Chromatography Forum

Dear All,
My best is approx. 10%RSD on 7 injections with liquid injection.
Top taper liner 3.4mm id 0.5ul split 250degC 100:1 clean silanized wool packed tightly for good peak shapes. Different polarity analytes all approx. 100ppm in hexane. I have the 10ul plunger in barrel syringe and have even tried "sandwiching" the liquid in between 2 air slugs. Its no better with plunger in needle injection manually.
Is this common or can someone suggest a better liner to use?
I believe the injector column trap to be all leak tight.
I have also tried "more scans per second"
Thanks in advance
WK

Make and model of the hardware ?

Peter

Hi Peter,
Sorry - Varian Saturn 2000 MS / 3800GC with 1079 injector.
Regards
WK

I suspect that a lot of small things are adding up to a detectable problem;

You are putting 1 ng per peak on the column, this is on the low side and you might be getting some sorbtive losse

0.5 ul is too little for a 10 ul syringe. Are the results any better with 1 ul injected (you have plenty of space to make the peaks bigger) ?, or with a 5 ul syringe

The positioning and packing of the glass wool can be critical - it might be worth trying one of the pre-packed "pecision" variants which have the glass wool held between two restrictions in the liner.

The dwell time of the needle inthe inlet before injection determines how hot the needle gets, and that affects how much sample boils out of it. Play with the pre-injection dwell settings.

Peter

Hi Peter,
Thanks for the replies - I will order up a precision liner.
I have all delays set at 0 seconds and have an injection speed of 25ul/second.
Regards
WK

Hi WK

Try increasing the preinjection dwel to 3 s - then the needle will get hotter, but it will also be more repeatably hot.

Peter

WK,

To speak to a couple of Peter's points. 100 ppm at 100:1. Why not try a much lower split ratio or even splitless at this level? Mixed polarities. Are some of them (z.b. non-polars) doing much better than others (polars)?

Best regards,

AICMM

Hi,
Thanks for the replies - I will post back once I have chance to try these solutions out.
Regards
WK