1. Sample sufficient peat (e.g. for very
fibrous and/or very wet peat, use 1 x 1 x 0.5 cm; for less fibrous
peat, use less) and place in weighing boat. Cut up peat if very
stringy; otherwise just leave in boat. Dry samples in boats in
an oven (~50ºC) or under infra-red heat lamps.
2. Prepare 1 litre 8% NaOH solution. To do this, dissolve 80g
NaOH granules of AnalaR grade in about 500 ml deionised water
and make up to 1 litre.
3. Grind up each peat sample separately in an agate pestle and
mortar, returning to weighing boats. *Note: clean the pestle and
mortar between each grind using dry paper or clean cloth - do
not wash.
4. Weigh out 0.2 g of sample accurately on a top-loading balance
(to 3 dp) - use a piece of paper and tare weight - then shake
into 150 ml beaker.
5. Turn on hotplate to preheat.
6. Add 100 ml of 8% NaOH solution to each beaker using a 100 ml
measuring cylinder.
7. Place beaker on hotplate and simmer. Do not cover or boil fiercely.
8. Top up beaker occasionally with deionised water to prevent
drying out and to ensure solution does not become too concentrated.
9. Turn hotplate off after 1 hour of slow boiling (simmering).
10. Pour beaker's contents into 200 ml labelled volumetric flask
using a funnel, and wash all residue into flask with deionised
water.
11. Top up flasks (when slightly cooled) to mark; stopper flask,
then shake well.
12. Filter 50 ml of contents of each flask into separate 50 ml
labelled volumetric flask, through filter funnel in rack using
Whatman No. 1 grade papers (size 15 cm). Use filter paper in a
corrugated folding mode, to speed filtration. Ensure only 50 ml
filtrate is transferred.
13. Decant filtrate into labelled 100 ml volumetric flask.
14. Turn on spectrophotometer to stabilise. Set to 540 nm.
15. Top 100ml flask up to mark with distilled water and stopper.
Then shake well.
16. When all flasks are ready, pipette small volume from first
one into each of three* cuvettes and using spectrophotometer (previously
allowed to stabilise), measure absorbance (upper scale) and %
transmission of first cuvette and record it.
* alternatively, re-use cuvette twice more
for the same sample only
17. Repeat for second cuvette (or for a second time) and, if a
different reading is obtained, repeat for third cuvette (or time).
N.B. DO THESE READINGS IN NUMERICAL FLASK ORDER!
References
Aaby, B.
and Tauber, H. 1975. Rates of peat formation in relation
to degree of humification and local environment, as shown by studies
of a raised bog in Denmark. Boreas 4, 1-14.
Blackford, J.J. and Chambers, F.M. 1993. Determining the degree of peat decomposition for peat-based palaeoclimatic studies. International Peat Journal 5, 7-24.