Kimia Analisa

Specstroscopic Methods of Analysis

Prof. Dr. Heru Setyawan, Jurusan Teknik Kimia ITS

Electromagnetic radiationE

lect

ric

fie

ld s

tre

ng

th

Time or distance

λ

Ae ( )Φ+= tAEe

πν2sin

vacuum) (in νν

λ cv ==

The oscillating electric field:

Wavelength depends on the electromagnetic wave’s velocity:

Electric field component of plane-polarized electromagnetic radiation.

FrequencyThe number of oscillation of an electromagnetic wave per second (ν).

Wavelength

The distance between any two consecutive maxima and minima of an electromagnetic wave (λ).

Wavenumber

The reciprocal of wavelength (1/λ).

vacuum) (in νν

λ ==

Particle properties of electromagnetic

radiation

� When a sample absorbs electromagnetic radiation (consists of a beam of energetic particles called photons), it undergoes a change in energy.

� When a photon is absorbed by a sample, it is “destroyed,” and its energy acquired the sample.

The energy of a photon, in joules, is related to its � The energy of a photon, in joules, is related to its frequency, wavelength, or wavenumber by the following equaions:

s) J106.626 constant sPlanck' ( 34- ⋅×===== hhc

hchE ν

λν

Electromagnetic spectrum

Electromagnetic spectrumThe division of electromagnetic radiation on the basis of a photon’s energy.

Measuring photons as a signal

� Spectroscopy is possible only if the photon’s interaction with the sample leads to a change in one or more of characteristic properties of electromagnetic radiation, including energy, velocity, amplitude, frequency, phase angle, polarization and direction of propagation.

� Two broad class of spectroscopy:� Two broad class of spectroscopy:� Energy is transferred between a photon of electromagnetic

radiation and the analyte, promoting the analyte from a lower-energy state to a higher-energy, or excited, state.

� The electromagnetic radiation undergoes a change in amplitude, phase angle, polarization, or direction of propagation as a result of its refraction, reflection, scattering, diffraction, or dispersion by the sample.

Spectroscopies involving energy exchange

Type of energy transfer EM spectrum Spectroscopy technique

absorption γ-ray Mossbauer spectroscopy

X-ray X-ray absorption spectroscopy

UV/Vis UV/vis spectroscopyAtomic absorption spectroscopy

infrared Infrared spectroscopyRaman spectroscopyRaman spectroscopy

microwave Microwave spectroscopyElectron spin resonance

spectroscopy

Radio waves Nuclear magnetic resonance spectroscopy

Emission (thermal excitation) UV/Vis Atomic emission spectroscopy

photoluminescence X-ray X-ray fluoroscence

UV/Vis Fluoroscence spectroscopyPhosphorescence spectroscopyAtomic fluoroscence spectroscopy

Photon measurement

� Absorbance:

� the attenuation of photons as they pass through a sample (A).

� Absorbance spectrum:

� a graph of a sample’s absorbance of electromagnetic radiation versus wavelength (or frequency or wavenumber).

Emission: � Emission:

� the release of a photon when an analyte returns to a lower-energy state from a higher-energy state.

Spectroscopies that don’t involve exchange

energy

Region of EM spectrum Type of interaction Spectroscopy technique

X-ray Diffraction X-ray diffraction

UV/Vis Refraction Refractometry

Scattering Nephelometry

Turbidimetry

dispersion Optical rotary dispersion

Basic components of spectroscopic

instrumentation

� Sources of energy� Electromagnetic radiation: (i) continuum source, emits radiation over a wide

range of wavelengths; (ii) line sources, emit radiation at a few selected, narrow wavelengths.

� Thermal energy: flames (2000–3400 K) and plasma (6000–10000 K).

� Chemical sources: exothermic reactions (chemiluminescence, bioluminescence)

� Wavelength selection� Nominal wavelength: the wavelength which a wavelength sector is set to pass.

Effective bandwidth: the width of the band of radiation passing through a � Effective bandwidth: the width of the band of radiation passing through a wavelength selector measured at half the band’s height.

� Resolution: in spectroscopy, the separation between two spectral features, such as absorption or emisson lines.

� Filter: a wavelength selector that uses either absorption, or constructive and destructive interference to control the range of selected wavelengths.

� Monochromator: a wavelength selector that uses a diffraction grating or prism, and that allows for a continuous variation of the nominal wavelength.

� Detectors

� Signal processors

Common sources of electromagnetic

radiation for spectroscopy

Source Wavelength region Useful for

H2 and D2 lamp Continuum from 160–380 nm UV molecular absorption

Tungsten lamp Continuum from 320–2400 nm Vis molecular absorption

Xe arc lamp Continuum from 200–1000 nm molecular fluoroscence

Nernst glower Continuum from 0.4–20 µm IR molecular absorption

Globar Continuum from 1–40 µm IR molecular absorption

Nichrome wire Continuum from 0.75–20 µm IR molecular absorption

Hollow cathode lamp Line source in UV/Vis Atomic absorption

Hg vapor lamp Line source in UV/Vis molecular fluoroscence

Laser Line source in UV/Vis Atomic and molecular absorption, fluoroscence and scattering

Typical grating monochromator

Collimating mirror

Focusing mirror

Spectroscopy based on absorptio

� Absorbance of electromagnetic radiation

� A beam of electromagnetic radiation passes through a sample in which much of the radiation is transmitted without a loss in intensity. At selected frequencies, the radiation is attenuated (the process is called absorption).

� Transmittance and absorbance� Transmittance and absorbance

� The attenuation of electromagnetic radiation as it passes through a sample is described quantitatively by two separate, but related terms: transmittance and absorbance.

� Transmittance: the ratio of the electromagnetic radiation’s power exiting the sample to that incident on the sample from the source.

Absorbance of electromagnetic radiation

• N=1 is the ground state of the atom. All other values of N represent various excited states. When an electron falls through paths a, b, c, or d, the atom emits visible light.

• If the atom absorbs energy, the orbit of the electron increases because the atom is in an excited state. If the atom emits energy, the electron falls into a more stable orbit closer

Energy level diagram showing difference between the absorption of IR, visible and UV radiations.

electron falls into a more stable orbit closer to the nucleus.

• When the electron falls from an outer to an inner orbit, the atom emits light. The energy of the emitted light is equal to the energy lost by the electron in its fall. The light may be ultraviolet, visible, or infrared. In the visible range it appears as a series of lines.

Infrared spectra

(a)

(b)

(c)

%Tr

an

smit

tan

ce

2410

1090

10601180

2915

621640C=O

CH2NH

Si–O–Si

0

1

2

3

4

5

6

7

8

9

10

Tran

smitt

ance

(%)

1022.313176.87

442580

OH

Fe3O4

Wavenumbers (cm-1)

500750100012501500175020002500300035004000

FTIR spectra of (a) silica, (b) gelatin and (c) silica-gelatin (Setyawan & Balgis, Asia-Pac

J Chem Eng, 2011, in press).

0

400900140019002400290034003900

Wavenumber (cm-1)

FTIR spectrum of magnetite particles preparedby electrochemical method (Fajaroh et al., Adv Powder

Technol, 2011, in press).

• The energy of IR radiation is sufficient to produce a change in the vibrational energy of a molecule or polyatomic ion.

• The energy for allowed vibrational modes, Ev, is

02

1 νhNEv

+=frequency lvibrationa lfundamenta sbond'

. . . 2, 1, 0, number quantum lvibrationa

0 ===

νN

UV/Vis spectra for molecules and ions

• When a molecule or ion absorbs UV or visible radiation it undergoes a change in its valence electron configuration.

• The valence electrons in organic molecules, and inorganic anions such as CO32-, occupy

quantized sigma bonding, σ, pi bonding, π, and nonbonding, n, molecular orbitals.• Unoccupied sigma antibonding, σ*, and pi antibonding, π*, molecular orbitals often lie

close enough in energy that the transition of an electron rom an occupied to n unoccupied orbital is possible.

UV/Vis spectra for molecules and ions

Transmittancethe ratio of the electromagnetic radiation’s power exiting the sample to that incident on the sample from the source

0P

PT

T= sample

P0 PTMultiplying the transmittance by 100 gives the percent transmittance (%T), which varies between 100% (no absorption) and 0% between 100% (no absorption) and 0% (complete absorption).

AbsorbanceAn alternative method for expressing the attenuation of electromagnetic radiation is absorbance, A, which is defined as

T

T

P

P

P

PTA

0

0

logloglog =−=−=

The more common unit for expressing the attenuation of radiation because it is a linear function of analyte’s concentration.

Absorbance and concentration: Beer’s law

When monochromatic electromagnetic radiation passes through an infinitesimally thin layer of sample, of thickness dx, it experiences a decrease in power of dP. The fractional decrease in power is proportional to the sample’s thickness and the analyte’s concentration, C; thus

CdxP

dP α=− • P = power incident on the thin layer sample• α = proportionality constant

∫∫==

=−bxPP

dxCdP

T

α ∫∫==

=−xPP

dxCP

dP

00

α

bCP

P

T

α=

0ln

P0 P P – dP PT

TP

PA

0log=

abCP

P

T

=

0log

abCA =

a = analyte’s absortivity (cm-1 conc-1)

bCA ε= C in molarity, a→ ε (molar absortivity, cm-1 M-1)

Depend on λ

Beer’s law and multicomponent samplesFor a two-component mixture of X and Y, the total absorbance is

YYXXYXtot bCbCAAA εε +=+=

Generalizing, the absorbance for a mixture of n components, Am, is given as

∑∑==

==n

i

ii

n

i

ibCAA

11

m ε

http://terpconnect.umd.edu/~toh/models/

Limitations to Beer’s law

The linearity of the Beer’s law is limited by chemical and instrumental factors. Causes of nonlinearity include:

� deviations in absorptivity coefficients at high concentrations (>0.01M) due to electrostatic interactions between molecules in close proximity

� scattering of light due to particulates in the sample

� fluoresecence or phosphorescence of the sample

� changes in refractive index at high analyte concentration

� shifts in chemical equilibria as a function of concentration

� non-monochromatic radiation, deviations can be minimized by using a relatively flat part of the absorption spectrum such as the maximum of an absorption band

� stray light

Limitations to Beer’s law

http://terpconnect.umd.edu/~toh/models/Comparison.GIF

UV/Vis Instrumentation

schematic diagram of a double-beam UV/Vis spectrophotometer

schematic diagram of a single-beam UV/Vis spectrophotometer

SpectrophotometerAn instrument for measuring absorbance that uses a monochromator to select the wavelength.

Quantitative applicationsAnalyte Method λλλλ (nm)

Trace metals

aluminum Reaction with Eriochrome cyanide R dye at pH 6produces red to pink complex

535

arsenic Reduce to AsH3 using Zn and react with silver diethyldithiocarbamate to form red complex

535

cadmium Extraction into CHCl3 containing dithizone from sample made basic with NaOH; pink to red complex

518

chromium Oxidize to Cr(VI) and react with diphenylcarbazide in acidic solution to give red-violet product

540give red-violet product

copper React with neocuprine in neutral to slightly acid solution; extract into CHCl3/CH3OH to give yellow solution

457

iron React with o-phenanthroline in acidic solution to form orange-red complex

510

lead Extraction into CHCl3 containing dithizone from sample made basic with ammonical buffer; cherry red complex

510

manganese Oxidize to MnO4- with persulfate 525

mercury Extraction into CHCl3 containing dithizone from acidic sample; orange complex

492

zinc Reaction with zincon at pH 9 to form blue complex 620

Quantitative applications (cont’d)

Analyte Method λλλλ (nm)

Inorganic nonmetals

ammonia Reaction with with ammonia, hypochlorite and phenol produces blue indophenol; catalyzed by manganese salt

630

cyanide Convert to CNCl by reaction with chloramine-T, followed by reaction with a pyridine-barbituric acid to form red-blue dye

578

fluoride Reaction with red Zr-SPADNS lake results in formation of ZrF62- and

decrease in concentration of the lake570

Chlorine (residual)

Oxidation of leuco crystal violet to form product with a bluish color 592(residual)

nitrate Reduction to NO2- by Cd, colored azo dye formed by reaction with

sulfanilamide and N-(1-naphthyl)-ethylenediamine543

phosphate Reaction with ammonium molybdate followed by reduction with stannous chloride to form molybdenum blue

690

Organics

phenol Reaction with 4-aminoantipyrine and K3Fe(CN)6 to form antipyrine dye 460

surfactants Formation of blue ion pair between anionic surfactant and the cationic dye methylene blue, which is extracted into CHCl3

Quantitative applications (Clinical samples)Analyte Method λλλλ (nm)

Total serum protein

Reaction with protein, NaOH and Cu2+ produces blue-violet complex

540

Serum cholesterol

Reaction with Fe3+ in presence of isopropanol, acetic acid and H2SO4 produces blue-violet complex

540

Uric acid Reaction with phosphotungstic acid produces tungsten blue 710

Serum barbiturates

Barbiturates are extracted into CHCl3 and then into 0.45 M NaOH

260

glucose Reaction with o-toludine at 100°C produces blue-green complex 630

Protein-bound iodine

Decompose protein to release iodide; I- determined by ita catalytic effect on redox reaction between Ce4+ and As3+

420