Preparación de buffer pH

[Jorge (Jorge G. Montesinos E.)]

I need the recipe to prepare the following pH electrode calibration buffers, from the corresponding salts:

• buffer pH 4.01 (biphthalate)
• buffer pH 7.00 (mixed phosphates)
• pH 6.86 buffer (mixed phosphates)
• buffer pH 9.01 (borate)
  Thanks in advance