I have a question.
how I can change the column in the gc/ms without stopped turbopump ? It is possible?
regards Azrael ?
I believe what @mhardacker is referencing with the flow calculation is that as soon as the restriction capillary is cut, the EPC is no longer controlling the amount of flow to the MSD, i.e. atmospheric pressure…
There is a product for this.
The only really fast & SAFE column change is only possible with Quick Swap technique suggested by james_jenkins.
On one hand, a restriction capillary is used to limit the flow to the pump & to stabilise the vacuum. In order to avoid a large O2/H20 entry in the short time: a "protective makeup gas" feed is used.
If my customers want to be particularly careful, I recommend to reduce the MS temperatures to 100°C before column change. This prevents ion source oxidation effects if the column change process takes longer (e.g. ferrule defective, column broken.. etc).
There is a product for this.
i can not to tell how often will change the column because other people will work. I just want to improve what is. I was asked about it. I would not touch this system. But there is interest in doing several tasks on one detector. i have two columns - polar and not polar and one port for the injector on analysis pesticide and lipid. and I am thinking how to implement this task. can buy another injector and a ferrule with two holes (what you talked about yestarday) and use two columns at once. And it is also possible to change columns, which is what James gave the link about, but I haven't looked into that yet. Therefore, I am interested in whether this can be done and how to do it correctly so as not to harm the detector (turbomolecular pump).
The above statements are correct & I would like to point out here from my experience as a service engineer:
1a) Azrael is probably responsible for several users
1b) many "modern" users do not come with our practical experience.
2) Pressfits are good, but in my opinion not suitable for less experienced users or GC novices =>
then metal ferrules like AT CFT (Capillary Flow Technology) or Siltite are the better/more reliable choice.
3) Short MSD restriction capillary: can I use any dimension? Please, NO
Why are the dimensions of the MS restriction capillary so important?
When the main column is removed, only the restriction capillary (inside the MSD) limits the air flow into the MSD/pump.
The dimensions of this capillary (iD & L) should be calculated, because more than 6(-10)ml into the MSD/pump should be avoided !
Examples for bad & good AIR flow values by restriction capillaries (no gas supply by EPC or main column):
Dimensions of restriction capillary [ID µm * L]
Air Flow into MSD,
(without main column)
Idea: where & who to use?
(not mandatory to do)
BAD, too high flow
250 * 1.0 m
250 * 2.5 m
if main column has ID 250µm.
extend the main column by 2.5m
200 * 1.0 m
if main column has ID 200µm.
extend the main column by 1 m
Calculation details: see screenshots below
Because of all these mentioned uncertainties I always recommend the Agilent QuickSwap.
Admittedly, QuickSwap might be not cheap (because of EPC) but in the environment of many users it’s the SAFEST hardware choice and it also protects expensive equipment very well.
Note: when changing columns the ion source/quad temperatures should be reduced to 100°C to avoid unnecessary oxidation.
Use 1 meter of deactivated fused silica tubing going into the source (the same diameter of your column), then use a union (either the press-fit glass type of, better yet, the SilTite brand) to connect to your column in the oven. When you want to change columns, cut the fused silica just after the union and plug it with an old septum while you do the change. Then affix the new column to the union and finally remove the old septum, cut a few mm of the fused silica to remove the rubber plug, clean and affix to the union. Done. I have been doing this for 30 years and it has never failed me.
Or you can go the expensive way and purchase the Agilent Quick Swap attachment. I have no experience with this, though.