Spectrometry

Question 1

What is absorption in spectroscopy?

Answer 1

Light energy excites electrons from a lower to a higher energy level.

Question 2

What is emission in spectroscopy?

Answer 2

Electrons release energy in the form of light as they return to lower energy levels.

Question 3

Why do larger atoms have more complex absorption and emission spectra?

Answer 3

Due to more valence electrons and energy levels.

Question 4

What does the principle of transmission in spectroscopy state?

Answer 4

Every element has unique spectral emissions, allowing for identification and quantification of substances.

Question 5

How does molecular absorption differ from atomic absorption?

Answer 5

Molecular absorption involves bonds between atoms, allowing more possible energy transitions.

Question 6

What is an absorption spectrum characterized by?

Answer 6

Defined by broad peaks.

Question 7

What is a chromophore?

Answer 7

The part of the molecule that enables UV radiation absorption.

Question 8

Where are chromophores typically found?

Answer 8

In molecules with lone pairs of electrons or double bonds.

Question 9

What does transmittance (T) represent?

Answer 9

Fraction of incident radiation transmitted by the solution.

Question 10

What is the formula for transmittance?

Answer 10

T = Po/P.

Question 11

What is the value of T if all light is absorbed?

Answer 11

T = 0.

Question 12

What is the value of T if no light is absorbed?

Answer 12

T = 1.

Question 13

What is absorbance (A) defined as?

Answer 13

A = log(Po/P).

Question 14

What is absorbance inversely proportional to?

Answer 14

Transmittance.

Question 15

What factors affect absorbance?

Answer 15

• Concentration
• Molar absorptivity
• Type of molecule

Question 16

What is the Beer-Lambert Law?

Answer 16

A = εcl.

Question 17

What conditions should measurements be taken under for better sensitivity?

Answer 17

At maximum absorption wavelength.

Question 18

What can cause non-linearity in absorbance measurements?

Answer 18

• High concentrations leading to electrostatic interactions
• Light scattering from particulates

Question 19

What is colorimetric analysis?

Answer 19

Converts a molecule without a chromophore into one with a chromophore.

Question 20

What does atomic spectroscopy require?

Answer 20

Atomization.

Question 21

What regions of the electromagnetic spectrum does atomic spectroscopy occur in?

Answer 21

UV and visible regions.

Question 22

What characterizes atomic spectra?

Answer 22

Consist of sharp lines or narrow peaks.

Question 23

What must match for absorption to occur in atomic spectroscopy?

Answer 23

The energy of the photon must match the energy difference between atomic levels.

Question 24

What is the first step in Atomic Absorption Spectroscopy (AAS) process?

Answer 24

Sample preparation: Convert sample to aqueous form.

Question 25

What is nebulization in AAS?

Answer 25

Convert sample into a fine mist.

Question 26

What occurs during flame desolvation in AAS?

Answer 26

Solvent evaporates, leaving an aerosol.

Question 27

What is formed during volatilization in AAS?

Answer 27

Free atoms that absorb radiation.

Question 28

What is the role of the hollow-cathode lamp in AAS?

Answer 28

Spectral light source that emits radiation at the same frequency absorbed by the analyte.

Question 29

What are spectral interferences in AAS?

Answer 29

When spectral lines of two elements are very close and interfere with each other.

Question 30

What are chemical interferences in AAS?

Answer 30

Stable oxides that are hard to atomize leading to low signal.

Question 31

What happens during ionization in AAS?

Answer 31

High temperature causes ionization instead of atomization, affecting absorption.

Question 32

What is self-absorption in AAS?

Answer 32

Atoms in the flame's center excite first and re-emit photons that are re-absorbed by atoms further away.

Question 33

How does ICP-AES (ICP-OES) work?

Answer 33

* Plasma formation at high temperatures * Ionization and excitation of atoms * Emission of characteristic radiation

Question 34

What are the advantages of ICP-AES (ICP-OES)?

Answer 34

* Minimal chemical interferences * Simultaneous quantification of multiple elements * Faster analysis * Chemically inert environment * Uniform temperature profile

Question 35

What are the disadvantages of ICP-AES (ICP-OES)?

Answer 35

* Expensive instrumentation * Spectral interferences * Time-consuming sample preparation

Question 36

What are the types of interferences in AES?

Answer 36

* Chemical interferences * Spectral interferences

Question 37

What is the principle behind X-ray fluorescence (XRF)?

Answer 37

X-rays are produced by high-energy electrons or electronic transitions.

Question 38

How is X-ray fluorescence generated?

Answer 38

High-energy X-rays knock out an inner orbital electron, creating a vacancy filled by an electron from a higher orbital.

Question 39

What provides an elemental fingerprint in XRF?

Answer 39

The emitted radiation.

Question 40

What are the advantages of XRF?

Answer 40

* Surface analysis (non-destructive) * Rapid elemental composition identification * Used in quality control for metals and alloys

Question 41

What are the disadvantages of XRF?

Answer 41

* Less sensitive than optical methods * Matrix effects affecting absorption

Question 42

What is one technique for XRF sample preparation?

Answer 42

Powders & Pressed Pellets: Grind sample into fine powder.

Question 43

What is the fusion method in XRF sample preparation?

Answer 43

Mix with flux and heat until it melts into glass.

Question 44

What is the best method for sample preparation in XRF?

Answer 44

Fusion (Glass Beads) for reducing matrix effects.