8-9(17) Flashcards
How is height in the flame at which maximum atomic absorption / emission observed manually optimized?
depends on:
element
fuel/oxidizer flow rate
nebulization speed
How much sample is required for flame?
5% of initial sample (minimum of 1-2mL)
How to decrease spectral interference? (for flame)
increase temperature
What is the advantage of graphite furnace?
more sensitive than flame due to increased residence time
require less sample (5-100uL)
Graphite furnaces uses _____ heated ________. (light source)
electrically; hollow graphite tube
What is residence time? And what is the residence time difference between flame and graphite furnace?
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
What is the disadvantage of the furnace?
require more operator skill
-> precision and reproducibility is more accurate with machine.
- manual injection 5-10%, auto sampler: 1%
- temperature must be carefully optimized!
What are the stages for furnace to generate atoms?
3 stages
drying(60 degree, 20s) = remove solvent ashing(1400 degree, 60s) = destroy organic matter atomization(2300 degree, 6s) clean(2700 degree, 3s) cool (60s)
During drying, we need to prevent ______. In Ashing the matrix was selectively burned off but we must prevent analyte loss because it is too ______.
Spatter; volatile
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.
oxidation; Ar
Every element have _____ optimal _______ during atomization.
unique; atomize temperature
If Ar gas flow rate is _____, the residue time increases, in which the _______ linger _____ in graphite tube.
reduced; atomic cloud; longer
Longer residue time causes _____ absorption, and result in _____ signal which will decrease ______.
more; stronger; detection limit
______ 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 ______.
difference;longitudinal; loss of analyte;
diffuse; condense;
transversely; faster;
increase; detection limit.
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.
carbide;
pyrolytically (coating);
detection limit;
The advantage of furnace that flame cannot achieve are ______ and ______.
1) pre-concentration = adding multiple injections that decrease detection limit
2) analyze solid sample =lower detection limit (100 times lower)
*furnace is more flexible
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.
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
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 ______
Ar gas; oscillating magnetic field;
ionized;6000 - 10,000K
Advantage of ICP ?
3 things
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
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.
volatile; hydride technique(heated quartz cell); separation; enrichment; interference; detection limit (*except Sn)
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 _____.
greater;
population; excited state; intensity
degree of sample break down; extent to which atom in ground/excited state/ions
_____ determines the relative ratio of population of excited state vs population of ground state at ______.
boltzman distribution; thermal equilibrium;
Atomic emission spectroscopy is usually carried out by ____ due to high temperature and there would be ______ population of excited state/ion
ICP (more stable-uses plasma); substantial
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 _______.
radiation source; atomic sample vapour;
absorbance; sample concentration;
_______ cannot isolate lines narrower than 10^-3 to 10^-2 nm therefore ______ must be used.
monochromators; hollow cathode lamp;
Atoms generation occurred at different ______ for elements
height
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.
volatilized; Ca oxide/ pyrophosphate formed (which is stable)
higher;
There are about 30 _______ element that form stable oxides.
refractory;
________ must be subtracted from total signal.
flames emit light
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 ______
wavelength;
less sensitive wavelength;
lose some sensitivity;
line width is governed by __________ principle, and shorter lifetime of ________ will result in more uncertain energy.
Heisenberg uncertainty;
excited state;
Hollow cathode tube contains _____ vapour of element that we want to analyze and Ne or Ar (in ______ )
very pure; low pressure(1-5 Torr);
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 ____.
ionize; ions; cathode;
cation;sputtered; gas phase; high energy; photons
Atoms in lamp ____ flame, which cause lamp emission _____.
smaller than; narrower;
______ does not require ______ and can measure as many as ___ elements simultaneously. They transform analyte in to mini _____ itself.
ICP-AES; any lamp; 70; lamp
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 ____.
Ar; O2; photomultiplier tubes; CID ( charge on pixel) -> each pixel read individually at any time, no blooming
_______ and _____ has similar detection limit for many element, ____ has lower detection limit, and ____ has lowest detection limit.
(ICP-AES,ICP-MS, FAAS, GFAAS)
ICP-AES; FAAS; GFAAS; ICP-MS
_____ 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)
standard solutions (due to high detection limit of FAAS); water and acids; contamination;
Ultrasonic nebulizer lowers detection limit for most elements by 1 order of magnitude due to the increased _____.
mass transfer of sample
*smaller sample droplets than pneumatic nebulizer
clear room conditions are advisable for an _____ to avoid _______ with dust.
ex: cannot _____ in room where Cd measured by it which would increase _____.
ICP-MS; contamination;
smoke; background
__________ have limited shelf life and evaporation will change _______ over time.
standard solutions; concentration;
Three types of interference and what causes them?
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
What is the difference between ions and neutral atoms? What method could use to compensate for many types of interference?
(in ionization interference)
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
ICP is good for eliminates many common interferences because?
2 times as hot as flame
atomization more complete and intense
no formation of refractory oxides/hydroxides
ICP is remarkably free of ________.
________ is a problem in FAAS, but not in ICP because ______ is more uniform.
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
What does ICP-MS do? What is it used to measure? What is it’s disadvantage?
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
One unique requirement for ICP-MS is?
atoms and ions travel in vaccum so they do not get deflected.
matrix can have profound effect on _____ of ions generated in plasma, and can be solved with ______, calibration standards in same matrix as unknown.
yield;
standard addition;
_______ 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).
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+
__________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 ______.
resolution power; similar mass
tunning of magnetic field and or changing the voltage on ion acceleration plate would _______.
(for MS/MS)
select the ions with different band width
____________ e- emitted from a hot filament and interact with incoming (neutral) molecules. Thus molecules converted in to ions.
Electron ionization;
Briefly explain how MS works
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
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.
all; fragmentation; M+
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)
lower energy; lower yield; higher chance;
base peak;
_________ 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.
chemical ionization; reagent gas; proton;
*also uses energy (100-200eV) enough to convert CH4
mass spectrograph separate ions differing in mass by ____.
Leads to the discovering of varies _____.
1%; isotopes;
advantage and disadvantage of furnace compare to flame.
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.
process of furnace atomic absorption
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
The advantage and disadvantage of inductive coupled plasma compared with flame.
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
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.
spectral; chemical;ionization; isobaric;
How to reduce spectral interference?
1) choose another wavelength for analysis
2) higher resolution spectrometers by resolving closely spaced lines.
how to reduce chemical interference?
1) releasing agent addition
2) fuel-rich flame reduces certain oxidized analyte species
3) standard addition
How to reduce isobaric interference?
1) high resolution mass spectrometers
2) check by measuring isotope ratio
3) dynamic reaction cell (thermal dynamically favourable reaction)
