determination of ii with dithizone by diffuse reflectance spectrometry on a fibrous anion exchanger

8/2/2019 Determination of II With Dithizone by Diffuse Reflectance Spectrometry on a Fibrous Anion Exchanger

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1061-9348/03/5806- $25.00 2003 AIK Nauka/Interperiodica0528

Journal of Analytical Chemistry, Vol. 58, No. 6, 2003, pp. 528532. Translated from Zhurnal Analiticheskoi Khimii, Vol. 58, No. 6, 2003, pp. 590594.Original Russian Text Copyright 2003 by Shvoeva, Dedkova, Savvin.

The Environmental Protection Agency specifiedmercury and some other heavy metals as priority pol-lutants. Mercury, along with cadmium and beryllium, isamong the most toxic inorganic pollutants [1] withextremely low maximum permissible concentrations(MPC) in water. In recent years, procedures have beendeveloped for the determination of mercury usinginstrumental methods: atomic-absorption, atomic-emission, and X-ray fluorescence spectrometry andstripping voltammetry. Because of the low MPC ofmercury (0.0005 mg/L), in the most cases samples arepreconcentrated by evaporation, adsorption, and other

techniques.Different methods were proposed for the sorption

spectrometric and test determination of mercury [210].However, the sensitivity of determination of all of thesemethods does not reach the MPC level. The determina-tion limit of copper is in the range of 0.0010.1 mg/L.Only the enzymatic test method for the determinationof mercury and organomercury compounds providesthe determination of 150 ng/mL mercury dependingon the solid phase in use [810]. The development ofsimple and highly sensitive procedures for the determi-nation of mercury remains a topical problem.

The aim of this work was to study possibilities of the

use of fibrous filled materials in the determination ofmercury. Sorbents of this type are polyacrylonitrilefiber in which the required ion exchanger is introducedin the process of fiber formation. As a result, a colorlessor weakly colored fibrous material filled with the ionexchanger is obtained. The degree of filling can be var-ied and is usually 5080%. Fibrous sorbents exhibitgood kinetic and ion-exchange characteristics. They arefine fibrous materials stable in the range from stronglyacidic to weakly alkaline solutions. These sorbents can

be conveniently used in sorptionspectrometric and testmethods, in flow analysis, and in the batch mode. Theyexhibit a rather high exchange capacity and servesimultaneously for the preconcentration and determina-tion of the adsorbed element on the solid phase.

EXPERIMENTAL

Reagents.

Chemically pure or analytical-gradereagents were used. Solutions of metal salts (0.01 M)were prepared according to known procedures by the

dissolution of corresponding nitrates or chlorides;working solutions were prepared by the dilution ofmore concentrated solutions. A stock 0.01 M mercurysolution was prepared by the dissolution of a weighedportion of Hg(NO

3

)

2

in 0.01 M HNO

3

; a working solu-tion with a concentration of mercury of 50

g/mL wasprepared by the dilution of the stock solution with0.01 M HNO

3

. A stock 0.05% solution of dithizone wasprepared by the dissolution of 0.05 g of the compoundin 100 mL of acetone; the solution was stored in arefrigerator. A working solution of dithizone was pre-pared by mixing 5 mL of the stock solution, 5 mL of a2.5% NH

3

solution, and 1 or 5 mL of a 0.05 M EDTA

solution and diluting to 50 mL with water. This workingsolution containing 0.005% dithizone, 10% acetone,0.25% NH

3

, and 1

10

3

or 5

10

3

M EDTA was usedfor 2 days and stored in a refrigerator. Solutions of KI,KCl, NaCl, NaNO

3

, Na

2

SO

4

, Na

2

S

2

O

3

, and EDTA(0.1 and 0.01 M) were prepared by the dissolution ofweighed portions of compounds in water or from com-mercial volumetric samples. The required acidity of thesolutions was adjusted using 0.1 and 0.01 M solutionsof HNO

3

and NaOH.

Determination of Mercury(II) with Dithizone by DiffuseReflectance Spectrometry on a Fibrous Anion Exchanger

O. P. Shvoeva, V. P. Dedkova, and S. B. Savvin

Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences,ul. Kosygina 19, Moscow, 119991 Russia

Received May 6, 2002; in final form, September 30, 2002

Abstract

The possibility of the determination of mercury(II) with dithizone on the solid phase of a fibrousion-exchange material filled with the AV-17 anion exchanger was studied. Mercury is adsorbed as an anioniccomplex. The sorption of mercury as chloride, iodide, sulfate, thiosulfate, nitrate, and EDTA complexes wasstudied. A procedure was proposed for the sorptionspectrometric determination of mercury with dithizone ona solid phase after sorption as the chloride complex. For improving the selectivity of the method, EDTA is addedto the solution. The determination is affected only by Pd(II). The time of analysis is 15 min. The procedure wastested in the analysis of tap and river water and a solution modeling natural water.

ARTICLES


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DETERMINATION OF MERCURY(II) WITH DITHIZONE 529

As a support, we used a fibrous material filled withthe strongly alkaline AV-17 anion exchanger; thedegree of filling was ~50%. The support was previouslywashed of cations with 1 M HCl until the negative reac-tion for iron(III) with thiocyanate ions and then withwater until the negative reaction with silver(I) for chlo-ride ions. The sorbent was used in the form of diskswith a diameter of 20 mm and a mass of 2530 mg in

the swollen state; for this purpose, the disks were heldfor a day and then stored in distilled water.

Instruments.

The acidity of the test solutions wasmeasured with a glass electrode using a pH-673 poten-tiometer. Support disks were placed in glass flow cells,and solutions were pumped though the disks using aPP-2-15 peristaltic pump at a flow rate of 10 mL/min.Diffuse reflectance spectra were recorded on a Spectro-ton colorimeter (Chirchik Experimental Design Bureauof Automatic Equipment, Tashkent, Uzbekistan). Thedifference between the diffuse reflection coefficients ofdisks after passing the reference and test solutions at theoptimal wavelength (

R

) was taken as the analytical

signal. The reference solution contained all the compo-nents of the reaction except the determined ion. It waspassed through all of the operations along with the testsolution.

Procedure.

A support disk was placed in a flow cell,and a test solution was pumped through the disk at aflow rate of 10 mL/min using a peristaltic pump. Next,1 mL of a reagent solution was pumped through thisdisk, the disk was transferred into the measuring cham-ber of a Spectroton colorimeter, and the diffuse reflec-tion coefficient was measured at the optimal wave-length.

RESULTS AND DISCUSSION

Mercury(II) forms stable complexes with manyinorganic and organic substances. Complex compoundsof mercury with halide ions are widely used in theirsorption with anion exchangers. The stability of halidecomplexes in aqueous solutions increases in the orderF

< Cl

< Br

< I

[11]. Mercury forms complexes withoxygen-containing ligands.

Among organic reagents for the photometric deter-mination of mercury, dithizone and 4-(2-pyridy-lazo)resorcinol (PAR) are widely used. We studied thecolor reactions of Cd(II), Pb(II), and Hg(II) withdithizone and PAR on the solid phase after their sorp-tion in the form of anionic complexes [12]. It was dem-onstrated that the maximum analytical signal isobserved at 590 nm. Mercury is partially adsorbed onthe anion exchanger even in the absence of the addi-tional anion. The analytical signal is detected in the

presence of 2 10

5

M (introduced together with

the mercury solution). The effect of the acidity of thesolution at the stage of sorption in the absence of the

NO3

additional anion is presented in Fig. 1. As seen in thefigure, nearly the same analytical signal is observed atpH 310. It was demonstrated previously that the larg-est difference in the reactivity of mercury, lead, andcadmium is observed at pH 45; therefore, subsequentstudies were performed at pH 4.85.2.

In the sorption from a 10

4

M KI solution in the pres-ence of equimolar amounts of cadmium and lead, mer-cury exhibits an individual analytical signal; cadmiumand lead do not interfere with the determination of mer-cury. The effect of different anions on the sorption ofmercury and the subsequent determination withdithizone on the AV-17 fibrous anion exchanger is pre-sented in Fig. 2. It is seen that the largest analytical sig-nals of the mercury complex of dithizone are observed

0.4

0.2

01 3 5 7 9 11pH

R

Fig. 1.

Dependence of the analytical signal of the mercurycomplex of dithizone on the AV-17 fibrous anion exchangeron the pH of the solution at the stage sorption; 0.2

g/mLHg(II),

V

= 25 mL, 590 nm.

0.4

0.3

0.2

0.1

1 2 3 4 5p

c

AN

n

R

1

3

4 2

5

6

Fig. 2.

Dependences of the analytical signals of the mer-cury complex of dithizone on the concentration of (

1

) KI,(

2

) Na

2

S

2

O

3

, (

3

) KCl, (

4

) EDTA, (

5

) Na

2

SO

4

, and(

6

) NaNO

3

in the solution; 0.2

g/mL Hg(II), V

= 25 mL,590 nm, and pH 4.85.2.


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.

on the sorption of mercury from solutions of KI,Na

2

S

2

O

3

, and EDTA. Sorption can be performed in the

concentration ranges of 10

3

10

5

M KI, 10

4

10

5

MEDTA, and 10

5

M Na

2

S

2

O

3

. The smallest analyticalsignals are observed in the sorption of mercury fromnitrate solutions. These dependences of the analyticalsignals on the nature of the anion are consistent with thestability of mercury complexes of these anions. For theleast stable nitrate complexes of mercury, the analyticalsignal is two times lower than for iodide, thiosulfate, orEDTA complexes. The curves in Fig. 2 demonstrate thesignificant decrease in the analytical signal upon

increasing the concentration of anions in the solution.At concentrations above 10

5

M S

2

, 10

4

M EDTA,

and 10

3

M and , the analytical signal dras-

tically decreases. For KI solutions (Fig. 2, curve 1

), thisrelationship is less pronounced. The decrease in theanalytical signal upon increasing the concentration ofanions in the solution can be explained by an increasein the stability of the anionic complex or a change in itscomposition because of the shift of the equilibrium ofcomplex formation upon increasing the concentration

O32

SO42

NO3

of one of the components of the reaction. In the sorptionof the anionic complex on the anion exchanger, somecorrespondence must exist between the stability of thecomplex and the strength of the binding of this complexwith the anion exchanger. This condition is fulfilled atthe plateaus of the curves. For the most stable anioniccomplexes, the masking of the cation with this anion isobserved, and these complexes are not adsorbed on the

anion exchanger. On the other hand, the adsorbed com-plex can be so stable that it does not react withdithizone. Finally, the saturation of the anionexchanger, on which sorption occurs, can be attained ata high concentration of anions in the solution. Gener-ally, note that complex competitive interactions occurbetween the introduced anion and the metal cation,between the anionic complex and the anion exchanger,and between the adsorbed anionic complex and thereagent. This issue was not studied in this work.

In the sorption of chloride complexes (Fig. 2, curve 3

),the analytical signals are nearly independent of the con-

centration of the ligand in a wide range of concentra-tions 10

2

10

5

M. To approximate the conditions ofanalysis of real water, in further studies we used thesorption of mercury from chloride solutions in spite ofsome loss in sensitivity.

It was important that the analytical signal was max-imum in 10

4

10

5

M EDTA solutions. Dithizone is agroup reagent and reacts with many elements, which, inturn, are readily masked with EDTA. The significantdependence of the analytical signal on the concentra-tion of EDTA precludes its use in the sorption of mer-cury because it is difficult to provide a certain excess of

EDTA in a rather mineralized solution, such as naturalwater. This will lead to nonreproducible results. There-fore, in the sorption of mercury we used a 0.01 M NaClsolution, and EDTA was introduced at the stage ofdetermination. EDTA was added to the solution of thereagent providing the masking of the concomitant cat-ions that were adsorbed together with mercury ions.The effect of the amount of EDTA in the solution ofdithizone on the analytical signal is presented in Fig. 3.For the subsequent studies, we used a solution contain-ing 1

10

3

M dithizone and 5

10

3

M EDTA.

p

c

EDTA

R

2 3

0.3

0.2

0.1

Fig. 3.

Dependence of the analytical signal of the mercurycomplex of dithizone on the concentration of EDTA in thereagent solution; 0.2

g/mL Hg(II), V

= 25 mL, pH 4.85.2,and 590 nm; the reagent is 1 mL of a solution containing0.005% dithizone, 10% acetone, and 0.25% NH

3

.

Table 1. Selectivity factors in the determination of mercury with dithizone on a fibrous anion exchanger filled with AV-17Foreign ion Selectivity factor Foreign ion Selectivity factor

Pd(II) 1000

Sn(II) 20

* The reagent contains 5

10

3

M EDTA; in the other cases, the reagent contains 1

10

3

M EDTA.


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DETERMINATION OF MERCURY(II) WITH DITHIZONE 531

Dithizone forms colored complexes with Mn(II),Fe(II), Co, Ni, Cu, Zn, Pb, Ag, In, Sn, Te, Pt, Au, Hg,Bi, etc. [13]. We studied the selectivity of the determi-nation of mercury with respect to these elements. Table 1presents the selectivity factors, i.e., the mass ratios ofthe foreign and analyte ions at which the error in thedetermination of mercury is within

10%. The selectiv-ity factors were determined for an adsorbed solution

with a Hg(II) concentration of 0.1

g/mL, a NaCl con-centration of 0.01 M, pH 4.85.2, and a variable con-centration of the studied concomitant cation. For thedetermination, we used 1 mL of a reagent solution con-taining 0.005% dithizone, 10% acetone, 0.25% NH

3

,

and 1 103 M EDTA. In the study of the interferingeffect of Au(III), Cu(II), Ag, and Fe(III), the selectivityfactors were determined with a reagent solution con-taining 5 103 M EDTA. As is seen in Table 1, a highselectivity is observed for Mn(II), Zn, Pb, Co, Cd, andNi; Pd(II) and fourfold amounts of Au(III) interferewith the determination of mercury. For the other ele-ments, the selectivity is satisfactory, which makes it

possible to use the proposed procedure for the determi-nation of mercury in natural water.

To expand the analytical range of mercury, we stud-ied the possibility of sorption of 05 g of mercuryfrom 20, 100, and 500 mL of a 0.01 M NaCl solutionwith pH 4.85.2. A dithizone solution containing 1 103 M EDTA was used as the reagent. For 500, 100,and 20 mL of the solution, the obtained calibrationplots are linear in mercury concentration ranges of0.0020.008, 0.0080.04, and 0.0250.2 g/mL,respectively, and are described by the equations R =25.84c + 0.13, R = 7.69c + 0.06, and R = 1.48c +0.06, respectively, where c is the concentration of mer-

cury, g/mL, and R is the analytical signal. At a vol-ume of the test solution of 500 mL, the detection limitof mercury calculated by the 3s value is 1 ng/mL. In thecase when the concentration of EDTA in the reagentsolution is five times higher and the volume of the testsolution is 100 mL, the equation of the calibration plotis R = 4.37c + 0.07. This equation was used in thedevelopment of a procedure for the determination ofmercury in natural water. The procedure for the sorp-tionspectrometric determination of mercury wastested with a solution modeling natural water and in theanalysis of river water (Moskva river) and tap water.The accuracy of the results was estimated by theaddedfound method.

Determination procedure.One milliliter of a 1 MNaCl solution and 1.52.5 mL of 1.0 M HNO3 (to pH4.85.2) are added to 100 mL of a sample, and the mix-ture is pumped at a flow rate of 10 mL/min through asupport disk with AV-17 placed in a glass cell. Next,1 mL of a reagent solution containing 0.005%dithizone, 10% acetone, 0.25% NH3, and 5 10

3 MEDTA is pumped through the disk (in the analysis ofdistilled water or a solution modeling natural water, the

reagent solution contained 1 103 M EDTA), andwithin 12 min the diffuse reflection coefficient is mea-sured at 590 nm. Analogously, the diffuse reflectioncoefficient is measured for a blank sample containingdistilled water instead of the test solution.

The concentration of mercury is calculated by theequation c (g/mL) = (R 0.07)/4.37 and, when thereagent solution contains 1 103 M EDTA, by theequation c (g/mL) = (R 0.06)/7.69.

Results of the analysis of water are presented inTable 2. The data in the table suggest that the procedurefor the sorptionspectrometric determination of mer-cury with dithizone on the solid phase of a fibrousmaterial filled with the AV-17 anion exchanger can beused for the analysis of natural waters. The relativestandard deviation is no higher than 20%. The time ofanalysis is 15 min.

Thus, this study makes it possible to recommend thenew sorptionspectrometric method for the determina-tion of mercury, which consists in the sorption precon-centration of anionic mercury complexes on a fibrousanion exchanger filled with AV-17 and the determina-tion of mercury with dithizone on the solid phase. Theuse of the sorption preconcentration of mercury in theform of anionic complexes and the determinationdirectly on the fibrous anion exchanger can signifi-

cantly decrease the detection limit, significantlyimprove the selectivity of the determination, simplifythe procedure, and decrease the time of analysis.

REFERENCES

1. Fresenius, W. and Dylick, C.E., Fresenius J. Anal.Chem., 2000, vol. 366, no. 5, p. 417.

2. Savvin, S.B., Trutneva, L.M., Shvoeva, O.P., and Effend-ieva, K.A.,Zh. Anal. Khim., 1991, vol. 46, no. 4, p. 709.

Table 2. Results of the determination of mercury(II) in wa-ter (n = 3, P = 0.95)

WaterAdded Hg,

mg/LFound Hg,

mg/LRSD, %

Distilled water 0.025 0.025 0.002 5

Solution modelingnatural water*

0.020 0.020 0.003 6

Tap water*


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3. Ostrovskaya, V.M., Aksenova, M.S., Osyka, V.F., et al.,Vysokochist. Veshchestva, 1992, no. 3, p. 152.

4. Gureva, R.F. and Savvin, S.B.,Zh. Anal. Khim., 1997,vol. 52, no. 3, p. 247.

5. Zaporozhets, O., Petruniock, N., and Sukhan, V., Tal-anta, 1999, vol. 50, no. 4, p. 865.

6. Amelin, V.G., Zh. Anal. Khim., 1999, vol. 54, no. 6,p.651; no. 7, p. 753.

7. Ivanov, V.M. and Kochelaeva, G.A., Vestn. Mosk. Univ.,Ser. 2: Khim., 2001, vol. 42, no. 1, p. 17.

8. Shekhovtsova, T.N., Chernetskaya, S.V., Belkova, N.V.,and Dolmanova, I.F., Zh. Anal. Khim., 1995, vol. 50,no.5, p. 538.

9. Shekhovtsova, T.N., Muginova, S.V., and Bagi-rova,N.A.,Anal. Chim. Acta, 1997, vol. 344, p. 145.

10. Shekhovtsova, T.N. and Chernetskaya, S.V.,Anal. Lett.,1994, vol. 27, p. 2883.

11. Gladyshev, V.P., Levitskaya, S.A., and Filippova, L.M.,Analiticheskaya khimiya rtuti (The Analytical Chemistryof Mercury), Moscow: Nauka, 1974.

12. Dedkova, V.P., Shvoeva, O.P., and Savvin, S.B.,

Zh. Anal. Khim., 2002, vol. 57, no. 4, p. 355.13. Iwantscheff, G.,Das Dithizon und seine Anwendung in

der Mikro- und Spurenanalyse, Weinheim: Chemie,1972. Translated under the titleDitizon i ego primenenie ,Moscow: Inostrannaya Literatura, 1961.

determination of ii with dithizone by diffuse reflectance spectrometry on a fibrous anion exchanger

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