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CHEMISTRY 59-320 ANALYTICAL CHEMISTRY Fall - 2012

CHEMISTRY 59-320 ANALYTICAL CHEMISTRY Fall - 2012. Lecture 1. What is Analytical Chemistry?. It is the Science of Chemical Measurements providing methods and tools needed for gaining insight into our material world. There are four basic questions about a material sample?

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CHEMISTRY 59-320 ANALYTICAL CHEMISTRY Fall - 2012

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  1. CHEMISTRY 59-320ANALYTICAL CHEMISTRYFall - 2012 Lecture 1

  2. What is Analytical Chemistry? • It is the Science of Chemical Measurements providing methods and tools needed for gaining insight into our material world. There are four basic questions about a material sample? • What? (What is the identity of the substance in the sample?) • Where? (Does the sample contain substance X?) • How much? (How much of substance X is in the sample?) • What arrangement, structure or form?

  3. Chemical analysis includes any aspect of the chemical characterization of a sample material.

  4. Techniques in Analytical chemistry

  5. What Do Chemical Analysts Do? • Analyst: Applies known measurement techniques to well defined compositional or characterization questions. • Research Analytical Chemist • Creates and /or investigates novel techniques or principles for chemical measurements. • or • Conducts fundamental studies of chemical/physical phenomena underlying chemical measurements. • or • Develops new measurement methods on existing principles to solve new analysis problems.

  6. 0-2 The analytical Chemist’s job

  7. Sampling: Procuring a representative sample Homogeneous: same throughout Heterogeneous: differs from region to region For a segregated heterogeneous material (in which large regions have obviously different compositions), a representative composite sample must be constructed. In a random heterogeneous material, differences in composition occur randomly and on a fine scale.

  8. Project 1: How to measure the caffeine content of a chocolate bar?

  9. Step 1: Sample Preparation --transforming a sample into a state that is suitable for analysis • Weighting • Removing fat with organic solvent

  10. 3. Extracting caffeine and theobromine (analytes) with water

  11. Step 2: Performing analysis with liquid chromatography

  12. Principles of liquid chromatography

  13. Step 3: Preparing calibration curves A graph of detector response as a function of analyte concentration is called a calibration curve or a standard curve. Standard solution: containing known concentrations of analytes.

  14. Step 4: Analyzing the results

  15. 0-3 General steps in a chemical analysis An analysis involves several steps and operations which depend on: • the particular problem • your expertise • the apparatus or equipment available. • The analyst should be involved in every step.

  16. Exercise 1: 0-6. The iodide (I−) content of a commercial mineral water was measured by two methods that produced wildy different results.7 Method A found 0.23 milligrams of I− per liter (mg/L) and method B found 0.009 mg/L. When Mn2+ was added to the water, the I− content found by method A increased each time more Mn2+ was added, but results from method B were unchanged. Which of the Terms to Understand describes what is occurring in these measurements? Answer:

  17. Exercise 2: When performing an analysis a chemist often uses a standard solution. What is a standard solution? (a) A solution that complies with standards established by the Environmental Protection Agency.(b) A solution that has a concentration of a chemical that is known to a high degree of certainty.(c) A solution that is prepared from a chemical that has been designated as a primary standard. Exercise 3: In a random heterogeneous material, (a) differences in composition occur randomly and on a fine scale.(b) large regions have obviously different compositions.(c) samples are collected by taking portions from the desired number of segments chosen at random.

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