toluidine blue

Susan Singer ssinger at CARLETON.EDU
Wed Oct 8 09:23:50 EST 1997

Hi! Ross Koning wrote:
>I have used the simple aqueous Tol blue solution and my students
>get fairly good results...but NEVER beating phloroglucinol/HCl.
>The secret to Phloroglucinol is making the phloroglucinol
>in an alcoholic solution.  I use HCl in a separate dropper
>bottle diluted 1 conc HCl to 4 parts water (resulting in about
>10% HCl final conc).  Apply the two drops to a specimen and
>in about 10 seconds the results are spectacular.  For long-term
>storage and classroom use, I prefer Nalgene dropper bottles
>with unitary caps.  You never get more than one drop at a time
>and nothing degrades in the acid.
>What I don't like about Phloroglucinol is the corrosion you can
>get on mechanical stages and the tips of objective lenses if
>the students aren't meticulous with the acid...and promptly
>removing the slides from the stages before storing the microscopes.
>I'm excited to try the tetraborate addition to see if it improves
>the contrast with Tol blue...that would be nice and might convince
>me to switch away from Phloroglucinol.  The tol blue w/o borate
>is just too murky to me.
I'd have to agree with Ross that phlorolucinol works a bit better for me as
well.  It is important to have the HCL separate.  Students seem to enjoy a
brief lab demo where I take a brown paper towel and spot it with
phloroglucinol and then add the HCL (it turns a beautiful shade of pink!).
Just be sure not to wiff the HCL and warn students not to lean too closely
over their preps as they add the HCL.


Susan Singer                                    Phone:  507-646-4391
Department of Biology                           Fax:    507-646-5757
Carleton College                                E-mail: ssinger at
Northfield, MN 55057

More information about the Plant-ed mailing list