This would make a very poor buffer indeed. A good buffer consists for example of a salt of a strong base (like KOH or NaOH) and a weak acid (carbonic, phosphoric, phthalic, acetic, formic) with a strong base or acid added. For pH 4.6, I can suggest mixing 50 mL 0.1 M potassium dihydrogen phosphate + 11.1 mL 0.1 M NaOH, and diluting to 100 mL.

(Electrolyte Solutions by Robinson and Stokes, Butterworth's Scientific Publications)

Incidentally, the mixture you cite above will not be affected if you autoclave it tightly closed. The buffer I suggest will not be affected either.

Thank you Sir