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Instrumental Analysis > Quiz 2 > Flashcards

Quiz 2 Flashcards

1
Q

What is the purpose of a radiation detector?

A

convert energy to electrical signal for detection and analysis

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2
Q

ideal detector properties

A

high sensitivity, high signal to noise ratio, constant response, good wavelength range, fast response, 0 output

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3
Q

can any detector combine high sensitivity, high signal to noise, constant wavelength response, and linear energy response?

A

no because of dark current

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4
Q

spectral response

A

slope vs wavelength

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5
Q

sensitivity

A

slope of response versus power

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6
Q

detection limit

A

smallest significant measure

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7
Q

Why can there never be an infinitely narrow spectroscopic line?

A

transition state lifetime

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8
Q

types of photon detectors

A

photon detectors, phototubes, photomultipliers, photoconductivity detectors, silicon diodes

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9
Q

types of thermal detectors

A

pneumatic cells, thermocouples, bolometers, pyroelectric detectors

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10
Q

types of multichannel detectors

A

photodiode arrays, vidicons, charge transfer devices

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11
Q

QM definition of spectral line broadening

A

atomic and molecular energy transitions occur at discrete, well defined energy

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12
Q

What is the classical approach to explain natural line broadening?

A

damped oscillating dipole function

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13
Q

How does energy decay result in a damped oscillating dipole function

A

decays from excited to ground

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14
Q

how is excited state lifetime related to damping constant

A

by lifetime of decay

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15
Q

How is the excited state lifetime related to the half width of a lorentzian distribution

A

longer ESL = sharper line

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16
Q

What is the most common form of the heisenberg uncertainty principle?

A

one cannot measure exactly both the momentum and position of the electron

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17
Q

How are experimentally measured line widths related to natural line widths

A

experimental&raquo_space; natural 10^3

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18
Q

How is the wavelength and frequency of molecules moving toward the detector affected by their motion?

A

towards detector shortens wavelength increasing frequency

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19
Q

How is the wavelength and frequency of molecules moving away from the detector affected by their motion?

A

moving away from detector lengthens wavelength decreasing frequency

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20
Q

How is the half width of a gaussian distribution related to temperature

A

increasing temp increases bandwidth

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21
Q

What would be one way to reduce the doppler line broadening mechanism?

A

cooling

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22
Q

How does molecular collisional frequency change with sample pressure or temperature

A

increasing pressure or temp increases frequency

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23
Q

what is the effect of collisions on spectroscopic excited states

A

decrease excited state, broaden bands

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24
Q

How is the half width of the pressure broadened line related to excited state lifetime?

A

decrease excited state lifetime broadens band

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25
Q

What would be one way to reduce the half width of a pressure broadened line shape?

A

lowering temp slows collisional broadening

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26
Q

What is johnson noise

A

thermal

27
Q

what is shot noise

A

particles crossing junction

28
Q

what is chopping

A

synchronous demodulation; signal in phase passes positive, blocks negative

29
Q

When should a lock in amplifier be used

A

when signals are obscurred

30
Q

What is transmittance

A

power after divided by power before

31
Q

What is the absorption coefficient (a)?

A

absorptivity, proportionality constant

32
Q

What is the molar absorption coefficient ε

A

used instead of (a) when mol/L and cm

33
Q

How do instrumental sources of deviation depend on concentration?

A

it does not

34
Q

How can the chemical and instrumental sources be distinguished when concentration is constant?

A

concentration only effects chemical; instrumental depends on b when c is constant

35
Q

How does polychromatic radiation affect beer’s law linearity?

A

increases deviations, increases ε’ + ε’’

36
Q

How does stray light affect beer’s law linearity?

A

negative

37
Q

How does slit width affect beer’s law linearity?

A

decreases absorbance

38
Q

How do high or low transmittance readings affect beer’s law linearity?

A

absorbance greater than 1 AU decreases precision

39
Q

How do chemical reactions and equilibria affect linearity?

A

What type of photochemical effects will influence linearity?

40
Q

What is the effect of fluorescence?

A

increases T, negative deviation

41
Q

What is the effect of light scattering?

A

decreases T, positive deviation

42
Q

What is spiking?

A

add increments of standard to identical volume samples

43
Q

what is the method of standard addition?

A

spiking, dilute, measure; all constituents but reagent should be identical

44
Q

What types of samples are most used with the method of standard addition?

A

complex samples with high potential matrix effects

45
Q

assumptions for method of least squares

A

assume linear relationship and measurement error (not x)

46
Q

what is ordinary or simple linear regression?

A

area peak versus concentration

47
Q

what is the independent variable in linear calibration curve

A

x

48
Q

what is the dependent variable in linear calibration curve

A

y

49
Q

how is external calibration performed

A

series of known [analyte] standards; obtain response signal vs concentration then plot and predict

50
Q

external calibation

A

calibrate when no matrix interference in analyte

51
Q

method of single addition

A

matrix almost identical for successive additions in standard

52
Q

For a standard addition method, what is the difference between the method of continuous variation and the method of single addition

A

single assumes linearity, uses only 2 increments

53
Q

What are the advantages of the method of single addition compared to the method of continuous variation?

A

saves time and sample

54
Q

Internal standard method

A

substance added in constant amount to all standards in analysis

55
Q

How is an internal standard used in a calibration

A

plot ratio of signals to concentration

56
Q

advantages of internal standard

A

compensate for errors

57
Q

disadvantages of internal standard

A

hard to find and introduce reproducibly

58
Q

How does a response factor influence the internal standard method

A

used when unknown and standard do not respond identically

59
Q

How is precision measured?

A

standard deviation, average, variation

60
Q

How is bias measured?

A

population mean minus the true value

61
Q

How is calibration sensitivity related to the slope of the calibration curve?

A

slope limits sensitivity

62
Q

How is the minimum detectable signal related to the blank signal and standard deviation of the blank?

A

LOD is the concentration that gives a signal equal to the blank plus 3 standard deviations of the blank

63
Q

How is dynamic range related to LOQ and LOL?

A

dynamic range is the distance between LOQ and LOL

Instrumental Analysis (45 decks)

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