CHAPTER - V

THIN-LAYER CHROMATOGRAPHIC SEPARATION OF SOME ANIONS ON COPPER SULFATE

IMPREGNATED SILICA GEL LAYERS

167

Krot'i the literature the TLC of anions has been much

less extensive co'ipared to that of cations fl-3l. Silica

^]e\ [4 8i, cellulose 19-Ll!, alumina [12], silufol [13] and

hydrated stannic oxide layers [14] have been used for the

separation and identification of anions although no work

has been reported on the use of silica gel impregnated with

inorganic salts.

In the present work, the thin-layer chromato­

graphic behavior of some common anions on plain and copper

sulfate - impregnated silica has been investigated in mixed

aqueous-organic solvent systems containing acetone.

EXPERIMENTAL

Test solutions. IX test solutions were either sodium or

potassium salts of all anions studies, except SCN which

was taken as ammonium thiocyanate. Double distilled water

was used for the preparation of solutions.

Reagents. Silica gel (E. Merck, India), formic acid,

hydrochloric acid, hydrobromic acid, sodium chloride.

aiimoniuiii hydroxide and acetone (B.D.H., India) were used.

These and all other reagents were analar grade.

168

Detectors. The detection reagents for various anions were

used as reported in chapter III.

Mobile phases. The following solvent systems were used as

I!:obi 1 e phases :

M HCl: Acetone (1:9)

HCl: Acetone (9:1)

NaCl: Acetone (1:9)

NaCl: Acetone (9:1)

HBr: Acetone (1:9)

HBr: Acetone (9:1)

NH,OH: Acetone (1:9)

NH,OH: Acetone (9:1) 4

Formic Acid: Acetone (1:9)

Formic Acid: Acetone (9:1)

"2

M,

M-

Mr

>\r

M 10

In all the solvent systems, HCl, NaCl, HBr, NH^OH and

formic acid were O.IM aqueous solutions while the acetone

\.'as pure .

Stationary phases,

S, Plain silica gel G

S. Silica gt'l impregnanted with O.l-'j.O/

aqueous solution of copper sulfate.

Preparation of TLC piates-

(i) Plain silica gel plates: Silica gel was mixed with

169

conductivity water in the ratio 1:3 with constant shaking

for 5 to 10 inin. The resultant slurry was coated on well-

cleaned glass plates to give a layer approximately 0.25nim

thick. The plates were dried at room temperature (30°C)

and then heated at 100+ 5°C for 1 hour. After activation

Che plates were stored in an air-tight chamber.

(it) Copper sul fate-impregnated silica gel plates: To

prepare impregnated silica gel layers, a slurry was made

by mixing an aqueous solution of O.l-5.07o, copper sulfate

with silica gel in the ratio 3:1. Thin layers were then

prepared as described above for plain silica gel plates.

Procedure. For qvialitative analysis, one or two drops of

the anion sulutions were spotted on the plates with glass

capillaries. The spots were dried and the plates developed

by the ascending technique, the ascent of the solvent was

fixed ac 10 cm in all cases. After development, the plates

were dried and the anion spots visualized with the

appro[)rlate spray reagent. Rp values of the leading front

(R, ) and of the trailing front (R,p) were measured and

reported as (R,-R^),

Rr. values were calculated from R, \ ' T

The limits of detection of the various anions were

determined as reported in chapter III.

summ

170

RESULTS AND DISCUSSION

The main points which emerge from this study are

arized below:

1. A small change in Rp values was sometimes observed

when mixtures of anions were developed as compared

with single substances.

2. The development time for a 10 cm run ranged between

45-70 min depending upon the mobile phase.

3. Silica gel impregnated with CuSO, gave excellent

results. Thin layers were of good quality. Generally,

the spots were compact and well formed in all solvent

systems at 0.1-17o impregnation. Plates impregnated

with 2-57o copper sulfate solution deformed during

development.

4. R,-, values reported in this paper represent the

averages of triplicate tests and were measured to the

center of the spots on the plates.

5. Sodium chloride-acetone (1:9 and 9:1), NH,OH-acetone

(1:9 and 9:1) and HCl-acetone (1:9) systems were found

most suitable for separations. A few anions showed

occasional tailing. HCl-acetone (1:9) was found to be

the best solvent system for multicomponent separation

with 1% copper sulfate impregnation. Formic acid-

171

acoLcjiu (1 :y) produced highJy compact spots of anions

on (). 1 "', copper sulfate layers,

b. Ihe copper sulfate travels with the solvent front upto

the iiicidle ot the plate in solvents M., , M, and M-IM-

Ihcse systems are therefore unsuitable for iinpregn.i t eci

1 ayers.

7. Solvent.^ containing 907o acetone gave better results

than those containing lOX acetone.

2- 2- 3-o. In all solvent systems, CrO^ , Cr20y , Fe(CN)^ and

l- eiLN'i, produced colored spots on impregnated layers

and thus were self detecting.

9. NO. could not be detected on 17o impregnated layers

while it was clearly detected on plain silica gel as

well as on O.IX impregnated layers.

10. In addition to the other ions, VO2 was also chromato-

graphed to assess the possibility of separating VO 2

fro!!, VOT-

Ihe results have been summarized in Figures 1-3 and Tables

1 and Z. Figure 1 summarizes the results of AR^ values

' A Kp Rp )>T plain silica - R,, on impregnated silica)

with various mobile phases. It is evident from Figure 1

that i.iipregnated layers are more selective (strongly

sorbing) than plain silica for most of the anions, as

.0 r

0.8

0.6

-0.2 -

-O.A -

H C i : A c e t o n e ( 1 : 9 )

( a )

1

1 r^t

O Z

1 1 2 U t / l

1

1 i_

00

1

rsi rx/

O >

1

1

O a

1

1 r-1

r> >

I

172

J Nl ^« O U

O

fvl ^

o o 2

• ^ - ^ O

l i . o

Q: <3

O.A

0?

0.0

-0 .2

-O.A

<3

O.A

0.2

0.0

- 0 2

-O.A

HBr ; A c e t o n e ( 1 : 9 )

( b )

_L _L _l

1 rsi U 2

1

Z U LO

PNI C%*

o >

1 n -t

O a

1 n O >

rsi ^

o L ,

f-J

r-i Z ^ -J ;?: ^ "X^^ y U O

u

F o r m i c A c i d ; A c e t o n e ( 1 : 9 )

(c )

A n i o n s F i g . l contfl

173

N a C i : A c e t o n e ( 1:9

<i

Li.

<3

0

0.4

0,2

0^0

-0 2

-0 4

N a C l : A c e t o n e ( 9 : 1 )

( f ) N H ^ O H : A c e t o n e ( 1 : 9 )

o-- 6 - i 5 ^ = S ^ ^

_1_

o 2

U 03

O > o

>

o

1 r~j v j

O O i

' • ' 7 U t>> u_

•-T ^

z U c u.

o

u o

A n i o n s

Fig . 1 contd.

U-cr < j

174

NH4OH : Ace tone ( 9 ; i )

--1 l- ( -. 1 _ _J I :z u in CD

(-Nj r s i

0 >

m vj 0 Q.

1 r~>

0 >

O U

• z u q

u

An ions

Fig. 1 Plot of ARp (Rp on plain silica gel - Rp on

CuSO, impregnanted silica gel layers) vs.

anions

o 1 Copper sulfate impregnation

A 0 .17„ Copper sulfate impregnation

175

indicate d by positive ARp values. There was no

significant ditt'ercnce in the mobility of anions when

chromatographed cm silica impregnated with \% or 0.1°

copper sulfate using HCl , HBr, NaCl or formic acid-acetone

(1:9) solvent systems. With formic acid-acetone, NO2 showed

increased mobility on VL impregnated layers ( Rp = -0.3)

compared to its mobility on plain silica or silica

impregnated with 0.17o CuSO^ ( A R p = +0.1). The reverse

trend was observed for I which moves faster on plain

silica ( ARp = 0.24) compared to W layers. However, 0.1%

CuSO, impregnation was found to be ineffective in changing

the mobility of I which behaved similarly in NH,OH-acetone

(1:9) where it moves faster on plain silica as compared to

1; CuSO/ layers. Sodium chloride-acetone (9:1) and

NH,OH-acetone (9:1) systems were found the most effective

in changing the mobility of most anions on impregnated

layers and thus open numerous possibilities for

separations. However, the tailed spots produced by some

anions limit their separation from other anions. With

NH^OH-ace tone (9:1), most of the anions were strongly

ndsorbecl on V, layers compared to plain or 0.1% layers.

Figure 2 summarizes the hR„ values of anions

chromatographed on silica gel impregnated with II CuSO,

and developed with solvents M. M„,M,,M^,M^,Mg and MQ.

176

o o r—

X

h. a: • — '

U-

rr X

100

80

60

AO

20

H C I : A c e I o n e ( 1:9 )

0

o o » — •

X Li.

cr —

[i-

ir JZ

100

8 0

60

AO

z'O

1 r-J O z.

t\^

-

-

-

7:

u ID

O L

T O O r

CO

4

r-i fsi O >

1

m <t O a

^ 1 m (J >

o

u ^

o O

u u o u

U

H Br : A c e t o n e ( i : 9 )

F o r t i l ic Ac i d ' A c e t o n e ( 1*.9 )

A ri I o n s

F i g . 2 contci .

100

o o < — X

u_ (T —^ LL

u.

80

60

AO

20

0 L_

I - N a C I : Ace tone ( i: 9 )

: i - N a C i : A c e tone ( 9:1 )

177

100

o 80 o

>< 6 0 ti­er - AO a: X 20

0

N H / ^ O H ; A c e t o n e ( 1:9 )

N H / O H: A c e ( o n e ( 9:1 )

A n i o n s

Fig. 2 Plot of hRp versus anions

htationarv phase: l7o copper sulfate imprrjniat cd

silica ii e 1

O Compact spots with R. -R. <0.3

L Tailed spots with K, "H^ >().3

¥: Badly tailed spots \M.th R,-R^ >0.4

178

IL is evident that the different mobile phases are able

to bring about different retention sequences of anions

leading to several binary, ternary and quaternary

separations. The mid R^ (Rp - 0.4-0.6) values of NO 2 in

M. and Br in M , My and M^ can be used for their

separations form all other anions with higher or lower Kp

Vi 'alues. Vol^, PO4", Mool", Cr207 , Fe (CN) 5 , Fe ( CN) 5 and

WO^ are strongly adsorbed on the impregnated layers (hRp

(J-IO) in all solvent systems containing 907o acetone

(Figure 2). The mobility of a few anions is increased when

the concentration of sodium chloride or NH/OH is increa' ed

2-ile phase (M, and Mo). However, CrO^ and in the mob

Cr ,0^ showed tailing. Likewise, M. and M^ can be utilized

for the ser)aration of MoO, (hR^ = 90-95) from the anions ' 4 F

with low R„ values. SCN , I , Br and NO,-, gave higher Rp

values in most of the .mobile phases and thus can be

separated from anions with lower Rp values.

In Figure 3, the results obtained on O.IZ copper

sulfate layers in various solvents have been summarized. A

major advantage of this adsorbent is that NO3, which could

not be detected on VL copper sulfate layers, was very

clearly detected on 0.17„ layers. Comparison of Figure 2

and 3 slio\.' almost identical chromatographic behaviour of

tht anions on both the adsorbents in HBr-acetone and

loTi'iic acid-acetone. Conversely, most of the anions do \'0\i

100

c o ; > - ' Lt

>

u J-' J,

8 0

6 0

^ 0

^0

1 Nf1/^UH W

A ( e (( M o ( 1:9 )

11- N H ^ U h l

A c e t o n e (9;1 )

- -. 1 _ 1 1.

1/1

-f o m >

1

1 r-1

o >

u__ 1

o u

(_J

1

1

—

1 1 , ^

nop. U tJ

u.

U3

1

•^z I.J W

u.

KO 1

1

O / • ^

U

179

0 0

r , ^ 0

- b 0 I

• . 1 ) 1 1. 1

20 1

o

- _x f \ ) r td ic Ac i d : Ac e t o n e 1 :9

+ r J fxj O >

1 r-i J O CL

1 r-^ O >

LT

' 0 0 ( 1

80 [ I

' 0 [

i> 0 [ I I

2i)

tU 1 : Ac e t o n e 1:9

A n i o n s

Fig . 3 contd

180

^-~•

o o X

u cr

u. Q:

r

100

fi 0

6 0

A 0

2 0

0

C)--

in O

NaC

NaC

Ac e t o n e 1:9

A c e t o n e 9:1

_L I . ^ 1 _ L

o I

o a

O O

I

o o 5

<f?'^^^'" r j -J-

C) o X

u a

u

1 0 0

8 0

6 0

AO

2 0

0

H B r : A c 0 t o n c f 1 : 9 )

c> <)

1 '••'

C)

^

1

z u 1/1

1 r-1 O 7

4-o >

Fig. 3 Plot of hRp versus anions

Srationary phase: 0 .1/„ copper sulfate i npre,"ii i ti H

silica gel

O Compact spots with R,-R^ <0.3

A lailed spots with R,-R^ >0.3

* Badly tailed spots with Rj-R^ ^0.4

u

<

U2

c o

• 1 - 1

JJ ct) 1-CO

a a;

CO

re •u c Q; E

•H

0) a X

u

a; 6 o

CO

I

>

•r-l

o ro tn C o

•r-l

m a CD

00

181

r~ 00

O

o

^H

oc oc o

c

•r-i

Ln oc o

o

T H

r--. 00

o

o

T-H

o C^

O

o T-i

^ CO

o

o

r-i

o CTN

o

o

—1

I I

z o 00

2 u 00

z o 00

z a 00

z o CO

< l • ^ o a ^ a ^ L n L o c N ^ - L O ' - ^ T H

O C O O O O O ' O - O I I I I I I I O I O I

M D - J - r - j i n c N j O L n i o i en

O O O O O O O T - ^ ^ r - ( 0

I I I I I I I Z I yj u u u )-i ^ ^ I O l >-i

C Q C Q C Q C Q m c Q c Q H C O i — l o q

o

o

z C/1

or

oc

I

ON cn

I I I I I

<t-1^

en ^ O LPl

U-1 CN CN CM

in

z

'7

O I

o o I 1 ^ o

o I

o I

LPl

o I o

I

o

O I

o I

o i

O I I

IP

O O o o o l o j losi l o j i c M i O s i i r s i i c s i O O O O O O O Z Z Z Z Z Z Z

I i I I I

I CNl I CvJ I ^^J

o o o z z z I I I

I CM o z

O >

o c ^

o c ; z

I

o o o

o o o

o o

o o

o o o

o o o

o o

o o

o o

o o o

o o o o o o o o

I I I I I I I o o O O O v£) <!• vO ^ t \r> <1" ^

I I Z Z I o j r~v

U O C N - J - Q i + c N - < f ^ ^ ^ - O r x i r o - c f c N C N O :D (\) y^ ^ O O o u. tu o o IX > s:

z o z

o z o 0)

z o z

o QJ

I

o o

<1-

y~

1)

en Ct!

x: a OJ

,—1

•M X^ o 5t

0) c 0 i J 0) CJ

< o ..

r - l r-l

o 3 :

CO

ra X a

> V-i

ro C O

• H

i J 03 U CO

.—, 1) 50

CO

U •rH

> 1

• H

oo

--t o

a oo di 3 -o O TO C C S'-S O DCr-f —4 0) U U S^ O

(xu ^ E -r-l O

•r-l 3 on

18?

—. L n

3 0

• o

1

o T H

• —

1—(

0 0 0 0

• o

1

m ON

o • w .

1 z o 01

-—-CT^ r^

• O 1

Csl

a

o —

1 1 — «

-—. T - J

v O

. o

1

r- 1 ^

o —-

1

>-! CQ

^ OC

0 0

• o

1

o T - l

-—-

1

(—(

'—. ^ TO

• c-j

1

o T-\

-— 1

2 : o LO

.— r^ 0 0

• o

1

o T H

• —

1

Z o CO

— ro 0 0

• o 1

C N I

ON

o -—

1 ro C Z

—. o ON

• o

1

o r-H

• —

1 ro O Z

--o r^

• O

1 ON I ^

o — •

1

)-CQ

^ 0 0

0 0

• o

1

^ (T-

O '-—'

1 ro O / ^ - i

,—. '£> CD

• O

1 0 0 CT>

O —

1 r o

O rf'-j

--<t C'

• o

1

o T - l

* „ -

1 1—(

^-^ m r^

•

o 1

-d-0 0

o —

1

u ca

— L O

cc •

o 1

o - H

—• 1 c^

o z

; X

" i

- • ^

•

•--1

i 2

O

cr

-—, 5 -r

^ 1

X X

^ 1

I--

a l

X /"

'; r~--

'^ w -

1

/' " x:

CO O J

• O

1

O u O

o r s j

O z 1

o o

o

ON

T H

• o 1

ro <t

O

1 <rsj

O Z

o o

o

1

-. r ^ r s i

o 1

UO

o 1 f N l

o z

1

o o

o

+

m r s i

•

o 1

i n

•<r

o

1 O J

O z

1

o o

o

+ • i -d " ro< t r \ i rMc^ r \ j O (X

o CL,

o >

o >

^ 0 0 CvJ

o 1

i n

o

1 CNI

o z

1

o c

o

1

o <t-

-o 1

UO L O

o

1 r s l

o z

1

o o

o

1

CM v - t f N l v t

o o

T.

o o .^

^ UO

o i

CN|

r^

o

1 CM

o z

1

o o

o 1

r o v£)

z o 0)

t i n

v D LO|

o 1

ONI

v D

O

1 CNJ O Z

1

o o

o 1

ro \£)

Z O

<1) U^

r - <

r s i

o 1

0 0 CM

O

1 CO

o >

1

o o

o 1

CO \0

z o 0) u

m i n

o 1

r ^

v D

O

1 C N I

O z

1

o o

o 1

<i-v D

o 1

U-)

r~^

o

1 CN

o z

1

o o

o 1

v l ' v D < } • ^

z o OJ u^

z c; 0) u-

a> T - l

O 1

vr> C^J

o

1 Ci

O >

1

o o

o 1

<t ^

z a OJ

lu

CT^

<r o

1 T — 1

^ o

1 Csl

o 2

1

O

o 1

ro O

1

CM < r

o >-u

-o i n

o 1

0 0

^ o

1 CNJ

O z

o

o 1

CO

c 1

Cvl - ^ j -

o v-< u

< ) •

^ o

1

0 0

• • ^

o

1 CN|

>^ 2

1

o 1

i n CsJ

o 1

^ J-C V--

C

o i n

1

'X v C

o

1 r .

C _

_ 1

O --'

r-si r ^

^ ^;

u

O

r-^

i r .

1 p ^

JD

—

1 -N^

^ y

z 1

-

--' V ^

-^ x j r ^

^ ' \ i

i - j

O

^ •L'

^ C^ 'Y~

-r

, -c ^

•

^-* ' x j

— '-^1 r

'^ u J

u ro

O •r-l E

> 0

Ci^

CU C O 4 J

OJ u <d

(T-

T-<

JZ 4 J •r-l

3

•xi r -1 0) -

0) -u o 0 0 ro C>0

C P ctl O C O U 0)

. - 1 P fr-o

r—1 C L T H

•r- l E •

0 0 • H O

t

C

o •r-l J-J

:3 , — 1

o 11

183

.—. LO

o > o 1

o T-l

1

cr r • o 1

OO

O 1 u

1

^-~-a 00

• o 1

o TH

1 ro O 2 1

-<f r--• o 1 OC

o 1

v-. m 1

<l-co • o 1

o o 1 r^

C

1

'-. ^ r-~ • o 1 00

o 1 ro i^^

1

~ CT' 00

• o 1

- T-H

1 ' ^

o

1

.— LO

r--• o

1 CTN

-1

>-4

1

r 00

• o 1

cr O

1 < ^

O

1

o ^ ' - - ' ^ o c ' - - < ^ m o o — •

v ^ . . . . . .

O O - C O O C O O I I O I I I I I I

o o r ^ I L n < ) - , - i r ^ r ^ < t ^ ^ o o v x j r - ^ - ^ c N v D r ^

O O O O O O C O O

I C N I I C N J I C N I C S J I C N J I C N J I O - , ' C N I C N J

O O O C O O O O O 2 2 2 ; Z 2 : z > 2 2 :

I I I I I I I I I

O o o

o o o

o o o

c c o

o o o

o o o

o o o

o o o

o o o

O O O C O O O O O

184

TABLE 2

Limit of Detection and Dilution Limit of Anions and VO „ on

Silica Go! Impregnated with 0.1X CuSO, with Formic Acid:

Acetone (1:9) Mobile Phase

S] .

No.

1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

11.

12.

13.

14.

a Dilution

, . Voli

Ions

Br~

3-PO

l'

2

V0~

NO-

NO'

SCN"

Fe(CN]

Fe(CN)

Cro2-

Cr202-

MoO?~ 4

wo^-

] imit

ame of

't 3-6

test

Salts

KBr

Na2HP0^

KI

V02S0^

NaV02.H20

NaNO^

NaN02

NH^SCN

K^Fe(CM)g.

K3Fe(CN)^

K2CrO^

K2Cr207

Na2Mo0^.2F

Na2W0^.2H2

solution (m

3H2O

I2O

0

1 ) X

Limit of detection

100 .0

10 .0

10 .0

10 .0

1.0

1.0

1.0

1.0

1.0

0 .5

0 .5

0 .5

0 .1

0 . 1

10^

Di1utton

11 n 11

2 1:10^

1:10^

1:10^

1:10^

iiio"^

1:10^

1:10^

IrlO'"''

i.-io''

1 :2x10'^

1 :2xl0'^

I -.ZxHy'

1 : 1 0 '

1:10^

Limit of detection { pg

185

behave similarly on both sorbeni:s in NaCl-acetone and

NH, OH-acctone. Thus, in addition to the separation of \'0 - ,,

from numerous anions on 0.1% layers many other m'-ti

separati(^ns oi' anions can be realized in NaCl -•icotf)n(. r

NH,OH-acetone.

The chromatographic systems developed pro\'ide

numerous possibilities for rapid, reproducible and cloTn

separations of anions from mul ticomponent mixtures. Sn- c

separations experimentally achieved have been .sumnari/ed

in Fabl e 1 .

Table 2 summarizes the limit of detection md

dilution limit of various ions. The proposed mcLhod is

highly sensitive for most ions except Br .

186

REFERENCES

1. U.A. Th. Brinkman, G. De Vries and R. Kuroda. f.

Chromatogr., 85, 187 (1973).

2. R. Kuroda and M.P. volynets, in CRC Handbi ol-- o:

(Chromatography: Inorganics, Vol. 1 (M. Qurcshi cd.),

CRC Press, Boca Raton, Fla., 1987, p. 89.

3. A. Mohammad and K.G. Varshney, in Handbook of Fhii

Layer Chromatography (J. Sherma and B. Fried eds.).

Marcel Dekker, Inc., New York, 1990, p. 463.

4. J. Benes, Collect. Czech. Chem. Commun., 44, 103^

(1979) .

5. J. BeuGs, Collect. Czech. Chem. Commun., 44, 'iQh

(1979) .

6. H.M. Chawla, N.N. Ralhan, N.K. Garg and S.S. Chibber,

J. High Resolut. Chromatogr. Chromatogr. Commun., 3.

651 (1980).

7'. K. Kawanbe and K. Maruyama, Yakugaku Zasshi, 101, 912

(1981);Chem. Abstr., 96, 45420K (1982).

8. J. Zuanon Netto, A.F.C. Graner and M. lonashiro.

Ecletica Quim , 9, 45 (1984).

9. G. Buchbauer and R.E. Markis, Sci. Pharm., 51. 48

(1983) .

10. R. Gallego, J.L. Bernal and A. Martinez, Quim Anal..

31, 3 (1977) .

187

11. R. Gal lego, J.L. Bernal and A. Martinez, Quir,. Anal.

31, 69 a977)

12. K. Ravindra Nath and P.B. Janardhan, Indian J. Cher'.

21A{2), 150 (1982).

13. J. Franc and E. Kosikova, J. Chromatogr., 187, 46;

(1980).

14. A.K. Sen and U.Gh. Ghosh, J. Liquid Chromator., 3. 7

(1980).