Chromatography Forum

We' re interested on a method development for a complex mixture of paraffins-vasellins.
Could you please advise regarding the analytical technique that has to be chosen? Does hplc could serve and if yes, which could be the adequate detector?
Otherwise, could someone experienced on such issues could propose a gc-fid method?

Thank you

High temperature GC.

Specialty high temperature thin-film capillary, maybe metal-clad. Can do up to C50 or so, easily.

Have used for candles.

Thanks for the information. It would also be useful to know if ''analytical markers'' (a kind of internal standards) could serve this way.

Another question: why not hplc?

Additionally and most important regarding the remaining time for submission: Any external labs that could arrange this for us? Method development at about 1 month - is this possible?

Thank you!

One month is rather short for developing a method! (One may be able to develop a separation in a day, but proving robustness of the various steps in sample preparation and chromatography across any range of materials you wish to analyze takes some time. And, I've taken an analysis in which I expected to have chromatographic conditions in an afternoon and spent several days trying to work out various problems.)

First, you need the exact objectives of the method - what are you going to measure with this method? Over what range? What range of matricies? What is the needed precision? Typicaly one would measure something that relates to product performance. For example are you working on a maximum concentration for aromatic hydrocarbons present? (Trace analysis takes longer to develop.)

If you just want a profile to see if "it looks to be the same." May I suggest you get one of the existing methods for profiling petroleum fractions. I know that ASTM has some and there are others available.

Thank you for answering my question. 1 month is the best case scenario,dependant the remaining time for submission. I know that it is rather unlikely to be performed that soon.

As far as the requirements are concerned, i would be interested in a quantitative determination at the range of 95 – 105% of paraffin and vaseline (usp specificated drug substances), which are two of three active substances of the formulation.
On a theoretical basis, a method could be developed with isolation (gradient temperature program optimization) of one peak in the complex mixture which would serve as internal standard (analytical marker). Standards of markers are commercially available and cover a wide range of C atoms. After quantitation of this hydrocarbon present in the mixture, it is all simple analytical calculations. Of course problems like full solubilisation of the two substances (in one solvent?) etc still remain. But the main step of this idea is the isolation – quantitation of a single peak.

Thanks again for your thoughts/ proposals.

Isolating a single peak to represent a petroleum distallate could be tricky. From my reading the compositin of vaseline is somewhat variable. So unless you have a specification for a particular chemical makeup of vaseline, the peak you selct can vary in the composition simply as the result of a change in source.