Bad reproducibility

Chromatography Forum: GC Archives: Bad reproducibility
Top of pagePrevious messageNext messageBottom of pageLink to this message  By Sonja B. Gudfinnsdottir on Wednesday, October 2, 2002 - 08:42 am:

I'm developing a GC-HS method, analysing DMF in DMI solvent. When running standards I never get the same peak size, and sometimes different shape.
The septa and vials are working fine and the instrument itself is ok. I just finished validating another method a few days ago.

With this DMF method I've been trying different split ratios, flow rates and oven temperature.

Does anyone have any suggestion on what might be wrong? As a matter of fact I ran another method on the same column using similar parameters and that turned out fine.

Is DMF and/or the DMI solvent in some way diffucult to work with?

Thanks for your consideration.

Top of pagePrevious messageNext messageBottom of pageLink to this message  By Rodney George on Wednesday, October 2, 2002 - 09:39 am:

The temperature required to perform adequate sample handling for DMF from DMI is most likely relatively high compared to other analytes, and its tendency to stick to bare metal and sealing components is probably giving you the variation you are experiencing. (levels were not disclosed)
I would prefer not to use HS for this analyte and would prefer a manual method, especially if water is involved or is a variable in this determination.
Salts are another issue, very important in this case, but is also not discussed.
You are welcome to email me or Supelco technical service for help if you wish.
Rodney George

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