Standard curve: quantity or concentration?

[greenhuntress]

I have a (perhaps) silly question: I have prepared a standard curve with 50ul injections, but my sample injections are either 70 or 75ul. Do I need to correct for this, or am I calculating a concentration?

Thanks!

[Slammy1]

Typically, your data acquisition software will deal with it using the injection volume as a parameter, otherwise to calculate concentration you will need to multiply by 50uL/70uL. This is NA if you're doing chromatographic purity (i.e. area percent analysis).

[MaryCarson]

What you are quantifying depends very much on how you are setting up your data system (or how it was set up for you). If you don't KNOW for sure whether injection volume is taken into account in the calculations, copy a set a peak responses into a spreadsheet and do the calculations "manually."

Of course, you could just inject 75 uL every time and not have to worry about it....

[HW Mueller]

green . . . , why don´t you inject 75 µL St. and see how it compares to 50
µL St injections.

[Carl Sanchez]

I assume you are performing external standardization with results expressed as mass/volume since you made a "standard curve". In this case the assumption is typically that the injection volume of the sample is the same as the standard. Since the peak area varies with the amount of analyte injected onto the column, varying the injection volume will affect the mass of analyte injected onto the column and thus peak area. If your datasystem does not automatically compensate for injection volume then your results will be skewed.