Ranges and Changes of pH in Zoological Alcohol Collections

Marion Kotrba Daniel Burckhardt Klaus Golbig Christoph Meier

Ranges and Changes of pH in Zoological Alcohol Collections

10 pH 9

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8 7 6 5 Pisces Amphibia Reptilia Mammalia Mollusca Crustacea Psyllidae Formicidae Diptera 4

0 50 100 150 200 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.

2 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

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n

60 50 40 30 20 10 0 3

visually classified as needing curation

4 5 6 60

n

50 40 30 20 10 0 3

before curation

4 5 6 7 7

visually classified as probably OK

8 8 9 9

pH after curation

10

pH

10 480 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.

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.

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).

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 &

4

exchange exhausted ampholyte only if deviating pH is detected exchange only the exhausted bout if deviating pH is detected

5 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 6

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.