Fluorimetric Determination of Aluminum: Standard Addition Method
Apparatus
Fluorimeter, pH meter, combination pH electrode, pH standards (7 and 10 preferably), cuvette - path
length 10 mm (check out from the stock room and clean, return); ring stands (6), 100 ml separatory
funnels (6), 50 ml volumetric flasks (6), funnels (6), burettes (3), 10 ml graduate cylinder (1).
Chemicals
200 ppm solution aluminum (standard-stock); 2% solution of 8-hydroxyquinoline in 1 M acetic acid;
chloroform; de-ionized water; anhydrous sodium sulfate; 2M ammonia; 6M HCl; acetone (for
washing in a wash bottle).
Procedure:
Prepare 100.00ml of 2 ppm aluminum (working standard) solution by diluting the standard 1:100 of the stock
aluminum solution. Prepare 100ml of 1 M (meaning the concentration of ‘NH3’ moiety is1M) ammonia/ammonium
chloride buffer of pH 9.4 by adding 6M HCl solution in a dropwise fashion to 50ml of 2M ammonia and perform the
appropriate dilution.
Add 25.00ml aliquots of de-ionized water in to each of the six clean separatory funnels (check for leaks and
stoppers). Pipette 2.00-ml aliquots of the unknown solution in to five separatory funnels from a burette. Transfer
0.00, 2.00, 4.00, 6.00 and 8.00 ml respectively of the Al+3 working standard solution (2ppm) in to the five labeled
separatory funnels from a burette. Add 2.0 ml of the 8-hydroxyquinoline solution and 4.0 ml of the buffer solution
into each of the separatory funnels from burettes. Prepare a blank in the sixth funnel (all but aluminum).
Extract the complex formed in each separatory funnel three times with three 10ml aliquots of chloroform (shake for
one minute each time after adding chloroform). Transfer carefully the chloroform aliquots from each separatory
directly in to a separate 50.00ml volumetric flask through clean funnels. Rinse the funnel with chloroform into the
flask (use a dropper). Fill each volumetric flask to the mark with chloroform, add about 2 g of anhydrous sodium
sulfate, shake well and let the sodium sulfate to settle to the bottom.
Obtain the emission (fluorescence) spectrum of the solution of the highest concentration in a 10mm cuvette by
exciting at ex,max  400nm i.e. holding the excitation monochromator at 400nm; and varying the emission
monochromator from 410nm, upwards. Locate the emission maximum, em,max. [Run the excitation (absorption)
spectrum; hold the emission monochromator at the emission maximum located and vary the excitation
monochromator from 200nm up to (em,max-10) nm. From the excitation (absorption) spectrum locate the ‘true’
ex,max of absorption (excitation wavelength) of the aluminum complex. Set the excitation monochromator at the
ex,max.]
Starting with the solution of highest concentration of aluminum, obtain the emission fluorescence spectrum of each
of the solutions in a 10mm cuvette by exciting at  max. Record all spectra on the same graph paper keeping the same
plotter settings.
Dispose all used chloroform into the proper waste container. Clean up and return all glassware (you may use a few
ml of acetone for cleaning).
Plot the fluorescence peak intensity (after subtracting the blank intensity) vs. the concentration of standard additions.
From the best fit line equation of the plot, calculate the concentration of the ‘unknown’ in the series of solutions.
Find the concentration (units of ppm and mol/l) of Aluminum in the original unknown solution.
According to the experiment concentration (C) of the added Al(III) in chloroform;
Std. addition(mL)
0.00
2.00
4.00
6.00
8.00
Conc. in chloroform (C, ppm)
0
0.08
0.16
0.24
0.32
Plot of If vs C yields concentration of unknown, x in the prepared series of solutions at the ‘x intercept’.
(x-intercept).(50/2) = concentration of the original solution.