Article pubs.acs.org/ac
Emergency Radiobioassay Method for Determination of 226 Ra in a Spot Urine Sample
90
Sr and
Baki B. Sadi,*,† Allison Fontaine,‡ Daniel McAlister,§ and Chunsheng Li† †
Radiation Protection Bureau, Health Canada, 775 Brookfield Road, A.L. 6302D, Ottawa, ON K1A 1C1, Canada Department of Chemistry, Carleton University, 1125 Colonel By Drive, Ottawa, ON K1S 5B6, Canada § Eichrom Technologies LLC, 1955 University Lane, Lisle, Illinois 60532, United States ‡
S Supporting Information *
ABSTRACT: A new radiobioassay method has been developed for simultaneous determination of 90Sr and 226Ra in a spot urine sample. The method is based on a matrix removal procedure to purify the target radionuclides from a urine sample followed by an automated high performance ion chromatographic (HPIC) separation of 90Sr and 226Ra and offline radiometric detection by liquid scintillation counting (LSC). A Sr-resin extraction chromatographic cartridge was used for matrix removal and purification of 90Sr and 226Ra from a urine sample prior to its introduction to the HPIC system. The HPIC separation was carried out through cation exchange chromatography using methanesulfonic acid (75 mM) as the mobile phase at 0.25 mL/min flow rate. The performance criteria of the method was evaluated against the American National Standard Institute ANSI/HPS N13.30-2011 standard for the root mean squared error (RMSE) of relative bias (Br) and relative precision (SB) at two different spiked activity levels. The RMSE of Br and SB for 90Sr and 226Ra were found to be satisfactory (≤0.25). The minimum detectable activity (MDA) of the method for 90Sr and 226Ra are 2 Bq/L and 0.2 Bq/L, respectively. The MDA values are at least 1/10th of the concentrations of 90 Sr (190 Bq/L) and 226Ra (2 Bq/L) excreted in urine on the third day following an acute exposure (inhalation) that would lead to an effective dose of 0.1 Sv in the first year. The sample turnaround time is less than 8 h for simultaneous determination of 90Sr and 226Ra.
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In traditional urine radiobioassay methods (for internal dose assessment for occupational exposure), a 24-h urine sample (1200−1600 mL) is subjected to wet digestion to mineralize the radionuclides, coprecipitation to separate and preconcentrate them from the urine matrix, and further purification of target radionuclides by chromatography or solvent extraction.5−8 In an R/N emergency, it will be more effective to collect a spot urine sample (50−100 mL) rather than a 24-h collection. To reduce sample preparation time, recent efforts have focused on using a spot urine sample and employing preconcentration via streamlined coprecipitation without any wet digestion, followed by separation and purification using radionuclide selective multiple stacked extraction chromatographic cartridges/columns.9−13 Rapid radiobioassay methods have also been developed in which initial wet digestion and coprecipitation steps have been eliminated, and smaller volumes ( Ra > Sr (in perchloric acid). An application for preconcentration and subsequent separation of a standard mixture (50 mL) of 85Sr, 133Ba, and 223Ra on Sr-resin (2 mL cartridge) has been demonstrated in the Supporting Information (Figure S2) using dilute perchloric acid (0.5 M) as the load conditions. However, this loading condition is not suitable for a sample containing high concentrations of K+ due to its high resin capacity factor, k′ (Figure S1). The k′ values for uptake of Sr, Ba, and Ra ions on Sr-resin in 0.5 M perchloric acid for various concentrations of K ion is shown in Figure S3 of the Supporting Information. The typical excretion of K+ in human urine is 1.6−3.9 g/day (95% range).34 As indicated in Figure S3, the concentration of K+ in urine (>1 g/L; assuming a typical excretion of 1.4−1.6 L urine/day) would be high enough, so that, the matrix effect due to K+ would significantly reduce the uptake of 90Sr and 226Ra on Sr-resin. In order to find suitable loading conditions for urine samples on Sr-resin, the concentration of perchloric acid in the loading solution was varied from 0.5 to 5.0 M. After matrix removal (using various concentrations of perchloric acid as loading conditions), the samples were introduced to the HPIC system for separation of 90 Sr and 226Ra. The effect of the perchloric acid concentration (as loading conditions) on retention of 90Sr and 226Ra on Srresin is shown in Figure 3. As anticipated, at low concentrations of perchloric acid (0.5−1.0 M), less than 3% of 90Sr and 226Ra was recovered after HPIC separation and radiometric measurement, indicating minimal retention on Sr-resin under these loading conditions. However, the retention of 90Sr and 226Ra on Sr-resin was found to increase significantly (as indicated by % recovery) when the concentration of perchloric acid increased up to 3.0 M for 90Sr and up to 4.0 M for 226Ra. As shown in Figure 3, the optimum loading conditions for simultaneous retention of 90Sr and 226Ra on Sr-resin and subsequent matrix removal for a 50 mL urine sample was found to be 4.0 M perchloric acid. The recovery of 90Sr and 226Ra was about 85%.
peak broadening and increased separation time. To compensate for this, the concentration of the mobile phase was increased to 75 mM. The stationary phase for the preconcentration column (MetPac CC-1) was a macroporous vinylbenzyl/divinylbenzene copolymer (17 μm, particle diameter) covalently bonded with iminodiacetic acid functional groups.29 In order to determine the optimum loading condition for this system, a 40 mL solution of a mixture of known activity of 90Sr, 133Ba, and 226Ra in 0.1 M ammonium acetate prepared at various pH (3−6) was loaded on to the preconcentration column followed by their separation on the analytical column. Chromatographic separation of 90Sr, 133Ba, and 226Ra was not achieved at a pH below 5, as only 226Ra was retained on the preconcentration column while 90Sr and 133Ba passed through it. The chromatographic separation of 90Sr, 133Ba, and 226Ra at loading pH of 5 and 6 is shown in Figure 2. As shown in Figure 2,
Figure 2. High performance ion chromatographic separation of 90Sr, 133 Ba, and 226Ra at loading pH of 5 and 6.
separation of 90Sr, 133Ba, and 226Ra with quantitative recovery and adequate resolution were achieved at both pH 5 and 6. However, when the pH of the loading solution was 6, the separation time was somewhat longer (
