Lecture7-9

Question 0

What is spectrometry?

Answer 0

Method used to acquire a quantitative measurement of the spectrum.
Practical application.

Question 1

What is spectroscopy?

Answer 1

Science of studying interaction between matter and radiated energy.
Theoretical approach.

Question 2

What is light?

Answer 2

Light is electromagnetic radiation which can be understood as an electromagnetic wave that travels through vacuum at the speed of light c and can be characterized by either its wavelength lenda or its frequency v.

Question 3

Any material that can _____ light of a certain _____ will also _____ light of that _____

Answer 3

emit
wavelength
absorb
wavelength

Question 4

What is atomic absorption?

Answer 4

Atomic absorption is the measurement of the absorption of optical radiation by atoms in the gaseous state.

Question 5

3 forms of atomic spectroscopy?

Answer 5

1. Atomic emission signal (–>monochromator–>detector)
2. Atomic absorption, Hollow-cathode lamp
3. Atomic fluorescence signal, Laser

Question 6

What does the atomic emission transitions look like?

Answer 6

two arrows pointing downward.

Question 7

How does atomic absorption transitions look like?

Answer 7

two arrows pointing upward.

Question 8

How does atomic fluorescence transitions look like?

Answer 8

one arrow pointing up, two blue arrows pointing down (emission), one black arrow pointing down at excited states (nonradiative).

Question 9

How does atomic absorption signal work?

Answer 9

Hollow cathode lamp - P0 - Flame - P - Monochromator - Detector - Amplifier - Computer

Question 10

Formula to calculate Absorption A

Answer 10

Absorption A = log(Io/It) = kcd

Question 11

AFS

Answer 11

Atomic Fluorescence Spectroscopy

Question 12

Why AFS use more often than AAS?

Answer 12

AFS is often more sensitive than AAS because weak fluorescence signal can be observed above a dark background; not widely use.

Question 13

AAS

Answer 13

Atomic Absorption Spectroscopy

Question 14

Atomization

• flame (____)
• electrically heated ____ ____ (GFAAS) }
• ____ ____ ____ (ICP) } of most practical relevance
• heated quartz cell (____ ____)

Answer 14

FAAS
graphite furnace
inductively coupled plasma
hydride technique

Question 15

Name of the tube that inject liquid to glass bead?

Answer 15

pneumatic nebulizer

Question 16

Minimum amount of sample that is needed for FAAS?

Answer 16

1-2mL

Question 17

Most common fuel oxidizer: ____/__
30 so-called ____ that from stable oxides -> need ____ flame to prevent this. Height in flame at which ___ atomic absorption/emission observed must be manually optimized and depends on:____, ____, ____

Answer 17

acetylene/air
“refractory elements” hotter maximum
element, fuel / oxidizer flow rate / nebulization speed

Question 18

Graphite furnaces: electrically heated ____ can also be used to generate atoms from sample analyte.
Advantages? (2 of them)

Answer 18

hollow graphite tube

1. less sample needed (5-100uL)
2. more sensitive than flame

Question 19

How long do atoms in the ground state reside in optical path? also called ____?

Answer 19

flame < 1s

furnace: several seconds b/c atomic “cloud” confined by tube

Question 20

How are atoms generated? What must be carefully optimized? What should be carefully for first step and second step?

Answer 20

dry - ash - atomize - clean - cool
temperature
avoid splatter
no analyte loss

Question 21

Ar gas passed through graphite tube, typical temperature program:

Answer 21

dry: 60C for 20s (remove solvent)
ash: 1400C for 60s (destroy organic matter)
atomize: (2300C for 6s)
clean: 2700C for 3s + cool (60s)

Question 22

For elements that form _____ with carbon from the tube, use ____

Answer 22

carbides

pyrolytically deposited carbon tubes

Question 23

Additional advantages of furnace:

Answer 23

1. pre-concentration
2. analyze solid samples
   (impossible with flame)

Question 24

Everything other than analyte in sample = _____, ideally _____ decomposes and vaporizes during ashing if ____ constitutes a problem -> need to add a _________, to increase volatility of ____ and decrease volatility of _____.

Answer 24

matrix matrix matrix matrix modifier matrix analyte

Question 25

NaCl + NH4NO3 = NaNO3 + NH4Cl, it's called ____

Answer 25

sublime (at 400C)

Question 26

Other matrix modifiers: Pd(NO3)2, added to seawater to ____ volatility of Sb: without modifier 90% of Sb lost during ____ step at 1250C; with the ______ seawater matrix can be evaporated at 1400C without loss of Sb.

Answer 26

decrease | matrix modifier

Question 27

Other matrix modifiers: Mg(NO3)2, raise ____ temperature of Al at high temperature of Al ____ by MgO (g). 3MgO(g) + 2Al(s) -> 3Mg(g) + Al2O3(s) when all MgO(g) evaporated reaction no longer occurs and Al2O3 decomposes.

Answer 27

atomization | retarded

Question 28

______ increases boiling point of ____ -> higher ____ temperature can be used without losing analyte.

Answer 28

matrix modifier analyte ashing

Question 29

Inductively coupled plasma: induction coil connected to a high ____ current generator -> generates ____ magnetic fields ____ oriented inside coil -> Tesla discharge ______ ionizes Ar -> free e- accelerated by _____ collide with ____ and ____ + transfer energy to entire gas (6000-10000K)

Answer 29

frequency oscillating axially ignition radio frequency field atoms ions

Question 30

Advantage of ICP: high temperature, _____ + _____ inert Ar environment, this eliminates _____ (flame), allows _____ multielement analysis.

Answer 30

stability relatively interferences simultaneous

Question 31

Heated quartz cell (hydride technique) advantage: _____ and _____ of analyte and complete _____ of interferences.

Answer 31

separation enrichment | elimination

Question 32

How temperature affects atomic spectroscopy: temperature determines: 1. ____ to which sample breaks down (FAAS/GFAAS) 2. ____ to which atom found in ____/____/____

Answer 32

degree extent ground/excited/ionized state

Question 33

Boltzmann distribution describes _______ of different states at _______. If _____ exists, _________ (N*/N) of any two states is _________. k (Boltzmann's constant) = _____

Answer 33

``` relative populations thermal equilibrium equilibrium relative population N*/No = g*/go *e^(-delta E/kT) k = 1.381*10^(-23) J/K ```

Question 34

Critical in atomic emission spectroscopy that ____ is very stable or _______ will vary significantly.

Answer 34

flame | emission intensity

Question 35

Instrumentation: atomic line widths. Beer's Law requires that _____ of _______ must be narrower than _____ in atomic sample vapor, otherwise measured _____ not be _____ to sample concentration.

Answer 35

linewidth radiation linewidth absorbance proportional

Question 36

Linewidth governed by ______

Answer 36

Heisenberg uncertainty principle

Question 37

Hollow cathode lamp: _____ cannot isolate lines narrower than _____-> produce narrow lines with correct lenda, we use hollow cathode lamps.

Answer 37

monochromators | 10^(-3) - 10^(-2)

Question 38

Hollow cathode lamp made of element we want to analyze for:1. when 500V applied -> gas ____ and + ions accelerated toward ____2. lamp maintained at ____ 3. ____ strike cathode -> metal ____ into gas phase -> gaseous atoms collide with high energy electrons to ____ protons 4. atoms in lamp lamp emission narrower

Answer 38

ionized cathode 2-30mA cations sputtered emit flame

Question 39

multi-element detection with inductively coupled plasma: an ______ does not require any ____ and can measure as many as ___ elements simultaneously.

Answer 39

ICP-AES lamps 70

Question 40

two types of configurations

Answer 40

1. color plate | 2. box purged with Ar to exclude O2 to observe lenda 100-200nm halogens + S,P,C and N

Question 41

Standard solutions for FAAS not necessarily suitable for _____ techniques and GFAAS: need extremely pure water and ___ to avoid contamination (_____, ____); clear room conditions (no dust). Standard solutions have limited ____ and _____ will change the _____ over time.

Answer 41

ICP-based aids trace metal grade acids, Teflon vessels shelf life evaporation concentration

Question 42

Definition of interference?

Answer 42

any effect that changes signal while analyte concentration remains unchanged.

Question 43

_____ interference: _____ reactions decreasing [ ] of analyte atoms. _____ interference: _____ of analyte atoms dereasing [ ] of neutral atoms. Desired signal is ____.

Answer 43

Chemical chemical | Ionization ionization decreased

Question 44

Virtues of inductively coupled plasma: eliminates many common ____: two times as hot as flame, _____ more complete and intense and no formation of ______.

Answer 44

interferences atomization refractory oxides/hydroxides

Question 45

____ remarkably free of background radiation. _____ is a problem in FAAS, but not in ____ because _____ more uniform.

Answer 45

plasma self-absorption ICP temperature

Question 46

ICP-AES: atomization at > ____, dominant form today. In contrast to AAS and AFS _____ is needed. ______ proportional to analyte [ ] in sample.

Answer 46

6000K no lamp emission intensity

Question 47

ICP-MS: ionization energy of Ar: ___, ___ than that of all elements except He, Ne and F. Ar plasma: analyte elements ionized by ____ with Ar+ excited Ar atoms or energetic e-, direct plasma at MS, can measure ___ and ___ at very low [ ].

Answer 47

15.8eV greater collisions | metals metalloids

Question 48

matrix can have ____ effect on yield of ions generated in plasma: ___________ in same matrix as unknown -> ______

Answer 48

profound calibration standards standard addition

Question 49

_____ interference: interference by ___ of similar mass-to-charge ratio. Use a high resolution _____ to resolve species.

Answer 49

isobaric ions ICP-MS

Question 50

What's normal mass?

Answer 50

integer mass of most abundant isotope of each of the constituent atoms.

Question 51

MS = a technique for studying masses of ___/___/______: desorb ____ species; ____ them; ____ ions; separate ions according to ___/___ ratio; ____. If all species have a charge of +1, m/z is ___ to mass; if an ion has a charge of +2, m/z is ___ of mass.

Answer 51

atoms/ molecules/ fragments of molecules gaseous ionize accelerate mass/charge (m/z) detection equal half

Question 52

magnetic sector mass spectrometer formula:

Answer 52

m/z = eB^2r^2/2V

Question 53

EI stands for? e- emitted from a hot ____ accelerated, ___ electrons interact with incoming (neutral) molecules. ____ of molecules (M) absorb ____, enough for ionization.

Answer 53

electron ionization filament 70eV 0.01% 12-15eV

Question 54

If we lower E in ______, _____ yield of ions + less ______, higher chance to observe M+. 70eV customarily used because it gives reproducible _____ that can be compared with spectra in a library. Most intense peak = _____. ____ of all other peaks expressed as % of _____

Answer 54

ionization source lower fragmentation fragmentation base peak intensities base peak intensity

Question 55

Resolving power: each mass spectral peak has ____, _____ how closely 2 peaks could be spaced and still be resolved the _____ the resolving power of a ___, better able to separate 2 peaks of similar mass.

Answer 55

width limits higher MS