Chromatography Forum

Hello, everyone!

Can someone please explain the concept and purpose of correction factors used in HPLC? And is there a formula we can use to calculate them?

Are correction factors added to the calibration standard values obtained from the HPLC run to calculate samples' 'true' values?

Can we also apply the same correction factors for a particular test in multiple HPLC instruments in the lab where the same set of standard solutions are used?

Thank you.

Based on what you've left out of your post, I'm going to assume the following:

• You're working with a UV method that has assorted analytes whose molar absorptivity varies at whatever wave length(s) you're method uses.
  Your "Correction factors" are actually relative response factors (rrf) that normalize the responses of some of these analytes to that of your standard material.

If this is true, these factors should hold no matter the system used, as long as your parameters are set the same.

These factors are (frequently) calculated by comparing the responses of different analytes at known concentrations at a given wavelength (or by comparing UV responses to responses from other detector types or at other wavelengths). Be careful to sort out whether, for your method, the rrfs are in the numerator or denominator of your formula and make sure you know how your data system handles these factors.

Are we talking "correction factor" or "calibration factor"?

Correction factor could be simply correcting a standard made from a 95% pure stock to what it would be if it was 100% pure. Example 1mg 95% pure Benzene diluted in 10ml Methanol would be 0.95mg/10ml Benzene actual concentration or 0.095mg/ml.

Calibration factor would be when a 10ul injection of the 0.095mg/ml standard is injected and gives a peak height of 10.5 absorbance units on the detector. cf=(0.095mg/ml)/10.5 = 0.0090476 which is normally a unitless number but could also be expressed as 0.0090476 (mg/ml)/absorbance unit. Then used to calculate an unknown which gives a peak height of 8.5 absorbance units to be 8.5 x 0.0090476 = 0.0769 mg/ml Benzene in the unknown injection.

Correction factors would be unique to the standard that is made and would apply to any instrument Calibration factors on the other hand are unique to the instrument because they take into account the response of each instrument to the standard injected. If a cell window is slightly thicker on one instrument versus another, or dirty, or the peak is a little wider or the injection is 0.1% different volume, all those things will make one instrument give a different response to the same standard injected on another instrument.

Theory says x amount of benzene should give y absorbance in UV, but that only applies under perfect conditions, like when in physics the basic laws are made with the caveat of having zero friction and in a vacuum, or in chemistry where standard temperature and pressure are assumed. Instrument calibrations are performed to take into account any and all imperfections in the instrument and process.

DR:
Thank you for your explanation
We are using RID detectors with a set wavelength.

James_Ball:

Thank you for your explanation
It is now easier to distinguish between the two terms (correction factor and calibration factor) as I could not find the correct information about this online (or any text books).