Introduction to Analytical Chemistry : Introduction to Analytical Chemistry Dr. David Davey
University of South Australia
Introduction to Analytical Chemistry Semester 2 : Introduction to Analytical Chemistry Semester 2
Introduction to Analytical Chemistry Semester 2 Practical Work : Introduction to Analytical Chemistry Semester 2 Practical Work Classical methods Instrumental methods Sampling
Standards
Simple equipment
Manipulative skills
Colour appreciation Complex equipment for final
measurement
Introduction to Analytical Chemistry Some Basic Questions : 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 ?
Introduction to Analytical Chemistry Yes. There has been A Revolution in Analytical Instrumentation : Introduction to Analytical Chemistry Yes. 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
Introduction to Analytical Chemistry A Revolution in Analysis continued : Introduction to Analytical Chemistry A Revolution in Analysis continued More detailed analyses Separation Methods GC; HPLC Detection of ultratrace amounts New Sensors New Instruments Optical Devices UV vis, FTIR
Introduction to Analytical Chemistry : 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
Introduction to Analytical Chemistry The Analytical Method : 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
Introduction to Analytical Chemistry The Analytical Method cont’d : Introduction to Analytical Chemistry The Analytical Method cont’d 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
Introduction to Analytical Chemistry The Analytical Method - Study in Toxicology : 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
Introduction to Analytical Chemistry Study in Toxicology continued : 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
Introduction to Analytical Chemistry - Study in Toxicology continued : 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
Introduction to Analytical Chemistry - Study in Toxicology continued : 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
Introduction to Analytical Chemistry Are Chemists providing answers with better accuracy and precision compared to years ago ? : Introduction to Analytical Chemistry Are Chemists providing answers with better accuracy and precision compared to years ago ? 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 The Analysis of
Complex Materials
Introduction to Analytical Chemistry The Analysis of Complex Materials : 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
Introduction to Analytical Chemistry Some Conclusions : 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