Chromatography Forum

we are using a Pona capillary column for detection of hydrocarbons, C1 to C10. Is this column suitable for detection of alcohols to? what column could I use for detection of alcohols and hydrocarbons together?

thx for your suggestions!

A non-polar column is usually used to analyze PONA.

Alcohols will generally have some tailing on a non-polar column, and look much better on a column with more polarity, such as a 5% phenyl or 20% Phenyl methyl silicone.

A Carbowax will give excellent results for alcohol analysis, but the hydrocarbons will elute together and quickly.

Which alcohols and which hydrocarbons do you wish to measure?

best wishes,

Rod

we would like to analyze C1 to C4 at least (if possible C1 to C10 like we used to do with the PONA) together with methanol and ethanol

In general, methanol will be separated on a PONA column if you start with alow initial temperature, however EtOH is often intermingled with some branched or unsaturated hydrocarbons.

You can identify the oxygenates by performing a water extraction of the gasoline, and analysing either the HC or water fraction.

If you know the source of the hydrocarbon fraction, you can make standards and perform a calibration, but generally alcohols will move around depending on the PONA column. Given that the HC profile can also change, that's real recipe for problems.

I think Restek did a comparison of alcohol peak shape and retention on competitive PONA columns and the results were very variable, suggesting that PONA stationary phases from various vendors are not as consistent. You need to ask the manufacturer of your column, or look at their application notes.

It really depends on what you want to use the numers for, if it's quality control of different hydrocarbon sources, then you should use one of the approved ASTM methods for oxygenates in gasoline, which may involve column switching or O-FID.

If it's just to investigate a research/development process, your column may be OK. Try it, you may be lucky...

Bruce Hamilton

Using multidimensional gas chromatography this analysis would not be difficult.

Do you have a 10 port valve system to plumb two columns where one is in a trap?

Inject the sample and trap the early eluting HC onto the trap and bypass the methanol and ethanol eluting from a Carbowax column. The trap column should be a 1% TCEP on Carbopack B column to separate the methane through butane, optionally a 5% Carbowax on Carbopack B to separate methane through pentane or higher.

Lengths are determined by the operating temperature you choose to use and the amounts you intend to inject. Since you can detect all of thse by FID you could use micropacked columns and do a very fast analysis.

You could add a 5% phenyl or VOCOL column after the trap and measure the higher HC with a second injection.

Conversely, if you use a VOCOL column you might be able to measure all the HC and the alcohols with one shot. The 5% Carbowax 20M column might be used to go up to C8 or even higher with oven programming.

I hope I have given you some ideas to try. If single dimensional chromatography is your game then I would try the VOCOL first.

best wishes,

Rod