> used in antigen retrieval.  I currently use a combination of citric acid
> and sodium citrate and recall there were some variations.  Your input

  That's exactly what a citrate buffer is! Adjust the pH
  by adding more acid to lower it, or more trisodium citrate
  to get a higher pH. This system is effective in the range
  3.0 to 6.2. Anything more alkaline is not a buffer, even if
  it successfully retrieves antigens. Citrate ions may, like
  EDTA ions, contribute to antigen retrieval by chelating calcium
  as well as by providing a favourable pH for the reversal of some
  of the reactions of fixation by formaldehyde. For an interesting
  and brief exposition of this theory, read the abstract by Jasani
  et al. in Histochemical Journal vol 29 (issue 6) p. 433.

 John A. Kiernan,
 Department of Anatomy & Cell Biology,
 The University of Western Ontario,
 LONDON,  Canada  N6A 5C1