If there is no analyte signal in the waste-water samples after SPE; you need to spike 1L of both ultra pure water and waste water samples with proper amount of standard solution (you need to spike at the concentration level which corresponds to mid point of your calibration plot). Then apply SPE and compare peak areas as follows:

%Recovery=(A s/A w)*100

(area of analyte signal in waste water sample(A s) and pure water (A w))

if you already have analyte signal in your sample simply subtract the peak area from the area of spiked sample then apply the aforementioned formula.

please note: there will be errors coming from extraction, sample preparation and even the relatively low reproducibility of DAD, always triplicate each step (or more) and use their mean areas.

There are other more techniques, this is just one example. If recovery values come out off range, you will need to perform matrix matching recovery. You can see my lcms publications' recovery sections for more detail.

regards

thanks for the valuable contribution prof Erhan...is one concentration level okay for recovery studies?

i will be grateful if you can provide link for me to get your publication and other possible techniques for recovery studies...thanks

Ideally you can apply the recovery at 3 different points as: a concentration close to the starting point of your calibration plot, mid point and top point.

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Regards