Analytical Method Flashcards by Loui Mojica

4 BASIC DISCIPLINES: ANALYTICAL
CHEMISTRY

Spectrometry = spectrophotometry, atomic absorption, and mass spectrometry

Luminescence = fluorescence, chemiluminescence, and nephelometry

Electroanalytic methods = electrophoresis, potentiometry, and amperometry

Chromatography = gas, liquid, and thin- layer

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MEASUREMENTS OF RADIANT ENERGY

+ Emitted
+ Transmitted
+ Absorbed
+ Scattered
+ Reflected

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There are two primary considerations in
every colorimetric analysis:

Quality of the color
Intensity of the color

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COLORIMETRY 2 types

a. Visual Colorimetry
b. Photoelectric Colorimetry -

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The primary analytical utility of spectrophotometry or filter
photometry is the isolation of discreet portions
of the spectrum for purposes of measurement.

Photoelectric Colorimetry

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2 types: photoelectric measurement

Spectrophotometric measurement

Photometric measurement

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light intensity in a narrower wavelength

Spectrophotometric measurement

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light intensity at multiple wavelengths.

Photometric measurement

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transmitted via electromagnetic waves that
are characterized by their frequency and Wavelength

Energy

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distance between two successive
peaks and it is expressed in terms of nanometer (n)

Wavelength

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Wavelength of visible spectrum

400-700m

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Wavelength of ultraviolet (UV)

<400nm

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Wavelength of infrared region (IR)

> 700nm

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What is the Planck’s formula:

E = hv

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E means

energy of a photon in Joules or constant (6.626
x 10^27 erg sec)

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V means

frequency

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number of vibrations of
wave motion per second

Frequency

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Wave frequency: lower
Wavelength:

Longer

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Wave frequency:
Wavelength: shorter

Higher

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TYPES OF RADIANT ENERGY

+ Cosmic rays
+ Gamma rays
+ X-rays
+ Visible
+ Ultra-violet (UV)
+ Infrared (IR)
+ Radio, TV, microwave, etc.

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measurement of the light transmitted ; determine the concentration

Spectrophotometer

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concentration of a substance is directly
proportional to the amount of the light absorbed or inversely proportional

BEER’S LAW/ BEER-LAMBERT’S-LAW

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ratio of the radiant energy transmitted

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Transmittance

amount of light absorbed

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Absorbance

Absorbance Mathematically derived from ________

A means

Absorbance

a means

Molar absorptivity

b means

Length of light (solution)

c means

concentration of absorbing (solution)

2 types of Spectrophotometer

Single beam spectrophotometer Double-beam spectrophotometer

• simplest type of absorption spectrometer • one measurement at a time at one specified wavelength. • single-beam instrument is used.

Single beam spectrophotometer

• splits the monochromatic light into two components • additional beam • recorded directly as the electrical output

Double beam spectrophotometer

2 Types of Double-beam Spectrophotometer:

Double beam in space Double beam in time

2 photodetectors; sample beam and reference beam

Double beam in space

one photodetector; sample of cuvet and sample of reference

Double beam in time

7 basic components of single or double- beam configuration spectrophotometer:

1. Stable source of radiant energy 2. Filter that isolates a specific region of the electromagnetic spectrum 3. Cuvets 4. Sample holder 5. Radiation detector 6. Signal processor and 7. Readout device

Parts of the Spectrophotometer: provides polychromatic light; intense beam of light is directed; must be linear.

Light/Radiant source

2 types of light source

Continuum source Line source

Type of light source: changes in intensity; widely used in the laboratory.

Continuum source

Examples of continuum source

Tungsten, deuterium and xenon lamps

light source in the visible and near infrared region

Tungsten light bulb

provide UV radiation in analytic spectrometers.

Deuterium lamp

source of radiation covers both the UV and the visible range

Xenon discharges lamp/ xenon lamp

Type of light source: limited radiation and wavelength.

Line source

Examples of line source

Mercury and sodium vapor lamp and hollow cathode lamp (AAS)

Line source wide us in

Atomic absorption, molecular, and fluorescent spectroscopy

used as light sources for spectrophotometry.

Light Amplification by Stimulated Emission of Radiation (LASER)

Factors for choosing a light source:

1. Range 2. Spectral distribution within the range 3. The source of radiant production 4. Stability of the radiant energy and 5. Temperature

Alternatives for tungsten bulb:

+ Mercury arc (visible and UV) + Deuterium lamp (165nm) - UV + Hydrogen lamp - UV + Xenon lamp - UV + Merst glower -IR + Globar (silicone carbide) - IR

• minimizes unwanted or stray light • prevents the entrance of scattered light

Entrance slit

• minimizes unwanted or stray light • prevents the entrance of scattered light

Entrance slit

• most common cause of loss of linearity • limits the maximum absorbance • causes absorbance error.

Stray light

isolates specific or individual wavelength

Monochromator

isolates specific or individual wavelength

Monochromator

• wedge-shaped pieces of glass, quartz or sodium chloride • can be rotated • narrow light focused

Prism

• the most commonly used kind monochromator • made by cutting grooves (parallel grooves) or slits • wavelengths are bent • Produces linear spectrum • light energy is absorbed by glass prism.

Diffraction gratings

Analytical Method Flashcards

(57 cards)