1. ERT 207 ANALYTICAL CHEMISTRY
ALINA RAHAYU MOHAMED
School of Bioprocess Engineering
University Malaysia Perlis
02600, Kangar
Perlis

2. LECTURE 2
13th July 2007

3. 1.3 STEPS IN QUANTITATIVE ANALYSIS
3.Obtain a
Representative
Sample
Define the
Problem
2.Select a Method

4. STEPS IN QUANTITATIVE ANALYSIS (continue)
5.Perform Any Necessary
Chemical Separations
4.Prepare the
sample for analysis
5. Perform the
Measurement

5. STEPS IN QUANTITATIVE ANALYSIS (continue)
6. Calculate the
Results and
Report

6. 1. Define the Problem
Before we begin defining the problem for an analysis procedure, we must have some information;
A)Who is the client(EPA, engineers)
B)The purpose of analysis
C)What type of sample to be analyzed

7. 1. Define the Problem
Factors to consider:
What is the problem—what needs to be found?
Qualitative and/or quantitative?
What will the information be used for? Who will use it?
When will it be needed?
How accurate and precise does it have to be?
What is the budget?

8. Once the problem is defined, next questions:
A) how sample is to be obtained
B) how much is needed
C)What separations may be required to eliminate interferences?

9. How to select a Method?

10. 2.Select a Method
Factors to be considered:
Sample type
Size of sample
Sample preparation needed
Concentration and range (sensitivity needed)
Selectivity needed (interferences)
Accuracy/precision needed
Tools/instruments available
Cost
Are methods available in the chemical literature?
Are standard methods available?

11. • Sample type/homogeneity/size • Sampling statistics/errors
3.Obtain a Representative Sample
Factors
• Sample type/homogeneity/size
• Sampling statistics/errors

12. The gross sample must be reduced in size to obtain a laboratory sample of several grams, from which a few grams to miligrams will be taken to be analyzed.

13. Obtaining a representative sample is the first step of an analysis.
The gross sample is several small portions of the sample.
This is reduced to provide a laboratory sample.
An aliquot of this sample is taken for the analysis sample.
Sampling

14. Some precautions should be taken during handling and storing samples to prevent or minimize contamination, loss, decomposition or matrix change.
We must prevent contamination or alteration of the sample by (1)light (2)atmosphere (3) container.

15. For example, some samples have to be protected from the atmosphere or light.
It maybe an alkaline substance that will react with CO2 in the air.
Blood samples to be analyzed for CO2 content shlould be protected from the atmosphere.

16. Next example, corrosive sample may react with the container.
In automobile exhaust SO2 is lost by dissolving in condensed water vapour from the exhaust.

17. 4.Prepare the Sample for Analysis
Factors
• Solid, liquid, or gas?
• Dissolve?
• Ash or digest?
• Chemical separation or masking of interferences needed?
• Need to concentrate the analyte?
• Need to change (derivatize) the analyte for detection?
• Need to adjust solution conditions (pH, add reagents)?

18. 4.Prepare the Sample for Analysis
Step 1:
Measure the amount being analyzed (volume or weight of the sample)
Replicate samples are taken for analysis
Why?

19. 1) to obatin statistical data on the precision of the analysis
2) to provide more reliable results.

20. Step 2: Sample pretreatment
Example: The organic materials sample are analyzed for inorganic constituents.
The organic constituents maybe destroyed by dry ashing.
How?

21. The organic materials is slowly combusted in a furnace at 400 oC to 700 oC.
Organic materials escape out, leaving behind an inorganic residue which is soluble in dilute acid.
Aim of step 2: to remove unwanted constituents that make up the whole sample.

22. Step 3: Optimizing sample condition
Aim of step 3: to prepare sample for the next stage of analysis (The separation or measurement step)
The solution condition is optimized.
How?

23. For example, the pH may have to be adjusted or reagent is added to mask interference from other constituents.
The analyte may have to be reacted with a reagent to convert it to a form suitable for measurement or separation.
For example, a coloured product maybe formed that will be measured by spectrometry.

24. 5.Perform Any Necessary Chemical Separations
• Distillation
• Precipitation
• Solvent extraction
• Solid phase extraction
• Chromatography (may be done as part of the
measurement step)

25. 5.Perform Any Necessary Chemical Separations
Why conduct chemical separation?
1.to eliminate interference
2.to provide suitable selectivity in the measurement
3. to preconcentrate the analyte for more sensitive or accurate measurement

26. 6. Perform the Measurement
Factors
• Calibration
• Validation/controls/blanks
• Replicates

27. 6. Perform the Measurement
Methods of carrying out the measurements:
1.gravimetric analysis
2.volumetric analysis
3. instrumental analysis.
What are these?

28. • Statistical analysis (reliability)
7. Calculate the Results and Report
• Statistical analysis (reliability)
• Report results with limitations/accuracy information

29. Quizzz time!
Close all of your notes!
10 minutes test.

30. Quiz 1:
1. Give one example of the application of analytical chemistry.(25 marks)
2.State the steps of carrying out tests using instrumentation for quantitative analysis. (25 marks)
3.Discuss each step in detail. (25 marks)
4. State the steps in quantitative analysis.
(25 marks)

31. Answers:
1.Any acceptable example like: carbon monoxide determination in public air or in trapped air (in car), blood glucose level in diabetics
2. Phase 1: Fast screening phase
Phase 2: Identification phase
Phase 3: Possible quantification

32. 3. Fast screening phase:
Urine samples are tested rapidly for the presence of classes of compounds different from normal samples. Techniques use: gas chromatography (GC), liquid chromatography (LC).
If samples have unknown compounds, that may or may not be prohibited, therefore further testing is needed for identification purpose.
Identification phase:
Using techniques such as gas chromatography-mass spectrometry (GC-MS). Complex mixtures are separated by GC. Then, detetcted by MS that gives molecular structural data on the compound.

33. Possible Quantification:
Precise quantification of some compounds. Meaning that, exact amount of compound must be determined. Therefore, we can verufy whether the substance is present is present at low level (permissible level) or high level (unpermissible level)

34. 4. 1.Define the Problem
2.Select a Method
3.Obtain a Representative Sample
4.Prepare the sample for analysis
5.Perform Any Necessary Chemical Separations
6. Perform the Measurement
7. Calculate the Results and Report

35. Basic tools in Analytical Chemistry

36. Fig. 2.1. Electronic analytical balance.
Modern balances are electronic. They still compare one mass against another since they are calibrated with a known mass. Common balances are sensitive to 0.1 mg.
Fig Electronic analytical balance.

37. Volumetric flasks are calibrated to contain an accurate volume
Volumetric flasks are calibrated to contain an accurate volume. See the inside back cover of the text for tolerances of Class A volumetric glassware.
Fig Volumetric flask.

38. Fig. 2.9. Transfer or volumetric pipets.
Volumetric pipets accurately deliver a fixed volume.
A small volume remains in the tip.
Fig Transfer or volumetric pipets.

39. Measuring pipets are straight-bore pipets marked at different volumes.
They are less accurate than volumetric pipets.
Fig Measuring pipets.

40. Fig. 2.11. Hamilton microliter syringe.
Syringe pipets precisely deliver microliter volumes.
They are commonly used to introduce samples into a gas chromatograph.
Fig Hamilton microliter syringe.

41. Fig. 2.12 Single-channel and multichannel digital
These syringe pipets can reproducibly deliver a selected volume.
They come in fixed and variable volumes. The plastic tips are disposable.
Fig Single-channel and multichannel digital
displacement pipets and microwell plates.

42. Fig. 2.14. Meniscus illuminator.
Position the black field just below the meniscus.
Avoid parallax error by reading at eye level.
Fig Meniscus illuminator.

43. Fig. 2.20. Wash botltles: (a) polyethylene, squeeze type;
Use these for quantitative transfer of precipitates and solutions,
and for washing precipitates.
Fig Wash botltles: (a) polyethylene, squeeze type;
(b) glass, blow type.

44. Next topic: accuracy and precision

45. 2. HANDLING OF DATA ANALYSIS
2.1.1 ACCURACY
2.1.2 PRECISION

46. Thank you
Q& A session.