Chromatography Forum

Hi,

I am trying to get a 5890 up and running. However when I inject a reference sample I only get a solvent peak.

Here are the details:
GC: 5890 FID dector and splitless injector with gooseneck liner
Column: ZD 5 ms, 30m, 0.25 ID, 0.25 thickness
Carrier gas: UHP H2 through suitable filters
FID gases: Grade zero Air, H2, N2 as make up through suitable filters
Splitless mode: purge time 1 min
Injection temp: 100C
Detector temp: 320C
Oven temp: 100c ramping 4 deg/min to 320
Sample: C14-C16 normal paraffin hydrocarbons in hexane
Injection Solvent: Hexane

If any one has any ideas why I cannot see my sample I would be very happy. I also have a representative chromatogram but cannot find instructions of how to attach.

Many thanks

Suggestions:

Do a split injection.

Lower your oven temperature to 40°C.

Add 50% decane to your injection solution to determine if you get any separation from hexane.

Check your amplifier setting.

Check your chart recorder setting.

Make certain your sample is authentic by making up a sample yourself so you know what is in the sample.

best wishes,

Rod

Hi Adam,

May I ask why your injection temp is 100°C or is that a typo?

Regards,

Ralph

Hi Ralph
100C was the suggested injector temp - can you suggest an alternative?
Cheers
Adam

adamhughes,

250 or maybe even a bit hotter would be good. 100 is way too low.

Best regards.

Your test mix is generally used for packed columns to determine the proper operation of an FID.

I suspect the peaks of interest are UNDER the BROAD hexane peak.

It will not take much heat to vaporize tetradecane onto a capillary column unless you were seeking quanitative transfer and even so, 100°C should be adequate, but not optimal.

Use a split injection and/or increase your injector temperature to 150°C. You don't want to back flash your sample up stream.

best wishes,

Rod

What is the retention time of the hexane peak ?, and what is the linear flow rate of carrier gas thorugh the column ?

Instructions for posting chromatograms are in a sticky at the top of the LC page.

Peter

Hi Peter,
The retention time for the hexane is about 90 secs, and the flow rate (measured with a bubble meter I am afraid) is 1.1 ml/min.

Cheers

Hi Adam

You have very low detector response in general - the solvent peak with a splitless injection should be way off scale and 2-3 min wide at settings that would give nice sized analyte peaks.

The flow rate and retention time are about right.

Check for leaks - they are probably big ones, and that the column is inserted the proper distance into the inlet and detector.

The baseline noise is high compared to the size of the hexane peak, there could be an electronics problem.

What is the concentration of the alkanes in the hexane ??

Peter

To follow up with Peter...is the detector even on? Is there exhuast that will fog up a watch glass?

Hi Thanks for the replies,

The detector is on (condensation on a chrom wrench). I have a problem with keeping the flame lit when I increase the air flow (the flame pops and goes out), and therefore this is probably below the recommended 450ml/min. Would this be causing the poor response?

Cheers for your help
Adam

Hi Peter
In response to your questions:
Been over the whole system with a leak detector and all seems OK
The column was placed so as 6 mm (as per manual) was protruding from nut and ferel and screwed into inlet.
The test solution was 0.03% (v/v) each of c14, c15, c16

I have changed over to a home made fames test (C19) and get a very small bump at approx 23 mins which is reproducible.

Cheers
Adam

Don't overlook trying a different syringe...

Your signal from your FID amp is quite low.

7 millivolts for a splitless injection ??????

Something is not right. It should be off scale.

Have you tried another FID (you have dual FIDs?) ?

Do you have your amp setting right? Are you putting your signal into a converter that is set for 10V full scale?

Do you have a cracked column?

Good luck,

Rod

Adam,

As everyone has suggested your hexane peak response is very poor. Several things to look into. First, do you hear your split/splitless solenoid going click when you switch between modes. Could be part of your problem but not all since, even split, your response is terrible. Also, what kind of inlet liner are you using and where is the column located in that liner. Also, what jet are you using and is your column almost at the jet tip, typically run all the way up till it hits the tip of the jet and then back of just a bit...

Finally, your hexane peak shape is poor but that is the least of your problems at the moment and could easily get solved when you resolve your sensitivity issues.

Best regards