Hi Jason--

In lieu of a proper manual, some tips:

     1.  Got Goo?  I phosphates have been run in your system, the Conflo
probably is coated on the inside with an orange goo/film/dust.

     2.  Clean open split (after closing off to mass spec ;) Especially
needed if capillaries coated in goo.  Carefully pull out capillaries and
wipe them down, wipe down rim of open split. Clip the ends of the
capillary, and re-insert to appropriate level.  If it does not look too
dirty, you may get away with just adjusting capillary levels, though you
may have to clip the line going to the mass spec.  IF you noticed that
the sample line is in too far, it might be blocked and just pulling that
back out will make a world of difference.

     3.  Benzoic acid tests.  Runs well, amt% wise, under almost any
conditions, but it does sublimate--so avoid drying it, esp. vacuum
drying.  That also means your sample bottle may have been homogeneous at
one point, but may not be that way now.

     4.  Phosphates don't mix with sulfates.  If you run silver
phosphate after barites, you CO signal disappears, but benzoic acid and
the sulfates themselves run fine.  So don't mix an match.  Cleaning and
repacking reactor fixes problem.

     5.  D/H and hetero atoms--not the best combination.  (look up D/H
on caffeine)

     6a.  Backgrounds.  it may take a day or so at temp for a newly
packed reactor's backgrounds to settle down.  The <200 (m/z 28) at 1325
oC after 3 days should happen sooner.  The background is due to glassy C
reacting to stuff in alumina tube at temp, to permeability of alumina
tube at temp, perhaps leaks in the alumina tube, and other leaks.  IF
there's "air" trapped in a capsule that slowly leaks out--there's your
virtual leak.  Ar levels, m/z 40, should be below 100 mV on middle cup,
but do an Ar leak check if level above 60 ish mV.  Check at 1325 and
compare to value at working temp--it shouldn't change much, unless you
have a leak/crack opening up at temp.  As long as Ar levels are low, you
do not have to worry about air leaks--and getting NOx forming in the source.

       6b. backgrounds.  Depends on temp you like to run at.  We run at
1450 and see high backgrounds for CO (m/z 28).  Waiting a day (or a bit
more) at temp to let levels stabilize is not uncommon.  We recently got
decent results with backgrounds at ca. 500 mV on m/z 28.  If it's stable
and Ar levels are low, try running.  Note, I've also seen backgound jump
as a storm blows thru and the humidity jumps up.

     7a. Autosampler.  Zero-blank?  Instead of purging for 5 min, try
pressurize-release (and I presume your samples are properly
encapsulated), with opening and closing of valve to reactor to flush
that out after the first few pressurize and release cycles. Test
flushing/seals by looking at baseline levels with and with out isolation
valve on autosampler open/closed--using regular He feed only (aka purge
valve closed).  Background levels should only shift by a few mV if
there's not a problem with the autosampler. If there is a problem, just
close isolation valve and re-flush/vent the autosampler.  If it still
persists after a few re-flushings, look for other leaks.

     7b. Autosampler.  seals.   Large o-ring and middle vent leaks
should be picked up via Ar leak check, unless leak is large--whereby it
could be picked up w/ a He leak detector. Rarely the seal on the tube
going to the isolation valve leaks, and that is hard to detect via Ar
leak checking.

    8.  But is it really packed properly?  Look down the view port (with
shade 3 glasses or perhaps sunglasses--too bright otherwise), and bottom
of crucible should be glowing just as bright are rest of crucible.  A
shade cooler could be ok, especially if glassy C chips underneath can be
seen glowing (if you can see down side of crucible).  Put a graphite
funnel on top if using a square crucible--make a short one out of
graphite tubing or rod--nothing fancy, just a beveled tube to keep
sample from falling outside crucible. Top or funnel might start to be
outside hot zone--that's ok.

   9.  Be patient.  We had better runs if we wait a hour or so after
loading samples before starting run.  Perhaps helps with air in capsules
or adsorbed water.

   10.  Conditioning set.  Sometimes the first set of standards appears
a bit anomalous. We'll start with a junk sample, benzoic, the set of 4
for house standard A, 4 of B, then 4 again of A.

    11.  Standards--lots of standards--house or commercial.  A standard
deviation of +/- 0.2 means you'll see 0.4 per mil spreads (yes 18O).  We
like to run them in groups of four to make sure we seeing trends and not
noise.  That means use the 100 position carousel.

    12.  D/H on hydrous minerals...yeah, that's actually tricky too....

Well, that's enough of that--the Friday softball and beer is about to
start...

take care,

gerry



On 6/9/2017 1:51 PM, Jason Curtis wrote:
> Hi All,
>
> I need some TCEA help.  Our TCEA is pretty new but very sporadically
> used and I have yet to develop good practices.  Each time I come back
> to it I seem to have to start from scratch!  I need some advice on
> basics such as what backgrounds are acceptable, what precisions are
> acceptable, what tailing is normal, etc.  I need info on running
> organics for dD and d18O.  Does someone have lab methods / standard
> operating procedures that they can share?
>
> I realize that is beyond a normal Isogeochem request so I am willing
> to pay for advice (maybe hire someone as a consultant?).
>
> Thanks on this Friday afternoon (after a week of trying to figure it
> out and a pile of samples waiting!).
> Jason
>
>
> Jason Curtis, Ph.D.
> Stable Isotope Mass Spec Lab manager
> Senior Associate-In Geochemistry
> Department of Geological Sciences
> University of Florida
> Gainesville, FL 32611
> +1-352-275-8642
>
>
>
>
>
>
>