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Analytical chem315 > 8-9(17) > Flashcards

8-9(17) Flashcards

0
Q

How is height in the flame at which maximum atomic absorption / emission observed manually optimized?

A

depends on:
element
fuel/oxidizer flow rate
nebulization speed

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1
Q

How much sample is required for flame?

A

5% of initial sample (minimum of 1-2mL)

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2
Q

How to decrease spectral interference? (for flame)

A

increase temperature

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3
Q

What is the advantage of graphite furnace?

A

more sensitive than flame due to increased residence time

require less sample (5-100uL)

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4
Q

Graphite furnaces uses _____ heated ________. (light source)

A

electrically; hollow graphite tube

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5
Q

What is residence time? And what is the residence time difference between flame and graphite furnace?

A

the time atoms in ground state in the optical path
->in flame 1s
->in furnace several seconds (more than flame)
due to-> atomic cloud confined by the tube

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6
Q

What is the disadvantage of the furnace?

A

require more operator skill
-> precision and reproducibility is more accurate with machine.

  • manual injection 5-10%, auto sampler: 1%
  • temperature must be carefully optimized!
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7
Q

What are the stages for furnace to generate atoms?

3 stages

A 
drying(60 degree, 20s) = remove solvent
ashing(1400 degree, 60s) = destroy organic matter
atomization(2300 degree, 6s) 
clean(2700 degree, 3s) 
cool (60s)
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8
Q

During drying, we need to prevent ______. In Ashing the matrix was selectively burned off but we must prevent analyte loss because it is too ______.

A

Spatter; volatile

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9
Q

We want to prevent ______ of graphite during ashing (20-1400 degree), or during atomization (to 2550 degree).
The solution is using ____ to pass through the graphite tube.

A

oxidation; Ar

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10
Q

Every element have _____ optimal _______ during atomization.

A

unique; atomize temperature

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11
Q

If Ar gas flow rate is _____, the residue time increases, in which the _______ linger _____ in graphite tube.

A

reduced; atomic cloud; longer

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12
Q

Longer residue time causes _____ absorption, and result in _____ signal which will decrease ______.

A

more; stronger; detection limit

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13
Q

______ in temperature in the _______ furnace would cause ______. It was due to 60% of atom _____in the cooler end of the tube and _____.
It can be solved with a _______ heated graphite furnace, which can reach higher temperature ______than normal furnace (voltage heating). It also ______ signal intensity, and decrease ______.

A

difference;longitudinal; loss of analyte;
diffuse; condense;
transversely; faster;
increase; detection limit.

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14
Q

Element in the sample may form _____ with graphite tube and is very stable. A solution would be using ______ deposited carbon tubes.
It improves _______ for Mo, V, Ti.

A

carbide;
pyrolytically (coating);
detection limit;

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15
Q

The advantage of furnace that flame cannot achieve are ______ and ______.

A

1) pre-concentration = adding multiple injections that decrease detection limit
2) analyze solid sample =lower detection limit (100 times lower)

*furnace is more flexible

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16
Q

Matrix should ideally ______ and ______ during ashing, but it may volatile analyte which could be prevented by _______, that increase _____ of analyte. Example would be addition of ______ to sea water to ____ salt.

A

decompose; vaporize;
matrix modifer; boiling point;
NH4(NO3); sublime;

  • Pb(NO3)2 for Sb detection ->decrease Sb volatility
  • Mg(NO3)2 for Al -> raising atomization temperature; prevent (retard)evaporation of Al
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17
Q

Inductively coupled plasma rips off electron from ___ using ______ generated by induction coil connected to a high frequency current generator.
Ar is ____ and lead to free electron accelerates collide with atoms and ions and transfer energy to entire gas, that heats up about ______

A

Ar gas; oscillating magnetic field;

ionized;6000 - 10,000K

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18
Q

Advantage of ICP ?

3 things

A

1) high temperature: eliminate interference in flame (due to flickering flame)
2) inert Ar environment: do not contain explosive Oxygen that would also become interference due to oxide formation
3) allow multiple element analysis at the same time

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19
Q

A technique that dissolves sample with acid and form gaseous hydride and _____ it for analysis is called ______.
It’s advantage is _____ and ____ of analyte and complete elimination of _____. Therefore the _____ is lower than graphite furnace.

A 
volatile; hydride technique(heated quartz cell);
separation; enrichment; interference;
detection limit (*except Sn)
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20
Q

Temperature affects emission _____ than absorption because emission depends on the _____ of_____ which is proportional to emission______.
Because temperature affects on atomic spectroscopy determines the _____ and _____.

A

greater;
population; excited state; intensity
degree of sample break down; extent to which atom in ground/excited state/ions

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21
Q

_____ determines the relative ratio of population of excited state vs population of ground state at ______.

A

boltzman distribution; thermal equilibrium;

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22
Q

Atomic emission spectroscopy is usually carried out by ____ due to high temperature and there would be ______ population of excited state/ion

A

ICP (more stable-uses plasma); substantial

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23
Q

The ____ line width/band width must be narrower than line width in ________ for Beer’s law. If that requirement was not met, ______ measured is not proportional to _______.

A

radiation source; atomic sample vapour;

absorbance; sample concentration;

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24
Q

_______ cannot isolate lines narrower than 10^-3 to 10^-2 nm therefore ______ must be used.

A

monochromators; hollow cathode lamp;

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25
Q

Atoms generation occurred at different ______ for elements

A

height

26
Q

In the determination of Ca, if solution containing HCl, CaCl2 is easily _____, signal if solution contains SO42- or PO43-, ______ formed. Therefore a _____ temperature was required.

A

volatilized; Ca oxide/ pyrophosphate formed (which is stable)
higher;

27
Q

There are about 30 _______ element that form stable oxides.

A

refractory;

28
Q

________ must be subtracted from total signal.

A

flames emit light

29
Q

Light absorption of various flame types depending on _______.
If the most sensitive is in this range, common fuel/oxidant: acetylene/air flame is not ideal, solution is to use a ______ or use an Argon/hydrogen flame that will ______

A

wavelength;
less sensitive wavelength;
lose some sensitivity;

30
Q

line width is governed by __________ principle, and shorter lifetime of ________ will result in more uncertain energy.

A

Heisenberg uncertainty;

excited state;

31
Q

Hollow cathode tube contains _____ vapour of element that we want to analyze and Ne or Ar (in ______ )

A

very pure; low pressure(1-5 Torr);

32
Q

In the hollow cathode tube, when 500V applied, gas ______ and _____ accelerate toward _____.
Lamp maintained at 2-30 mA, then _____ strike cathode and metal _____ into ______. Gaseous atoms collide with _______ electrons to emit ____.

A

ionize; ions; cathode;

cation;sputtered; gas phase; high energy; photons

33
Q

Atoms in lamp ____ flame, which cause lamp emission _____.

A

smaller than; narrower;

34
Q

______ does not require ______ and can measure as many as ___ elements simultaneously. They transform analyte in to mini _____ itself.

A

ICP-AES; any lamp; 70; lamp

35
Q

The box of ICP-AES is purged with ____ to exclude _____ and it observe wavelength 100-200 nm, for halogen and S,P,C,N analysis.
ICP-AES separate wavelength of light from plasma in one dimension for _____, and two dimension for ____.

A

Ar; O2; photomultiplier tubes; CID ( charge on pixel) -> each pixel read individually at any time, no blooming

36
Q

_______ and _____ has similar detection limit for many element, ____ has lower detection limit, and ____ has lowest detection limit.
(ICP-AES,ICP-MS, FAAS, GFAAS)

A

ICP-AES; FAAS; GFAAS; ICP-MS

37
Q

_____ for FAAS is not necessarily suitable for ICP based techniques and GFAAS. Therefore extremely pure ________ needed to avoid _______ (such as trace metal grade acids, telon vessels)

A 
standard solutions (due to high detection limit of FAAS); 
water and acids; contamination;
38
Q

Ultrasonic nebulizer lowers detection limit for most elements by 1 order of magnitude due to the increased _____.

A

mass transfer of sample

*smaller sample droplets than pneumatic nebulizer

39
Q

clear room conditions are advisable for an _____ to avoid _______ with dust.
ex: cannot _____ in room where Cd measured by it which would increase _____.

A

ICP-MS; contamination;

smoke; background

40
Q

__________ have limited shelf life and evaporation will change _______ over time.

A

standard solutions; concentration;

41
Q

Three types of interference and what causes them?

A

1) spectral interference: unwanted signals overlapping with analyte signal
Ex: As and Cd lines
2) chemical interference: chemical reactions decreasing concentration of analyte atoms
Ex: SO42- and PO43- hinder the atomization of Ca 2+ in FAAS
3) ionization interference: ionization of analyte atoms decreasing concentration of neutral atoms
Ex: analysis of alkali metals at relatively low temperature
-> low ionization potential = most extensively ionized

42
Q

What is the difference between ions and neutral atoms? What method could use to compensate for many types of interference?
(in ionization interference)

A

ions have different energy levels from neutral atoms(ions in ground state diminishes):
-> cause decrease of desired signal (wavelength set is not useful)

Standard addition

43
Q

ICP is good for eliminates many common interferences because?

A

2 times as hot as flame
atomization more complete and intense
no formation of refractory oxides/hydroxides

44
Q

ICP is remarkably free of ________.

________ is a problem in FAAS, but not in ICP because ______ is more uniform.

A

background radiation;
Self-absorption; temperature;

  • problem due to temperature varies dramatically
  • self-absorption = emission goes to cooler part of the flame -> atom in ground sate: lower light intensity
45
Q

What does ICP-MS do? What is it used to measure? What is it’s disadvantage?

A

generating positive charge Ar cations
Ar has greater ionization energy than all element except He, Ne and F
Analyte elements ionize by collision with Ar cation, Ar atoms or energentic electrons
->and direct plasma at MS

Can measure metals and metalloids at very low concentrations and isotope ratios

inter face cannot tolerate >1% of salt

46
Q

One unique requirement for ICP-MS is?

A

atoms and ions travel in vaccum so they do not get deflected.

47
Q

matrix can have profound effect on _____ of ions generated in plasma, and can be solved with ______, calibration standards in same matrix as unknown.

A

yield;

standard addition;

48
Q

_______ interference is only present for ICP-MS, and it is due to the similarity of ____________ ratio.
The solution to the problem is using a ________ ICP-MS to differentiate or a _____________ to remove some ions (addition of NH3).

A

isobaric; higher resolution; DRC (dynamic reaction cell);

  • DRC allows measure of Cr by removing ArC+ interference
    by taking away the positive charge with NH3+
    *interference such as ArH+,ArC+, ArN+, ArCl+
49
Q

__________is the limit how closely 2 peaks could be spaced and still be resolved.
The better it is, the capability of separating 2 peaks of ______.

A

resolution power; similar mass

50
Q

tunning of magnetic field and or changing the voltage on ion acceleration plate would _______.
(for MS/MS)

A

select the ions with different band width

51
Q

____________ e- emitted from a hot filament and interact with incoming (neutral) molecules. Thus molecules converted in to ions.

A

Electron ionization;

52
Q

Briefly explain how MS works

A 
adsorb gaseous species (from condensed phase) and ionize them.
Accelerated ions (due to electric field) -> separate ions according to mass/charge ratio then detection.
if charge =+1-> mass/charge = mass
if charge = +2 -> mass/charge=1/2 mass
53
Q

Since almost _____ stable molecules have even number of electrons, when one electron kicked out, M+ may have so much energy (more than the required ionization energy) that would causes _____.
Thus do not exhibit _____ peak at the correct mass on the spectrum.

A

all; fragmentation; M+

54
Q

Solution to fragmentation is _____ in ionization source. But would also result in _______ of ions. But ______of observe M+.
Most intense peak is the ______ on the spectrum.
(EI-MS)

A

lower energy; lower yield; higher chance;

base peak;

55
Q

_________ produce less fragmentation than EI. Because ionization source filled with _______ (CH4, isobutane, NH3) at 1 torr.
Example, CH4 become the _______ donor and react with neutral molecule give it a + charge but also extra mass (1).
The observed MH+ peak need to -1.

A

chemical ionization; reagent gas; proton;

*also uses energy (100-200eV) enough to convert CH4

56
Q

mass spectrograph separate ions differing in mass by ____.

Leads to the discovering of varies _____.

A

1%; isotopes;

57
Q

advantage and disadvantage of furnace compare to flame.

A

Adv: more sensitive and require less sample than flame (1-2mL vs 1uL)
Disadv: requires more operator skill to find proper conditions for each type of sample -> poorer reproducibility with manual sample introduction. automated sample introduction gives good precision.

58
Q

process of furnace atomic absorption

A

1) drying (remove solvent) 20 -100 degree
2) ashing (remove as much matrix as possible without evaporating analyte) 100-500
3) atomization (vaporizes most of the rest of the sample for absorption measurement)500-2000 degree

59
Q

The advantage and disadvantage of inductive coupled plasma compared with flame.

A

adv: 2x as hot as flame-> uniform temperature -> reduce self-absorption. no lamps required, decrease chemical interference which allow emission instead of absorption. environment is Ar instead of oxygen(combustion gases). multiple element analysis at the same time.

Disadv: cost more to purchase and operate

60
Q

Four different interference:
______ overlap of analye signal with signals due to other element or molecules in the sample or with signals due to flame or furnace.

______ any component of the sample that decrease the extent of atomization of analyte through chemical reaction.

______ during the analysis of alkali metals at relatively low temperature and in the analysis of other elements at higher temperature. (loss of analyte due to ionization).

_______ overlap of different species with nearly the same mass to charge ratio in a mass spectrum.

A

spectral; chemical;ionization; isobaric;

61
Q

How to reduce spectral interference?

A

1) choose another wavelength for analysis

2) higher resolution spectrometers by resolving closely spaced lines.

62
Q

how to reduce chemical interference?

A

1) releasing agent addition
2) fuel-rich flame reduces certain oxidized analyte species
3) standard addition

63
Q

How to reduce isobaric interference?

A

1) high resolution mass spectrometers
2) check by measuring isotope ratio
3) dynamic reaction cell (thermal dynamically favourable reaction)

Analytical chem315 (5 decks)

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