Transcript CHEMISTRY 59-320 ANALYCAL CHEMISTRY Fall

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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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.
Techniques in Analytical chemistry
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.
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Conducts fundamental studies of chemical/physical
phenomena underlying chemical measurements.
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Develops new measurement methods on existing principles to
solve new analysis problems.
0-2 The analytical Chemist’s job
Sampling: Procuring a representative
sample
Homogeneous: same throughout
Heterogeneous: 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.
Project 1: How to measure the
caffeine content of a chocolate bar?
Step 1: Sample Preparation
--transforming a sample into a state that is suitable for analysis
1. Weighting
2. Removing fat with organic solvent
3. Extracting caffeine and theobromine (analytes) with water
Step 2: Performing
analysis with liquid
chromatography
Principles of liquid
chromatography
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.
Step 4: Analyzing the
results
0-3 General steps in a chemical
analysis
An analysis involves several steps and
operations which depend on:
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the particular problem
your expertise
the apparatus or equipment available.
The analyst should be involved in every
step.
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:
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.