Dear colleagues,

while fighting with water in my Delta V Adv connected to Trace GC via a 
Combustion III interface, I have discovered something that needs to be 
clarified to me.

I mean gas inlet manifold - or what is the proper name for it - 'trident' 1/4" SS 
tube that feeds gas to the ion source.  

I have tried to replace the original manifold to a right-angle bent 1/4" SS tube 
from Swagelok (not electropolished..). My tube was 0.049" wall thickness 
instead of 0.035" of Thermo one. After pumping down I have observed almost 
2-fold decrease of the MS response, either to Ref Gas (CO2) or to standard 
alkane mix. I know that in capillaries flow restriction is 4th power proportional 
to their ID. So in this particular case increase in restriction should be 1.9 (the 
same as I had), but actually I don't know if this statement is valid for pretty 
short and wide tubes..

In addition, I have noticed that Thermo manifold has such a feature that outer 
diameter of SS tube (from MS side) is slightly and precisely decreased (turned) 
at the distance of ca. 1 cm from the tip. I have no idea why and if this is 
important for gas flow.

Finally, is the insertion depth (ca. 7 cm) that important? i.e., if a 2-mm 
deviation in either side could result in 2-fold signal decrease? 

Anyway, if I would like to change the original trident-style manifold to a single-
inlet tube, would electropolished SS tube from Restek (cat. no. 22539) be 
good enough?

Thank you and
warm regards,

Tim 
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Tim Sobolevsky, PhD
Moscow Anti-Doping Centre
Russia