We run our off-line acid digests in a solid metal heater block (VWR)
with 72 positions.
We "calibrated" the temperature control dial by measuring the
temperature in a mock-up digest vial with an old fashioned thermometer
(and later with a thermocouple). The vial was placed in the centre
position of the block and every other position was occupied to create
real life conditions.
For the vial to reach 50 C we had to set the dial to 54.5 C. However,
this we did only (a) because we wanted to know what the offset was under
typical conditions of use and (b) for reasons of writing an SOP and
related record keeping. As other correspondents have already pointed
out, as long as the principal of identical treatment is observed (i.e.
standards are run concurrently and used for scale correction) absolute
temperature is a secondary consideration.
Temperature and reaction time become an issue when you are dealing with
awkward customers such as ankerite, which even after a couple of days
does not react with phosphoric acid at 25 C.
Dr W Meier-Augenstein, CChem, FRSC
E-mail: [log in to unmask]
URL (SCRI): http://www.scri.ac.uk/staff/wolframmeieraugenstein
URL (MRS): http://www.isotopesignatures.co.uk
From: Stable Isotope Geochemistry [mailto:[log in to unmask]] On
Behalf Of A. Schauer
Sent: 21 July 2010 05:35
To: [log in to unmask]
Subject: [ISOGEOCHEM] 25*C
1) How do you obtain a controlled 25*C for phosphoric acid digestion of
carbonate in your lab? My lab varies around 22*C. It seems as though
most water baths with heating option only control from 5*C above ambient
to 99*C. Do you use a chiller model then or are you lucky enough to have
a lab that is 20*C? Please either outline your method if home-built or
provide a part number and manufacturer for your bath.
2) How do I know that my 25*C will be the same as your 25*C?
Earth and Space Sciences
University of Washington
Seattle, WA 98195
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