This makes a litre of full-strength. I dilute an aliquot tenfold and use the diluted stock in making TAP

A) Dissolve 50g of acid free EDTA in 250 ml of ddH2O. Heat to dissolve.

B) Dissolve the following, one by one, in order, heating to approximately 100° in 550 ml ddH2O.

BO3H3 11.40 g
ZnSO4·7H2O 22.00 g
MnCl2·4H2O 5.06 g
FeSO4·7H2O 4.99 g
CoCl2·6H2O 1.61 g
CuSO4·5H2O 1.57 g
Mo7O24(NH4)6·4H2O
(Ammonium Molybdate) 1.1 g

Mix the two solutions (A & B) together. The resulting solution should be blue-green.
Heat to 100°C. Cool slightly, but don't let the temperature drop below 80°-90°.
Adjust pH to 6.5 to 6.8 with 20% KOH (approximately 83 ml). Don't let the temperature drop below 70 ° until after the pH is adjusted.
Make up to 1L and let stand in a 2L Erlenmeyer flask, stoppered loosly. The color should change from green to purple over a period of days.
Remove the rust-coloured precipitate by filtering, with suction, through 3 layers of Whatman #1 filter paper in a Buchner funnel. Repeat until no more precipitate is seen on the filter paper
Store in a brown bottle at 4°.