Gc/Autosample inyeccion reproducibility

[dcobice]

Hi all, I trying to perform an inyeccion reproducibility test on my GC.
The vendor told me that 0.5 ul ist suitable for the inyeccion volume, but with my experince I think that ist more fewer than normal inyeccion volume used in GC ( capillary columns) because the RSD values for 10 inyeccion will be greater than 2.
Its suitable to perform the reproducibility test with 1.0ul?

Thank a lot, I hope I will have answers!

Dcobice

[Consumer Products Guy]

I've had good injection reproducibility with 0.5ul injections (from water) with 0.53 mm capillary in Agilent GCs.

[dcobice]

I've had good injection reproducibility with 0.5ul injections (from water) with 0.53 mm capillary in Agilent GCs.

first, thank a lot for your reply. My GC vendor used an hydrocarbon in Meoh to perform the test and inyected 0.5ul for 10 times and then he calculated the RSD for these inyeccion and sometimes the test failed.Almost in Gc, the adecuate inyeccion volume is about 1.0ul. Its suitable if I´ll perform the reproducibility test with 1.0ul?
In ours GC-methods almost the inyeccion volumens are abuot 1.0ul.Why the GC vendors almost did the test with 0.5? Is there any technical reason
s?

Regards!

[Ron]

The syringe you are using can make a difference in the reproducibily. If you are making 0.5 uL injections from a 10 uL syringe I would expect the precision to be slightly worse than making 0.5 uL injections from a 5 uL syringe. I would expect reasonable precision from a 0.1 uL injection from a 1 uL syringe, but not from a 10 uL syringe. With a modern autosampler in good condition using a syringe in good condition I don't see any issue with 0.5 uL injection.

[dcobice]

The syringe you are using can make a difference in the reproducibily. If you are making 0.5 uL injections from a 10 uL syringe I would expect the precision to be slightly worse than making 0.5 uL injections from a 5 uL syringe. I would expect reasonable precision from a 0.1 uL injection from a 1 uL syringe, but not from a 10 uL syringe. With a modern autosampler in good condition using a syringe in good condition I don't see any issue with 0.5 uL injection.

Hi Ron, Thanks for your reply! Im using a 5 ul syringe but sometimes I dont Know the precision test failed.I will be check the autosampler and then I will runa new test perhaps something wrong in the autosampler was happends!

Regards!

[BG]

Hello, By chance I fell on your question, can be a little tardily, but it seems to to me that if your supplier injects little is also because its solvent of dilution is methanol and thus compared to its volume of expension, to inject more would be very dangerous for the analysis and especially the shape of the peaks. But in the absolute to make a calculation of RSD on 1 µl is not aberrant

[chromatographer1]

Sometimes a bad result tells us something we SHOULD know, and is not necessarily bad information, just not the results we want.

Perhaps there is something that is not quite right with the situation.

Your autosampler may not be reproducing the right volume of liquid consistently

or

Your injection may be too quick and producing a backflash in the too small volume of your injection liner

or

your injection port septum may be leaking

or

you may have a leak in your injector or in your column connections

or

your splitter may not be working properly (if you are using one)

or

your vials may be of different pressure due to sealing differences and thus affect the injection volume taken by the autosampler (really, this happened to me once)

or

something else unrelated like the temperature in your autosampler sample holding area.

Trouble check your system thoroughly until you achieve a proper RSD.

If you have poor reproducibility in std injections you do not want to use this machine for regulated work.

good luck