CHEM. RES. CHINESE UNIVERSITIES 2012, 28(5),

CHEM. RES. CHINESE UNIVERSITIES 2012, 28(5), 807—813 Determination of Vanadyl Porphyrins by Liquid-liquid Microextraction and Nano-baskets of p-tert-...
Author: Rodney Parks
0 downloads 2 Views 346KB Size
CHEM. RES. CHINESE UNIVERSITIES 2012, 28(5), 807—813

Determination of Vanadyl Porphyrins by Liquid-liquid Microextraction and Nano-baskets of p-tert-Calix[4]arene Bearing Di-[N-(X)sulfonye Carboxamide] and Di-(1-propoxy) in Ortho-cone Conformation MOKHTARI Bahram and POURABDOLLAH Kobra* Razi Chemistry Research Center(RCRC), Shahreza Branch, Islamic Azad University, Shahreza, Iran Abstract Dispersive liquid-liquid microextraction technique was introducd to remove the centrifuging step and conduct inclusion microextraction of charged porphyrins by nano-baskets. For nano-baskets of p-tert-calix[4]arene bearing di-[N-(X)sulfonyl carboxamide] and di-(1-propoxy) in ortho-cone conformation was synthesized and used. The related parameters including ligand concentration, the volume of water disperser, salt effect, and extraction time were optimized. The linear range, detection limit(S/N=3) and precision(RSD, n=6) were determined to be 0.2―50, 0.07 μg/L and 5.3%, respectively. The results reveal that the new approach is competitive analytical tool and an alternative of the traditional methods in the crude oil and related systems. Keywords Nano-basket; Dispersive liquid-liquid microextraction; Vanadyl porphyrin; Calix[4]arene Article ID 1005-9040(2012)-05-807-07

1

Introduction

Determination of metalloporphyrins in crude oil is of interest in understanding the geochemical origins of petroleum reservoirs, the diagenetic and catagenetic pathways in the oil formation, and the maturation, depositional[1] and environmental reconstruction studies[2]. Treibs[3] discovered the petroleum porphyrins(petroporphyrins) in 1934. Vanadyl porphyrins were the first petroleum biomarkers[4] and they are molecular fossils of tetrapyrrolic pigments such as bacteriochlorophylls and chlorophylls[5]. Vanadium in crude oil causes corrosion prob-

lems that derive from the formation(in the combustion chamber of power plants) of sodium vanadates(with low mel- ting point), which react with the metal surface of the superheaters and form the metal oxide[6]. According to the literature[2], five main types of porphyrins along with their homologues are present in crude oil including etioporphyrins(Etio), deoxophylleoerythroetioporphyrin(DPEP), tetrahydrobenzo DPEP, benzo-Etio and benzoDPEP. Fig.1 illustrates the chemical structures of some scaffolds.

Fig.1 Chemical structures of five main types of vanadyl porphyrins Up to 30% of vanadium and 25% of nickel in Tatarstan copy for the determination of porphyrins(low levels) in the crude oil are found as porphyrin complexes. Ion et al.[7] anakerogen fraction. After that, Premovic et al.[5] used the eleclyzed the vanadyl porphyrin distribution of Romanian petrotron spin resonance(ESR) to quantify the high levels of vanadyl leogenetic rocks by UV-Vis spectrophotometry, Fourier transporphyrins in kerogens. form infrared(FTIR), inductive coupled plasma(ICP)-atomic Saitoh et al.[9] used a series of preliminary separation emission spectrometry, electron spin resonance(ESR) and procedures for the preconcentration of metalloporphyrins and X-ray fluorescence spectroscopy. Holden and coworkers[8] the determination by reversed-phase high-performance liquid developed the method of high-resolution reflectance spectroschromatography(HPLC). Ali et al.[2] extracted the nickel and ——————————— *Corresponding author. E-mail: [email protected] Received November 9, 2011; accepted December 21, 2011. Supported by the Islamic Azad University(Shahreza Branch) and the Iran Nanotechnology Initiative Council.

808

CHEM. RES. CHINESE UNIVERSITIES

Vol.28 [17]

kinetic and thermodynamic points of view . vanadyl porphyrins in the residue of Saudi Arabian Crude Oils. Demulsifiers are molecules that aid the separation of water The nickel porphyrins were separated from vanadyl porphyrins from oil and prevent the formation of water in oil mixture. via adsorption chromatography on alumina and silica gel by Some demulsifiers are polymers, others have calixarene solvents of increasing polarity. They monitored the chromatostructures. Calixarenes have been subjected to extensive regraphic separation by UV-Vis spectrophotometry. searches[18―21](using gas chromatagraph, Teif Gostar Faraz Co., New sample-preparation methods, which are easy to use, Iran) and reviews[22―30] in development of extractants, transinexpensive, fast, environmental friendly and compatible with a porters, stationary phases, electrode ionophores, optical sensors range of analytical instruments, are outspreaded. More recently, and medical researches over the past decades. efforts have been placed on the development of the dispersive In this paper, a novel approach was introduced and used liquid-liquid microextraction(DLLME)[10] procedure, which is based on a ternary component solvent system. The dispersion for the determination of vanadium porphyrins in the live crude oil. The main objectives are (I) using water as disperser phase; of extraction solvent by disperser solvent within the aqueous (II) removing the centrifuging step; (III) settling the water solution leads to a large contact area between the aqueous phase and the extraction solvent. Other examples of sample droplets by calix[4]arenes; (IV) conducting DLLME in an organic system; (V) inclusion microextraction of charged porpreparation by DLLME have been presented for the trace dephyrins by ionizable calix[4]arenes. This method deals with the termination of pesticides in soils[11], organophosphorus pesti[12] [13] [14] cides in water , nickel and Cu(II) in water, and chlorotwin role of calixarene scaffolds as the settling and complexing benzenes in water[15]. agent. Flocculation, which is the first action of the demulsifier on 2 Experimental an emulsion, involves the joining of the small water droplets. When magnified, the flocks take on the appearance of fish-egg 2.1 Materials bunches. If the emulsifier film surrounding the water droplets is very weak, it will break under this flocculation force and the Doubly distilled and deionized water(DDW) with a specoalescence, which is the rupturing of the emulsifier film and cific resistivity of 18 MΩ·cm, from a Milli-Q water purification the uniting of water droplets, will take place without further system(Millipore, Bedford, MA), was used as disperser. chemical action. Once the coalescence begins, the water dropAccording to the literature methods[2], the vanadyl porphyrins lets grow large enough to settle out. were separated from the oil matrix and were used as standard Asphaltenes are the high polar fraction of the petroleum solutions. The oil samples were collected from one of the Iraand play an important role in the formation and stabilization of nian offshore oil fields and their chemical characteristics are the water in crude oil emulsions[16]. The goal of demulsifier presented in Table 1. action is to offset the stabilization of emulsion from both the Table 1 Chemical characteristics of blend crude oil used in the experiments* Component N2 CO2

Stream liquid(%, molar fraction) 0.04 0.35

Flashed gas(%, molar fraction) 0.31 2.78

Flashed liquid(%, molar fraction) 0 0

H2S

0.57

4.52

0

CH4

3.76

30.14

0

C2 H6

1.50

12.02

0

C3 H8

3.77

21.90

1.18

i-C4H10

1.92

7.25

1.16

n-C4H10

7.23

12.40

6.49

i-C5H12

2.79

3.21

2.73

n-C5H12

3.80

2.81

3.94

C6

7.30

1.86

8.08

C7

8.76

0.68

9.91

C8

9.61

0.12

10.97

C9

8.77

0

10.02

C10

6.75

0

7.71

C11

3.60

0

4.12

C12+

29.48

0

33.69

* Total sulfur(%, molar fraction): 0.85; asphaltenes(%, molar fraction): 0.32; waxes(%, molar fraction): 5.00.

2.2

Synthesis of Ortho-cone Conformers(1―4)

In the present work, the synthesis of four derivatives of p-tert-calix[4]arene bearing di-[N-(X)sulfonyl carboxamide] and di-(1-propoxy) in ortho-cone conformation and the preparation of its bonded silica stationary phase were described[X=

phenyl(1), p-CH3phenyl(2), p-OHphenyl(3), p-NO2phenyl(4)]. Fig.2 shows the expanded chemical structure of derivatives 1―4.

2.2.1

Instruments and Apparatus

Elemental analysis was performed with a Flash EA 1112 elemental analyzer. 1H NMR spectrum was recorded with a Bruker 400 MHz spectrometer in CDCl3. IR spectra were

No.5

MOKHTARI Bahram et al.

recorded with a Bruker Vector 22 instrument.

2.2.2 Synthesis of Intermediates 5,11,17,23-Tetrakis(1,1-dimethylethyl)-25,26-dihydroxy27,28-di(1-propoxy)calix[4]arene was synthesized via the procedure, which is reported here. Briefly, 7.00 g(10.80 mmol) of p-tert-butylcalix[4]arene was added to a solution of dimethyl sulfoxide(DMSO, 50 mL) and 40% aqueous NaOH(7.06 mL, 100.00 mmol). After that, the mixture was warmed to 50 ºC and 9.20 g(43.00 mmol) of propyl tosylate(PrOTs) was added to the

809

solution. The mixture was stirred for 24 h at 70 ºC. Having been cooled to room temperature, the reaction mixture was poured into a 5% aqueous HCl solution(100 mL). The crude product was extracted with dichloromethane and the solution was dried over MgSO4. The dichloromethane was evaporated in vacuo and the residue was washed with MeOH to give 5,11,17,23-tetrakis(1,1-dimethylethyl)-25,26-dihydroxy-27,28di(1-propoxy)calix[4]arene(6.31 g, 88%) with m. p. 168― 170 °C.

Fig.2 Chemical structures of derivatives 1―4 A mixture of THF(32 mL) and NaH(0.56 g, 22.19 mmol) thylethyl)-25,26-bis(chlorocarboxymethoxy)-27,28-di(1-propowas stirred and a solution of THF(25 mL) and 5,11,17,23-texy)calix[4]arene in THF(10 mL) was added to a mixture contrakis(1,1-dimethylethyl)-25,26-dihydroxy-27,28-di(1-protaining NaH(0.58 g, 24.0 mmol) and 9.50 mmol of phenyl sulpoxy)calix[4]arene(2.75 g, 3.70 mmol) was added dropwise to fonamide in 100 mL of THF, and the mixture was stirred under it. The solution was stirred at room temperature under nitrogen nitrogen for 6 h at room temperature. Then 2 mL of H2O was for 3 h, and then ethyl bromoacetate(2.4 mL, 22.19 mmol) was added to decompose the excess NaH and the THF was evapoadded to the solution. The reaction mixture was refluxed for 24 rated in vacuo and 200 mL of CH2Cl2 was added to the residue. h and was quenched with 25 mL of 5%(mass fraction) aqueous The organic layer was washed with 200 mL of 1 mol/L HCl and HCl. After evaporating the THF in vacuo, the residue was alwater, and was dried over MgSO4 and was evaporated in vacuo lowed to cool to room temperature. The residue was washed to give the crude di-ionizable calix[4]arene. After purification, with 5% HCl(150 mL) and dichloromethane was used to exthe product was dissolved in CH2Cl2, washed with 10% aquetract 5,11,17,23-tetrakis(1,1-dimethylethyl)-25,26-bis-[(ethoous HCl and water, and dried over MgSO4. The solution was xycarbonyl)methoxy]-27,28-di(1-propoxy)calix[4]arene. The evaporated in vacuo to give derivative 1, which was obtained in organic layer was washed with water, dried over MgSO4, and a yield of 90% after chromatography on silica gel with evaporated in vacuo. The crude product was recrystallized from CH2Cl2-MeOH(80:1, volume ratio) as eluent. MeOH to obtain 5,11,17,23-tetrakis(1,1-dimethylethyl)-25,26White solid; m. p. 130―142 ºC; FTIR, ߥ෤max(film)/cm–1: bis[(ethoxycarbonyl)methoxy]-27,28-di(1-propoxy)calix[4]3240(NH), 1724(C=O), 1360 and 1188(S=O); 1H NMR arene(2.72 g, 78%) as a white solid with m. p. 78―80 ºC. (CDCl3), δ: 0.96(brs, 18H), 1.24(brs, 18H), 2.00―4.28(brm, A solution of 5,11,17,23-tetrakis(1,1-dimethylethyl)26H), 6.22―7.32(brm, 8H), 7.68(t, J=7.52 Hz, 4H), 7.82(t, J= 25,26-bis[(ethoxycarbonyl)methoxy]-27,28-di(1-propoxy)calix7.42 Hz, 2H), 7.98(d, J=7.52 Hz, 4H), 9.32(brs, 2H); 13C NMR [4]arene(3.54 mmol), 10% aqueous Me4NOH(75 mL) and (CDCl3), δC: 171.20, 171.00, 155.68, 153.70, 144.50, 138.12, THF(75 mL) was refluxed for 24 h. The reaction mixture was 133.90, 132.60, 129.02, 128.20, 125.80, 72.88, 60.22, 33.88, cooled to room temperature and was stirred with 6 mol/L 33.12, 33.14, 31.82, 31.04, 25.30. Elemental anal.(%) calcd. HCl(30 mL) for 2 h. After evaporating the THF in vacuo, a for C66H82N2O10S2: C 70.30, H 7.36, N 2.42; found: C 70.20, white precipitate was filtered and dissolved in CH2Cl2(75 mL). H 7.28, N 2.52. The aqueous filtrate was extracted with CH2Cl2(75 mL×2). The 2.2.4 Synthesis of 5,11,17,23-Tetrakis(1,1-dimethycombined organic layers were washed with 6 mol/L aqueous lethyl)-25,26-bis[N-(4-methylphenyl)sulfonyl CarbaHCl until pH=1 and dried over MgSO4. The dichloromethane moylmethoxy]-27,28-di(1-propoxy)calix[4]arene(2) was evaporated in vacuo to give 5,11,17,23-tetrakis(1,1-dimeFirst, 2.40 mmol of 5,11,17,23-tetrakis(1,1-dimethylethylethyl)-25,26-bis(carboxymethoxy)-27,28-di(1-propoxy)thyl)-25,26-bis(chlorocarboxymethoxy)-27,28-di(1-propoxy)calix[4]arene(3.40 g, 96% yield) as a white solid with m. p. calix[4]arene was dried by benzene-azeotropic distillation. 169―171 ºC. Then 24.0 mmol(3.04 g) of oxalyl chloride was added to it and 2.2.3 Synthesis of 5,11,17,23-Tetrakis(1,1-dimethythe reaction mixture was refluxed for 4 h under nitrogen lethyl)-25,26-bis(N-phenylsulfonyl Carbamoylmethoatmosphere. The solvent was removed in vacuo to provide the xy)-27,28-di(1-propoxy)calix[4]arene(1) corresponding acid chloride. A solution of the acid chloride in A solution(2.40 mmol) of 5,11,17,23-tetrakis(1,1-dime10 mL of THF was added to a mixture of 9.60 mmol of

810

CHEM. RES. CHINESE UNIVERSITIES

(p-methyl)phenyl sulfonamide and 0.58 g of NaH(24.0 mmol) in 100 mL of THF, and the mixture was stirred under nitrogen for 4 h at room temperature. H2O(2 mL) was added to decompose the excess NaH. The THF was evaporated in vacuo and 200 mL of CH2Cl2 was added to the residue. The organic layer was washed with 200 mL of HCl(1 mol/L) and water, dried over MgSO4 and evaporated in vacuo to give the di-ionizable calix[4]arene. After purification, the product was dissolved in CH2Cl2, washed with 10% aqueous HCl and water and dried over MgSO4. The solution was evaporated in vacuo to give product 2, which was obtained in a yield of 88% after chromatography on silica gel with CH2Cl2-MeOH(80:1, volume ratio) as eluent. White solid; m. p. 148―154 ºC; FTIR, ߥ෤max(film)/cm–1: 3254(NH), 1720(C=O), 1342 and 1188 (S=O); 1H NMR (CDCl3), δ: 0.98(brs, 18H), 1.24(brs, 18H), 2.08―4.16(brm, 32H), 6.50―7.10(brm, 8H), 8.22(d, J=4.76 Hz, 4H), 8.32(d, J=4.68 Hz, 4H), 9.38(brs, 2H); 13C NMR (CDCl3), δC: 174.42, 170.62, 152.62, 150.82, 144.42, 143.68, 134.26, 132.48, 129.32, 125.84, 124.66, 34.24, 33.42, 33.12, 31.28, 31.04, 25.26, 21.28. Elemental anal.(%) calcd. for C68H86N2O10S2·0.1CH2Cl2: C 65.12, H 7.38, N 4.52; found: C 65.24, H 7.28, N 4.62.

2.2.5 Synthesis of 5,11,17,23-Tetrakis(1,1-dimethylethyl)-25,26-bis[N-(4-hydroxyphenyl)sulfonyl Carbamoylmethoxy]-27,28-di(1-propoxy)calix[4]arene(3) 5,11,17,23-Tetrakis(1,1-dimethylethyl)-25,26-bis(chlorocarboxymethoxy)-27,28-di(1-propoxy)calix[4]arene of 2.40 mmol was dried by benzene-azeotropic distillation, to which oxalyl chloride of 24.0 mmol(3.04 g) was then added and the reaction mixture was refluxed for 5 h under nitrogen atmosphere. The solvent was removed in vacuo to provide the corresponding acid chloride. A solution of the acid chloride in 10 mL of THF was added to a mixture of 9.60 mmol of (4-hydroxy)phenyl sulfonamide and 0.58 g of NaH(24.0 mmol) in 100 mL of THF, and the mixture was stirred under nitrogen at room temperature for 4 h. Then, 2 mL of H2O was added to decompose the excess NaH. The THF was evaporated in vacuo and 200 mL of CH2Cl2 was added to the residue. The organic layer was washed with 200 mL of HCl(1 mol/L) and water, dried over MgSO4 and evaporated in vacuo to give the crude di-ionizable calix[4]arene. After purification, the product was dissolved in CH2Cl2, washed with 10% aqueous HCl and water and dried over MgSO4. The solution was evaporated in vacuo to give product 3, which was obtained in a yield of 84% after chromatography on silica gel with CH2Cl2-MeOH(80:1, volume ratio) as eluent. White solid; m. p. 170―176 ºC; FTIR, ߥ෤max(film)/cm–1: 3238(NH), 1724(C=O), 1362 and 1168 (S=O); 1H NMR (CDCl3), δ: 0.96(brs, 18H), 1.24(brs, 18H), 2.08―4.04 (brm, 26H), 6.38―7.46(brm, 8H), 7.62(t, J=7.76 Hz, 4H), 8.02(d, J=7.42 Hz, 4H), 8.54(t, J=7.30 Hz, 2H), 9.44(brs, 2H); 13 C NMR(CDCl3), δC: 171.38, 171.02, 155.06, 153.72, 144.18, 138.96, 133.32, 132.44, 129.20, 128.34, 125.28, 73.06, 60.08, 34.28, 33.96, 33.42, 31.14, 31.06, 22.27. Elemental anal.(%) calcd. for C66H82N2O12S2: C 70.66, H 7.42, N 2.44; found: C 70.28, H 7.32, N 2.40.

Vol.28

2.2.6 Synthesis of 5,11,17,23-Tetrakis(1,1-dimethylethyl)-25,26-bis[N-(4-nitrophenyl)sulfonyl Carbamoylmethoxy]-27,28-di(1-propoxy)calix[4]arene(4) 5,11,17,23-Tetrakis(1,1-dimethylethyl)-25,26-bis(chlorocarboxymethoxy)-27,28-di(1-propoxy)calix[4]arene of 2.40 mmol was dried by benzene-azeotropic distillation. Then 3.04 g (24.0 mmol) of oxalyl chloride was added to it and the reaction mixture was refluxed for 7 h under nitrogen atmosphere. The solvent was removed in vacuo to provide the corresponding acid chloride. A solution of the acid chloride in 10 mL of THF was added to a mixture of 12.20 mmol of (4-nitro)phenyl sulfonamide and 28.8 mmol of NaH(0.70 g) in 100 mL of THF, and the mixture was stirred under nitrogen at room temperature for 6 h. Then, 2 mL of H2O was added to decompose the excess NaH. The THF was evaporated in vacuo and 200 mL of CH2Cl2 was added to the residue. The organic layer was washed with 1 mol/L HCl(200 mL) and water, dried over MgSO4 and evaporated in vacuo to give the crude di-ionizable calix[4]arene. After purification, the product was dissolved in CH2Cl2, washed with 10% aqueous HCl and water and dried over MgSO4. The solution was evaporated in vacuo to give product 4, which was obtained in a yield of 68% after chromatography on silica gel with CH2Cl2-MeOH(80:1, volume ratio) as eluent. Yellow solid; m. p. 174―176 ºC; FTIR, ߥ෤max(film)/cm–1: 3232(NH), 1704 (C=O), 1358 and 1196(S=O); 1H NMR (CDCl3), δ: 0.96(brs, 18H), 1.24(brs, 18H), 2.10―4.02 (brm, 26H), 6.32―7.48(brm, 8H), 7.44(t, J=7.08 Hz, 4H), 8.26(d, J=7.38 Hz, 4H), 9.42(br s, 2H); 13C NMR(CDCl3), δC: 171.02, 171.24, 155.62, 153.24, 144.28, 138.82, 133.38, 132.66, 129.04, 128.48, 125.24, 73.20, 60.15, 34.40, 33.28, 33.00, 31.38, 31.10, 20.14. Elemental anal.(%) calcd. for C66H80N4O14S2: C 70.16, H 7.18, N 4.48; found: C 70.26, H 7.24, N 4.52.

2.3

Apparatus

The extractions and injections were performed by means of microsyringe(Agilent, CA, USA) bearing an angledcut needle tip(needle i. d.: 0.11 mm and glass barrel i. d.: 0.6 mm). Atomic absorption spectrometer of Shimadzu(model AA-670G) with deuterium lamp background correction and a graphite furnace atomizer(GFA-4B) was used. A reversed phase(RP) C18 column(diameter: 4.6 mm, length: 100 mm, macropore size: 2 μm, mesopore size: 13 nm) was obtained from Merck(Darmstadt, Germany). A RP-C18 guard column was fitted upstream of the analytical column. The mobile phase was optimized to be methanol-water(45:55, volume ratio) and was delivered by an HPLC pump(Waters LC-600). The UV detection wavelength was set at 254 nm and the flow rate of the mobile phase was adjusted to be 3 mL/min.

2.4

Sample Preparation

Pre-washed crude oil of 5.0 mL was placed into a 10-mL screw-cap glass centrifuge tube with conic bottom. Then 100.0 μL of distilled water(as dispersive solvent) containing 0.001 g of calix[4]arene(as extraction ligand) was rapidly transferred into the above-mentioned centrifuge tube and was gently

No.5

MOKHTARI Bahram et al.

811

shaked. The calixarene demulsifier caused the dispersed fine droplets of the extraction phase to sediment at the bottom of the conical test tube. The volume of the sedimented phase was determined with a 50.0 μL microsyringe, and it was completely transferred to another 100 μL centrifuge tube. After evaporation of the water under a gentle nitrogen flow, the residue was re-dissolved in 25 μL of LC-grade methanol and injected into HPLC for analysis.

3

Results and Discussion

The effects of all parameters(that can probably influence the performance of extraction) were investigated. They were the concentration of demulsifier or extraction ligand (calixarene), the volume of disperser(water), the extraction time and the salt addition that were investigated and optimized in order to achieve the higher enrichment factor and recovery of vanadyl porphyrins from the samples of live oil.

3.1

Effect of Calixarene Concentration

In order to evaluate the effect of calixarene concentration on the extraction efficiency and the separation of phases, the following experiments were performed using 0.50 mL of DDW containing different concentrations of calix[4]arene. Figs.3―5 depict the traces of recovery of vanadyl porphyrins, enrichment factor and volume of sedimented phase versus the calixarene

Fig.3

Effect of calixarene concentration on the recovery of vanadyl porphyrins Extraction conditions: oil sample volume, 5.00 mL; disperser solvent(water) volume, 0.50 mL; ambient temperature.

Fig.4

Effect of calixarene concentration on the enrichment factor of vanadyl porphyrins Extraction conditions are the same as those in Fig.3 and concentration of calixarene is 10 mg/L.

Fig.5

Effect of calixarene concentration on the volume of sedimented phase(N=3) Extraction conditions are the same as those in Fig.3.

concentration, respectively. As illustrated in Fig.3, the extraction recovery is almost increasing(from 62.0%―95.5%) owing to the quantity extraction and high distribution coefficient of vanadyl porphyrins under the conditions of high concentration. Obviously, in Fig.4, the enrichment factor decreases from 880 to 200. Thus, 10 μL of vanadyl porphyrins was selected in order to obtain high enrichment factor, and hence low detection limit and high recovery. According to Fig.5, with increasing the calixarene concentration from 10 mg/L to 26 mg/L, the volume of sedimented phase increases(6.0―20.5 μL).

3.2

Effect of Disperser Volume

As discussed above, water was selected as the best disperser solvent; hence, it was necessary to optimize the disperser volume. As a rule, the water disperser(at low volumes) can not disperse the extracting calixarenes properly. On the other hand, under such conditions, the cloudy solution is not formed completely. For obtaining an optimized volume of water, some experiments were conducted with different volumes of water(0.25, 0.5, 1.0, 1.5, 2.0 and 2.5 mL) containing 10.0, 12.5 16.0 and 24.0 μg/L vanadyl porphyrins, respectively. It is necessary to change the volume of vanadyl porphyrins by changing the volume of water in order to obtain a constant volume of sediment phase in all the experiments. Fig.6 illustrates the trace of vanadyl porphyrin’s recovery versus the volume of water. Based upon the results, a 0.50 mL of water was chosen as the optimum volume of disperser.

Fig.6

Effect of the volume of water disperser on the recovery of vanadyl porphyrins obtained from DLLME(N=3) Extraction conditions are the same as those in Fig.3.

812

3.3

CHEM. RES. CHINESE UNIVERSITIES

Effect of Extraction Time

The interval time between the injection of the water disperser(containing the extraction ligand) and starting to decant it was defined as the extraction time. The effect of extraction time on the performance of DLLME is a key factor, which is evaluated here. Different extraction time in a range of 0 to 90 min(with constant experimental conditions) was investigated. Based upon the results, the extraction regime is timeindependent since an infinitely large surface area is available between the aqueous phase(extraction solvent) and the oil medium. According to Fig.7, this method is very fast and this is a common advantage of DLLME.

Vol.28

by studying the applicability of this approach to determine the concentration of vanadyl porphyrins in the crude oil samples taken from one of the Iranian offshore fields. The samples were extracted via DLLME method and analyzed by means of HPLC-UV. The samples were spiked with vanadyl porphyrin standards at different concentration levels to investigate the matrix effects. A typical chromatogram representing the vanadyl porphyrins is depicted in Fig.9. The responses of different concentrations of vanadyl porphyrins for 3 replecates are presented in Table 2.

Fig.9

Fig.7

Effect of extraction time on the peak area of vanadyl porphyrins obtained from DLLME(N=3)

Chromatogram of decanted water with spiked sample at concentration level of 12.5 μg/L vanadyl porphyrins Table 2 Responses of different concentrations of vanadyl porphyrins(N=3)

Concentration of vanadyl porphyrins/(μg·L−1)

Run 1

Peak area count/a.u. Run 2

Run 3

0.1 0.2

259 288

285 287

264 295

Extraction conditions are the same as those in Fig.3.

3.4

Effect of Salt Addition

The influence of ionic strength on the performance of DLLME was studied by adding different amounts of NaCl(0―5%), while the other experimental conditions were kept constant. Fig.8 presents the effect of increasing the ionic strength on the volume of sedimented phase of vanadyl porphyrins. Obviously, with increasing the ionic strength(from 0 to 1%), the volume of sediment phase decreases and then increases rapidly(from 1% to 5 %).

Fig.8

Effect of salt addition on the volume of sedimented phase obtained from DLLME(N=3) Extraction conditions are the same as those in Fig.3.

3.5

Real Sample Analysis The matrix effects on the extraction were also evaluated

4

0.9

402

399

398

10.1

1348

1334

1336

15.4

1764

1770

1773

41.6

4329

4312

4314

57.5

5410

4398

5492

72.0

5893

5893

5901

Conclusions

This study introduced a new approach and a DLLME method combined with HPLC-UV for the separation, preconcentration and determination of vanadyl porphyrins in crude oil. This method deals with the dual role of calixarene scaffolds as the settling and complexing agent. Removing the centrifuging step and performing the inclusion microextraction of vanadyl porphyrins by means of ionizable calix[4]arene was the novelty of this project to enhance the preconcentration speed and extraction the vanadyl porphyrins The results of this study reveal that the proposed approach is acceptable for the preconcentration of vanadyl porphyrins from crude oil samples. The linear range, detection limit(S/N=3) and precision(RSD, n=6) were determined to be 0.2―50, 0.07 μg/L and 5.3%, respectively.

References [1] Pourabdollah K., Zarringhalam Moghaddam A., Kharrat R., Mokhtari B., Energy Fuels, 2010, 24, 4396 [2] Ali M. F., Perzanowski H., Bukhari A., Al-Haji A. A., Energy Fuels,

No.5

MOKHTARI Bahram et al. 1993, 7, 179

[3] Treibs A., Annales des Chemie, 1934, 509, 103

813

[16] Ramalho J. B., Ramos N., Lucas E., Chem. Chemical Technol., 2009, 3(1), 53

[4] Premovic P. I., Jovanovic L. S., Fuel, 1997, 76(3), 267

[17] Rondon M., Bouriat P., Lachaise J., Energy Fuels, 2006, 20, 1600

[5] Premovic P. I., Allard T., Nikolic N. D., Tonsa I. R., Pavlovic M. S.,

[18] Mokhtari B., Pourabdollah K., J. Coord. Chem., 2011, 64(17), 3081

Fuel, 2000, 79, 813 [6] Lepri F. G., Wel B., Borges D. L. G., Silva A. F., Vale M. G. R., Heitmann U., Anal. Chim. Acta, 2006, 558, 195 [7] Ion R. M., Dumitriu I., Fierascu R. C., Environ. Eng. Manage. J., 2010, 9(6), 827 [8] Holden P. N., Sundararaman P., Gaffey M. J., Geochimica et Cosmochimica Acta, 1991, 55, 3893 [9] Saitoh K., Tanji H., Zheng Y., Anal. Sci. Supplement, 2001, 17, 1511 [10] Rezaee M., Assadi Y., Millani M. R., Aghaee E., Ahmadi F., Berijani S., J. Chromatogr. A, 2006, 1116, 1 [11] Fu L., Liu X., Hu J., Zhao X., Wang H., Huang C., Wang X., Chromatographia, 2009, 70, 1697 [12] Farajzadeh M. A., Seyedi S. E., Safi Shalamzari M., Bamorowat M., J. Sep. Sci., 2009, 32, 3191 [13] Shirkhanloo H., Rouhollahia A., Zavvar Mousavi H., J. Chin. Chem. Soc., 2010, 57(5B), 1 [14] Hashemi P., Hosseini S. M., Kakanejadifard A., Azimi G. H., Zohrehvand S., J. Chin. Chem. Soc., 2010, 57(1), 111 [15] Rahnama Kozani R., Assadi Y., Shemirani F., Milani Hosseini M. R., Jamali M. R., Talanta, 2007, 72, 387

[19] Gu J., He W., Shi X., Ji L., Chem. Res. Chinese Universities, 2008, 24(1), 106 [20] Han J., Ge Y., Yan C., Chem. Res. Chinese Universities, 2006, 22(4), 537 [21] Yang F., Ji Y., Guo H., Lin J., Peng Q., Chem. Res. Chinese Universities, 2006, 22(6), 808 [22] Mokhtari B., Pourabdollah K., Dalali N., J. Incl. Phenom. Macrocycl. Chem., 2011, 69(1/2), 1 [23] Mokhtari B., Pourabdollah K., Dallali N., J. Radioanal. Nuclear Chem., 2011, 287(3), 921 [24] Mokhtari B., Pourabdollah K., Dalali N., Chromatographia, 2011, 73(9/10), 829 [25] Mokhtari B., Pourabdollah K., Asian J. Chem., 2011, 23(11), 4717 [26] Mokhtari B., Pourabdollah K., Dalali N., J. Coord. Chem., 2011, 64(5), 743 [27] Mokhtari B., Pourabdollah K., J. Coord. Chem., 2011, 64(18), 3189 [28] Mokhtari B., Pourabdollah K., J. Incl. Phenom. Macrocycl. Chem., 2012, 73(1/4), 1 [29] Mokhtari B., Pourabdollah K., J. Coord. Chem., 2011, 64(23), 4029 [30] Mokhtari B., Pourabdollah K., J. Coord. Chem., 2011, 64(23), 4079