How can you validate precision and accuracy?

Short Answer

Expert verified

Precision is validated by the repeatability of analyses of replicate samples and replicate portions of the same sample and accuracy is validated by analyzing certified reference materials, by relating results from different analytical methods.

Step by step solution

01

Precision and Accuracy

Precision is validated by the repeatability of analyses of replicate samples and replicate portions of the same sample.

Accuracy:

Accuracy is validated by analyzing certified reference materials, by relating results from different analytical methods,

They are,

Fortification (spike) recovery,

Standard additions,

Calibration checks,

02

Ways to illustrate accuracy

There are several ways to illustrate accuracy. Such actions include:

1. Performing calibration checks in order to assure that the instruments are properly calibrated and therefore would work properly;

2. Testing for fortification/spike recoveries - in this process, we can see if the response from a calibration curve matches the response to the spike;

3. Introducing quality control samples for the elimination of any bias introduced; and

4. Introducing blanks to account for the interference of other species in the sample. To demonstrate precision, we can replicate both our samples, and portions of the same sample.

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Most popular questions from this chapter

What is the difference between an instrument detection limit and a method detection limit? What is the difference between robustness and intermediate precision?

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 m=2.24x104M-1Find the concentration detection limit with Equation 5-5.

(c) Find the lower limit of quantitation with Equation 5-6.

State when standard additions and internal standards, instead of a calibration curve, are desirable, and why.

Europium is a lanthanide element found at parts per billion levels in natural waters. It can be measured from the intensity of orange light emitted when a solution is illuminated with ultraviolet radiation. Certain organic compounds that bindEu(III)are required to enhance the emission. The figure shows standard addition experiments in which10.00mLof sample and20.00mLcontaining a large excess of organic additive were placed in 50-mL volumetric flasks. Then Eu(III) standards (0,5.00,10.00,or15.00mL) were added and the flasks were diluted to50.0mLwithH2O. Standards added to tap water contained0.152ng/mL(ppb) of Eu(III), but those added to pond water were 100 times more concentrated (15.2 ng/mL).


(a) Calculate the concentration of Eu(III)(ng/mL) in pond water and tap water.

(b) For tap water, emission peak area increases by.4.61units when 10.00mL of 0.152ng/mL standard are added. This response is4.61 units/1.52ng = 3.03units per ng ofEu(III). For pond water, the response is12.5units when10.00mLof15.2ng/mLstandard are added, or0.0822units per ng. How would you explain these observations? Why was standard addition necessary for this analysis?

Internal standard calibration curve. Figure 5-10 is a graph of Ax/Asversus[X]/[S]=(mol%vinylacetateunits)/(mol%ethyleneunits)=q/p in Reaction 5-13.

(d) From the uncertaintyubof the intercept, find the95%confidence interval for the intercept. Does this interval include the theoretical value of zero?

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