The following quality control method was used to measure EDTA in blood using fortification and allowing the calculation of detection limit.

 

(a) To measure accuracy and precision of the method, blood was fortified with EDTA to known levels. Accuracy = 100 x (mean value found known value)/(known value) Precision = 100 x (standard deviation / mean) = coefficient of variation For each of the three spike levels in the table below, find the precision and accuracy of the quality control samples. EDTA measurements (ng/mL) at three fortification levels Spike: 22.2 ng/mL 88.2 ng/mL 314 ng/mL Found: 33.3 322 19.5 305 23.9 282 20.8 329 20.8 276 For the fortification level of 22.2 ng/mL what is the percent precision? 4.0 52.8 X % For the fortification level of 22.2 ng/mL what is the percent accuracy? 4.0 6.58 X Check the number of significant figures.% For the fortification level of 88.2 ng/mL what is the percent precision? 4.0 37.6 X % 83.6 69.0 83.4 100.0 76.4 For the fortification level of 88.2 ng/mL what is the percent accuracy? 4.0 -6.49 X Check the number of significant figures.% For the fortification level of 314 ng/mL what is the percent precision? 4.0 17.5 X % For the fortification level of 314 ng/mL what is the percent accuracy? 4.0 -3.57 X Check the number of significant figures.% (b) Low concentrations of EDTA near the detection limit gave the following dimensionless instrument readings: 175, 104, 164, 193, 131, 189, 155, 133, 151, and 176. Ten blanks had a mean reading of 60.0. The slope of the calibration curve is 1.75 x 10 M-. Estimate the signal detection limit for EDTA. 4.0 531 X What is the concentration detection limit? 4.0 269e-9 X M What is the lower limit of quantitation? 4.9 898e-9 X M