Chromatography Forum

Greetings,

My team and I are having trouble using a Clarus 580 GC. We are injecting pure ethanol manually and the areas keep varying by 20% or so (retention time is reproducing though). Can someone give some suggestions of what we could do to get better analysis? I will include some info about our setup.

Injection mode: Manual
Sample volume: 0.1 uL (1 uL syringe)
Carrier flow: 1 mL/min (30:1 split)
Injector temperature: 150 C
Column: elite 5ht (id: 0.25mm)
(Our septum and liner have been changed recently)

Thank you all very much!

We are injecting pure ethanol manually

As an old timer, let me say that manual injection is a technique that must be strictly repeated.

Also: what exactly are you trying to determine with this assay?? If ethanol content/percentage, this is not a good technique.

We are injecting pure ethanol manually

As an old timer, let me say that manual injection is a technique that must be strictly repeated.

Also: what exactly are you trying to determine with this assay?? If ethanol content/percentage, this is not a good technique.

Hello and thank you for your reply!

We are still trying to determine good conditions for the GC operation to use in future analysis in which methanol is expected to show up a as a reaction product. The goal here is to calibrate methanol using ethanol as solvent. Ethanol is being used right now just to test the equipment reproductivity.

Thank you again

Autosampler would be nice. Could try replacing syringe, redo column installation, increase split ratio. Can you attach a chromatogram?

Also add internal standard

So you are saying you are measuring ethanol, and the only substance you are injecting is 0.1ul of ethanol. That seems like alot for a MS I would argue. Try to use some solvent to dissolve your EtOH in a lower concentration. From personal experience I can say that when concentrations of the substance you are detecting is on the high or low end of what your detector can take or detect, you'll get bigger variance. With a pure sample I would expect a huge blob coming out in your MS detection with lots of jagged peaks. Variation on injection will always occur. Which should be irrelevant if you have a internal standard.

If you want to quantify please use an internal standard. (this does not have to be a C13, but just something simular) Guess Ethanol would be nice for a Methanol detection, just need a 3rd solvent for dissolving your EtOh and MeOH in. I'm working with pretty complicated samples and without an internal standard my data would be utterly useless.

Take my knowledge with a grain of salt, i'm a mere labtech/research assist. But the only one in our lab that can run a GC.

We used internal standard of 2-propanol or acetonitrile when assaying for ethanol and methanol. We used water as solvent, kept injection volume below 0.5 microliters.

Greetings,

My team and I are having trouble using a Clarus 580 GC. We are injecting pure ethanol manually and the areas keep varying by 20% or so (retention time is reproducing though). Can someone give some suggestions of what we could do to get better analysis? I will include some info about our setup.

Injection mode: Manual
Sample volume: 0.1 uL (1 uL syringe)
Carrier flow: 1 mL/min (30:1 split)
Injector temperature: 150 C
Column: elite 5ht (id: 0.25mm)
(Our septum and liner have been changed recently)

Thank you all very much!

Another thing to remember when using the 0.25mmID column is that the loading mass has an upper limit of 50-100ng. At a 0.1ul injection of ethanol you are putting 2600ng on column even after the 30:1 split. If you dilute the sample by 100x then you would be in a good range to quantify ethanol at ~26ng on column. 50x would put it in the upper range and give a little lower detection limit for impurities if you need that.