How to upgrade MS source to Extractor 350?

EhsanKhedive  What is the model number listed along with the serial number label on your system?  For example, this one is a G7077C, a 5977C system with a turbomolecular high vaccum pump and an extractor ion source.

Hi paulsalverda ,

Thank you for your attention! The model numberd is G7080B with a diffusion oil pump.

First recommendations and some questions:

Thank you for your valuable recommendations!

• I will increase the equilibrium time.
• My solvent is Chloroform and from Vapor Volume Calculator I realized it will occupy ~82% of liner volume (~900ul) at 260C/7psi. So, I thought its feasible to inject 2ul. Chloroform boiling point is 61C, but I wasn't aware of this. Thank you!
• I will increase the delay to 1-2 sec.
• Liner is single taper.
• Thank you for the pulsed splitless injection recommendation. I will use it. What would be the optimum injection pressure and time in that case?
• I thought keeping inlet cooler than oven by ~10C prevents compound buildup and carry-over. That was the reason I keep it cooler. That's also the reason I put TL 10C higher than column.
• Purge flow: I thought it might be problematic. I try to save gas since it's grade 5 (9.9999) and expensive. I will change the split vent flow. Is it possible to put the split vent on 3ml/min in standby mode and then increase it to 50ml/min a couple of hours before the start of analysis?
• Most of the compounds of interest have very low mass (as low as 100). Even for some of them mass 27 is among the main mass peaks. I was even thinking to reduce it to 25m/z. What problem would this make? I usually put the maximum mass as my molecular weight+30Da in case they are methylated during derivatization.
• Since I keep my split vent low, sometimes I see m/z 32, especially during my blank run before the batch.

I mean 99.999%

The lower the injection port pressure, the less realistic is the vapor volume calculator. It's not perfection in there and 82% is too much.  With Chloroform you'd want the initial oven temperature to be 40° C or even lower. You say your compounds are very light, so reducing it to even 35° C might help chromatographic peak shapes.

Pulsed splitless.30×250×.25 at 1 ml/min is your normal column flow with the inlet at 7.2892 psi at 45°C.  The diffusion pump in your system has a maximum allowable flow of 2 ml/min and the gas calculator says 16.497 psi to get that, so a pulse of 16 psi until 0.5 minutes and then purge flow 50 to split vent at 1.00 minutes would be a good starting point.  Then have gas saver on 25 ml/min at 2.00 minutes. 2 µL of chloroform at 16 psi and 260° C inlet gives 52% expansion, much better, much more realistic/safe/usable.

The split splitless and multimode inlets require a minimum of at least 15 ml/min of total flow to function properly.  That 15 ml/min is not really enough to eliminate the possibility of air diffusion into the system, so I recommend 25 ml/min at all times.    If you need to save helium, Agilent sells a Helium Conservation Module that will let you switch to nitrogen whenever the system is not being used.

You can scan from 10 m/z if you'd like as long as you understand that the TIC baseline will include 18, 28, and 32. 

ANY 32 - oxygen -- in your system degrades the column and oxidizes the ion source requiring more cleaning. 

Thank you for your time and valuable information Paul! I really appreciate it! I am aware of water (18), N2 (28), and O2(32) and constantly check their presence.

Best!

Ehsan

Hi paulsalverda 

Just wanted to ask a question out of curiosity. We are located in Fort Collins, 5,000 ft above sea level. So, the atmospheric pressure would be ~12.2 psi here. Is it possible to put inlet pressure at 12.5 psi along with a low septum purge (e.g. 3 ml/min) to prevent air from diffusing to GC when GC is in standby instead of having septum purge of 50ml/min? In this case column flow would be 1.48 ml/min for my setup.

Thanks!

Ehsan

Hi paulsalverda 

Just wanted to ask a question out of curiosity. We are located in Fort Collins, 5,000 ft above sea level. So, the atmospheric pressure would be ~12.2 psi here. Is it possible to put inlet pressure at 12.5 psi along with a low septum purge (e.g. 3 ml/min) to prevent air from diffusing to GC when GC is in standby instead of having septum purge of 50ml/min? In this case column flow would be 1.48 ml/min for my setup.

Thanks!

Ehsan

For standby method I'd recommend inlet pressure ~5 psi.  This is gauge pressure so it'll work to prevent air diffusing into the inlet if there are any small leaks.  Keep in splitless mode, set purge flow to 20 mL/min, septum purge to 3 mL/min.