Chromatography Forum

The ethanol can be static headspace, SPME or P&T but Lipid oxidation products is either SPME or P&T.

For LOP's I came across a good article that compares SPME to P&T
http://www.ncbi.nlm.nih.gov/pubmed/9987853
The conclusion was that SPME had significantly better calibration linearity and precission.

I'm still ascertaining what exactly I have in terms of the Purge and Trap and What I need. I know I am missing the sparge tube and a lot of the plumbing up front. I have the cryo module, and 1 pocket heater. I am going to want to obtain the 2016 ALS and pocket heaters if I want to enable it.

I'll have to see how much moolah they allot me for capital aquisitions. Usually not much. Though my first choice would be a Combi-Pal that could do liquids, SH, and SPME. Flavors and Fragrances aren't doing much P&T anymore.

If you hook a P&T to the inlet by cutting the carrier gas lines is the inlet still usable if you need to do a liquids injection?

Also I read on another thread another concern is water getting into and messing up newer GC/MS's like my 5975b.

Today I just came accross some literature on Lipid Oixdation products using Static Headspace. They are quoting LOD's on a FID for these aldehydes down to 50 ppb. If so that would make my life alot easier.

http://waset.org/publications/9997968/s ... d-matrices

It that believable though? I thought in general FID's can't detect much of anything below 1ppm. In anycase I would definately use a GC/MS and SIM mode for extra sensitivity.

Also how do you inject 2.0ml of headspace into a S/SL GC injector with a liner volume of ~900ul and what kind of liner do you use?

AIM you mentioned you have some Tekmar 7000's From what I understand they do SH as well as DH. The paper quotes a combi-pal with a 2.5 ml syringe injecting 2.0ml from a 10ml vial incubated at 90 deg C. Can your 7000 perform this? You can reach me at sschoenfeld[at]Innovaflavors.com

If you plumb the P&T in as stated above you do not need concern yourself about liner volume as the sample is in the gas state durring desorb. I use a 1mm iner dia liner for 524 and split 150:1. with great results using a 0.18 dia column.

The method of SH of aldehydes in oils injects 2.0ml with a combi-pal that is a heated syringe type sampler with a 10:1 split. I am just shocked they are able to quantitate down to 50ppb on a FID. I thought even splitless most stuff on a FID is limited to 1ppm or more. If I program a SIM method on the GC/MS I should have all the sensitivity in the world and if all I need is static headspace which I had always dismissed as not sensitive enough for flavors work, my options are wide open. I see Agilent 7694's and Varian samplers for as little as $4k.

BTW If I was injecting that high a volume (2.0ml) would I need a retention gap to focus the analytes?

Shouldn't need a retention gap. It's most useful when doing solvent re focussing where you set the oven to 10 C below the bp of the solvent. If you are injecting a gas sample the analytes should foccus at the head of the column if the temp is low enough. You may want to try lowering the injection port to a temp that will not condense your sample.

Except the analytes need to be refocused don't they? Assuming I inject a 1-2ml. Even pulsed splitless (~ 3 ml/min) that plug is nearly a minute long. 10:1 split isn't as bad the plug is about 0.2min.

Except the analytes need to be refocused don't they? Assuming I inject a 1-2ml. Even pulsed splitless (~ 3 ml/min) that plug is nearly a minute long. 10:1 split isn't as bad the plug is about 0.2min.

We do 1ml injections with our Flex for headspace and found that if you set the syringe to deliver the 1ml over a few seconds is it equal to doing a fast injection at 10:1 split or there abouts. The split mode is on so the excess is split off out the vent. This is still equivalent to injecting almost 1ml of sample instead of 1ul so that gives you nearly 1000x more sensitivity.

If you hook a P&T to the inlet by cutting the carrier gas lines is the inlet still usable if you need to do a liquids injection?

Also I read on another thread another concern is water getting into and messing up newer GC/MS's like my 5975b.

Yes you can still use the injection port for regular injections, you just switch liners from a low volume 1mm liner to a 2mm or 4mm liner you would normally use. I currently have our new Agilent 7000QQQ setup with a purge and trap and can switch between sampling modes just by telling it to use the autosampler or not to use it when doing purge and trap. Just build methods for either and save the settings. Just make sure the union in the gas line does not interfere with the autosampler when it is in position, we have ours under the center cover just to the side of the injection port.

Thanks for all the advice. I'm am currently try to decide if I can get away with an Agilent 7694 and just do static headspace for $4k or If I should get a CombiPal with SPME holder and actually ITEX II looks interesting as well but that is $16.5k. I am thinking based on the article SH is sufficient for both Ethanol and lipid oxidation products especially if I setup a SIM method.

We do 1ml injections with our Flex for headspace and found that if you set the syringe to deliver the 1ml over a few seconds is it equal to doing a fast injection at 10:1 split or there abouts. The split mode is on so the excess is split off out the vent. This is still equivalent to injecting almost 1ml of sample instead of 1ul so that gives you nearly 1000x more sensitivity.

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Though if you are doing splitless injection your flow rate is ~ 1ml per minute and the liner volume on a 1mm ID is not big. Isn't there a chance of backflash or is it forced into the column at a high rate?

We do 1ml injections with our Flex for headspace and found that if you set the syringe to deliver the 1ml over a few seconds is it equal to doing a fast injection at 10:1 split or there abouts. The split mode is on so the excess is split off out the vent. This is still equivalent to injecting almost 1ml of sample instead of 1ul so that gives you nearly 1000x more sensitivity.

Though if you are doing splitless injection your flow rate is ~ 1ml per minute and the liner volume on a 1mm ID is not big. Isn't there a chance of backflash or is it forced into the column at a high rate?[/quote]

With splittless injections the excess will vent out the septum purge port, so for this type of injection you will still get some type of split action happening. If it can't vent it will cause the injection port pressure to rise which will increase the column flow. For the headspace injections we are using a regular 4mm double gooseneck liner, no need for glass wool since you are injecting a gas. I only use a 1mm liner if I am doing Purge and Trap, which would also work with the Static Headspace unit since it transfers the sample similar to desorbing from a P&T. The autosampler type head space units though will be injecting so you have to optimize the injection speed to your column flow and split flows.