CHEMISTRY 59-320 ANALYTICAL CHEMISTRY Fall - 2012
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Transcript of CHEMISTRY 59-320 ANALYTICAL CHEMISTRY Fall - 2012
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CHEMISTRY 59-320CHEMISTRY 59-320ANALYTICAL CHEMISTRYANALYTICAL CHEMISTRY
Fall - 2012Fall - 2012
Lecture 1
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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?
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• Chemical analysis includes any aspect of the chemical characterization of a sample material.
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Techniques in Analytical chemistry
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What Do Chemical Analysts Do?• Analyst: Applies known measurement
techniques to well defined compositional or characterization questions.
• Research Analytical ChemistCreates and /or investigates novel techniques or principles
for chemical measurements.– or
Conducts fundamental studies of chemical/physical phenomena underlying chemical measurements.
– orDevelops new measurement methods on existing principles
to solve new analysis problems.
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0-2 The analytical Chemist’s job
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Sampling: Procuring a representative sample
Homogeneous: same throughoutHeterogeneous: differs from region to region
In a random heterogeneous material, differences in composition occur randomly and on a fine scale.
For a segregated heterogeneous material (in which large regions have obviously different compositions), a representative composite sample must be constructed.
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Project 1: How to measure the caffeine content of a chocolate bar?
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1. Weighting2. Removing fat with organic solvent
Step 1: Sample Preparation
--transforming a sample into a state that is suitable for analysis
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3. Extracting caffeine and theobromine (analytes) with water
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Step 2: Performing analysis with liquid chromatography
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Principles of liquid chromatography
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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.
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Step 4: Analyzing the results
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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.
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.
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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:
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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.