1. CHM 410/1410
Lecture 3

3. What is more important, precision or accuracy?
Erin
Rob
Bernadette
Hanin
What is more important, precision or accuracy?
Why?

4. Some Definitions Arithmetic mean Geometric mean
Appropriate for normally distributed data
Appropriate for log normally distributed data
Standard deviation
Standard error
Describes uncertainty around the mean
Describes scatter in the data
Report your data:
100 ± 10 mg/L
What does is mean?

5. Some Definitions 95% of the data falls in 2 standard deviations
95% confidence interval is 1.96x standard error

6. Signal to Noise

7. Calibrations!

8. Detector Response Analyte Detector Resonse Sample
Standards
Conc Analyte (ng/mL)
Detector Response Analyte 1 3 5 32 25
120
100
420
External Calibration
Samples
Detector Resonse Sample
Conc Analyte (ng/mL) 42
8.2 26
4.3 13
1.2

9. Internal Calibration Standards Samples Conc Analyte (ng/mL)
Conc Internal Standard (ng/mL)
Detector Response Analyte
Detector Response Internal
Standard
Response Factor
(Analyte/IS) 1 2 3
9.5
0.32 5 32
10.5
3.0 25
120
10.3 12
100
420
9.1 46
Internal Calibration
Samples
Detector Response Sample
Detector Response Internal Standard
Response Factor
Conc analyte (ng/mL) 42
5.3
7.9 17 26
10.1
2.6
5.0 13 2
6.5 14

10. Standard Addition Sample alone Sample + 5 ng/mL Sample + 10 ng/mL
+ conc (ng/mL)
Detector Response
3.2 5
6.2 10 50 32
Sample alone
Sample + 5 ng/mL
Sample + 10 ng/mL
Sample + 50 ng/mL
Choice of concentration to add is not arbitrary!
Need to add 1x, 2x and 10x the concentration of the unknown

11. Project line onto x-axis Concentration in this sample
Standard Addition
+ conc (ng/mL)
Detector Response
3.2 5
6.2 10 50 32
Project line onto x-axis
let y=0
lxl = conc in sample
Concentration in this sample
6.2 ng/mL

12. Response of sample

13. If you were interested in analyzing for a novel contaminant how would you go about determining an appropriate calibration technique?