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Split Flow Online Solid-phase Extraction Coupled with ICP-MS system for One-shot Data Acquisition of Quantification and Recovery Efficiency Makoto Furukawa, and Yoshitaka Takagai Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.analchem.6b03195 • Publication Date (Web): 04 Sep 2016 Downloaded from http://pubs.acs.org on September 20, 2016

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Analytical Chemistry

Split Flow Online Solid-phase Extraction Coupled with ICP-MS system for One-shot Data Acquisition of Quantification and Recovery Efficiency Makoto Furukawa†, ††, ††† and Yoshitaka Takagai*†, †††† † Cluster of Science and Technology, Fukushima University, 1 Kanayagawa, Fukushima 960-1296, Japan, ††Faculty of agriculture, University of Tokyo, 1–1-1 Yayoi, Bunkyo-ku, Tokyo 113–8657, Japan, ††† PerkinElmer Japan Co., Ltd., 134 Godo, Hodogaya, Yokohama, Kanagawa 240-0005, Japan, and †††† Institute of Environmental Radioactivity, Fukushima University. Online solid-phase extraction (SPE) coupled with inductively coupled plasma mass spectrometry (ICP-MS) is a useful tool in automatic sequential analysis. However, it cannot simultaneously quantify the analytical targets and their recovery percentages (R%) in one-shot samples. We propose a system that simultaneously acquires both data in a single sample injection. The main flowline of the online solid-phase extraction is divided into main and split flows. The split flow line (i.e., bypass line), which circumvents the SPE column, was placed on the main flow line. Under program-controlled switching of the automatic valve, the ICP-MS sequentially measures the targets in a sample before and after column preconcentration and determines the target concentrations and the R% on the SPE column. This paper describes the system development and two demonstrations to exhibit the analytical significance, i.e., the ultra-trace amounts of radioactive strontium (90Sr) using commercial Sr-trap resin and multi-element adsorbability on the SPE column. This system is applicable to other flow analyses and detectors in online solid phase extraction.

Introduction On-line solid phase extraction (SPE) coupled with ICP-MS or ICP-OES is an automatic hyphenation analytical system that measures various metallic species with high sensitivity, good repeatability, high-speed data provision, and very simple handling. Due to these advantages,1 2 coupled SPE–ICP-MS systems have been widely employed in many fields such as environmental science,1 nuclear energy,3 medical science,4 and pharmaceuticals5. In radionuclide analysis, the coupled system provides radiological protection to operators by suppressing the exposure dose. Therefore, this system is expected to be applied in the radioactivity monitoring6 and decommission7 of nuclear power plants. Quantification by SPE is affected by many factors such as coexisting ingredients and their concentrations, pH, temperature, the state of the adsorption surface, and viscosity, all of which disturb the distribution of the targets. Physical problems such as column clogging, column degradation and velocity fluctuations also disturb the target distributions. Therefore, the true quantitative values are calculated using the recovery percentage (R%), which accounts for these variations. Typical R% measurements can be acquired by several techniques. In one method, the analytical target concentrations are measured before the column treatment (i.e., original solution) and after the column preconcentration, and the R% is calculated as the ratio of the decrease.8,9 Otherwise, the addition and recovery method obtains the R% by preparing an original solution and a spiked solution, and calculating the differences between the target amounts in the two solutions. Another

method adds indicators that are chemically similar to the analytical targets into the sample (i.e., surrogate materials such as artificial isotopes), then measures the indicator concentrations before and after the column preconcentration. In this method, the decrease ratio defines the R% of the indicator, representing small amounts of analytical targets.10,11,12 However, adding artificial isotopes is unavailable in radiochemical analysis, because of the nature of the target. Thus far, the R%s of radionuclides are determined by adding large known quantities of the stable isotope to the sample, and measuring the concentrations before and after preconcentration of the stable isotope. The calculated R% of the stable isotope represents those of the radioisotopes (analytical targets). Unfortunately, the concentration of the spiked material (which is added as milligrams of stable isotope) vastly differs from that of the analytical targets (which present as femtograms of radioisotope). As the two concentrations differ by many orders of magnitude, they must be measured by different analytical instruments based on different principles. Radioactive strontium and its stable isotope are usually analyzed by a low-background alpha/beta counting system and atomic absorption spectrometry, respectively13. All of the above analyses require two or more individual measurements per sample solution. To enhance the precision and accuracy of the analysis and the efficiency of the procedures, the analytical targets and R% values should be simultaneously measured in a single sample injection. In particularly, online SPE–ICP-MS analyses could not ensure the R% because intermediates flowing through the flow-line are very difficult to measure.

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This paper presents a new split flow system for online solidphase extraction coupled with an ICP-MS system. The time lag required for pre- and post-SPE measurements in the ICPMS is introduced by an automatic valve, and the target amounts and R% values are simultaneously determined on the column. The proposed system is evaluated in two applications; 90 Sr radionuclide analysis and a rapid-scanning survey of the adsorption properties of multiple elements on the online SPE.

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and discharges to the drain. (6) The preconcentrated targets are eluted by the eluant and carried into the ICP-MS, which provides the characteristic transient signal profile (Figure 1 [C]). In this profile, peaks (7) and (8) are the signals from the split flowline (the original solution) and main flowline (the preconcentrated solution), respectively. Analytical targets with low concentrations are replaced with surrogate isotopes (stable or radioisotope). The m/z values of both analytical targets and surrogate materials are simultaneously measured by ICP-MS.

Experimental Instruments As the analytical system for 90Sr, we adopted the online solid phase extraction coupled to ICP-MS, as described in the previous literature.6 All experiments in this analytical system were performed at the optimized detection limit of 90Sr (10 Bq/L, or 1.9 pg/L for 10 mL injection). The reagents and their preparations are written in the Supporting Information (SI). In addition, the mass concentration of the nuclide (pg/L; ppq) was converted to activity concentration (Bq/L) as shown in SI. The measurement conditions of the ICP-MS and the stepprogram for the valve and pump system are included in Table S1, S2 and S3 in SI. The splitter and micro-volume mixer components of the split-line were obtained from GL Science Co. Ltd, Tokyo, Japan. The velocity of the solution in the tube was measured by TruFlo (Glass Expansion, Melbourne, Australia). The velocity was controlled by varying the tube diameters as follows. For Type A (split ratio; main:split ratio = 23:1), the internal diameters (IDs) of the solution feeder (main tube), split line, and internal standard solution feeder were 0.76, 0.13, and 0.19 mm, respectively. All of these tubes were peristaltic pump tubes made of polyvinyl chloride (PVC). Other flow tubes were constructed from fluorophenylalanine (PFA) tubing with an ID of 0.8 mm. Under this condition, the volume ratio between the main and split flows was 100:4. For Type B (split ratio; main:split ratio= 1:1), both the main and split flow lines were PVC tubes with an ID of 0.76 mm. One-shot data acquisition of target quantification and SPE recovery by the proposed system Figure 1 is a schematic of our proposed system. The split flowline was placed on the main flowline and connected to the front and back of the online SPE column. The split flowline bypasses the SPE column line, and the lab-on-valve controls the flow direction of the bypass end point (connection point at the back of the SPE column). Switching the automatic lab-onvalve channels the proper flowlines into the ICP-MS. The oneshot data acquisition system operates through the following steps (Figure 1 [A]): (1) the sample solution is injected from the injector and merges into the carrier solution in the main flowline. (2) Part of the sample solution diverts and flows into the two-way system (main and split flowlines). (3) In the main flowline, the objective elements (adsorbable elements) in the sample solution preconcentrate on the SPE column, and the unadsorbed elements discharge to the drain. (4) Meanwhile, the sample in the split flowline (without column treatment) directly enters the ICP-MS, where its targets are measured. Once the sample loading is complete, all flow lines (main and split) are washed with 20% HNO3 sol. The valve position then switches, altering the flowline as shown in Figure 1 [B]. (5) The divided carrier solution passes through the spilt flowline

Figure 1. Mechanism of the one-shot quantification of the concentrations and recovery percentages in the split-flow line system. Panel [A] schematizes the direct measurement of targets in the original solution and the targets condensed in the column: (1) sample is injected with the carrier; (2) sample is divided into two flowlines; (3) targets in the sample volume are preconcentrated (collected) in the column; (4) targets split are measured by the detector. Panel [B]: Measurement of the preconcentrated targets: (5) The valve position is switched, eluting the preconcentrated targets from the column with the eluate, while the branch-line is washed with elute or wash solution (6). Panel [C] shows the obtained transient signals. Peaks (7) and (8) are the signals from the branch and main lines, respectively. When the target has a very low concentration in the sample, such that the preconcentrated peak from the column is detectable but the peak from the branch is not, we spike the sample with surrogate materials and measure their m/z values.

8-channel flow design with double 4-way switching valves for the split flowline. Figure 2 shows the eight-channel flow map of the valve system (double 4-way switching valves). Panel [A] shows the initial position of the valve. In the Type A configuration, (see subsection Instruments), the sample solution was injected by peristaltic pumps (P1 and P2). The injection volume was controlled within the range 5–50 mL. Four percent of the total sample volume was diverted through the splitter into the split flowline. The flow rates of the samples into the main and split flowlines were 3.2 and 0.14 mL/min, respectively. After the column passage, the residues were discharged to the drain. Meanwhile, the eluate (H2O) and internal standard solution


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(ISTD; 5 ppb of indium sol. in 20v/v% HNO3) were fed by P2 at 3.2 and 0.25 mL/min, respectively. The ISTD solution was merged into the main flow via mixers. Here, the split sample was diluted total 26 times (v/v) with eluate (H2O) and ISTD in series. Finally, to prevent the memory effect caused by the highly concentrated stable isotope, the dilute solution was introduced to the ICP-MS at 3.6 mL/min. After the sample injection, the column and flowlines were cleaned with washing solution (20v/v% HNO3) for 50 s. Next, P1 was stopped by switching the automatic valve position (Figure 2 [B]). At this time, P2 directed the eluate (H2O) through the column at 3.2 mL/min, immediately eluting the preconcentrated Sr (both radiostrontium and stable Sr). The preconcentrated Sr was merged with ISTD and introduced to the ICP-MS at 3.6 mL/min. The ICP-QMS specific operational conditions are listed in Table S3 in the SI. In the Type B configuration, 10 mL of the sample was injected by P1, and 50% was diverted into the split flowline (recall that the split ratio is 1:1). The sample flow rate in both flowlines was 3.2 mL/min.

Figure 2. Eight-channel flow map of the lab-on-valve system (double 4-way switching valves) with a split-flow line system. Panel [A]: Initial position. (1) the sample solution is pulled by peristaltic pump #1 (P1) and divided into two lines by the splitter; (2) part of the sample passes through the column, which preconcentrates the targets; (3) the other portion passes through the splitline and mixes with the internal standard solution (ISTD); the solution is then measured by ICP-MS. Panel [B]: valve position switched for elution. (5) P1 temporarily stops while P2 flows the eluate and ISTD. (6) The targets on the resin are eluted with the eluant and mixed with ISTD, then measured by ICP-MS.

Quantification and calculation of R% The IS and IP represent the intensities of the target in the split flowline and the preconcentrated target, respectively. The intensity of the bypassed solution equaled that of the original sample solution before column treatment, and both intensities (IS and IP) increased with increasing amount of target. When the split volume (VS) is known, the target concentration in the original solution (CS) can be quantified from the calibration curve (internal standard method), which is preliminarily prepared by flowing the standard solution through the split flowline, and determining the linearity equation I = αC + β. Here,

α and β represent the slope and y-intercept (measurement background), respectively. The target concentration after the column preconcentration (CP) was quantified from another calibration curve, preliminarily prepared by eluting standard solution from the main flowline. The preconcentrated sample volume provided by the column (VP) was calculated from the peak width (retention time width) of the transient signal and the flow rate (see Figure S1 in SI). Specifically, VP was calculated as Vp = vp × (tF(P)-tS(P)), where vP is the flow rate in the main flowline, and ts and tF are the initial and final times of the target elution, respectively. The R% was then determined as R% = (CP × VP)/(CS × (V0-VS)) × 100 eq.(1), where V0 represents the injected volume and (V0-VS) means the volume into column. Here, Vs can be obtained by the calculation of the multiplication between the time width of splitline signal peak (s) and the actual flow-rate in split-line (mL/s) provided by flow meter.

Results and discussion Validity of split flow online SPE coupled with ICP-MS As a model for constructing the proposed system, we adopted the stable isotope of Sr. The signals profile of 88Sr at a split ratio of 1:1 is shown in Figure 3. The signal in region A was contributed by the split flowline. The divided 5 mL sample yielded a trapezoidal peak with a width of 100 s. The obtained peak width appropriately indicates the injection volume (3 mL/min). Although the solution in the split flowline was diluted twice with the eluate (H2O) to prevent the memory effect, the signal intensity was sufficient for evaluating the R% (i.e., 3.0 × 104 cps in 1.5 ng injection). The valve switched at 290 s on the profile, diverting the flowline of the connection to ICPMS from the split flowline to the main flowline. The preconcentrated sample in the column (main flowline) gave rise to the signal in region B, which appears as a chromatographic curve (Gaussian distribution) due to the elution from the column. The condensed peak was 15 s wide at the flow rate of 3 mL/min, so the eluted volume was 0.77 mL. At a split ratio of 1:1, the actual preconcentration factor in the SPE was calculated as 6.5 (5.0 mL → 0.77 mL), and the peak areas of regions A and B were equal (3.05 × 106). On the other hand, the calculated R% of commercial Sr resin was 97%, identical to that of the conventional method. In summary, the proposed method determined the sample quantification, the preconcentration factor and the R% in SPE in a one-sample injection.

Figure 3. Transient signal profile of 88Sr (m/z =88) using the proposed split-flow system with ICP-MS. Split ratio of main flow to split flow was 1:1. Injection sample was 10 mL of 300 ng/L Sr (stable isotope). Signal A presents the 88Sr signal from the splitline (representing the original sample solution), and signal B presents the preconcentrated 88Sr signal from the main flow, which passes though the solid extraction column.



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90

Application to radioactive Sr analysis In the first demonstration, the feasibility and analytical performance of the proposed parallel-split flow methodology was evaluated on radioactive 90Sr. In reported radiometric analyses of 90Sr (which are numerous), excess stable Sr isotope (ppm) is added to a sample solution containing ultra-trace amounts (several Bq/L, or sub-ppq levels) of radioactive 90Sr. The R% is then calculated from measurements of the stable isotopes and radioisotope on different appropriate instruments.14 Because of these different requirements, as far any articles have not reported the simultaneous measurement of 90Sr concentrations and R% values. In this demonstration, 10 mL of Srcontaining sample solution was injected into the Type A configuration (split ratio =23:1) of the proposed system. The transient signals originating from the split flowline are presented in Figure 4 [A]. The peak height was a sufficiently linear function of the concentration of surrogate (stable Sr) in the sample. The intensities of the peak profiles after column elution also linearly increased with stable isotope concentration (Figure 4 [B]). The SPE preconcentration factor was 12 (10 mL → 0.81 mL). The enrichment factor was calculated by passing 9.6 mL of the 10 mL sample into the column (diverting 4% into the split flowline). When 100 µg/L Sr was injected at 3.2 mL/min, the width of the preconcentrated peak was 15.3 s. Accordingly, the volume of the preconcentrated zone was calculated as 0.81 mL. From the ratio of the injection volume (9.6 mL) to the volume of the preconcentration zone (0.81 mL), the preconcentration factor was determined as 12.

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Figure 5 shows the 90Sr target signal eluted after the column. The 90Sr concentration was 1.2 kBq/L (0.24 ppt) in the presence of stable Sr isotope as surrogate (the transit signal of the stable isotope was similar to that of Figure 4). The 90Sr signal was a strongly linear function of the 90Sr concentration and the detection limit (3σ) was 10.8 Bq/L. This split flow system preserves the original sensitivity of the 90Sr analysis. In addition, the retention time of the 90Sr signal corresponded to that of the surrogates (Figure 4 [B]).

Figure 5. Quantifying the signal profile of 90Sr. Split ratio of main flow to bypass flow was 100:4. Injection sample was 10 mL containing 1.2 kBq/L radioactive 90Sr and natural isotope of Sr.

R% measurements in the presence of an interfering ingredient, and its application to quantitative correction The high Ba concentration in commercial Sr resin disturbs the Sr recovery.15,16,17 To demonstrate the correcting ability of our proposed method in the presence of Ba, we varied the Ba concentration from 0 to 100 mg/L (up to 3.3 × 105 times the Sr concentration of 300 ng/L). As shown in Table 1, the R% of Sr was successfully monitored at various inhibitor concentrations. In addition, when corrected by the R%, the original quantitative values were recovered and satisfactorily consistent with the initial added amount. Table 1 Monitoring of R% at various concentrations of inhibitor (Ba) and the correction approach.

Figure 4. Quantitative signal profiles of surrogate 88Sr in the oneshot sample injection (10 mL solution containing 1.2 kBq/L radioactive 90Sr plus various concentrations of Sr as the stable isotope). Split ratio of main flow to bypass flow was 100:4. Panel [A] indicates the 88Sr signal from the bypass-line. Inset plots the surrogate concentration versus intensity. Panel [B] presents the signal of preconcentrated 88Sr from the column; again, the intensities are a linear function of the stable isotope concentration (inset).

The profile behaviors were similar for 88Sr, 84Sr, and 86Sr. Therefore, we adopted 88Sr or 86Sr, which are much more abundant than 84Sr and 87Sr, as the surrogates in this study. The R%s obtained in the proposed and traditional methods are compared (as shown in Table S5 in SI). The recovery efficiencies of the two methods were comparable. In addition, the errors of value in the proposed method were the range from 0.8 to 3.4% (as shown in Table S4). The high performance of the proposed method stems from the simultaneous measurement before and after the column in the one-shot automatic analysis, which reduces the measurement errors. In addition, the proposed method completed the measurements in 10 min.

[Ba]T / mg L−1

Detected [Sr] / ng L−1

R% of Sr

Correction value/ ng L−1

Correspond spondence, %

0

285

95

299

100

0.5

278

93

283

94

1.0

175

62

281

94

5.0

49

17

290

97

10

26

9.0

288

96

Experimental conditions: Injection sample was 300 ng/L natural isotope of Sr. Split ratio of main flow to bypass flow was 100:4. The recoveries were calculated using eq.(1) in text.

Application to natural water To imitate radioactive-contaminated natural samples, we spiked spring water and rainwater (stagnant water) with 90Sr at 1.2 kBq/L, resembling the ground contamination level within the Fukushima Daiichi Nuclear Power Plant. The results are presented in Table 3. The concentrations of stable Sr isotope (natural) in the spring water and rainwater samples were 83


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and 0.47 µg/L, respectively, with respective R% values of 95.5% and 76.5%. The corrected quantitative values corresponded well with the spiked amount (1.2 kBq/L). These results confirm the efficacy of the proposed method in both target quantification and R% measurement (the comparison with conventional method was shown in Table S5 in SI). Table 2 Spike and recovery test on a sample.

90

Sr-contaminated

ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website at http://pubs.acs.org.

Corresponding Author *To whom correspondence should be addressed E-mail: [email protected]

Acknowledgment Sample Rain water

0

—

0

100

Rain water

1200

76.5

1195

99.6

Spring water

1200

95.5

1188

99.0

R%

Correction value / Bq L−1

Correspondence, %

Spiked / Bq L−1

Experimental conditions: [90Sr]Total = 1.2 kBq/L; total sample volume = 10 mL.

Evaluation of multi-element adsorption As a second demonstration, we applied the proposed system to the adsorpability of 52 elements on commercial resin in a one-shot survey. When synthesizing a new adsorptive material or using various packed materials, we must determine the multi-element adoptability properties of the materials to the target resins. In this demonstration, we used the commercial Sr and TEVA resins as models, and applied the helium collision method with a 10 mL sample injection and a split ratio of 1:1. The results are shown in Table S6 in the SI. The proposed method was compared with the traditional method, which measures the concentrations before and after the column treatment. Both datasets almost corresponded and were consistent with commercial data. The 52 element adsorpabilities on the resin were evaluated within 10 min in the one-shot sample, confirming that the proposed method rapidly acquires the adsorpability data of many elements in the preconcentrated online column. Such rapid data acquisition is desired in the environmental, medical, pharmaceutical, and material sciences.

Conclusion Split-flow online SPE was coupled to an ICP-MS system, and the data acquisition performance of the combined system was evaluated. The proposed system synchronously and speedily quantified the targets and computed the online SPErecovery percentage. To overcome the conventional problems in online SPE, the split flowline was placed on the main flowline (column line) and the automatic valve position was switched to the appropriate flowline, enabling continuous measurement before and after column pretreatment. The proposed system was applied to radioactive 90Sr radionuclide analysis and rapid adsorpability scanning of 52 elements on the online SPE. This split flow system rapidly quantified the analytical targets and determined the adsorpabilities of many elements on the proper SPE resin in a one-shot sample. In addition, the systematic error was lower in the proposed method than in the conventional method. This method is applicable not only to ICP-MS but also to other detectors, and can potentially expand and contribute to various disciplines relying on ultra-trace analysis.

The authors gratefully acknowledge funding by the Ministry of Education, Culture, Sports, Science & Technology in Japan (MEXT), Human Resource Development and Research Program for Decommissioning of Fukushima Daiichi Nuclear Power Station, and JSPS Grant-in-Aid for Scientific Research (B) (# 15H03842). In addition, we thank Dr. Yutaka Kameo, Dr. Kenichiro Ishimori, Mr. Kiwamu Tanaka, and Mr. Makoto Matsueda from Japan Atomic Energy Agency for experimental cooperation and useful discussions.

References (1) Das, D.; Dutta, M.; Cervera, M. L.; de la Guardia, M. TrA Trends Anal. Chem. 2012, 33, 35–45. (2) Liang, P.; Qin, Y.; Hu, B.; Peng, T.; Jiang, Z. Anal. Chim. Acta 2001, 440 (2), 207–213. (3) Truscott, J. B.; Bromley, L.; Jones, P.; Evans, E. H.; Fairman, B. J. Anal. At. Spectrom. 1999, 14, 627–631. (4) Sun, Y.-C.; Lu, Y.-W.; Chung, Y.-T. J. Anal. At. Spectrom. 2007, 22 (1), 77–83. (5) Moein, M. M.; Said, R.; Bassyouni, F.; Abdel-Rehim, M. J. Anal. Methods Chem. 2014, 2014. (6) Takagai, Y.; Furukawa, M.; Kameo, Y.; Suzuki, K. Anal. Methods 2014, 6 (2), 319–630. (7) Tokyo Electric Power Company. Start of introducing ICP‐MS method for analyzing water samples for Strontium; 2014. (8) Takagai, Y.; Akiyama, R.; Igarashi, S. Anal. Bioanal. Chem. 2006, 385 (5), 888–894. (9) Takagai, Y.; Igarashi, S. Anal. Bioanal. Chem. 2002, 373 (1-2), 87–92. (10) Lehto, J.; Hou, X. J. Chemistry and Analysis of Radionuclides; Wiley-VCH Verlag GmbH & Co. KGaA: Weinheim, 2011. (11) Kosarac, I.; Kubwabo, C.; Foster, W. G. J. Chromatogr. B. Analyt. Technol. Biomed. Life Sci. 2016, 1014, 24–30. (12) Patnaik, P. Handbook of Environmental Analysis: Chemical Pollutants in Air, Water, Soil, and Solid Wastes, Second Edition; CRC Press, 2010. (13) Lehto, J.; Xiaolin, H. In Chemistry and Analysis of Radionuclides: Laboratory Techniques and Methodology; Wiley-VCH Verlag GmbH & Co. KGaA, 2011; p 110. (14) Research and Development Bureau, Atomic Energy Division. Analytical methods of the radioactive strontium http://www.kankyo-hoshano.go.jp/series/lib/No2.pdf. (15) Philip Horwitz, E.; Chiarizia, R.; Dietz, M. L. Solvent Extr. Ion Exch. 1992, 10 (2), 313–336. (16) Horwitz, E. P.; Dietz, M. L.; Chiarizia, R. J. Radioanal. Nucl. Chem. Artic. 1992, 161 (2), 575–583. (17) Technologies, E. Sr Resin http://www.eichrom.com/products/info/sr_resin.aspx.



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Insert Table of Contents artwork here

Table 1 Monitoring of recovery percentages at various concentrations of inhibitor (Ba) and the correction approach using the proposed method. [Ba]T / mg L−1

Detected [Sr] / ng L−1

R% of Sr

Correction value/ ng L−1

Correspondence, %

0

285

95

299

100

0.5

278

93

283

94

1.0

175

62

281

94

5.0

49

17

290

97

10

26

9.0

288

96

Experimental conditions: Injection sample was 300 ng/L natural isotope of Sr. Split ratio of main flow to bypass flow was 100:4.


6

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Table 2 Spike and recovery test on a 90Sr-contaminated sample. Spiked / Correction valCorrespondR% Bq L−1 ue/Bq L−1 ence, % Rain water 0 — 0 100 Rain water 1200 76.5 1195 99.6 Spring water 1200 95.5 1188 99.0 Experimental conditions: [90Sr]Total = 1.2 kBq/L; total sample volume = 10 mL. Sample


7


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Figure 1. Mechanism of the one-shot quantification of the concentrations and recovery percentages in the split-flow line system. Panel [A] schematizes the direct measurement of targets in the original solution and the targets condensed in the column: (1) sample is injected with the carrier; (2) sample is divided into two flowlines; (3) targets in the sample volume are preconcentrated (collected) in the column; (4) targets split are measured by the detector. Panel [B]: Measurement of the preconcentrated targets: (5) The valve position is switched, eluting the preconcentrated targets from the column with the eluate, while the branch-line is washed with elute or wash solution (6). Panel [C] shows the obtained transient signals. Peaks (7) and (8) are the signals from the branch and main lines, respectively. When the target has a very low concentration in the sample, such that the preconcentrated peak from the column is detectable but the peak from the branch is not, we spike the sample with surrogate materials and measure their m/z values. 8


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Figure 2. Eight-channel flow map of the lab-on-valve system (double 4-way switching valves) with a split-flow line system. Panel [A]: Initial position. (1) the sample solution is pulled by peristaltic pump #1 (P1) and divided into two lines by the splitter; (2) part of the sample passes through the column, which preconcentrates the targets; (3) the other portion passes through the split-line and mixes with the internal standard solution (ISTD); the solution is then measured by ICP-MS. Panel [B]: valve position switched for elution. (5) P1 temporarily stops while P2 flows the eluate and ISTD. (6) The targets on the resin are eluted with the eluant and mixed with ISTD, then measured by ICP-MS.

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Figure 3. Transient signal profile of 88Sr (m/z =88) using the proposed split-flow system with ICP-MS. Split ratio of main flow to split flow was 1:1. Injection sample was 10 mL of 300 ng/L Sr (stable isotope). Signal A presents the 88Sr signal from the split-line (representing the original sample solution), and signal B presents the preconcentrated 88

Sr signal from the main flow, which passes though the solid extraction column.

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Figure 4. Quantitative signal profiles of surrogate 88Sr in the one-shot sample injection (10 mL solution containing 1.2 kBq/L radioactive 90Sr plus various concentrations of Sr as the stable isotope). Split ratio of main flow to bypass flow was 100:4. Panel [A] indicates the 88Sr signal from the bypass-line. Inset plots the surrogate concentration versus intensity. Panel [B] presents the signal of preconcentrated 88Sr from the column; again, the intensities are a linear function of the stable isotope concentration (inset).

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Figure 5. Quantifying the signal profile of 90Sr. Split ratio of main flow to bypass flow was 100:4. Injection sample was 10 mL containing 1.2 kBq/L radioactive

90

Sr and

natural isotope of Sr.

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Split Flow Online Solid-Phase Extraction Coupled ... - ACS Publications

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