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1. Chapter 5 Calibration Methods
2. Calibration Methods Calibration Curve
Standard Addition
Internal Standards
3. Calibration Curve Graphs the instrumental response to
Standard Solutions
Analyte solutions of known concentrations
Blank Solution
Solution that contains all reagents and solvents except the analyte
Negates effects caused by impurities and interfering species
4. Calibration Curve Construction and Use Prepare the standard solutions
Varying concentrations of analyte
Ideally incorporates the concentration of unknown
Collect data for each of the standards
3 or more recommended
discovery of inconsistent measurements
Calculate the Corrected Absorbance value for each standard concentration
Corrected Absorbance = standard solutions average absorbance - blank solutions average absorbance
5. Calibration Curve Construction and Use Plot a graph of corrected absorbance values versus analyte concentration
Obtain Calibration Curve
Method of Least Squares
Determinants
6. Obtain Calibration Curve Method of Least Squares
di2 = (yi - y)2 = (yi - mxi -b)2
Determinants
7. Calibration Curve Construction and Use Find the Uncertainties associated with the slope, y-intercept, and y (corrected absorbance)
d(bar) - 0 for best straight line
2 degrees of freedom are lost in determination of slope and y-intercept
8. Calibration Curve Construction and Use Find the Uncertainties associated with the slope, y-intercept, and y (corrected absorbance)
9. Calibration Curve Construction and Use Calculate the Uncertainty associated with the x-value
Analyze the unknown
10. Calibration Curve Example
11. Standard Addition Method Unknown concentrations of analyte are determined via deduction obtained from the calibration curve resulting from adding quantities of known standards to unknown concentrations of analyte.
Important when the sample composition is unknown or complex
12. Standard Addition Curve Construction and Use Procedure 1
Prepare samples to be analyzed
Add the same quantity of unknown to each of several volumetric flasks
Add varying quantities of known standard to all but one of the volumetric flasks
Dilute all volumetric flasks to their mark
13. Standard Addition Curve Construction and Use Analyze the samples
Construct a graph using the data obtained
14. Standard Addition Curve Construction and Use Construct a graph using the data obtained
x-intercept of the extrapolated line is the concentration of the unknown [X]f after it has been diluted to the final volume
Method of Least Squares - construct the line
uncertainty in x-intercept
15. Standard Addition Curve Construction and Use Procedure - 2
Sample 1
Add a quantity of unknown to a volumetric flask
Analyze the sample
Sample 2
Add a quantity of known standard to sample 1
Analyze the sample
Sample 3
Add a quantity of known standard to sample 2
Analyze the sample
Additional Samples - repeat procedure for Sample 3
16. Standard Addition Curve Construction and Use Calculation of the standard solutions and the unknown are completed using
17. Internal Standard Compares the intensity of the absorbance of an internal standard compared to that of the analyte
Important when instrument response may vary slightly from one run to the next
18. Internal Standard Preparation Procedure
Prepare a sample of unknown analyte concentration
Add an amount of known standard to the solution
Analyze the sample
Compare the area under each signal - Response Factor
19. Chapter 5 - Homework Problems - 2, 7, 18, 21, 22