Chapter 5: Q29P (page 117)
State when standard additions and internal standards, instead of a calibration curve, are desirable, and why.
The cause of desirability is described in the below steps
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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?
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.
Correlation coefficient and Excel graphing. Synthetic
data are given below for a calibration curve in which random Gaussian
noise with a standard deviation ofwas superimposed on
y values for the equation
. This exercise shows that
a high value of
does not guarantee that data quality is excellent.
(a)Enter concentration in column A and signal in column B of a
spreadsheet. Prepare an XY Scatter chart of signal versus concentration
without a line as described in Section
. Use LINEST
(Section 4-7) to find the least-squares parameters including
.
(b)Now insert the Trendline by following instructions on page 88.
In the Options window used to select the Trendline, select Display
Equation and Display R-Squared. Verify that Trendline and LINEST
give identical results.
(c)Add confidence interval y error bars following the instructions
at the end of Section 4-9. The
confidence interval is 6tsy,
where
comes from LINEST and Student’s tcomes from Table 4-4
forconfidence and
degrees of freedom. Also, compute
t with the statement .
How is a control chart used? State six indications that a process is going out of control.
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
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