Sample Preparation for Analytical Characterization

1. Making a Solution from a Solid

1. Choose the correct glassware to make solution.
2. Clean the glassware thoroughly via an acid bath of 1% HCl or HNO₃ along with soap to remove any impurities (safety warning: with any strong acid use gloves, goggles, and other appropriate personal protective equipment).
3. Rinse the glassware several times with distilled water. Dry in an oven if needed.
4. To make a solution from a solid, mass out the correct amount of solid.
5. Put the solid in the volumetric flask and then fill about ¾ full with solvent.
6. Swirl to fully dissolve the solid before filling the volumetric flask fully.
7. Fill the volumetric flask to the line. The meniscus should just touch the fill line. Then invert the flask several times with the cap on to further mix if necessary.

2. Making a Solution from a Liquid

1. Choose the correct glassware to make solution. To deliver a liquid using a transfer pipette, fill the pipette to the line using a pipette bulb.
2. Release the liquid into the volumetric flask for making the solution. Do not blow out the last drop.
3. Fill the volumetric flask to the line so the meniscus touches the line. Mix the solution by inverting several times.

3. Filtering

1. For a filter flask setup, place a piece of filter paper on the fritted glass filter.
2. Attach the fritted glass filter to a filter flask.
3. Attach a vacuum to the arm of the filter flask. A trap can also be used to prevent any liquid from going into the vacuum.
4. Turn on the vacuum and pour the sample through the filter paper.
5. Filter until a dry powder is left. Continue to dry the sample in an oven if a dry precipitate is desired.
6. To syringe filter, add the sample to a clean syringe with a Luer lock end.
7. Screw the syringe filter into the Luer lock. Push the plunger on the syringe and collect the liquid after the filter.
8. For a spin filter, pre-rinse the filter with buffer or ultrapure water.
9. Insert the spin filter into a microcentrifuge tube.
10. Load the sample on top of the filter and cap the tube.
11. Put the tube into a centrifuge, making sure to balance it properly with another tube on the other side, and centrifuge for 10–30 min, depending on the type of spin filter.
12. Remove the filter and the liquid in the bottom is the filtered solution.
13. If the sample cannot go through the membrane — such as a big protein — it will remain at the top of the filter. In this case, turn the filter over, put it in a new tube, and spin again. This will produce a concentrated sample.

4. Masking and Chelating

1. For masking and chelating, adjust the pH to an appropriate value depending on the formation constants of the masking agent and the chelating agent.
2. Add the masking agent to the solution and allow it to react for at least 10 min with the metal ion of choice.
3. Add the chelating reagent. For EDTA, it typically forms a 1:1 complex with the metal ion, so add as many moles of EDTA as metal that will be chelated.
4. After chelation, demask by adding a chemical that will react with the masked metal ion. The masked substance can then be analyzed or recovered by precipitation.