Ranges and Changes of pH in Zoological Alcohol Collections

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Ranges and Changes of pH in Zoological Alcohol
Collections

• Marion Kotrba
• Daniel Burckhardt
• Klaus Golbig
• Christoph Meier

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Ranges and Changes of pH in Zoological Alcohol
Collections

pH
Amphibia- Reptilia
Mammalia
Mollusca
Crustacea
Psyllidae
Formicidae
Diptera
Pisces
Comparison of pH values in museum collections of
Basel (black) and Munich (white). Values arranged
in rising order within taxa 30 samples per taxon
and collection i. e. 480 in total assessed with
pH electrode. 13 of samples in acidic range
below pH 6 and 13 in alkaline range above pH 8.
Similarities between compared collections regard
e. g. the very large overall range in Formicidae
and Diptera and the comparatively alkaline
conditions in Crustacea. Note the small range in
Basel Psyllidae (recently curated).
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Ranges and Changes of pH in Zoological Alcohol
Collections

• 480 specimen jars were visually classified a
  priori as in need for curation (series B) or not
  (series A) based on evaporation, colour, opacity
  etc. of the preservation fluid. pH values were
  subsequently measured with a pH electrode.
• Visual assessment largely fails to recognize
  problematic jars.

n
visually classified as probably OK
visually classified as needing curation
After the first pH assessment 320 jars a priori
classified as needing curation (series B) were
topped up with alcohol. Then the pH values were
measured again. Standard topping up procedure
hardly improves the pH.
pH
n
Statement of problem Measurement and
interpretation of pH in alcohol collections is
time consuming and problematic. Reconstitution of
desired pH is likewise problematic (usually
requiring complete exchange of preservation
fluid).
before curation
after curation
pH
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Ranges and Changes of pH in Zoological Alcohol
Collections

Suggested approach Part I Stabilize pH by
buffering preservation fluid with solid
ion-exchange material such as
a substrate-bound ampholyte i. e. a polymeric
substrate (e.g. polystyrene or cellulose)
provided with positively and negatively charged
groups (e.g. carboxyl grous, sulfuric acid or
phosphoric acid groups, various amino gorups).
or a combination of acidic and alkaline
ion-exchange substrates in separate dispensers
exchange only the exhausted bout if deviating pH
is detected
exchange exhausted ampholyte only if deviating pH
is detected
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Ranges and Changes of pH in Zoological Alcohol
Collections of Basel and Munich

Suggested approach Part II Combine ion-exchange
material with color pH indicator for easy pH
assessment using
a substrate-bound ampholyte
or a combination of acidic and alkaline
ion-exchange substrates in separate dispensers
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Ranges and Changes of pH in Zoological Alcohol
Collections of Basel and Munich

Suggested approach Part III Advantages
pH stabilized right from the start reducing risks
for specimens and curatorial efforts buffering
agent and its reaction products not interacting
directly with stored specimens, e.g. by forming
insoluble deposits on their surface detected pH
deviations easily amended by exchanging exhausted
buffering agent instead of exchanging
preservation fluid, i. e. without disturbing
specimens or furthering additional leaching of
lipids etc. solid ion-exchange material may be
regenerated after exhaustion recognition of
problematic jars substantially facilitated by
combining the ion-exchange material with pH
indicator Reference Kotrba, M. and Golbig, K.
A new approach to stabilize the pH in
fluid-preserved natural history collections.
Submitted to Collection Forum.
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