Dear Paul,

we compared glasfiber filters with quartz fiber filers for field sampling
of marine plankton and found no significant differences in the isotopic
composition for 13C and 15N. We used quartz fiber instead of glas fiber out
of the same practical reasons you mentioned. The only disadvantages of
using quartz fiber are:
1: the reduced capacity of our ANCA system because the volume of quartz
fiber stay nearly the same before and after oxidation, filling up the
oxidation tube quickly
2: difficulties to to press the quartz filters in tin vials to get them
into a spherical shape for the autosampler (we normaly use a special hand
press for filter samples)
3: differences in poresizes between commericial available quartz and glas
filters (classical definition of dissolved versus particulate matter in
marine POM studies)
4: we had higher blank values for quartz fiber filters during the acid
fuming step, most probable reason is the higher amount of fiber in the
thick quartz fiber filters we used in comparison to the normal thin GF/F´s.

Altogether we are quit happy with the quartz fiber filters since
(1) evenso we have to clean the oxidation tube more often this job is much
more easy with quartz fiber/ash than with molten glas and the tube it is no
longer damaged by molten glas sticking to the inner walls and metal oxide
packing of the tube
(2) with some tryouts it was possible to find a suitable folding technique
for the tin foil
(3) depending on the application different poresize can often be used
without a problem
(4) blanks were only a problem at very smal sample sizes

I hope this helps,

Klaus-Uwe Richter

Alfred-Wegener-Institut fuer Polar- und Meeresforschung
Am Handelshafen 12
27570 Bremerhaven, GERMANY
Tel: 0471 48311482
Fax: 0471 48311425