Dear Lars,

Assuming you have checked the obvious such as capillaries, valves,
and pressure in your CO2 cylinder, you might wish to consider a
change of filament (and while the system is down, an oil change of
your vacuum pumps). As to whether the source needs to be cleaned
depends on the result of your optical inspection (if it's not broken,
don't fix it). Unless the colour is a metallic dark blue bordering on
the black you should be fine (ideally only inert gases should
have entered your ion source).

You can gain some sensitivity by playing around with tuning and
focus. However, this gain will be achieved at the expense of
linearity.

Sample requirement for C in terms of amount injected on column is of
the order of 100 pmol to 1 nmol. If your samples are too diluted you
need to change your sample preparation to end up with a higher
concentration. Under no circumstances should you inject volume of the
size you suggested (10 - 100 ul). (1) The injector volume (liner
volume) is too small to cope. You have to take into account that your
liquid will expand once injected into to the hot injector.  (2) You
would flood your column. Result: poor peaks bearing more resemblance
to the outline of a beached whale.

At higher concentrations (e.g. 10nmol/ul) you run the risk of
overloading your column (I presume you use columns with a film
thickness of 0.25 um?). If you really need more compound on the
column you have to swap your column for a thick-film column (0.5 um,
1 um) of the same diameter (0.25 or 0.32).

Hope this helps.



Best wishes,
                             Wolfram




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Dr. W. Meier-Augenstein
Lecturer/Research Fellow

University of Dundee, Dept. of Anatomy & Physiology,
Small's Wynd, DUNDEE  DD1 4HN, United Kingdom

Tel.: +44-(0)1382-34/5124, /4968
      +44-(0)468 -314563
Fax:  +44-(0)1382-34/5514

e-mail: [log in to unmask]

URL: http://www.dundee.ac.uk/anatphys/wma/wolfram.htm
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