Spectrophotometric study of ternary complexes of Cr (VI) and Co (II) Текст научной статьи по специальности «Химические науки»

164

CHEMICAL PROBLEMS 2020 no. 2 (18) ISSN 2221-8688

UDC 543.422.3; 543.42.062; 535.8

SPECTROPHOTOMETRY STUDY OF TERNARY COMPLEXES

OF Cr (VI) and Co (II)

A.Z. Zalov1, Sh.A. Mammadova1, N.S. Hasanova2, Sh.A. Ibrahimova3

'Azerbaijan State Pedagogical University, U.Gadjibekov street 68. Baku, AZ1000, 2Azerbaijan State University of Oil and Industrial, Azadlig str. 34, Baku, AZ 1000, 3Baku State University, Z. Xalilov str. 23. Baku, AZ 1000 e-mail: [email protected]

Received 06.02.2020 Accepted 17.05.2020

The following reagents were used: thiocatechols (TCs, H2L):2-hydroxy-5-iodthiophenol (HBTP), and 2-hydroxy-5-nitrothiophenol (HNTP); and aminophenols (HAs): -2(N, N-dimethylaminomethyl)phenol - (AP1) and 2(N, N-dimethylaminomethyl) -4- methylphenol (AP2). The TCs were characterized by physicochemical methods: IR and NMR spectroscopy. Cr(VI) is reduced to Cr(III) by the reagent itself during the complex formation. After a single extraction with chloroform, 98.4-98.7% of chromium and cobalt was extracted as an ion associate. For the formation and extraction of chromium (III) and cobalt (II) complexes, pH 1.3-5.8 and 1.0-7.2, respectively, are optimal. The optimal condition for the formation and extraction of these codents is concentration (1.3-1.5) x 10-3 M TCs and (1.2-1.5) x 10-3 M AP. For Cr3+ and Co2+ ions, the Beer law is valid in the ranges 0.2-19 and 0.2-20 p.g / ml, respectively. The maximum optical density of chromium (III) complexes and cobalt (II) is reached within 12 and 10 minutes, respectively. The absorption maxima of the Cr (III) - HITP-AP triple complexes lie in the range 438-442 nm (in the case of cobalt 540-555 nm). The molar absorption coefficients for chromium complexes (3.57 - 3.73 4) x 104 (in the case of cobalt (2.43 - 2.94) x 104). The molar relationships between the components of the ternary complex were found by several methods (Cr:TCs:AP=1:3:3 and Co:TCs:AP=1:2:2). It was established by Nazarenko's method that the complexing form of chromium (III) and cobalt (II) is Cr3+ and Co2+, respectively. The calculations showed that the MLC in the organic phase does not polymerize and is in monomeric form (y = 1.01-1.05). The proposed method, within the established optimal conditions, was used to determine Cr (III) and Co(II) in milk, sour cream and cottage cheese. Keywords: chromium, cobalt, extraction, spectrophotometry, thiocatechols, aminophenols DOI: 10.32737/2221-8688-2020-2-164-173

Introduction

According to the analogy hypothesis, reactions with reagents of the R-SH type are possible for ions of elements forming sulfides that are poorly soluble in water [1]. Chromium and cobalt are some of the metals that have chromophore properties, so among many photometric methods for their determination there are both methods based on the use of color reagents with chromophore groups and methods that use colorless reagents. Most methods are very selective.

Numerous methods are known for the photometric determination of chromium and

cobalt using reagents belonging to various classes of organic compounds [2-8]. Methods have been developed for determining elements in the form of multiligand complexes (MLC) with 2-hydroxy-5-nitrrothiophenol [5] and 2,6-dithiol-4-alkiylphenols in the presence of hydrophobic amines [6]. However, research aimed at finding and researching new spectrophotometric reagents with various functional groups is still ongoing.

The following reagents were used in this work: thiocatechols (TCs, H2L): 2-hydroxy-5-iodothiophenol (HITP) and 2-hydroxy-5-

CHEMICAL PROBLEMS 2020 no. 2 (18)

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nitrothiophenol (HNTP); and aminophenols (AP): -2- (N,N-dimethylaminomethyl) phenol

(APi) and 2- (N,N-dimethylaminomethyl)-4-methylphenol (AP2).

Materials and methods

Reagents. The initial solution of Cr (VI) and Co (II) was prepared by dissolving K2&2O7 and Co(NO3)2 x 6H2O, respectively, in distilled water. Working solutions of Cr (VI) and Co (II) (0.1 mgL-1) were prepared by appropriate dilution of the stock solution. The concentration of the chromium and cobalt solution was adjusted gravimetrically [9].

TCs was synthesized according to the procedure [10]. Chloroform solutions of TCs (0.01 mol/l) and AP (0.02 mol/l) were used.

OH

SH

J

HITP

To create the optimum acidity, 0.1 mol/l solutions of HCl, NaOH, or ammonium acetate {CH3COOH+CH3COONH4 (pH 4-12)} buffers were applied.

Complexing agents may be a dibasic (HITP, HNTP) weak acid, and depending on pH of the medium may be in molecular and anionic forms. Some characteristics of the studied reagents are presented below.

OH

SH

NO2 HNTP

pKi=5.0; pK2=10.2

pKi=3.52; pK=9.72

pH neutral form of existence:

0 - 3.4 (X=280 nm);

The synthesized compounds were characterized by physicochemical methods: IR and NMR spectroscopy: IR (KBr) [1] - { HITP [3458 cm-1 v(OH), 2568 cm-1 v(SH), 1550 cm-1 v(C6H5)]; HNTP [3462 cm-1 v (OH), 2571cm-1 v(sH), 1579 cm-1 v(C6H5) (Fig.2)]}and 1H NMR (300.18 MHz, C6D6) - {HITP [5 5.60 (s, 1H-OH), 5 3.35(s, 1H- 1SH), 5 6.85 (s, 1H Ar-H), 5 7.15 (s, 2H Ar-H)]; HNTP [5 5.72 (s, 1H- OH), 5 3.41(s, 1H - SH), 5 7.06 (s, 1H Ar-H), 5 6.25 (s, 2H Ar-H)].

Apparatus. The absorbance of the extracts was measured using a SP 26 spectrophotometer and KPK 2 photocolorimeter. Glass cells with optical path of 5 or 10 mm were used. pH of aqueous phase was measured using an I-120.2 potentiometer with a glass electrode.

Studies on the oxidation state of Chromium. It is known that TCs have reducing properties in acidic medium [12]. Previous

0 - 2.6 (X=295 nm) investigations with Cr (VI)-TCs and Cr(III)-TCs suggested that only Cr(III) forms stable complexes with this reagent. To elucidate the oxidation state of chromium in the presence of other TCs (HITP and HNTP), we conducted two series of experiments. In the first series we used Cr(VI), while in the second series we used Cr(III) obtained by addition of a supplementary reducing agent (SnCI2 or KI). The comparison of the obtained spectra showed that Àmax Cr(VI)-HITP =Àmax Cr(III)- HITP. This fact can be regarded as an indication [12] that Cr(VI) is reduced to Cr(III) by the reagent itself during the complex formation.

General procedure for the determination of chromium (VI) and cobalt (II). Portions of stock solutions of chromium (VI) and cobalt (II) varying from 0.1 to 1.0 mL with a 0.1ml step, a 2.5 ml portion of a 0.01 M solution of TCs, and a 2.0 ml portion of a 0.01M

solution of AP were placed in to calibrated test tubes with ground-glass stoppers (the volume of the organic phase was 5 ml). The required value of pH was adjusted by adding 0.1M HCl. The volume of the aqueous phase was increased to 20 ml using distilled water. In 10 minnute after the complete separation of the phases, the organic phase was separated from the aqueous phase and the absorbance of the extracts was measured on KPK-2 at room temperature and 490 nm (in case of cobalt 540 nm) (£=0.5cm).

Determination of chromium and cobalt content in milk. A sample of milk (10 ml) is evaporated in a water bath in a porcelain dish to dryness, charred and 1 ml of conc. HNO3, evaporated, then calcined in a muffle furnace at 450-500°C. 5-7 ml of a 1 M solution of KOH, 0.4-0.5 ml of a 3% solution of H2O2 are added to the dry residues, the solution is heated to 70-80°C for 5-10 minutes, evaporated to dryness, poured 5-7 ml of the pod, again evaporated to dryness. Then 1 M HCl is added, heated to 60-70°C, and filtered in a 25 ml flask with a capacity of 1 M HCl. A portion of aliquot

of the resulting solution is selected, transferred to a in a separatory funnel, the desired pH is adjusted by the addition of 0.1 M HCl, 2.2 ml of 0.01 M TCs and 0.01 M AP were added. The volume of the organic phase was adjusted to 5 ml of chloroform and a total of up to 25 ml of distilled water. 10 minutes after shaking, a portion of the organic extract was transferred through filter paper to the well and the absorbance was read at I = 440 nm (in the case of cobalt = 540 nm) against chloroform. The content of chromium and cobalt was found on the calibration graph.

Determination of chromium content in sour cream and cottage cheese. A portion of sour cream (10 g) or cottage cheese (10 g) in a porcelain crucible is charred on a plate, 1 ml of conc. HNO3, evaporated and then calcined in a muffle furnace at 450-500°C. The determination of chromium and cobalt continues in accordance with the above described procedure for determining the chromium and cobalt content of the milk.

Results and discussion

The choice of solvent. As TCs is

insoluble in water, an organic solvent was used for the system. For the extraction of complexes we used CHCb, CCU, C6H6, C6H5CH3, C6H4(CH3)2, C2H4O2, iso-butanol and iso-pentanol. Extractability of complexes was estimated in coefficient of distribution (D) and extent of extraction (R%) [12]:

D =

W ]o [W ]

R =

aq

100 x D

V~

D + - aq

V„

The extractivity of the complexes was estimated by the distribution coefficient and recovery. CHCI3 and CCI4 appeared to be the best extractants. All the further investigations were carried out with chloroform. After a single extraction with chloroform, 98.4-98.7% of chromium and cobalt was extracted as an ion associate. The content of chromium and cobalt in the organic phase was determined photometrically by diphenylcarbazide [3] and a-nitros-ß-naphthol [2], after stripping

respectively, and in the aqueous phase by the difference.

Effect of pH of the aqueous phase. For

the formation and extraction of Cr (III) and Co (II) complexes, pH 1.3-5.8 and 1.0-7.2, respectively, are optimal. At the beginning, with increasing acidity of the initial solution, the extraction of Cr (III) and Co (II) increases, and with further increase - gradually decreases, which is obviously associated with a decrease in the concentration of the ionized form of H2L, and is most likely in solution in undissociated form. With an increase in pH> 7.2, the formation of MLC is practically not observed, which is apparently due to a decrease in the degree of protonation of amines. The dependence of the optical density on pH is shown in Table 1.

Effect of reagent concentration and aging time. The optimal condition for the formation andexpression of these codents is concentration (1.3-1.5)*10"3 M TCs and (1.2-1.5)x 10-3 M AP. Extracts of Cr3+ and Co2+ ions obey the basic law of light absorption at concen-

trations of 0.2-20 and 0.2-22 pg / ml, The maximum optical density of Cr (III)

respectively. MLC are resistant to water and complexes and Co (II) is reached within 8 and

organic waste, and they are not diluted for three 12 minutes, respectively. days, and after extraction more than a month.

Table 1. Optimal formation conditions and analytical characteristics of MLC of chromium

(III) and cobalt (II) with T Cs anc AP

Compound pH range complexation The pH range of maximum extraction ^Max, nm ^x10"4 lgKeq lgKex R,% Working range / ^g ml-1

Cr-HITP-AP1 1.3-5.4 2.5-4.1 438 3.73 4.27 10.4 98.4 0.2-18

Cr-HITP-AP2 1.5-5.8 2.2-3.9 442 3.57 4.74 10.6 98.5 0.2-19

Co- HNTP -AP1 1.0-7.2 3.3-5.2 540 2.94 5.68 12.8 98.7 0.2-20

Co- HNTP -AP2 1.5-6.6 3.5-4.8 555 2.43 5.83 12.7 98.6 0.2-16

Electronic absorption spectra. The Fig. 1). The molar absorption coefficients for

absorption maxima (Vax) of the Cr (III) - HITP- chromium complexes (3.73 - 3.57) x 104 (in the

AP triple complexes lie in the range 438-442 case of cobalt (2.94 - 2.43) x 104). nm (in the case of cobalt 540-555 nm) (Table 1,

Fig 1. Absorption of mixed-ligand complexes

1- Cr-HITP-APi; 2- Cr-HITP-AP2; 3- Co-HNTP-APi; 4- Co-HNTP-AP2

Ccr (VI) =3.84x10-5 M; Cco(ii) = 2.035x10-5 M; Ctcs=(i.3-1.5)x10-3 M; Chap=(1.2-1.5) )x10-3 M; SP-26, £=1.0 cm

Composition, structure and stability.

The molar relationships between the components of the ternary complex were found by several methods: the method of relative profitability of the old Barbanel, the linear method, and the equilibrium shift method [13]. When three chromium ions interact with three HITP molecules, they form triple-charged

anionic complexes that are extracted by three protonated AP molecules (Cr:HITP:AP=1:3:3). in the case of cobalt the results suggest the complex composition of Co:HNTP:AP= 1:2:2. These AP are included into the complex as double charged molecules.

The existence of clearly defined absorption bands at 2410 - 2415 cm1 in the IR-

spectrum of the complex indicates the coordination of the AP in the protonated form [11]. The disappearance of the band at 2580 cm-characteristic for the spectrum of TCs, and appearance of corresponding bands in the spectrum of the complex, which are shifted toward lower frequency, suggests that the sulphur atoms are involved in complex

formation. The observed decrease in the intensity of the absorption bands at 3200-3600 cm-1 with a maximum at 3460 cm-1 and the appearance of a broad band in the region of 3050-3150 cm-1 shows that the hydroxyl group participates in the formation of a coordination bond (Fig 2.).

Frequency, cm 1

Fig 2. IR spectrums of HNTP(a) and the Co(II)-HNTP-APi (b).

It was established by Nazarenko's method that the complexing form of chromium (III) and cobalt (II) is Cr3+ and Co2+, respectively [14]. The calculations showed that the MLC in the organic phase does not polymerize and is in monomeric form (y = 1.01-1.05). The degree of

kAo-*/ v

o

polymerization of the complexes was calculated from the equation given in [15]. Proceeding from the obtained data, we propose the following structure for the extracted ternary complex:

The mechanism of MLC formation can be represented as follows: Ions Cr3+ and Co2+ interact with H2L molecules to form anionic complexes that are extracted from protonated

HAP. The composition of the extractable complexes can be represented by the formula (HAP)3[Cr(HL)3] and (HAP)2[Co(HL)2]. Suppose that complexation processes occur:

Cr3+ + 3H2L ^[Cr(HL)3]3~ + 3H+ (1)

Co2+ + 2H2L ^[Co(HL)2]2~ + 2H+ (1")

[Cr(HL)3]3~ + 3HAP+ <^HAP)3[Cr(HL)3] (2)

[co(hl)2]2~ +2HAP+ <=> (hap)2[co(hl)2] (2")

After solving equation (1) and (2), the values of extraction constant (lgKex) calculated by the equilibrium constant (lgKeq) and the equationsl

lg^eq =lgD-3lg[HAP+] and lgXex = lgP - 3lg[TCs] - 3lg[HAP] (in the case of cobalt, lgKeq = lgD-lg[HAP+] and lgKex = lgD-2lg[TCs]-2lg[HAP]) are respectively shown in Table 3. In Table 3 the main spectrophotometry characteristics of the procedure for determining chromium and cobalt are presented.

Influence of foreign ions. The effect of a number of cations and anions on the accuracy of the determination of chromium and cobalt was studied. The experiments were carried out according to the recipe on which the calibration

curves were plotted, with the only difference being that a certain amount of the corresponding ions was introduced into the solution of chromium and cobalt. The selectivity of the spectrophotometry determination of chromium and cobalt in the form of the studied complexes is shown in table 2. It has been established that large amounts of alkali, alkaline earth elements, rare earth elements, F-, CI-, Br-, SO32-, SO42- and C2O42- do not interfere with the determination of chromium and cobalt. The selectivity of the determination is significantly increased in the presence of masking agents.

Table 2. Effect of foreign ions (FI) on the extraction of chromium (III) (30 pg) and cobalt (II) (20

pg) (n = 5, P = 0.95).

FI Molar excess of the ion Masking agent Found Cr, ^g; (Sr) Found Co, ^g; (Sr)

HITP-AP1 HITP-AP2 HNTP-AP1 HNTP-AP2

Cr Co

Co(II) 60 - NaNO2 30.4 (0.06) 30.7(0.02) 20.3 (0.04) 19.56 (0.04)

Ni(II) 40 50 29.6 (0.03) 29.2(0.03) 19.9 (0.04) 19.7 (0.04)

Fe(II) 10 200 PO43- 30.2 (0.05) 29.3(0.03) 19.9 (0.05) 20.3 (0.05)

Fe(III) 10 60 Ascorbic acid 30.3 (0.02) 30.3(0.03) 20.2 (0.02) 19.7 (0.04)

Cd(II) 70 20 Nal 30.4 (0.05) 29.8(0.02) 19.6 (0.05) 19.8 (0.04)

Al(III) 15 20 NaF 29.8 (0.03) 29.7(0.05) 19.6 (0.04) 19.8 (0.04)

Bi(III) 20 112 CS(NH)2 29.7 (0.06) 30.3(0.03) 20.1 (0.04) 20.0 (0.04)

Nb(V) 20 40 Wine acid 30.2 (0.02) 29.5(0.01) 19.6 (0.02) 19.8 (0.05)

Zr(IV) 45 40 29.6 (0.03) 29.6(0.05) 19.4 (0.02) 19.6 (0.02)

Cu(II) 50 25 CS(NH)2 30.5 (0.03) 30.4(0.01) 19.3 (0.02) 20.3 (0.06)

Hg(II) 30 50 30.0 (0.0) 20.3(0.01) 19.7 (0.02) 20.6 (0.02)

Ti(IV) 20 30 Wine acid 29.6 (0.01) 19.7(0.02) 19.8 (0.02) 19.8 (0.04)

V(V) 70 50 EDTA 29.8 (0.06) 19.8(0.06) 20.4 (0.02) 20.0 (0.07)

W(VI) 40 50 NaNO2 29.7 (0.03) 20.6(0.03) 19.4 (0.01) 19.2 (0.02)

Mo( VI) 140 10 30.0 (0.0) 20.0(0.0) 20.2 (0.04) 19.2 (0.04)

Ta(V) 45 45 Wine acid 29.5 (0.03) 20.3(0.01) 20.3 (0.04) 19.8 (0.02)

U022+ 50 40 Wine acid 30.7 (0.05) 20.5(0.06) 19.4 (0.04) 19.1 (0.02)

Cr(VI) - 60 CS(NH)2 30.6 (0.05) 20.0(0.05) 19.1 (0.02) 20.1 (0.02)

Mn(II) 50 40 29.7 (0.01) 20.0(0.05) 20.3 (0.04) 19.56 (0.04)

Analytical Characteristics. In table 3 chromium and cobalt complexes with TCs and shows the analytical characteristics of certain AP.

Table 3. Analytical characteristics of some ternary complexes of chromium and cobalt with TCs

and HAP

Compound Sandell's sensitivity, ^g cm-2 Limit of detection , ng ml-1 Limit of quantificat ion, ng ml-1 The equation of calibration curves Correlation coefficient

Cr-HITP-AP1 0.0037 13 37 0.035+0.27x 0.9986

Cr-HITP-AP2 0.0035 14 43 0.029+0.26x 0.9975

Co-HNP-AP1 0.0043 16 52 0.017+0.23x 0.9890

Co-HNTP-AP2 0.0047 15 48 0.015+0.22x 0.9958

Table 4 demonstrates the data which allow a comparison of the analytical parameters of the procedures for the determination of chromium

and cobalt with the earlier known procedures [24, 7].

Table 4. Comparative characteristics of the procedures for determining chromium and cobalt

Reagent* pH ( solvent) X, nM s-10"4 Beer's law range, |g [Ref.]

Cr-5-Br-DMPAP 0.1-10 M HCl (CHCI3) 546 7.8 0.02 - 0.56 [7]

Cr-PAR 4-5 540 4.7 3.2-13.0 [2,3,7]

Cr-PAN 0.2-0.8 M HCl (aseton) 400 1.28 0.3 - 2.0 [2,3,7]

Cr-Br-PADAP 4.7 600 7.93 0.6 - 15.0 [7]

Cr - diphenylcarbazide 1N HCl (aseton) 540 2.7 0.25-1.0 [3]

Co-PAR-TTC 5.2-5.8(CHCl3) 525 4.26 0.2 - 1.5 [4]

Co-Nitroso-R-salt weakly acidic medium 415 3.5 [2]

Co-1-nitroso-2-naphtol 3.4-6.9 (CHCl3) 415 2.9 [2]

Co- 2-nitroso-1-naphtol 3.0-7.2 (CHCl3) 365 3.7 [2]

Cr-HBTP-APi 2.5-4.1 (CHCl3) 438 3.73 0.2-18 Proposed method

Cr-HBTP-AP2 2.2-3.9 (CHCl3) 442 3.57 0.2-19

Co-HNTP-APi 3.3-5.2(CHCl3) 540 2.94 0.2-20

Co-HNTP-AP2 3.5-4.8(CHCl3) 555 2.43 0.2-16

*Note: 5-Br-DMPAP - 2-(5-bromo-2-pyridylazo)-5-dimethylaminophenol); PAR - 4-(2-pyridylazo)resorcinol; PAN - 1-(2-Pyridylazo)-2-naphthol; 5-Br-PADAP - 2-(5-brorno-2-pyridylazo)-5-diethylaminophenol; ; TTC - 2,3,5-triphenyl-2H-tetrazolium chloride.

Analytical Applications. The proposed method, within the established optimal conditions, was used to determine Cr (III) and Co(II) in milk, sour cream and cottage cheese. The results presented in Table 7 show successful

applicability of the proposed method to real analysis of samples. The correctness of the results of the analysis is verified by the method of additives.

Table 5. Determination of chromium and cobalt in milk, sour cream and cottage cheese. The

An Chromium, ^g Cobalt, ^g

object Introduced Found sr A G± tax s -¡=, ßg sjn Introduced Found Sv A G± tax S ~i=,ßg Vn

Milk 5.2 5.21 0.37 5.21±0.040 5.0 6.92 0.29 6.92±0.030

5.3 5.43 0.50 5.43±0.030 5.0 5.96 0.46 5.96±0.041

Sour 5.1 5.23 0.50 5.23±0.030 5.2 5.52 0.52 5.52±0.023

Cream 10.0 10.10 0.90 10.10±0.015 10.0 10.41 0.88 10.41±0.029

Cottage 5.0 5.92 0.81 5.92±0.042 5.4 5.43 0.73 5.43±0.035

Cheese 10.0 10.94 0.41 10.94±0.043 10.0 10.24 0.28 10.24±0.044

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Cr (VI) Vd Co (II)-IN MUXTOLiFLiQANDLI KOMPLEKSLdRiNiN SPEKTROFOTOMETRiK

TSDQiQi

B.Z. Zalov1, §.A. Mammadova1, N.S. Hzsznova2, §.A. ibrahimova3

1Azarbaycan Dovlat Pedaqoji Universiteti, U. Hacibayov 68. Baki, AZ1000, 2Azarbaycan Dovldt Neft va Sanaye Universiteti, Azadlga 34, Baki, 1000, 3Baki Dovldt Universiteti, Z. Xalilov, 23. Baki AZ 1148 e-mail: [email protected]

Agagidaki reagentlardan istifada edilmigdir: tiopiropkatexin (TP): 2-hidroksi-5-yodotiofenol (NITF) va 2-hidroksi-5-nitrotiofenol (HNTF); va aminofenollar (AF): -2 (N,N-dimetilaminometil) fenol - (AF1) va 2 (N,N-dimetilaminometil)-4-metilfenol (AF2). TP fizik-kimyavi metodlarla - iQ va NMR spektroskopiyasi ila tadqiq edilmigdir. Kompleks amala galan zaman HiTF Cr (VI) -dan Cr (III)-a qadar reduksiya edir. Xrom va kobalt muxtalifligandli kompleksi (MLK) gaklinda xloroformla 98.4-98.7% ekstraksiya olunur. Xrom (III) va kobalt

(II) komplekslarinin amala galmasi va ekstraksiyasi ugun uygun olaraq optimal pH 1.3-5.8 va 1.0-7.2-dir. Reagentlarin optimal qatiligi muayyan edilmigdir: (1.3-1.5)x10-3 M TP va (1.2-1.5)x10-3 M AF. Ber qanunu Cr3+ va Co2+ ionlari ugun muvafiq olaraq 0.2-19 va 0.2-20 mkq/ml intervalinda ozunu dogruldur. Xrom (III) va kobalt (II) komplekslarinin maksimum optik sixligi muvafiq olaraq 12 va 10 daqiqa arzinda alda edilir. Cr

(III) - HITP-AF MLK maksimum igiqudmasi 438-442 nm dalga uzunlugunda (kobalt 540-555 nm) bag verir. Xrom komplekslari ugun molar udma amsali (3.57 - 3.73 4) x 104 (kobalt olduqda (2.43 - 2.94) x 104) barabardir. Komplekslardaki komponentlarin molar nisbati bir nega usulla muayyan edilmigdir (Cr: TP: AF = 1: 3: 3 va Co: TP: AF = 1: 2: 2). Nazarenko metodundan istifada edarak xrom (III) va kobaltin (II) kompleks amala gatiran ion formasinin muvafiq olaraq Cr3+ va Co2+ oldugu muayyan edilmigdir. MLK uzvi fazada polimerlagmir va monomer formadadir (y = 1.01-1.05). iglanilmig yeni metodika sud, xama va kasmikda xrom va kobalti tayin etmak ugun istifada edilmigdir.

Agar sozldr: xrom, kobalt, ekstraksiya, spektrofotometriya, tiopirokatexinlar, aminofenollar

СПЕКТРОФОТОМЕТРИЧЕСКОЕ ИССЛЕДОВАНИЕ РАЗНОЛИГАНДНЫХ КОМПЛЕКСОВ

Cr (VI) И Co (II)

А.З. Залов1, Ш.А. Маммедова1, Н. С. Гасанова2, Ш.А. Ибрагимова3

1 Азербайджанский государственный педагогический университет, AZ1000, Баку, ул. Гаджибекова 68.

2Азербайджанский государственный университет нефти и промышленности,

AZ1000, Баку, ул. Азадлыг ,34 3Бакинский государственный университет, AZ1148 Баку ул. З. Халилова, 23 e-mail: [email protected]

Были использованы следующие реагенты: тиопирокатехины (ТП): 2-гидрокси-5-йодтиофенол (НИТФ) и 2-гидрокси-5-нитротиофенол (ГНТФ); и аминофенолы (АФ): -2 (N, N-диме-тиламинометил) фенол - (АФ1) и 2(N, N-диметиламинометил) -4-метилфенол (АФ2). ТП были охарактеризованы с помощью физико-химических методов: ИК и ЯМР спектроскопия. Cr (VI) восстанавливается до Cr (III) самим реагентом во время образования комплекса. После однократной экстракции хлороформом 98.4-98.7% хрома и кобальта экстрагировали в виде разнолигандных комплексов (РЛК). Для образования и экстракции комплексов хрома (III) и кобальта (II) оптимальными являются рН 1.3-5.8 и 1.0-7.2 соответственно. Оптимальным условием для формирования и извлечения этих комплексов является концентрация (1.3-1.5) х 10-3 М ТП и (1.2-1.5) х 10-3 М АФ. Для Cr 3+ и Co2+ закон Бера выполняется в интервалах 0.2-19 и 0.2-20 мкг/мл соответственно. Максимальная оптическая плотность комплексов хрома (III) и кобальта (II)

достигается в течение 12 и 10 минут соответственно. Максимумы поглощения тройных комплексов Сг (III) - ГИТФ-АФ лежат в диапазоне 438-442 нм (в случае кобальта 540-555 нм). Молярные коэффициенты поглощения для комплексов хрома (3.57 - 3.73 4)*104 (в случае кобальта (2.43 - 2.94) х104). Молярные соотношенш компонентов в комплексах определены несколькими методами (Сг:ТП:АФ = 1:3:3 и Со:ТП:АФ = 1: 2: 2). Методом Назаренко было установлено, что комплексообразующая форма хрома (III) и кобальта (II) представляет собой Сг3+ и Со2+ соответственно. Расчеты показали, что РЛК в органической фазе не полимеризуется и находится в мономерной форме (у = 1.01-1.05). Предлагаемая методика используется для определения хрома и кобальта в молоке, сметане и твороге.

Ключевые слова: хром, кобальт, экстракция, спектрофотометрия, тиопирокатехины, аминофенолы