Chromatography Forum

Hi,

What is the best way to determine the LOQ of an HPLC quantitation method for a single component? By best I mean quickest and requiring the least amount of samples but still giving a reasonable estimate of the methods capabilities.

Thanks,

KarenJ

Determine the height of the baseline noise from a blank injection. Multiply that by 10 and read the concentration from your calibration curve. You should also confirm the injection precision at LOQ level.

I'm assuming you want the overall method LOQ. Instrumental LOQ is usually not the limiting factor in real-world samples.

The quick way is to estimate the signal/noise ratio. If you have some blank matrix, measure the noise in the retention window of your analyte. (Most chromatography data systems have this function.) Now look at the peak height of your standard. A reasonable LOQ is 20x the noise. LOQ = (dil. factor)*(std conc.)*20*(noise)/(pk height). Of course noise measurements are, well noisy, so expect the result to bounce around.

This is still no substitute for a proper spike recovery study, but at least it will get you in the right general area.

Thanks for the help. Does anyone know how to obtain the noise level (as Mark suggested) using Agilent Chem Station?

Thanks,

KarenJ

Hi Karen,
In ChemStation's Data Analysis view (after loading signal), from pull down menu choose: Report/System Suitability/Edit Noise Ranges and fill as many ranges for noise determination as you want provided not more than 7.
Then go back to Report/Specify Report ... and select Performance+Noise Report Style.
That's it. Print your report and find noise level values in last part of report.

However I don't suspect, names of menu items may slightly differ from above 'cause you have HPLC ChemStation and mine's is GC.

Wojtek