Ingredients

• agarose
• potassium chloride (KCl; MW = 74.54 g/mol)
• glass capillaries
• ethanol burner
• syringe

Procedure

1. Prepare bent capillary tubes. Alight an ethanol burner by dipping the wick in EtOH, e.g. filling a 1.5 ml tube (eppendorf) with ethanol and dipping the wick in it. Hover the capillary (at 1/3 of its length) over the fire and keep pushing on the short end with a pen until the capillary is bent at a right angle.
2. Prepare a 20 ml solution at 1% agarose. Weight 0.2 g agarose and dissolve it in 20 ml ddH2O in a 50 ml Falcon tube.
3. Weight the appropriate amount of KCl in order to achieve a final concentration of 3 M. I need:
   0.020 l x 3 mol/l = 0.06 mol KCl
   0.06 mol x 74.54 g/mol = 4.4724 = 4.47 g KCl

DO NOT ADD THE KCl TO THE AGAROSE SOLUTION BEFORE MICROWAVING THE AGAROSE!!! (COULD CAUSE SPARKS IF KCl IS MICROWAVED)

4. Microwave the agarose solution.
5. Add the KCl and dissolve it.
6. Aspire the solution with the syringe.
7. Fill bent capillary tubes with the solution. Tip: hold the connection between capillary and syringe in order to prevent the mixture from spilling around the capillary. Quickly dry capillaries. Trim the ends of capillaries with a diamond cutter.

Capillaries should not contain any bubbles.

Storage

Store the capillaries, i.e. agar bridges, at room temperature in a 3 M KCl solution.