SOLVATION METHODOLOGY FOR SEPARATION AND MICRO
DETERMINATION OF LEAD (II) IN DIFFERENT SAMPLE
Sahar Aqeel Hussain
1and Safa Majeed Hameed
2 1Department of Pharmaceutical Chemistry, Faculty of Pharmacy, University of Kufa, Al-Najaf, Iraq
2Department of Chemistry, Faculty of Education for girls, University of Kufa, Al-Najaf, Iraq
E-Mail: [email protected]
ABSTRACT
In this paper, separation, preconcentration and determination of Pb(II) as solvation species have been achieved by using methyl isobutyl ketone (MIBK) as an organic reagent. The spectrophotometric study of extracted solvation species shows that maximum absorption wavelength is 287nm. Accordingly, the experimental studies of extraction have optimum concentration of salting out KNO3 to form solvation species with higher extraction efficiency of 0.5M in the presence of 100µg of Pb+2 with 1×10-4 M from MIBK dissolved in chloroform and shaking the two layers for 10 minutes. Besides, this study involves thermodynamic and interferences investigations with application of spectrophotometric determination of Pb (II) in different environmental and vital samples.
Keywords: lead (II), solvation method, solvent extraction, MIBK, separation methods.
INTRODUCTION
Sensitive solvation method was used for separation and spectrophotometric determination of micro amount Ni (II) in aqueous solution with N-(2-hydroxybenzylidene) aniline in the absence and presence of Methyl-Isobutyl Ketone in chloroform [1]. Methyl Isobutyl Ketone and acetophenone were presented as suitable agents for removal of Fe (III) from concentrated HCl solutions [2]. HBTA-TOPO-kerosene extraction system was verified an effective method to recover Li from alkaline brine [3]. Cloud point extraction and solvation methods are functional for separation and determination of La (III) by using 2,4-Dimethyl pentane-3-one for extracting formed solvation species. This method applied for the spectrophotometric determination of La (III) in different samples [4]. Separation and extraction of Zn (II) and Cd(II) have been performed by methyl stearate as extractant dissolved in chloroform [5]. Cloud point extraction has been achieved for the spectrophotometric determination of tiny amounts of Fe3+andHg2+. This method used for characterization of trace metal ions in different [6]. Joined of solvation and cloud point extraction, micro amount of Ce (III) has been separated and determined from aqueous solutions by using 2,4-Dimethyl pentan-3-one as extractant and the surfactant TritonX-100. The experimental study shows the solvation species of Ce+3 extracted into cloud point layer that have λmax of 295nm, the study has involved the effect of different kinds and concentrations of salting out [7]. The extraction method has been used for separation and spectrophotometric determination of microamount different metals [8-15].
In this research used Methyl–Isobutyl Ketone as extractant to form solvation species in the presence of salting out agent KNO3 we do not find in previous studies any using of this compound as extractant, after formation solvation species and calculate all parameters for spectrophotometric determination the method used for determination microamount of lead (II) in different samples.
EXPERIMENTAL
For spectrophotometric application and absorbance measurements, spectrophotometer double beam (UV-Vis) spectrophotometer, Abiochrom (biochrom libra 560) has been used. The electrical balance was based on (A&D Company, limited, dool, CE, HR200, Japan). Electrical shaker, HY-4 vibration and the AD are just about speed multiple usage functions based on international trip crop in Italy.
The stock solution of lead (II) at a concentration (1000µg /mL) was prepared by dissolved 0.1598 of lead nitrate Pb(NO3) in 100mL volume. The prepared 1M of methyl isobutyl ketone (MIBK) was by dissolved 10.06 gm in 100 mL chloroform in a volumetric flask.
Calibration curve for determination lead (ii) in aqueous solution
By the spectrophotometric Dithizone method[16] on series of 5mL aqueous solution, rising concentration of Pb+2 ion was at the rang (1-10)µg and after the absorbance of dithizone complex against the quantity of Pb+2 ion in the solution obtained by straight line relation as in Figure-1.
Figure-1. Calibration curve of Pb(II) by Dithizone method.
y = 0.0094x + 0.0003 R² = 0.9971
0.00 0.20 0.40 0.60 0.80
0 20 40 60 80
A
bs.
Comprehensive method
Prepare 5mL aqueous solution containing fixed quantity of Pb+2 ion at optimum pH in separation funnel shaking with 5mL chloroform organic solution of 1×10-4 M of MIBK for optimum shaking time. Afterward, separate the organic phase from the aqueous phase and then measure the absorbance of organic phase at wavelength of maximum absorbance to solvation species formed and extracted against blank prepared at the same manner at absence of Pb+2 ion. The aqueous phase was treated according to Dithizone spectrophotometric method[16] and based on the calibration curve determine the remainder quantity of Pb+2 ion aqueous solution after extraction. By subtraction remainder quantity of Pb+2 ion from the original quantity in aqueous solution, determine the transferred quantity of Pb+2 ion into organic phase to form solvation species. Lastly, calculate distribution ratio (D) according to the relation blow:
𝐷 =[𝑃𝑏[𝑃𝑏2+2+]]𝑜 𝑎𝑞
RESULTS AND DISCUSSIONS
Spectrophotometric study
For pinpointing the wavelength of maximum absorbance of extracted solvation species, take 5mL aqueous solution containing 50µg of Pb+2 ion in the presence of 0.5 M KNO3, and shake for 10 minutes with 5mL organic solution of 1×10-4 M MIBK dissolved in chloroform. After separation of organic phase from aqueous phase, take the spectrum of organic phase against blank prepared at the same manner in the absence of Pb+2 ion. The spectrum is shown as in Figure-2.
Figure-2. UV-Visibile Spectrum for solvation species of Pb+2 ion with
MIBK extracted.
The spectrum shows the wavelength for the maximum absorbance of solvation species of Pb+2 ion with MIBK at λmax=287nm.
Variation of salting out the concentration
Extracted Pb+2 ion as solvation species from 5mLaqueous solution has rising concentration of salting out KNO3 by shaking with 5mL solution of 1X10-4 M MIBK dissolved in chloroform. Complete the procedure according to the general method. The results were as in Figures (3 and 4).
Figure-4. Effect of salting out concentration on extraction efficiency and D-values.
The results demonstrated that 0.5 M KNO3 has optimum concentration of higher extraction efficiency because this concentration motivates reaching to favourable thermodynamic equilibrium of formed solvation species. All concentrations less than this optimum value cannot be reached to the most favourable thermodynamic equilibrium and decrease extraction efficiency. So, all concentrations more than optimum
0.02 0.22 0.42 0.62
0 0.2 0.4 0.6 0.8 1
A
bs
.
[KNO]
0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2
0 0.2 0.4 0.6 0.8 1
Log D
Variation shaking time effect
According to comprehensive method extraction, Pb+2 ion is considered as solvation species from 5mL aqueous solution of 100 µg Pb+2 ion in the presence 0.5 M KNO3 by shaking with 5mL of 1×10-4 M MIBK dissolved chloroform at rising shaking time at room temperature. The results were as in Figures (5 and 6).
Figure-5. Effect shaking time on formation and stability of solvation species.
Figure-6. Effect shaking time on distribution ratio and D-values.
The results show that (10 minutes) was the optimum shaking time to reach the best thermodynamic equilibrium and higher extraction efficiency. Any shaking time less than optimum value cannot be appropriate to reach the favourable thermodynamic equilibrium. To be taken into account for shaking time, consider it as kinetic for extraction method. Any shaking time more than optimum value leads to an increase in the kinetic energy in aqueous solution, which prevents the formation of solvation species and decreases the extraction efficiency.
Variation of Pb+2 ion concentration effect
Sequentially, increase Pb+2 ion in 5mL aqueous solution extracted according to the comprehensive method at the optimum value of KNO3salting out concentration and shaking time. The results were as in Figures (7 and 8).
Figure-7. Effect of Pb+2 ion concentration on formation
and stability of solvation species.
Figure-8. Effect of Pb+2 ion concentration on
extraction efficiency.
The results explain that there is a linear relation for extraction efficiency with increasing metal ion concentration of higher extraction efficiency because of the increased rate of forwarding direction of thermodynamic equilibrium for formed solvation species to reach maximum rate at 100µg Pb+2 in 5mL aqueous solution.
𝑃𝑏+2 + 2𝑁𝑂3−+ 𝑀𝐼𝐵𝐾 ↔ 𝑀𝐼𝐵𝐾 → 𝑃𝑏(𝑁𝑂3)2 Any concentration of Pb+2 ion more than optimum value leads to a decrease in extraction efficiency to increase the rate of the backward direction of thermodynamic equilibrium according to mass action law effect.
Effect of salting out kinds
According to a comprehensive method, extracted Pb+2 ion is done in the presence of different kinds of salting out. The results show that there are a different behaviour and extraction efficiency with different levels of salting out using an extraction method. This has the role of salting out in the formation and stability of solvation species extraction that affects on the thermodynamic equilibrium from the rate of the forward direction of thermodynamic equilibrium based on the behaviour of salting out in aqueous solution.
0.3 0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.7
0 5 10 15 20
A
bs
.
Shaking time (min.)
0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3
0 5 10 15 20
Log D
Shaking time (min.)
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
0 50 100 150
A
bs
.
µg Pb(II)/5mL
0 0.2 0.4 0.6 0.8 1 1.2 1.4
0 50 100 150
Log D
Figure-9. Effect of concentration different kinds of salting out on formation and stability of solvation species.
Figure-10. Effect of concentration different kinds of salting out on extraction efficiency and D-value.
Thermodynamic
According to comprehensive method, extracted Pb+2 ion has been set as solvation species at the optimum condition and different temperatures. The results were as in Figures (11 and 12).
Figure-11. Effect of temperature on formation and stability of solvation species.
Figure-12. Effect of temperature on extraction efficiency and D-value.
After calculating extraction combatant at each temperature by applying the relation below, the results were as in Figure-13.
Figure-13.Variation extraction constant with
temperature change.
From a slope of linear relation in Figure-15 and relation below, the calculated thermodynamic details were explained in Table-1.
Table-1.Thermodynamic date for extraction Pb+2 ion as solvation species.
ΔHex ( 𝒔𝒍𝒐𝒑𝒆 =𝟐.𝟑𝟎𝟑𝑹𝜟𝑯𝒆𝒙) ΔGex (ΔGex= -RT ln Kex) ΔSex (ΔGex= ΔHex -TΔXex)
0.0829 KJmol-1 -59.74KJmol-1 191.13Jmol-1K-1
-0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
0 0.2 0.4 0.6 0.8 1
A
bs
.
[Salting out]
KNO3
LiNO3
0.2 0.4 0.6 0.8 1.0 1.2
0 0.2 0.4 0.6 0.8 1
Log D
[Salting out]
KNO3
LiNO3
Ca(NO3)2
0 0.2 0.4 0.6 0.8 1 1.2 1.4
0 20 40 60
A
bs
.
TᵒC
0 0.5 1 1.5 2 2.5
0 10 20 30 40 50 60
logD
TᵒC
8.0 8.5 9.0 9.5 10.0 10.5
3.1 3.2 3.3 3.4 3.5 3.6 3.7
Lo
g
Ke
x
Effect of methanol presence
By extracting 100µg of Pb+2 in 5mL aqueous solution in the presence of 0.5M KNO3 and sequentially increasing methanol by MIBK according to the general method, the result was as in Figures(14 and 15).
Figure-14. Eeffect of methanol on formation and stability of solvation species.
Figure-15. Effect of methanol on extraction efficiency and D-value.
The results state an increasing in the extraction efficiency as well as increasing in the formation and stability of solvation species in the presence of methanol in aqueous solutions. The increased extraction efficiency is continuous with increased percentage of methanol in aqueous solution to 25% that declines extraction efficiency by increasing percentage of methanol more. Methanol has effect to decrease dielectric constant of water, destroy the hydration shell of Pb+2 and NO3- ions and increase the formation of Pb(NO3)2 and the solvation species by coordinately binding of MIBK such as the case of MIBK → 𝑃𝑏(𝑁𝑂3 )2.
Effect of interferences
Extracted Pb+2ion as solvation species was according to the general method at the optimum condition and in the presence of foreign ions in the aqueous solution
with Pb+2 ion for each atom. The results were as in the Table-2.
Table-2. Effect of foreign ions on extraction efficiency of Pb+2 ion as solvation species.
Foreign ions Cd2+ Ni2+ Zn2+ Ag2+
Absorbance 0.34 0.45 0.22 0.18
D 8.52 14.51 4.76 1.83
The results demonstrate that the presence of foreign ions in aqueous solution has effect to decline extraction efficiency of Pb+2 ion, by interference effects of these foreign ions to form solvation species extracted to the organic phase. Also, it has effect to decrease concentration of KNO3 and MIBK from optimum value and decrease the rate of forward direction for foreign solvation species. So that the different foreign ions have given different effects according to behaviour of each foreign ion in aqueous phase.
Effect of different extractant
Extraction of 100 µg Pb+2 ion in 5mL aqueous solution at optimum condition was according to a general method using different organic reagents as extractants at 1×10-4M dissolved in chloroform. The results were as in Table-3.
Table-3.Effect of different reagent on extraction efficiency.
Organic reagent Abs. D
Acetophenone 0.68 20.45
Tributyl phosphate 0.56 16.32
2,4-Dimethyl
pentan-3-one 0.88 35.37
The results show that there is different extraction efficiency by using different reagents as extractants and exhibit 2,4-Dimethyl pentan-3-one with higher absorbance and D-value than MIBK. But acetophenone as tributyl phosphate has less extraction efficiency than MIBK. This is in accordance with the ability to bind coordinately with Pb+2 ion in Pb(NO3)2.
Spectrophotometric determination
To determine the quantity of lead accumulated on or in a different sample, prepare the calibration curve for spectrophotometric determination by application comprehensive method on a series of aqueous solutions of sequentially rising concentration of Pb+2 ion at optimum conditions. The result was as in Figure-16.
0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4
0.75 10.75 20.75 30.75 40.75
A
bs
.
CH3OH%
1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2
0 10 20 30 40 50
logD
Parameters for the determination of Pb(II)
by solvation method
values
λmax (nm) 287
RSD% (n=3) 0.742
Molar absorptivity
(L.mol-1.cm-1) 6.907×10
3
Sandell’s sensitivity
(µg . cm2-) 2.999×10
-7
Limit of Detection
(µgmL-1) 9.269×10
-5
Figure-16. Calibration curve for spectrophotometric determination of Pb+2 ion different samples.
Sample solution prepared by following wet digestion method [17], after that applied the comprehensive method and added the suitable masking agents on a different sample and return to the calibration curve, the results were detailed in Table-4.
Table-4. Accumulated quantity of Pb(II) in or on different samples.
Sample name ppm Pb(II)
Non-Agriculture soil 11.78
Agriculture soil 28.88
Cucumber 0.120
Tomatoes 0.103
Beef 0.168
Local chicken meat 0.163
CONCLUSIONS
In this research used solvation method for separation and spectrophotometric determination of Pb(II) by using MIBK to form solvation species, the study show that the kind and concentration of salting out agent effect on extraction method, so that we must use the suitable salting out agent. The solvation method effect by extractant kind, the spectrophotometric determination of Pb(II) by solvation method giving high sensitivity.
ACKNOWLEDGEMENT
We are thankful to our colleague [Prof. Dr. Shawket Kadhim Jawad from the Faculty of Education for Girls-University of Kufa] who provided expertise that greatly assisted the research.
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y = 0.0333x - 0.0048 R² = 0.998
0.0 0.2 0.4 0.6 0.8
0 5 10 15 20
A
bs
.
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