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Recover calculated field

okay so this example is going to think and work through a problem having to do with percent recovery and percent recovery is a performance test for your method essentially to test whether the matrix of your sample is going to affect the concentration that you calibrate from an external calibration curve so let's say that we run a sample using HPLC let's say we run a Coke Zero sample and I'm totally making up this data so don't call Coke Zero and tell them that I said this but let's say we we run our unknown after we've run a calibration curve and determined that the concentration of caffeine in our unknown is 15 ppm and so that's gonna be the concentration of our own which is our the concentration of our unknown which is the same as the concentration of the on spiked sample so this is our unspoken and we know that the matrix are the solution of Coke Zero is very different from the matrix in which we made our calibration standards which was just in a mixture of methanol and water so we're gonna take our same sample that we ran and that we determined to have a concentration of caffeine of 15 ppm and we're going to add a little bit of standard caffeine and we call this a spike or a fortification and so let's say that we add 5 ppm of caffeine to my sample now in theory when I now measure the concentration of my unknown plus the added spike the concentration should be the sum of these two values and that would give me a hundred percent recovery okay so let's say we we run our spiked sample and we get a concentration of our spiked sample based on using our calibration curve of eighteen point seven ppm so we can see right off the bat that eighteen point seven is not the sum of fifteen and five so we don't have a hundred percent recovery but what is our percent recovery well we take the concentration of our spike sample which we measure to be eighteen point seven ppm minus the concentration of our unspoken and divide that or normalize it by the fortification concentration or the concentration of the spike and then multiply by 100 to get percent so you take that into my calculator okay so I get a recovery percentage of 74% which falls outside of the acceptable range we'll talk about that acceptable range in class so this tells us that our matrix is really affecting the concentration of our analyte or caffeine so we might have to consider doing a different calibration method other than an external calibration curve okay thanks