Sr Chromatography Chemistry
Sr Sample prep/Dissolution
Supplies needed: Scale, weigh paper, dropper bottle of 3.5M HNO3, Savillex beaker, and a scope.
Place weigh paper on to the scale, after the scale has settled hit the tare button. Once you have tared the scale weight out between 2 to 5 mg of sample. If you do not have a lot of sample aim more for between 2-3mg. that way if you need to run the sample a second time you still have sample. If your samples are in powder, static electricity in the lab can make it difficult. An easy fix for this is to fill a few beakers with water and place them near the scale. Once this is complete gently reach into the scale and pick up the weigh paper. It helps if you fold the paper before putting it on the scale. Gently pour the sample into the Savillex beaker, and add 550 uL of 3.5M HNO3, this is around 15 drops from the dropper bottle. Cap and let stand overnight.
Supplies needed per sample: waste beaker, Dropper bottle of 3.5N HNO3, dropper bottle of MilliQ H2O, Dropper bottle of H3PO4, Sr spec resin bottle, water squirt bottle, columns.
The purpose of the Sr Chromatography chemistry is to separate the Sr cations from other metals in the sample. This is an on-off column, which means that unlike Nd columns there is no worry about timing the collect stage to capture the peak. The sample is dissolved in 3.5M HNO3, because at this molarity Sr strongly partitions to the resin while other metals do not. Figure 1 shows the distribution coefficient plotted against HNO3 Molarity (Chiarizia et al 1992). Note that at 3.5 molar is the D value for Sr is considerably higher, and that the D value for other cations is decreasing.
Figure 1. Weight Distribution coefficients for selected cations plotted against HNO3 molarity. At 3.5 Molar D values for other
Place you waste beakers on the bench in a line. The columns are stored in a dilute HNO3 container to keep clean. Using the blue plastic forceps pull one column out of the acid and rinse with MilliQ water so you can hold it in your hand. After you have rinsed the column use the milliQ squirt bottle to rinse the inside of the column. The start by squirting water in through the bottom of the column first until the skinny neck of the column is filled with water. Then flip the column over and fill the reservoir with water, and dump the water out. Repeat this step three times. Refill the column with water a fourth time and check that it is draining correctly and that there are no air bubbles in the neck of the column as this will cause the column to stop. Before the water drains from the reservoir, place the column on to the waste beaker and put resin into the column. It is important that you get the resin to the desired level before the water drains out of the reservoir, as this will result an air bubble in the neck which will prevent the column from functioning. The desired height of the resin bed is at top of the neck. This is important because if it is lower than the top surface tension will result in air bubbles being trapped on top of the resin each time that a liquid is put in the column. If you run into this problem the best method to correct it is each time that you put anything on the column is to use the 20-200 uL pipetter any suction out the air bubble.
The first part of the chemistry is a rinse using MilliQ water. This step will be done two times. Using the MilliQ squirt bottle fill the reservoir with water, don’t worry too much if the top of the resin bed is disturbed it will settle back out. The purpose of this rinse is to remove any residual Sr that may be in the resin. While Sr partitions to the resin when in a 3.5 Molar solution, Sr strongly partitions to water over the resin. During these water rinses it is helpful to prepare your samples to put onto the columns. The samples should be centrifuged to remove any solid particulate that maybe leftover after dissolution. Following centrifuge keep the samples upright in order to prevent any solid material from remixing with the sample.
After the water had completely drained the columns are preconditioned with 3.5 molar HNO3. Next the samples are loaded on to the columns using the 100-1000 um pippeter. When pippeting the sample out of the centrifuge tube start at the top of the sample and work your way down as you draw up the sample. Once you near the bottom make sure that you do not remove any solid material at the bottom of the centrifuge tube, as the solid material may interfere with the column.
Following sample loading you will do several rounds of bulk rinses with 3.5 Molar HNO3. The purpose of these rinses is to remove other Ions from the sample, while the Sr will remains in the resin. During the bulk rinses, it is helpful to prepare beakers for the collect stage. After the final bulk rinse ensure that all of the columns have completely drained. Uncap the clean Savillex beakers and place the columns over the beakers. During this stage of columns you will be collecting the Sr sample. The collection is done with milliQ water. After two rounds of collection, the column is removed and one drop of H3PO4 is added directly into the beaker and NOT through the column. After adding the H3PO4 place the samples uncapped on to the hotplate at ~160°C to dry down. The sample will dry down into a small brown or black bead at the bottom of the beaker. As a tip the samples tend to dry down faster if they are closer to the center of the hotplate. After dry down remove from hotplate and cap. The samples are now ready for loading.
After Columns are complete wash the columns out using MilliQ water. This is done the same way that set up, start by squirting the water in through neck of the column and dump into the sink. Do this three times for each column and then place in the dilute HNO3 bath. Dispose of the waste in the waste beakers in the HNO3 waster container and rinse the waste beakers with tap water and place next to sink to air dry. After this is completed wipe down all work stations with water and Kimwipe and make sure all supplies are put away in appropriate spot.