Spectrophotometry Review

This flashcard set covers the fundamental definitions, laws, and components of Spectrophotometry and Spectroscopy as presented in the Quality Control 2 course.

Spectroscopy

The study of molecular or atomic structure of a substance by observation of its interaction with electromagnetic radiation.

Quantitative Spectroscopy

The use of radiation interaction to determine the amount of material in a sample.

Qualitative Spectroscopy

The use of radiation interaction to identify the chemical structure of a sample.

Spectrophotometry

A branch of spectrometry which embraces the measurement of the absorption by chemical species of radiant energy of definite and narrow wavelength approximating monochromatic radiation.

Colorimetry

A branch of spectrophotometry in which the absorption measurement is made in the visible region of the spectrum.

Electromagnetic spectrum

The complete system of energy propagated in wave form, appearing in different forms such as sunlight, color, and radiowaves.

Radiant energy

Energy in the UV, visible, and IR regions of the electromagnetic spectrum.

Wavelength ($\lambda$)

The length of a complete wave or cycle from peak to peak; measured in units such as micrometer ($\mu\text{m}$), nanometer ($\text{nm}$), or angstrom ($\text{\r{A}}$).

Wavenumber ($\tilde{v}$)

The number of waves per centimeter, equivalent to $\frac{1}{\lambda\text{ (cm)}}$.

Frequency ($\nu$)

The complete cycle which pass a given point per second, measured in cps or hertz ($1\,\text{hertz} = 1\,\text{cps}$).

Monochromatic radiation

Radiation consisting of a single wavelength, typically obtained using a prism or diffraction grating.

$200\text{--}380\,\text{nm}$ .

UV Region Range

$$380\text{--}780\,\text{nm}$$

Visible Region Range

Group Frequency Region

The IR region from $3$ to $8\,\mu\text{m}$ where absorption peaks are due to functional groups like carbonyl, amine, or hydroxyl. wave number of

4000-1300cm-1

Fingerprint Region

The IR region from $8$ to $15\,\mu\text{m}$ which gives a spectrum characteristic of the molecule as a whole. wave number of 1300 - 400cm-1

Chromophore

A functional group which absorbs radiant energy in the UV or visible regions, such as Ethylene, Acetylene, or Ketones.

Velocity of Radiation ($C$)

A constant in vacuum value of $3 \times 10^{10}\,\text{cm/sec}$.

Planck's constant ($h$)

A fundamental constant used to calculate the energy of a photon, valued at $6.626 \times 10^{-34}\,\text{erg-s}$.

Electronic transitions

Transitions associated with the overall motion of electrons around the nuclei, typically occurring in the UV region.

Vibrational transitions

Transitions associated with the motion of atoms within the molecule, typically occurring in the Infrared (IR) region.

Fluorescence

The process where an electron raised to an excited state decays back to the ground state while emitting UV or visible light.

Phosphorescence

A delayed transition from an excited electronic state back to the ground state.

Stretching Vibration

A molecular vibration where the distance between two atoms increases or decreases; can be Symmetrical or Asymmetrical.

Bending Vibration (Deformation)

A vibration where the position of an atom changes relative to the original bond axis; includes scissoring, rocking, wagging, and twisting.

Beer's Law

States that the power of a transmitted radiant beam decreases exponentially as the concentration of the solution increases; absorbance is directly proportional to concentration.

Bouguer's Law

States that the power of a transmitted radiant beam decreases exponentially as the thickness of the solution increases; absorbance is directly proportional to path length.

Transmittance ($T$)

The ratio of the radiant power transmitted by the solution ($P_{\text{Solution}}$) to the radiant power transmitted by the blank ($P_{\text{Blank}}$).

Absorbance ($A$)

Also known as optical density or extinction coefficient; defined as $\log\left(\frac{1}{T}\right)$ or $2 - \log(\%T)$.

Absorptivity ($a$)

The value obtained by dividing the absorbance by the product of concentration (in g/L) and path length (in cm).

Molar Absorptivity ($\epsilon$)

The value obtained by dividing the absorbance by the product of concentration (in mol/L) and path length (in cm).

Cuvette

A small sample holder of circular or square cross-section made of plastic, glass, or fused quartz.

Tungsten Lamp

The standard light source used for Visible Spectrophotometry.

Deuterium Lamp

A common light source used for UV Spectrophotometry, alongside Hydrogen gas and Mercury lamps.

Xenon Lamp

The light source typically used in a Spectrofluorometer.

Spectra

reflected, scattered, absorbed, fluoresce and cause photochemical reaction like bond breaking

Spectrometry

Defined as method of analysis which deals with the measurement of spectra. the measurement of the interactions between light and matter, and the reactions and measurements of radiation intensity and wavelength.

QUANTITATIVELY

For determining the amount of material in a sample

QUALITATIVELY

For identifying the chemical structure of a sample

Spectrophotometry

is a branch of spectrometry which embraces the measurement of the absorption by chemical species of radiant energy of definite and narrow wavelength approximating monochromatic radiation

Radiant energy

refers to energy in the uv, visible, and ir regions of the electromagnetic spectrum.

X-Ray, γ Rays

High energy sources produce breaking of bonds

Infrared Energy

Low energy sources produce vibrations in chemical bonds

Microwaves and Radio waves

Very low energy sources produce rotation of the chemical bonds

Wavenumber

number of waves per centimeter, equivalent to 1/wavelength

FREQUENCY

complete cycle which pass a given point per second

200 – 380 nm

UV number

380 – 780 nm

Visible number

780 – 3000 nm

Near IR

3.0 – 15 um

Medium

15 – 300 um

Far IR

Monochromatic radiation

radiation of single wavelength

Group Frequency Region

The region from 3 to 8 um, because the absorption peaks which appear in this region are due to functional groups (carbonyl, amine, hydroxyl, etc.) formed in the organic compounds.

Fingerprint Region

The region from 8 to 15 um because this region gives a spectrum of the molecule as a whole.

prism or diffraction grating.

Monochromatic radiation is obtained by using

single wavelength.

Monochromatic radiation is radiation of a

WHITE

If the material completely REFLECTS all light it appears

GREY

If the material absorbs a constant fraction of the light across the spectrum it appears

BLACK

If the material completely ABSORBS all the light it appears

Violet ; Yellow - Green

380-430; Absorbed Colour ; Absorbed Colour Seen By Eye

Blue; Yellow

430 - 480 Absorbed Colour ; Absorbed Colour Seen By Eye

Green - Blue ; Orange

480 - 490 Absorbed Colour; Absorbed Colour Seen By Eye

Blue - Green ; Red

490 - 500 Absorbed Colour; Absorbed Colour Seen By Eye

Green ; Purple

500 - 560 Absorbed Colour ; Absorbed Colour Seen By Eye

Yellow - Green ; Violet

560 - 580 Absorbed Colour ; Absorbed Colour Seen By Eye

Yellow Blue

580 - 590 Absorbed Colour ; Absorbed Colour Seen By Eye

Orange Green - Blue

590 - 610 Absorbed Colour ; Absorbed Colour Seen By Eye

Red Blue - Green

610 - 750 Absorbed Colour ; Absorbed Colour Seen By Eye

Chromophore

functional group which absorbs radiant energy in the uv or vis regions

Ethylene

Acetylene

Ketones

Organic acids

Aldehydes

Azomethines

Chromophore functional groups:

Stretching

distance bet two atoms increases or decreases

IR radiation

______ causes the vibrations of covalent bonds within that molecule.

stretching and bending

These vibrations include the ____ and ____ modes

Beer’ s Law

states that the power of a transmitted radiant beam decreases exponentially as the concentration of the solution containing the absorbing chemical species increases arithmetically.

Bouguer’ s Law

Law states that the power of a transmitted radiant beam decreases exponentially as the thickness of the solution containing the absorbing chemical species increases arithmetically.

Beer – Lambert or Beer – Bouguer’ s Law

is a combination of the above law and relates the power of the incident and the transmitted radiant beam to the thickness and concentration of the solution containing the absorbing chemical species.

Absorbance

Also called optical density, absorbancy, extinction coefficient.

Concentration

Expressed in grams of solute per liter of solution.

Absorptivity

The value obtained by dividing the absorbance (A) by the product of concentration, expressed in grams per liter, and the path length, expressed in centimeters.

Molar Absorptivity

The value obtained by dividing the absorbance (A) by the product of concentration of the solution, expressed in moles per liter, and the path length, expressed in centimters.

Absorption Spectrum

The graph obtained when absorbance or any function of is plotted against absorbance wavelength.

UV Spectrophotometer

Sample cell Quartz (crystalline silica)

Visible Spectrophotometer

Sample cell Glass

IR Spectrophotometer

sample cell NaCl

Quart

Spectrofluorometer uses what

1. Hydrogen Gas Lamp

2.Mercury Lamp

3. Deuterium

UV Spectrophotometer Light source

1. Tungsten Lamp

Visible Spectrophotometer Light source

Carborundum (SIC)

IR Spectrophotometer Light source

1. Xenon lamp

2. Alkaline halide lamp

Spectrofluorometer Light source

Cuvette

a small tube of circular or square cross section, sealed at one end, made of plastic, glass or fused quarts ( UV lights)designed to hold a sample.

456 – 705 nm

Glass cuvette

380 – 780 nm

Plastic cuvette

below 380 nm

Fused quarts cuvette

null-balance

a ______ manually is operated instrument the Beckman DU-2 spectrophotometer. This instrument which covers the UV, visible and near IR regions has continuous range from 190-1000 nm isolating spectra region from 0.5 - 1.5 nm.

240 – 950 nm.

An manually example of a direct-reading operated spectrophotometer is the Bausch and Lomb Spectronic 20. This instrument has an operating range of _______

SA curve

spectral absorbance curve, plot of absorbance values against wavelength

Beer’s plot

plot of absorbance values against a series of known solute concentration