gum arabic update

John True jtrue at acpub.duke.edu
Fri Dec 2 16:31:31 EST 1994


        A few weeks ago I posted a request for information on sources of
flake gum arabic.  Due to some mail problems I inadvertantly deleted most
of the responses and "me too" requests that I received, so I thought I'd
post what I found out.
        The most helpful response from a net.person was to check in a
reference called _Handbook of Pharmaceutical Excipients_.  The medical
library here had the 1986 edition which listed 13 vendors for gum arabic
(acacia).  Of these 13, 7 no longer existed under the listed name of the
firm in the listed city, 2 sold powder only (Ruger Chemical, Hillside NJ,
201-926-0331, Colloides Naturales, Far Hills NJ, 800-872-1850), one no
longer carried the compound (Dr. Madis Laboratories, S. Hackensack NJ), one
sold acacia only as a whole root (Indiana Botanic Gardens Inc., Hammond IN,
800-644-8327), and 2 didn't answer their phone or return phone messages
(Meer Corp. N. Bergen NJ, 201-861-9500,  M.F.Neal & Co., Richmond VA,
804-644-6177).  Add to this list 3 companies that we already had catalogs
for that only supply the powder form (Sigma, Aldrich, ICN).
        The technical assist person at Colloides Naturales was by far the
most helpful.  According to him, there is only one supplier in the world of
flake gum arabic, a company in Germany (didn't get the name).  So I've
pretty much given up on finding the flake form.  Colloides Naturales did
send me a sample of "Technical Grade Gum Arabic", which the technician said
was less refined and went into solution faster.  I just got the sample
today.  Unfortunately the spec sheet said that the color of a 25% solution
was "Black", which means that this material is no good for my application
(clearing/mounting insect cuticular specimens).  I tried dissolving 5g in
50ml dH20 and indeed, although it seems to go in faster than the powder
from Sigma, the final color is a deep brown.  Rats.
        Anyway, I've decided that the powder from Sigma (which we have
virtually a lifetime supply of) is not so bad.  We use it to make Hoyer's
solution, which has the following recipe:

        50 ml H20
        200g chloral hydrate (a controlled substance, requires lots of     
    fun paperwork to obtain)
        30g gum arabic
        25 ml glycerine

The final volume is 200-250 ml.  The problem with powdered gum arabic is
that it is really fine, wets quickly, and makes really slowly dissolving
clumps.  The way to get it in is to add it slowly by sifting through a fine
strainer while the solution is stirring on a fast magnetic stirrer.  Add it
a sift at a time (it took me about 4 days to add the full amount) and vary
the speed ocasionally so that the powder doesn't pile up in the middle on
the stir bar.  As soon as you get a few grams in, it will start to form a
thick foam (like meringue) if you stir fast.  This is OK.  A couple of
times during the 4 days I stopped stirring and let it settle overnight. 
After a few hours most of the bubbles (which rise to the top) went away. 
At the end, the rest were decanted.  This procedure takes a long time but
eventually you will get it all in.  Much of the particulate matter in the
gum arabic powder (impurities) settles out and the remainder is not a
problem for us.  I now have enough Hoyer's to finish my thesis work.
        For people with other applications, I recommend contacting
Colloides Naturales.  They're really helpful and very generous with
samples.  Thanks to those who recommended alternatives (such as Aquamount
from Gurr).  I will try these out as well.

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John True                                       Zoology Dept./DCMB Group
jtrue at acpub.duke.edu                            B338 Levine SRC Box 91000
voice: 919-613-8150                             Duke University
fax:   919-613-8177                             Durham, NC 27708-1000
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