GC-TOF

[Carrie Wild]

Hi
I'm new on this forum and I hope this question has not been asked before
We currently run routine GC-MS profiling of silylated derivatives on an Agilent 6890/5973 and are planning to buy a second GC-MS system, ans why not a GC-TOF
I would like to understand the differences between the Waters GCT and the LECO systems Pegasus and TruTOF : if any of you have been using some of these systems could you tell me which advantages and drawbacks you see in each of them ?
Thanks
Carrie

[che313]

are u looking for qualitative or quantitative analysis?

[Carrie Wild]

both, primarily quantitative but also qualitative (identification of unknowns)

[sindhu]

Primarily when it is for quantitative applications then you must choose GC-MS/MS ( QQQ ) instead of GC-TOF as TOF can not be useful for quantitative applications. With QQQ you can able to do qualitative applications as well off course not much like TOF systems.

You can call both Waters & Varian and buy either of them.

In my opinion Varian system seems to better than Waters in specifications wise

[zokitano]

Primarily when it is for quantitative applications then you must choose GC-MS/MS ( QQQ ) instead of GC-TOF as TOF can not be useful for quantitative applications. With QQQ you can able to do qualitative applications as well off course not much like TOF systems.

You can call both Waters & Varian and buy either of them.

In my opinion Varian system seems to better than Waters in specifications wise

When did Waters start to manufacture GC-MS/MS or any GC system?

[bhuvfe]

When did Waters start to manufacture GC-MS/MS or any GC system?
[/quote]

Zokitano,

They don't produce any GC system but only the MS part. You can easily recongnize a Agilent 6890 or 7890 in their systems.
As far as I know they have been around in high-end MS systems for years.

[zokitano]

Zokitano,

They don't produce any GC system but only the MS part. You can easily recongnize a Agilent 6890 or 7890 in their systems.
As far as I know they have been around in high-end MS systems for years.

I know that Waters produces LC-MS and LC-MS/MS systems, but I wasn't aware that they produce MS detectors for other GC systems as well.

Thank you for the information

[bhuvfe]

Carrie,


The GCT is a 6000 resolution MS. So it will help you to get elemental compositions for your unknowns. I'm not aware if it can be used for quantitative work. As pointed out by others a QQQ is generally better ( if you really need all that selectivity..).
Before considering it you may want to understand the way the ions are recorded. Waters uses TDC others use ADC. See this good article from
JEOL:
http://www.selectscience.net/downloads/ ... of_app.pdf

It's for a LC-TOF but they have a GC-TOF too; or this article from agilent



http://www.chem.agilent.com/Library/tec ... 1728EN.pdf ( but they don't sell GC-TOF systems)



The LECO is a unit resolution instrument (such as your 5973).

The only advantage of the latter is the high acquisition rate (i.e. more points per peak) so it should give you an edge in fast GC and more sensitivity compared to a quadrupole in scan mode (but I wouldn't bet in SIM mode...)
I had a demo on a TruTOF. I wasn't particularly impressed. Since the noise it's quite high you need software to dig up your analytes (AMDIS or similar ).

Consider also that there's quite a big difference in price too. The LECO is 1.2-1.3 times a single-quad the GCT should be more than 2-2.5 times.

Best wishes.

bhuvfe

[Stryder08]

You can definitely use a Tof for quantitation. A tandem quad is much better, but a ToF can do it.

[Ron]

The LECO system is low resolution as pointed out about, and the sensitivity is not very good. The quoted sensitivity specification is signal to noise of greater than 10:1 for 2 pg of hexachlorobenzene on column. Most GCMS systems use octafluoronaphthalene for sensitivity measurements, so the numbers aren't directly comparable, but generally range from 100 to 400 signal to noise for 1 pg. I have known people that have tried to move trace analysis to a LECO TOF from a quadrupole and have given up because of lack of sensitivity.

The LECO can aquire up to 500 mass spectra/sec, but does that really matter in the real world? A single quad can acquire data at a rate of 30 to 50 spectra/sec, depending on the scan range, with much better sensitivity.

The Waters system is high resolution, and can be very useful for compound identification, as pointed out above, but is not generally used as a general purpose instrument.

A TOF can be used for quantitative work, but the linear dynamic range is limited compared to a quadrupole instrument.

For general purpose work such as you are doing, a single quadrupole instrument is probably the best balance between price and capablility.

[Ron]

I forgot to add that all Waters mass spectrometers except for the newest ones are the old MicroMass systems. Waters purchased MicroMass, and re-branded the systems with the Waters name, so there is a long history with GCMS.

[Don_Hilton]

There are two kinds of TOF instruments out there for GC. The Waters GCT is high resolution and the LECO is unit mass. There is a tradeoff between mass resolution and dynamic range. The last time I looked at the GCT, the dynamic range was significanly less than the LECO - but if you need exact masses, the high resolution is a lot more helpful than the unit mass instrument.

Some folks expect all GC-TOF instruments to have a limited dynamic range and to be high resolution - including some "experts" in the field.

As far as the question of someone trying to move a method from a quadropole to a TOF and having sensitivity issues. This could be operator or instrument. And from my experience, the LECO TOF gives good sensitivity - and this can be found in published literature. Some training in the use of the instrument is helpful. If you try to drive the instrument like you drive a quadropole, you will not get the best out of the instrument.

I suggest that you contact each vendor of interst and ask for a demo. Tell them that you have specific analytes in your particular matrix and need to see the compunds with a specific RSD at some level. See how they do.

And, if you do this, many of us who watch this board would love to see how the comparison turns out.

[msuk]

My question would be why you are considering a TOF? The two types of conventional GC-TOF system out there are very different as discussed - Waters for acc mass, or Leco for fast scanning. Do you need to do either? If not then personally I would steer well clear of GC-TOFs.

If you're looking for acc mass of the parent and not bothered about any EI fragmentation, are you aware of the GC-APCI-TOF interface launched by Bruker at ASMS last year? Having used both LC-TOF instruments are far more robust than their GC- equivalents. I wouldn't be surprised if we see these interfaces from other vendors too