Temperature profiles for a nature gas/air flame.

1
(No Transcript)
2
Temperature profiles for a nature gas/air flame.
3
(No Transcript)
4
(No Transcript)
5
How does AA work?
The light transmitted through the flame is
measured by the detector. The absorbance has
linear dependence on the population of Cu atoms
in flame, and therefore the concentration of the
Cu2 in sample solution.
Hollow cathode lamp emits light at a wave- length
that can be absorbed by Cu atoms.
Lamp
Acetyleneair
Sample soln containing Cu2 is aspirated to
a flame. At high temp, solvent evaporates
Cu-salts dissociate into atoms. Cu atoms
absorb light from the lamp, so the intensity of
light transmitted through the flame is
attenuated.
6
(No Transcript)
7
(No Transcript)
8
(No Transcript)
9
(No Transcript)
10
(No Transcript)
11
(No Transcript)
12
Expt. VIII. Trace Copper by Atomic Absorption
Important-- Instrument time is assigned,
check. --One week before your scheduled time
slot, finish micropipet calibration and solution
preparation (2hr)
You will do the following --Calibrate micropipet
-- obtain sample (Ni/trace Cu) and standard
(pure Cu) --dissolve metal sample and standard in
HNO3 --prepare std. and sample solutions
(standard addition) --AA measurement
13
Outline of Procedure
1. Sample stock soln Ni/Cu sample weighed by
difference, in dilute HNO3, in hood, dilute
to 250 mL. 2. Std stock soln dissolve Cu wire
(weighed on weighing paper) in dilute HNO3.
dilute to 500 mL. Important make sure to use
deionized water, distilled water contains Cu2
gives large blank signal. 3. Multiple standard
addition technique (use micropipet) In order to
minimize matrix effects (e.g. high conc. of Ni in
sample affect accurate quantitation of Cu2 at
low conc. 0.01-0.42) Important Don't dilute to
volume (50 mL) until day of analysis. Because
Cu2 conc. is low, relative error due to
adsorption of Cu2 to glass would be large.
14
4. Measure absorbance TA will give
instructions. --always have soln aspirating (e.g.
H2O) in order to cool the burner. --aspirate in
order specified, then repeat series --enter only
one digit to right of decimal for
volumes(49.3) 5. Use and calibration of 50 mL
piston-operated micropipet. --depress and release
slowly--immerse 0.5cm -- no liquid outside
tip--six times, RSDlt1 or repeat. --save tip
until the exp. is done--record kit , get the
same 6. Calculations computer print out graph,
find intercept.
Least squares pp72-75
15
(No Transcript)