Chromatography Forum

Hi,
I heard that instead of going through the process of making different concentration standards, that you can inject different volumes to create a calibration curve. I'm not quite sure how the math works out on this, nor am I very familiar with GC work at this point. Could someone clarify how this works for me?
Thanks!

I have never done this before, but lets say you have a 100% standard and want to do a curve of 80%, 100% and 120%. You could do a 4 µL, 5 µL and 6 µL injection of your 100% standard. Assuming your injection volume is 5 µL.

Sadly while this barely worked back in the time of packed columns with today's smaller injection volumes, very few chemists can do this with good reproducibility and linearity.

It is much better and more accurate to use liquid dilutions and to use a Chaney adapter on your syringe.

best wishes,

Rod

This is only an option if you don't use an internal standard. If you want accuracy, then you'll need to make dilutions I'm afraid, and use an internal standard (ideally)

Thanks for the responses. Is there a good source of methodology for internal standards anywhere? I'm only looking at N2O using an ECD with a HP-Polot-Q column, so if anyone knows of a good paper that covers this I would be more than grateful for the push in the right direction.

aegunkle,

Are you doing gas or liquid injections? Assuming gas since you are talking N2O by ECD, then you have options. First, you can change loop size, very tedious but very do-able. Second, you can dilute a higher level standard down to low level standards by ratio of dilutent gas to standard gas. Two flow meters and a mixing T. Third, you can make dilutions of your standard in an external container like a tedlar or can.

Regarding internal standard, if gas, then you could look at a perm tube (with all the commensurate complications) as a good way to add IS.

Best regards,

AICMM

I am doing gas head space analysis. Is there a good book out there that goes through these methods?

You may have to purchase gas stds at different concentrations.

Call Perkin Elmer for a list of suggested books.

best wishes,

Rod

I have been doing these calibrations by different standard volumes on fixed gases and VOCs tests with Tekmar Autocan and Entech autosampler for years . The precision is good. For example, I had 20, 40, 100, 200, and 400 mL injections of 100 ppbv TO-15 standard for 5, 10, 25, 50, and 100 ppbv levels.