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[gcmol]

solved

[Don_Hilton]

A time of flight spectrometer pulses ions into the flight tube at a phenominal rate - like 5000 times per second, but the signals are summed and sums of several acquisitions are delivered to the use as a spectrum. I've used the LECO system for a number of years and it acquires 5000 spectra per second - but give acquisition rates of 500 or lower spectra per second to the user. So, you have a sum of at least 10 "spectra" to give a spectrum that you see. I have never used that rate for acquisition - but watch out. An acquisition rate of 2 Hz will only give you 20 data points across a 10 second wide peak (at base). If you use any fast chromatographic techniques, this will limit how fast you can run.

With all of the things that get done by the software and hardware, ask each vendor to show you the results of running a typical sample. It is best to have a sample that you know and understand. And, ask to talk with a a customer or two who are failry close by. See how well the organization supports the instruments when they get into the customers' labs.

[bhuvfe]

I am looking at purchasing either an Almsco Bench TOF-dx or a Waters GCT Premier.

Comparing the two has been ok apart from one aspect, the Almsco quotes "Data range: 5000 spectra per data point (2 Hz)" in some application notes whereas the Waters quotes "a spectral sampling rate of up to 20 spectra per second".

My question is which is better? What exactly are Almsco quoting here?

Has anyone any experience with either system?

Thanks in advance.

Gcmol,

I don't have neither of them but in these days I'm looking in that direction too.

These are two different systems. The Almsco is a low resolution (probably similar to a LECO) the Waters is high resolution. What are your plans for a GC-TOF? Characterization, GCxGC?



Regards,
bhuvfe

[gcmol]

solved

[bhuvfe]

Then, as Don suggested, a demo on both is the best way to go... (even because one supplier uses OFN the othe hexachlorobenzene in their specs).

Have you considered a Almsco + Massworks post-processing software?

[DanCooper]

Hi all,

I came across this paper in CTMS where they use the Almsco Bench TOF-dx for GCxGC analysis. In it they state a data rate of 50Hz and the chromatograms look pretty good.

http://chromatographyonline.findanalyti ... ail/667522

I guess different chromatographic separations require different data rates.

Hope this helps!

Dan

[Don_Hilton]

Note that the article cited is written by a person working for the vendor. Not that this is bad, but don't expect much discussion on limitations. The claim that tradidional TOF instruments do not produce spectra classic spectra that can be searched in libraries is bogus. I've been doing it for years on a GC-TOF. With that claim I'd be careful of the "facts" given. (I have to assume that the author of the article has confused spectra from differnt types on ion sources, such as those seen in LC/MS into the mix - but GC-TOF instruments typically use EI, just like quads, sectors, etc.)

Do your homework. Talk to prospective vendors. Let them tell you the advantages over other instruments, but check to see if those advantages are real.

[Peter_D]

solved

There's no need to erase the original question if it has been solved. I've found the answers to many questions just by searching to see if it has been asked before (and it usually has). It's a great forum and source of information.

cheers

Pete