Chapter 1: The Nature of Analytical Chemistry CHE 321: Quantitative Chemical Analysis Dr. Jerome Williams, Ph.D. Saint Leo University
Overview A Typical Analysis: The Real World Feedback Control Systems
A Typical Analysis: The Real World How does one solve a “real world” problem?
Figure 1-2 p5
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)
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.
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.
A Typical Analysis: The Real World Important distinction we need to clarify We analyze samples, and determine substances.
A Typical Analysis: The Real World Processing the Sample Preparing laboratory samples, if needed Defining replicate samples for analysis Preparing solutions
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
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)
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.
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
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.
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