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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

Let C stand for concentration. One definition of spike recovery is%recovery=Cspikedsample-CunspikedsampleCadedร—100

An unknown was found to contain10.0ฮผgof analyte per liter. A spike ofrole="math" localid="1654945506958" 5.0ฮผg/Lwas added to a replicate portion of unknown. Analysis of the spiked sample gave a concentration of15.3ฮผg/LFind the percent recovery of the spike.

Internal standard graph -- Data are shown below for chromatographic analysis of naphthalene (C10H8), using deuterated naphthalene (C10D8, in which D is the isotope 2H) as an internal standard. The two compounds emerge from the column at almost identical times and are measured by a mass spectrometer.

(a) Using a spreadsheet such asFigure 4-15, prepare a graph of Equation 5-12 showing peak area ratio(C10H8/C10D8)versus concentration ratio role="math" localid="1663559632352" ([C10H8]/C10D8) . Find the least-squares slope and intercept and their standard uncertainties. What is the theoretical value of the intercept? Is the observed value of the intercept within experimental uncertainty of the theoretical value?

(b) Find the quotientrole="math" localid="1663559638520" [C10H8]/[C10D8]for an unknown whose peak area ratio (C10H8/C10D8) is 0.652. Find the standard uncertainty for the peak area ratio.

(c) Here is why we try not to use 3-point calibration curves. For n = 3 data points, there is n - 2 = 1 degree of freedom, because 2 degrees of freedom are lost in computing the slope and intercept. Find the value of Student's for confidence and 1 degree of freedom. From the standard uncertainty in (b), compute the 95 % confidence interval for the quotient[C10H8]/[C10D8] . What is the percent relative uncertainty in the quotient[C10H8]/[C10D8]? Why do we avoid 3-point calibration curves?

Explain the meaning of the quotation at the beginning of this chapter: โ€œGet the right data. Get the data right. Keep the data right.โ€

Internal standard. A solution was prepared by mixing 5.00mLof unknown elementXwith2.00mLof solution containingrole="math" localid="1654777035083" 4.13ฮผgof standard elementSper millilitre, and diluting to10.0mL. The signal ratio in atomic absorption spectrometry was (signal fromX)/ (signal fromS)=0.808. In a separate experiment, with equal concentrations ofXandS, (signal fromX)/signal fromS)=1.31. Find the concentration ofXin the unknown.

(a) From Box 5-3, estimate the minimum expected coefficient of variation,CV(%)

, for interlaboratory results when the analyte concentration is (i) 1 wt % or (ii) 1 part per trillion.

(b) The coefficient of variation within a laboratory is typically~0.5-0.7of the between-laboratory variation. If your class analyzes an unknown containing10wt%NH3, what is the minimum expected coefficient of variation for the class?

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