M HCl and stripped with 20 ml of M HCl. The first elution curve contained only La, Ce, Pr, Nd, Gd, Eu and Sm, which

6 Fig. 5 Am, Cm and Cf retention on DGA resin k' on TODGA Resin vs. HCl µm, 1 h contact time, 22(1) o C 10 6 k' on TODGA Resin vs. HNO µm, 1 h contact time, 22(1) o 3 C Cf(III) Cm(III) k' 10 3 k' 10 3 Am(III) 10 2 Cf(III) 10 1 Cm(III) 10 0 Am(III) [HCl], M [HNO 3 ], M were measured by MP-AES. 241 Am and 147 Pm, respectively were added to the stable rare earth solution to generate the second and third elution curves. 241 Am was determined by counting on a Packard Cobra Autogamma sodium iodide detector. 147 Pm was determined by liquid scintillation counting on a Packard Tricarb 2250 TR/AB using Packard Ultima Gold LLT scintillation cocktail. Although not included in this elution study, previous testing [8] has shown that Am and Cm behave in a very similar way on DGA Resin. Figure 5 also illustrates that Am and Cm retention on DGA Resin are very similar, with californium (Cf) having slightly higher retention under the conditions shown. After 90 Y elution from DGA Resin using 0.25 M HCl in this seawater method, a small volume of the final purified eluent was taken for ICP-MS assay to determine the chemical yield of the stable Y. A Perkin Elmer DRC-e (using standard ICP-MS mode) was used to perform the stable Sr and Y measurements. Instrument operating conditions are shown in Table 1. Cerium fluoride microprecipitation was used to prepare the purified samples for gas flow proportional counting by adding 100 lg Ce and 2 ml 28 M HF to the 90 Y eluent solution. After waiting 15 min, the solution was filtered using a 25 mm polypropylene filter (disposable Resolve TM filter funnel, Eichrom Technologies, Inc.). Each tube was rinsed with *5 ml deionized water, followed by ethanol to facilitate drying. The filters were heated briefly under a heat lamp to ensure dryness. If liquid scintillation counting (LSC) or Cerenkov counting is desired, the purified eluent can be evaporated to dryness or near dryness, redissolved in a very dilute HNO 3 or HCl solution. The redissolved sample can be transferred to a liquid scintillation vial with scintillation cocktail added for LSC counting or without scintillation cocktail for Cerenkov counting. In this work, however, gas flow proportional counting was used to demonstrate the method with the counting technique capable of the lowest MDA. Results and discussion Table 2 shows the measured values for the determination of 90 Sr ( 90 Y) in a set of seven seawater samples. The seawater aliquot volumes vary between 10 and 40 L, spiked with 90 Sr standard, using the rapid DGA Resin method and gas flow proportional counting. The average Y carrier yield was 84.2 ± 6.8 % at 1 SD (standard deviation), and 90 Y results were corrected for the Y carrier yield. The average bias for the seven 90 Sr measurements was -0.3 %, with 1 SD of 2.9 %. Sample 3, which had a slightly lower chemical yield of *72 %, had some undissolved solids in the DGA Resin column load solution. Without this one lower yield, the overall average yttrium chemical yield increased to *87 %. The uncertainties for the individual 90 Sr results were typically ±6 8 % (1 SD), with a 2 h count time. The high Y carrier recoveries and excellent results for 90 Sr versus known values indicate the sample preparation and measurement steps were very effective. The L sample preparation can be performed in \8 h. Samples may be counted for much longer count

7 Table 1 Operating conditions for Perkin Elmer Elan DRC-e Plasma conditions RF power 1,400 W Torch depth 5.5 mm Plasma gas 15 L/min Carrier gas 1 L/min Nebulizer gas 0.98 L/min Sample pump 5 rps Ion lens/quadrupole E1 lens voltage 6.25 V E1 lens slope E1 lens intercept Cell path voltage -12 CPV Cell rod offset -17 V Q-pole Rod offset -4V Detector Discriminator 17 V Analog HV -1,550 V Pulse HV 900 V Typical tune Counts [300,000 cps In-115 at 10 ug/l RSD % \5 % Oxide 156/140 \5 % Background \10 cps at Mass 220; \10 cps at Mass 8.5 (vacant mass - noise detection only) Resolution amu at 10 % peak height Data acquisition Integration 1,000 ms Dwell time 50 ms Replicates 3 with 20 sweeps/reading times to lower MDA. This is feasible with gas flow proportional counters using a drawer system that allows simultaneous counting of up to 12 samples. A recount may be needed to verify the 90 Y decay profile, when 91 Y (58.5 day half-life) could be encountered. The MDA (Minimum Detectable Activity) for 90 Sr using this method with gas flow proportional counting was calculated according to equations prescribed by Currie: [12] MDA ¼ ½2:71 þ 4:65 p B Š= ðct R V Eff 0:060Þ where B is the total background counts is the BKG (rate) * sample count time, CT is the sample count time (min), R is the chemical recovery, V is the sample aliquot (L), EFF is the detector efficiency, is the conversion from dpm to mbq. Figure 6 shows MDA plotted versus sample aliquot size for a 240 min count time using *58 % efficiency gas flow proportional detectors and *90 % chemical yield, with an assumption of 1.5 cpm (counts per minute) average background count rate. Figure 7 shows how the MDA varies with count time with a 40 L sample aliquot. An MDA of *150 lbq L -1 can be achieved for 40 L sample with a 1,000 min count. The method provides very rapid measurements for 90 Sr by collecting and purifying 90 Y from 40 L seawater aliquots. The faster throughput for seawater processing and analysis can result in labor cost and waste handling cost savings versus older solvent extractant methods. The enhanced chemical yields and robust removal of interferences make very low detection limits possible for a very difficult sample matrix. This new sample preparation approach using iron hydroxide coupled with lanthanum fluoride matrix removal, successfully used to assay actinides in seawater [9] and now 90 Sr ( 90 Y) in seawater could have important applications for other high salt content liquids. For example, this approach would likely have benefit in the analysis of uranium and thorium in hydraulic Table 2 Results for spiked seawater samples Sample ID Sample aliquot (L) Y carrier (%) 90 Sr reference value (pcil -1 ) 90 Sr reference value (mbq L -1 ) 90 Sr measured value (mbq L -1 ) Difference (%) Avg SD % RSD 8.1 Y carrier by ICP-MS 2 h count time

8 Fig. 6 MDA by gas flow proportional counting versus sample aliquot size 1,400 1,200 MDA(µBq/L) for 240 min Count Time vs. Sample Volume (L) Assumes a Detector Background of 1.5 cpm 1,000 MDA (µbq/l) Sample Volume (L) Fig. 7 MDA by gas flow proportional counting 40 L aliquot versus count time MDA(µBq/L) for 40L Aliquot vs. Sample Count Time (min) Assumes a Detector Background of 1.5 cpm 400 MDA (µbq/l) Count Time (min) fracturing liquids used in the shale oil and gas industry [13]. While a small batch of samples can be processed quickly (\8 h), larger number of samples in a batch may require additional sample preparation time. It should be noted that 90 Y decay is about 1 % per hour from the point at which 90 Sr is removed. For example, after 12 and 24 h, 90 Y has decayed to about 88 and 78 % of its secular equilibrium value, respectfully. This decay must be factored into activity calculations and delays should be minimized. Fortunately, the sample processing from the point of 90 Sr removal using rapid preconcentration with vacuum-assisted DGA Resin separation, is very fast, minimizing 90 Y decay. The drawer system gas flow proportional counters allow simultaneous counting of samples, unlike sequential systems. This represents a significant improvement over older methods which require more time-consuming separation steps to collect 90 Y and only allow for sequential measurements.

9 Conclusions A new method to determine 90 Sr in seawater samples has been developed that allows the rapid separation of 90 Yin seawater samples up to 40 L with effective removal of interferences. The method uses Fe(OH) 3 coprecipitation followed by a LaF 3 matrix removal step. The sample preparation method takes\8 h and provides high chemical yields. An MDA as low as *150 lbq L -1 can be achieved using this method for seawater samples with a 1,000 min count time. An MDA of *300 lbq L -1 can be obtained with a 240 min count time. Acknowledgments This work was performed under the auspices of the Department of Energy, DOE Contract No. DE-AC09-96SR The authors wish to acknowledge Staci Britt, Phil Demaere, Jack Herrington and Becky Chavous for their assistance with this work. References 1. National Council on Radiation Protection and Measurements (NCRP) (2008) Management of persons contaminated with radionuclides. Report No. 161, vols 1 & 2. Available for purchase at 2. TEPCO (2014) Admits to record level of Strontium-90 in water last July. Accessed 5/12/ Borcherding J, Nies H (1986) An improved method for the determination of 90 Sr in large samples of seawater. J Radioanal Nucl Chem 98(1): Shipman W (1966) Determination of Strontium-90 in seawater after concentration by manganese dioxide. Anal Chem 38(9): Yang HS, Hwang DW, Lee HP, Kim G (2002) Distribution of 90 Sr in coastal seawater, sediments and organisms off two atomic power stations in Korea. J Environ Radioact 59: Maxwell S, Culligan B, Utsey R (2013) Rapid determination of radiostrontium in seawater samples. 298(2): Butkalyuk P (2009) Rapid determination of Sr-90 in seawater. Mosc Univ Chem Bull 64: Maxwell S, Culligan B, Hutchison J, Utsey R, McAlister D (2014) Rapid determination of actinides in seawater samples. 300: Horwitz P, McAlister D, Bond A, Barrans AB Jr (2005) Novel extraction chromatographic resins based on tetraalkyldiglycolamides: characterization and potential applications. Solv Extr Ion Exch 23(3): Zhang J, Nozaki Y (1996) Rare earth elements and yttrium in seawater: ICP-MS determinations in the East Caroline Coral Sea, and South Fiji basins of the western South Pacific Ocean. Pergamon Geochimica et Cosmochimica Acta 60(23): Coralife marine salt mix. duct/marine-salt/. Accessed Currie LA (1968) Limits for qualitative and quantitative determination. Anal Chem 40: Natural gas extraction-hydraulic fracturing. hydraulicfracturing. Accessed

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