Troubleshooting help on Separation of peaks

I am currently working on Calibrating a HP 6890 Series GC. I am newer to GC (limited to college experience). I ran close to 20 solvents for my full calibration. Used a series of four for each solvent ranging from 1mL to 10mL. Majority of my solvents came out well and had good calibration curves. However, for two sets of solvents Isopropanol/Ethanol, and Toluene/Normal Propyl alcohol I am having separation issues. I attempted to change the temperature ramping, pressure flows, and even switched the detectors, but with my limited knowledge and not wanting to toy around with too many parts I am unsure what to try next. Thought about switching the column which is currently a 112-2032 J&W Carbowax/20m but again unsure due to previous statement. Looking for some advice or just knowledge to help me out.

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crystalnipp over 4 years ago +1

Hello there. Please see attached. Not sure how well the chromatogram will show, but we achieve separation of ETOH and IPA as well as Tol/NBuOH on a wax. Our set-up is a bit different than yours, we do…

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0 helgalea over 4 years ago

Hi Vinny,

A Carbowax 20M column like the 112-2032 or any other Wax variant is not a good choice for the separation of ethanol/isopropanol or n-propanol/toluene. See attached retention data for solvents on different columns.
For these 4 compounds, I recommend a "624" type of column like the DB-624 UI, for example 30mx0.25mmx1.4µm PN 122-1334UI. A longer column might be needed for complex separations.
You need to check in the solvent retention data if the rest of the solvents you are interested in are separated with the 624 column type before making any purchase.

I hope this helps.

Best regards,

Hélène

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0 vinqc over 4 years ago in reply to helgalea

Hi Hélène,

Thank you for the insight. The Carbowax column was bought prior to me working in my current position and was the replacement column before beginning. I will most definitely look into a new column to help resolve the issues that I am having and take your advice into consideration.

Thanks,

Vinny
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0 vinqc over 4 years ago in reply to helgalea

Hi Hélène,

Thank you for the insight. The Carbowax column was bought prior to me working in my current position and was the replacement column before beginning. I will most definitely look into a new column to help resolve the issues that I am having and take your advice into consideration.

Thanks,

Vinny
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