Atomic Absorption

Question 1

how do atomic absorption and emission wavelengths differ?

Answer 1

Absorption:

Question 2

what type of lamp is used in atomic absorption spec?

Answer 2

hollow-cathode lamp

Question 3

how does a hollow-cathode lamp differ from deuterium and tungsten lamps?

Answer 3

atomic absorption experiments require lamps that produce light only at characteristic wave - lengths for the element(s) being analyzed.

Question 4

what would this lamp need in it to analyze Fe?

Answer 4

Fe
Hollow-cathode - it only produces light at the characteristic wavelengths for Fe, Ni, and Cr

Question 5

what is the simple schematic of an atomic absorption instrument?

Answer 5

lamp –> atomizer –> monochromator –> detector

Question 6

what is the role of the atomizer?

Answer 6

breaking the analyte down into gaseous atoms.

Question 7

how does the location and role of the monochromator differ in an atomic absorption instrument vs a UV/Vis instrument?

Answer 7

Atomic Absorption: removing light from the flame from other wavelengths from reaching detector.
UV/Vis: selecting the wavelengths of light that will go through the sample.

Question 8

how do molecular and atomic absorption bands differ?

Answer 8

Molecular: uses solutions in a cuvette. (non-destructive)
Atomic: cannot analyze directly in a cuvette. (destructive)

Question 9

what is the role of the flame in atomic absorption experiments?

Answer 9

flame atomizes samples to produce atoms that are primarily in the ground electronic state.

Question 10

what is the tole of the flame in a flame atomic emission experiment?

Answer 10

promotes some atoms to excited electron states from which they can emit photons to return to lower energy states

Question 11

how much of the sample actually gets to the flame? why?

Answer 11

~5% because once the sample becomes an aerosol, the excess liquid is flowed out into waste.

Question 12

what is signal to noise (S:N) what is it used for?

Answer 12

determines the lower limits of detection and quantitation
determines what can be reported reliably.

Question 13

what is LLOD and LLOQ?

Answer 13

LLOD (detection): where signal is 3x the noise.
LLOQ (quantitation): where signal is 10x the noise.

Question 14

how does a furnace differ from the flame?

Answer 14

furnace is like a tube, Ar gas flows through to keep it from igniting, and it uses longitudinal heating, leaving cool spots at the end.

Question 15

in general, how does the furnace work? - what are the four stages of the heating steps?

Answer 15

1. Drying - dries the sample
2. Charring - decomposes the sample
3. Atomizing - atomizes the sample
4. cleaning - cleans out remaining residue

Question 16

why is transverse more consistent? what sometimes happens with longitudinally heated furnaces?

Answer 16

The transverse is more consistent because it is more evenly heated.

Question 17

what is the L’vov platform?

Answer 17

small platforms in the furnace

Question 18

when do we know the furnace needs replacing?

Answer 18

degradation of peak shape
loss of precision
large change of slope of a calibration curve

Question 19

what do we use a matrix modifier for?

Answer 19

added to matrix to suppress unwanted background signals from matrix
(increases volatility of matrix - vapor at lower temp)
(decreases volatility of anayte - vapor at higher temp)

Question 20

what is plasma?

Answer 20

a gas hot enough to contain ions and free electrons

Question 21

how do ICP and MP differ?

Answer 21

ICP: inductively coupled plasma (liquid sample is pumped slowly into nebulizer)
MP: microwaved plasma (uses nitrogen, can look for more than 1 element at a time)

Question 22

what is the impact of temperature on atomic emission spectroscopy?

Answer 22

the degree to which the a sample breaks down into atoms
the extent to which a given atom is found in its ground, excited, or ionized states

Question 23

what is the role of monochromator in atomic spectroscopy?

Answer 23

to stop polychromatic light emitted from the flame form burying the signal form lamp (AA) and sample (emission)

Question 24

how do we perform background correction?

Answer 24

beam chopping and deuterium lamp

Question 25

how does beam chopping work?

Answer 25

A) when the chopper transmits the hollow-cathode lamp, light from both lamp and flame to reach the detector
B) When it blocks, only flame light can reach the detector
(subtracting signal A from signal B)

Question 26

how does deuterium lamp correction work?

Answer 26

light from lamp is alternated through the flame

Question 27

what are four types of interferences??

Answer 27

1. spectral: unwanted signals overlapping analyte signal
2. physical: viscosity / density of solutions altering nebulation and transport of analyte atoms
3. chemical: chemical reactions decreasing the [] of analyte atoms
4. ionization: ionization of analyte atoms decreasing the [] of neutral atoms.

Question 28

why might I pick one technique over the other? Flame, furnace, and plasma

Answer 28

Cost of fuel (acetylene vs argon)
sensitivity needs
desire to analyze multiple compounds simultaneously.