Instrumental Analysis (CHM4001) Text book Principles of Instrumental Analysis, 6th Edition, by Dougals A. Skoog and others

Analytical Chemistry (分析 化學) Qualitative Analysis Identify chemical signature Supporting other fields Quantitative Analysis Clearly measure content (concentration) Need to understand analytical instruments Instrumentation Develop new analytical instruments Need Combined knowledge

Instrumental Analysis Molecular Spectroscopy IR, NIR, Raman, Ultra-Violet/Visible, NMR Fluorescence, Mass Atomic Spectroscopy Atomic Absorption, Atomic Emission Separation GC, HPLC, GPC, Electrophoresis Electrochemical Voltammetry, Potentiometry

Electromagnetic Radiation Wave Property (Reflection, Scattering, Diffraction………) Particle Property (Photon) (Emission, Absorption…)

Wave Parameters

Important Terminologies Amplitude (A): Maximum length of electric vector Period (P) : Time (second) required for the passage of successive maxima or minima. Frequency () : Number of oscillation per second (1/P, Hz) wavelength () : Linear distance between two equivalent points Velocity of propagation: vi=i in vacuum c =  = 3 ×108 m/s Wavenumber (cm-1) : Reciprocal of wavelength in centimeters Power (P) : energy of the beam reaches a given area per second

Electromagnetic Spectrum

Mathematical Descriptions of Wave y: electric field, A: amplitude, t: time  : phase angle,  : angular velocity (=2)

Superposition of Waves

Constructive Interference: (1-2)= 0, 360, or n360 Destructive Interference: (1-2)= 180, or 180 + n360

Same Amplitude, different frequency

Fourier Transform

Square Wave

Magnitude Wavelength

Diffraction Parallel beam is bent as it passes by a sharp barrier or through a narrow opening Consequence of interference

Diffraction Grating and Monochromator

Ml = d sinθ

n

Coherent Radiation Two radiations must have identical frequency Phase relationships must remain constant

Transmission of Radiation Velocity of radiation is decreased when it passes a medium The decrease depends on kinds and concentrations of atom, ion, molecules No Frequency change Refractive Index (RI)  (liquid:1.3~1.8, solid:1.3~2.5 or higher)

Transmission of Radiation Periodic Polarization Temporal deformation of electron cloud by alternating electromagnetic field 10-14 ~ 10-15 second No net energy change Rate of propagation is slowed Stepwise process involving polalization

Dispersion Variation of RI with wavelength or frequency Good for Prism Good for Lens, window

Refraction Snell’s Law Abrupt change in light direction from difference in velocity Snell’s Law

Structure of Optical Fibers

Reflection Abrupt change in light direction from difference in velocity I0: intensity of incident beam, Ir : reflected intensity

Scattering Rayleigh Scattering (elastic scattering) - scattering by molecules small than wavelength - proportional to 1/4, (polarizability of the particle)2 Scattering by Large Molecules: Tyndall Effect - determine the size and shape of polymer molecules and colloidal particles Raman Scattering (inelastic scattering) - scattering with frequency change

Polarization

Quantum-Mechanical Properties Photoelectric Effect Photocathode - coated with alkali metals h impinges on the surface - electrons are emitted with a range of kinetic energy Large Voltage - produce a current in circuit Decrease Voltage - small current Stopping Voltage (Vo) - photocurrent = zero

E = h = eV0 +  Work Function () : minimum work needed to eject electron from metal Photocurrent is proportional to the intensity of radiation Stopping voltage depends on the frequency of radiation Stopping voltage depends on the chemical composition of the coating Stopping voltage is independent of the intensity of incident radiation

Energy States of Chemical Species Atoms, ions, and molecules can exists only in certain discrete states characterized by definite amounts of energy When atoms, ions, and molecules absorb or emit radiation from one energy state to a second E1 – E0 = h = hc/ Electronic State Vibrational State Rotational State Ground State Excited State

Emission of radiation M + Energy  M*  M + h Bombardment of electron beam  X-ray Electrical current, flame, arc, furnance  UV, visible, IR Beam of electromagnetic radiation  fluorescence Exothermic chemical reaction  chemiluminescence

Line Spectra Band Spectra Continuum Spectra Radiating from individual atomic particle that are well separated Sharp spectral lines Band Spectra Gaseous radicals or small molecules Not fully resolved Bands from many quantized vibrational levels superimposed on the electronic energy level Continuum Spectra Radiation from heated solid: incandescence Called black-body radiation High temperature needs to emit UV region

Continuum Spectra

Absorption of Radiation Atomic Absorption Molecular Absorption Absorption Induced by a magnetic field E = Eelectronic + Evibrational + Erotational

Relaxation Process

Quantitative Aspects of Spectrochemical Measurement electrical signal (S) radiant power (P) S= k P S= k P + kd dark current (kd ) Signal without radiation

Transmittance (T) Absorbance (A)

Beer’s Law a:(absorptivity, L g-1cm-1) b: thickness, c: concentration(g/L) molar absorptivity (L mol-1cm-1)