Low Injection Volume - Poor Reproducability of Peak Areas.

[murphyjames]

GC - Agilent 8860
ALS - G4513A - 7693A Autoinjector

Currently moved to a 10m x 0.1mm x 0.1um Column on Hydrogen Carrier Gas for speed gain. Previously 30m x 0.25mm x 0.250um Column.

Samples that come into lab are concentrated, to prevent column overload I have attempted to move to a smaller injection volume. I have purchased Agilent Blue Line 0.5ul and 1ul syringes attempting to inject 0.1-0.5ul into the inlet. The split is currently at 200:1, with that being as high as i would like to allow for multiple instruments on the same gas generator. I have been having reproducibility issues at low inj volumes. I noticed whenever i manually dispensed the needle the sample stays as a droplet so i added a dwell time of 0.5 post injection which seemed to improve the chromatography but my RSD for my injections are all over the place. I am also using fast injection. Can someone help me?

ALS Parameters
Syringe Size - 1ul
Inj Vol - 0.1ul (Smallest i have attempted)
Solvent washes - 6Pre&6Post
Sample washes - 6
Sample pumps - 5
Dwell time (PreInj) - 0 min
Dwell time (PostInj) - 0.5 min
Injection Dispense Speed - 600ul/min
Viscosity Delay - 0sec

[rb6banjo]

I do manual injections for this but I recently found a way to get around poor precision for determination of methanol in substantially aqueous matrices. Actually distilled spirits. I only inject the syringe needle full of sample. I fill the syringe, make sure there are no air bubbles, then slowly set the plunger to zero while the needle tip is immersed in the sample. I then just insert the syringe needle into the hot inlet and allow it to vaporize out. It works really well for that application and my inlet pressure doesn't go nuts from overfilling the inlet with water vapor.

I don't know if the auto sampler will allow you to make a "zero volume" injection or not but it may be worth a try. I assume you have an internal standard in your sample.

[Consumer Products Guy]

We cGMP-validated a procedure for ethanol in hand sanitizers; we diluted samples with water, used 0.5 microliter syringes, then GC on wide bore capillary.

We used internal standard technique.

[AICMM]

MurphyJames,

Agilent makes a plunger in needle syringe for their AS. I do not have the part number but saw a presentation that referenced it not that long ago. You might be able to get them to give you a part number if you can actually get through to someone who will talk to you. Your odds are pretty good because you can present them with a serial number....

Best regards,

aicmm

[Peter Apps]

What are you analysing, dissolved in what ?

What is your inlet temperature ?

[James_Ball]

If it is not in an aqueous solvent then it may be easier to dilute and inject 1ml for better reproducibility. If concentration is part of the sample preparation then maybe concentrate less, which will have the same effect and save time at preparation.