In message  writes:
> Martin W. Wessendorf writes:
> > We use p-phenylenediamine in buffered glycerol...
> It has been noticed by some authors (Eskelinen et al.,
> European Microscopy and Analysis, May 1992) that
> p-phenylenediamine can induce yellow autofluorescence
> of nuclei. Has this been observed by you as well,
> or is the finding of Eskelinen et al. the exception
> to the rule that p-phenylenediamine can be safely used?
>
> Lauran Oomen
 
--I can't say that I've EVER noticed that one.  Although that may be due to poor
powers of observation on my part, it may also be due to differences in pH (we
use pH 8.0), concentration (we use about 1 mg/ml p-phenylenediamine), tissue
(I'm generally looking at rat CNS) or differences in among the products that the
various chemical companies allege is p-phenylenediamine.  We buy ours from
Sigma; the lot number of the bottle that we have is  14F-0419.  How pure it is,
or whether bona fide p-phenylenediamine is even a major contaminant of the
preparation, I don't know.
 
Since meta-phenylenediamine has been reported to react in the presence of weak
acid to form a yellow-fluorescing basophilic stain, I'd avoid anything that
might be a mixture of the para- and meta- isomers.
 
Martin Wessendorf