Jonanthan - its most likely the H2 gas you are using for your reference -
many, if not most,  North American suppliers of H2 compressed research gases
have dD values lower than -1000 permil, making the peak very hard to find.
You may need to find a different supplier or get someone to send you an
ampoule of H2 gas with "normal" dD values. Len

Leonard I. Wassenaar, Ph.D.
National Water Research Institute
Environment Canada
11 Innovation Blvd.
Saskatoon, SK
S7N 3H5

tel: (306) 975-5747
fax: (306) 975-5143

-----Original Message-----
From: Jonathan Horton [mailto:[log in to unmask]]
Sent: Monday, January 22, 2001 11:18 AM
To: [log in to unmask]
Subject: [ISOGEOCHEM] HD problems on Finnegan delta plus


Hello all.

I am using a new delta plus and am struggling to find hydrogen on it
  (dual-inlet mode). I fill the bellows, and have looked for a peak with
  BDAC value around 1000; I have tried retuning the source, but to no avail.
 The instrument has been used with the precon for N2O, where it worked just
  fine. Specifically what I've done is:

  1) close SGE and look at background on cups 3,2,and 1 using B-scan (a
  little water, N2, nothing else) (I can't figure out how to do a B-SCAN
  using cups 7 and 8, which would be more useful in this case...)
  2) put Oztech standard H2 into inlet A1 and into bellows (pressure
  increases in bellows to >100) (I've tried 2 different standard bottles to
  rule out bad gas)
  3) leave source tuning as was for CO2; adjust BDAC from 10 to 3000 in
  ACON-D, INST-control
  4) I find a very large peak (>10V) in cup 7 (mass 2) at around BDAC 2500;
  small peak (0.2 V) in cup 7 at BDAC 1300; but at no point during the scan
  is there ANY change in the voltage on cup 8 (mass 3) - it stays constant
at
  0.001V
  5) changed source tuning settings to match values given for old (returned)
  delta plus for HD mode (I don't have a record of source tunings used for
  HD during install); repeat step 3, result same as item 4
  6) when I get a peak (the large one at BDAC 2500 and the small one at BDAC
  1300), I've looked at the peak shape - cup 7 has a peak shape, cup 8 is
  always a flat line.
  7) I've done a baseline check to see if the amplifiers are working: the
  baselines (source off) for cups 7 and 8 are around 185, voltage readings
  are -10 and -8 (respectively). With the source on, baselines are 210 and
  185, voltage readings +8 and -8. So, turning the source on does not change
  the baseline in cup 8, but does slightly change it in cup 7. I hope this
  doesn't mean there's anything wrong with the amplifiers on cup 8... ???

  I'm assuming that I still don't have the right combination of BDAC, HVDAC
  and source settings (X1, extraction, etc.) to find the right signal. What
  procedure should I use to try to find the correct settings? I assume there
  are standard starting points, and that one simply tweaks the knobs in a
  particular order to find the right settings. Or, maybe not! Is there a
mass
  calibration procedure for HD? In short, what do you do with a new
  instrument to find the HD peak?

Thank you in advance for your help,

Jonathan

******************************
Jonathan Horton
Research Associate
Department of Biology
Virginia Polytechnic Institute
  and State University
Blacksburg, VA 24060-0406
phone: (540) 231-8713
fax: (540) 231-9307
email: [log in to unmask]

******************************