Effective Carbon Number (ECN)

[Ashraf_Khan]

Is the ECN approach a reliable way to calculate relative response factors (without running any calibration) of compounds by FID ? Can it replace gravimetrically determined calibrations ? How does it compare with actual calibrations ?

AZK

[Bruce Hamilton]

The ECN is a last resort approach. If you have some members of simple homologous series of compounds their ECN can be used to calibrate for other members, however the presence of other atoms ( especially oxygen, nitrogen, sulphur ) will invalidate the assumption.

The approach was initially used for alkane hydrocabons, however you have to be certain that your peaks are part of the same homologous series of hydrocarbons/alcohols etc. as your calibration standards. That usually involves using some other technique, rather than just retention time.

You still have to bracket the sample with large and small members to cover instrumental variations such as injector discrimination and detector response.

In general, using ECN is difficult to justify when any reasonable standards are available. It's OK for quick and dirty work, but then so is area %, without the nausea of ECN. Area % is often used for research on FAMEs, and simple hydrocarbon fuels, because multiple peak standards derived from commercial products will confirm the instrument is giving reasonable answers.

Bruce Hamilton

[Ashraf_Khan]

Bruce,

Thanks for your comments on ECN. I agree that it should be used as a last resort. But there is a growing tendency that ECN is a substitute for gravimetrically detrmined calibrations, particularly in some U.S. chemical industries, although the chemicals under question are commericially available. I don't know what are the actual rationals, but some people like ECN and some even made careers out of it.

When the ECN concept was introduced in the early 1960s by Steinberg et al., they never advocated for replacing actual calibrations. Rather they said that by substracting the contributions of functional groups (hydroxyl, carbonyl et al.) from the carbon number, an estimated value could be obtained that could be used for calculating relative respons factors for chemiclas that are scarcely available. A good number of oxygenates, amine, glycols and their ethers were investigated by FID and they were close to experimental values. However, as Scanlon and others pointed out - this ECN approach has not gained popularity in the chromatographic community in spite of its use for more than 40 years.

Anyway, there should be an option for calibrating the FID if the heteroatom-containing hydrocarbons are not commercially available or do not exist in pure forms.

Thanks.


Ashraf Khan
Philadelphia, PA

[Bruce Hamilton]

I don't know what are the actual rationals, but some people like ECN and some even made careers out of it.

When the ECN concept was introduced in the early 1960s by Steinberg et al., they never advocated for replacing actual calibrations. ... However, as Scanlon and others pointed out - this ECN approach has not gained popularity in the chromatographic community in spite of its use for more than 40 years.

Anyway, there should be an option for calibrating the FID if the heteroatom-containing hydrocarbons are not commercially available or do not exist in pure form.

IIRC, the early problems with ECN were more to do with the effect of design and stoichiometry of each FID on actual response. The response variability affected portability of any developed methods. Yes, there are still papaers published on ECNs for chemicals, and presumably they are used usuccessfully in industry.

ECN is probably a good last resort, but I'd still want to calibrate response against a known compound. If standards existed, and were reasonably available, I would require a very good reason to use ECN instead.

Bruce Hamilton