Chromatography Forum

I read recently in 'Basic Gas Chromatography' (by Harold McNair and James Miller) that "manual injection is usually unsatisfactory and limits the value" of using external standards for quantitative analysis with manual injection.

Have any of you guys ever seen external standards used successfully with manual injections to generate reproducible calibration curves?

So far the two USP determination methods I've looked up used internal standards.

Thanks!

I read recently in 'Basic Gas Chromatography' (by Harold McNair and James Miller) that "manual injection is usually unsatisfactory and limits the value" of using external standards for quantitative analysis with manual injection.

Have any of you guys ever seen external standards used successfully with manual injections to generate reproducible calibration curves?

Autosamplers don't accompany GCs from the begining. Definitely it is possible to calibrate GC methods with manual injections (and with satisfactory results).

So far the two USP determination methods I've looked up used internal standards.

Thanks!

Then you probably have to use internal standards to be in compliance with USP.

5890Hacker,

Two comments. 1) Set up a small lab to measure THC with manual injections and external standards and RSD was not that great. 2) Set up an autosampler method to measure ethanol in wine with AID using external standard and was surprised at the RSD (not that great.) Added IS to the dilution solvent in the second application and was much happier. Would also advise the same in first case. BTW, both applications were split injections which may have had something to do with it.

In short, I would recommend one.

Best regards,

AICMM

I would rather have an internal standard even with an autosampler.

I have managed to perform acceptable external standard calibrations with manual injection (ye olde solvent flush), but I would not recommend it.

I would rather have an internal standard even with an autosampler.

I have managed to perform acceptable external standard calibrations with manual injection (ye olde solvent flush), but I would not recommend it.

We have also had acceptable external standard calibrations with manual injection, but we've used autosamplers (Agilent) for at least 30 years now. Manual injections are not as precise, don't work during lunch or off hours. Tell your boss to get with it, to purchase modern equipment to boost your productivity and precision.

We use internal standard for samples over 60% alcohol. Otherwise, all our other GC stuff, and all our HPLC stuff, is external standard quantitation.

Internal standard use - to me - mostly means that a procedure was developed before modern instrumentation, in this case: autosamplers. Like when I see an HPLC procedure employing 254nm detector wavelength: a throwback to the days of single wavelength UV detectors.

Thank you, I appreciate your replies.

What, by the way does the acronym "IS" stand for? That is a hard one to search for.

Thank you, I appreciate your replies.

What, by the way does the acronym "IS" stand for? That is a hard one to search for.

internal standard