Extra Practice AA
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Most common absorption peaks result from
3S -> 3p adn 4p transition
What are resonance Lines
Energy level of diagram of sodium
AA happens in _______ shell electron
Two types of broadening:
- Doppler boradening: Caused by atomsback and fourth movement.
- pressure boradening: Higher flow rate, causeing more atoms to interact with other species( the most affect happens in higher T)
What is the purpose of Chopper?
- It alternates HCL signal between the sample and reference beam
- it corrects for power fluctuation and electron noise
How do you distingush between lamp electrical transition and atoms electrical transition?
Lamp electrical transition resonance line width is narrowe because it happens at lower tempreture and pressure than atoms in the flame
- Electrodless Discharge Lamp
- Used as an alternative to HCL
Formation of fine suspension of liquid
- Graphite Furnace
- Cold Vapor
Name two methods of flame atomization? what is the main differece between them?
- Total consumption Burner
- Laminar Flow Premix Burner
- the main difference is in total consumption burnerthe sample,fuel, and oxidant enter the flame without being mixed, while they are mixed before entering the flame in Laminar Flow method.
What is the advantage and disadvantage of the two method of flame atomization?
- 1-Total Count Burner:
- Advantage: Reduce the chace of explosion
- Disadvantage: Not stable flame due to large sample droplets and shorter flame path length 2-Laminar Flow Premix Burner
- Advantage: Quiter flame and longer path length.
- the previous mixing of sample,fule, and oxidant enhance sensitivity
- High velocity flame prevents flash back
- Disadvantage: less than 1% of the sample reaches the flame
Name two oxidants in Flame AA
- Air Acetylene
- N2O ( hottor and noiser Flame)
___________ region of flame is rich in atoms
What is the purpose of sensitivity check?
- To find the optimum spot of the burner head
- Burner head changes depending on the characteristics of the analyte
How could you adjust the temperature?
- Control the air flow, air acetylene
- fule flow
- burner head position
ways to turn the samples into solution on AA
- slight acidification
- Hot plate
- Microwave digestion
Which technic has the lowest detection limit between Flame and Flameless atomization method
Flameless method because the sample stays longer in the light beam
Which gas is used to purge the graphite tube and why?
- Ar is used to purge the tube and it is used to avoid oxygen gas from reaching inside to prevent explosion
- Ar is used to clean up the tube after usage; remove excess material during the dry and char phase
- Reduce oxidation of the tube
- Provides a protective layer from C reacting with N to produce Cyanogen
How does Matrix modifire works?
- Reacts with the analyte, tighten it up so the analyte does not evaporate, while other contamination evaporte at lower temperature
- Tighty up the contaminants and let the analyte to evaporate
why sample can not be heated up to atomization temperature at once?
it will splatter
Stages of temperature programming in graphite furnace
- Fixed Temperature and time
- used to remove solvent
- 2- Char (ashing)
- decompose matrix( 200-800 C)
- Evaporating the analyte
What type of samples are usually analyzed on GF?
In hydride Generation, the sample is mixed with __________ and ____________
acid , reducing agent (1% NaBH4)
What type of metals are analyzed on Hydride generation
Rank the following in decreasing of detection limit
ICP, AA, Hydride, GF
Flame AA, ICP, Graphite Furnace, Hydride Generator
What is Hydride
Hydrogen gas being on group 7: H-
HGAA requires nebulizer. (T/F)
- although HGAA has identical system to AA
How the compounds are atomized in HGAA
How metalloids samples are converted to volatile hydride in HGAA
Through adding HCl and sodium borohydride (NaBH4)
Type of pump used in HGAA
What type of container is used for waste collection in AA and why?
The container if glass because 50% of the waste is high in acid
What type of AA causes sepeciation?
Which of the following is/are affected by HGAA
As3+, As5+, Se2+,Se4+
As3+ and Se4+
What is the optical cell in HGAA
Silica glass tube
Characteristics of Silica tube in HGAA
- Transparent to UV/Vis light
- thermally stable at high T
What is the purpose of optical cell in HGAA
It is where the decomposition of metalloides to their elemental form takes place, so they can absorb HCL light beam
How to oxidize and reduce Se
- Reduce: Boiling HCl
- Oxidized: Adding HNO3 or H2O2 ( Strong Oxidizing agent)
_________ is the metal that is volatile at room T
Hg can be measured on AA without the use of atomizer (T/F)
- True, because Hg has a high vapour pressure due to it volatility
- This reduces the interferences, for the sample evaporates while the matrix are left behind
Gaseous mercury is acheive by________
using a reduction reaction ( Oxidizing agent ex: KMNO4) to convert Hg to it elemental form :Hg22+
How does the A is measured in Cold AA
Peak height vs Hg conc.
How to solve the problem of spectral interferences?
- Use another wavelength
- use chemicals which precipitate the matrix and free the analyte
- Use ICP if possible
- Alternating between AA lamp and D2 lamp
Background correction relies on _________ and usually is ___
- atomic line being very narrow
____________ has a broader band of light.
Composition of background in D2 depends on ___________
position on a flame
what is Zeeman Effect
Graphite Furnace is covered with strong and big magnatic field. this cause a line up of molecules based on their charge. This results in the change of the excitation wavelength.
In Zeeman effect, pi compoundas polarized________ to the direction of magnatic field, and absorbed by ___________; while Sigma compounds polarized ________ to the direction of magnatic field and is absorbed by ___________.
- parallel; analyte and background
- perpendicular; only background
What are the outcome of chemical interferences and how they are solved?
- Chemical interferences :
- 1-A compound will react with other chemicals
- produces precipitate
- causes a low detection limit
- 2- Ionization Interferences
- To solve the problem:
- Use releasing agent ( Sr or La): so the reagent reacts with matrix, leaving the analyte free
- 2-use Masking agent
- EDTA: bonds with analyte, preventing the anlayte from forming precipitation with other interferences
- Form stable but volatile complex with analyte
How to solve ionization interferences?
Add ionization suppressor in which it will provide the needed electrons ( EIE: Easily Ionized Elements)
Why Polyethylen bottoles are not suitable for holding up HC's
Polyethylen bottoles absorb HC's
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