Orifice contamination/block.

[achikafu]

Hi all,
I'm currently running my drug of abuse project on abs 3200 qtrap Lcms/ms.. However,recently I found that after few days of my run, the signal will became unstable, and the vacuum gauge reading will drop.. I suspect that this is due to contamination/blockage in the orifice plate. And as each time it happened, I wud clean the orifice, and find that the signal will turn alright again and the vacuum gauge reading will increase back to normal.
What has really been bugging me, is that this problem has been occurring for few times, in about 3 weeks time...which is not normal, as this problem shud not happened so frequent.
I check for the instrument status, on each of my run.. And it turns out to be okay,: the operating temperature reached, and everything else is normal..except for the vacuum gauge reading, which will drop.. I set the temp to 550 degrees, and both gas 1 and gas2 at 40..

I doubt that it is due to improper sample cleanup, as I do spe to extract my samples..
Has this problem ever occurred to anyone before?

[yangz00g]

It is unlikely the orifice contamination will cause the vacuum problem (add in your case), you may want to call service for possible bigger problem. In addition, you can record the vacuum gauge at equilibration step and after MS starts, compare them for a few days to see the variation. Usually they should be very stable.

Dealing with blood or urine samples, you may want to increase the temp to over 600 degree and adjust GS2 (tubo gas) higher (also dependent on the flow rate). In addition, adjust the capillary needle position, too.

Hope this helps

[trozen]

It is unlikely the orifice contamination will cause the vacuum problem ...

in my TSQ Vantage fore pressure readings do change from 1.3 Torr (clean ion transfer tube) to 0.8 Torr after about 1000 injections of urine samples prepared by dilute-n-shoot
well, this is not the vacuum problem but just a hint that the tube should be cleaned..

[yangz00g]

It is unlikely the orifice contamination will cause the vacuum problem ...

in my TSQ Vantage fore pressure readings do change from 1.3 Torr (clean ion transfer tube) to 0.8 Torr after about 1000 injections of urine samples prepared by dilute-n-shoot
w

Please read previous post carefully. Your comment doesn't do any help in this case. Yes, if you seal the orifice entirely, you will see vacuum reading drop.

[Alp]

I am unfamiliar with the 3200. If it is anything like the 3000 then you might want to check that you are not aimed directly at the orifice with your ionspray or APCI.

I agree, a blocked orifice will cause your symptoms.

What is your mobile phase composition and molarity?

Alp

[achikafu]

My mobile phase are :
A : water +2mM ammonium formate +0.2% formic acid
B : acetonitrile +2mM ammonium formate + 0.2% formic acid..
My LC condition are as such :
Total flow : 0.5ml/min
Column temp: 35 degrees
Injection Vol : 30 ul
Column: Restek PFP, 2.1x 50 mm
I'm excluding the LC part as the source of prob, as my pressure is still running okay.

I tried adjusting the spray probe, so it won't get too near to the curtain plate, but it doesn't make any change.
But I noticed that the ceramic balls, which are contained in the turbo heater have been coming out a little. Is it possible, because of those ceramic balls, could have turn the heat to become uneven, thus affecting the vaporization, and contaminate the orifice?

[Alp]

In my last reply I had thought that the ionspray/apci source configuration was similar to that of the ABS API 3000 which can "spray" directly towards the orifice. I have since found that the ABS 3200 QTrap ion source is directed 90 degrees away from the axis of the orifice.
It looks like the ion sources for this instrument are the same as those used on the API 4000, but I do not remember any ceramic balls. If they are "coming out" as you say then maybe some fine particulates from these balls are also coming out in the nebulizer gases.
As I no longer have access to an API 4000 (or a 3200) I can not help with this possibility you have raised.

Something else to consider...
What is the source of your curtain gas?
Do you use a filter on the curtain gas (charcol or zeolite or such) which may introduce particulates into the gas flow?
Is the line for your curtain gas clean?

Alp