A sensitive method for the determination of gold and palladium based on dispersive liquid-liquid microextraction combined with flame atomic absorption spectrometric determination using: N -(6-morpholin-4-ylpyridin-3-yl)- N ′-phenylthiourea

Article abstract of DOI:10.1039/c5ra26575d

A new method for the determination of gold and palladium was developed by dispersive liquid-liquid microextraction separation-preconcentration and flame atomic absorption spectrometry detection. In the proposed approach, N-(6-morpholin-4-ylpyridin-3-yl)-N′-phenylthiourea (MPPT) was synthesized as a complexing agent. The complexation ability of the MPPT was explored by examining the effect of a series of heavy metal ions, including Mn²⁺, Pd²⁺, Ni²⁺, Cd²⁺, Co²⁺, Cu²⁺, Au³⁺, Pb²⁺, Zn²⁺ and Fe³⁺, using the DLLME procedure. The MPPT exhibited pronounced selectivity toward Pd²⁺ and Au³⁺ ions at different pH levels. Factors influencing the extraction efficiency and complex formation were examined, i.e. the pH of the sample solution, the concentration of the chelating agent, the extraction and dispersive solvent type and volume, the sample volume, and foreign ions, etc. Optimal conditions for quantitative recoveries were pH 5.5 for gold and pH 1.5 for palladium, 125 μL of % 0.4 MPPT, 1200 μL of methanol and 125 μL of carbon tetrachloride. The presented method showed a good linearity within a range of 30-230 and 25-200 μg L^-1 with the detection limits of 1.75 and 1.65 μg L^-1 for Au and Pd, respectively. The relative standard deviation (RSD) was below 2.8% at 50 μg L^-1 for both ions (n = 10). The developed method was simple, fast, cost efficient, and sensitive for the extraction and preconcentration of gold and palladium in samples of liquids (sea, stream water) and solids (stream sediment, ores, and electronic waste).

Full text of DOI:10.1039/c5ra26575d

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A sensitive method for the determination of gold
and palladium based on dispersive liquid–liquid
microextraction combined with flame atomic
Cite this: RSC Adv., 2016, 6, 6896
absorption spectrometric determination using N-
0
(
6-morpholin-4-ylpyridin-3-yl)-N -phenylthiourea
a
b
a
c
Zekeriyya Bahadir, Volkan Numan Bulut, Hakan Bekta ¸s and Mustafa Soylak*
A new method for the determination of gold and palladium was developed by dispersive liquid–liquid
microextraction separation–preconcentration and flame atomic absorption spectrometry detection. In
0
the proposed approach, N-(6-morpholin-4-ylpyridin-3-yl)-N -phenylthiourea (MPPT) was synthesized as
a complexing agent. The complexation ability of the MPPT was explored by examining the effect of
2+
2+
2+
2+
2+
2+
3+
2+
2+
3+
a series of heavy metal ions, including Mn , Pd , Ni , Cd , Co , Cu , Au , Pb , Zn and Fe
,
2+
3+
using the DLLME procedure. The MPPT exhibited pronounced selectivity toward Pd and Au ions at
different pH levels. Factors influencing the extraction efficiency and complex formation were examined,
i.e. the pH of the sample solution, the concentration of the chelating agent, the extraction and dispersive
solvent type and volume, the sample volume, and foreign ions, etc. Optimal conditions for quantitative
recoveries were pH 5.5 for gold and pH 1.5 for palladium, 125 mL of % 0.4 MPPT, 1200 mL of methanol
and 125 mL of carbon tetrachloride. The presented method showed a good linearity within a range of
Received 12th December 2015
Accepted 5th January 2016
ꢀ
1
ꢀ
1
3
0–230 and 25–200 mg L with the detection limits of 1.75 and 1.65 mg L for Au and Pd, respectively.
ꢀ1
The relative standard deviation (RSD) was below 2.8% at 50 mg L for both ions (n ¼ 10). The developed
method was simple, fast, cost efficient, and sensitive for the extraction and preconcentration of gold and
palladium in samples of liquids (sea, stream water) and solids (stream sediment, ores, and electronic waste).
DOI: 10.1039/c5ra26575d
www.rsc.org/advances
determining trace amounts of Pd and Au ions, but are both
time-consuming and expensive. FAAS, an alternative, offers
1
. Introduction
Gold is an important element in our life due to its high ductility, covetable characteristics such as low cost in terms of opera-
10
corrosion resistance, and catalytic properties, and is widely tional facilities. However, the determination of trace metal
used in a variety of industries such as electronics, electro- ions in environmental samples is sometimes insufficient due to
1,2
plating, ne-chemicals, and jewellery. Although it is not their low concentrations and the effects of their matrices.
a toxic element, experiments regarding allergic eczematous Hence, pre-concentration and separation methods are oen
3
dermatitis have been published. Palladium is an element of required rst. For the separation and pre-concentration of Pd,
11
increasing importance nowadays because of its physical and several methods exist including coprecipitation, liquid–liquid
1
2,13
14,15
chemical properties. It is used in as an automotive catalyst as extraction (LLE),
solid-phase extraction (SPE),
cloud
4
16
well as in electronics and dentistry. Palladium is biologically point extraction (CPE) and hollow bre liquid phase micro-
17
inactive, however certain palladium compounds have been re- extraction (HFLPME). These techniques can oen be time-
ported as having potential cytotoxic effects on humans consuming and, the use of large organic solvents limit their
including liver and kidney damage, asthma, allergies, and applications. As a counter to this, there has been growing
various other health problems. Concentrations of palladium interest in the development of miniaturized preconcentration
0.01–0.02 mg L ) and gold (0.004 mg L ) in environmental methods known as microextraction, which include solid phase
and biological samples are reportedly very low. Sensitive microextraction (SPME)
analytical techniques like ICP-MS and GFAAS are necessary for (SDME). In this context, dispersive liquid–liquid micro-
extraction (DLLME) consists of a miniaturization of the LLE
5
ꢀ
1
ꢀ1
(
6,7
18,19
and single drop microextraction
8
9
20
based on the ternary component solvent systems whereby the
extraction (mL) and disperser (mL) solvents are rapidly injected
into the aqueous sample using a syringe. The formation of
a cloudy solution contains ne droplets of extraction solvent
a
Department of Chemistry, Giresun University, Giresun, Turkey
b
Macka Vocational School, Karadeniz Technical University, Macka, Trabzon, Turkey
c
Department of Chemistry, Faculty of Sciences, Erciyes University, Kayseri, Turkey.
E-mail: soylak@erciyes.edu.tr
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fully dispersed into the aqueous phase. Aer centrifugation, The Milestones Ethos D (Milestore Inc., Italy) with a closed
this causes the accumulation of the extraction phase at the vessel microwave system was standardized for the digestion of
21
bottom of the test tube. The DLLME method has gained the solid samples, and programmable for a pressure of 1450 psi
ꢁ
widespread attention due to its simplicity of operation, rapidity, and temperature of 300 C.
A pH meter, the Hanna
low cost consumption of organic solvents and reagents, and pH-211model digital glass electrode, was used for measuring
high recovery and enrichment factors. It has proven to be pH values of the aqueous phase. A Sigma 3-16P model centri-
a suitable preconcentration procedure for palladium and gold fuge (Sigma laborzentrifugen GmbH, Germany) was employed
22–24
ions.
to centrifuge the solutions. Ultra-pure water, produced by the
In this study, we synthesized a new N-(6-morpholin-4-ylpyr- Merck – Millipore Direct-Q 8UV system (Darmstadt, Germany),
0
idin-3-yl)-N -phenylthiourea ligand and used it in dispersive was used throughout.
liquid–liquid microextraction for the preconcentration of Au
and Pd ions in environmental samples, at trace levels, using
ame atomic absorption spectrometry. The DLLME technique
used an appropriate mixture of carbon tetrachloride (extraction
2
.2. Reagents

ꢀ
1
The stock standard solution (1000 mg L ) of Au and Pd was
obtained using the Merck (Darmstadt, Germany). Working
standard solutions were obtained by appropriate dilution of the
stock standard solution. The chelating agent, N-(6-morpholin-4
solvent), methanol–ethanol (dispersive solvent), and MPPT
(chelating agent) for determining gold and palladium ions from
solid and aqueous samples. The complex stability constants
0
ylpyridin-3-yl)-N -phenylthiourea (MPPT) was synthesized and
3
+
2+
and complex compositions of Au and Pd cations with the
new ligand were examined using spectrophotometric titrations.
puried in our laboratories. A 0.4% (w/v) solution of the
chelating agent was prepared by dissolving the proper amount
of the agent in methanol/dimethylsulfoxide (4 : 1). Phosphoric
acid/sodium dihydrogen phosphate (0.1 mol L ) was used to
adjust the pH 1–3. Ammonium acetate buffers (0.1 mol L
ꢀ1
2. Experimental
ꢀ
1
)
2.1. Apparatus
were prepared by adding an appropriate amount of acetic acid
A Perkin-Elmer A Analyst 400 ame atomic absorption spec-
trometer (Waltham, United States) in an air/acetylene ame
with a 10 cm-long burner head ame atomic absorption spec-
trophotometer was used. The gold and palladium hollow
cathode lamps, operated at 12 mA and 6 mA, were utilized as the
radiation source. Measurements were carried out in the peak
height mode at 242.80 and 244.79 nm, respectively. A deuterium
lamp was used for background correction. The absorption
spectra of the compound were recorded using a Specord 210
Plus model spectrophotometer (Jena, Germany). The IR spectra
were recorded as potassium bromide pellets using a Perkin-
to ammonium acetate solutions resulting in solutions of pH
ꢀ1
4–6. For pH 7, a phosphate (0.1 mol L ) buffer solution was
prepared by adding an appropriate amount of disodium
hydrogen phosphate to sodium dihydrogen phosphate.
ꢀ1
Ammonium chloride buffer solutions (0.1 mol L ) were used
for pH 8–10. 2-Chloro-5-nitropyridine (97%, Sigma-Aldrich),
morpholine (99%, Sigma-Aldrich), hydrazine hydrate (100%,
Darmstadt, Merck), palladium on carbon (10% Pd, Sigma-
Aldrich), and phenylisothiocyanate (98% Acros-Organics, New
Jersey, USA) were used for the synthesis of N-(6-morpholin-4-
0
ylpyridin-3-yl)-N -phenylthiourea. The remaining used chem-
1
13
Elmer 1600 series FTIR spectrometer (USA). H NMR and
NMR spectra were registered in CDCl on a BRUKER AVENE III
00 MHz NMR (USA). The mass spectra of the reagent were
C
icals, including dimethylsulfoxide (analytical), carbon tetra-
3
chloride
(analytical),
chloroform
(analytical
grade),
4
dichloromethane (analytical grade), carbon disulde (for spec-
troscopy), methanol (for spectroscopy), ethanol (for spectros-
copy), acetone (suprasolv), acetonitrile (HPLC grade), and tetra
hydro furan (suprasolv) were provided by Merck (Darmstadt,
Germany). All other reagents used were of the highest available
purity and of at least analytical reagent grade. The sandy soil
obtained on an Agilent LC/MS-TOF instrument (USA). The
melting points of the synthesized compounds were determined
in open capillaries on a B u¨ chi B-540 melting point apparatus.
(CRM-SA-C) certied reference material used in the DLLME
studies was acquired from High-Purity Standard Inc., USA.
0
2
.3. Synthesis of N-(6-morpholin-4-ylpyridin-3-yl)-N -
phenylthiourea (MPPT)
2-Chloro-5-nitropyridin (1.410 g, 0.010 mol) was dissolved in
morpholine 1 (0.020 L) and the reaction mixture was stirred and
heated under reux for 8 hours. Aerwards, the reaction
mixture was cooled down to room temperature and the product
was precipitated. The crude solid product was crystallized from
ethanol and obtained a pure compound 2 (yield: 1.920 g, 92%).
Then, a mixture of compound 2 (1.920 g, 0.091 mol), palladium-
carbon catalyst (0.590 g, 0.005 mmol) and hydrazine hydrate
(2.50 mL, 0.050 mmol) in butanol (0.050 L) was heated under
Fig. 1 The synthesis scheme of the MPPT.
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reux for 6 hours, then cooled down to room temperature and added to the residues. The suspensions were ltered through
the catalyzer ltered off. The solvent was evaporated and the a blue band lter paper (Macherey-Nagel, Duren, Germany). The
crude product was crystallized from ethanol and obtained pure nal solutions were completed to 25 mL (stock solutions) for
compound 3 (yield: 1.320 g, 74%). Finally, a solution of each solid sample using ultrapure water (UP water). The stock
compound 3 (1.320 g, 7.3 mmol) and phenylisothiocyanate solution was diluted at 12.5-fold for the ore-1, 16.6-fold for the
(0.36 mL, 0.003 mol) in 50 mL of butanol was heated under ore-2, 25-fold for the ore-3, 6.6-fold for the sediment and 16.6-
reux for 7 hours. At the end of the reaction, the crude product fold for the electronic waste samples before the analysis
collapsed. The precipitate found was ltered and crystallized because of a high iron and copper ion concentration. The
from ethanol. This compound was characterized by means of diluted samples were analysed using the same general proce-
1
13
IR, H NMR, C NMR and TOF-LC/MS spectroscopies. The dure described in Section 2.4. The determination of Pd(II) and
synthetic pathways to the MPPT are presented in Fig. 1. Au(III) ions in the nal measurement solution (0.5 mL) was
IR (KBr pellet, n cm ): 3212 (NH), 3171 (NH), 3034 (Ar-CH), performed by FAAS.
ꢀ
1
1
1
3
537 (C]N), 1234 (C]S), 1109 (C–O). H NMR (CDCl
.55 (t, 4H, N–2CH
, J ¼ 10.0 Hz), 3.83 (t, 4H, O–2CH
3
, d ppm):
Sea and stream water samples were collected in polytetra-
2
2
, J ¼ 9.6 uoroethylene containers from Trabzon, Turkey. Water samples
Hz), 6.68 (d, 1H, Ar-H, J ¼ 8.8 Hz), 7.28 (s, 1H, CH), 7.39–7.47 (m, were collected in acid leached polyethylene bottles, and acidi-
ꢀ
1
4
(
H, Ar-H), 7.67 (d, 2H, 2CH, J ¼ 8.0 Hz), 7.84 (brs, 1H, NH), 8.11 ed to a pH level with 0.1 mol L HNO
3
in order to prevent the
, d ppm): 181.19 (C]S), adsorption of metal ions on the walls of the ask. The water
ArC: [158.11 (C), 145.59 (CH), 136.93 (C), 136.52 (2CH), 129.72 samples were ltered through a 0.45 mm cellulose nitrate
1
3
d, 1H, NH, J ¼ 2.4 Hz). C NMR (CDCl
3
(
(
CH), 127.23 (CH), 125.34 (2CH), 125.25 (C), 106.61 (CH)], 66.63 before analyses.
O–2CH ), 45.51 (N–2CH ). TOF-LC/MS (ESI): m/z (%) 315.12
2
+
2
+
[M + H] , (100), 337.11 [M + Na] .
2.6. Preparation of standard reference material
In order to conrm the validity of the developed procedure, the
method has been applied to the determination of the content of
2.4. Recommended procedure
The aliquots of 10.0 mL sample solution containing 0.5 mg of Au gold and palladium in the Certied Reference Material (CRM-
pH 5.5) were placed in a 10 mL screw cap glass test tube with SA-C sandy soil C). An accurately measured sample (0.4 g) of
a conic bottom. The amount of 1200 mL of methanol (disperser reference matter was dissolved in a microwave digestion system
solvent), 125 mL % 0.4 MPPT (chelating agent) and 125 mL of mixture of HNO (3.5 mL), HCl (3.5 mL) and HF (1.0 mL). The
(
3
carbon tetrachloride (extraction solvent) was injected rapidly solution was evaporated to near dryness and ltrated by adding
into the sample solution. A cloudy solution (water, ethanol, UP-water. The residue was completed to 25 mL (stock solution)
carbon tetrachloride) was formed in the test tube. In this step, volumetric ask with UP-water. An aliquot of 1.25 mL (for Au)
Au reacted with MPPT and was extracted into the ne droplets and 8.0 mL (for Pd) of this solution was diluted to a nal volume
of carbon tetrachloride. Then, aer 5 minutes of standing time, of 10 mL, followed by applying the preconcentration procedure.
the solution was centrifuged at 3000 rpm for 3 min, and the
dispersed ne droplets of carbon tetrachloride were deposited
3
. Results and discussion
into the bottom of conical test tube. The residue phase was
ꢀ1
diluted to 0.5 mL with 0.1 mol L HNO
3
containing methanol The selective sensing of heavy metal ions is a very important
(as dilute solvent) and injected into the FAAS for Au analysis. topic in various chemical systems. We know that organic
1
0 mL of the solution containing 0.5 mg Pd (pH ¼ 1.5) was compounds, having sulphur and nitrogen donor atoms have the
25
2+
transferred into a 15 mL PTFE conical-bottomed tube, and then capacity to undergo complexation with so metal cations. Pd
a mixture of 1200 mL ethanol, 125 mL % 0.4 MPPT and 125 mL and Au ions are especially known as so metal cations and
3
+
carbon tetrachloride was added quickly to the solution. prefer nitrogen and sulfur donor atoms in complexation with
26
Following that, all the necessary procedures as described above ligands. Herein, we report the newly synthesized N-(6-mor-
0
were applied.
pholin-4-ylpyridin-3-yl)-N -phenylthiourea ligand for the deter-
3
+
2+
mination of Au and Pd ions combined using DLLME.
Furthermore, in order to obtain high extraction efficiency,
different parameters like the volume and nature of both the
disperser and extraction solvents, as well as the pH of the
aqueous solution, the concentration of chelating agent, and the
volume of the sample were optimized.
2
.5. Sample preparation
Microwave digestion was chosen for the decomposing of all
solid samples. Solid samples of 0.4 g ore-1 (Akoluk, Ordu,
Turkey), 0.4 g ore-2 (Bolkarda ˘g , Ni ˘g de, Turkey), 0.4 g ore-3
(
T u¨ prak, U ¸s ak, Turkey) and 0.4 g sediment (Maçka stream,
Trabzon, Turkey) were accurately weighed and dissolved into
a mixture of HNO , HCl, HF and H (3.5 : 3.5 : 1 : 1 volume
3.1. Characterization of the complexes
3
2 2
O
ratio) into a polytetrauoroethylene vessel. Electronic waste The absorption spectrum of the MPPT in methanol has not
samples (0.15 g) were weighed and transferred into Teon displayed absorption signals at 370–440 nm. Fig. 2 and 3 shows
3
+
2+
vessels, 3.5 mL concentrated of HNO and 3.5 mL of HCl were the effect of Au and Pd cations on the absorption spectra of
3
3
+
2+
added for the digestion. Aer the digestion procedure, all the the ligand. The presence of 10 equivalents of Au and Pd ions
solutions were evaporated to near dryness. Puried water was cations caused a decrease in the absorption of the ligand aer
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3+
Fig. 4 Effect of pH of the sample solution on the Au (0.5 mg) and
2
+
Pd (0.5 mg) signals; sample volume 10 mL, amount and type of
extraction solvent: 150 mL of CCl , amount and type of disperser
3
+
Fig. 2 Variation of absorbance of MPPT with concentration of Au
,
ꢀ
5
4
added as 0–1 equivalent of HAuCI
mol L , measurements were carried out at 380 nm.
4
, MPPT concentration: 6 ꢂ 10
solvent: 1000 mL of methanol for Au, 1000 mL of ethanol for Pd,
ꢀ1
amount of MPPT: 125 mL (0.5 mg, 0.4%), centrifugation time and rate:
3
min and 3000 rpm, standing time 5 min, N ¼ 3.
3
70 nm. The stoichiometry of the developed complexes, i.e.
3
+
2+
3.2. Effect of pH
Au –MPPT and Pd –MPPT in methanol–water solutions, were
determined by the mole ratio method. The general complex The performance of DLLME process is also tied with the
formation equilibrium is assumed by the following eqn (1):
formation of the hydrophobic complex and stability of the
complex. The pH of the solution system plays an important role
in this step. In order to evaluate the effect of the pH on the
n+
M
aq + nMPPTorg 4 [M(MPPT)
n
]
org
(1)
28
extraction efficiency, the pH of 10 mL sample solutions con-
taining 0.5 mg gold and palladium ions was adjusted to t into
the range of 1–10. As can be seen in Fig. 4, the red and blue lines
have crossed at pH 3–4, but the recoveries were not quantitative
for either ion. The maximum recoveries for both ions were ob-
tained in the pH range of 5–6 and 1–2 for Au and Pd,
respectively.
3
+
Fig. 2A and 3A (inset) shows the molar-ratio plot for Au and
Pd , A
2
+
o
and A are the absorbance of free ligand and the
absorbance of the solution involving metal cation, respectively.
The inection point was 0.5 ([Au ]/[L]) and ([Pd ]/[L]). It can
thus be concluded that ligand formed a stable 1 : 2 (M : L)
complex with Au and Pd . In order to determine the complex
stability constant according to valuer's method, the ratio
A /(A A) was plotted versus 1/[M], which yielded a straight line
3
+
2+
3
+
2+
27
3.3. Effect of amount of the MPPT
o
o
(
Fig. 2B and 3B). A and A are the absorbance of the free ligand The amount of complexing agent is a signicant parameter that
and the absorbance of the solution containing the Au and has been found to affect the extraction performance in the
o
3
+
2
+
0
Pd . The stability constant was calculated from the ratio preconcentration methods. N-(6-Morpholin-4-ylpyridin-3-yl)-N -
3
+
intercept/slope. The result is the stable complex of an Au
complex with a log K value of 6.998, and a Pd complex with the MPPT amount on DLLME were studied in the range of 0–
a log K value of 7.045. All absorbance results were examined at 175 mL of MPPT (0.4%, w/v). The results were showed in Fig. 5.
phenylthiourea (MPPT) was used for this purpose. The effects of
2
+
380 nm.
The recovery values for Au(III) and Pd(II) at the DLLME procedure
3
+
Fig. 5 The effect of the amount of MPPT on the extraction of Au
(
2+
0.5 mg) and Pd (0.5 mg); sample volume 10 mL, amount and type of
extraction solvent: 150 mL of CCl , amount and type of disperser
4
2
+
Fig. 3 Variation of absorbance of MPPT with concentration of Pd
,
solvent: 1000 mL of methanol for Au, 1000 mL of ethanol for Pd,
centrifugation time and rate: 3 min and 3000 rpm, standing time 5 min,
N ¼ 3.
ꢀ
5
added as 0–1 equivalent of Pd(NO
mol L , measurements were carried out at 380 nm.
3
)
2
, MPPT concentration: 6 ꢂ 10
ꢀ1
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ꢀ1
Table 1 Tolerant limits of coexisting ions for the extraction 50 mg L
of palladium and gold ions, N ¼ 3
3
+
2+
Concentration Au
(mg L )
,
Pd
,
ꢀ
1
Ion
Added as
recovery (%) recovery (%)
+
Na
K
Ca
NaCl
KCl
15 000
5000
500
100 ꢃ 2
97 ꢃ 3
97 ꢃ 3
97 ꢃ 1
96 ꢃ 2
99 ꢃ 3
96 ꢃ 1
97 ꢃ 3
97 ꢃ 2
101 ꢃ 2
105 ꢃ 2
101 ꢃ 3
98 ꢃ 3
94 ꢃ 2
94 ꢃ 2
102 ꢃ 3
95 ꢃ 23
99 ꢃ 2
97 ꢃ 2
97 ꢃ 3
97 ꢃ 1
96 ꢃ 2
99 ꢃ 2
96 ꢃ 1
97 ꢃ 3
97 ꢃ 2
93 ꢃ 2
95 ꢃ 3
95 ꢃ 2
—
+
2+
CaCl
Mg(NO
BaCl
Mn(NO
Zn(NO
2
2
+
Mg
3
)
2
500
2
ꢀ
Fig. 6 (a) Effect of type of disperser solvent (b) effect of volume of Ba
2
50
40 –25
20–25
3
+
2+
a
c
methanol for Au and ethanol for Pd; sample volume 10 mL (0.5 mg Au
Mn
3
)
2
2+
2+
c
and 0.5 mg Pd ), amount of MPPT: 125 mL (0.5 mg), 150 mL of CCl
4
, N ¼ 3. Zn
3
)
2
3+
Al
Al(NO
Pb(NO
3
)
3
25
2+
Pb
Cu
3
)
2
20
80 –100
2
+
a
c
Cu(NO
Fe(NO
Ni(NO3)2
Y$2H
Cr(NO
Na SO
NaF
Na PO
3
)
2
without MPPT were below 5%. It was found that the recovery of
3+
2+
b
c
Fe
Pd and Au increased with the increasing of the MPPT Ni
3
)
3
100 –100
2
+
3+
a
c
30 –25
amount, and then it remained constant at 100 mL of the 0.4% EDTA Na
2
H
2
2
O
1500 c
3+
Cr
3
)
3
20–25
96 ꢃ 2
96 ꢃ 2
—
94 ꢃ 2
ligand. Therefore, 125 mL of MPTT (0.5 mg) amount was chosen
2
ꢀ
c
SO
4
2
4
750–1000
3000
400
for further experiments.
ꢀ
F
3
ꢀ
PO
4
3
4
a
b
c
Masked with 15 mg EDTA. Masked with 20 mg NaF. Ions
concentration for Pd.
3.4. The effect of type and volume of the disperser solvent
The most important point for the selection of a suitable
disperser solvent is its mutual miscibility in both extraction
solvent and aqueous sample. For this purpose, different
solvents such as methanol, ethanol, acetone, acetonitrile and
tetra hydro furan were tested. Thus, under the same experi-
mental conditions, a series of sample solutions were prepared
by using 1200 mL of each disperser solvent containing 125 mL of
carbon tetrachloride. The recommended procedure was then
followed. Among the four candidate solvents, methanol and
ethanol were selected as disperser solvents for Au and Pd,
respectively (see Fig. 6a).
The effect of the volume of methanol on the extraction effi-
ciency of Au and Pd ions was examined. To obtain the optimized
volume of methanol, various experiments were performed using
different volumes of methanol (200–3000 mL) containing 150 mL
CCl4 for Au. It was found that (Fig. 6b), at a low volume of
methanol, the cloudy solution was not formed completely
while, at high methanol volume, the solubility of carbon tetra-
chloride in the aqueous solution was increased. A volume of
methanol of 1200 mL was nally chosen. The same results were
obtained using the volume of ethanol (200–3000 mL). The
optimum ethanol volume of 1200 mL was selected for Pd.
3.5. The effect of type and volume of the extraction solvent
The type of extraction solvent used in DLLME is an essential
consideration for efficient extraction. It should have low solu-
bility in water, high affinity to analytes, and a higher density
than water. Chloroform (CHCl ), carbon disulde (CS ), car-
3
2
bontetrachloride (CCl
4
2 2
) and dichloromethane (CH Cl ) were
studied as extraction solvent using 1200 mL of ethanol, and
methanol as the dispersive solvent. The results revealed that
carbon tetrachloride has the highest extraction efficiency
Table 2 Analytical figures of the DLLME-FAAS method for determi-
nation of gold and palladium
Ion
Characteristics
Figures of merit
3
+
ꢀ1
Au
Linear range with DLLME (mg L
)
30–230
0.4–10
19.3
20
1.75
5.76
2.77
10
25–200
0.3–10
19.5
20
1.65
5.43
2.52
10
ꢀ
1
Linear range without DLLME (mg mL
Experimental enrichment factor
Theoretical enrichment factor
)
ꢀ
1
Limit of detection (LOD, mg L ), 3Sb/m
ꢀ
1
Limit of quantication (LOD, mg L
Precision (RSD, %), 50 mg L , n: 10
)
ꢀ
1
Sample volume (mL)
2+
ꢀ1
Pd
Linear range with DLLME (mg L
)
ꢀ1
Linear range without DLLME (mg mL
Experimental enrichment factor
Theoretical enrichment factor
)
ꢀ
1
Limit of detection (LOD, mg L ), 3Sb/m
ꢀ
1
Fig. 7 (a) Influence of type of extraction solvent on DLLME (b) influ-
Limit of quantication (LOD, mg L )
Precision (RSD, %), 50 mg L , n: 10
ꢀ
1
ence of volume of CCl
4
on the extraction of Au and Pd; sample volume
3+
2+
1
0 mL, pH ¼ 5.5 for Au , pH ¼ 1.5 for Pd , amount of MPPT: 125 mL
.5 mg, N ¼ 3.
Sample volume (mL)
0
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Table 3 The analysis results of CRM-sandy soil C certified reference mass transfer process and generally offers a fast extraction
material (N: 3)
procedure. Therefore, this method is independent from time,
29,30
one of its most important advantages.
was investigated by varying the stirring rate in the range of 1000,
000 rpm. The recoveries were slightly enhanced up to 3000 rpm
The extraction recovery
Certied value
Found
(mg g )
Recovery
(%)
ꢀ1
ꢀ1
Ion
(mg g
)
4
a,b
Au
Pd
25
4
23.1 ꢃ 1.5
3.8 ꢃ 0.2
92.4
95.0
and remained at a 4000 rate. Finally, a stirring rate of 3000 rpm
was chosen. In the next step, the extraction recovery was studied
a,b,c
a
b
Non certied values, provided for information only. Diluted 3.3 fold at time intervals of between 1 and 15 min using a stirring rate of
c
and added 10 mg NaF because of high iron content. Diluted 1.25 fold.
3000 rpm. The results showed that the agitation time had no
signicant impact of the extraction recovery and, therefore,
a practical time of 3 min was selected for further studies.
(97.0%) in comparison with carbon disulde (31.8%),
dichloromethane (19.2%), and chloroform (40.2%) in Fig. 7a.
3
.7. Effect of sample volume
Thus, CCl was selected for further experiments.
4
To get high preconcentration factor, sample volume is a key
factor.
dure was further considered by studying the effect of an
aqueous volume on the recovery of 0.5 mg of gold and 0.5 mg of
palladium from different sample volumes of between 5 mL to
A suitable volume of extraction solvent is crucial in this
method. The effect of carbon tetrachloride volumes on the
extraction performance was studied in the range of 50–300 mL.
According to Fig. 7b, the recovery of Au and Pd ions increased
signicantly by increasing the volume of carbon tetrachloride. It
was found that the best quantitative recovery was >97% for Au and
31–34
The preconcentration capability of DLLME proce-
30 mL. The results showed that the extraction was quantitative
with the aqueous phase volume up to 10 mL. Based on the nal
extract volume (0.5 mL) and the maximum sample volume, the
extraction was quantitative (10 mL) and therefore a theoretical
preconcentration factor of 20 was determined for both ions.
>
4
95% for Pd when using 125 mL CCI . As result, in order to obtain
a higher extraction recovery value, 125 mL of the extraction solvent
was used as the optimal volume in subsequent experiments.
3.6. Effect of the centrifugation rate and time, standing time
3.8. Interference studies
35–38
Due to the formation of the microdroplets in DLLME, the large Matrix effects
are a big problem in the instrumental deter-
surface of the contact between both phases leads to a very fast mination of gold and palladium at trace levels. The efficiency of
3+
2+
Table 4 Addition and recovery tests for the microextraction of Au and Pd in water and solid samples (N: 5)
Au
Pd
Sample
Added (mg)
Found (mg)
Recovery (%)
Found (mg)
Recovery (%)
Stream water-1
0
<LOD
—
<LOD
—
0
1
0
0
1
0
0
1
0
0
1
0
0
1
0
0
1
0
0
1
0
0
1
.5
.0
0.48 ꢃ 0.02
0.97 ꢃ 0.02
<LOD
0.48 ꢃ 0.01
0.97 ꢃ 0.03
<LOD
96 ꢃ 4
97 ꢃ 2
—
96 ꢃ 2
97 ꢃ 3
—
98 ꢃ 2
98 ꢃ 2
—
96 ꢃ 2
95 ꢃ 2
—
0.48 ꢃ 0.01
0.98 ꢃ 0.02
<LOD
0.48 ꢃ 0.01
0.97 ꢃ 0.02
<LOD
0.48 ꢃ 0.01
0.96 ꢃ 0.02
<LOD
0.48 ꢃ 0.02
0.98 ꢃ 0.00
<LOD
0.49 ꢃ 0.01
0.98 ꢃ 0.03
<LOD
0.48 ꢃ 0.01
0.95 ꢃ 0.02
0.39 ꢃ 0.01
0.87 ꢃ 0.02
1.35 ꢃ 0.03
<LOD
96 ꢃ 2
98 ꢃ 2
—
96 ꢃ 2
98 ꢃ 2
—
96 ꢃ 4
98 ꢃ 2
—
96 ꢃ 4
98 ꢃ 0
—
Stream water-2
Sea water
.5
.0
.5
.0
0.49 ꢃ 0.01
0.98 ꢃ 0.02
0.30 ꢃ 0.01
0.78 ꢃ 0.02
1.25 ꢃ 0.04
0.12 ꢃ 0.01
0.60 ꢃ 0.02
1.10 ꢃ 0.04
0.49 ꢃ 0.03
0.96 ꢃ 0.02
1.46 ꢃ 0.02
0.40 ꢃ 0.02
0.87 ꢃ 0.04
1.37 ꢃ 0.05
<LOD
a
Ore-1
.5
.0
b
Ore-2
.5
.0
96 ꢃ 4
98 ꢃ 4
—
98 ꢃ 2
98 ꢃ 3
—
c
Ore-3
.5
.0
94 ꢃ 3
96 ꢃ 2
97 ꢃ 3
95 ꢃ 2
d
Electronic waste
.5
.0
94 ꢃ 2
97 ꢃ 2
—
96 ꢃ 4
96 ꢃ 3
—
e
Sediment
.5
.0
0.47 ꢃ 0.02
94 ꢃ 4
0.48 ꢃ 0.02
96 ꢃ 4
0.96 ꢃ 0.02
96 ꢃ 2
0.98 ꢃ 0.02
98 ꢃ 2
a
b
c
1
2.5 fold diluted for Au, 6.6 fold diluted for Pd. 10 mg EDTA, 10 mg NaF added and 16.6 fold diluted for Au, only 6.6 fold diluted for Pd. 10 mg
EDTA, 10 mg NaF added and 25 fold diluted for Au, only 6.6 fold diluted for Pd. 10 mg EDTA added and 20 fold diluted for Au, only 16.6 fold
diluted for Pd. 10 mg EDTA added and 20 fold diluted, only 6.6 fold diluted for Pd.
d
e
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41
Table 5 The application of the presented method for the analysis of extraction for both ions. The calibration graph was prepared
gold(III) and palladium(II) in water and solid samples, N: 3
against the aqueous standards by submitting to the same
DLLME procedure. Blank determinations were carried out as
Concentration,
mg g , Au
Concentration,
mg g , Pd
ꢀ1
ꢀ1
parallel to the measurements made for the calibration stan-
dards and sample solutions. The blank signals were 0.0024A
and 0.0020A for gold and palladium in FAAS. Limits of detection
Sample
Stream water-1
Stream water-1
Sea water
Ore-1
Ore-2
Ore-3
<LOD
<LOD
<LOD
23.1 ꢃ 1.1
12.8 ꢃ 0.8
76.3 ꢃ 4.2
132.2 ꢃ 5.2
<LOD
<LOD
<LOD
<LOD
<LOD
<LOD
<LOD
(LODs) were calculated based on 3Sb/m (Sb is the standard
deviation of ten replicate blank measurements and m is the
slope of the calibration graph) and found as 1.75 for Au and 1.65
ꢀ
1
mg L for Pd. The relative standard deviation (RSD) for the ten
replicate measurements of 10 mL of standard solutions,
including 0.5 mg Au(III) and Pd(II) ions was found to be 2.77 and
Electronic waste
Sediment
108.6 ꢃ 4.1
<LOD
2.52%, respectively (Table 2).
the development method in preconcentration of gold and
palladium in the presence of various cations and anions was
examined. A 10 mL model solution, which included 0.5 mg of
Au(III) and Pd(II) as well as different amounts of other ions was
prepared and the proposed extraction method was applied to
the solution. The obtained results are shown in Table 1. As the
results show, several species did not interfere even at high
concentrations. This is applicable to the analysis of different
samples. No interferences were observed from most of the ions
3
.10. Applications of the method
The Certied Reference Material (CRM-SA-C sandy soil C) was
analyzed to validate the accuracy of the proposed method. The
analytical results are shown in Table 3. The experimental results
ꢀ
1
were in agreement with the values of the CRM 25 mg g for
3
+
ꢀ1
2+
Au , 4 mg g for Pd (the values are not certied. They are
provided for information purposes only). The presented
microextraction method was applied to the determination of
palladium and gold in seawater, stream water, ore, sediment,
and electronic waste samples. Recovery studies were developed
for samples spiked at known concentration levels of Pd and Au.
The results are shown in Table 4. The analytical results
demonstrated that the suggested method was applied to the
analysis of aqueous and solid samples (Table 5).
3
+
2+
2+
2+
tested except for Fe , Cu , Ni and Mn ions. In order to
eliminate the interference effects of these ions, EDTA, NaF were
39,40
used as the masking agent.
3.9. Analytical gures of merit
Under optimum conditions, the calibration equation observed
3
.11. Comparison with other preconcentration techniques
by the DLLME procedure were found A ¼ 0.6438C(Au) + 0.0020
2
(
R ¼ 0.997) for Au(III) and A ¼ 0.7415C(Pd) + 0.0035 for Pd(II). The presented DLLME method with other sample preparation
Where A is absorbance for Au and Pd ions in the enriched techniques, in combination with FAAS for the extraction and
phase, C(Au) and C are gold and palladium have concentra- determination of gold and palladium, was compared in Table 6.
(Pd)
ꢀ1
tions of mg L in the sample solution. The linear calibration As can be seen from Table 6, they are mostly one-element
equation without preconcentration was A ¼ 0.0334C(Au) + 0.0030 methods, with the exception of our presented method. The
2
(
R ¼ 0.997) for Au and A ¼ 0.0380C(Pd) + 0.0026 for Pd. The DLLME-FAAS has a comparatively low detection limit (1.65
ꢀ
1
ꢀ1
theoretical enrichment factor was calculated by the ratio of mg L for Pd and 1.75 mg L for Au) except ref. 36 and 40. The
volumes of the sample (10.0 mL) and the nal solutions lower detection limit was reported with some references that
(0.5 mL). The experimental enrichment factor was calculated could be the result of the determination system. We have good
based on the slopes of the calibration curves with or without the linear dynamic ranges and a good enrichment factor for both
a
Table 6 Comparison of proposed DLLME with published preconcentration methods
Analytical technique/
detection method
ꢀ1
ꢀ1
Ion
EF
45.7
138
166.5
10
23.7
48.7
40
LOD, mg L
LDR, mg L
RSD, %
Ref.
2
+
+
+
Pd
DLLME/FAAS
DLLME/FAAS
DLLME/GFAAS
IL-LME/FAAS
IL-DLLME/FAAS
DLLME/GFAAS
IP-DLLME/FAAS
DLLME/FAAS
DLLME/FAAS
90
19
100–2000
40–800
0.05–1.0
190–3820
0.9–400
0.02–40
8–100
0.7
3.2
3.5
—
42
43
44
45
46
47
48
2
Pd
2
Pd
0.02
72
0.13
0.0048
1.8
3
3
3
3
+
+
+
+
+
Au
Au
Au
Au
—
4.1
3.2
2.52
2.77
2
Pd
Au
20
20
1.65
1.75
30–230
25–200
This work
This work
3
+
a
LDR: linear dynamic range, LOD: limit of detection, IP-DLLME: ion-pair dispersive liquid–liquid microextraction, UIL-DLLME: ionic liquid-based
dispersive liquid–liquid microextraction.
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ions. The previously reported methods only were used in water 11 N. Ozturk, V. N. Bulut, C. Duran and M. Soylak, Desalination,
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several environmental liquid and solid samples. All these 2001, 54, 37–43.
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1
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. Conclusion
0
In this procedure, the N-(6-morpholin-4-ylpyridin-3-yl)-N -
phenylthiourea (MPPT) reagent was successfully used as
a complexing agent for the preconcentration of gold(III) and
palladium(II) ions. The DAT reagent was synthesized rst in our
laboratory. Complexation behavior of MPPT towards the
selected series of metal ions worked using the A novel dispersive
liquid–liquid microextraction procedure. Experimental obser-
1
1
2003, 60, 839–844.
1
9 M. Ghaedi, M. Ghayedi, S. N. Kokhdan, R. Sahraei and
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2
2
+
vations revealed that it is efficient and selective for Pd and
3
+
21 M. Rezaee, Y. Assadi, M. R. M. Hosseini, E. Aghaee,
Au ions in aqueous solutions. It has fast kinetic properties and
is also stable in solutions for long periods of time. The DLLME
approach associated with FAAS detection can be proposed as an
extraction technique tool for the determination of trace
elements with a short extraction time, good precision, minimal
organic solvent use, and environmentally friendliness factor.
This is a novel method suitable for the simple and accurate
determination of gold and palladium in a variety of water and
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