chemistry 59-320 analytical chemistry fall - 2012

CHEMISTRY 59-320CHEMISTRY 59-320ANALYTICAL CHEMISTRYANALYTICAL CHEMISTRY

Fall - 2012Fall - 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?

– 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?

• 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 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.

0-2 The analytical Chemist’s job

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.

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

1. Weighting2. Removing fat with organic solvent

Step 1: Sample Preparation

--transforming a sample into a state that is suitable for analysis

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:

• 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.

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.