Quiz 2

Question 1

What is the purpose of a radiation detector?

Answer 1

convert energy to electrical signal for detection and analysis

Question 2

ideal detector properties

Answer 2

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

Question 3

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

Answer 3

no because of dark current

Question 4

spectral response

Answer 4

slope vs wavelength

Question 5

sensitivity

Answer 5

slope of response versus power

Question 6

detection limit

Answer 6

smallest significant measure

Question 7

Why can there never be an infinitely narrow spectroscopic line?

Answer 7

transition state lifetime

Question 8

types of photon detectors

Answer 8

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

Question 9

types of thermal detectors

Answer 9

pneumatic cells, thermocouples, bolometers, pyroelectric detectors

Question 10

types of multichannel detectors

Answer 10

photodiode arrays, vidicons, charge transfer devices

Question 11

QM definition of spectral line broadening

Answer 11

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

Question 12

What is the classical approach to explain natural line broadening?

Answer 12

damped oscillating dipole function

Question 13

How does energy decay result in a damped oscillating dipole function

Answer 13

decays from excited to ground

Question 14

how is excited state lifetime related to damping constant

Answer 14

by lifetime of decay

Question 15

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

Answer 15

longer ESL = sharper line

Question 16

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

Answer 16

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

Question 17

How are experimentally measured line widths related to natural line widths

Answer 17

experimental&raquo_space; natural 10^3

Question 18

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

Answer 18

towards detector shortens wavelength increasing frequency

Question 19

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

Answer 19

moving away from detector lengthens wavelength decreasing frequency

Question 20

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

Answer 20

increasing temp increases bandwidth

Question 21

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

Answer 21

cooling

Question 22

How does molecular collisional frequency change with sample pressure or temperature

Answer 22

increasing pressure or temp increases frequency

Question 23

what is the effect of collisions on spectroscopic excited states

Answer 23

decrease excited state, broaden bands

Question 24

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

Answer 24

decrease excited state lifetime broadens band

Question 25

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

Answer 25

lowering temp slows collisional broadening

Question 26

What is johnson noise

Answer 26

thermal

Question 27

what is shot noise

Answer 27

particles crossing junction

Question 28

what is chopping

Answer 28

synchronous demodulation; signal in phase passes positive, blocks negative

Question 29

When should a lock in amplifier be used

Answer 29

when signals are obscurred

Question 30

What is transmittance

Answer 30

power after divided by power before

Question 31

What is the absorption coefficient (a)?

Answer 31

absorptivity, proportionality constant

Question 32

What is the molar absorption coefficient ε

Answer 32

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

Question 33

How do instrumental sources of deviation depend on concentration?

Answer 33

it does not

Question 34

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

Answer 34

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

Question 35

How does polychromatic radiation affect beer's law linearity?

Answer 35

increases deviations, increases ε' + ε''

Question 36

How does stray light affect beer's law linearity?

Answer 36

negative

Question 37

How does slit width affect beer's law linearity?

Answer 37

decreases absorbance

Question 38

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

Answer 38

absorbance greater than 1 AU decreases precision

Question 39

How do chemical reactions and equilibria affect linearity?

Answer 39

What type of photochemical effects will influence linearity?

Question 40

What is the effect of fluorescence?

Answer 40

increases T, negative deviation

Question 41

What is the effect of light scattering?

Answer 41

decreases T, positive deviation

Question 42

What is spiking?

Answer 42

add increments of standard to identical volume samples

Question 43

what is the method of standard addition?

Answer 43

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

Question 44

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

Answer 44

complex samples with high potential matrix effects

Question 45

assumptions for method of least squares

Answer 45

assume linear relationship and measurement error (not x)

Question 46

what is ordinary or simple linear regression?

Answer 46

area peak versus concentration

Question 47

what is the independent variable in linear calibration curve

Answer 47

x

Question 48

what is the dependent variable in linear calibration curve

Answer 48

y

Question 49

how is external calibration performed

Answer 49

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

Question 50

external calibation

Answer 50

calibrate when no matrix interference in analyte

Question 51

method of single addition

Answer 51

matrix almost identical for successive additions in standard

Question 52

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

Answer 52

single assumes linearity, uses only 2 increments

Question 53

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

Answer 53

saves time and sample

Question 54

Internal standard method

Answer 54

substance added in constant amount to all standards in analysis

Question 55

How is an internal standard used in a calibration

Answer 55

plot ratio of signals to concentration

Question 56

advantages of internal standard

Answer 56

compensate for errors

Question 57

disadvantages of internal standard

Answer 57

hard to find and introduce reproducibly

Question 58

How does a response factor influence the internal standard method

Answer 58

used when unknown and standard do not respond identically

Question 59

How is precision measured?

Answer 59

standard deviation, average, variation

Question 60

How is bias measured?

Answer 60

population mean minus the true value

Question 61

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

Answer 61

slope limits sensitivity

Question 62

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

Answer 62

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

Question 63

How is dynamic range related to LOQ and LOL?

Answer 63

dynamic range is the distance between LOQ and LOL