Qualitative Analysis of Cations Using Paper Chromatography Thomas McCullough, CSC and Marissa Curlee St. Edward's University, Austin, TX 78704 This paper describes a simple, efficient laboratory experiment that separates and identifies five common metal ions using paper chromatography.
Materials acetone, 4 volumes 6 M HCI. 1volume cone. N&OH cone. (NHS2S 1%dimethylglyoxime in alcohol 600-mL beaker 2 beakers (30-mL) 2 beakers (1-L) 11-x 14-cm Whatman #1 papers plastic wrap and rubber bands 0.05 M solutions of Nia+,Coa+,Cu2', Cd%, H p as nitrates, sulfates, or chlorides Procedure Enoueh of t h e chromatoeram solvent (acetone16 M ~ ~ 1 : 4 / 1 ~ vis/ vplaced ) in the-600-ml beake; to cover the bottom. Durine .* a 20-min oeriod of eouilibration the oaoer . . is spotted with knowns and an unkown wing capillnries. These soots should be aoolird about 10 mm above the bottom edge of the paper, Ghich is formed into a vertical cylinder held by a plastic clip. For best results the solvent should rise to the top of the paper, which requires 45-50 min. After the run, air dry the paper for 10 min before placing i t in the ammonia chamber (5 mL of conc NHaOH in a 30mL heakersitting in a dry 1-L heaker,. When the blue mlor of the Cu" ion appears, remove the paper from the chum-
her and carefully apply a drop of dimethylglyoxine from a n eyedropper just above the original nickel spot and unknown. Apink color indicates the presence of nickel. Place the paper in the (NH&S chamber (similar to the NH,OH setup). Cadmium will turn pale yellow while the other ions will turn brown or black. A total of 31 different unknowns can be prepared from these five ions.
13values Ni Co Cu Cd Hg
0.08 0.35 0.60 0.78 0.95
The most satisfying aspect of this experiment is the complete separation of all five ions, with no overlap and not even anv touching of adiacent soots. Other advantages are that nobipping or spraying of>apers is needed acd that ions from both sulfide m u o s of classical oualitative analysis can be included inone 'fell swoop. Caution: The fumes from the sulfidechamber are toxic so a hood should be used. Acetone is highly flammable. No flames allowed. We thank the Welch Foundation for its financial support of this project.
General References Pollard,et al. 3. Ckm.S a . 1951,470. Ritchie,A.S. J. C h .Edue. 1961,38,4W. MeCullough, B.T J Chem.Edue. l989.66.490.
Volume 70 Number 4 April 1993
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