Indian Journal of Chemical Technology Vol. 7, November 2001 pp.452-457

Thin-layer chromatography of heavy metal-diethyl dithiocarbamate complexes

B R Rao•, H S Rathoreb*, S Mitalb & Y N Singhb

"Indian Institute of Chemical Technology, Hyderabad 500 007, India bDepartment of Appl ied Chemistry, Zakir Hussain College of Engineering and Technology, Aligarh Muslim University,

Aligarh 202 002, India

Received 17 November 2000; revised II June 2001 ; accepted 9 July 2001

Thin-layer chromatographic behaviour of some heavy metal-diethyldithiocarbamate complexes has been studied using calcium carbonate, calcium citrate, calcium oxalate, calcium phosphate dibasic, calcium sulphate dehydrated, cellulose and silica gel G as stationary phase and acetonitrile, acetone, benzene, butanol, chloroform, 1,4-dioxan, dist illed water, ethyl acetate, EDT A-ammonia buffer (I : I) , methanol and propanol as mobile phase. Cd(II) and Pb(H) from Mn(II), Fe( III), Co(! I). Ni(Ir ), Cu(H), Hg(l) and Hg(H) have been practically separated on cellulose impregnated with sodiu diethyldithio­carbamate in ethyl acetate.

Recently, Espinola et al. 1 have developed immobilized dithiocarbamate by the reaction of 3-propy lethylenediamine group, covalently bonded to silica gel G, with carbon disulphide in toluene. This modified surface has 6.7 x 10-4 mole g·' ligand sites available to extract Co(II), Ni(II), Cu(II) and Zn(II) in water. The following cation-exchange process occurs in ethanolic solution:

Si (edAh (soln) + M2+ (soln)~ Si (edh M (Soln) + 2A + (soln)

where the tetramethyl ammonium cation (A+), ionically bonded to the surface, is displaced by the M2+ and equivalence of this exchange is related to the number of available ligand groups anchored on the matrix. The cations are sulphur-bonded to the anchored ligand. The cations-exchange properties observed on anchored dithiocarbamate are very similar to the general dithiocarbamate behaviour seen in dithiocarbamate coordination chemistry. Six years later in 1999, Wen et a!? prepared a new ion­exchange chelating fibre with polyacrylonitrile and used it for the simultaneous preconcentration of Be, Mn, Co, Cu, Ga, Ag, Cd, In, IPb and Bi in sea water. These metal ions can be concentrated 200 times in a short period of time. It becomes a promising method by coupling with ICP-MS for the determination of trace elements in sea water. Elena et az3 . discussed several analytical techniques for the analysis of heavy metal ions in water. However, no efforts have been

* For correspondence (Fax: 0571-700528; E-mai l:hamirrathore@ usa. net)

made to use thin-layer chromatography (TLC) of metal-diethyldithiocarbamate (DOC) complexes for analyzing heavy metal ions. Therefore, in continuation to previous work on synthesis, characterization and analysis of dithiocarbamate4

·8

,

now an attempt has been made to demonstrate the use of TLC of metal-DOC complexes in separation or clean-up of heavy metal ions. The results obtained are described in this paper.

Experimental Procedure

Apparatus TLC applicator (Stahl , India), glass plates (15 x 3

em), glass jars (chromatographic chamber), capillary, calibrated micropipette (Gilson, France), temperature controlled electric oven (Tempo, India), desiccator, sieves and glass atomizer were used.

Reagents and Chemicals All reagents and chemicals of analytical grade were

used.

Preparation of solutions Aqueous solutions (I %) of sulphate, nitrate and

chloride of metal ions were prepared in distilled water (OW). The corresponding mineral acid (2-3 drops 4 N) was added to stabilize the solution. Different concentrations of sodium diethyldithiocarbamate (NaDDC) (0.001M, 0.01 M and 0.1 M) were prepared inDW.

Preparation of detectors a) NaDDC (0.1 M) and (b) sodium sulphide (1 %)

were prepared in OW, (a) was used as detector for

RAO et at. : TLC HEAVY MET AL-DIETHYL DITHIOCARBAMATE COMPLEXES 453

Mn(II), Fe(III), Co(ll) and Ni(II) and Cu(II), and (b) was used for Mn(II), Fe(III), Co(II), Ni(II), Cd(II), Hg(l), Hg(II) and Pb(II).

Preparation of buffer solutions Acetate buffer (pH-3.42, 4.05, 4.45 and 5.89) and

ammonia buffer (pH-10) were prepared as usual9.

Preparation of chromatoplates The following adsorbents (20g) were slurried with

suitable volume (20-1 00 mL) of OW or 0.1 M aqueous solution of NaDDC and immediately coated uniformly (0.25-0.5 mm thickness) on the clean glass plates by using Stahl applicator: calcium carbonate (CC), calcium citrate (CCi), calcium oxalate (CO), calcium phosphate dibasic (CP), calcium sulphate dehydrated (CS), cellulose (CE) and silica gel (SG). The adsorbents slurried or impregnated with NaDDC solution are abbreviated as CC-NaDDC, CCi­NaDDC, CO-NaDDC, CP-NaDDC, CE-NaDDC and SG- NaDDC.

The chromatoplates so obtained were allowed to dry at room temperature (28 oC) and then activated for I h at l00-ll0°C in an electric oven. The plates impregnated with NaDDC were activated at 80°-90°C for I h. The activated chromatoplates were stored in a desiccator at room temperature for TLC analysis.

Spotting of test solution The test solution (1 %) was spotted on the middle of

a lower edge of the thin-layer chromatoplates with the help of a fine capillary tube or micropipette. The spots were dried at room temperature or the solvent was removed by blowing hot air.

Development of chromatoplates The spotted plates were developed to lO em in a

mobile phase by ascending mode of development in a closed glass jar. The plates were dried at room temperature to evaporate the mobile phase and then analyte was located on the chromatogram by spraying the detector.

Documentation of mobility of metal ions Rr and Rm values were calculated m the manner

described earlier 10•

Results and Discussion

Dithiocarbamates of general formula (I) are known 11

. Alkali metal dithiocarbamates including ammonium dithiocarbamate are water soluble.

(S r---------....,......-------, N - Mn(ll) ! I . .

1-Fe(llll i :......_Co(ll) i ! ~Ni(ll) j

\---Cu(ll) !'

!........._Cd(ll)

~ -+-Hg(l) j

•-Hg(ll) i

c=-_P~~J

oL----~----~----~ 0 .001 0 .01 0.1

Molar Concentration (NaDDC)

Fig. !-Mobility of metal ions on paper strip in NaDDC solution of varying concentration.

R1 & IRz =alkyl groups

These water soluble salts form a large number of metal complexes. Earlier work 12

-14 shows that alkaline

earth metal-dithiocarbamate complexes are slightly soluble, while the heavy metal-dithiocarbamate complexes are insoluble or sparingly soluble in water and ethanol. These complexes are stable in neutral medium while they decompose in acidic medium and hydrolyse in alkaline medium, (pH lO or above). Hence it seems that the TLC behaviour (Rr values) of heavy metal-DOC complexes is the function of their precipitation or solubility on different acidic, basic or neutral stationary phases and in different mobile phases of varying acidity, basicity and polarity . This mechanism is supported by the results obtained. The salient features of analytical importance of these results are discussed below:

Effect of NaDDC concentration on mobility of metal-DDC complexes on paper strips

Fig. 1 shows that on the basis of change in mobility (Rr values) with varying concentration of NaDDC on chromatographic paper, the metal ions can be divided into three groups (i) no change in mobility of Cd(II), (ii) slight change in mobility of Mn(II), Fe(III),

454 INDIAN J. CHEM. TECHNOL., NOVEMBER 2001

Mn(ll) Fe(lll) Co(ll) Nl(ll) Cu(ll) Cd(ll) Hg(l) Hg(ll) Pb(ll)

Meta~ lon

Fig. 2a- Mobility of metal ions on different stationary phases in OW.

~

~ 1 >

~ :c 05 0 ::!:

Mn(ll) Fe(lll) Co(ll) Ni(ll) Cu(ll) Cd(ll) Hg(l) Hg(ll) Pb(ll)

Metal ion

Fig . 2b---Mobi lity of metal ions on di fferent stationary phases impregnated with NaOOC in OW.

Co(Il), Ni(ll), Cu(II) and Pb(II) and (iii) considerable change in mobility of Hg(l) and Hg(II). As a result Cd(II) and Hg(II) can be separated from other metal ions understudy on paper strips in NaDDC solution. The mobility trend depends on the solubility of metal­DOC complexes.

Effect of stationary phases Oil the mobility of metal­DDC complexes in DW

Figs 2a & b show that (i) the mobility trend of heavy metal ions on paper strip and cellulose layer is the same, (ii) Rr values are lower on CE-NaDDC than those on CE, and (iii) Rr values are lower on SG than those on SG-NaDDC using DW as a mobile phase. Thus metal-DOC complexes behave differently onCE and SG. CE-NaDDC and SG both seem to be good adsorbents for the adsorption and recovery of heavy metal ions in water.

Effect of mobile phase on the mobility of metal-DDC complexes

Figs 3a & b show that the Rr values of metal ions are different in ethyl acetate than those in DW (Figs 2a & b) on paper strip, paper strip impregnated with NaDDC, SG, SG-NaDDC, CE and CE-NaDDC. The

1.5 .------------------,

Mn(ll) Fe(lll) Co(il) Ni(ll) Cu(ll) Cd{H) Hg{l) Hg(ll) Pb(ll)

Metallon

Fig. 3a-Mobility of metal ions on different stationary phases in ethyl acetate.

r----::;:-Papor-NaDOC -- ..

/ ---SG-NaDDC

1 .:::-ce-Na~ __

Mn(li) Fe{lll) Co(ll) Ni(ll) Cu(ll) Cd(ll ) Hg(l) Hg(ll) Pb(ll)

Metallon

Fig. 3b---Mobility of metal ions on different stationary phases impregnated with NaOOC in ethyl acetate.

impregnated stationary phases give differential Rr values in ethyl acetate. The following binary separations have been achieved practically on CE­NaDDC in ethyl acetate:

Mn(II) (0.62)-Cd(II) (0.00); Co(II) (0.65) - Cd(II) (0.00); Ni(II) (0.77)- Cd(II) (0.00); Cu(II) (0.70) -Cd(II) (0.00); Hg(J) (1 .00) - Cd(Il) (0.00); Hg(II) ( 1.00)- Cd(II) (0.00); Mn(II) (0.62) - Pb(II) (0.00); Fe(III) (0.75) - Pb(II) (0.00); Co(ll) (0.65) - Pb(II) (0.00); Ni(II) (0.77)-Pb(ll) (0.00) ; Cu(Il) (0.70) -Pb(II) (0.00); Hg(l) ( 1.00) - Pb (II) {0.00); and Hg(II) ( 1.00)- Pb (II) (0.00).

Figs 4a - e show that polarity of the mobile phase plays an important role in separating the metal-DOC complexes. For example, Rr values are 0.15 - 0.85 and zero in benzene and 0.00-1.00 and 0.75-1.00 in I ,4-dioxan of metal ions and their complexes respectively. The role of another complexing agent, EDT A is also very significant i.e. all these metal -DDC complexes have very low Rr values (0.00-0.25) on CE-NaDDC in EDTA solution while the corresponding metal ions have very high Rr values (0.75 to 1.00) onCE in EDTA solution. It is also clear that Cd(II) (0.25) and Hg(II) (0.75) can be separated

RAO et al. : TLC HEAVY METAL-DIETHYL DITHIOCARBAMATE COMPLEXES 455

1.5

.... " ii >

~ ~ :a 0.5 0

::11

~1 =·

Mn(ll) Fe(lll) Co(Jl) Nl(ll) Cu(ll) Cd(ll) Hg(l) Hg(ll) Pb(ll)

Metallon

Fig. 4a-Mobility of metal ions on cellulose in methanol, ethanol and acetone.

1.5 ~--------------------,

-a- Cl"lc~ctorn

--6-- 1.4·Di»xit ':

- ~Et17"A

Mn(ll) F~(ili) Co(!l) Ni(ll) Cu(ll) Cd(ll) Hg(l) '-lg(ll) ~t(ll)

Metal ion

Fig. 4c-Mobility of metal ions on cellulose in benzene, chloro­form, I ,4-dioxan and EDT A.

1.n

-Ql ::J liS > ~

C( .._. >. ::: :ii C . ~ 0 :s:

0

"i' " • > ~ ~ :;;; j

1.5

0.5

Mn(ll) Fe(lll) Co(ll) N~ll) Cu(li) Cd(ll) Hg(l) Hg(ll) Pb(ll)

Metallon

Fig. 4b--Mobility of metal ions on cellulose in propanol, butanol and acetonitrile.

o; ~ .. >

~

~ :0 0 :z

~ . 5 .------------------,

o.s

--+-- Methanol

-e-Etilanol

Propanol

-e-Butanol

---- Aceto:'litri:e

M.V.II) Fe(lll) Co(ll) Ni(ll) Cl.{ ll) Cd('lj Hg(l) Hg('l) f't (l l;

Metal ion

Fig. 4d-Mobility of metal ions on cellulose impregnated with NaDDC in methanol, ethanol, propanol, butanol and acetonitrile.

-+-Acetone

---- Ber.LEHle

--...- Chlorcfor Ill

---M- ~ ,4 .Oioxan

----&-- EDTA

Mn(ll) Fc(lll} Co(ll} Ni(ll) Cu(ll) C:l( II) Hr:{l} IIH{II; Pb( ,I)

Metal ion

Fig. 4e-Mobility of metal ions on cellulose impregnated with NaDDC in acetone benzene, chloroform, 1,4-dioxan and EDTA.

456 INDIAN J. CHEM. TECHNOL., NOVEMBER 2001

1.5 .--------------

" " ;;; > 1

~

~ :0 ~ 0.:,

--+-CC

-G-CP

-.-cc; -&-CO

---cs

Mn(ll) Fe:lll) Co(ll) Ni(ll) Ct:(ll) Cd(lll Hg(l) :-4;(11) Pbillj

Melallon

Fig. Sa-Mobility of metal ions on less familiar stationary phases in ethyl acetate.

Mn(ll) Fe(lll) Co(ll) Ni(ll). Cu(ll) Cd(ll) Hg(l) Hg(ll) Pb(ll)

Melallon

Fig. 5b-Mobility of metal ions on less familiar stationary phases impregnated with NaDDC in ethyl acetate.

from Mn{Il), Fe(JII), Co(II), Ni(II), Cu(II), Hg(I) and Pb(II) on CE and CE-NaDDC respectively using EDT A solution as a mobile phase.

Effect of less familiar stationary phases on mobility of metal-DDC complexes

Figs Sa & b show the results of mobility of metal ions as well as their complexes on different stationary phases in ethyl acetate. The following is the sequence of time taken for ascending to 10 em in ethyl acetate on different stationary phases:

CCi-NaDDC (12 h)> CO-NaDDC (3h) > CS-NaDDC (50 min) > CP -NaDDC (20-25 min) > CC-NaDDC (I 5-20 min) .

The following is the sequence of brightness of colour of metal-DOC complexes on different stationary phases: CC-NaODC > CS-NaOOC > CO­NaDDC > CP-NaDOC > CCi-NaDOC. It is also clear that Hg(I) or Hg(II) or Mn(II) or Co(II)-OOC complexes show the same behaviour on different stationary phases. However Cd(II) or Cu(II) or Ni(II) or Pb(II)-DDC complexes show differential mobility on different stationary phases in ethyl acetate. Thus CC-NaDDC has a better separation potential for separation of heavy metal ions.

3.42 4.05 4.45

pH

5.69

j...-....:..Wn> , ....... FII(III)

1---Co(ll) , ....... Ni(ll) .

, ....... cu(ll) . ·---Cd(ll)

; ....... HQ(I) . , __ Hg(ll) i

i.~Pb(lll i

10

Fig. 6--Mobility of metal ions on cellulose impregnated with NaDDC in mobile phases of varying pH values.

1.5 .--------------------,

; --+- P•per striP-' :-a- slica gel G

-&-CelkJiose -·---·-·· - .

Mn(ll) Fe(lll) Co(ll) Ni(ll ) Cu(ll) Cd(ll) Hg(l) Hg(ll) Pb{ll)

~tallon

Fig. ?a-Mobility of metal ions on stationary phases in 0. 1 M acetic acid.

1.5 r------------------·--.

I , .. ~ i j 0.5

r.:...:: pape;·~iriP!

i--alcag•IG ! ~~~ i

"'(M) h(Ml) Co(ll) Ni(ll) Cu(ll) Cd(N ) Hg{l) Hg(N) Pl>{l~

Metal Jon

Fig. 7b-Mobility of metal s ions on stationary phases in 0.1 M NaDDC solution.

Effect of pH on mobility of metal - DDC complexes Fig. 6 · shows that mobility of some metal ions

remains unchanged at pH 3.42-10.00. The similar observation has also been reported by Wen et at. 2

Effect of metal-acetate complexes and metaf.-DDC complexes

Figs 7a & b show that the mobility of metal-acetate complexes is different than the mobility of metal­DOC complexes i.e. Rf values of metal-acetate complexes are higher than metal-DOC complexes.

RAO eta/. : TLC HEAVY MET AL-DIETHYL DITHIOCARBAMATE COMPLEXES 457

Conclusion Heavy metal-diethy ldithiocarbamate complexes,

thin-layer chromatography is a versatile technique for the separation or clean-up of heavy metal ions. The TLC data reported in this paper may be utilized for developing column chromatography for the enrichment of heavy metal ions in water.

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Colloids and surfaces A, Physicochem Eng Aspects, 87 (1994) 33.

2 Wen B, Shan x -Q, Liu R -X & Tang H -X, Anal Chem, 363 (1999) 257.

3 Elena G-S, Elia A-R & Dario P R, Handbook of Water Analy­sis, edited by Nollet LML (Marcel Dekker, New York), 2000, 439.

4 Rathore H S, Kumar S & Singh Y N, J Indian Chem Soc, 178 (2001) 422.

5 Rathore H S, Mital S, Kumar S & Singh Y N, The Nat Acad Sci, 7l(A) (2001) I

6 Rathore H S, J Chromatogr, 733A (1996) 5. 7 Rathore H S & Mital S. J Planer Chromatogr. 10 (1997) 124. 8 Rathore H S, Sharma R & Mital S, Water Air Soil Pollut, 97

(1999) 431. 9 Bassett J. Denny R C. Jeffery G H & Mendham J, Vogel's

TestBook of Quantitative Inorganic Analysis (ELBS, Lon­don), 1986, Chap. 2.

10 Rathore H S & Begum T, J Chromatogr, 643 (1993) 321. II Cotton F A & Wilkinson G, Advanced Inorganic Chemistry:

A Comprehensive Test (lnterscience Publish~rs Division of John Wiley & Sons), 1962, 229.

12 Rathore H S & Mital S, J Indian Chem Soc, 76 (1999) 355. 13 Rathore H S, Mital S & Chaudhary S K, Pesticide Research

J, 12 (2000) 103. 14 Rathore H S & Miial S, Indian J Chem Techno/, 7 (2000) I.