ANALYTICAL CHEMISTRY

1. ANALYTICAL CHEMISTRY deals with methods for determining the chemical composition of samples. Dr Seemal Jelani ENVR-303

2. Qualitative Analysis (identification) provides information about the identity of species or functional groups in the sample (an analyte can be identified). • Quantitative Analysis provides numerical information of analyte (quantitate the exact amount or concentration). Dr Seemal Jelani ENVR-303

3. Analytical Methods • Classical Methods: Wet chemical methods such as precipitation, extraction, distillation, boiling or melting points, gravimetric and titrimetric measurements. • Instrumental Methods Analytical measurements (conductivity, electrode potential, light absorption or emission, mass-to-charge ratio, fluorescence etc.) are made using instrumentation. Dr Seemal Jelani ENVR-303

4. Types of Instrumental Methods 1. Spectroscopic methods: • Atomic spectroscopy • Molecular spectroscopy 2. Chromatographic methods (separations): 3. Electrochemistry: Dr Seemal Jelani ENVR-303

5. Block diagram of an instrumental measurement Dr Seemal Jelani ENVR-303

6. Applications of Instrumental Methods • Bioanalytical: biological molecules and/or biological matrices (e.g., proteins, amino acids, blood, urine) • Environmental: pesticides, pollution, air, water, soil • Material science: polymers, characterization of new materials • Forensic science (application of science to the law): body fluids, DNA, gun shot residue, hair, fibers, elemental analysis, drugs, alcohols, poisoning, fingerprints, etc. Dr Seemal Jelani ENVR-303

7. Analytical Methodology • Plan: Qualitative or quantitative or both; what kind of information have; which technique is suitable etc. • Sampling: Accuracy depends on proper sampling, characteristic of sample is very important, required good representative sample (from top, middle and bottom and mix up and take average sample). Dr Seemal Jelani ENVR-303

8. 4Sample preparation: depends on analytical techniques. 5Analytical measurement: 6Data Analysis: Whether the data make sense or not. Dr Seemal Jelani ENVR-303

9. Selecting an Analytical Method • In order to select an analytical method intelligently, it is essential to define clearly the nature of the analytical problem • In general, the following points should be considered when choosing an instrument for any measurement. Dr Seemal Jelani ENVR-303

10. Accuracy and precision required • Available sample amount • Concentration range of the analyte • Interference in sample • Physical and chemical properties of the sample surrounding substance • Number of sample to be analyzed • Speed, ease, skill and cost of analysis Dr Seemal Jelani ENVR-303

11. Figures of Merit • Precision • Bias • Sensitivity • Detection limit • Concentration range (Dynamic range) • Selectivity Dr Seemal Jelani ENVR-303

12. Precision • How close the same measurements are to one another • The degree of mutual agreement among data that have been obtained in the same way • Precision provides a measure of the random or undetermined error of an analysis. Dr Seemal Jelani ENVR-303

13. Accuracy • How close the measurement approaches the real value Dr Seemal Jelani ENVR-303

14. Bias Bias provides a measure of the systematic, or determinate error of an analytical method. bias =  - xt, where, is the population mean and xt is the true value Dr Seemal Jelani ENVR-303

15. Dr Seemal Jelani ENVR-303

16. Absolute standard deviation • In statistics the absolute deviation is a measure of how much a particular sample deviates from the average sample. Read more: Dr Seemal Jelani ENVR-303

17. Relative standard deviation • In probability theory and statistics, the relative standard deviation (RSD or %RSD) is the absolute value of the coefficient of variation • A similar term that is sometimes used is the relative variance which is the square of the coefficient of variation Dr Seemal Jelani ENVR-303

18. Also, the relative standard error is a measure of a statistical estimate's reliability obtained by dividing the standard error by the estimate; then multiplied by 100 to be expressed as a percentage Dr Seemal Jelani ENVR-303

19. Sensitivity • Sensitivity of an instrument is a measure of its ability to distinguish between small differences in analyte concentration • The change in signal per unit change in analyte concentration • The slope of the calibration curve at the concentration of interest is known as calibration sensitivity. S = mc + Sbl S = measured signal; c= analyte concentration; Dr Seemal Jelani ENVR-303

20. Sbl = blank signal; m = sensitivity (Slope of line) Analytical sensitivity ()  = m/ss m = slope of the calibration curve ss = standard deviation of the measurement Dr Seemal Jelani ENVR-303

21. Detection Limit (Limit of detection, LOD) • The minimum concentration of analyte that can be detected with a specific method at a known confidence level. LOD is determined by S/N, where, S/N = Signal-to-noise ratio = (magnitude of the signal)/(magnitude of the noise) Dr Seemal Jelani ENVR-303

22. Noise • Unwanted baseline fluctuations in the absence of analyte signal (standard deviation of the background) • The detection limit is given by, Cm = (Sm – Sbl)/m, where, Cm = minimum concentration i.e., LOD, Sm = minimum distinguishable analytical signal (i.e., S/N = 2 or S/N = 3), Dr Seemal Jelani ENVR-303

23. Sbl = mean blank signal m = sensitivity (i.e., slope of calibration curve) • The amount of analyte necessary to yield a net signal equal to 2 or 3x the standard deviation of the background. Dr Seemal Jelani ENVR-303

24. Dynamic Range • The lowest concentration at which quantitative measurements can be made (limit of quantitation, or LOQ) to the concentration at which the calibration curve departs from linearity (limit of linearity, or LOL). Dr Seemal Jelani ENVR-303

25. The lower limit of quantitative measurements is generally taken to be equal to ten times the standard deviation of repetitive measurements on a blank or 10 Sbl. Dynamic range is the range over which detector still responds to changing concentration (at high concentrations – usually saturates – quits responding) An analytical method should have a dynamic range of at least two orders of magnitude, usually 2-6 orders of magnitude. Dr Seemal Jelani ENVR-303

26. Selectivity • Selectivity of an analytical method refers to the degree to which the method is free from interference by other species contained in the sample matrix • No analytical method is totally free from interference from other species, and steps need to be taken to minimize the effects of these interferences. Dr Seemal Jelani ENVR-303

27. Selectivity coefficient gives the relative response of the method to interfering species as compared with analyte • Selectivity coefficient can range from zero (no interference) to values greater than unity. • A coefficient is negative when the interference caused a reduction in the intensity of the output signal of the analyte. Dr Seemal Jelani ENVR-303

28. Spectroscopic methods • Spectroscopy measures the interaction of the molecules with Electromagnetic radiation Spectroscopy consists of many different applications such as Atomic absorption spectroscopy, • Atomic emission spectroscopy • Ultraviolet visible spectroscopy • X-Ray fluorescence spectroscopy Dr Seemal Jelani ENVR-303

29. Spectroscopic methods • Spectroscopy measures the interaction of the molecules with Electromagnetic radiation Spectroscopy consists of many different applications such as Atomic absorption spectroscopy, • Atomic emission spectroscopy • Ultraviolet visible spectroscopy • X-Ray fluorescence spectroscopy Dr Seemal Jelani ENVR-303

30. Infrared spectroscopy • Nuclear magnetic resonance spectroscopy • Photoemission spectroscopy Dr Seemal Jelani ENVR-303

31. In type of spectroscopy , the main division is between optical and mass spectrometry • Mass spectrometry generally gives significantly better analytical performance, but is also significantly more complex. • Extremely expensive and complex as compared to optical spectroscopy Dr Seemal Jelani ENVR-303

32. Atomic absorption spectrometers are one of the most commonly sold and used analytical devices. Dr Seemal Jelani ENVR-303

33. Atomic spectroscopy • Determination of elemental composition by its Electromagnetic or Mass spectrum • It is related to other forms of spectroscopy Can be divided by: Atomization source Type of spectroscopy used Dr Seemal Jelani ENVR-303

34. Optical spectroscopy • Electrons exist in energy levels within an atom • These levels have well defined energies and electrons moving between them must absorb or emit an energy equal to the difference between them Dr Seemal Jelani ENVR-303

35. In optical spectroscopy, the energy absorbed to move an electron to a more energetic level and/or the energy emitted as the electron moves to a lower energy level is in the form of a Photon (a particle of light). Dr Seemal Jelani ENVR-303

36. Because this energy is well-defined, an atom's identity can be found by the energy of this transition • The wavelength of light can be related to its energy. Dr Seemal Jelani ENVR-303

37. It is usually easier to measure the wavelength of light than to directly measure its energy. • Optical spectroscopy can be further divided into absorption, emission, and fluorescence Dr Seemal Jelani ENVR-303