Chromatography Forum

Can I inject different volumes for standard curve construction?

You can, but if this is correct is another question.
For our PQ of our instruments, we test the injection accuracy by injecting different volumes.

The problem by this approach is that your injection volume is almost certain not correct, so your calibration curve is not as accurate as it could be. (eg 21µl instead of 20, 11µl instead of 10µl, ....)

If this is a problem or not depends on your application.

HTH

Ace

In my experience it doesn't work well. If you have your standards made in the exact solution as your beginning mobile phase it will work somewhat, but if your injection solvent is not the same as your mobile phase( standard is in Methanol, mobile phase is 80%H20/20%MeOH) then the increasing amounts of pure Methanol injected will effect the overall response and retention times of your peaks.

If you are using EPA methods it is not allowed as you are required to hold all variables such as injection volume, injection solvent, gradient conditions, temperatures, ect the same for all injections including standards and samples.

Can I inject different volumes for standard curve construction?

You could. But if you want to be correct or accurate or following regulations, keep the injection volume constant and vary your standards concentration.

I'll play "devil's advocate" for a moment (because I generally prefer to keep injection volume constant, for all of the reasons cited above).

First of all, in a validated / regulatory method, you have to follow it as written, so you really don't have a choice.

If you are developing / validating a new method you could, in principle, do it either way. Aside from diluent and matrix effects as mentioned above, the major question is "can my autosampler inject with better linearity than I (or my technician) can prepare solutions?". If my standard prep technique is poor, then changing volume is better -- of course, in that case, I have to worry about the prep of the initial standard and the samples!

We are applying "calibration from a single standard solution" quite frequently.
This actually applys for partial loop injections as well as for preconcentration techniques. This is possible a we are using the 800 Dosino (a dosing device which initially was developed for titration).

Application Note C-117 shows this for partial loop injection.

In partial loop injection a concentration range of 1 : 100 may be covered. In preconcentration we may go up to 1 : 1000.