Hello everyone,
I have come across a discussion (related to PAHs) where it is stated that as the level of spiking increases (from lower spiked concentration to higher spiked concentration), the percent recovery must also increase either linearly or exponentially. As per the papers I have read, I have found that there is no increasing or decreasing pattern obtained for recoveries while moving from lower spiking concentration to higher spiking concentration.
I would like to know is there seriously a trend needed for recoveries as per the spiking level, are there any guidelines and regulations for the same? And if there is no trend or pattern with respect to recoveries, what is the possible reason for the observed variability?
I request to provide the answers for the same with some authentic source and guidelines.
Thank you.
The answer depends on what instrument you are using (especially the detector), the sample matrix, the expected concentration (especially relative to the LOQ). The USEPA had a good method for drinking water back in the 70's.
The authors who claim an increase in recovery with an increased concentration of the spikes probably do so referring to their specific application. It would not make sense otherwise. You can get systematic recoveries bellow 100% due the inability of your full method to extract the whole amount of the compounds of interest from the sample (as for example, with liquid-liquid extractions if the coefficient of distribution between the phases is not high enough). You can also have a constant loss of analyte due to matrix effects which is limited to a maximum value per volume (example, free SCN in brines which are complexed by some ions). In this case, the recovery should increase with increasing concentrations, and be particularelly visible if the matrix effect is limited to small amounts. You can get signal suppression which makes it impossible to see your analyte or only small parts of it in very high concentrations (example, the effect of proteins on the generation of ions when ESI is used on LC-MS). Finally, you can get recoveries around 100% with random variations due also to random effects of the full analytical method.
Cheers
Thank you @ Bruce Neagle sir and Mario Silva sir for the responses. The answers have helped me a lot. Thank you
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