Analytical > Atomic Spectroscopy > Flashcards

Atomic Spectroscopy Flashcards

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1
Q

Write the electron configuration

How do electrons fill orbitals

A

1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6

The 4s is filled before the 3d

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2
Q

Electron configuration of calcium

A

20 electrons

1s2 2s2 2p6 3s2 3p6 4s2

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3
Q

Atomic Absorption Spectrometry

A

AAS

energy absorbed by atoms to allow it to enter and excited state

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4
Q

Atomic Emission Spectrometry

A

AES

Energy emitted by an excited electron when it falls back to the ground state

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5
Q

Principle quantum number :

A

The number of the period that electron is in

n = 1,2,3,4

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6
Q

Orbital quantum number

A

oqn

l

s = 0
p = 1
d = 2

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7
Q

Delta n rules

A

Δ n = 0, +/1- 1,2,34

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8
Q

Delta l rules

A

Δ l = +/- 1

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9
Q

Allowed transitions of electrons are possible

A

Are only permitted if the rules for Δ n and Δ l are satisfied

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10
Q

Is the transition from _ possible

2p to 3p

A

Ground state 2p
Excited state 3p
Can an electron make this transition

Δn = 2 - 3 = -1 this rule is satisfactory
Δl = 1 - 1 = 0 not allowed

This transition can’t happen

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11
Q

Is the transition from _ possible

2p - 4s

A

Δ n = 2 - 4 = -2 satisfied
Δ l = 1 - 3 = - 2 not allowed

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12
Q

Energy formula

A

E = hf

E = c / λ

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13
Q

Difference between atomic emission and absorbance spectroscopy and how are they both measured

A

AAS = energy absorbed by an atom to reach an excited state

AAS instrument

AES = energy released or emitted by an excited atom

AES instrument

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14
Q

Plasma

A
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15
Q

Spectral lines

A

The wavelengths absorbed by an element which corresponds to allowed transitions the outer electron can undergo

eg sodium absorbs are 3 wavelengths therefore sodium has 3 spectral lines which corresponds to 3 transition that the outer electron can u servo in sodium

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16
Q

Use an element to describe the events when an element is excited and light is omitted by atoms which has been inserted into a flame

A

Sodium has its outer electron in the 3s orbital

It can undergo these 3 transitions

These transitions correspond to the 3 different wavelengths we see in the spectral for sodium

3s-3p,4p,5p

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17
Q

Use a specific element, eg ____, to explain the atomic events occurring when the element is excited and light is emitted by atoms which have been inserted into a flame.

A

Find outer electron
See possible transitions that would be characteristic of ____
Would be able to measure the wavelength of them and identify them as aluminium

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18
Q

AAS v AAS

How are the measured and the instrument

A
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19
Q

Basic theory of atomic emission

A

Electronic excitation

Excited electrons give off an amount of energy when they fall back down and you can measure it and it equates to UV Vis radiation ie light

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20
Q

Standard addition approach when is it used

A

Very complex matrix / complex sample eg colour

Take the sample and add it to standards

X intercept is the concentration of your standard

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21
Q

Calibration method when there is lots of variation in your experiment due to the instrument

A

Use internal standard

concentration v ratio

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22
Q

Transition metals valence electrons

A

2

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23
Q

Why is it important to use the same acids, etc, in standards as in samples?

A

To match standards to sample and avoid interference

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24
Q

In atomic spectroscopy, distinguish clearly between atomic emission and atomic absorption methods. Briefly outline why one might choose to use emission methods in certain situations.

A

AAS measures energy absorbed to excite an electron

AES measures the energy released by an excited electron

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25
In atomic absorbance spectroscopy, absorbance is associated with:
electronic transitions
26
The purpose of the flame in a flame AA spectrometer is to:
Desolvate and atomise the sample
27
The Principle Quantum Number describes:
The energy level of an electron.
28
The ground state electron configuration of Ga, Galium, with atomic number 31 is:
1s2 2s2 2p6 3s2 3p6 3d19 4s2 4p1
29
A hollow-cathode lamp is:
A narrow-band light source
30
Internal standard
Prepare a set of standard solutions for analyte (A) but add a constant amount of a second species (B) to each solution. Add the same amount of the second species to the sample. Prepare a plot of SignalA/SignalB versus [A]. Use the ratio of signals for the sample to find the unknown
31
Standard addition
Add one or more increments of a standard solution to sample aliquots of the same size. Each mixture is then diluted to the same volume. Prepare a plot of Analvtical Signal versus: volume of standard solution added, or concentration of analyte added
32
External standard
Prepare a series of standard solutions (analyte solutions with known concentrations).Plot [analyte] vs. Analytical Signal. Use signal for unknown to V find [analyte].
33
Atomic and Molecular Spectroscopy techniques are similar yet different, select the true statement(s) below.
UV/Visible absorption spectra of atoms is a line spectra with multiple lines while the UV/Visible Spectra of molecules consists generally of a few intense broad absorption bands.
34
Outside energy can excite all electrons in an atom if identical to the difference between ground state and excited state energy levels ?
False
35
The rules for allowed transitions in Atomic Spectroscopy are
Δn = 0, ‡1, ‡2, ‡3, ‡4: Δl = ‡1
36
Select the true statement(s) for Atomic spectroscopy:
Absorbance is proportional to concentration
37
Which one of the following is are part of an inductively-coupled plasma. atomic emission spectrometer?
Plasma torch Induction coil Nebulizer
38
Spectroscopy
the interaction of atoms and molecules with Electromagnetic Radiation.
39
Effect of uv-visible radiation on double and triple bonds
The pi bonds electrons Easily affected – promoted from ground to excited state The absorbance peak nm is due to an electron printed from ground to excites state
40
Chromophore
Structure or group which absorbs Eg ethene C=C Lambda max at 171nm
41
Chromagen
Molecule containing chromophore eg ethene H3C=CH3
42
Spectrometer parts
Light source Wavelength selection eg grating has good resolution Sample in sample holder glass, plastic, quartz detector photo diode array
43
Qualitative uses spectrometer
Identify substance from Spectrum: Position of peaks Position of troughs Widths of peaks and troughs Peak ratios Unambiguous identification is difficult, so UV- Visible Spectroscopy not very commonly used for identification – IR better
44
Quantitative Use spectrometer
Most important use – Beer-Lambert Biochemical analyses – enzymes, proteins (and nucleic acids Hospitals Detection of drugs in horses, athletes Monitor pollution, pesticide levels Identify confiscated narcotic drugs
45
Deviations in B/L Law
High concentration Changes to sample eg precipitation Cloudy sample eg particles scatter light which raises absorbance when it settles absorbance changes Could also be instrument factors coming into play
46
What happens in a nebuliser? Use a diagram.
The process of converting a solution into a fine spray of droplets Sample in solution is mixed with the oxidant and the fuel and them combined are sprayed into a glass bead and this causes the liquid to break into five droplets, 10% of the droplets are small enough to pass through the baffles to reach the burner head and flame.
47
Write a note of flames in atomic spectroscopy
48
Why is the lamp cathode hollow?
The cathode is hollow for two reasons To direct the light energy it is producing in one direction To increase the chances of the metal being redepoisites on the cathode which means the lamp will last longer
49
What happens in the flame, step by step?
50
Explain why the monochromator in AAS is positioned where it is. 30. What kind of monochromator (and detector) is mostly used for AAS?
Positioned after the sample Reduces interference from light of other wavelengths reaching the detector Deflection grating is most commonly used splits light up into different wavelength s and the exit slit is positioned so a particular wavelength is selected Detector most commonly used is the photo multiplier tube
51
What could you do if you had calcium phosphate in your sample?
To use a high temperature flame by switching to oxidant to nitrous oxides and acetylene instead of air and acetylene
52
Draw a series of labelled diagrams to show the construction, and main principles of operation, of the following: hollow cathode lamp, nebuliser, graphite tube burner
Hallow cathode lamp : Hollow cathode Anode Glass tube that all this is positioned in Gas like neon inside the lamp
53
What kind of radiation does a hollow cathode lamp produce?
The radiation produces by a hollow cathode lamp is very narrow and specific wavelength for example if you want to measure iron in a sample you need to use a hollow cathode lamp made of iron , that cathode will only produce energy that is enough to excite iron atoms in the sample Suited only the metal we are interested in measuring
54
Compare flame and graphite furnace AAS.
55
Describe the structure of an AAS and explain in detail the functioning and usefulness of such an instrument
Block diagram
56
Discuss the advantages and disadvantages of flameless AAS compared with flame AAS.
Compare graphite burner with flame AAS
57
Why is it important to use the same acids, etc, in standards as in samples?
Match sample to blank to avoid interference We use acids to put metals into solutions It’s important to use the same acid and quantity in your standard
58
Explain the circumstances under which it is appropriate to use the standard addition method in atomic spectroscopy and advantages of this method.
Adding standards to your sample and measure absorwbance Produces a standard addition curve Line of best fit crosses x and y axis Label x axis Concentration of added Used for complicated matrix eg blood urine Concentration of actual sample is where the line crosses the z axis and ignite the minus sign Avoids interference from the matrix from interfering with results Ensures results are true to real compositions
59
Write a note on interferences in AAS and how to overcome them
5 types of interference Spectral: iron and platinum Inflated absorbance Use a different wavelength to overcome it Chemical: refractory compounds don’t dissociate in flame no free atoms produced in the flame Changed to nitrous oxide and acetylene use a chelating EDTA agent Which will break down these compounds, common with calcium Use a releasing agent : prevents formation of refractory complexes Ionisation complexes: atoms absorbing energy become ions Add a ion surpressoer or use a cooler flame Physical / efficiency of nebuliser Use standard addition Molecular: molecules that remain despite the process of atomisation eg molecules not evaporating or decomposing Use background correction will overcome this
60
What could you do if you had calcium phosphate in your sample?
This is chemical interference abs there’s theee things you can do to overcome this Increase temperature is flame chelating agent use a releasing agent
61
What are the uses of chelating and releasing agents in AAS? Give some examples.
To prevent chemical interference break down the stable complexes that are formed EDTA Strontium chloride Prevents formation abs breaks them down to complete atomisation
62
What would you do if your sample contained an element which absorbs at the same wavelength as your analyte of interest?
Spectral interference Use a different wavelength eg iron and platinum remover e wavelength
63
The problems associated with AAS can be listed as follows: Background molecular absorption Chemical interference Ionisation Physical interference Spectral interference Describe what these processes are and some of the ways of dealing with these problems
Causes How to overcome
64
What is Plasma?
Very hot conducting gas usually argon that has a significant concentration of cations and electrons
65
Explain the flame photometer with reference to atomic spectroscopy.
Diagram of flame photo metre had no lamp first thing you include is the sample the monochromiter and the sample Sample is sucked up into nebuliser where it is combined with an oxidant and a gas the gas is ignited and burned , atomisation happens in the flame emitted energy is filtered through a mocochronotet and detected on the detector
66
In atomic spectroscopy, distinguish clearly between atomic emission and atomic absorption methods. Briefly outline why one might choose to use emission methods in certain situations.
The energy amount is the same Use energy diagram ICP is a powerful instrument and can looked at a broader range of periods this is why emission might be usrd
67
Give the functions of the three streams of Argon in an ICP torch.
The argon in the outer tube helps to cool the source and the sample is introduced into the inner tube by the nebuliser A spark ionises the argon in the intermediate tube ( the curl) the resulting kind and electrons and this gives the plasma
68
Why do we not need a lamp in Atomic Emission spectroscopy?
Measuring emission we don’t want to use a lamp that could give an energy source that could be absorbed Flame photometer Plasma icp Heat energy excites electrons which give off uv abs visible radiation that radiation can. S measured abs us specific to each element
69
If you are measuring two elements with emission lines very close together, what might you be able to do?
Spectral interference Switch the spectral ljne ie switch the wavelength
70
Draw a diagram of the arrangement of the various component parts of a simultaneous ICP spectrometer.
71
What are the advantages of both sequential and simultaneous ICP spectrometry systems?
Sequential Flexible measure at any wavelength but time consuming uses a lot of sample Simultaneously: measure many enn my enemy’s at the same time uses little sample but is expensive and come with a pre set wavelength
72
State the advantages and disadvantages of the ICP compared with conventional flame in atomic spectroscopy.
See icp v flame photometer Give 8
73
Explain how an inductively coupled plasma torch works and why it is used.
In emission it provides very high energy for excitation of electrons that is measured as emission
74
Describe simultaneous and sequential atomic emission spectroscopy systems. Use diagrams.
Sequential One monochromitee and one detector Simultaneously: polyomyre multiple detectors can measure multiple samples at the one time
75
Draw a diagram of the arrangement of the various component parts of a simultaneous ICP spectrometer.
76
Absorbance
The light energy that is absorbed by a chromophore which has double or triple bonds
77
Transmittance
The light energy that reaches the detector Not a very useful parameter to use as it does not give a straight line but this value can be converted to absorbance which can give a trend line with an equation of a line
78
UV vis sources
Deuterium (2H) discharge lamp Tungsten in glass and vacuum Tungsten Hallogen
79
The effective bandwidth
is defined as the width of the radiation at half of its maximum throughput
80
Sample holders in spectroscopy
Visible: plastic UV vis: quartz
81
Detectors in spectroscopy
Photomultiplier Photo diode Photo diode array
82
Spectroscopy uses
Proteins and nucleic acid analysis Drug detection in humans and horses Pollution pesticide levels Indemnify narcotics
83
Deviations in Beer LL
Instrument factors Large bandwidth leads to non monochromatic radiation Electronic problems Or possible the sample under analysis doesn’t actually absorb light in this portion of the EM spectrum you could over come this by mixing the sample with a reagent to form a coloured complex
Analytical
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