Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Forensic Chemistry > Lecture 7: Heavy metal detection > Flashcards

Lecture 7: Heavy metal detection Flashcards

1
Q

What are heavy metals?

A

-High density
-Can’t be degraded or destroyed
-Persistent in the environment

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What are examples of heavy metals?

A

-Mercury
-Lead
-Chromium
-Cadmium
-Cobalt

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is AAS?

A

Atomic absorption spectroscopy

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is AAS used for?

A

A technique used to detect metals and metalloids

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What are the advantages of using AAS to detect metals?

A

-Reliable
-Sensitive (Can go to very low wavelengths)
-Quantitative
-Can analyse over 62 elements

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What does AAS look at when analysing?

A

Atoms, rather than molecules

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is measured during AAS analysis?

A

Atoms absorb energy and we measure the emission (The degree they emit energy back)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is the energy gap for emission?

A

The energy gap for emission is the same as the energy gap for absorption

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is Planck’s equation?

A

E=hf

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What does the E in Planck’s equation stand for?

A

Energy

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What does the h in Planck’s equation stand for?

A

Planck’s constant

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What does the f in Planck’s equation stand for?

A

Frequency

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is the principle of AAS?

A

Free atoms that are generated in an atomiser can absorb radiation at a specific frequency;
Each element absorbs at a different frequency

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What does AAS quantify?

A

Quantifies the absorption of ground state atoms in the gaseous state

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is the concentration of the analyte in AAS determined by?

A

The analyte concentration is determined by the amount of energy absorption

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What law is AAS governed by?

A

Beer-Lambert Law:
Absorption=constant x conc

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What is the AAS instrument calibrated with ?

A

Standards of a known concentration

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What is the Beer-Lambert equation?

A

A=EbC
*For any wavelength

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What is the A in the Beer-Lambert equation?

A

A=Absorbance

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What is the b in the Beer-Lambert equation?

A

b=Path length

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What is the E in the Beer-Lambert equation?

A

E=Molar absorbtivity

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What is the C in the Beer-Lambert equation?

A

C=Conc (mol/L)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What is heavy metal detection using AAS based on?

A

The properties of specific metal atoms to absorb specific wavelengths of light

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What does the electronics on the AAS instrument do?

A

The electronics will measure light attenuation (How much light is held by an atom) & convert to the metal concentration of the sample

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

What are the elements of the AAS instrument?

A

-Light source
-Sample cell (flame/furnace)
-Specific light measurement:
-Monochromator
-Detector
-Electronics
-Readout

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

What is the purpose of the furnace in the AAS instrument?

A

Heats up the sample to convert it to the gaseous state

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

What is the process of sample atomisation in AAS?

A

-Desolvation
-Vaporization
-Volatilization

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

What is desolvation in AAS?

A

The liquid sample evaporates and the dry sample remains

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

What is vaporization in AAS?

A

Solid sample vaporizes into gas

30
Q

What is volatilization in AAS?

A

Compounds that make up the sample are broken into free atoms

31
Q

What is the light source component of the AAS instrument?

A

-A hollow cathode lamp emits a specific spectrum, focused through the sample cell into the monochromator

32
Q

What does the light source contain?

A

-A tungsten anode
-Hollow cylinder cathode made of the element of interest

33
Q

Where is the light source sealed?

A

In a glass tube with an inert gas

34
Q

What is the Nebuliser component of the AAS instrument?

A

-Aspires liquid at a controlled rate
-Creates a fine aerosol particle to be introduced to the flame

35
Q

What is the Atomiser component of the AAS instrument?

A

-Separates particles into individual molecules & breaks molecules into atoms
-Occurs under high temp in a furnace

36
Q

What are the 2 types of atomiser?

A

-Flame atomiser
-Graphite tube atomiser

37
Q

What is a flame atomiser in AAS?

A

A mixture of oxidant gas and a fuel
e.g. Air-acetylene flame

38
Q

What is a graphite tube atomiser in AAS?

A

Uses graphite coated furnace to vaporise sample.
Sample deposits in small graphite coated tube, heated to vaporise and analyte is atomised

39
Q

What are the basic steps of atomisation?

A

-Nebulisation
-Desolvation
-Volatilisation
-Dissociation
-Ionisation
-Excitation

40
Q

What is the monochromator component of the AAS instrument?

A

-Selects the specific wavelength of light absorbed by the sample and excludes other wavelengths
-Allows the detection of the specific elements

41
Q

What is the detection component of the AAS instrument?

A

-Photomultiplier tubes are the most common detector;
-Converts a light signal to an electric
signal , proportional to the intensity of
light

42
Q

What is XRF?

A

X-Ray emission spectroscopy

43
Q

What is the principle of XFR?

A

-Deals with characteristic X-rays
-When a sample is exposed to X-rays an electron could be displaced

44
Q

What is the energy associated withe these X-rays sufficient enough to do?

A

Displace electrons from inside the orbitals of atoms (K,L,M)

45
Q

What do X-rays release energy as?

A

X-ray photons

46
Q

What is electron transition?

A

The movement of electrons between energy levels

47
Q

What is the energy of emitted X-ray photons equal to?

A

The differences in energy levels involved in electron transition

48
Q

What is Ka electron transition?

A

Electron moves from L to K shell

49
Q

What is Kb electron transition?

A

Electron moves from M to K shell

50
Q

What is La electron transition?

A

Electron moves from M to L shell

51
Q

What is emission intensity in XRF?

A

Proportional to the concentration of the atom in the sample

52
Q

What happens when X-rays encounter matter?

A

-They can be absorbed or transmitted through the sample (medical)
-Can be Diffracted or scattered from an ordered crystal (Crystal structure)
-Can cause generation of X-rays in diff colours (Fluorescence)

53
Q

What does an atom consist of?

A

-Nucleus (contains protons and neutrons)
-Electrons in shells

54
Q

What is the atomic number of an element?

A

-Number of protons and electrons
-Rep by letter Z

55
Q

What are the 4 electron shells?

A

-K
-L
-M
-N

56
Q

What is the K electron shell?

A

-Closest to the nucleus
-Holds 2 electrons
-Electrons are bound more tightly and harder to remove

57
Q

What is the L electrons shell?

A

-2nd from the nucleus
-Holds 8 electrons

58
Q

What is the M electron shell?

A

-3rd from the nucleus
-Holds 18 electrons

59
Q

What is the N electron shell?

A

-Furthest from the nucleus
-Holds 32 electrons

60
Q

Which shells do X-rays typically only affect?

A

Inner K & L shells

61
Q

Why are the electrons in the K shell more difficult to move?

A

-They have the highest binding energy
-Requires more energy X-rays to move electrons out of the shell

62
Q

Why will N shell electrons release more energy when falling between shells?

A

-They have the highest potential energy

63
Q

What is X-ray attenuation?

A

Initial electrons may be scattered

64
Q

What are the 2 types of scattering?

A

-Coherent
-Incoherent

65
Q

What is coherent X-ray scattering?

A

-The X-ray collides with an atom & deviates without a loss in energy
-An electron in an alternating electromagnetic field, will oscillate at the same frequency

66
Q

What is incoherent X-ray scattering?

A

-Incident X-ray loses some of it’s energy to the scattering electron

67
Q

What is the X-ray tube source on the XRF instrument?

A

-High energy electrons are fired at the anode
-Can vary excitation and current
-Can use filters to tailor source profile for lower detection limits

68
Q

What are the components of the XFR instrument?

A

-X-ray tube source
-Silicon drift detector
-Digital pulse processor
-Analyser software

69
Q

What is the analyser software of the XRF instrument?

A

-Converts spectral data to a direct readout of results

70
Q

What is the energy of a photon related to?

A

-The type of element

71
Q

What is the emission rate related to?

A

-The concentration of the element

72
Q

What does the detector do on the XRF instrument?

A

-Monitors the energy & the number of photons over a preset time

Forensic Chemistry (7 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions