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The solvent effect occurs when the sample solvent is vaporized during injection and condenses on a cool column. Where "cool" is relative to the boiling point of the injection solvent and is often ten to twenty degrees below the boiling point of said solvent. Typically, this serves to trap analytes in a narrow band producing sharp peaks. However, solvent effects can also have a negative impact. In this example we have two main solvents as listed in the following table:

Solvent	Boiling Point
Acetone	56.5°C
Acetonitrile	82°C

The GC method in use, is one using splitless injection with an injector temperature of 250°C and an initial oven temperature of 70°C. Based on the boiling points we can see that there will be solvent effects from both acetone and acetonitrile. In the following chromatograms the concentration of acetone is increased while the concentration of acetonitrile is decreased and the concentration of the analytes is held constant. In effect this creates multiple solvent effects at the head of the column, resulting in the greatest peak distortion when the ratios are around 50:50. We can see that increasing acetone concentration decreases the amount of peak distortion until sharp peaks are obtained at a concentration of 90% acetone.

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Vial fill effecting reproducibility was mentioned in an Agilent document called something like "Maximizing Reproducibility in GC/MS Analysis." In this paper one of the suggestions was consistent vial fill volume with a suggested fill of 1mL. Can vial fill level have an impact on reproducibility? To find out I ran five replicates at 0.5mL, 1.0mL and 1.5mL. All samples were transferred using a Rainin EDP pipette. The method is a rapid ethanol analysis with acetonitrile as the internal standard and acetone as the solvent. The working ethanol concentration was 0.6% with a 100:1 split ratio and a injection volume of 0.1uL. A 5uL syringe was in the 7683 ALS. As you can see the 1mL fill was indeed the most reproducible.

Agilent recently published information on decreasing the delay volume on the 1100. I like to save time whenever possible so I decided to give this a try. The method in question is the same one that I described here. The method was modified with an injector program to switch the valve to bypass at one minute into the run. This is before the gradient starts so switching back to main-pass before during the next injection will not effect the retention times or the second sample. As you can see the elution time of the last peak decreased significantly.

This decrease and setting the autosampler to pre-fetch the net vial saves about 50 seconds per sample. This can add up fast when you have 20 or more samples to run.