What benefits of GCT & TruTOF?

[Chitra]

Hi,

Please help me by giving some suggestions. I am planning to buy a GC-MS system for our Pesticide residual analysis in food products. I have finalized my selection of GC-MS to use the TOF technology and have stream lined to the GCT Premier and TruTOF system. I am having difficulty in understanding the benefits and terms used with the GCT; such as exact mass measurement and deconvolution, and with the TruTOF such as high acquisition rate and true signal deconvolution. Can anyone please expend your thoughts on this?
Thank you.

[jh1]

From the little I know the Waters GCT is a better system if you typically have heavy background/matrix effects (herbs and spices) and would like to use exact mass (i.e ion 254.51 as supposed to just 254.5 to help remove matrix interferences with similar ions) whereas the Leco TruTOF allows for very high scanning rates allowing you to have very short run times while still seeing a large range of compounds.

One thing to keep in mind is what level of sensitivity you need, standard tabletop TOF units will be more sensitive than a MS-Quadrupole in Scan mode but typically less sensitive than quadrupoles in SIM mode.

[yangz00g]

Why TOF for pesticide analysis, if not for a quick screening method?

[Don_Hilton]

The deconvolution on the TruTOF can help dig stuff out of a complex matrix. High resolution helps to dig stuff out of a comples matrix as long as there is not a coelution that is close enough in mass to confound the signal. And, I don't know how high the resolution is on the GCT. If you have not done so already, I would suggest sending a typical sample, spked at high and low levels to each vendor and have them show you what the advantages are.

On the question of screening. You should be able to do both screening and quantitation with a TOF

[Chitra]

Thank you all for your valuable inputs.
From what I gather, the TOF technology is the best choice for FAST screening and quantitation / qualitative work. On the other end, exact mass measurement would only be good for structural elucidation and more of target analysis but has better sensitivity. Am I correct in saying this?
However, we are working on the determination of OPPs & OCPs from 300pg/ul down to 5pg/ul in fruits and vegetables. Will the TruTOF with acquisition rate and true signal deconvolution be able to do the fast screening job better then GCT?

[yangz00g]

I am pretty sure that you will struggle with TOF to quantify as low as 5ppb pestcides. Even after Quecher, you will find matrix troubling your analysis.

You say TOF has better sensitivity for target analysis, than what? a comparable triple quadrupole MS? come on!

[Don_Hilton]

A TOF can get down to 5 ppb. The tradeoff between the TOF and an MS/MS instrument is that the TOF is acquireing full mass range spectra through the entire run. You can use this for screening and retrospective data analsysis. The MS/MS, on the other hand monitors one or a few masses in the chromatogram and obtains sensitivity by looking for specific secondary fragments. YOu need to pick the tool for the job at hand.

And, this is another good reason to run a samle by the vendor. While you can get 5 ppb llmits of detection for some pesticides, you need to be sure of the typical analytical range for the ones of interst to you - and in your matrix.

[lmh]

It's particularly important to run trial samples with different vendors as different vendors take very different attitudes to publishing sensitivity values.

Some manufacturers give figures that they expect to be maintained by a typical machine 5 years after installation, others give figures that they expect to achieve the day the engineer finishes setting it up, but don't care much whether the instrument continues to perform at that level after the sale.

Unfortunately you can't compare brochure values.

[Chitra]

Thank you all for the inputs. Sorry; for my delayed response as I had so much of lab work to be done. I think that is the reason why we need the fast TOF screening technology to help us identify the component of our interest.

Once again thank you all for the valuable inputs; I will now bring it up with the vendor.