mined by taking the average of n peak-to-peak measurements of noise o n the sample (or background) means and dividing by a factor usually taken to be 5 (9, IO). The rms noise may also be determined by taking the standard deviation of the n signal (0- B) measurements. The significance of the statistical approach to evaluating
experimental limiting detectable simple concentrations resides in the lack of human bias and the generality and uniformity of use.
RECEIVED for review March 6, 1967. Accepted August 4, 1967.
Ion-Exchange Paper Chromatography of Certain Metal Ions with Aqueous-Organic Wash Liquids Joseph Sherma Department of Clienristrjs, Lafayette College, Easton, Pa. 18042
WE RECENTLY REPORTED a preliminary direct comparison between ion-exchange chromatography using aqueous-organic wash-liquid mixtures in columns and o n Amberlite ion-exchange papers ( I ) . It was shown that the two techniques yielded very similar metal-ion separations, as is true in totally aqueous systems, and that the results could be successfully translated from one media to the other. This report extends the study of eight representative metal cations to two other ion-exchange papers which have recently become commercially available. To date, no reports of their use with wash liquids of this type have appeared. These papers are supplied by Machery-Nagel and Co., Diiren, West Germany, and are composed of chemically modified cellulose rather than cellulose interspersed with ion-exchange resin, as in the case of the Amberlite papers. They have lower exchange capacities but have the advantage of being white so that zone detection is facilitated. Results on these papers are compared with corresponding ion-exchange column and batch equilibrium results, Amberlite ion-exchange papers and in some cases with Whatman No. 1 cellulose paper. Moreover, the major separations which are possible in the systems studied are presented. EXPERIRIENTAL
Materials and Reagents. M N quaternary ammonium anion-exchange paper, 0.4 meqigram capacity, supplied in the chloride form; M N sulfonic acid cation-exchange paper, 0.5 meq/gram capacity, and Amberlite SA-2 sulfonic acid cation-exchange paper, 2.0 meq/gram capacity, both supplied in the sodium form, converted to the hydrogen form before use (1); Whatman No. 1 pure cellulose paper; wash liquids were prepared from reagent grade chemicals in (v/v) ratios; individual test solutions were 0.050M in Bi(III), Cd(II), Co(II), Cu(II), Fe(III), Ni(II), Pb(II), V(V) ( 2 ) ; mixtures were 0.050M in each ion. Procedure. Use paper sheets 20 X 25 cm. Apply initial zones ( 5 pl) with micropipettes, one inch apart and one inch up along the long side. Air-dry the spots, fasten the paper into the form of a cylinder with tongued clips and stand in a n equilibrated developing tank with the origins at the bottom. (Shandon Unikit tanks lined with filter paper and equilibrated for a t least 15 minutes with 50 ml of wash liquid were used throughout.) Develop by the ascending method (1) J. Sherma, Sepuration Sci., 2, 177 (1967). (2) J. Sherrna, ANAL.CHEM., 36,690 (1964).
until the wash liquid has traveled 15 cm past the origin. Remove the paper, air dry, and spray with ammonium sulfide followed by dilute HCl to locate the zones. Chromatograph individual ions for reference alongside of mixtures. RESULTS
R p values were measured to the centers of the zones, which were generally regular and compact unless otherwise noted. All results are based on a t least duplicate runs in which good reproducibility was obtained. Cation-Exchange Systems. Table I shows batch distribution coefficients, K d , previously reported for Dowex 50 and R,,. values o n SA-2 and M N ion-exchange papers when the molarity of 1 0 % HCI mixed with 90% methanol was varied. As in our previous study ( I ) , R p values on SA-2 paper reflected in general the magnitude of Kd values: ions with Kd values of 2 or lower had Rr values of 0.4-0.5; ions with Kd values of 5-250 had R,,. values of greater than 0.0, usually 0.1-0.2; and ions with Kd values of 300-lo3 had R,. values of 0.0. The migration of bismuth was anamolous and will be discussed further below. This correspondence between techniques can be appreciated by focusing on the data for cobalt, copper, iron, o r nickel in Table I. F o r example, the decrease in Kd values from > l o 3 to io3 >io3
>80b >5
0.00
0.56 0.29
147 2 561 58 123 700 73
0.066
0.59
>5
0.1@ 0.13 0.00 0.00 0.00 0.00
0.72 0.72 0.62d 0.64 0.72
0 . 15c
0.77 0.82 0.64 0.67 0.80 0.60 0.33" 0.63
0 . 39e
0.00 0.055 0.080 0.00 0.031 0,061
MN-H+
RF, Kd
RF, SA-2
MN-H+
0 . 16c 0.39. 0.13 0.47# 0,476 0.13 0.O8Sc 0.29
0.71 0.92 0.73 0.82 0 ,92d 0.70 0.3% 0.76
