On Fri, 31 Mar 2000, Sebree Linda A. wrote:

> My common sense tells me the citric acid only buffer is easier and less
> fussy.  But I will consider the citric acid/sodium citrate buffer if there
> are compelling reasons to use it instead, ie it works better, is gentler on
> tissue, intensifies staining more, etc.

   For any particular pH, the chemical composition of the solution
   will be the same. It does not matter if you use citric acid and
   sodium hydroxide or citric acid and sodium citrate. The
   buffering capacity (stability of pH when a bit of acid or alkali
   is thrown in) increases as the total concentration of citrate (be
   this from neutralized citric acid or pre-made sodium citrate)
   rises.

   It's also necessary to know that citric-citrate buffers are 
   effective only in the range pH 3.0 to 6.2.  Within this range,
   a solution 0.1M in citrate/citric acid is not going to change
   its pH when diluted with small (? 5%) additions of fairly
   clean water.  There are other citrate buffers that extend the
   range of controllable pH well into the alkaline region. All
   textbooks of practical biochemistry, chemistry, histology 
   and histochemistry contain instructons for making buffers. An
   old, cheap, 2nd-hand reference book is a great investment
   for anyone who works in a lab and likes the work.

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