Light And Matter

Question 1

Describe the process of Atomic Emission spectroscopy

Answer 1

• analyses multiple elements simultaneously
• not as sensitive as AA

1. Analyte vaporised by flame
2. Atoms riven to high energy levels
3. Return to ground state and emit specific photons (LIGHT)
4. Emission wavelengths determined = elements present

Question 2

Define the term ‘Electromagnetic radiation’

Answer 2

Various forms of energy in the forms of waves (light)

- consists of tiny packets of energy (photons)

Question 3

List the order of the Electromagnetic spectrum

Answer 3

1. Gamma rays
2. X-rays
3. UV
4. Visible
5. IR
6. Microwaves
7. Radio waves

Question 4

Describe UV light

Answer 4

• quantised process = molecule can absorb exact amount of energy corresponding to the differing in energy between occupied and unoccupied energy levels
• absorbs certain photons of particular energy

Question 5

Describe the UV Spectrophotometer process

Answer 5

• emits all wavelengths of UV light
• monochromator = selects one wavelength for exposure to sample
• detector = amount transmitted wavelength is known
• sample in a solvent that doesn’t absorb light
• setector = sensitive to changes in intensity of UV (photocell)

Question 6

What is Beer’s law?

Answer 6

Relates the concentration of a light absorbing substance to the amount of light it absorbs

Question 7

Describe the Fluorescence spectrophotometer process

Answer 7

• detector at 90 degree angle = detector won’t see light that leaves the source
• two monochromators = one between source and sample = wavelengths that reach sample are detected and one between sample and detector = excitation and emission detected

Question 8

What are 3 uses of UV spectroscopy in forensics?

Answer 8

1. Determining exact colour of something
2. Comparing colours of fibres
3. Identifying automotive clear coats

Question 9

What are 2 uses of fluorescence in forensics?

Answer 9

1. Certain illicit drugs (ie. LSD)

2. Objects containing optical brighteners

Question 10

Describe the process of IR microspectrophotometry

Answer 10

• through light path = source of radiation channeled through microscope then object then detector
• transmittance and reflectance spectra obtained

Question 11

What are 4 uses of IR in forensics?

Answer 11

1. Fibres
2. Paint chips
3. Drugs
4. Dyes and pigments

Question 12

What are 2 limitations of IR spectrometry?

Answer 12

1. Relies on the presence of a pure substance

2. Purification of very small samples isn’t efficient nor effective

Question 13

Describe the process in Mass Spectrometry

Answer 13

SAMPLE INTRODUCTION - solids/liquids/gases

IONISATION - 1. Bombarding with energetic e’s, absorb energy and lose e’s forming cations

                     2. Using small molecules of methane to ionise 
                     3. Lasers for analyte to ionise 

SEPARATION - 1. Ions accelerated through curved magnetic field
2. Trapped in a quadrupole

DETECTION - ions amplified to boost signal and detected

Question 14

Describe the process of Atomic Absorption Spectroscopy

Answer 14

• analyte must be vaporised
• elements must be known in advance

1. Material dissolved in solvent
2. Vaporised by flame
3. Lamp chosen by the wavelengths emitted the substance can absorb
4. Amount of light absorbed determined at each wavelength