Chromatography Forum

Hi,

Apologies if this has been posted before, I have'nt used this forum for a while.

I am doing a bit of research into using TOF-MS as an alternative to GCMS (more specifically I'm interested in the LECO TruTOF as an alternative to an agilent 6890/5973)

A few areas I'd like to shed some light on are:

- Suitability of TOF for high-throughput organic work: Could TOF-MS be an economically viable alternative to GC/MS for organic methods? Or is this technology better suited as part of a low-throughput, high-spec system? I am running PAH/Phenols, OCOPs, PCBs, SVOC, methods based on the USEPA standard methods (8270 etc.)

- Advantages of higher scan rate associated with TOF-MS: More scans/sec should allow easier identification of peaks, also more datapoints allows software algorithms to deconvolute peaks, leading to shorter run-times as chromatographic resolution is less important. Would the GC be a time-limiting step in the system? i.e. would the length of a run be limited only by the capability of the GC oven to ramp at the appropriate rate? Could new methods take advantage of the high scan rate by increasing the suite of analytes that can be distinguished in one run?


- Increased linear dynamic range: A high range of linearity can be achieved with TOF-MS. What aspect of TOF-MS gives an increased linear range?

- TOF-MS versus quadrupole: Can TOF-MS match the sensitivity of a quad running SIM mode? i am not referring to the high-end instruments such as tandem MS, GC/GC etc. just straight GC/TOF-MS

- GC/TOF-MS versus LC/TOF-MS: Leco promote their ‘Pegasus’ and ‘TruTOF’ GC/TOF-MS models as high-throughput instruments, how do the Agilent LC/TOF-MS systems (6200,6500 series) compare with the Leco GC/TOF-MS systems? Is TOF-MS particularly suited to either separation technique?

- Practical considerations: Reliability? Cost/availability of parts/consumables? maintenance issues? common problems associated with TOF-MS? Ease of installation? Any modifications to laboratory required (e.g. temperature control)? Any implications regarding using Leco MS with agilent GC? (would this affect Agilent warranty?).


Any help greatly appreciated

It looks like you have some of the sales literature. I strongly reccomend that you talk with the sales representative and see a real live demo. This will move you from hearing what the instruments ought to do to seeing what they do.

As far as service issues - ask your sales rep for references.

And, I can help you contact your LECO rep if that will help. There should be an e-mail link at the bottom of this post.

Thanks Don,

I have a contact from LECO

just trying to get more of an idea from people already using this

thanks

One of the main things to consider is sensitivity. The TOF instruments are typically much less sensitive than the quadrupole instruments. You need to be sure the TOF will meet the detection limits you need if you are running low concentration samples.

In most cases a TOF will not have as broad a linear dynamic range as a quadrupole instrument for quantitation, again a demo is probably in order to verify your application.

Modern quadrupole instruments should have high enough aquisition rates to get enough points across the peaks, e.g. 16 mass spectra/sec, mass range 35 to 500.

Deconvoluton can help, but is not a substitute for chromatography, especially in some of the EPA methods where internal standards and surrogates should be chromatographically separated for best results.

Hello; I am agree with Rom regarding limits of detection could be an issue; one alternative could be Waters too, ask what they have for TOf instruments.

One adeventage of Tof; is the great selectivity for general screening; with a proper softwere you can analyze turget and untarget components; this means too probably you could reduce you cleanup sample procedure to a more generic way.

As far as I know the dinamic range for Tof is lower that Quads.

Very important is to remember, a Tof Instrument do not scan as far as I remember; the instruments take "every thing"
I think a Tof Instrument is suitable in trems of screening; but I suppose there are people who know more about it

Why re-invent the wheel.....your analysis ( running PAH/Phenols, OCOPs, PCBs, SVOC, methods based on the USEPA standard methods (8270 etc.))
have been well characterized by GC/MS ...Quads....make life easier and get one of those.

If you are looking to expand your "portfolio" of applications...look into a LC/TOF, and by the way their dynamic range and sensativiets have greatly improved....I believe in that arena, Agilent is the leader.

My 2 cents worth and probably less then that.

thanks for all the replies.

I personally am quite happy using quad GCMS but my boss asked me to do a bit of research. i think the prospect of increasing run speed is quite appealing but if it is at the cost of not being able to perform our more sensitive analyses there woul'dnt be much point. in my humble opinion we are probably running our SVOC analyses just a little too fast as it is. I once accidentally ran a SVOC run on a method with a slow ramp and got great results.

The PAH method i run has a low cal level of 0.1ppm for most compounds which translates to 100pg on-column. Leco claim that their trutof has S/N ratio of >10 for 2pg Hexachlorobenzene on-column, so it would be interesting to see how bad/good the S/N ratio would be at 100pg.

We have a Leco TOF in our lab that was purchased with the same intent you have, running somewhat routine environmental analysis. It has never been used for anything other than specialty analyses due to the level of effort required to bring it online.
The software on our sytem is not well suited to rapid quantitation so any time saving on the GC/MS is quickly eaten up on the data reduction.

There are LECO TOF's in several laboratories doing environmental analysis day in and day out. I know of one lab that is using an instrument for rapid analysis and either is purchasing or has purchased a second because they like it so well.

Steve, I'd love to provide you with whatever assistance I can. (One feature of LECO, we do not need a purchase order for an applications chemist to talk with you over the phone for a while.) There is an e-mail link at the bottom of this post. Please drop me a note so I can contact you.

Hi all,

I heard that Bruker Daltonics has recently released a GC/APCI source which allows for a GC or LC to be coupled with any of their ESI-TOF-MS instruments. Depending on your workflows, this could be a good option as it allows you to run as a GC system when you need it and then swap to an LC system when required (and it only takes a couple of minutes to change between the two).

I found an application note which was published in LCGCEurope in July and it is available on their website (http://www.bdal.com/library/literature- ... 1/419.html)

Most TOF instruments need some level of temperature control in the laboratory to ensure the mass accuracy of the data recorded. Wild temperature swings can lead to poor results.

As with any large instrument purchase, I would definately recommend talking to your local sales office and insist on having your samples run on their system - it is the only way to know if the system can do what the brochures say. I also know that Bruker will put you in touch with their applications scientists prior to any purchase.

Cheers,
Leith

Thanks guys

Hi all,

I heard that Bruker Daltonics has recently released a GC/APCI source which allows for a GC or LC to be coupled with any of their ESI-TOF-MS instruments. Depending on your workflows, this could be a good option as it allows you to run as a GC system when you need it and then swap to an LC system when required (and it only takes a couple of minutes to change between the two).

I found an application note which was published in LCGCEurope in July and it is available on their website (http://www.bdal.com/library/literature- ... 1/419.html)

Most TOF instruments need some level of temperature control in the laboratory to ensure the mass accuracy of the data recorded. Wild temperature swings can lead to poor results.

As with any large instrument purchase, I would definately recommend talking to your local sales office and insist on having your samples run on their system - it is the only way to know if the system can do what the brochures say. I also know that Bruker will put you in touch with their applications scientists prior to any purchase.

Cheers,
Leith

The temperature issue is very true. I have a couple of Waters LCT Premier XE's in the lab and we recently had to fix the temp. issues, as the swings in temperature really hurt the mass accuracy.

Going to a TOF takes you in one of two directions. You go either to an integer mass instrument or to a high resolution instrument. The integer mass instrument is more able to take temperature swings - in part because you are not trying for that high mass resolution. The high resolution TOF may be a bit more sensitive for temperature -- but if you need to go to high mass resolution, you are working on solving a problem that you could never dream of solving with a quad. And, as they say -- nothing in life is free. (But, yes, we can always ask!)

And, all of these instruments keep improving as time goes by. And to think, when I started in the lab, we were looking forward to this new device that was allowing some research groups to do GC/MS. It was the jet separator. And, there was the possibility we would have to go for a powerful computer, like a PDP-11, just to acquire the data. (The capillary column arrived and the jet separator got sidelined.)