HI Tim--

If I got this right, it sounds l

Tim Sobolevsky wrote:
> 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 
> *****************************
> Tim Sobolevsky, PhD
> Moscow Anti-Doping Centre
> Russia
>
>