INSTRUMENTAL ANALYSIS CHEM 4811

INSTRUMENTAL ANALYSIS CHEM 4811
CHAPTER 2 DR. AUGUSTINE OFORI AGYEMAN Assistant professor of chemistry Department of natural sciences Clayton state university

INTRODUCTION TO SPECTROSCOPY
CHAPTER 2 INTRODUCTION TO SPECTROSCOPY

DEFINITIONS Spectroscopy
- The study of the interactions of electromagnetic radiation (radiant energy) and matter (molecules, atoms, or ions) Spectrometry - Quantitative measurement of the intensity of one or more wavelengths of radiant energy Spectrophotometry - The use of electromagnetic radiation to measure chemical concentrations (used for absorption measurements)

DEFINITIONS Spectrophotometer
- Instrument used for absorption measurements Optical Spectrometer - Instrument that consists of prism or grating dispersion devise, slits, and a photoelectric detector Photometer - Instrument that uses a filter for wavelength selection instead of a dispersion device

ELECTROMAGNETIC RADIATION
- Also known as radiant heat or radiant energy - One of the ways by which energy travels through space - Consists of perpendicular electric and magnetic fields that are also perpendicular to direction of propagation Examples heat energy in microwaves light from the sun X-ray radio waves

Visible Light: VIBGYOR
ELECTROMAGNETIC RADIATION Wavelength (m) 10-11 103 Radio frequency FM Shortwave AM Gamma rays Ultr- violet X rays Visible Infrared Microwaves Frequency (s-1) 104 1020 Visible Light: VIBGYOR Violet, Indigo, Blue, Green, Yellow, Orange, Red 400 – 750 nm - White light is a blend of all visible wavelengths - Can be separated using a prism

λ1 node amplitude ν1 = 4 cycles/second λ2 peak ν2 = 8 cycles/second λ3 ν3 = 16 cycles/second trough one second

Wavelength (λ) - Distance for a wave to go through a complete cycle (distance between two consecutive peaks or troughs in a wave) Frequency (ν) - The number of waves (cycles) passing a given point in space per second Cycle - Crest-to-crest or trough-to-trough Speed (c) - All waves travel at the speed of light in vacuum (3.00 x 108 m/s)

Plane Polarized Light - Light wave propagating along only one axis (confined to one plane) Monochromatic Light - Light of only one wavelength Polychromatic Light - Consists of more than one wavelength (white light) Visible light - The small portion of electromagnetic radiation to which the human eye responds

- Inverse relationship between wavelength and frequency λ α 1/ν c = λ ν λ = wavelength (m) ν = frequency (cycles/second = 1/s = s-1 = hertz = Hz) c = speed of light (3.00 x 108 m/s)

- Light appears to behave as waves and also considered as stream of particles (the dual nature of light) - Is sinusoidal in shape - Light is quantized Photons - Particles of light

h = Planck’s constant (6.626 x J-s) ν = frequency of the radiation λ = wavelength of the radiation E is proportional to ν and inversely proportional to λ

INTERACTIONS WITH MATTER
- Takes place in many ways - Takes place over a wide range of radiant energies - Is not visible to the human eye - Light is absorbed or emitted - Follows well-ordered rules - Can be measured with suitable instruments

- Atoms, molecules, and ions are in constant motion Solids - Atoms or molecules are arranged in a highly ordered array (crystals) or arranged randomly (amorphous) Liquids - Atoms or molecules are not as closely packed as in solids Gases - Atoms or molecules are widely separated from each other

Molecules Many types of motion are involved - Rotation - Vibration - Translation (move from place to place) - These motions are affected when molecules interact with radiant energy - Molecules vibrate with greater energy amplitude when they absorb radiant energy

Molecules - Bonding electrons move to higher energy levels when molecules interact with visible or UV light - Changes in motion or electron energy levels result in changes in energy of molecules Transition - Change in energy of molecules (vibrational transitions, rotational transitions, electronic transitions)

Atoms or Ions - Move between energy levels or in space but cannot rotate or vibrate The type of interactions of materials with radiant energy are affected by - Physical state - Composition (chemical nature) - Arrangement of atoms or molecules

Light striking a sample of matter may be - Absorbed by the sample - Transmitted through the sample - Reflected off the surface of the sample - Scattered by the sample - Samples can also emit light after absorption (luminescence) - Species (atoms, ions, or molecules) can exist in certain discrete states with specific energies

Transmission - Light passes through matter without interaction Absorption - Matter absorbs light energy and moves to a higher energy state Emission - Matter releases energy and moves to a lower energy state Luminescence - Emission following excitation of molecules or atoms by absorption of electromagnetic radiation

Ground State: The lowest energy state Excited state: higher energy state (usually short-lived) Excited state Energy Ground state Absorption Emission

- Change in state requires the absorption or emission of energy - Matter can only absorb specific wavelengths or frequencies - These correspond to the exact differences in energy between the two states involved Absorption: Energy of species increases (ΔE is positive) Emission: Energy of species decreases (ΔE is negative)

- Frequencies and the extent of absorption or emission of species are unique - Specific atoms or molecules absorb or emit specific frequencies - This is the basis of identification of species by spectroscopy Relative energy of transition in a molecule Rotational < vibrational < electronic - The are many associated rotational and vibrational sublevels for any electronic state (absorption occurs in closely spaced range of wavelenghts)

Absorption Spectrum - A graph of intensity of light absorbed versus frequency or wavelength - Emission spectrum is obtained when molecules emit energy by returning to the ground state after excitation Excitation may include - Absorption of radiant energy - Transfer of energy due to collisions between atoms or molecules - Addition of thermal energy - Addition of energy from electrical charges

ATOMS AND ATOMIC SPECTROSCOPY
- The electronic state of atoms are quantized - Elements have unique atomic numbers (numbers of protons and electrons) - Electrons in orbitals are associated with various energy levels - An atom absorbs energy of specific magnitude and a valence electron moves to the excited state - The electron returns spontaneously to the ground state and emits energy

- Emitted energy is equivalent to the absorbed energy (ΔE) - Each atom has a unique set of permitted electronic energy levels (due to unique electronic structure) - The wavelength of light absorbed or emitted are characteristic of a specific element - The absorption wavelength range is narrow due to the absence of rotational and vibrational energies - The wavelength range falls within the ultraviolet and visible regions of the spectrum (UV-VIS)

- Wavelengths of absorption or emission are used for qualitative identification of elements in a sample - The intensity of light absorbed or emitted at a given wavelength is used for the quantitative analysis Atomic Spectroscopy Methods - Absortion spectroscopy - Emission spectroscopy - Fluorescence spectroscopy - X-ray spectroscopy (makes use of core electrons)

MOLECULES AND MOLECULAR SPECTROSCOPY
Molecular Processes Occurring in Each Region 10-11 103 Gamma rays Ultr- violet Radio frequency FM Shortwave AM X rays Visible Infrared Microwaves 1020 104 Electronic excitation rotation vibration Bond breaking and ionization

MOLECULES AND MOLECULAR SPECTROSCOPY Rotational Transitions
- Energy states are quantized Rotational Transitions - Molecules rotate in space and rotational energy is associated - Absorption of the correct energy causes transition to a higher energy rotational state - Molecules rotate faster in a higher energy rotational state - Rotational spectra are usually complex

MOLECULES AND MOLECULAR SPECTROSCOPY Rotational Transitions
- Rotational energy of a molecule depends on shape, angular velocity, and weight distribution - Shape and weight distribution change with bond angle - Molecules with more than two atoms have many possible shapes - Change in shape is therefore restricted to diatomic molecules - Associated energies are in the radio and microwave regions

MOLECULES AND MOLECULAR SPECTROSCOPY Vibrational Transitions
- Atoms in a molecule can vibrate toward or away from each other at different angles to each other - Each vibration has characteristic energy associated with it - Vibrational energy is associated with absorption in the infrared (IR region) Increase in rotational energy usually accompanies increase in vibrational energy

MOLECULES AND MOLECULAR SPECTROSCOPY Vibrational Transitions
- IR absorption corresponds to changes in both rotational and vibrational energies in molecules - IR absorption spectroscopy is used to deduce the structure of molecules - Used for both qualitative and quantitative analysis

MOLECULES AND MOLECULAR SPECTROSCOPY Electronic Transitions
- Molecular orbitals are formed when atomic orbitals combine to form molecules - Absorption of the correct radiant energy causes an outer electron to move to an excited state - Excited electron spontaneously returns to the ground state (relax) emitting UV or visible energy - Excitation in molecules causes changes in the rotational and vibrational energies

MOLECULES AND MOLECULAR SPECTROSCOPY Electronic Transitions
- The total energy is the sum of all rotational, vibrational, and electronic energy changes - Associated with wide range of wavelengths (called absorption band) - UV-VIS absorption bands are simpler than IR spectra

MOLECULES AND MOLECULAR SPECTROSCOPY Molecular Spectroscopy Methods
- Molecular absorption spectroscopy - Molecular emission spectroscopy - Nuclear Magnetic Resonance (NMR) - UV-VIS - IR - MS - Molecular Fluorescence Spectroscopy

ABSORPTION LAWS Radiant Power (P)
- Energy per second per unit area of a beam of light - Decreases when light transmits through a sample (due to absorption of light by the sample) Intensity (I) - Power per unit solid angle - Light intensity decreases as light passes through an absorbing material

ABSORPTION LAWS Transmittance (T)
- The fraction of incident light that passes through a sample 0 < T < 1 Io = light intensity striking a sample I = light intensity emerging from sample Io I

Percent Transmitance (%T)
ABSORPTION LAWS Transmittance (T) - T is independent of Io - No light absorbed: I = Io and T = 1 - All light absorbed: I = 0 and T = 0 Percent Transmitance (%T) 0% < %T < 100%

ABSORPTION LAWS Absorbance (A) - No light absorbed: I = Io and A = 0
Percent Absorbance (%A) = %T - 1% light absorbed implies 99% light transmitted - Higher absorbance implies less light transmitted

ABSORPTION LAWS Beer’s Law A = abc A = absorbance a = absorptivity
a = ε [molar absorptivity (M-1cm-1) if C is in units of M (mol/L)] b = pathlength or length of cell (cm) c = concentration

ABSORPTION LAWS Beer’s Law
- I or T decreases exponentially with increasing pathlength - A increases linearly with increasing pathlength - A increases linearly with increasing concentration - More intense color implies greater absorbance - Basis of quantitative measurements (UV-VIS, IR, AAS etc.)

ABSORPTION LAWS Absorption Spectrum of 0.10 mM Ru(bpy)32+
λmax = 452 nm

ABSORPTION LAWS Absorption Spectrum of 3.0 mM Cr3+ complex
λmax = 540 nm

Maximum Response (λmax)
ABSORPTION LAWS Maximum Response (λmax) - Wavelength at which the highest absorbance is observed for a given concentration - Gives the greatest sensitivity

Deviations from Beer’s Law
ABSORPTION LAWS Deviations from Beer’s Law - Deviations from linearity at high concentrations - Usually used for concentrations below 0.01 M - Deviations occur if sample scatters incident radiation - Error increases as A increases (law generally obeyed when A ≤ 1.0

CALIBRATION METHODS Calibration
- The relationship between the measured signal (absorbance in this case) and known concentrations of analyte - Concentration of an unknown analyte can then be calculated using the established relationship and its measured signal

Calibration with External Standards
CALIBRATION METHODS Calibration with External Standards - Solutions containing known concentrations of analyte are called standard solutions - Standard solutions containing appropriate concentration range are carefully prepared and measured - Reagent blank is used for instrumental baseline - A plot of absorbance (y-axis) vs concentration (x-axis) is made

CALIBRATION METHODS Calibration with External Standards

CALIBRATION METHODS Calibration with External Standards - Equation of a straight line in the form y = mx + z is established m = slope = ab z = intercept on the absorbance axis - Concentration of unknown analyte should be within working range (do not extrapolate) - Must measure at least three replicates and report uncertainty

Method of Standard Additions (MSA)
CALIBRATION METHODS Method of Standard Additions (MSA) - Known amounts of analyte are added directly to the unknown sample - The increase in signal due to the added analyte is used to establish the concentration of unknown - Relationship between signal and concentration of analyte must be linear - Analytes are added such that change in volume is negligible

CALIBRATION METHODS Method of Standard Additions (MSA) - Different concentrations of analyte are added to different aliquots of sample - Nothing is added to the first aliquot (untreated) - Concentrations in increments of 1.00 is usually used for simplicity - Plot of signal vs concentration of analyte is made

CALIBRATION METHODS Method of Standard Additions (MSA) Useful - In emergency situations - When information about the sample matrix is unknown - For elimination of certain interferences in the matrix

Internal Standard Calibration
CALIBRATION METHODS Internal Standard Calibration - Signal from internal standard is used to correct for interferences in an analyte - The selected internal standard must not be already present in all samples, blanks, and standard solutions - Internal standard must not interact with analyte Internal Standard - Known amount of a nonanalyte species that is added to all samples, blanks, and standards

CALIBRATION METHODS Internal Standard Calibration - For an analyte (A) and internal standard (S) Signal ratio (A/S) is plotted against concentration ration (A/S) Concentration ratio (A/S) of unknown is obtained from the linear equation

CALIBRATION METHODS Internal Standard Calibration Corrects errors due to - Voltage fluctuations - Loss of analyte during sample preparation - Change in volume due to evaporation - Interferences

ERRORS ASSOCIATED WITH BEER’S LAW
- Indeterminate (random) errors are associated with all spectroscopic methods Examples - Noise due to instability of light source - Detector instability - Variation in placement of cell in light path - Finger prints on cells

EVALUATION OF ERRORS - ΔT is the error in transmittance measurement
- The relative error is high when T is very high or very low - For greatest accuracy, measurements should be within 15% - 65% T or A - Samples with high concentration (A > 0.82) should be diluted and those with low concentrations (A < 0.19) should be concentrated

EVALUATION OF ERRORS Ringbom Method
(100 – %T) is plotted against log(c) - The result is an s-shaped curve (Ringbom plot) - The nearly linear portion of the curve (the steepest portion) is the working range where error is minimized (100-%T) Log(c)

OPTICAL SYSTEMS IN SPECTROSCOPY
Fundamental Concepts of Optical Measurements - Measurement of absorption or emission of radiation - Providing information about the wavelength of absorption or emission - Providing information about the intensity or absorbance at the wavelength

OPTICAL SYSTEMS IN SPECTROSCOPY Main Components of Spectrometers
- Radiation source - Wavelength selection device - Sample holder (transparent to radiation) - Detector

OPTICAL SYSTEMS IN SPECTROSCOPY
- FT spectrometers do not require wavelength selector - Radiation source is the sample if emission is being measured - External radiation source is required if absorption is being measured - Sample holder is placed after wavelength selector for UV-VIS absorption spectrometry so that monochromatic light falls on the sample - Sample holder is placed before the wavelength selector for IR, fluorescence, and AA spectroscopy

COMPONENTS OF THE SPECTROMETER
Absorption (UV-Vis) b Po P Light source monochromator (λ selector) sample detector readout

Absorption (IR) Light source monochromator (λ selector) detector readout sample

Emission Source & sample monochromator (λ selector) detector readout - Sample is an integral portion of the source - Used to produce the EM radiation that will be measured

Fluorescence Source λ selector sample monochromator (λ selector) detector readout

RADIATION SOURCE - Must emit radiation over the entire wavelength range being studied - Intensity of radiation of the wavelength range should be high - A reliable and steady power supply is essential to provide constant signal - Intensity should not fluctuate over long time intervals - Intensity should not fluctuate over short time intervals Flicker: short time fluctuation in source intensity

Two types of radiation sources
Continuum Sources and Line Sources

RADIATION SOURCE Continuum Sources
- Emit radiation over a wide range of wavelengths - Intensity of emission varies slowly as a function of wavelength - Used for most molecular absorption and fluorescence spectrometric instruments Examples - Tungsten filament lamp (visible radiation) - Deuterium lamp (UV radiation) - High pressure Hg lamp (UV radiation) - Xenon arc lamp (UV-VIS region) - Heated solid ceramics (IR region) - Heated wires (IR region)

RADIATION SOURCE Line Sources
- Emit only a few discrete wavelengths of light - Intensity is a function of wavelength - Used for molecular, atomic, and Raman spectroscopy Examples - Hollow cathode lamp (UV-VIS region) - Electrodeless discharge lamp (UV-VIS region) - Sodium vapor lamp (UV-VIS region) - Mercury vapor lamp (UV-VIS region) - Lasers (UV-VIS and IR regions)

RADIATION SOURCE Tungsten Filament Lamp
- Glows at a temperature near 3000 K - Produces radiation at wavelengths from 320 to 2500 nm - Visible and near IR regions Dueterium (D2) Arc Lamp - D2 molecules are electrically dissociated - Produces radiation at wavelengths from 200 to 400 nm - UV region

RADIATION SOURCE Mercury and Xenon Arc Lamps
- Electric discharge lamps - Produce radiation at wavelengths from 200 to 800 nm - UV and Visible regions Silicon Carbide (SiC) Rod - Also called globar - Electrically heated to about 1500 K - Produces radiation at wavelengths from 1200 to nm - IR region

- NiChrome wire (750 nm to 20000 nm)
RADIATION SOURCE Also for IR Region - NiChrome wire (750 nm to nm) - ZrO2 (400 nm to nm)

RADIATION SOURCE Laser - Produce specific spectral lines
- Used when high intensity line source is required Can be used for UV Visible FTIR

WAVELENGTH SELECTION DEVICES
Two types Filters and Monochromators

- The simplest and most inexpensive
FILTERS - The simplest and most inexpensive Two major types Absorption Filters and Interference Filters

FILTERS Absorption Filters - A piece of colored glass
- Stable, simple and cheap - Suitable for spectrometers designed to be carried to the field Disadvantage - Range of wavelengths transmitted is very broad (50 – 300 nm)

FILTERS Interference Filters - Made up of multiple layers of materials
- The thickness and the refractive index of the center layer of the material control the wavelengths transmitted - Range of wavelengths transmitted are much smaller (1 – 10 nm) - Amount of light transmitted is generally higher - Transmits light in the IR, VIS, and UV regions

MONOCHROMATORS - Disperse a beam of light into its component wavelengths - Allow only a narrow band of wavelengths to pass - Block all other wavelengths Components - Dispersion element - Two slits (entrance and exit) - Lenses and concave mirrors

MONOCHROMATORS Dispersion Element
- Disperses (spreads out) the radiation falling on it according to wavelength Two main Types Prisms and Gratings

MONOCHROMATORS Prisms - Used to disperse IR, VIS, and UV radiations
- Widely used is the Cornu prism (60o-60o-60o triangle) Examples Quartz (UV) Silicate glass (VIS or near IR) NaCl or KBr (IR)

MONOCHROMATORS Prisms
- Refraction or bending of incident light occurs when a polychromatic light hits the surface of the prism - Refractive index of prism material varies with wavelength - Various wavelengths are separated spatially as they are bent at different degrees - Shorter wavelengths (higher energy) are bent more than longer wavelengths (lower energy)

MONOCHROMATORS Diffraction Gratings
- Consists of a series of closely spaced parallel grooves cut (or ruled) into a hard glass, metallic or ceramic surface - The surface may be flat or concave - Reflective coating (e.g. Al) is usually on the ruled surface - Used for UV-VIS radiation (500 – 5000 grooves/mm) and IR radiation (50 – 200 grooves/mm)

MONOCHROMATORS Diffraction Gratings d Side view Top view

- Size ranges between 25 x 25 mm to 110 x 110 mm - Light is dispersed by diffraction due to constructive interference between reflected light waves - Separation of light occurs due to different wavelengths being dispersed (diffracted) at different angles

- Constructive interference occurs when nλ = d(sini ± sinθ) n = order of diffraction (integer: 1, 2, 3, …) λ = wavelength of radiation d = distance between grooves i = incident angle of a beam of light θ = angle of dispersion of light

Dispersive Resolution
MONOCHROMATORS Dispersive Resolution Resolving Power (R): - Ability to disperse radiation - Ability to separate adjacent wavelengths from each other λ = average of the wavelengths of the two lines to be resolved δλ = difference between the two wavelengths

MONOCHROMATORS Resolution of a Prism
t = thickness of the base of the prism dη/dλ = rate of change of the refractive index (η) with λ - Resolving power increases with thickness of the prism and decreases at longer wavelengths - Resolution depends on the prism material

Resolution of a Grating
MONOCHROMATORS Resolution of a Grating R = nN n = the order N = total number of grooves in the grating that are illuminated by light from the entrance slit (whole number) Increased resolution results from - Longer gratings - Smaller groove spacing - Higher order

Dispersion of a Grating
MONOCHROMATORS Dispersion of a Grating dλ = change in wavelength dy = change in distance separating the λs along the dispersion axis Units: nm/mm

Dispersion of a Grating
MONOCHROMATORS Dispersion of a Grating Spectral bandwidth (bandpass) = sD-1 s = slit width of monochromator d = distance between two adjacent grooves n = diffraction order F = focal length of the monochromator system - D-1 is constant with respect to wavelength

ECHELLE MONOCHROMATOR
Echellette Grating - Grooved or blazed such that it has relatively broad faces from which reflection occurs - Has narrow unused faces - Provides highly efficient diffraction grating

ECHELLE MONOCHROMATOR
- Contains two dispersion elements arranged in series - The first is known as echelle grating - The second (called cross-dispersion) is a low-dispersion prism or a grating Echelle grating - Greater blaze angle - The short side of the blaze is used rather than the long side - Relatively coarse grating - Angle of dispersion (θ) is higher - Results in 10-fold resolution

OPTICAL SLITS - Slits are used to select radiation from the light source both before and after dispersion by the λ selector - Made of metal in the shape of two knife edges - Movable to set the desired mechanical width

OPTICAL SLITS Entrance Slit
- Allows a beam of light (polychromatic) from source to fall on the dispersion element - Radiation is collimated into a parallel beam with lenses or front-faced mirrors - One (selected) wavelength of light (monochromatic) is focused on the exit slit after dispersion

OPTICAL SLITS Exit Slit
- Allows only a very narrow band of light to pass through sample and detector - The dispersed light falls on the exit slit - The light is redirected and focused onto the detector for intensity measurements - Slits are kept as close as possible to ensure resolution

CUVET (SAMPLE CELL) - Cell used for spectrometry
Identical or Optically Matched Cells - Cells that are identical in their absorbance or transmittance of light Fused silica Cells (SiO2) Transmits visible and UV radiation Plastic and Glass Cells - Only good for visible wavelengths NaCl and KBr Crystals - IR wavelengths

DETECTORS - Used to measure the intensity of radiation coming out of the exit slit - Produces an electric signal proportional to the radiation intensity - Signal is amplified and made available for direct display - A sensitivity control amplifies the signal - Noisy signal is observed when amplification is too much - May be controlled manually or by a microprocessor (the use of dynodes)

DETECTORS Examples - Phototube (UV) - Photomultiplier tube (UV-VIS)
- Thermocouple (IR) - Thermister (IR) - Silicon photodiode - Photovoltaic cell - Charge Transfer Devices (UV-VIS and IR) Charge-coupled devices (CCDs) Charge injector devices (CIDs)

SINGLE-BEAM OPTICS - Usually used for all emission methods where sample is at the location of the source Drift - Slow variation in signal with time - Can cause errors in single-beam methods Sources of Drift - Changes in Voltage which changes source intensity - Warming up of source with time - Deterioration of source or detector with time

Single-Beam Spectrometer
SINGLE-BEAM OPTICS Single-Beam Spectrometer - Only one beam of light - First measure reference or blank (only solvent) as Io b Io I Light source monochromator (selects λ) sample detector computer

DOUBLE-BEAM OPTICS - Widely used
- Beam splitter is used to split radiation into two approximately equal beams (reference and sample beams) - Radiation may also alternate between sample and reference with the aid of mirrors (rotating beam chopper) - Other variations are available - The reference cell may be empty or containing the blank - More accurate since it eliminates drift errors

Double-Beam Spectrometer
DOUBLE-BEAM OPTICS Double-Beam Spectrometer - Houses both sample cuvet and reference cuvet b P Light source monochromator (selects λ) sample detector computer Po reference

Photodiode Array Spectrophotometers Dispersive Spectrophotometers
- Records the entire spectrum (all wavelengths) at once - Makes use of a polychromator - The polychromator disperses light into component wavelengths Dispersive Spectrophotometers - Records one wavelength at a time - Makes use monochromator to select wavelength

FOURIER TRANFORM SPECTROPHOTOMETERS
- Have no slits and fewer optical elements Multiplex - Instrument that uses mathematical methods to interpret and present spectrum without dispersion devices - Wavelengths of interest are collected at a time without dispersion - The wavelengths and their corresponding intensities overlap - The overlapping information is sorted out in order to plot a spectrum

FOURIER TRANFORM SPECTROPHOTOMETERS
- Sorting out or deconvoluting the overlapping signals of varying wavelengths (or frequencies) is a mathematical procedure called Fourier Analysis - Fourier Analysis expresses complex spectrum as a sum of sine and cosine waves varying with time - Data acquired is Fourier Transformed into the spectrum curve - The process is computerized and the instruments employing this approach are called FT spectrometers

FOURIER TRANFORM SPECTROPHOTOMETERS Advantages of FT Systems
- Produce better S/N ratios (throughput or Jacquinot advantage) - Time for measurement is drastically reduced (all λs are measured simultaneously) - Accurate and reproducible wavelength measurements

INSTRUMENTAL ANALYSIS CHEM 4811

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