1. Chapter 1: The Nature of Analytical Chemistry
CHE 321: Quantitative Chemical Analysis
Dr. Jerome Williams, Ph.D.
Saint Leo University

2. Overview
A Typical Analysis: The Real World
Feedback Control Systems

3. A Typical Analysis: The Real World
How does one solve a “real world” problem?

4. Figure 1-2 p5

5. A Typical Analysis: The Real World
Selection of Method involves striking a balance between the following:
Level of Accuracy required
Cost of analysis
Time required to complete analysis
No. of samples to be analyzed
Complexity of sample (no. of components)

6. A Typical Analysis: The Real World
Acquiring the Sample has to do with obtaining samples that have the same composition as the bulk of source material.

7. A Typical Analysis: The Real World
Most difficult step in an analysis; it is very challenging if sample is heterogeneous.
Assay is process of determining how much of a given sample is the material indicated by its name.
Sample matrix is all of components in the sample containing the analyte.

8. A Typical Analysis: The Real World
Important distinction we need to clarify
We analyze samples, and determine substances.

9. A Typical Analysis: The Real World
Processing the Sample
Preparing laboratory samples, if needed
Defining replicate samples for analysis
Preparing solutions

10. A Typical Analysis: The Real World
Eliminating Interferences involve removing substances that can interfere with what we are trying to measure.
Interferences (interferents) cause errors in an analysis by making measurements too high (enhancement) or too low (attenuation).
Specific vs. Selective Techniques

11. A Typical Analysis: The Real World
Calibrating & Measuring Concentration
Important step in most analysis
Calibration involves determining how concentration of analyte varies with measured property X
Relationship is usually linear (CA = kX)

12. A Typical Analysis: The Real World
Calculating Results
Modern calculators & computers have simplified calculations
Computations based on experimental data collected; characteristics of instruments used; and stoichiometry of reaction.

13. A Typical Analysis: The Real World
Evaluating Results (Estimating Reliability)
An analytical result without an estimate of reliability is of no value
Statistical methods used to evaluate and report results

14. Feedback Control Systems
Process of continuous measurement and control is called a feedback system.
Cycle of measurement, comparison, and control is known as feedback loop.

15. Figure 1-3 p9