EPA 525.2 Optimum parameters.

[ricard]

Hi,

I'm using an agilent 7690A GcC, with 5975c MSD and 7893a injector to achive trace levels os semivolatiles with 525.2 EPA method. Now i'm interesting for changing some parameters to optimize the method (Someone using that method whit similar instrumen can position about it???). Till now, i fix the ion source at 230ºC, the quadrupole at 150 ºC, ms transfer line at 250, injector dispense speed 6000 ul/min, holdup time in splitless mode at 1,45 min, injector temperature 250 º, column flow 0,9 ml/min.

i think that risen the ion source/quadrupole temperatures can improve responses of the majority of the components of the method, also i Know that rising temperatures will degraded the source faster, altough perhaps a consensus point is far above 230/150ºC. Also, a lot of refernces use a 300º C injector temperature (i'm using a 900 ul liner, 4 mm, single, taper with wool), moreover other columns flows, injector dispense speeds (1 ul) holdup times. Whic are our recommendations????!!

About ms transfer lines, the references are abot 280 ºC. But, which is the relation between the ms tranfer line temperature and the ion source temperature, which is the allowed diferences, etc.....?¿?¿?¿

Thanks for,

[Bigbear]

I use the standard ms temps of 150 source and 230 quads with no problems. My transfer is @ 280 and I inject @250.

I use a Restek direct connect liner with the hole at the top and use a pulsed splitless injection ( 50 psi for 0.49 min).

I was talking with my Agilent guy today and he told me they ave a new uber single taper liner with wool that works well for 8270.

[tlahren]

I would agree with Bigbear's recommendations on the temps. I found that for reactive SVOCs the Restek liners with the Siltek treatment and deactivated wool worked best. They now have the SkyBlue liners. I believe the glass wool is actually deactivated while in the liner during this process so they have far fewer active sites than any other deactivation process (in theory).

Another way to increase sensitivity on this system is to have the "Inert" ion source if you don't have it already. All the parts in the source have a "dot" imprinted on them to mark that they are "Inert." If you have the inert source you can opt for the larger 6 mm drawout plate for the source optics. It allows more ions (and neutrals) through the source and down to the quad. I have seen on two instruments at least an order of magnitude wider linearity as well as enhanced sensitivity for SVOCs and PCBs. A friend of mine also did this for VOCs 8260 with remarkable results. The Agilent part # is G2589-20045 Description is "73 G2860A DrawoutP". It's about $370. It works for both the 73 and 75 instrument sources and this specific one is for the "inert" source. If you don't have the "inert" I believe they have a different part number for that, but I would recommend the Inert source if you are trying to optimize sensitivity.

Ty

[ricard]

Thanks both,

I've an inert source but i've to check what the draw-out plate is?!! I see that, one or the other, restek liners seems better for this kind of analysis....

Following your recomendations i will rise only the ms tranfer line to 280ºC, although agilent application notes and others establishes frequently much higher tempertures:

http://www.chem.agilent.com/Library/app ... 4199EN.pdf
http://www.chem.agilent.com/Library/app ... 8342EN.pdf
http://www.chem.agilent.com/Library/app ... 4823EN.pdf
http://www.go-jsb.com/media/file/5990-3416EN.pdf
http://www.chromacademy.com/application ... y_GCMS.pdf

http://www.restek.com/images/cgram/gc_ev00695.pdf

Also, it seems there is no problem to establish a 50 ºC difference between 280 MS transfer line and 230 ion source temp, isn't it'¿?

About the pulse splitless i didn't experiment on it. Can i simply change the hot splitless mode alone without changing the present liner or some parameter of the method???

Ricard

Thanks a lot....

[tlahren]

It seems you've been doing your homework! I wouldn't worry about the source or quad temps. The reason these are heated is to prevent analytes and/or matrix from condensing on the source and "dirtying" it up. But remember that the MS is under vacuum so you need far less heat to bring them to vapor point. To me, 300°C seems overkill and is about the max that any source can/will reach. The 50° difference between Txfr line and source is fine. If you're still worried about it you can run a source temp of 250°C with no problems at all. I run with these exact parameters for SVOCs for years as well as my current compound list which includes decabromodiphenyl ether (about 959 amu). My source stays very clean and I have excellent sensitivity.

I don't know much about your GC (7690A). If it says it can do pulsed injection it is worth trying for SVOCs as some of these can be reactive in the GC system. The goal of a pulsed injection is to increase the head pressure (higher flow rate) for a brief period so as to transfer the analytes out of the hot injector and into the head of the column as fast as possible. This reduces the chances of reactions taking place on the glass wool or some other active sites in the injector. Bigbear's parameters seem like they would be a great starting point for you. The pulse pressure parameter isn't always as important as splitless time (pulse time) to optimize. Try a few different methods at 50 PSI for lets say 0.5, 1.0 and 1.5 min. Inject a standard in duplicate for each method. See which gives you better response and go from here.

See these tech notes about the Drawout Plate (i.e. extended linearity kit).
http://www.chem.agilent.com/Library/Sup ... a20917.pdf

This is a really good one: It addresses a lot of your questions.
http://www.chem.agilent.com/Library/app ... 3072EN.pdf

Ty

[Bigbear]

As I said I use a 50 psi pulse for 0.5 min and open my split vent solenoid @ 0.49 min.

About the 6mm drawout plate, it's my understanding that you use this if you are having linearity problems with PAH's. By going to a large drawout plate you give up sensitivity.
I use the 3mm, calibrate from 0.1-10ppb( equivalent) and things work quite well. The gotcha is my auditors don't like that some of my MDl's are "too high". Funny thing that the cpds are halogenated ( whos MCL's were determined with ECD methods). The EPA promulgated 525 so ......We tell the auditors it's their problem as we run the method they promulgated.