Hi there! I have a question regarding the LOQs, I'll explain my case. I have created a matrix-matched calibration curve following these steps: I used a sample volume of 200 mL, which I subjected to an SPE process. The extract obtained from the SPE was divided into 9 parts, which were dried and reconstituted with the corresponding concentration for the 9 concentration levels (prepared in organic solvent) to construct the curve, each point having a final volume of 0.5 mL. When injecting the curve, the lowest point that I use in the curve is 10 µg/L, which I consider as my LOQ. To express this LOQ in ng/L, How should calculate it? Should I consider the concentration factor (as it is do it in the samples) or simply change the units?
The confusion is due to I express the concentration in the samples in ng/L (considering the concentration factor and recoveries) and the LOQ is what i see in the extract. So, if a concentration in the sample is 95 ng/L (after adjustment, 28 ug/L in extract, recovery of 80%), I can´t express a LOQ of 10000 ng/L (just changing the units).
Thanks in advance!