Unless your instrument lacks sensitivity you will not need to run 400ug carbon. Most likely you can obtain suitable precision at 200ug, possibly even down to 100ug. Perhaps try running a few standards at these lower levels to see how the instrument performs.
You are likely to get better combustion with smaller samples and certainly less build up of ash so smaller could well be better.
It would be a different story if you were also measuring N isotopes …
Mr Chris Pullan
Goss Scientific Instruments Limited
Phone: 01270 580888
Fax: 01270 581455
Registered E&W, Company Number 01175784
15 Mainwaring Close, Nantwich. CW5 7GT
From: Stable Isotope Geochemistry <[log in to unmask]> On Behalf Of Matthew Von Tersch
Sent: 31 July 2018 12:04
To: [log in to unmask]
Subject: [ISOGEOCHEM] Low %C soil bulk isotope analysis - how much is too much?
We have been asked to run some soil samples taken from a salt marsh in Australia, the majority of which are from the surface, but there are also some from a core. The samples have been dried and ground and analysed for TOC.
Based on a requirement of 400 ug carbon per sample for our system (Sercon 20-22), some of the samples will require between 5 and 15 mg of soil per capsule. I spend the majority of my time working with collagen in the 1 mg range, so this venturing into the unknown.
For those of you working with soils, is there anything I need to be aware of when running this type of material for delta 13C, and how much material per capsule is too much?
Many thanks for any assistance.
Please note that I check emails only twice a day, so urgent or quick queries may be resolved more efficiently by telephone or face-to-face.
Mr Matthew von Tersch
BioArCh Laboratory Manager
Department of Archaeology - University of York
Room 229, Environment Building
York YO10 5DD
Tel: 01904 328282
E-mail: [log in to unmask]