Dear Sir. Concerning your issue about the calculation of the percent recovery . The spiked sample solutions are analyzed according to the analytical procedure and the recovery is calculated with the following equation:

 Recovery (%) =  (SSpiked * RReal ) / SSpiked *100 %

 where SSpiked = calculated Pb in spiked sample (µg/mL or ppm) and RReal = Pb in the real sample solution (µg/mL or ppm). I think the following below links and the attached file may help you in your analysis:

https://static.fishersci.com/cmsassets/downloads/segment/Scientific/pdf/WaterAnalysis/Log112tipMatrixSpikeWhySpikeHowtoDoIt.pdf

https://www.scribd.com/document/185911318/Calculating-Percent-Recovery-Percent-Yield

http://environmentalet.hypermart.net/env1221/leadinpaint.htm

Thanks

While calculating recovery, unit may be anything but both the variables (In your case, Spike result and Raw result) should posses the same unit and multiply with 100 to express in percentage.

let me simplify it 

(mean value found/added)*100

http://onlinelibrary.wiley.com/doi/10.1002/bmc.3805/abstract

I may add to the previous comments that the added value must not exceed the sample concentration to have reasonable and representative recovery.

Can recovery spike values be negative?

Recovery % = (practical concentration /Theoretical concentration )X 100%

Or = 100 +_ Percent error

Very interested question.

Thank you so much all for helping out to understand this... i really apprecite it!

What value would you use for the unspiked sample concentration when it is below your limit of quantitation?

Somewhat late to answer the original question, but just to note, in Isam Eldin Hussein Elgailani 's answer, the equation should be a subtraction, i.e.:

 Recovery (%) =  (SSpiked minus RReal ) / SSpiked *100 % ,

[not multiplied as shown in the answer above].

For example, spiking a known 1,000 unit sample with 200 units would be:

(1,200 - 1,000)/200 * 100% = 200/200 * 100% = 100% recovery.

Depending on the technique (e.g. titration vs HPLC), and the concentrations involved (% or parts per billion) and possibly the compounds of interest, recovery of 99-101% might be necessary for your study, or 80-120% is an acceptable degree of recovery.

Chem Na the actual formula is

((spiked sample - unspiked sample)/spiked sample)*100

when u multiply it by 100 its automatically becomes percentage and as such the unit is %

hope that helps

The accuracy and reproducibility of the analytical method of sequential extraction were tested by comparing the total amount of metal extracted from each sample by different reagents during successive extraction steps with the results of total digestion of the same sample (using ICP-OES analytical method).

The Internal recovery of the sequential extraction method was calculated as follows:

Recovery = [CiF1 +‏ CiF2+‏ CiF3+ ‏CiF4 + ‏CiF5) / Citotal] × 100

In my study, the results about the 6 soil samples show that the sum of the values of the five fractions are in good accordance with the results of the total digestion of the samples, with a satisfactory recoveries rate (92.5-114.1%).

How recovery can be >100%, i.e. more than total? Does it indicate an erroneous result?

2ml of 1000ppm Pb was diluted to 100mL (DF of 50) and then was further undergone a DF of 10. So, totally dilution factor will be 500. The final concentration of Pb in the analysed solution is 2 ppm and only 0.5 ppm was found. Therefore, % recovery =(0.5x100)/2 =25%. No unit!

The relation of recovery calculation is the following (spiked sample - unspiked sample)/spiked sample)*100%. Please if you can help me to calculate the Standard deviation (%recovery+ - SD)?

https://www.scribd.com/document/185911318/Calculating-Percent-Recovery-Percent-Yield

Hello, everyone, May I get the reference pdf version for the calculation of percent recovery in the above link?? I need to use this equation in a research paper.

Thank you so much!