Tim

We have had this problem of a large water peak on our Delta V Advantage 
for a while now. What is strange is that with the inlet valve shut the 
mass 18 peak would be 850mV but if we remove the left hand side panel, 
the signal would drop to 350mV. Replacing the panel would cause the 
signal to go back up again. We also had an instance with a large signal 
of 4000mV at mass 18 with the Conflo connected only to find that the 
helium cylinder was empty!
I came in yesterday after being away and find the whole system had 
tripped off. I found that the oil seal on the DUO 2.5 rotary pump which 
backs the TMH 262 turbo had failed. According to Pfeiffer this will 
cause a high back pressure on the turbo causing it to over-heat and 
removing the panel probably cooled it. However, we now have to start all 
over again. I replaced the pump and the water peak on the middle cup 
this morning is 1750mV with valve shut and argon at 15mV. When the 
signal has stabilized I will open the inlet valve to the ConFlo and EA.
Our Delta V was one of the early instruments without any baking 
facility. I have since fitted a stick-on heater (200W) to the analyser 
with a controller so we are able to bake it at 45-50C.

Regards

John Hill
UCL Chemistry


Tim Sobolevsky wrote:
> Dear colleagues,
> 
> for 2 weeks my Delta V Advantage was off. After that I changed the needle 
> valve to Swagelok SS-DLVS4 (according to http://isogeochem.wikispaces.com/
> space/showimage/2005-11-18,+SGE+replacement+valve+on+IRMS.pdf), and 
> started the MS. 3 weeks has passed since that time, vacuum is ok (2.3x10E-6 
> mbar valve open, and 4.1x10E-8 with valve closed), but I still have a lot of 
> water coming, supposedly, from the GC Combustion III interface (with inlet 
> valve closed water is around 2 Volts – also pretty bad...).
> 
> Current values are (all measured at the middle cup after peak center; system 
> in backflush mode):
> 
> mass 18 ca. 20V (!) decreasing very-very slowly..
> mass 28 - 350 mV
> mass 32 – 1200 mV (slowly increasing)
> mass 40 – 17 mV (no leak, I believe)
> mass 44 – 400 mV (not too good).
> 
> I have installed Supelco High Capacity Gas Purifier (cat. no. 23801) in helium 
> line (supplied helium is 99.9999%) but nothing changed, so I don’t think that 
> water and oxygen are from the tank. 
> 
> My first question: may oxygen be produced in the ion source due to a reaction 
> of tungsten filament with water? If I switch the filament off overnight, than 
> the next day the oxygen signal is 4-times lower, but it starts increasing with 
> time and after several hours it’s about 1000 mV or higher. Should I keep the 
> filament constantly ON while equilibrating the system (when water is that 
> high)?  
> 
> The second question: what is reasonable time for the system to equilibrate 
> when starting from the ‘cold’ state? I mean how long does it take – usually (for 
> GCC/IRMS system) - for water to reach at least 2 Volts? I used heat gun to 
> heat the open split and reference gas inlet, but this did not change the 
> situation dramatically. The inlet valve heater is on, bulbs are on, I also 
> switched on analyzer heater several times for 48 hrs (max allowable time), but 
> still unlucky. Do I have a chance that if I leave my system for 1 week more, it 
> will eventually equilibrate and ‘dry’, or something is getting wrong?
> 
> Sorry if I gave too much of unnecessary wording and too few of key details!
> 
> P.S. For those Delta V users who is going to replace SGE needle valve to 
> Swagelok according to aforementioned manual, please note that you won’t 
> need SS-401-PC port connector as the valve is to be directly attached to the 
> ‘trident’ tube in mass spec. What is more important that you won’t be able to 
> put inlet valve heater block back until you slightly ‘modify’ it with a file. You 
> will need to remove ca. 3 mm of aluminum to fit the heater block to the valve. 
> 
> Warm regards,
> Tim 
> ---------------------
> Tim Sobolevsky, PhD
> Senior Chemist
> Moscow Anti-Doping Center
> Russia
> 
> 
>