SCCH 211: Analytical Chemistry I Analytical Techniques Based on Optical Spectroscopy Course Details September 22 October 10 September 22 November 7 November 17 December 1 Topic Period Introduction to Spectrometric Methods An Introduction to UV-Vis Molecular Absorption Spectrometry UV-Vis Molecular Absorption Spectrometry: September 22 Atitaya Siripinyanond Office Room: C218B Email: atitaya.sir@mahidol.ac.th Instrumentation Applications of UV-Vis Molecular Absorption Spectrometry October 10 Course Details September 22 October 10 September 22 November 7 November 17 December 1 Textbook Topic Molecular Luminescence Spectrometry Atomic Absorption Spectrometry Period November 17 December 1 D. A. Skoog, J. J. Leary, Principles of Instrumental Analysis, Saunders College Publishing (any edition) Atomic Emission Spectrometry
Handouts Evaluation (30-35%) http://chemistry.sc.mahidol.ac.th/en/ people/faculty/atitaya-siripinyanond/ Teaching Courses SCCH 211 Homework Assignments (10%) Quiz (10%) Paper Examination (80%) Assignment 1 Classification of Analytical Methods Take a group photograph and annotate a name of each person Save a file name as CHxx_xx.ppt or BTxx_xx.ppt Email to atitaya.sir@mahidol.ac.th by September 29, 2014 Classical methods gravimetric titrimetric (volumetric) Instrumental methods spectroscopy electroanalytical chromatography
Instrumental Methods of Analysis Selecting an Analytical Method Analytical Techniques Defining the problem Performance characteristics of instruments Spectroscopy Electrochemistry Separation Defining the Problem Method Selection Define clearly the nature of the analytical problem / requires answers to the following questions: What accuracy is required? How much sample is available? What is the concentration range of the analyte? What components of the sample might cause interference? What are the physical and chemical properties of the sample matrix? How many samples are to be analyzed? Concentration Complexity Cost Accuracy Amount Availability
Amount Concentration Macro analysis > 0.1 g Semi-micro analysis 0.1-0.01 g Micro analysis 10-4 10-2 g Major Constituent 1 100% Minor Constituent 0.01-1% Trace Constituent <0.01% Performance characteristics of instruments Figures of Merit Permit us to narrow the choice of instruments for a given analytical problem Criterion Precision Bias Sensitivity Figure of Merit Absolute standard deviation, relative standard deviation, coefficient of variation, and variance Absolute systematic error, relative systematic error Calibration sensitivity, analytical sensitivity Detection limit Blank plus three times standard deviation of the blank Dynamic range Selectivity Concentration limit of quantitation (LOQ) to concentration limit of linearity (LOL) Coefficient of selectivity
Spectroscopy An Introduction to Spectrophotometric Methods Study interaction between electromagnetic radiation and matter 1. Transmission Department of Chemistry reflection scattering 2. Reflection 3. Scattering Faculty of Science, Mahidol University I 0 I 4. Polarization 5. Absorption absorption 6. Emission Classification of Spectrophotometric Methods Interaction - absorption, emission Electromagnetic Radiation - UV, IR, X-ray Matter - molecular, atomic Energy Source - flame, plasma, spark, etc. Spectroanalytical Techniques Molecular spectroscopy Absorption techniques (UV, VIS, IR) Emission technique (Fluorometry) Atomic spectroscopy Absorption techniques Emission techniques
Electromagnetic Radiation Wave nature of a beam of single-frequency EMR EM radiation has an electric and magnetic field component which oscillate in phase perpendicular to each other and to the direction of energy propagation. Electromagnetic radiation is classified into types according to the frequency of the wave. Wave Characteristics Electromagnetic Spectrum Amplitude Length of the electric vector at a maximum in the wave Frequency Number of oscillations of the field that occur per second Wavelength Linear distance btw any two equivalent points on successive waves Velocity of propagation The product of frequency and wavelength http://en.wikipedia.org/wiki/electromagnetic_spectrum
Regions of the electromagnetic spectrum Optical methods http://en.wikipedia.org/wiki/electromagnetic_spectrum
Mo-W complex at various concentrations of gallic acid UV-Visible Spectrophotometry b cm Incident radiation of wavelength λ and intensity IO After absorption, intensity of radiation becomes I Absorbance Concentration of analyte, c M (log IO ) λ = Aλ = ε λ bc I 0 ppm 2 ppm 4 ppm 6 ppm 8 ppm UV-Vis Molecular Absorption Spectrometry: Instrumentation A C B http://en.wikipedia.org/wiki/ultraviolet-visible_spectroscopy
Instrumentation Instrumentation Spectrometer Spectrophotometer Using a monochromator as a wavelength selector Photometer Using a filter as a wavelength selector Colorimeter Applicable to VIS range region only Radiation Sources Wavelength Selectors Sample Containers Radiation Transducers Signal Processors and Readout Devices Radiation Source Radiation Sources Must generate a beam with sufficient radiant power for easy detection and measurement Output power should be stable for reasonable periods Requirements Intense output Uniform with wavelength Wide wavelength range Stable Intensity Continuum Discrete Continuum Discharge lamp Electrical excitation Incandescent lamp Blackbody radiation Wavelengt h
Sources Wavelength Selectors Deuterium and Hydrogen Lamps Tungsten Filament Lamps Light-Emitting Diodes Xenon Arc Lamps A narrow bandwidth enhances the sensitivity of absorbance measurements A narrow bandwidth may provide selectivity to both emission and absorption methods Ideally, the output from a wavelength selector would be radiation of a single wavelength or frequency Filters Monochromators Output of a Typical Wavelength Selector Components of Monochromators It is desirable to be able to continuously vary the wavelength of radiation over a broad range. An entrance slit that provides a rectangular optical image A collimating lens or mirror that produces a parallel beam of radiation A prism or a grating that disperses the radiation into its component wavelengths A focusing element that reforms the image of the entrance slit and focuses it on a planar surface An exit slit in the focal plane that isolates the desired spectral band
Czerney-Turner Monochromator Czerney-Turner Grating Monochromator Bunsen Prism Monochromator http://en.wikipedia.org/wiki/monochromator Performance Characteristics of Grating Monochromators Purity of its radiant output Ability to resolve adjacent wavelengths Spectral bandwidth Light-gathering power Sample Containers Cells that hold the sample must be constructed of a material that allows the passage of radiation in the spectral of interest With a monochromator, one can select the wavelength as desired
Radiation Transducers Convert radiant energy into an electrical signal Types of Transducers Responds to photons Photoelectric or quantum detectors Responds to heat Thermal detectors Photomultiplier Tubes PMT Similar to a phototube Contains additional electrodes (nine) called dynodes Dynode is maintained at a voltage approximately 90 V more positive than the cathode. D2 is +90 V more than D1. http://www.shsu.edu/~chm_tgc/sounds/pushmovies/pmt.html