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Chapter 5: QCE (page 113)
In Figure 5-6, the x-intercept is and its standard uncertainty is. Find theandconfidence intervals for the intercept.
Theandconfidence interval for the intercept has to be calculated asand.
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What is the difference between a calibration check and a performance test sample?
In a murder trial in the 1990 s, the defendant's blood was found at the crime scene. The prosecutor argued that blood was left by the defendant during the crime. The defense argued that police "planted" the defendant's blood from a sample collected later. Blood is normally collected in a vial containing the metal-binding compound EDTA (as an anticoagulant) at a concentration of after the vial is filled with blood. At the time of the trial, procedures to measure EDTA in blood were not well established. Even though the amount of EDTA found in the crime-scene blood was orders of magnitude below
, the jury acquitted the defendant. This trial motivated the development of a new method to measure EDTA in blood.
(a) Precision and accuracy. To measure accuracy and precision of the method, blood was fortified with EDTA to known levels.
For each of the three spike levels in the table, find the precision and accuracy of the quality control samples.
(b) Detection and quantitation limits. 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 45 - 1 . The slope of the calibration curve is. Estimate the signal and concentration detection limits and the lower limit of quantitation for EDTA.
What is the difference between repeatability and reproducibility? Define the following terms: instrument precision, intra-assay precision, intermediate precision, and interlaboratory precision. Which type of precision is a synonym for reproducibility?
1.00 mL of blood serum was diluted to 25.00 mL in each flask of a standard addition experiment like Figure 5-7 to measure a hormone with a molecular mass of 373 g/mol. The x-intercept of the graph was 4.2 ppb (parts per billion). Find the concentration of hormone in the serum and express your answer in ppb and molarity. Assume that the density of serum and all solutions is close to 1.00 g/mL
Detection limit. In spectrophotometry, we measure the concentration of an analyte by its absorbance of light. A low-concentration sample was prepared and nine replicate measurements gave absorbances of 0.0047,0.0054,0.0062,0.0060,0.0046,0.0056,0.0052,0.0044, and 0.0058. Nine reagent blanks gave values of 0.0006,0.0012, 0.0022,0.0005,0.0016,0.0008,0.0017,0.0010, and 0.0011.
a) Find the absorbance detection limit with equation 5-3.
b) The calibration curve is a graph of absorbance versus concentration. Absorbance is a dimensionless quantity. The slope of the calibration curve is Find the concentration detection limit with Equation 5-5.
(c) Find the lower limit of quantitation with Equation 5-6.
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