Automated ⁹⁰Sr Separation and Preconcentration in a Lab-on-Valve System at Ppq Level

AutoRad allows to characterize target radionuclides more effective and rapid than traditional sampling and laboratory analysis. The main advantage is the separation and online determination using flow scintillation counting fully automated. Thus, it allows the on-site determination of hard-to-measure radionuclides, such as strontium-90.

To begin the system preparation, connect the modular valve positioner exit port to the entry port of a radiation flow detector. Connect the trigger line constructed from a single board micro-controller to the radio flow detector. Connect the radio flow detector to a container of at least 10 milliliters of scintillator liquid with a high flash point.

Place a fresh glass-fiber filter in the column channel of the lab on-valve assembly. Ensure that the modular valve positioner is connected both to a waste container, and to the LOV assembly. Check the connections of the autosampler and the reagent and waste containers to the LOV.

Ensure that sufficient volumes of the liquid reagents are available, so that the liquid sampling tubing will remain submerged throughout the experiment. Confirm that the multi-syringe pump is equipped with a 10 milliliter glass syringe in a three-way syringe valve. Ensure that the in-valve position is connected to ultrapure water.

Connect the out position to the center channel of the LOV, via a 10 milliliter PTFE holding coil. Ensure that the autosampler is on, and load one or more 1.3 milliliter samples into the autosampler. Place a 1%nitric acid solution in the autosampler rack, to be used in the cleaning sequence.

Open the LOV system software. From there, open the autosampler software and initialize the autosampler. Then, confirm that the instrument communication ports are correctly assigned in the LOV software.

Initialize the software and open the method editor. Use the method editor to create a new sequence for system cleaning. In the cleaning method, first set the syringe valve position to in, to bypass the LOV.

Draw 10 milliliters of ultrapure water directly into the syringe at 90 milliliters per minute, or 1.5 million nanoliters per second. Then, set the syringe valve position to out, and flow the water through the holding coil directly to waste at 90 milliliters per minute. In the next step, draw three milliliters of ethanol into the holding coil, at three milliliters per minute.

Then, set the MVP to the detector coil. Inject the ethanol into the detector coil at three milliliters per minute as the final step. Save and run the cleaning sequence.

Prior to loading the resin, ensure that the 12 milligram per milliliter suspension of strontium-90 resin in ultrapure water is stirring in its container. To create the resin loading sequence, first set the system to draw three milliliters of the resin suspension into the holding coil, at three milliliters per minute. Set the MVP to waste, and load the resin into the column channel at 1.2 milliliters per minute.

Then, set the syringe valve to in, and draw nine milliliters of ultrapure water directly into the syringe, at 90 milliliters per minute. Flow the water through the holding coil, and the column channel to waste, at three milliliters per minute, to rinse residual resin onto the column. Save the resin loading method, and prepare a new method for the analysis.

In this sequence, first draw two milliliters of four molar nitric acid into the holding coil, at six milliliters per minute. Flow the nitric acid through the column to waste, at 1.2 milliliters per minute, to condition the column. Then, draw a 1.3 milliliter sample from the autosampler into the holding coil, at six milliliters per minute.

Load the sample onto the column at 1.2 milliliters per minute. Next, draw 0.5 milliliters of four molar nitric acid into the holding coil, at six milliliters per minute. Rinse the column with this nitric acid at 1.2 milliliters per minute, to elute matrix interferences.

Then, draw five milliliters of ultrapure water into the holding coil, at six milliliters per minute. Set the trigger for the radio flow detector to start the measurements. In the detector software, set the scintillation liquid flow rate to two milliliters per minute, and the dwell time to at least 10 seconds for the triggered measurements.

Then, in the method, set the MVP to the detector, and elute the sample into the detector coil with the ultrapure water at 1.2 milliliters per minute. Save the sequence. Create a new method for rinsing the column.

In this method, draw 0.6 milliliters of 1%nitric acid into the holding coil, at six milliliters per minute from the autosampler, followed by 0.6 milliliters of air at the same flow rate. Flush the liquid-air mixture directly to waste, at six milliliters per minute. Create another method for the resin replacement.

To dispose of the resin, first load 0.2 milliliters of ethanol into the holding coil, at three milliliters per minute. Rinse the column with the ethanol at 1.2 milliliters per minute. Then, flush 0.5 milliliters of ultrapure water through the column, at 0.45 milliliters per minute.

Set the MVP to the flush position to discharge the used resin directly to waste. Save the sequence when finished. Arrange the sequences in order, and run the sequences for each sample to evaluate the strontium-90 activity.

The experiment conditions were initially optimized by coupling the system to an ICPMS, and evaluating the elution profiles of the stable isotope strontium-86 as a surrogate for strontium-90. The relative standard deviation of the peak area was less than 4%for three repeated runs over the range of 10 to 120 picograms per gram. The lab-on-valve assembly was able to effectively separate strontium-90 in aqueous samples, with an overall recovery rate of about 70%The residence time of strontium-90 in the radio flow detector coil was 40 seconds.

Investigation into stop-flow techniques to extend the residence time, and therefore improve sensitivity, is ongoing. The dependence of the radio flow detector signal on strontium-90 concentration in aqueous samples was shown to be linear within the concentration range of interest. The derived detection limit was about 320 femtograms per gram, with a relative standard deviation of around 30%within the studied concentration range.

The analysis can be done in situ, and only takes ten minutes. AutoRad can provide valuable help in the field of nuclear decommissioning and environmental remediation.