Purchase of a GC/MS or LC/MS system?

[Ruben]

Hi

We are looking to purchase a new instrument and I would like to know which would be the best choice. I am looking at a Varian GC/LC/MS system compared to a Agilent. I was told that the dual GC/LC system is not the best system to work with. The MS is a QQQ system for both the systems. However, Agilent recoomends that we purchase a QQQ GC/MS system and a single quad LC/MS system. I am looking at analysing environmental samples for some of the following compounds: PAHs,TPHs,pesticides(chlorinated,nitrogen and phosphorus based),aliphatic hydrocarbons,Organometallic compounds(orgaontins),endocrine disrupting compounds,PCBs,flame retardants and emrging environmental contaminants.

What would be the best choice of instruments. Varian's option or Agilents option?

[carras]

Hi Ruben

Most of the analytes you cite can be done using GC and some of them (like PCBs) must be done with GCso that a GC7QQQ should be fine . I haven't worked with the Varian system but I seem to recollect some negatives opinions about it, besides I think it must be a pain in the ass to change from GC to LC and back. The offer from Agilent looks more operative but I have my doubts about a single quadrupole LC/MS coping with the interferences you are likely to find.

And do not forget to evaluate customer service in your area!!

Best regards

[Ron]

First, I would not go with the Varian recommendation, GCMS and LCMS are very different, and it is not easy to optimize one MS to do both techniques well.

I find the Agilent recommendation very odd. For environmental samples most people run EPA methods, and there are currently no EPA methods using GCMS/MS, all methods for GCMS are for one stage of fragmentation and depend on generating know fragmentation patterns. To follow EPA methods you would be using only one stage (Q1), and that is a really expensive single quad. There are some advantages to MS/MS in a complex matrix, but in most cases the matrix in environmental samples is clean enough to use a single quad GCMS without major problems.

The really strange part of the Agilent recommendation is to use a single quad LCMS for these samples. Since the goal of single quad LCMS is to produce a molecular ion without fragmentation all you have is nominal mass to identify the compounds. I wouldn't even consider trying to identify endocrine disrupting compounds in a clean matrix with a single quad, I would insist on a triple quad MS.

I would reject both recommendations and go with a single quad GCMS and a triple quad LCMS. This is your best avenue for doing routine applicaitons. If you are doing research and developing new methods for your own use I probably would consider the triple quad GCMS/MS.

[krickos]

Hi

I think Ron has offered some good advice.

Another thing you may have to consider is what "extra equipment" you might need when deciding to have "one instrument " or 2 stand alone ones.

You listed a bunch of compunds and for instance if you aim at flame retardants like octa-deca brominated PBDEs you will likely need some on-column/PTV injector beside your standard split/splitless injector.

Perhaps a purge & trap also is needed for some applications?

[i.horsting]

Hi Ruben,

I would consider as an additional OPTION an OPTIC 3 with cryotrap and
backflush option.
With OPTIC you can do cold injections, which helps with the thermal instable components. And you can use Large Volume Injections. Which can reduce your sample prep.
And With OPTIC, you can buy silanised Liners which are from very high quality (Antwerpse Waterwerken, they use them for some very difficult compounds, like Dimethoat, Carbamezopine, Phosfor compounds).
And If you use a backflush, you can also introduce watery samples. (done by E.Kaal with polymers.)
When you put a OPTIC on a system, it becomes much more versatile. Split/less, Thermal desorpsion, Pyrolysis, LVI. Fast ramp rates (30°C/sec).

I'm sorry if this looks like a sales talk, but i don't understand why people are still using 1 ul hot split/less injections.

More remarks about Antwerpse Waterwerken.
They have 2 OPTIC's, one on a Shimadzu 2010 for PAH's.
and 1 on a LECO TOF/MS. This is a complex system. it's a SPE-LVI-GCxGC-TOF/MS system. (this is were they use the silanised liners).
(they only use the systems for enviromental control of water)

I would consider (i don't know your budget).
A LECO TOF/MS with GCxGC (if you have complex samples)
With an OPTIC-3 with cryotrap and backflush option.

And if you want lower budget.
Use a Quad MS from Agilent or Shimadzu (they both have GCxGC options). and an OPTIC-3.