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 Acetylene+air 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.
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
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.
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, RSD<=1% 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