- Email: [email protected]
Paper and thin-layer chromatography applied to the separation of chromium(III) from chromium(VI)
208
NOTES
Analyses made in this manner were quantitative when an average of 24 spots (from 4 sheets) was taken. On each sheet were 3 runs of the original solution and 3 runs of the original solution diluted with one or three times its volume of water. ‘This routine was followed for samples prepared according to either procedure I or II. Thus there was found in pure zinc silicate 41.5 y0 of total silica (19.4 y0 Si). Theory requires x9.8 oh Si for ZnSiO,. On analysis, artificial mixtures consisting of 4g O/~of silica (particle size less than 2.6 ,u) and of 51 o/ozinc silicate (particle size less then I ,u) there was found 48 % free silica (SiOs). In this method the particle size of the sample, whether free silica or silicate or a mixture thereof, is immaterial as compared with physical methods such as differential thermal analysis, X-ray diffraction, or phase contrast microscopy. A more detailed description will appear elsewhere in the near future. lutstit&e oJr1nd~~st~iaEL IJygiene and Occa@ationaZ Medicine, Bratislava (Czechoslovakia)
E.
z E. Mhr_$, Pafier presented at lice 2nd Pafier Clwomadog~*aj5hyConfe~*e~ace,Pval&a,June 21-24, N. G. PomzWhEv, Gigielza i Sad., 22, No. II, (1951) 91.
MALP
I&r.
2
Received
January gth, 1965
J. Chromalog.,
Paper and
Ig (1965) 206-2q8
thin-layer
chromium(lll)
from
chromatography
applied
to the separation
of
chromium(W)
There are not many publications available dealing with the chromatographic separation of chromium ions of different valence (Cr3+ from Cr0,2-). BIGI& mentions the separation of non-radioactive chromium ions (Cr2+, Cr3+ and CrO,s-) by paper chromatography (Whatman paper No. I) using butanol-acetic acid-ethyl acetatewater (50 : IO : 5 : 35) as developer. POLLARD et aL2 separated Cr3+ from CrO,s- on paper y$ng methanol-ethyl ether-cont. WCl-water (30 : 50 : 4 : IS). For this purpose paper impregnated with zirconium phosphate was also used by SASTRI AND RAO~, with saturated Na,SO, solution as developer. LEDERER et aZ,4-a and OSSICLNI’ described the adsorption of chromate ions and other ionic species on paper impregnated with ion-exchange resin from different media. There are no publications available which deal with the chromatographic separation of radioactive carrier-free chromium(II1) from chromium(V1). The hexavalent chromium may be reduced in solution to lower valencies by different, organic substances or radicals formed by ionizing radiations of recoil phenomena. Other authors investigated and described the radiation-induced reduction of chromium(V1) solution@ and y-ray-induced exchange between trivalent and, hexavalent chromium ions in aqueous acid solutions s. The reduction of chromate or dichromate by different organic substances, such as formic acidlo, liquid ammonia and J. Cltvomatog., IQ (1965) 208-213
NOTES
209
liquid ammonia solutions of potassium amiderr, sugars12, and ethanols or hydrazine perchlorate and kydroxylamincla have also been published. For the determination of radiochemical purity, we have reproduced BIGHI’+ and SASTRI'S~ experiments using carrier and carrier-free chromate and chromium chloride labelled with % r. In the course of these experiments we observed a supplementary reduction of chromate ions by the reducing action of chromatographic paper and/or solvents (Figs. I and 2). When the concentration of chrcmate ions in the solutions is very low (carrier-free) (Fig. I) this reduction is increased and may be a source of error in the analysis or determinations of radiochemical purity of some labelled compounds of chromium. Therefore other systems were sought.
cm
Fig. I. Paper chromatography of radioactive carrier-free chromium chloride and sodium chromate on Whatman No. I paper impregnated with zirconium phosphate. Developer: saturated solution (I’) filCrC1a after clevelopment, ;f N&SO4 (ascending, t = 2 11). (I) GICrCI, before development: = 0.92; (2) Na,elCrO,‘before development; (2’) Na, GrCrO, after clevclopment, Rp Cr”+ = = 0.38. 0.: r ; Rp CrO,+
Resaclts
A summary of these experiments is given in Table 1. Radioactive GrCr wasused as tracer in many of these experiments. On zirconium phosphate impregnated paper, Crac behaved in a very variable manner. When macroscopic amounts of CrCl, were developed with saturated solution of sodium sulphate, approximately 60% migrated with an Rp of 0.85, but the remainder did not move (Fig. 3). When, however, the con-
10
12
14
18
18
20
22
24
Fig. 2. Paper chromatography of ‘radioactive sodium chromate with carrier, on Whatman No. 1 paper impregnated with zirconium phosphate. Developer: saturated solution of Na,SO, (ascending, + CrCl, after development, (I’) Na2 %rO, 2 = 2 h), (I) Na,brCrO, + CrCI, before development; + K,CrO, before development; (2') Naa51Cr0, RF Cr3+ = 0.90; Isp CrOd2- = 0.36; (2) Na,%ZrO, + K,CrO, after development, Rp Cr0,,2- = 0.68. J. CAromalog.,
zg (1965) 208-213
+ Ml,
WCl,
Na,wo,
Na,zlCrOl + K&O,
4
5
6
7
:;.?A
WCl, carrier-free
+ CrCl,
+ K,CrO,
w-cl,
3
Na,SO, satd. soln. .
Na,SO, satd. soln.
Xa,SOI satd. soln.
Xa,SO, satd. soln.
Na,SO, satd. soln.
(4O:j:IO)
Na,SO, satd. soln. Acetone-4 M HCl-H,O
Glass paper Filter paper Whatman No. I impregnated with zirconium phosphate Filter paper Whatman No. I impregnated with zirconium phosphate Filter paper Whatman No. I impregnated with zirconium phosphate Filter paper Whatman No. I impregnated with zirconium phosphate Filter paper Whatman No. I impregnated with zirconium phosphate Filter paper Whatman No. I impregnated with zirconium phosphate
I
CrCl, + K,CrO, CrCl, + K&O,
COMPOUNDS
3
AND cr(vI)
Developer
OF Cr(IlI)
Adsorberzt
SEPARATION
Chromium con~por~~~ds
CHROllATOGRAPHIC
TABLE I
a
2
2
2
2
5
2
(h)
Dwatiolt
0.90
-
O.Sj
O.Sj
0.00
-
0.66
0.36
-
0.67
0.33
-
0.00
CYO,2_
RF fl.Y+
‘
1 ii
The reduction of s1Cr042-is decreased
Cr0,2- is partially reduced to Crz+
-
CrOa2- is partially reduced to Wf
Not separable CrO,s- is partially reduced to Ci3+
Observatiom
Z El !Z
SQTES
x c
-t-c 9
!
jk
I.
coot
oooc
6663
NOTES
212
centration of W+ was very low by using carrier-free WrC13, only 8 o/omigrated. Intensive reduction of chromate was observed in these systems, partjcularly when carrier-free chromate was used and this made accurate determination of mixtures of Cr3+ and chromate ions ikpossible (Figs. I and 2).
Fig. 3, Paper chromatography of radioactive chromium chloride with Carrier on Whatman No. I paper impregnated with zirconium phosphate. Developer: saturated solution of Na,SO, (ascending, RF = 2 11). (I) WrCl, + CrCl, before development; (I’) GlCrCl, + CrCl, after development, L+J+ = 0.55; after development, (2) WrCl, + K,CrO, before development: (2 ') GlCrCl, + K,CrO, I Rp Cr3+ = 0.91.
In attempts to avoid the reduction of chromate ions, the behaviour of Cr”+ and chromate ions was studied by the thin-layer method on plates of silica gel, zirconium phosphate and aluminium oxide, using inorganic solvents such as sodium Experiments with silica gel and sulphate or carbonate solutions as developers. zirconium phosphate did not give satisfactory results. Better effects were obtained using plates of aluminium oxide (Grade Merck nach Stahl). The following method was used. Chromatographically pure aluminium oxide (80 g) was ground in an agate mill for 40-50 minutes to 150-200 mesh. Calcium sulphate (IO g) was added and the mixture stirred for 30 min. Then 67 ml of bidistilled water were added and thoroughly mixed. The suspension obtained was spread on plates (20 x 30 cm) by means of a
Fig. 4. Thin-layer chromatographic separation of chromium(II1) and chromium(V1) ions from radioactive carrier-free sodium chromate solution, on aluminiurn oxide plates. Developer : saturated I mC/ml, a = 16 pC; b = 17 1tC; c = solution of Na,SO, (ascending, t = 2 h). Specific activity: 23 ,uC; d = 15 @. J. Clwomalng.,
19 (1963) 208-2r3
213
NOTES
Desaga apparatus to a layer thickness of 0.2 mm. After drying at 110~ for I 11,different samples of WrCl, and Na,6lCrO, solutions, with carrier and carrier-free, were pipetted on the plates (Table I). The plates were developed with a saturated solution of Na,SO, for 2 h. After development the radioactivity of the plates was measured by G.M. counting and the autoradiochromatograms were prepared ,(l?ig. 4) using “Kodak X-ray film” as well as Kodak developer and fixative. Under these conditions, Cr +3 ions do not move but the chromate ion migrates with an RF of 0.60. Even with carrier-free chromate the major part of the radioactivity migrated.The fraction of activity remaining at the start was believed to be due to the presence of Cr3+ ions in the original solution. This was checked on the original chromate solution by radiochemical methods. Carrier chromate and Cr3+ ions were added to the solution and the chromate was precipitated by the addition .of lead ions. After centrifuging the precipitation was repeated, and any Crs+ ions remaining in solution were oxidised by hydrogen peroxide to chromate which was precipitated by lead. The percentage of Cr 3+ obtained was in good agreement with the result obtained from chromatographic separation. Chromium was determined by the y activity of the Wr and the radiochemical purity of the preparation was checked by y-ray spectroscopy on all fractions. The radiometric measurements and the autoradiogram of the AlsO plates still in the chromatographic’ development of showed, however, the presence of “tailing’: chromate ions. It is believed that this is mainly kinetic in origin due to the high velocity of migration (IO cm/z h) as has been suggested by GIDDINGS~“.
Discussions with Dr. G. B. COOIC (I.A.E.A. fully acknowledged.
Laboratory,
Interrtational Atomic Energy Agency Laboratory, Seibersdorf, Niederlkterreich (Aztstria)
Seibersdorf)
IOAN
are grate-
GALATEANU
Ann, CJt%m. (Rome), 4.5 (1955) 1087. I-I. POLLARD, J. F. W. MCOMIE AND A. J. B,\NISTER. Chenz. I?ld.(London). 4g (1955) 1598. 3 M. N. SASTRI AND A. I?.RAO,J. Cltromalog.g. (1962) 250. 4 M. LEDERER AND L. OSSICINI,J. Clwomatog., 13 (1964) 188. 5 M. LEDBRER AND V, MOSCATELLI.J. Cltromalog., 13 (1964) 194. 15G. BAGLIANO, G,GRASSINI,M.LEDERER AND L. OSSICINI,J.C~Y~NU&~.. 14 (1964) 238. 7 L. OSSICINI,J, Chromalog., g (1962) 114. 8 H, A. DROLL AND W. ‘IT. LINDSAY, JR., U.S. Al. Energy Comnz., WRPD-TM.-12 (x956);C.A., 51 (1957) 55719 gM. LEPORT AND M. LIZDERER,CONZ~~. Rend., 242 (1956) 2458. Chem., 5 (1957) 123. IO E. PuN00~ AND J. TRoMPLER, J. Inovg. Ed. II R. S. DRAGO AND H. 13.SISLER, J, Am. Chem. SOL, 79 (1957) 1815. 23 (1950) 18 1. 12M, N. TUL'CWINSICII,J. Appl. Chcm. USSR (EnglisJb Transl.), Ada PJtys. Cltem.,4 (1958) 54. 13 M, T. BECK AND J, BhRDI, Acta Univ. SzegerZ., 14 J. C. GIDDINGS; Anal. Cl&em., 35 (1963) 1999.
I C.
BIGWI,
2 I?,
Received
December
7th, 1964 J. Clwqmatog., .
a
xg (1965)
208-z
13
NOTES
Analyses made in this manner were quantitative when an average of 24 spots (from 4 sheets) was taken. On each sheet were 3 runs of the original solution and 3 runs of the original solution diluted with one or three times its volume of water. ‘This routine was followed for samples prepared according to either procedure I or II. Thus there was found in pure zinc silicate 41.5 y0 of total silica (19.4 y0 Si). Theory requires x9.8 oh Si for ZnSiO,. On analysis, artificial mixtures consisting of 4g O/~of silica (particle size less than 2.6 ,u) and of 51 o/ozinc silicate (particle size less then I ,u) there was found 48 % free silica (SiOs). In this method the particle size of the sample, whether free silica or silicate or a mixture thereof, is immaterial as compared with physical methods such as differential thermal analysis, X-ray diffraction, or phase contrast microscopy. A more detailed description will appear elsewhere in the near future. lutstit&e oJr1nd~~st~iaEL IJygiene and Occa@ationaZ Medicine, Bratislava (Czechoslovakia)
E.
z E. Mhr_$, Pafier presented at lice 2nd Pafier Clwomadog~*aj5hyConfe~*e~ace,Pval&a,June 21-24, N. G. PomzWhEv, Gigielza i Sad., 22, No. II, (1951) 91.
MALP
I&r.
2
Received
January gth, 1965
J. Chromalog.,
Paper and
Ig (1965) 206-2q8
thin-layer
chromium(lll)
from
chromatography
applied
to the separation
of
chromium(W)
There are not many publications available dealing with the chromatographic separation of chromium ions of different valence (Cr3+ from Cr0,2-). BIGI& mentions the separation of non-radioactive chromium ions (Cr2+, Cr3+ and CrO,s-) by paper chromatography (Whatman paper No. I) using butanol-acetic acid-ethyl acetatewater (50 : IO : 5 : 35) as developer. POLLARD et aL2 separated Cr3+ from CrO,s- on paper y$ng methanol-ethyl ether-cont. WCl-water (30 : 50 : 4 : IS). For this purpose paper impregnated with zirconium phosphate was also used by SASTRI AND RAO~, with saturated Na,SO, solution as developer. LEDERER et aZ,4-a and OSSICLNI’ described the adsorption of chromate ions and other ionic species on paper impregnated with ion-exchange resin from different media. There are no publications available which deal with the chromatographic separation of radioactive carrier-free chromium(II1) from chromium(V1). The hexavalent chromium may be reduced in solution to lower valencies by different, organic substances or radicals formed by ionizing radiations of recoil phenomena. Other authors investigated and described the radiation-induced reduction of chromium(V1) solution@ and y-ray-induced exchange between trivalent and, hexavalent chromium ions in aqueous acid solutions s. The reduction of chromate or dichromate by different organic substances, such as formic acidlo, liquid ammonia and J. Cltvomatog., IQ (1965) 208-213
NOTES
209
liquid ammonia solutions of potassium amiderr, sugars12, and ethanols or hydrazine perchlorate and kydroxylamincla have also been published. For the determination of radiochemical purity, we have reproduced BIGHI’+ and SASTRI'S~ experiments using carrier and carrier-free chromate and chromium chloride labelled with % r. In the course of these experiments we observed a supplementary reduction of chromate ions by the reducing action of chromatographic paper and/or solvents (Figs. I and 2). When the concentration of chrcmate ions in the solutions is very low (carrier-free) (Fig. I) this reduction is increased and may be a source of error in the analysis or determinations of radiochemical purity of some labelled compounds of chromium. Therefore other systems were sought.
cm
Fig. I. Paper chromatography of radioactive carrier-free chromium chloride and sodium chromate on Whatman No. I paper impregnated with zirconium phosphate. Developer: saturated solution (I’) filCrC1a after clevelopment, ;f N&SO4 (ascending, t = 2 11). (I) GICrCI, before development: = 0.92; (2) Na,elCrO,‘before development; (2’) Na, GrCrO, after clevclopment, Rp Cr”+ = = 0.38. 0.: r ; Rp CrO,+
Resaclts
A summary of these experiments is given in Table 1. Radioactive GrCr wasused as tracer in many of these experiments. On zirconium phosphate impregnated paper, Crac behaved in a very variable manner. When macroscopic amounts of CrCl, were developed with saturated solution of sodium sulphate, approximately 60% migrated with an Rp of 0.85, but the remainder did not move (Fig. 3). When, however, the con-
10
12
14
18
18
20
22
24
Fig. 2. Paper chromatography of ‘radioactive sodium chromate with carrier, on Whatman No. 1 paper impregnated with zirconium phosphate. Developer: saturated solution of Na,SO, (ascending, + CrCl, after development, (I’) Na2 %rO, 2 = 2 h), (I) Na,brCrO, + CrCI, before development; + K,CrO, before development; (2') Naa51Cr0, RF Cr3+ = 0.90; Isp CrOd2- = 0.36; (2) Na,%ZrO, + K,CrO, after development, Rp Cr0,,2- = 0.68. J. CAromalog.,
zg (1965) 208-213
+ Ml,
WCl,
Na,wo,
Na,zlCrOl + K&O,
4
5
6
7
:;.?A
WCl, carrier-free
+ CrCl,
+ K,CrO,
w-cl,
3
Na,SO, satd. soln. .
Na,SO, satd. soln.
Xa,SOI satd. soln.
Xa,SO, satd. soln.
Na,SO, satd. soln.
(4O:j:IO)
Na,SO, satd. soln. Acetone-4 M HCl-H,O
Glass paper Filter paper Whatman No. I impregnated with zirconium phosphate Filter paper Whatman No. I impregnated with zirconium phosphate Filter paper Whatman No. I impregnated with zirconium phosphate Filter paper Whatman No. I impregnated with zirconium phosphate Filter paper Whatman No. I impregnated with zirconium phosphate Filter paper Whatman No. I impregnated with zirconium phosphate
I
CrCl, + K,CrO, CrCl, + K&O,
COMPOUNDS
3
AND cr(vI)
Developer
OF Cr(IlI)
Adsorberzt
SEPARATION
Chromium con~por~~~ds
CHROllATOGRAPHIC
TABLE I
a
2
2
2
2
5
2
(h)
Dwatiolt
0.90
-
O.Sj
O.Sj
0.00
-
0.66
0.36
-
0.67
0.33
-
0.00
CYO,2_
RF fl.Y+
‘
1 ii
The reduction of s1Cr042-is decreased
Cr0,2- is partially reduced to Crz+
-
CrOa2- is partially reduced to Wf
Not separable CrO,s- is partially reduced to Ci3+
Observatiom
Z El !Z
SQTES
x c
-t-c 9
!
jk
I.
coot
oooc
6663
NOTES
212
centration of W+ was very low by using carrier-free WrC13, only 8 o/omigrated. Intensive reduction of chromate was observed in these systems, partjcularly when carrier-free chromate was used and this made accurate determination of mixtures of Cr3+ and chromate ions ikpossible (Figs. I and 2).
Fig. 3, Paper chromatography of radioactive chromium chloride with Carrier on Whatman No. I paper impregnated with zirconium phosphate. Developer: saturated solution of Na,SO, (ascending, RF = 2 11). (I) WrCl, + CrCl, before development; (I’) GlCrCl, + CrCl, after development, L+J+ = 0.55; after development, (2) WrCl, + K,CrO, before development: (2 ') GlCrCl, + K,CrO, I Rp Cr3+ = 0.91.
In attempts to avoid the reduction of chromate ions, the behaviour of Cr”+ and chromate ions was studied by the thin-layer method on plates of silica gel, zirconium phosphate and aluminium oxide, using inorganic solvents such as sodium Experiments with silica gel and sulphate or carbonate solutions as developers. zirconium phosphate did not give satisfactory results. Better effects were obtained using plates of aluminium oxide (Grade Merck nach Stahl). The following method was used. Chromatographically pure aluminium oxide (80 g) was ground in an agate mill for 40-50 minutes to 150-200 mesh. Calcium sulphate (IO g) was added and the mixture stirred for 30 min. Then 67 ml of bidistilled water were added and thoroughly mixed. The suspension obtained was spread on plates (20 x 30 cm) by means of a
Fig. 4. Thin-layer chromatographic separation of chromium(II1) and chromium(V1) ions from radioactive carrier-free sodium chromate solution, on aluminiurn oxide plates. Developer : saturated I mC/ml, a = 16 pC; b = 17 1tC; c = solution of Na,SO, (ascending, t = 2 h). Specific activity: 23 ,uC; d = 15 @. J. Clwomalng.,
19 (1963) 208-2r3
213
NOTES
Desaga apparatus to a layer thickness of 0.2 mm. After drying at 110~ for I 11,different samples of WrCl, and Na,6lCrO, solutions, with carrier and carrier-free, were pipetted on the plates (Table I). The plates were developed with a saturated solution of Na,SO, for 2 h. After development the radioactivity of the plates was measured by G.M. counting and the autoradiochromatograms were prepared ,(l?ig. 4) using “Kodak X-ray film” as well as Kodak developer and fixative. Under these conditions, Cr +3 ions do not move but the chromate ion migrates with an RF of 0.60. Even with carrier-free chromate the major part of the radioactivity migrated.The fraction of activity remaining at the start was believed to be due to the presence of Cr3+ ions in the original solution. This was checked on the original chromate solution by radiochemical methods. Carrier chromate and Cr3+ ions were added to the solution and the chromate was precipitated by the addition .of lead ions. After centrifuging the precipitation was repeated, and any Crs+ ions remaining in solution were oxidised by hydrogen peroxide to chromate which was precipitated by lead. The percentage of Cr 3+ obtained was in good agreement with the result obtained from chromatographic separation. Chromium was determined by the y activity of the Wr and the radiochemical purity of the preparation was checked by y-ray spectroscopy on all fractions. The radiometric measurements and the autoradiogram of the AlsO plates still in the chromatographic’ development of showed, however, the presence of “tailing’: chromate ions. It is believed that this is mainly kinetic in origin due to the high velocity of migration (IO cm/z h) as has been suggested by GIDDINGS~“.
Discussions with Dr. G. B. COOIC (I.A.E.A. fully acknowledged.
Laboratory,
Interrtational Atomic Energy Agency Laboratory, Seibersdorf, Niederlkterreich (Aztstria)
Seibersdorf)
IOAN
are grate-
GALATEANU
Ann, CJt%m. (Rome), 4.5 (1955) 1087. I-I. POLLARD, J. F. W. MCOMIE AND A. J. B,\NISTER. Chenz. I?ld.(London). 4g (1955) 1598. 3 M. N. SASTRI AND A. I?.RAO,J. Cltromalog.g. (1962) 250. 4 M. LEDERER AND L. OSSICINI,J. Clwomatog., 13 (1964) 188. 5 M. LEDBRER AND V, MOSCATELLI.J. Cltromalog., 13 (1964) 194. 15G. BAGLIANO, G,GRASSINI,M.LEDERER AND L. OSSICINI,J.C~Y~NU&~.. 14 (1964) 238. 7 L. OSSICINI,J, Chromalog., g (1962) 114. 8 H, A. DROLL AND W. ‘IT. LINDSAY, JR., U.S. Al. Energy Comnz., WRPD-TM.-12 (x956);C.A., 51 (1957) 55719 gM. LEPORT AND M. LIZDERER,CONZ~~. Rend., 242 (1956) 2458. Chem., 5 (1957) 123. IO E. PuN00~ AND J. TRoMPLER, J. Inovg. Ed. II R. S. DRAGO AND H. 13.SISLER, J, Am. Chem. SOL, 79 (1957) 1815. 23 (1950) 18 1. 12M, N. TUL'CWINSICII,J. Appl. Chcm. USSR (EnglisJb Transl.), Ada PJtys. Cltem.,4 (1958) 54. 13 M, T. BECK AND J, BhRDI, Acta Univ. SzegerZ., 14 J. C. GIDDINGS; Anal. Cl&em., 35 (1963) 1999.
I C.
BIGWI,
2 I?,
Received
December
7th, 1964 J. Clwqmatog., .
a
xg (1965)
208-z
13