(2' x 11/2") for recording the gross gamma-activity of T u (12.8 hours). The method is fast enough to permit the use of 6 C u (5.1 minutes). Based on earlier work (6),the sensitivity using T u is estimated to 0.1 p.p.m. using 2 grams of fat and a Sminute irradiation a t a thermal neutron flux of 2-3 X IO1* neutrons per sq. cm. per second. The reproducibility, using the data for sample B, was found to be *7% (standard deviation). The radiochemical separation resulted in a sufficient high purity of the isolated copper. All decay curves showed that the initial activity of the impurities amounted to 1% or less of the initial activity of copper. DISCUSSION
In view of the work of Souliotis on the determination of nickel in hydrogenated fats (7) and that of Brune (4) on the application of the Szilard-Chalmers effect in the neutron activation analysis of biological samples, it was not surprising that it was possible to exQact the induced copper activity with 6N hydrochloric acid from a toluene solution of the irradiated fat. Although this most probably can be fully ascribed to copper existing in the nonirradiated fat as simple ions or organic complexes which are readily extractable in 6 N hydro-
chloric acid, it is possible that part of the radioactive copper is extracted due to a Szilard-Chalmers effect on copper (which is nonextractable in nonirradiated fat), or that radioactive copper, still bound owing to recombination, is extracted through isotope exchange with the copper carrier (4). Although the extraction procedure was checked on only two samples of mixed hydrogenated fats, the induced copper activity will probably also be extracted with 6N hydrochloric acid from all types of fats which can be dissolved in organic solvents having a low solubility in 6N hydrochloric acid. The apparent inhomogeneity of sample A with respect to copper prior to the filtration step might be due to copper associated with particulate matter inhomogeneously distributed in the fat or copper dissolved in a possible water phase also inhomogeneously distributed. Both particulate matter and water can be retained on the filter used. Obviously, one should be aware of the possibility of having also other trace elements inhomogeneously distributed in similar samples. The usefulness of the recommended method is, of course, not restricted to the 24 hours irradiation time, nor the flux and instrumentation used. Although several days were required to get the
results of the analysis in our work, a reduction of the required time could easily have been achieved by reducing the irradiation time and using a multichannel analyzer for recording the activity and checking the purity of the isolated activity. However, the most important point is that the time required for the radiochemical separation and the measurement of the absorbance of the two diluted copper-dibenzyldithiocarbamate solutions in only 15-20 minutes. The procedure is, therefore, most suitable for analyzing series of samples. LITERATURE CITED
(1) Abott, D. C., Pohill, R. D. A,, Analyst 79, 547 (1954). (2) Borchardt, L. G., Butler, J. P., ANAL.CHEM.29, 414 (1957). (3) Bowen, H. J. M., I n i a . J . Appl. Radialia and Isotopes 4, 214 (1959). (4) Brune, Dag, Anal. Chzm. Acta 34, 447 (1966). (5) Fritze, K., Aspin, N., Holmes, T. H., Radiochim. Acta 3 , 204 (1964). (6) H#gdahl, 0. T., Meinke, W. W., U. S. At. Energy Comm. Rept. TID17272, 62 (1962). (7) Souliotk, A. G., ANAL.CHEM.36, 1385 (1964).
OVET. H ~ G D A H L SIGURD MEISOM
Central Institute for Industrial Research Blindern, Oslo 3, Norway
Fast Quantitative Separation of Iron(l1) and lron(ll1) by Pa per Chromatography SIR: The importance of the separation of Fe+*and Fe+3has been reviewed (6) and some qualitative separations have also been developed (1,5,6,9, IO). Stevens (9) made a few quantitative studies on the separation of these ions and Pollard et al. (5) carried out a comprehensive and detailed study of the materials and conditions of their Fe+L Fe+3 separation on paper chromatograms. A qualitative separation of these ions by paper chromatography was reported from these laboratories earlier (6). Because time is an important factor in the separation of the different valence states of a metal (79, it was considered worthwhile to study the quantitative and other aspects of this separation in detail. The present communication summarizes the results of such a study. EXPERIMENTAL
Apparatus. Development was performed in 20- by 5-cm. glass jars using the ascending technique. The dimension of the paper strips was 14 by 3.5 cm. &timation was done on a Hilger Spekker absorptiometer.
Reagents. Whatman No. 3 M M paper was used in quantitative work only. For qualitative studies, Whatman No. 1 was used. Solutions, 0.1M of nitrates, chlorides, or sulfates of the metal ions, containing a little acid to prevent hydrolysis, were used. Solutions, 0.1M of the sodium, potassium, or ammonium salts were taken for the study of anions as impurities. The stock solutions of ferrous ammonium sulfate (British Drug Houses Analar grade) and ferric ammonium sulfate (Riedel) containing 15,000 and 20,OOO p.p.m. of iron, respectively, were prepared in 1% sulfuric acid and standardized according to the usual procedure (S, 4 ) . A 10% solution of hydroxylamine hydrochloride (8) and a 0.3% aqueous solution of l,l0-phenanthroline were used. The phthalate buffer of pH 3.98 was prepared according to the procedure of Harvey, Smart, and Amis (9). The developer was a mixture of 4M HC1, n-butanol, acetic acid, and acetone by volume in a ratio of 1 : l : l : l . Fe+* and Fe+' were detected usually by exposure to ammonia gas and occasionally with ferro- and ferricyanides and 1,10phenanthroline. The detection with ammonia makes the use of pilot papers
unnecessary in quantitative work. Other cations were detected by the usual, specific color reagents. Procedure for Quantitative Studies. SEPAFLATIONAND DETERMINATION OF Fe+l AND Fe+3 IN ABSENCEOF IMPURITIES. The solution containing ferrous and ferric ions was streaked on the line of application by means of a micropipet. The paper was then conditioned for 15 minutes and the developer was allowed to ascend 10 cm. Blank paper was streaked with 1% sulfuric acid and treated similarly. The paper strips were taken out of the jars and treated with ammonia gas. Zones were cut and eluted successively with 30 ml. of 1% hydrochloric acid and 30 ml. of distilled water. The extract was reduced to 1 ml. by evaporation, cooled, and diluted to 10 ml. with distilled water. To 1 ml. of this solution, 2 ml. of hydroxylamine hydrochloride solution, 2 ml. of buffer solution, and 4 ml. of I ,10-phenanthroline solution were added. The volume was made up to 10 ml. with distilled water. The absorption was measured after 5 minutes and the amount of iron present was determined with the help of the calibration curve drawn previously. VOL 38, NO. 10, SEPTEMBER 1966
0
1415
DETERMINATION OF TOTAL IRONIN PRESENCE OF IMPURITIES. The mixture of Fe+2and Fe+3and the impurity under study was treated with H2O2to oxidize Fe+2to Fe+3. For this, 2 ml. of the ferrous solution and 2 ml. of ferric solution were added to 6 ml. of the solution of the impurity along with 2 ml. of Hz02 (100 volumes). The mixture was heated for 4 hours to remove excess of HtO2, then cooled and diluted to 25 ml. with distilled water. The resulting solution was used as the spot solution.
RESULTS
Efficiency of Separation of Fef2 and Fe+3in a Short Interval of Time. The distance between the outer boundaries of Fe+2 and Fe+3 was determined arbitrarily for a development time of 15 minutes. The average distance for four separations a t 24' C. was 1.5 cm. Solutions, 1.9 pg. of O.lM, of both ferrous and ferric sulfates were taken for this study. Average RI values for Fe+3 and Fe+* were 0.68 and 0.17, respec-
Table 1.
Separation and Determination of Small Amounts of Fe+l and Fe+3 in Different Ratios (Distance of migration = 10 cm.) VOl. Amt. applied, pg. R/ applied, ml. Fe +2 Fe +a Fe +2 Fe+3 28 5.6 14 1.4 0.14 0.07 0.14 2.8 2.8 28 28 5.6 0.28 0.14 0.028
0.001 0.001 0.005 0.005 0.002 0,001 0.005 0.001 0.001 0,001 0,001 0.001 0.001 0.001 0.001
Table II. Ag + I Pb +2
T1
Hg +? c u +2 Cd +2 As +a
Sb + 3 Sn +4
0.24 0.24 0.25 0.23 0.31 0.30 0.33 0.23 0.25 0.30 0.29 0.27 0.21 0.26 0.30
28 5.6 14 1.4 0.14 0.07 0.14 28 2.8 0.14 2.8 0.28 28 28 28
0.54
0.60 0.70 0.69 0.61 0.60 0.68 0.68 0.70 0.57 0.71 0.73 0.56 0.67 0.56
RI Values of Metal Ions in Solvent System 4M HCI,-n-Butanol-Acetic Acid-Acetone ( 1 : 1 : 1 : 1 ) Sn+l (0.66) Ca+l ( 0 . 1 7 ) Ce+3 (0.12) (0-0.41) Ba+2 (0.08) Al+3 (0.14) Pt+' (0.60) ( 0 - 0 ,40) Cr +a (0.14) Ti+' (0.22) Sr+2 (0.14) (0-0.43) Fe+2 (0.17) Mg+Z ( 0 . 1 6 ) Pd +z (0.58) (0.84) Fe+a (0.75) U O Z +(0.38) ~ v +I (0.21) (0.36) Ni+2 (0.13) Be+l (0.37) V+' (0.23) (0.72) (0.10) Y+3 (0.10) co+2 (0.19) (0.59) (0-0.20) Bi+a (0.63) Mn+* (0.23) (0.85) Zn+2 (0.68) Th+4 (0.12) (0.86)
Quantitative Separation of Fe+2and
Table 111.
Amt. applied, pg. Fe+z Fe+a
applied, Vql.
ml. 0.02 0.02 0.02 0.02
200 200 200 200
200 200 200 300
Amt. recovered, crg. Fe+z Fe+3 195 190 200 210
Fe+3
Error,
210 195 205 305
Fe+2
Fe +a
-2.5 -5 0 +5
+5 -2.5 +2.5 +1.75
Table IV. Determination of F e + S in Presence of Impurities Total vol. Impurity Amt. of Fe+a Amt. of Fe+a applied, ml. present applied, pg. recovered, pg. Error, % 0.02 0.03 0.05 0.025 n n.5 -.-0.02 0.025 0.05 0.05 0.04 0.05
1416
Cr +a
Cr +a Cr +a
~1+3 AI +a ~
~~
c o +2
co
+f
c o +2 Ni+'
Ni+*
Ni+'
ANALYTICAL CHEMISTRY
84 126 210 105 210 84 105 210 210 168 210
85 125 195 100 195 80 100 220 200 170 215
$1.2 -0.9 -7.1 -4.7 -7.1 -4.7 -4.7 +4.7 -4.7 +0.8 +2.4
Table V.
Determination of Total Iron in Presence of AI+S Amt. Amt. of iron of iron Total applied, detd. as. Error, vol., ml. pg. Fe+$,rg. % 0.03 0.04 0.05
134 179 224
125 170 215
-6.6 -5.0 -4.0
tively, for a development time of 15 minutes. This separation was also studied for small amounts of Fe+2and Fe+3. The ratio of the two ions was also varied. Results are summarized in Table I. Interference from Other Cations. To study the interference due to different ions in the separation of Fe+2 and Fe+3, numerous metal ions were chromatographed. The results are given in Table 11. Separation in Presence of Impurities. Because it is useful to separate Fet2 and Fe+3in the presence of other ions, numerous separations were studied by taking synthetic mixtures of Fe+2 and Fet3 and the cations concerned in the ratio of 1 : l : l O . In all cases, the two valence states separated. Uranyl (0.34), palladium (0.54), and copper (0.36) were successfully separated from both Fe+2and Fe+3. Separation in Presence of Different Anions. Fe+2, Fe+3, and the anions concerned were mixed in the ratio of 1 : 1 : 10. Fluoride, phosphate, acetate, oxalate, molybdate, tungstate, citrate, tartrate, selenite, tellurite, chloride, sulfite, sulfide, sulfate, thiosulfate, nitrite nitrate, and thiocyanate did not interfere with the separation. F e f 2 could not be detected in the presence of Br-, I-, c104-,BrOd-, IO'-, CrOa-2, and Cr207-2. Ferro- and ferricyanides produced tailing. Both Fe+l and Fe+3 were also chromatographed as sulfate, nitrate, chloride, oxalate, phosphate, and ammonium sulfate. The solutions were prepared in 1% aqueous solutions of the corresponding acid. Thus, ferric and ferrous chlorides were prepared in 1% HC1. The phosphates of both Fe+3 and Fef2 were prepared in 4 to 590 HaPo4 by heating. For all cases, good separations were obtained. Fe+2 had an R/ value close to 0.21; and Fe+3, approximately 0.85 for an average distance of migration of 10 cm. However, when Fe+3 was taken as ammonium sulfate, its R, value was 0.68. Quantitative Separation of Fef2 and Fe+9 Fe+2 a n i Fe+3 were separated and determined according to the procedure given above. Results are summarized in Table 111. Separation and Determination of and Fe+3 in Presence of Impurities. I n this method, common
Table VI.
Total vol., ml.
Determination of Fe+a and Total Iron in Presence of Cr+*
Tot4 Amt. Amt. of Fe+a Amt. of Fe+* amt. of iron Amt. of Fe+' of Fe+*by applied, pg. applied, pg. recovered, pg. recovered, pg. subtraction
0.05 0.05
100 100
90 90
impurities-i.e. Al+a, Co+2, Ni+' interfere with Fe+Z and not with Fe+8. Hence, the quantitative separation of Fe+s from these impurities was studied. The sample contained Fe+a and the impurity in the ratio of 1 :3. Results are shown in Table IV. When quantitative separation of Fe+* in the presence of impurities had been achieved, the mixture containing Fe+2 and Fe+' and the impurity was oxidized with H2O2. The total iron was then separated as Fe+S by paper chromatography and determined. Determination of Total Iron in Presence of Impurities. The total iron was determined according to the procedure given above. Results are summarized in Table V. When it was found that Fe+sand total iron could be quantitatively determined, the method was applied to the quantitative separation and determination of Fe+* and Fe+* in the presence of Cr+a. The results are shown in Table VI. When chromatography is performed in the presence of Cu+', some interesting results are obtained. If Fe+z, Fe+a, and Cu+2 we taken in the ratio of (1:1:l), the separation is normal-i.e., the spots appear a t their expected positions. When a mixture of 0.01M Fe+*, 0.01M Fe+', and 0.1M Cu+* was taken in the ratio of 1:l:l by volume, then Fe+a and Cu+f appeared at their normal positions. However, between Fe+a and Cu+' a new spot appeared which gave positive tests for Fe+' and Cu+2, This may be explained on the assumption that Fe+' and Cu+2 probably form a mixed species with an R, value intermediate between those of Fe+a and
190 198
105 100
85 98
CU+*,and this species is formed when Cu+' is in excess. Other Useful Separations Achieved. The possible separations can be predicted from Table 11. However, the following interesting separations were actually achieved:
(a) Fe+S-UO2+LTi+4
+"Be +2 (b) Cu+' from Cd+*, Bi+', As+*,Pt+4, Zn+a, or Co+2 A l + a from Be+* Zn+2 from Mn+2 Fe+2 from Pd+' Fe+S from Tl+a Pt+4 from UO2+l Th+' from U02+Z (c) Sb+* can be separated from: Fe+2, Ni+z, Co+*, Mn+*, Al+s, Cr+), Ca+f, Ba+*, Srfn, Mg+', La+a, Ce+s, Th+', Zr+(, Ti+', V+4 V+), Be+*, UO2+*, Y+a, Pdi2, Pt+', Pb+*, Cu+*, As+', and Bi+' (Figure 1). DISCUSSION
The solvent system has a high elution capacity and it can easily separate approximately 200 pg. of Fe+s from similar quantities of Fe+'. Many cations have R, values close to Fe+'. Hence, by determining Fe+a alone and then total iron as Fe+a, it is possible to determine both Fe+' and Fe+a quantitatively in the presence of common impurities l i e Cr+', Al+', Co+*, and Ni+', which have R f values close to Fe+*. Of the anions studied, the ferro- and ferricyanides interfere by forming insoluble precipitates. Chlorate, bro-
Fe+* 5 0
Emor, % Fe+*
Total
-5.5 +8.8
0.00 +4.2
mate, iodate, chromate, and dichromate interfere by oxidizing Fe+'. Fe+' could not be detected in the presence of bromide and iodide, probably because it forms insoluble salts with them. Anions corresponding to the weak acids-i.e., phosphate, acetate, oxalate, molybdate, tungstate, sulfide, etc.-did not interfere in this separation because, in the presence of hydrochloric acid, the chlorocomplex is preferably formed. Even in the presence of thiocyanates, the R, values were not altered. This method of separation offers certain advantages over the methods of Stevens (9) and Pollard (6). Only 15 to 30 minutes are needed to achieve a AR, of 0.5, while the earlier methods needed 2.5 to 3.5 hours. It is also applicable to a larger variation in Fe+fFe+S concentration (1:200 and 200:l). It gives good separation in the presence of anions, which were not studied by either Stevens or Pollard. Owing to these advantages, the method may be used in the separation of iron valencies where interfering material is presente.g., in minerals and biochemical media. ACKNOWLEDGMENT
The authors are grateful to A. R. Kidwai for his interest and facilities provided. LITERATURE CITED
(1) Bighi, C., Ann. Chim. (Rome) 45, 532 (1955). (2) Harvey, A. E.,Smart, J. A., Amis, E. s., ANAL.CHEM. 27, 26 (1955). (3) Knop, J., J . Am. Chem. Soc. 45, 263 (1924). (4) Ko!thoB, I. M;, Belcher, R., "Volumetno Analysu, Vol. III, 3rd ed., p. 626, Interscience New York, 1957. (5) Pqllard, F. H., Mamie, J. F. W.,
Bamter, A. J., Nicklesa, G., Analyst
82. 780 (1957). (6) €)uresk& M.; Akhtar, I., ANAL.CHEW. 34 1341 (1962). (7) &mahi, M. Khan, M. A., Ibid., 35, 2050 (19631. ( 8 ) Sandell E. B. "Colorimetric Metal Analysts," 3rd p. 541, Interscience, New York, 1957. (9) Stevens, H. M., A d . Chim. A d a 15, 538 (1956). (10) Ssarvav, P., Balogh, T., A& Unw. Debrmiensis 3, 89 (1956).
ed.,
MOHSIN URFSHI IoS*LLTAR
K. G.V-HNEY METAL lows
Figure 1.
Separation of
Sb+*from various metal ions
Chemical Lsboratories Aligarh Muslim University Aligarh, India VOL 38, NO. 10, SEPTEMBER 1966
1417
