Chromatography Forum

Hi everybody!

When I inject the same sample in my Master GC Dani, the area of the peak change so much... I tried to use a manual injection and an autosampler, but it doesn't solve the problem..
The split ratio is changing a little... it is set to 200 ml/min and the range during the analysis is from 199 to 201... the septum purge also are changing...

Someone know how to solve it?

Thank you!!!

Hello. More information would be helpful.

What brand and model instrument are you using? Do you know what the liner is, and how much you are injecting? Is this with a capillary column, or packed?

First thing to check: How is your septum? Is the septum nut reasonably tight? Do not use too much force if it is loose- finger tight, plus a small turn with the wrench for many models.

What are the analytical conditions? Start and finish temperature, ramp rate, and any changes in these factors will be useful in helping you. Can you discuss the analyte(s) you are looking for? Is the sample particularly viscous?

Hello!

I'm using a Master GC (model) by Dani (brand). The lenght of the liner is 7 cm and the diameter is 4 mm. I'm using split mode. I'm injecting 1 microliter.
I'm using a capillary column, with polyethylene glycol as
stationary phase. (50 x 0,25 x 0,2).

I changed the septum recently. I also tried reconect the column and changed the ferrule and the glasswool.

The temperature starts at 60°C during 2 minutes, the rate is 15°C/min until 120°C (maintain for 3 minutes) and then the rate is 50°C/min until 200°C (maintain for 1 minute). The flow is 2 mL/min. Split ratio 1:100. The carrier gas is nitrogen. The detector is a FID.

The analyte is methanol and I'm using 4-methyl-2-pentanol as internal standart. The samples are wine. Before to inject, the samples are distilled.

However, I changed nothing in this parameters... The only thing that I noticed that is changing is the flow's split ... I can't keep it constantly... It is setted to 200 mL/min, but it keep changing from 199 until 201...

Thank you!

Hello. Individual areas variability is OK, areas relation (analyte to internal standard) should be robust.

Since the split ratio is high , you must do fast injections , please check your autoinjector parameters.

Also you may want to check the split out trap and split lines , there may be some blockages.

dap wrote:
Hello. Individual areas variability is OK, areas relation (analyte to internal standard) should be robust.

yeah...the internal standart try to fix the area of the analyte's peak...but the areas change a lot that the internal standard can't do it correctly...Besides that, I can't make a new curve while the internal standart have to fix all the areas....