A recent study published in Analytical Chemistry used the standard addition cali
ID: 586274 • Letter: A
Question
A recent study published in Analytical Chemistry used the standard addition calibration method to determine the amount of AFP (a-fetoprotein), a cancer biomarker, in human plasma. Levels of AFP in adults higher than 500 ng mL-1 are only observed when testicular, ovarian or liver cancers are present. The standard addition calibration curve is shown below. In this case, 3.0 mL of human blood was collected for analysis, processed, and 0.2 mL aliquots of the plasma were added to a 10.00 mL volumetric flask and made up to the mark with buffer. Varying amounts of AFP were added to create the calibration standards. Determine the concentration of AFP in the undiluted plasma sample for this patient. What can you say about the likelihood of cancer in this patient?
Standard Addition Calibration Curve for AFP Determination 0.07 0.06 0.05 0.04 y = 0.0026x + 0.0096 R2 0.9966 0.02 0.01 0 10 15 20 Concentration of added standard ng mL1Explanation / Answer
We will assume that the absorbance of the solution is zero when no standard is added from outside; therefore, put y = 0 and obtain
0 = 0.0026x + 0.0096
====> -0.0026x = 0.0096
====> x = (0.0096)/(0.0026) (ignore the negative sign)
====> x = 3.692
The concentration of AFP in the diluted sample is 3.692 ng/mL.
0.2 mL blood plasma was diluted to 10.0 mL to get the final solution; the dilution factor is (10.0 mL)/(0.2 mL) = 50.
The concentration of AFP in the undiluted plasm = (concentration in dilute sample)*(dilution factor) = (3.692 ng mL-1)*(50) = 184.6 ng mL-1 (ans).
The concentration of AFP is much lower than the 500 ng mL-1 limit observed in adults infected with cancer and hence, the individual isn’t at risk at the moment.