MS vs traditional detectors

[lgchrom]

If cost does not matter, are there many applications where traditional detectors (FID, ECD etc) are advantegeous compared to a GC-MS system?

[DSP007]

If cost does not matter, are there many applications where traditional detectors (FID, ECD etc) are advantegeous compared to a GC-MS system?

Hi
As we say "[ kopejka ruble berejot] ( one cent saves $)" , and economic quest is critical.
"Can I do without MS"? It determinate .This is determined by objective research.
If we are interested in the well-known substances - "why pay more? ((c.) - "Schweppes Advertising" )

[Don_Hilton]

Select the detector based on what you need to do. Mass spec detectors are great if you need the kinds of things that mass spectra can provide. And this can be spectra to confirm analytes or the abilty to detect specific ions, resulting in detection of specific compunds when the signal for all compunds passing through the detector would show unresolved peaks.

But, that does not mean that the mass spectrometer is a superior detector. FID gives more sensitivity than mass spectrometers. And, if you need conrimation of identity, you may be able to obtain adequated confirmation by running the sample on two different types of chromatography columns. Electron capture detectors offer some specificity in detection and senstivity, allowing for some kinds of comounds to be detected at lower leves than can be detected with a mass spectrometer and when coeluting with compounds that are not detected by the ECD.

Sometimes the lower cost, "lower technology" solution is the better solution.

[lgchrom]

Well the ability to identify the eluting peaks combined with the lack of necessity for perfect chromatographic separations are a couple of huge advantages.

My goal would be to do routine (no research) determinations of various kinds.

I already own a GC-FID which is great for quite a few applications.

But I would like to get into pesticides soon, and PCBs and PAHs. In addition to that sometimes I will have to do some qualitative tests on completely unknown organic samples.

Surely I will look into the applications to see the optimum detector for my needs, but I wonder if the MS detector can be an alternative for some ECD and other det. applications, and if it can replace those for routine analysis. This way there would be no need for spending on additional detectors.

Nevertheless I think your post is "to the point".

[Don_Hilton]

There are many labs where MS is the default detector. The only lack is in sensitivity, particularly when acquiring full range spectra. And if you use TOFMS, you get very good sensitivity and capabilty to acquire full range spectra at the same time. It all depends on what you want to spend....

[AICMM]

mariosapm,

Your answer is actually a pretty complicated one. In my opinion, there are compounds that are still done best by a GC detector. The best example of these are the fixed gases like H2, CO/CO2, N2, and O2. These are pretty hard to do with MS for reasons that can be found in the forum.

If, on the other hand, you have access to different MS’s, then there are lots of things that MS can do as well as selective detectors. For example, if you have access to a negative CI MS, you can probably (have not done it myself) do an excellent job selectively detecting pesticides and PCB’s in a manner similar to ECD. Or you might do sulfur compounds by MS with EI source (if you already know what ions to look for) instead of an SCD.

Finally, to confound things further, there are features of some detectors, like equimolar response on an FID (more or less) and very wide dynamic ranges, that are very convenient about conventional GC detectors.

Since you made money no object (aaahhh to be in that situation...) there are lots of things different MS’s can do that are similar to selective detectors. Usually, people are not in this situation and will use a combination of selective detectors (usually cheaper) and MS to accomplish a variety of analytical methods. Can one MS do all these things? I doubt it, but maybe someone knows about an MS that can...

Best regards,

AICMM

[lgchrom]

Thank you for the reply.

I set money as no object in order to get a theoretical view on detectors.

To reverse the question then, what are the advantages of the MS detector that make it irreplaceable? What applications can the detector do exclusively?

From a practical standpoint, would the purchase of a GC-MS system be a good solution to avoid the purchase a variety of other detectors for methods that are to be implemented more scarcely? Also to minimize bench space from having one instrument rather than multiple instruments.

[jymmit]

Non-MS detectors such as FID and ECD are great "generalised" detectors, in the sense that if you want to detect total "TPH" or "PCB" then these detectors, respectively, beat MS hands down, in terms of simplicity and detection limits.

[AICMM]

mariosapm,

From what you describe, an MS is probably an excellent detector. Would do PAH's and a variety of other semi-volatile compounds. Would not do really low level PCBs all that well without some work, but if you had the time to do the work it would probably get you there. ECD for PCB's and Pesticides would probably be better. Remember, too, that you can put an ECD and an MS on the same GC chassis (at least with Agilent) so that does not take up any extra space.

The question really comes down to how you are going to use the system(s).

Best regards,

AICMM