SPECTROPHOTOMETRY Flashcards by Cait Lyn

Study that observe how radiated matter and energy interact with each
other

Spectroscopy

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It involves measurement of the light transmitted by a solution to determine
the concentration of the light – absorbing substance in the solutio

Spectrophotometry

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Classification of Spectroscopic Methods

Gamma Rays
X- rays
Ultraviolet (UV
Visible
Infrared
Microwave
Radio – frequency (RF)

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provide the most widely used tools for
the elucidation of molecular structure as well as the quantitative
and qualitative determination of both inorganic and organic
compounds

Spectrochemical Methods

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is a form of energy that is transmitted through space at enormous
velocities
- described as a wave with properties of wavelength, frequency, velocity,
and amplitude
- treated as discrete packets of energy or particles called photons or
quanta

Electromagnetic Radiation

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It is a vector quantity of an electromagnetic wave that provides a measure of the electric of magnetic field strength at a maximum in the wave

Amplitude

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-It is the time in seconds of electromagnetic wave for successive maxima or minima to pass a point in space

Period (p)

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It is the number of oscillation that occur in one second
- oscillations of the electric field vector per unit time and is equal to 1/p

Frequency (v)

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Is the linear distance between successive maxima or minima of a wave

Wavelength (λ)

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Is the energy of a beam the reaches a given area per unit time
- Unit is in Watts (W

Radiant Power (P)

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Is the radiant power-per-unit solid angle

Intensity

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States that the relationship between wavelength and energy are
INVERSELY PROPORTIONAL.

Planck’s Law:

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E = hv

Planck’s Law:

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<400 nm wavelength

UV region

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400 - 700 nm

visible spectrum

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> 700 nm

infrared region

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Samples are stimulated by applying energy

Heat
Electrical energy
Light
Particles
Chemical reaction

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Lowest Energy

Ground State

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Higher energy

Excited State

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Refers to the methods in which the stimulus is heat or electrical energy

Emission Spectroscopy

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Refers to excitation of the analyte by a chemical reaction

Chemiluminescence Spectroscopy

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s found in the light emitted by a firefly

Chemiluminescence

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Chemiluminescence involving a biological or enzyme reaction is often
termed

bioluminescence

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Amount of light absorbed is measured as a function of wavelength
- Absorption measurement can give both qualitative and quantitative
information about the sample

Absorption Spectroscopy

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The emission of photons is measured following absorption

Photoluminescence Spectroscopy

Forms of Photoluminescence

1. Fluorescence 2. Phosphorescence

States that the concentration of the unknown substance is directly proportional to the absorbed light (absorbance or optical density) and inversely proportional to the amount of transmitted light (% Transmittance). - Mathematically establishes the relationship between concentration and absorbance

Beer’s Law

It is the amount of light absorbed - It is proportional to the inverse log of transmittance - Mathematically derived from %T (% transmittance)

Absorbance (A)

It is the ratio of radiant energy transmitted (T) divided by the radiant energy incident (I) on the sample.

Percent Transmittance

Is an apparatus for measuring the intensity of light in a part of the spectrum, especially as transmitted or emitted by a particular substances

Spectrophotometer

The distance between 2 successive peaks; It is expressed in terms of nanometer (nm)

WAVELENGHT

: measurement of light intensity without consideration of wavelength

PHOTOMETRIC MEASUREMENT

measures light intensity in a narrower wavelength. (spectrum of light)

SPECTROPHOTOMETRIC MEASUREMENT

Parts of Spectrophotometer

1. Light Source 2. Entrance Slit 3. Monochromator 4. Cuvette/ Sample Cell/ Analytical Cell 5. Exit Slit 6. Photodetector 7. Readout device

Provides energy that the sample will modify or attenuate by absorption - The light is polychromatic ( all visible wavelength is present)

Light Source

emits radiation that changes in intensity - most common

* Continuum Source

most commonly used light source in the visible and near infrared region

Tungsten Light Bulb

emits limited radiation and wavelength - limited number of discrete line or bands of radiation

* Line Source

- Mercury Arc - Deuterium Lamp - Hydrogen Lamp

UV Spectrum <400 nm

Minimizes stray light - Prevent entrance of scattered light - “GATE” only permits the needed light

Entrance Slit

Wavelength outside the band - Can cause absorbance error - Stray light limits the maximum absorbance that spectrophotometer can achieve - Most common cause of loss of linearity at high analyte concentration

STRAY LIGHT

Isolates specific/individual wavelength of the light - DEGREE OF ISOLATION is affected the the monochomator and the with of entance and exit sli

Monochromator

Simple least expensive , not precise but useful - Made by placing semi – transparent silver films on both sides of dielectric such as magnesium fluoride produce monochromatic light based on the principle of constructive interference of light waves. - Usually pass a wide band of radiant energy and have an ion transmittance of the selected wavelength

Colored Filters

Wedge – shaped pieces of glass, quarts, or sodium chloride - A narrow light focused on a prism is refracted as it enters more dense glass - Can be rotated allowing only the desired wavelength to pass through exit slit

Prisms

“Most Commonly Used”, better resolution than prism - Made by cutting grooves ( parallel groves) or slit into an aluminized surface of a flat pieceof crown glass - wavelengths are bent as they pass a sharp corner

Diffraction Gratings

the breaking up of a ray of light into component wavelengths based on the principle that WAVELENGTHS BENDS AS THEY PASS A SHARP CORNER

DIFFFRACTION

It holds the solution whose concentration is to be measured - It should be scratched free which can cause erroneous result - Most common is rectangular shape, it is easier to maintain the length of light

Cuvette/ Sample Cell/Analytical Cell

It controls the with of light beam (band pass). It only allows a fraction of the spectrum to reach the sample cuvette. - Spectral purity of the spectrophotometer is reflected by the band pass – the narrower the band pass, the greater the resolution. - Accurate absorbance measurement requires a band pass < 1/5 the natural band pass of the spectrophotometer. - The degree of wavelength isolation is a function of the type of device used and the with of entrance and exit slit

Exit

– the range of wavelength between point at which transmittance is one half peak transmittance

BAND PASS

Converts transmitted radiant energy into an equivalent amount of electrical energy

Photodetector

– simplest and least expensive, low sensitivity and fatigue are the downfall of this, needs frequent replacemen

PHOTOCELL

contains anode and cathode in a tube, it gives off electron when energy strikes it

PHOTOTUBE

more sensitive than vacuum phototube but less sensitive than Photomultiplie

PHOTOTRANSISTOR/PHOTODIODE

most common, detect wide range (Visible and UV) - 200 x more sensitive, it amplifies radiant energy - detect very low light energy and quick bust of light

PHOTOMULTIPLIER TUBE

It displays the output of the detection system

Read Out Device

it is an important instrument that splits the monochromatic light into two components - One beam passes through the sample and the other through a reference solution of blank - The additional beam corrects for variation in light source intensity - The absorbance of the sample can be recorded directly as the electrical output of the sample beam

Double – Beam Spectrophotometer

uses 2 photodetectors (for the sample beam and reference beam)

* Double – Beam in Space

uses one photodetector and alternatively passes the monochromatic light through the sample cuvette and then reference cuvette using a chopper

* Double – Beam in Time

Measures the light (wavelength) emitted by a single atom burned in flame

Flame Emission Photometry FEP

Measures the light absorbed by atoms dissociated by heat

Atomic Absorption Spectrophotometry

Used to check wavelength accuracy

Didymium or Holmium Oxide Filter

Verify absorbance accuracy on linearity

Neutral Density filters and Dichromate Solution

contain all the components of the solution to be analyzed except to the one compound being tested

Blank Solution

corrects absorbance caused by the color of the reagents

Reagent blank

measures absorbance of the sample and reagent in the absence of the end product and corrects the measurement for the optical interference

Sample blank

SPECTROPHOTOMETRY Flashcards

(65 cards)