Question

TAE is a commonly used buffer for DNA el ectrophoresis. This buffer contains 40 mM Tris, 20 mM Acetate, 1 mM EDTA as the final concentrations. A 50X stock solution (50X the final concentration) is normally prepared. You have Tris powder (mol. wt. 121.14), glacial acetate acid (a liquid with a density of 1.05 g/mL and a mol. wt. of 60) and 0.5 M EDTA stock solution. You need to make up 1 Li ter of 50X TAE. How would you make it up? Please explain and provide correct answer.

Answer 1

TAE buffer is commonly prepared as a 50X stock solution for laboratory use. A 50X stock solution can be prepared by dissolving 242g Tris base in water, adding 57.1mL glacial acetic acid, and 100mL of 500mM EDTA (pH 8.0) solution, and bringing the final volume up to 1 liter.

you need 1 L with
50 x 40 mM Tris = 2 M Tris
50 x 20 mM acetate = 1 M acetate
50 x 1 mM EDTA =50 mM EDTA

2 moles Tris = 2 x 121.14 = 242.28 g
1 M acetate = 60 g of acetate = 60 / 1.05 = 57.14 mL

50 mmoles EDTA from a 500 mM solution are 100 mL
(50 mM is a 10 fold dilution of a 500 mM solution)