Introduction to Analytical Chemistry

1. Introduction to Analytical Chemistry Dr. David Davey University of South Australia

2. Introduction to Analytical Chemistry Semester 2

3. Introduction to Analytical Chemistry Semester 2 Practical Work Classical methods

4. 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 ?

5. 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

6.   Introduction to Analytical ChemistryA Revolution in Analysis continued 

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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

15. 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

16. 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