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Atomic Spec > Exam 1 > Flashcards

Exam 1 Flashcards

1
Q

What is Spectrometry

A

The reactions and measurements of Radiation Intensity

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2
Q

Assumptions of External Calibration

A

1.) There is no error in the [conc] of standards - careful prep of samples is required
2.) No errors in measurement - careful observation and measurement required
3.) Signal response is the same for standards and samples - done by instrument or blank measurement
OVERALL no CORRECTIONS
Assumes matrix effect are absent or have little impact in the analytical (use of certified pure substances)

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3
Q

Systematic Errors

A

from inaccurate gravimetric and volumetric measurements

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4
Q

Matrix Effect

A

Species not within blank, present in sample, will cause samples/standards different responses.
Differences in experimental variables at the time of measurement of blanks, standards and samples

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5
Q

Precision

A

Reproducibility of results from a measurement.
Represented as stdev, relative stdev,
standard error of mean, coefficient of variant and variance

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6
Q

Bias

A

A measure of the systematic error of an analytical method, technique, equipment or calibration. Proper instrument calibration and use blanks to reduce bias

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7
Q

Sensitivity

A

The ability to discriminate between small differences in analyte [conc] limited by the slope of the calibration curve and precision of the measurement.

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8
Q

Detection Limit

A

The minimum concentration or mass of an analyte that can be detected (Sm = signal(blank) + k * blank(stdev)

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9
Q

Dynamic Range

A

Concentration over which measurement is reliable

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10
Q

Selectivity

A

Freedom from interferences

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11
Q

What is more sensitive?
a.) slope= 3.0 E3 ; R^2 = 0.9393
b.) slope= 3.0 E4 ; R^2 = 0.8326

A

B.) - When talking about sensitivity, the slope express the sensitivity. Not the R^2

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12
Q

Standard Addition Method

A

Used to eliminate matrix in samples by spiking the sample with known aliquots of a standard
Must use if standard and unk. have drastically different solution environments

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13
Q

Standard add. Method: How does it work?

A

Constant is added to remove proportionality ( i.e. we are changing from proportionality to equaling)

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14
Q

Internal Standard Method (Quality Control Method)

A

I.S. should have similar properties to the test samples and standards; producing a distinct signal from both sample/standards

Added in constant amount
or present in excess, assumed to be constant

Corrects both measurement and instrument error.

Using a ratio of both sample/standard provides a better R^2

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15
Q

Signal

A

The measurement that contains the information of the analyte

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16
Q

Noise

A

Contains no information regarding the analyte and overall decrease accuracy and precision - overall limiting the amount of analyte that can be detected

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17
Q

Signal-to-Noise Ratio (S/N)

A

Best describes the quality of an analytical measurement of an analytical method or the performance of an instrument and is defined as the stdev of the measurement of the signal

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18
Q

Sources of Instrumental error

A

Faulty calibrations
Calibration errors in meters
Weights
volumetric glassware

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19
Q

Chemical Noise

A

Variations in experimental onditions cause a change in the chemistry of the analyte

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20
Q

Instrumental Noise

A

This is associated with components of the instrument

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21
Q

Thermal Noise / Johnson Noise

A

Caused by electron or charge agitation which leads to fluctuations
Measure results of signal changes in temp
Voltage Measurement
Bandwidth dependent

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22
Q

Shot Noise

A

Fluctuations of electrons in semiconductors
Dependent on Bandwidth

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23
Q

Hardware - Signal to noise enhancement

A

1.) Grounding/Shielding
2.) Electronic filtering
3.) Modulation

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24
Q

Grounding/Shielding

A

Surrounding critical instrument components with a conducting material attached to the ground to remove noise and electromagnetic radiation from the environment

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25
Q

Electronic Filtering

A

Removes frequencies that are different from the signal frequency (use low or high pass filter to reduce noise)

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26
Q

Modulation

A

Move signal to quieter region of the spectrum

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27
Q

Software - signal to noise enhancement

A

Ensemble Averaging
Smoothing
Digital filtering

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28
Q

Ensemble Averaging

A

Noise is often random, signal is not. By recording repetitive signals, random noise can be reduced
Entirely dependent on times measured (n)
Provides stronger signals

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29
Q

Smoothing

A

Averaging successive points from rough data - the more successive points, increases smooth character of line

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30
Q

Digital Filtering

A

Mathematically remove selected fragments
Signal is low so use a low pass filter to reduce background - converts from signal domain to frequency domain

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31
Q

True or False

A

Hardware is out of our control, we cannot change it, however we can control the software methods that can shape our data from hardware

32
Q

Electronic Transition

A

When an electron is excited from one energy level to another in a molecule or atom.

When electrons jump from one energy level to another, they absorb energy equivalent to the energy difference between the two levels.

33
Q

Excited Singlet State

A

The electron is promoted in the same spin orientation as it was in the ground state (paired)

34
Q

Internal Conversion

A

The radiation less transition between energy states of the same spin

The intermolecular process in which a molecule crosses to a lower electronic state without emitting radiation

35
Q

Intersystem Crossing (ISC)

A

radiation- less process involving a transition between two electrons states with different states spin multiplicity

Is the process in which a molecule in one spin state changes to another spin state with nearly the same total energy (e.g. single to triplet)

36
Q

Nonradiative Relaxation

A

A step-wise loss of energy by an excited atom (no fluorescence)

37
Q

Non-resonance Fluorescence

A

Due to vibrational energy loss, the emitted radiation has a lower energy level or longer wavelength

38
Q

Resonance Fluorescence

A

Process in which the emitted and excited radiation have identical frequencies

Produced by atoms in the gaseous state with no vibrational energy levels

There is no radiative or vibrational energy loss upon excitation making the excited species fluoresce at the same energy as excitation

39
Q

Singlet State

A

The spins of the electrons of an atom or molecule are all paired so there is not a net spin angular momentum

40
Q

Triplet State

A

Is one in which the spins of the electrons of an atom or molecule are unpaired so that their spin angular moments add to give a net-zero moment

41
Q

Vibrational Relaxation

A

is the process by which a molecule loses its excess vibrational energy without emitting radiation

42
Q

External Conversion

A

Is a radiation- less process in which a molecule loses electronic energy while transferring that energy to the solvent or another solute

43
Q

Quantum Yield

A

The fraction of excited molecules that undergo fluorescence

44
Q

When does fluorescence occur?

A

Rate of Diffusion ( 10E-8) sec

45
Q

Fluorescence excitation spectra
-Where is fluorescence and why?

A

Fluorescence is on the right of excitation because of energy loss from vibrational relaxation

As a result, fluorescence bands occur at longer wavelengths than absorption bands

46
Q

How does Temperature Affect Quantum Yield?

A

QY decreases with the increase in temp, due to an increase in frequency of collision at high temps and a high probability of deactivation by external conversions

47
Q

How does Viscosity Affect Quantum Yield?

A

Increase in viscosity, reduces the frequency of collisions and increase the fluorescence. Increases QY

48
Q

How does Structure Affect Quantum Yield?

A

Aromatic functional groups, pi-pi* transitions, fused-ring structures are rigid and produce more fluorescence. Less rigid aromatic structures undergo high frequency vibrations and loss in energy. I

I.e. More rigid/support, higher fluorescence = Increased QY

49
Q

What is Fluorescence dependent on?

A

Structure
Energy
Time

50
Q

How do Halogens decrease fluoresce?

A

Halogens decrease fluorescence via heavy-atom effect. Cause orbital spin interactions resulting in high intersystem crossing effect and increase the rate of triplet formation .

Halogens are useful for slowing down fluorescence to get to phosphorescence (slows down transition - 2 secs)

Effect on QY: Decreases by keeping excited species longer (Quenching Fluorescence) past the point of fluorescence.

51
Q

What do carboxylic acid and carbonyl groups do to fluorescence ?

A

Inhibit due to lower n-pi* transition energy than pi-pi*

Overall don’t want lone pairs, as they decrease fluorescence

52
Q

Absorbance

A

Absorbance is always a fraction Po/P

Specifically, abs is related to ratio of Incident and transmitted beam, Max you can get is 1. Overall absorbance can be limited by concentration

Po is incident beam power and P after passing through the medium

A = Po/P
A= Ebc

53
Q

What is Directly proportional to fluorescence?

A

F = Kc
Fluorescence intensity is directly correlated to concentration

54
Q

How low can fluorescence be detected?

A

Can detect low pico molar range

55
Q

Spectrometry

A

Measurement of radiation intensity with an electronic transducer

56
Q

Wave Model

A

Describes electromagnetic radiation as a wave characterized by wavelength, frequency, velocity and amplitude

57
Q

Particle Model

A

Electromagnetic radiation is a stream of discrete particles/wave packets of energy called photons

58
Q

Frequency (Weird V)

A

Number of oscillations of the radiations/sec

59
Q

Wavelength

A

Linear distance between 2 successive equivalent points

60
Q

What is important about Frequency?

A

The frequency of a beam of radiation is determined by the source and remains fixed and invariant (CONSTANT)

In vacuum frequency = 3.0 * 10^8 m/s

Frequency is not proportional to wavelength as it is constant

61
Q

What happens when a beam is impeded? i.e. does it have an effect on Frequency, Velocity or Wavelength

A

Frequency is always constant

Velocity and Wavelength decrease

62
Q

What is the frequency or wavelength of radiation related to?

A

Energy differences between states

63
Q

What happens when an atom or ion changes its state?

A

It absorbs or emits an amount of energy exactly equal to the energy difference between the states

64
Q

Constructive Wave

A

2 or more waves in phase with each other

The amplitude of the resultant wave is additive and greater than the individual waves

Add both energies from the waves to provide a stronger wave

65
Q

Destructive Wave

A

2 or more waves travel in opposite directions (out of phase) to each other

The amplitude of the resultant wave is less than (dampened) the individual waves

more noise (measuring too low of amplitude)

66
Q

What is the lifetime of excited vibrational transition?

A

10E-12 sec

67
Q

What is the lifetime of electronic transition?

A

10E-8 sec

68
Q

Emission Spectrum Vocab:
Lines?
Bands?
Continuum?

A

Lines - From individual atomic particles behaving independently of each other (Brine spectrum examples - Na, K, Ca)

Bands - From small molecules or gaseous radicals is due to numerous vibrational levels superimposed on each other (Brine spectrum examples - CaOH)

Continuum - A feature of the temperature of the emitting surface rather than the material composing the surface (Dependent on Radiation sources from instrument, i.e. The sun, tungsten lamp, deuterium lamp)

69
Q

Continuum Radiation Sources

A

Xenon arc
Carbon arc
Tungsten lamp
Nernst glower

70
Q

UV Absorption Spectra Vocab:
Line Spectra
Band Spectra
Continuum

A

Line Spectra
- Absorption of Monoatomic vapor
- Fewer number of possible energy states

Band Spectra
-Absorption of Polyatomic molecules
-Greater number of possible energy levels in molecule than isolated atoms

Continuum
-Interaction with solvent molecules leads to broadening

71
Q

Sources of Band Broadening

A

1.) Pressure Broadening
2.) The Uncertainty Effect
3.) Doppler Effect
4.) Electric and Magnetic Effect

72
Q

Pressure effect

A

Due to collisions between atoms of the same kind and with different atoms

73
Q

The Uncertainty Principle

A

Spectra lines have finite width because the lifetimes of the upper and lower states of the transition are finite which leads to uncertainty in energy

The energy of a particle can be known with zero uncertainty only if it is observed for an INFINTE period

74
Q

Doppler Effect

A

High frequency: Decrease in wavelength
Low frequency: Increase in wavelength

75
Q

Electric and Magnetic Effect:

A

Cannot do anything to fix this.
Can cause variations of varying electromagnetic radiation changes energy levels; leading to Band Broadening.

When atomic vapor is exposed to a strong magnetic field, a splitting of the electronic energy levels of the atom occurs and leads to the formation of several abs lines for each transition

76
Q

Effect of temperature on atomic spectra

A

Temp causes efficient atomization and increase in the number of excited atoms
Leads to line broadening due to particles traveling at higher velocities

Temperature increases the ratio of the number of excited and unexcited atomic particles in an atomizer

Atomic Spec (1 decks)

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