Hi,

Cetrifuging blood samples to separate the plasma from red blood cells is
used routinely in bioligocal studies. Has anyone had any experience whether
this process leads to isotopic fractionation?

A current project for energy expenditure has D-labelled samples (sealed in
capillaries, 50 microlitres of blood max.) up to 22,000 permil.
Traditionally we vacuum distill the water from the blood capillary and
subsquently inject the water into a self-made chrome furnace on line to our
VG Optima. The chrome reduction works very well, the problems lie in vacuum
distilling the sample. The internal surface area of the vacuum line is
large compared to the amount of water released from the capillary. With
such high enrichment samples a lot of care has to be taken to counteract
memory effects. While the chrome furnace has memory problems associated
with high enrichment samples these are more easily alleviated than the
problems with the vacuum line, and easier to test for.
Another recent project has shown that injecting a plasma separate into the
chrome furnace gives comparable ppm D data to water vacuum distilled from
faecal samples (don't I have a nice job?) so I'm hapy enough to inject
plasma directly into our chrome furnace. However, these centrifuged plasma
samples were a much larger volume (at least 5 mls) and a much lower
enrichment, only about 1000 permil, so I'd like more information to be
confident retaining such isotopic integrity will also work with
centrifuging <50microlitre capillaries at higher enrichments.

Our plan is to spin down the capillaries sealed so fractionation due to
evaporative loss should be not be a problem. Once the plasma samples is
separated then cut open the capillary and inject the plasma (1 microlitre)
into our furnace.

I've carried out a literature search prior to posting this message, butI've
only found 4 references in (to an isotope biogeochemists) pretty obscure
journals to the extent that the abstracts are accessible.

Any insight greatly appreicated,
Susan


*********************************************************
Dr. Susan Waldron,
Life Sciences Community Stable Isotope Facility,
Scottish Universities Research and Reactor Centre,
East Kilbride G75 0QF,
Scotland.

Tel: (01355) 270142
Fax: (01355) 229898
email: [log in to unmask]
http://www.gla.ac.uk/surrc/research/nerclifesci.html
 http://www.gla.ac.uk/surrc/personnel/waldrons/
*********************************************************