Chromatography Forum

Hello,

My supervisor has asked me to come up with a screening method for unknown samples. Could anyone suggest sample prep/ GCMS methods for the following intrument setups that will give us as much information about unknown samples as possible?

Thanks!

Drinking water- river water

Shimadzu GC-17A MS- QP 5000 with EST Encon purge and trap
Vocarb 3000 & MORT in P/T
DB-624 column 60m x 0.25 x 1.4um

Agilent GC- 7890A MS-5975C S/SPL inlet
Capable of running liquid & SPME injections
DB-5 column 30Mx 0.25 x0.25um

If you need more information pls let me know!

here's one:

http://www.epa.gov/waterscience/methods ... /524_2.pdf

I just wanted to add that for the unknown samples they may be contaminated and not be just water, if anyone has any suggestions for those as well I'd appreciate it!

For "water" samples that may have too much non-water in them a fast extraction of 1 to 2 mL in 1 mL of DCM analyzed using a fast GC program will tell you if a low level Semi-volatile method is going to be trouble. For volatiles I use a headspace system for screening but a high dilution 1:1000 with a P&T can be substitued, you just won't see as much. As long as your sample isn't pure product your system will survive and with that high of dilution you shouldn't have foam-overs. Of course when you don't see anything you will have to reanalyze but cest la vie.

To: Steve Reimer

What do you mean by a fast extration? Is that just putting 1-2 mL of sample in DCM and using the DCM layer?

Thanks!

[ a fast extraction of 1 to 2 mL in 1 mL of DCM analyzed using a fast GC program will tell you if a low level Semi-volatile method is going to be trouble. ][/quote]

Hi there LWC,

Please let me know if you are interested in using other materials than SPME or Twister for your sample preparation.

Cheers,
ES

ES,

I am open to just about anything.

Hi LWC,

Pls see here for your sample preparation:

http://www.glsciences.com/products/monotrap/index.html

You will have an incredible wide selectivity with MonoTrap. The base material is monolithic silica and C18 and carbon is medified. There are 2 types of MonoTrap: 1 is for solvent extraction and the other 1 is for thermal desorption.

Hope this could be another option for you. Let me know if you need more info.

Cheers,
ES

LWC,

I would recommend headspace screening as the technique of choice based on what you describe here. I have set up a 7890/5975 for a customer to do just such headspace screening on water samples. Put a mL in an ALS vial, shake it for a minute or two and inject 10-20 uL of the headspace with a decent split ratio and you should have a good handle on what you are faced with. Since you are using MS, I would also compress the chromatography in order to do the screening rapidly. Remember, it's screening.

Best regards,

AICMM

[quote="AICMM"]LWC,

I would recommend headspace screening as the technique of choice based on what you describe here. I have set up a 7890/5975 for a customer to do just such headspace screening on water samples. Put a mL in an ALS vial, shake it for a minute or two and inject 10-20 uL of the headspace with a decent split ratio and you should have a good handle on what you are faced with. Since you are using MS, I would also compress the chromatography in order to do the screening rapidly. Remember, it's screening.

Best regards,

AICMM[/quote]

Hi AICMM,

I know this post is a little old, but what kind of inlet/oven temps do you recommend for this sort of screening?

LWC,

Inlet on the 7890 is at 250 C. Transfer line is at 280 C. Oven initial temp 60 (probably a bit warm but it is a 60 meter column and it is easier to get to this temp), hold for 1, 14 C/min to 220C for 1 min, run time 13.5 minutes. Lightest component peak shape is a little bit ugly but it works well enough.

Best regards,

AICMM

Sort of off topic, but I feel you would be better served using the 20M X 0.18 624 column in your P&T setup. You can run it @ 0.6-0.7 cc/min and still resolve the gases with the initial oven temp of 35. The benefits are less water getting to the ms.

This is what 8260 and 8270 were designed to do. They're in SW-846 - you can find it online on the US EPA site. You've already got the hardware - just follow the methods.

www.usepa.gov/

If you're screening for unknowns you'll want to meet tune criteria - it'll give you more confidence in you tentative identifications (TIC).