In our lab we have an old autosampler for static GC headspace with loop injection of 1 mL.
In view of replacing it we are evaluating other instrument with loop or syringe sistem for sampling/injection.
With our loop system, for some determinations, we have experienced carry over from one sample and the following and difficult to purging transfer line.
Syringe system can resolve these problems?
Anyone have experience with both system?
Any suggestions are greatly appreciated
Thanks in advance
By Anonymous on Monday, October 14, 2002 - 06:15 am:
There is another system besides the loop or syringe system. It is Perkin-Elmer's HS analyzer.
It uses a timed pressure injection system.
In my experience it produces the least amount of carryover compared to any loop or syringe system I have seen.
Each system has its strengths and weaknesses, especially a loop system that does not have an inert transfer line and valve-loop treatment.
Review all the available options of the three systems before you make your decision.
a PE HS-40 user
By Ron on Monday, October 14, 2002 - 06:21 am:
The loop systems I have used have a flush through the loop between samples. When I have seen carryover it is usually because of inadequate flow through the loop during the purge process, although as mentioned above the inertness of the system may be an issue. A temperature set too low will also increase carryover.
Syringe systems also have a flush mechanism, and the first time I used one I was surprised to see how low the carryover was. The system was more effective than I had ezpected, and was about the same as the loop systems I had used. Again, the low carryover is a function of a properly set purge flow, time, and temperature.
No experience with PE, but it is possible to get low carryover on a loop or syringe system by adjusting parameters.
By Anonymous on Tuesday, October 15, 2002 - 12:02 am:
Thanks to Ron and Anonymous for your useful suggestions.
By j.vloet on Friday, October 18, 2002 - 04:44 am:
Do not change to syringe injection.
I tested different systems and gas/loop injection shows best injection precision. Precision of 1 to 3 % (external standard calc with split injection) are normal, whereas syringe injections show precisions of 5 - 10 %.
I never met the carry over problem. The used Tekmar 7000/7050 system can flush the system (with exception of the transfer line). The nickel transfer line never showed carry over problems.
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