Paper Chromatography and Spot Tests:
N. S. Poonia Vikrarn University Ujjain, India
A Useful Combination of Techniques
Spot tests for inorganic ions frequently arc invalidated by interferences. Often t,he interfering ions can be removed by precipitation, masking by camplexation, or adjustment of acidity. The author herc reports on the combination of a technique that has long been recognized as a devicc for differential separation (paper chromat,ography) with the specificity of identification afforded by spot test reagents.' Thc solvent system, rhloroforn-acetone-isopentanol-HCI, has hecn found most useful for the separation of many similar inorganic ionsz Rt values for a list of ions typical of qualit,ative analysis unknowns is given in the tablc.
'
See for example FEIOL, F., "Spol.Test,s inlnorgsnic Analysis," Elsevier Publishing Co., New York, 1958. The author also will provide irlterest,ed readers with a complete list, of tests which have proved l,o be most sst,iaft~ctoryrmder the enndilions here described. B~:vr~.Acan, It. P., AND Poourh, N. S., Anal. Chem., 34, 1325 (I!K2): A n d . Chirn. Ada, 30, 211 (1064).
The simple procedure is to spot the solution containing the ions at the center of a filter paper disc (Whatman No. 1, 4.5 cm diameter); the paper is dried, a narrow wick cut to bring solvent to the center of the spot, and the elution allowed to proceed slowly (l(t-30 min). Conventional procedures' were used to develop the rings. Where it was necessary, the acid of the solvent was ~icutralizedby NH3 prior to development. I t will be noted from the data in the table that it is possible to distinguish readily the different oxidation states of an element [cf. Fe(II), R, = 0.07; Fe(III), R, = 0.92; or thc values for the anions of Se(1V) and Se(VI)]. The figure illustrates t,he separation of a mixture of ions, all of which respond to the same spottest reagent (potassium ferrocyanide). I n this casc the separation required 3.5 hours.
R , Values of Inorganic Ions in the Solvent Chloroform-Acetone-lsgpentanol-HCI (2: 1 : 1 :0.2 v/v) Ion
Rrvalw
Ion
Rr value
Figure 1 . Shawr the reparation of Feillll, Cuilll, VIIVI. U O i I I l . Till\ ond Mo(VI1. Detection reagent, potosium ferrocyonide.
Volume 43, Number 8, August 1966
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