Introduction to Analytical Chemistry

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Introduction to Analytical Chemistry

• Dr. David Davey
• University of South Australia

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Introduction to Analytical Chemistry Semester 2
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Introduction to Analytical Chemistry Semester 2
Practical Work

• Classical methods

Sampling Standards Simple equipment Manipulative
skills Colour appreciation

• Instrumental methods

Complex equipment for final measurement
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Introduction to Analytical Chemistry Some Basic
Questions

• Have Chemical Instruments improved in recent
  years ?
• Do Chemists provide meaningful answers to
  problems ?
• Are Chemists providing answers with better
  accuracy and precision compared to 60 years ago ?

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Introduction to Analytical ChemistryYes. There
has been A Revolution in Analytical
Instrumentation

• New Instruments
• Computing power and improved quality of
  information through computing
• More detailed analyses can be done
• Detection of ultratrace amounts
• Faster methods of sample preparation
• microwave ultrasonics

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Introduction to Analytical ChemistryA
Revolution in Analysis continued
More detailed analyses Separation Methods
GC HPLC Detection of ultratrace amounts New
SensorsNew Instruments Optical Devices UV vis,
FTIR
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Introduction to Analytical Chemistry

• Do Chemists provide meaningful answers to
  problems ?
• Are Chemists providing answers with better
  accuracy and precision compared to 60 years ago ?
• These questions bring us to examine the
  Analytical Method

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Introduction to Analytical Chemistry The
Analytical Method

• Define the Problem
• Obtain and Prepare the sample
• Select a method of measurement
• Data acquisition and treatment
• Assess the quality of results
• Report the solution in terms
• relevant to the problem

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Introduction to Analytical Chemistry The
Analytical Method contd

• Obtain a representative sample
• Preparing the laboratory sample
• Define replicates
• Dissolve samples
• Adjust sample for method

• Define the Problem
• Select a Method
• Calibrate the Method
• Eliminate Interferences
• Measure the samples
• Calculate Results
• Estimate the precision
• Report the solution to the problem

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Introduction to Analytical Chemistry The
Analytical Method - Study in Toxicology

• Did a Herbicide kill a Deer ?
• Possible use of Arsenic Compounds
• as herbicides ?
• Test for presence of As in grass
• Test for presence of As in Deer organs
• Measure levels of As in grass
• Measure levels of As in Deer organs

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Introduction to Analytical Chemistry Study in
Toxicology continued

• Select a Method
• As in biological samples ?
• Examine a Method and make sure workable
• Form AsH3
• Arsine is volatile (an advantage as we will see)
• Select a sample
• Obtain a representative sample, kidneys
• Grind the selected samples finely
• Other deer samples

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Introduction to Analytical Chemistry - Study in
Toxicology continued

• Prepare a sample
• Dry and ash the sample giving H3AsO4
• H3AsO4 is reduced to H3AsO3
• Eliminate Interferences
• Form AsH3 which is volatile
• The gas is separated from solution and other
  elements
• It forms a red coloured complex with
  dithiocarbamate

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Introduction to Analytical Chemistry - Study in
Toxicology continued

• Analytical Results
• Grass 600 ppm
• Two deer
• 16 and 22 ppm

• As toxic above 10 ppm - Literature

• Conclusion
• Chemical Analysis indicates a Toxic Level of As
  present in the Deer
• Supports the Contention that herbicide caused
  death

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Introduction to Analytical Chemistry Are
Chemists providing answers with better accuracy
and precision compared to years ago ?
The Analysis of Complex Materials

• New Instruments are not the complete solution
• The accuracy of analysis is dependent on the
  nature and complexity of the material
• Errors of 1-2 are excellent
• Errors of 5-10 are common
• Higher errors observed for trace amounts

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Introduction to Analytical Chemistry The
Analysis of Complex Materials

• Precision for most Analyses has not improved over
  the years due to-
• neglect of sample preparation, and
• poor knowledge of chemical interferences

Precision sd
Year
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Introduction to Analytical Chemistry Some
Conclusions

• Better Instruments are available
• The Analyst must solve the problem presented
• Method Selection and Sample Preparation are key
• Chemical Interferences must be considered
• Difficult Samples still give poor results