Unit 7

Question 1

define chromatographic detector

Answer 1

a device that measures the change of composition of the effluent

gives you the retention time

Question 2

what is the qualitative and quantitative information pertinent to chromatography?

what is each defined by?

Answer 2

qualitative: identity of chemicals in the sample
- retention time of chemical entering detector
- detector specific (ie. absorbance wavelength, m/z in mass spectrum)

quantitative: mass or concentration of chemicals entering the detector
- signal intensity vs amount of chemical

Question 3

detectors are coupled w/ what?

Answer 3

liquid chromatography
ion chromatography
capillary electrophoresis

Question 4

what wavelength is used for UV-Vis?

Answer 4

190-600nm

Question 5

what is an important law for UV-vis?

Answer 5

beers law

Question 6

how is the wavelength for UV-Vis selected?

Answer 6

it is wavelength that provides max absorbance

Question 7

what is the equation of beer’s law?

what are each of the variables?

Answer 7

A=E.L.c

A= absorbance
e= molar extinction coefficient
K= path length of cell
C= molar sample concentration

Question 8

what are systems used for UV-Vis?

Answer 8

1. one fixed wavelength
2. one variable wavelength
3. multiple variable wavelengths (DAD or PDA)

Question 9

what is UV-vis coupled to usually?

Answer 9

HPLC
IC
CE

Question 10

what is DAD?

Answer 10

diode array detector

Question 11

what is PDA?

Answer 11

photodiode array PDA

Question 12

define fluorescence

Answer 12

measures optical emission of light by molecules after they have been excited at a higher energy wavelength

Question 13

what does the conductivity detector measure?

what is it common for?

what are disadvantages?

Answer 13

electric conductivity (presence of ions) of the solution eluting out from the column

common for analysis of inorganic ions and small organic substances (organic acids and amines)

disadvantages: limited working range, low sensitivity and specificity, strong dependence on temperature

Question 14

what does TCD stand for?

what does TCD do?

what does it detect?

Answer 14

thermal conductivity detector

compares the thermal conductivities of 2 gas flows: the pure reference gas and the mobile phase coming from the GC

in the presence o the sample, the power required to keep the wire temp constant changes

it is a universal detector

Question 15

what does FID stand for? what does it detect? how is the signal produced?

Answer 15

flame ionization detector

detects carbon:

signal production:

• the combustion of organic molecules in the flame generates ions
• the current produced by collecting ions is proportional to the number of carbons in the molecule

Question 16

what does ECD stand for?

what does it detect?

how is the signal produced?

advantageS?

Answer 16

electron capture detector

detects: electronegative halogen-containing organis SO2

signal prod:

• e emitted by beta source (63Ni) ionizes the gas
• the presence of electronegative functional group reduces the current

adv

• insensitive to amines, alcohols, hydrocarbons
• relatively cheap

Question 17

what does GC olfactometry (GC-O) detect?

how is the signal produced?

Answer 17

detects odours

signal is produced from using human assessors as a sensitive and selective detector for odour-active compounds

Question 18

what do you do if a peak valley is <25-50% of the peak height of the smaller peak?

Answer 18

separate the two peaks with a line drawn from the valley bottom to the projected baseline

Question 19

what is the valley criterion?

Answer 19

25% or 50%

Question 20

in a chromatogram, how many points per peak is needed for identification? and for quantification?

Answer 20

identification: 10 points
quantification: 15-20 points

Question 21

what is IDL? what is it also known as?

define it.

Answer 21

instrument detection limit

also known as sensitivity

smallest amount of material detectable in a matrix relative to the amount of material analyzed. Given in atomic mole or wt fractions

Question 22

what equation is associated with IDL?

Answer 22

S/N=3

Question 23

what is the dynamic range?

Answer 23

the ratio between the maximum usable indication and the minimum usable indication (detection limit)

Question 24

what is the equation to determine linear dynamic range?

Answer 24

response = response factor * concentration

Question 25

how can you differentiate linear and non-linear dynamic range?

Answer 25

linear: response is directly proportional to concentration

non-linear: dynamic range is non-linear to concentration, especially at high concentrations

Question 26

when does the signal plateau, even if concentration is high

Answer 26

at saturation

Question 27

what needs to be considered to select an appropriate detector?

Answer 27

• compatibility w/ sample matrix and mobile phase
• acquisition speed (HPLC vs UHPLC)
• sensitivity (quantity of analyte in sample vs noise)
• selectivity (presence of interfering material and elements)
• linearity (does it cover the concentration range expected in the samples?
• destruction of sample (non-destructive = serial detectors)