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CIRCULAR-PAPER CHROMATOGRAPHY IN QUALITATIVE ANALYSIS JOHN 6. SURAK and ROBERT -J. MARTINOVICH -Marquette University, Milwaukee, Wisconsin
PAPER
chromatography, as developed by Consden, Gordon, and Martin (1) in 1944, has undergone many modifications and has been utilized in the analysis of many diversified mixtures. The introduction of the circular-paper chromatographic technique of Brown (b), a distinct phase of paper chromatography, has proved to be a very convenient and versatile analytical tool. This relatively new technique possesses several advantages over the conventional methods of paper chromatrographic analysis. In general, the method has a greater sensitivity, resolving power, and reproducibility. I n view of these facts, very exact quantitative determinations can be carried out. The apparatus, because of its compact nature, can be stored readily in an oven or refrigerator when temperature control is necessary. Its greatest advantage, however, lies in the relatively short time of development of a chromatogram. Some of the features which differentiate circularpaper chromatography from linear methods are the following: the components are resolved in circular zones, a central feed technique is employed, and the solvent flow is in a horizontal direction. For this reason it has been referred to hy many as the horizontal migration method. Although much work has been accomplished with circular-paper chromatography in the analysis of amino acids, sugars, etc., only a slight fraction of the reported literature has been devoted t o inorganic procedures. Rutter (3), who generally is credited with the met,hod of horizontal migration, was the first t o apply this technique to the separation of inorganic ions. Pollard and McOmie (4), as well as Martin ( 5 ) ,used the preceding technique in reporting the Rf values of a number of common cations. This same scheme was used for the qualitative and quantitative determination of copper, iron, nickel, and zinc in aluminum alloys (6). Methods
a, Pet" dish.
b, oirou1sr filter paper.
e,
wick immemed in aolvent.
have also been reported for the separation of cobalt, nickel, and copper (7), and radium D, E, and F (a), using the horizontal migration method of Rao and Beri (9). Since the movement of the solute goes both in the
Pigun, 2.
Modified R"ttrrr Techniqu.
n, b, ~ n k n u w nsolutiam.
c, k ~ ~ o wsolution n of o
and b.
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fulfilled for direct comparison with published Ttf values (ld, 1%14). . Circular Rf values decrease with an increase in the Type of paper ' Whatmen No. 1 distance of the initial spot from the center of the filter Time 0 . M . 7 5 hour Solvent 40% tertiarv paper, or stated in another way, with an increase in the " butvl alcohol 40% aoetone length of the tail (Id, 15). Accordingly, the variation 12% water of the length of the wick can significantly alter the mode 8% ronr. nitric acid of separation of mixtures. For example, an increase in Cation Identifying reagent Color Rfc the length of the wick made possible the separation of 0.25 H2E black 0.M) manganese from nickel using tertiary hutyl alcohol and Hgt+ tan 0.81 concentrated hydrochloric acid (7:3) as the developing Phi+ hmum n nn solvent. This is assumed t o result f ~ o mthe preferential adsorption of acid and/or water by the paper, thus gradually resulting in a change in the composition of the developing solvent and consequently a change in the Rfc values. 11% water A change in concentration of the solute does not alter 4.5'% nitric acid (6 N) 4.5% acetyl acetone the Rfc values if the measurements are made to the Catia Jdmtifving reagent Color Rfc "center of gravity" of the zone. An increase of conPb++ HB black 0.15 centlation, however, though not affecting Rfc values Cd++ yellow 0.32 directly, may nevertheless cause overlapping of the Cut+ dark brown 0.40 Bi'f brown 0 76 zones and result in incomplete separation. The overIIg tan 0.90 lapping in this case is due to an increase in the diffusion of the zones which accompanies an increase in concenGroup IIB (Arsenic @oup) Type of paper Whatman iYo.-1 tration. It may be noted here that for separation to Time 0.5-0.75 hour occur between two solutes the difference in Rfc values Solvent 45% tertiar butyl alcohol should be greater than 0.06 (16). 45% chloroLm 8% hydrochloric acid (8 N ) The relationship between the width of the wick and 2% acetyl acetone the rate of flow of the solvent has also been determined Cation Identifying reagent Color Rfc (17). As would he expected, an increase in the width Sb'+ dithiyne red-orange 0.85 of the wick will cause a proportional increase in the Asaf yellow 0.64 rate of flow of the solvent with no change in Rfc values. an++ purple 1.00 Thus, variation of the wick width can serve to increase the distance with which a solvent moves in a given time. The diameter of the filter paper plays a predominant direction of the flow of the solvent toward the edge of the paper and also in the direction orthogonal part in the resolution of mixtures. Circular filter paper to the direction of flow of the solvent, circular-paper varies in size from 11 to 35 cm. in diameter. The use of chromatography has been considered by some to be a large filter paper is found to be advantageous for better two-dimensional phenomenon (10). I n fact, it is the resolution and increased accuracy in the Rfc measuretwo-dimensional movement which is responsible for ments (18, 19). However, for student work, satisthe higher Rf values obtained in circular-paper chro- factory results are obtained ~vithfilter paper as small matography as opposed to linear-paper chromatog- as 11.5 cm. raphy. For this reason i t has been suggested that the PROCEDURE Rf values obtained by the horizontal migration method The method of chromatographic analysis employed be referred to as circular Rf values (9). The authors are in favor of such a suggestion and propose the by the authors is a modification of the Rao and Dickey method (16) for the direct positional comparison of unsymbol Rfc, which is defined thus: known substances. The apparatus consists of two distance from the initial spot to center of each zone Petri dishes of the same diameter, a capillary pipet, Rfc = distance from the initial spot to the solvent front Whatman No. 1and No. 2 circular filter paper (11.5 cm. I n circular-paper chromatography, identification of in diameter), and the developing solvent. A diagram the unknowns can be accomplished either by measuring of the apparatus is illustrated in Figure 1. the circular Rf values (Rfc) or by the technique of The procedure is as follows: A chromatogram is premixed chromatograms ( l l ) , which permits the identi- pared according to the method of Rutter (3). A 120" fication of the unknown by reference t o the known run arc of a circle of 4-cm. radius is drawn in such a way on the same chromatogram. The latter method is rec- that the edge of the wick forms a chord of the circle ommended for student use in qualitative analysis be- (see Figure 2). The samples of the unknown to be cause of its simplicity. Rf values are dependent upon analyzed are placed a t each corner of the wick and the temperature, pH, solvent system, time of development, known in the center of the arc segment. The paper is humidity, etc.; and these specified conditions must be dried and placed over a Petri dish in such a way that the TABLE 1
.
"
g++
++
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97
tail is immersed in the developing solvent (10 ml.) contained within the dish. The paper is then covered with another Petri dish of the same diameter in order to contrnl t"..h e -~trnnsnhew chromatoeram. ".-& , . . . . u F . . . . - r~~rrnunrlinn ..... - . ~---a- the ~ After development the chromatogram is d ~ i e dand treated with a suitable chromogenic reagent to reveal the location of the ions. Development of the paper results in the formation of three arcs separated from one another by a distance of one to two millimeters. Identification of the unknowns can he accomplished by the
Figure 3.
A , lllodified Rutter teohnirjrre.
dirert cornparison of the outer zones to the central zone. SEPARATION OF
I AND II CATIONS
The silver and copper groups call be conve~~iel~dly identified by means of an aqueous solution of hydrogeu sulfide. The corresponding colors of the sulfides are listed in Table 1. I t should be noted that since silver sulfide is soluble in an acid medium the chromatogram must first be neutralized with ammonia or else
separation of the copper Group
8 , Giri method.
I.
led.
2, copper.
3,
bi~motll. 4, meroury.
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the silver will fade when the chromatogram is dried. Members of the arsenic group should be permitted to dry thoroughly in air for a t least 15 minutes before development. The chromatogram, after development, is dried and immersed in a large Petri dish containing a 0.2 per cent solution of dithizone in chloroform and subsequently dried again in an oven a t a low temperature. A chromatogram showing the separation of the copper group is shown in Figure 3. SEPARATION OF GROUPS III-V CATIONS
I n the preparation of the solutions for use in Groups JII-V the nitrates of the metals were used. However, for the separation of the alkali metals the acetates were employed in later experiments because better resolution was obtained with these salts. The concentration of the various salts did not exceed 5 per cent ( W I V ) .
TABLE 2 (Aluminum C r m.~.v ) Whatman No. 1 1.5-2 hours 40% tertiary butyl alcohol 40y0 acetone 20% 3 N hydrochloric aoid Identifying rmgat Color Rfc Z ~ B B P ~ red 0.55 violet 1.00
Crouv I I I A Type of psper Time Solvent Cation AIS+ Zn++
C l m ~ vI I I R ( I m n Group) Whatman No. I Type of paper Time 0.75-1 hour Solvent 90% acetone 10% HCI (6 N ) Cation Idedifving reagent Color Rfc cnl dimethyl red 0.25 ~
-
~
*
.
Crouv I V (Alkaline Earth Grouv1 .. Whatman No. 1 Type of paper Time 1.5-2 hours Solvent 50% tertiary hutyl alcohol 50% 6 N HCI Cation Identifying reagent Color Sr++ potassium rhodieonate orange Ba++ red C. n ++ alizarin violet ~
~~
+
T i+
Identifying reagent violuric acid
Color yellow-brown yellow-brown violet
LITERATURE CITED ( 1 ) CONSDEN, R., A. H. GORDON, AND A. J. P. MARTIN,Biochem. J., 38, 224 (1944). W. G., Nature, 143, 377 (1939). ( 2 ) BROWN, L.. ibid.. 161. 435 (19481. 13) RUTTER. i~ 4-,i POLLARD. H.. AND J. F. W. M C O ~ E . Endrauour., 10., 213 (1951); ~ c h Shd . Rev., 122, 21 (1952). E. C., Anal. Chim. Ada, 5, 511 (1951). ( 5 ) MARTIN, G., AND A. M. GHE,zbid., 7 , 267 (1952). ( 6 ) VENTURELLO, Science and Culture (Indza), ( 7 ) A m o ~J, . W., AND J. BARNABAS, 18, 89 (1952); ibid., 18, 438 (1953). ( 8 ) DrcnEY, E. E., J. CHEM.EDUC.,30, 525 (1953). 19). RAO.P. S.. AND R. M. BERI.Proe. Ind. Acad. Sd... 33.. 368 (1851). ' (10) RAO, T., AND K. V. GIRI, J. Indian Inst. Sci., 35A, 77
.
Rfc 0.35 0.50 0.60
Grouv Metals) . V (Alkali . Whatman No. 1 Type of paper Time 0.75-1 hour Solvent methanol (absolute) Cation K+ Na
While H2Swas a satisfactory agent for revealing the presence of the cations in Groups I and 11, chromogenic agents which gave colored complexes were needed for the other cations. The identification of aluminum, zinc, and calcium was accomplished by means of a 2 per cent solution of alizarin in alcohol. Barium and strontium were identified with a 2 per cent aqueous solution of potassium rhodizonate. Ammoniacal dimethyl glyoxime was used for identifiying members of the iron group and a 0.2 per cent alcoholic solution of violuric acid revealed the positions of the alkali metals. Table 2 contains data which were found to separate the cations of Groups 111, IV, and V. The Rfc value, chromogenic reagent, and color are listed for each cation. The table also indicates the separations that are possible by developing inorganic mixtures unidirectionally with a single solvent system. Improved sepalations are obtained by the technique of multiple development, that is, the paper is dried and developed again in the same direction using the same solvent system. This method resolves the zones which originally were diffuse into clear and defined zones. Circulal-paper chromatography places the application of chomatography nithin the capabilities of beginning chemistry students and also within the budgetary limits of educational institutions. I t is a very rapid method of analysis and can be performed within a one-hour laboratory period. The experiments are very simple and can he carried out by even the most inexperienced personnel.
Rfc 0.20 0.42 0.68
(1453) ,.*--,.
(11) GIRI,K. V., Cunent Sci. (India),20, 295 (1951). Anal. Chem., 25, 1539 (1953). (12) SAIFER,A,, AND I. ORESKES, (13) RUTTER,L., Analyst, 75, 37 (1948). J. G., N . LEPFLER, AND R. MARTINOVICE, J.CREM. (14) SURAK, EDUC.,30, 20; 457 (1953). (15) Rao, T., A X D K. V. GIRI, J. Indian Inst. Sci., 35A, 457 (1953). Sciace, 117, 666 (1953). (16) Rho, P. S., AND E. E. DICKEY, (17) MULLER,R. H., AND D . L. CLEW, Anal. Chem., 23, 408 (141)
(18) GIRI,K. V., Nature, 171, 1159 (1953). V. K., Ezperientia, 9 , 151 (1953). (19) Rno MORAN,
