Chromatography Forum

Hi

I was wondering if there were any books or other literature on the basics/theory/method development etc for GC-TOFMS???

Method development for GC-TOFMS will be very much like method development for orther GC/MS instruments. In general, establish good chromatography - particullarly in the portion of the chromatogram with analytes of interst and acquire data in an appropriate mass range, using detector conditions optimized according to the method of optimization prescribed by the manufacturer. For theory of TOFMS, look at the manufacturers' web sites (there are several manufacturers of TOFMS systems). GC-TOFMS uses the same kind of ionization that you find with MSD's, so understanding fragmentation patterns works the same way as with the other types of instruments.

If you have encountered a partiular problem or have questions on a specific application, feel free to post. There are a few of us who post here who work with GC-TOFMS or GCxGC-TOFMS.

Method development for GC-TOFMS will be very much like method development for orther GC/MS instruments.

I this is an area I would like to get more familiar with. I saw that Agilent just came out with a GC-QTof Instrument this month.

Is GC-ToF or GC-QTOf used much? And what type of ionization source is most common? I don't think brochure for the new Agilent GC-QTof mentions the type source that comes standard with it.

For exact mass instruments such as TOf and even more so for QToF I would think one would want to use a soft ionization technique in preference to EI. In ToF mode I would think you would want an unambiguous parent ion, and with a QTof in MS/MS mode it seems to me you would want the fragmentation to happen in the collision cell.

So to me that would suggest using something other than EI. Atmosphere Chemical Ionization maybe?

- Karen

There are several GC-TOF systems avaialble and there is gowing use. EI is commonly available. Various vendors have other offerings as well. So far, I believe you will find chemical ionization and field ionization.

If Agilent does not have PCI and NCI sources for this instrument available now, I would look for them in the future. (I looked for the new instrument on the Agilent web site, but missed it if it is there...)

GC triplequad instruments have these types of sources available. The use of a TOF rather than a final quad is an exciting idea. And the idea of being able to do a scan the first quad and get complete fragmentation patterns of each ion in an EI spectrum is intriguing as well.

If Agilent does not have PCI and NCI sources for this instrument available now, I would look for them in the future. (I looked for the new instrument on the Agilent web site, but missed it if it is there...)

It was announced this month... It may not actually be available yet. Here is the info:

http://www.chem.agilent.com/en-US/produ ... ation.aspx

The use of a TOF rather than a final quad is an exciting idea. And the idea of being able to do a scan the first quad and get complete fragmentation patterns of each ion in an EI spectrum is intriguing as well.

LC-QToF instruments that can be interfaced to GCs using Atmospheric Chemical Ionization (APCI) sources have been around a number of years now, but I don't know if EI-QToF is common.

- Karen

http://www.amazon.com/Mass-Spectrometry ... 3540407391

This is a great text book with information about all different types of MS instrumentation. It also has several chapters devoted to interpreting spectra. It doesn't necessarily have information dedicated to method development, but would be a good starting point. Its also not too expensive, and worth the price.

The Agilent is the first commercial GC-QTOF (EI), and is not available yet. As of about 3 weeks ago Agilent only had one system running I believe with 3 more on their way. Other EI TOF options are the Waters GCT Premier and the LECO systems. APGC is worth a look at, Bruker, Waters, Agilent all now produce atmospheric interfaces so a wide range of mass analysers available. We're planning on looking at some APGC-FT-ICR later this year.

We have the GCT Premier and an Agilent LC QTOF. In a couple of weeks we will have an Almsco bench top TOF installed too. A steep learning curve.....

It should be noted that there are some benefits to TOF and some potential drawbacks. TOFs add increased scan speed (as they are not actually scanning masses) to traditional single quad MS. This helps for Fast and Ultra Fast GC analyses. However, Agilent's latest single quads have faster electronics than before and offer extremely increased scan speed as well as simultaneous SIM/Scan capabilities. Other benefits to TOF are high mass accuracy (for most TOF systems).

A potential drawback is extremely large data files (Agilents's new Q-TOF says in the GB per file range)

Many are capable of 10,000 resolution power or better which is a required parameter for certain types of analytes such as dioxins, furans, PCB congeners etc. Most often TOFs are used on a GC for either really fast GC analyses with short large bore columns at high flow rates and/or they are used to increase analyte sensitivity and reliability through high mass accuracy analysis. I currently use a Thermo DFS (dual focusing magnetic sector) for GC/HRMS. This type of MS is quite a bit different than both the quads and the TOF and also way way more expensive. I'm still not sure if it was worth the extra money (about $700k). It has a comparable SIM scan rate to a traditional single quad but it has extremely high mass accuracy (>50,000 R) while maintaining unmatched sensitivity. I have been "learning" this instrument for over a year now and I would still say I'm quite a novice. I found that there seems to be more of a learning curve involved the more you spend on an instrument.

It is all about matching the tool to the task. In for GC/MS systems in our lab, we have DFS instruments, quadropoles, and TOFMS's. They have different tasks because each instrument offers some unique capability...

Well put Don. TOFs, Sectors, Orbitraps, Quads etc. all have different applications and thus why none of them have emerged as the "BEST" MS detector.

Don,

You wouldn't happen to be at the CDC would you? I know they have a couple DFS instruments as well as older MAT95s.

I'm at CDC. There are some great instruments here and some great people running them.

A TOF for rapid 'scanning' for fast chromatography is a very different beast to one built for high resolution/high mass accuracy. Pegasus will give much better results with fast chromatography than a GCT or future Agilent QTOF.

A TOF for rapid 'scanning' for fast chromatography is a very different beast to one built for high resolution/high mass accuracy. Pegasus will give much better results with fast chromatography than a GCT or future Agilent QTOF.

We'll have to see how the Almsco performs! We're hoping well!!