I need to work at pH 3.70 with high regulatory capacity and low Abs. at 240 nm. In this time I use buffer acetate 500 mM but I have problems with it. Could anybodie help me?

What problem do you have? Is the absorbance too high? How about a phosphate-acetate buffer, you can reduce the acetate to about half your present concentration. Another possibility: Formate buffer. If MP absobance is a problem you should forget citrate.

500 mM is fairly high. Can you reduce the concentration? Alternatively, you may still get away with a phosphate buffer. While this is far away from the pKa, you are working at a concentration that is 10 to 50 times higher than common RPLC buffer concentrations. This may still give you a reasonable buffer capacity. Check how reproducibly the pH can be adjusted.

Acetate pKa = 4.76 and formate pKa = 3.75. Therefore, at pH 3.7 a 50 mM formate buffer would have about the same buffering capacity as 500 mM acetate.