SCCH 4: 211: 2015 SCCH

Transcription

1 SCCH 211: Analytical Chemistry I Analytical Techniques Based on Optical Spectroscopy Atitaya Siripinyanond Office Room: C218B atitaya.sir@mahidol.ac.th Course Details October 19 November 30 Topic Period Introduction to Spectrometric Methods An Introduction to UV-Vis Molecular Absorption Spectrometry UV-Vis Molecular Absorption Spectrometry: October 19 Instrumentation November 9 Applications of UV-Vis Molecular Absorption Spectrometry December 4: Electrochemistry by Dr.Duangjai Nacapricha Course Details Textbook October 19 November 30 Topic Molecular Luminescence Spectrometry Atomic Absorption Spectrometry Period November 13 November 30 D. A. Skoog, J. J. Leary, Principles of Instrumental Analysis, Saunders College Publishing (any edition) Atomic Emission Spectrometry December 4: Electrochemistry by Dr.Duangjai Nacapricha

2 Handouts Evaluation (30-35%) 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 to atitaya.sir@mahidol.ac.th by October 26, 2015 Classical methods gravimetric titrimetric (volumetric) Instrumental methods spectroscopy electroanalytical chromatography

3 Instrumental Methods of Analysis Analytical Techniques Spectroscopy Electrochemistry Separation An Introduction to Spectrophotometric Methods Department of Chemistry Faculty of Science, Mahidol University Spectroscopy Study interaction between electromagnetic radiation and matter Classification of Spectrophotometric Methods Interaction - absorption, emission reflection I 0 scattering I 1. Transmission 2. Reflection 3. Scattering 4. Polarization 5. Absorption Electromagnetic Radiation - UV, IR, X-ray Matter - molecular, atomic Energy Source - flame, plasma, spark, etc. absorption 6. Emission

4 Spectroanalytical Techniques Molecular spectroscopy Absorption techniques (UV, VIS, IR) Emission technique (Fluorometry) Atomic spectroscopy Absorption techniques Emission techniques 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

5 Regions of the electromagnetic spectrum Optical methods

6 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

7 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

8 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

9 Czerney-Turner Monochromator Czerney-Turner Grating Monochromator Bunsen Prism 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

10 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.

11 Types of Instruments Single-Beam Instruments Single beam Double beam in space Double beam in time Multichannel Requires a stabilized voltage supply to avoid errors resulting from changes in the beam intensity during the time required to make 100%T measurement and determine %T for the analyte

12 Double-Beam-in-Space Double-Beam-in-Time Double-Beam Instruments Multichannel Instruments Compensate for all but the most short-term fluctuations in the radiant output of the source as well as for drift in the transducer and amplifier Double-beam-in-time is preferred because of the difficulty in matching the two detectors needed for the double-beam-in-space design Dispersive system is a grating spectrograph placed after the sample or reference cell The array detector is placed in the focal plane of the spectrograph, where the dispersed radiation strikes it

13 Multichannel Instruments Probe-type photometer Spectronic 20 spectrophotometer Double-beam spectrophotometer for the UV-visible region Multichannel diode-array spectrophotometer