Chromatography Forum

I am looking for a GC-FID headspace system basically for volatile analysis in soil & sludge Which system would be performance wise better PE Clarus 580 or Agilent 7890. Thanks

The most inert system is the better one.

Fixed loop injectors that use valves with rotors are inherently less inert than a timed injection system that allow the column to be a few centimeters from the headspace vial, if this is your definition of performance.

Given a properly designed loop system with special deactivated parts and using special chromatography techniques it is possible to inject twice as much sample onto a column using a fixed loop system. But few know how or understand the technique to perform this.

Fixed loop system have fewer parts but require more service.

Timed injection systems generally are more expensive. (and worth it according to some).

Take your choice. Both may perform admirably.

best wishes,

Rod

The most inert system is the better one.

I agree.

Given a properly designed loop system with special deactivated parts and using special chromatography techniques it is possible to inject twice as much sample onto a column using a fixed loop system. But few know how or understand the technique to perform this.

Besides having essentially all flow coming from the HS sampler into the inlet and turning off the septum purge, What else is there?

Fixed loop system have fewer parts but require more service.

Assuming I understand what for mean by fixed loop, I've used them (agilent) for over 15 years with very few problems... maybe I've just been lucky!

Timed injection systems generally are more expensive. (and worth it according to some).

I'm not sure what you mean by "time injection' ... do you have a link to such system?

Soon I will also have a system that can do headspace using a CombiPAL so with a heated syringe. I'm sure i will have some learning to do!

- karen

chromatographer1 wrote: The most inert system is the better one.

Karen wrote: I agree.

Quote:

Given a properly designed loop system with special deactivated parts and using special chromatography techniques it is possible to inject twice as much sample onto a column using a fixed loop system. But few know how or understand the technique to perform this.

Besides having essentially all flow coming from the HS sampler into the inlet and turning off the septum purge, What else is there?

Karen, the technique of taking 2mL of headspace vapor and injecting it directly onto a capillary column and focusing the plug without cyrogenics and without using a splitter or a septum purge is not well known. Time and space limitations require I keep this answer short.

Quote: Fixed loop system have fewer parts but require more service.

Assuming I understand what for mean by fixed loop, I've used them (agilent) for over 15 years with very few problems... maybe I've just been lucky!

Not lucky, but fortunate in that your work did not require it. The PE HS analyzers do not use a fixed loop valve system. You can peruse their web site for details. Fixed loop sample systems can be contaminated and require replacement or cleaning of parts. Clean or unreactive samples may not require the fixed loop system to be serviced for months, or even years, depending upon the volume of use. Likewise, the PE system will eventually require service, but it is not so easily performed. It is a matter of comparison.

Quote: Timed injection systems generally are more expensive. (and worth it according to some).

I'm not sure what you mean by "time injection' ... do you have a link to such system?

The fixed loop system pioneered by PE back in the 1960s has been used in violation of the PE patent for many years by Tekmar and Agilent. Perkin Elmer did not go to the expense of protecting their patent as PE felt that design was made obsolete by the timed injection system they patented during the 1980s(?).

Soon I will also have a system that can do headspace using a CombiPAL so with a heated syringe. I'm sure i will have some learning to do!

The heated syringe system is not the most inert system used today, but it may be adequate for most common HS applications. Often an inexpensive instrument is adequate to perform routine work. There is no need to buy a Lotus when a Cadillac will suffice. And some prefer a nice Kia.

- karen

Chromatographer1 aka Rod

Agilent 7694 HS sampler (and its italian analog) - is a " good work old hopse" , but 7890 and new HS - is a "problem device". PE500 isn't know .