Classification of Analytical Methods

Analytical chemistryis the science of identifying

the components in a sample (qualitative analysis) and the relative amounts of each of the components (quantitative analysis).

Generally a separation step is required to isolate the components in a sample prior to analysis.

The methods used for analysis fall into two general classes:

Classical Methods

Instrumental Methods.

Classical Methods

Separation of Analytes- extraction, - distillation,- precipitation, - filtration, - etc.

Qualitative Analysis- BP, - MP, - color, - odor, - density, -- refractive index, etc. refractive index, etc.

Commonly referred to as wet chemistry.

Quantitative Analysis-titration -gravimetric

Instrumental Methods

exploit the physical or chemical properties of an analyte to obtain qualitative and quantitative information

Electrometry Spectroscopy Chromatography Radioactivity etc

Spectroscopy ? Spectrometry ? Spectrometer ? Spectrophotometry ? Spectrophotometer ?

What for are they ? How it is work ? How to use it?

Spectrometry isAnalysis method of the measurement and interpretation of electromagnetic radiation absorbed, or emitted by atoms, molecules, or other chemical species

Spectroscopy isThe study of interaction of electromagnetic radiation with matter

Spectrometer isThe instrumen that use spectrometry method

Spectrophotometry isAnalog with spectrometry, but specially for photon measurement

What is Electromagnetic (EM) Radiation ?

At 90 to the direction of propagation is an oscillation in the electric field.

At 90At 90 to the direction of propagation and 90to the direction of propagation and 90 from the electric field oscillation from the electric field oscillation (orthagonal) is the magnetic field oscillation. (orthagonal) is the magnetic field oscillation.

x

y

zx

y

z Electric Fieldx

y

z Electric Fieldx

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z Electric Fieldx

y

z Electric Fieldx

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z Electric Fieldx

y

z Electric Fieldx

y

z Electric Fieldx

y

z Electric FieldMagnetic Field

x

y

z Electric FieldMagnetic Field

x

y

z Electric FieldMagnetic Field

x

y

z Electric FieldMagnetic Field

x

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z Electric FieldMagnetic Field

x

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z Electric FieldMagnetic Field

x

y

z Electric Field

Magnetic Field

The electric field is responsible for most important optical properties. The electric field is responsible for most important optical properties.

Wave Parameters

PeriodPeriod (p)(p) the time required for one cycle to pass a fixed point in space. the time required for one cycle to pass a fixed point in space. Time or Distance-

+

Elec

tric

Fiel

d

0Amplitude (A)

Wavelength (O)

FrequencyFrequency ((QQ)) the number of cycles which pass a fixed point in space per second. the number of cycles which pass a fixed point in space per second. QQ = 1/p ( s= 1/p ( s--11 = Hz )= Hz )

QQdepends on the source, but is independent of the propagating depends on the source, but is independent of the propagating (transmitting) material.(transmitting) material.

AmplitudeAmplitude (A)(A) The maximum length of the electric vector in the wave (Maximum The maximum length of the electric vector in the wave (Maximum height of a wave). height of a wave).

WavelengthWavelength ((OO)) The distance between two identical adjacent points in a wave The distance between two identical adjacent points in a wave (usually maxima or minima). (usually maxima or minima).

Einstein had proposed a relationship between energy and frequency of light in 1905:

c = QO or Q = c/O

EE = = hhQQ

Recasting Einsteins equation in terms of wavelength of radiation. Recasting Einsteins equation in terms of wavelength of radiation.

EE = = hh ccOO

Energy Matter Interaction effectName of

TechniqueApplication

Gamma Ray AtomSubstancesnuclear

transitionGamma Spect Qualitative &

quantitativeX - Ray Atom Transition of XRF Qualitative &

quantitativeSubstances Inner shell elect XRDUV Visble

RayAtom Transition of A.A.S Quantitative

Valence elect Spectrofluorometry Quantitative

Mol. / Subst. Transition of UV-Vis Spectr. QuantitativeValence elect Spectrofluorometry Quantitative

I.R. Ray Mol. / Subst Vibration rotation

IR Spectr. Identification of functional FT IR Spect

MW - Radio Mol. / Subst Elctron spin transition

NMR Spect Identification and structure analysis

Electron Mol. / Subst fragmentation MS Spect Identification and structure analysis

If a substance is irradiated with electromagnetic radiation:

The energy of the incident photons may be transferred to the atom or molecules.

It will raising them from the ground state to an excited state

This process, known as absorption

EXPLAIN ABOUT ABSORPTION,EMISSION, FLUORESENCE, PHOPHORESENCE !

AtomOr

MoleculesENERGY ??

Gamma rays can cause changes in the nucleus X rays cause the ejection of inner electrons from matter Ultraviolet dan Visible rays causes change in the energy of the

valence electron Infra red rays causes in rotational and vibration energy state of

molecul Microwave region, causes change in electron spin states for

substances with unpaired electrons when in a magnetic field Radio wave range, energy transitions are concerned with reorientation

of nuclear spin states of substances

ME

ENERGY SPECIFIC ENERGY

ONLY SPECIFIC ENERGYWILL BE INTERACTION

1 2 3 4 5 6 7

Schematic of basic diagram of Spectrophotometer

1 Source of electromagnetic radiation2 Polychromatic rays 3 Wavelength selector4 Monochromatic rays with Io 5 Matter (atom or molecules or substances)6 Monochromatic ray with It (transmitancy)7 Electromagnetic radiation detector

Five Basic Optical Instrument Components

1)1) SourceSource --A stable source of radiant energy at the desired wavelength (or A stable source of radiant energy at the desired wavelength (or OO range). range).

2)2) Sample HolderSample Holder -- A transparent container used to hold the sample (cells, A transparent container used to hold the sample (cells, cuvettes, etc.). cuvettes, etc.).

3)3) Wavelength SelectorWavelength Selector -- A device that isolates a restricted region of the EM A device that isolates a restricted region of the EM spectrum used for measurement (monochromators, spectrum used for measurement (monochromators, prisms, & filters). prisms, & filters).

4)4) Photoelectric TransducerPhotoelectric Transducer -- (Detector) Converts the radiant energy into a (Detector) Converts the radiant energy into a useable signal (usually electrical). useable signal (usually electrical).

5)5) Signal Processor & ReadoutSignal Processor & Readout -- Amplifies or attenuates the transduced signal Amplifies or attenuates the transduced signal and sends it to a readout device such as a meter, and sends it to a readout device such as a meter, digital readout, chart recorder, computer, etc. digital readout, chart recorder, computer, etc.

Optical spectroscopic methods are based on six phenomena:1) absorption 2) fluorescence 3) phosphorescence 4) scattering 5) emission 6) chemiluminescence

General Design of Optical Instruments

Absorption

All of these instruments contain the same five basic components (source, sample All of these instruments contain the same five basic components (source, sample holder, wavelength selector, detector, and signal processor) but differ in the holder, wavelength selector, detector, and signal processor) but differ in the configuration of these components.configuration of these components.

Fluorescence, Phosphorescence, and Scattering

Emission andChemiluminescence

PERHITUNGAN KUANTITATIF DALAM SPEKTROMETRI

I.6.1 Hukum Lambert-BeerJumlah radiasi yang diserap oleh suatu larutan sampeldigambarkan oleh hukum Beer-Bouguer-Lambert yangumumnya dikenal dengan istilah hukum Beer.

Po = Intensitas sinar datangC = Konsentrasi spesies penyerap radiasib = Tebal media yang dilalui sinarP = Intensitas sinar yang diteruskan.

Menurut Bouguer (1729) dan Lambert (1760): Apabila energiradiasi elektromagnetik diabsorpsi oleh suatu spesies denganketebalan b, maka kekuatan energi radiasi yangditransmisikan akan turun secara deret geometri(eksponensial).

Po PC

b

Secara metematis pernyataan tersebut dituliskan dalam bentuk eksponensial sebagai berikut:

T = P/Po = 10-kb

Dimana k adalah suatu konstanta dan T adalah transmitansi, yaitu fraksi energi radiasi yang ditransmisikan setelah melewati medium dengan ketebalan b. Persamaan di atas dapat disusun ulang dalam bentuk logaritmis sebagai berikut:

Log T = Log P/Po = - kb

Pada tahun 1852, Beer dan Bernard menyatakan bahwa suatu hukum yang serupa dengan hukum Lambert-Bouguer juga berlaku untuk ketergantungan T pada konsentrasi C, yaitu:

T = P/Po = 10-kc

Dimana k adalah konstanta yang baru yang nilainya berbeda dengan k. Dalam bentuk logaritmik persamaan di atas dapat ditulis:

Log T = Log P/Po = - kc

Jika persamaan Bouguer-Lambert dan Bernard-Beer digabung maka akan diperoleh hubungan sebagai berikut:

T = P/Po = 10-abc

a merupakan konstanta gabungan dari k dan k. Dalam bentuk logaritmik persamaan diatas dapat ditulis:

Log T = Log P/Po = - abc

Persamaan yang terakhir ini sering ditulis dalam bentuk positif pada sisi kanan sehingga diperoleh:

A = - Log T = Log 1/T = Log Po/P = abc

Di mana A adalah absorbansi. Persamaan ini merupakan bentuk umum dari hukum Lambert-Beer.

Perhatian: yang berbanding lurus dengan konsentrasi larutan sampel adalah absorbansi (A), bukan transmitansi (T) atau sinar yang diserap (Po P).

Prosen transmitansi diberikan oleh persamaan:% T = P/Po x 100

Karena T = % T/100, maka A = log (100/%T) = log 100 log %T

AtauA = 2,00 log % T, dan% T = antilog (2,00 A)

Jika b dinyatakan dalam cm dan c dalam gram/liter, maka konstanta a disebut absorptivitas. Harga konstanta ini tergantung pada panjang gelombang dan sifat materi (sampel) penyerap radiasi sinar. Jika c dinyatakan dalam satuan mol/liter, maka absorbansi (A) menjadi:

A = H b c

Dengan e adalah absorptivitas molar. Satuan untuk e dan a adalah :H = cm-1 . mol-1 . litera = cm-1 . g-1 . Liter

sedangkan tebal media (b) dalam praktek biasanya dibuat konstan, sehingga absorbansi hanya merupakan fungsi dari konsentrasi sampel.

Tabel I.2 Istilah-istilah dan simbol yang dipergunakan pada pengukuran absorbansi

Istilah dan simbol Definisi Nama dan simbol alternatif

Kekuatan radiasi (P, Po)

Absorbansi (A)Transmitansi (T)Tebal media (cm), bAbsorptivitas molar, H

Energi radiasi yang mencapai area tertentu pada detektor per detik.Log (Po/P)P/Po---A/b.c

Intensitas radiasi (I, Io)

Kerapatan optis, D Ekstingsi, ETransmisi, Tl, dKoefisien ekstingsi molar

Contoh-contoh soal:1. Suatu larutan sampel dalam sel 1,0 cm setelah diukur dengan spektrofotometer

mentransmisikan 80 % cahaya pada suatu panjang gelombang tertentu. Jikaabsorptivitas zat pada O ini = 2,0. Hitunglah konsentrasi zat tersebut.

2. Suatu larutan yang mengandung besi 1,00 mg/100 ml (sebagai kompleks besi-tiosianat) teramati mentransmisikan 70 % dari sinar yang masuk. Berapakahabsorbansi larutan pada O tersebut. Berapakah fraksi cahaya yang akanditeruskan jika konsentrasi larutan besi tersebut 4 kali lebih besar.