American Journal of Anal yt ical Chemistry, 2011, 2, 243-249
doi:10.4236/ajac.2011.22029 Published Online May 2011 (
Copyright © 2011 SciRes. AJAC
Ultrasound-Assisted Emulsification Dispersive
Liquid-Liquid Microextraction Based on Solidification of
Floating Organic Droplet for Separation of Trace Gold
Prior to Flame Atomic Absorption Spectroscopy
Sayed Zia Mohammadi1,2, Mohammad Ali Karimi1,3, Ali Shiebani4, Laleh Karimzadeh2
1Payame Noor University, Te hran, Iran
2Department of Chemistry, Payame Noor University, Kerman, Iran
3Department of Chemistry & Nanoscience and Nanotechnology Research Laboratory (NNRL),
Faculty of Sciences, Payame Noor University, Sirjan, Iran
4Department of Chemistry, Islamic Azad University, Yazd Branch, Yazd, Iran
Received January 3, 2011; revised January 16, 2011; accepted January 17, 2011
In the present work, a ultrasound-assisted emulsification dispersive liquid-liquid microextraction based on
solidification of floating organic droplet method has been developed as a sample preparation method prior to
flame atomic absorption spectrometry determination of trace amounts of gold in the standard, wastewater
and river water samples. In the proposed method, 1-dodecanol and 5-(4-dimethylamino-benzylidene) were
used as extraction solvent and chelating agent, respectively. Several factors that may be affected on the ex-
traction process, such as type and volume of the extraction solvent, ionic strength, pH of the aqueous solu-
tion, extraction temperature and extraction time were studied and optimized. Under the best experimental
conditions, the calibration curve exhibited linearity over the range of 8.0 ng·mL1- 3.0 µg·mL1 with a corre-
lation coefficient of 0.9978 and detection limit based on three times the standard deviation of the blank sig-
nal was 1.5 ng·mL1. Eight replicate determinations of 0.2 and 1.0 g·mL1 of gold gave a mean absorbance
of 0.051 and 0.253 with relative standard deviations of ±2.3% and ±1.5%, respectively. Finally, the devel-
oped method was successfully applied to the extraction and determination of gold ions in a silica ore, waste-
water, river water and standard samples and satisfactory results were obtained.
Keywords: Ultrasound-Assisted Emulsification, Microextraction, Solidification, Floating Organic Droplet,
Preconcentration, Gold Determination, Silica Ore
1. Introduction
Gold belongs to the group of elements which occur on
the Earth in very low natural contents. The concentration
of gold in the natural waters is extremely low and is in
the range of 0.05 - 0.2 ng·mL1 in seawater and river
water, respectively [1]. It is well known that gold is one
of the most interesting micro amount elements due to its
significant role on biology, environment and industry. It
could be used as a drug in the supervised therapy of ar-
thritis and cancer [2] in the forms of different Au(I) and
Au(III) compounds, or in radiotherapy of cancer in the
form of radioactive isotope 198Au. Also, it could be very
toxic for human, animal and plants and account as a pol-
lutant, because of its inhibiting effect upon the activity of
many enzymes and its preventing effect upon the DNA
separation [2]. Numerous methods such as, spectrometric
methods [1], UV-Vis spectrophotometry [2,3], electro-
thermal atomic absorption spectrometry [4], inductively
coupled plasma combined with optical emission spec-
trometry [5,6] or mass spectrometry [7] and flame atomic
absorption spectrometry (FAAS) have been proposed for
the determination of gold in different environmental
samples. However, most of aforementioned methods
except to FAAS involve a greater cost and increased in-
strumentation complexity, limiting its widespread appli-
cation to routine analytical works. FAAS is still being
used because it combines a fast analysis time, a relative
simplicity and a cheaper cost. All of these features have
been responsible for its broad utilization in the determi-
nation of trace elements in different samples [8-10].
However, trace level determination of gold by FAAS is
difficult due to lower levels of gold than detection limit
of FAAS and effects of the matrix components [9]. To
overcome these limitations on the determination of gold
by FAAS, separation-enrichment techniques including
solid phase extraction (SPE), cloud point extraction, liq-
uid–liquid extraction (LLE), coprecipitation, etc. [11-17]
have been used by the researchers around the world.
For many decades, the most common methods for the
performing of the analytical separation were LLE. LLE
is time-consuming and needs to large amounts of toxic
organic solvents. These shortcomings have led to the
development of the new cost-effective methods with
special emphasis on resolving the mentioned difficulties
and detecting analytes at very low concentrations. Re-
cently, efforts have been directed towards miniaturiza-
tion of the LLE procedure by reducing of the amount of
organic solvent and leading to the development of liq-
uid-phase microextraction methods. Liquid-phase mi-
croextraction (LPME) was introduced by Jeannot and
Cantwell in 1996 [18], however, the major disadvantage
of LPME is time-consuming. Efforts to overcome of this
particular limitation led to the development of dispersive
liquid–liquid microextraction (DLLME) method [19]. In
this method, an appropriate mixture of extraction and
disperser solvent are used. The surface area between the
extraction solvent and sample solution are infinitely large
because a cloudy solution can be formed. Therefore, the
extraction equilibrium can reach quickly. The method
has attracted much attention due to their advantages such
as fast analysis, low consumption of organic solvent and
simplicity [20,21]. However, the extraction solvent is
limited in solvents, which should have higher density
than water, such as chlorobenzene, chloroform, tetrachlo-
romethane and carbon disulfide, and all of them are toxic
and environment-unfriendly.
The application of ultrasounic-assisted radiation in the
LLE methods (USALLE) has been reported by Luque de
Castro and Priego-Capote [22,23]. They also success-
fully applied ultrasound-assisted emulsification (USAE)
for the first time to determine some polar and non-polar
compounds in solid plant samples [24]. High extraction
efficiency in a short period of time is the main advantage
of the USALLE. Regueiro et al. applied a miniaturized
approach to USALLE by using a micro volume of or-
ganic phase to provide the advantage of both DLLME
and USALLE [25]. They successfully applied ultra-
sound-assisted emulsification microextraction (USAEME)
to determination of some emergent contaminants and
pesticides in environmental waters. Fontana et al. applied
this method for determination of polybrominated flame
retardants in water samples [26]. They demonstrated that
USAEME is an efficient, simple, and rapid as well as
cheap extraction technique prior to the GC analysis.
Recently, a new mode of liquid-phase microextraction
based on solidification of floating organic droplet
(LPME-SFO) was developed [27,28]. In this method, no
specific holder, such as the needle tip of micro syringe,
the hollow fiber and polychloroprene rubber tube, is re-
quired for supporting the organic micro drop due to the
using of organic solvent with low density and proper
melting point. Furthermore, the extractant droplet can be
collected easily by solidifying it in the lower temperature.
However, the extraction time was somewhat long, thus it
cannot satisfy the demand of fast analysis.
Recently, Xu and co-workers in 2009 [29] combined
the advantages of the two methods (DLLME and LLME-
SFO) and develop a new method named dispersive liq-
uid–liquid microextraction based on solidification of
floating organic droplet (DLLME-SFO). In this method,
the enormous contact area between the organic droplets
and sample solution is beneficial for the fast mass trans-
fer from the aqueous phase to the organic phase. Accord-
ingly the analysis time is shortened greatly. Moreover,
the transfer of the solidified phase from aqueous phase
can be carried out easily.
Pourreza [30] and Afzali [31] reported that 5-4-dime-
thylamino-benzylidene (rhodanine) is suitable as a sensi-
tive and selective reagent for gold. Therefore, rhodanine
was selected as chelating agent in the present work.
The aim of this work is combination of USAEME with
SFO and developing a new method as name USAEME-
SFO for the determination of trace gold in river water
and wastewater samples. All main factors were investi-
gated and optimized. The USAEME-SFO method was
evaluated by analyzing Certified Reference Materials
and spiked samples.
2. Experimental
2.1. Instrumentation
A SensAA GBC (Dandenong, Australia) atomic absorp-
tion spectrometer equipped with deuterium background
correction and gold hollow cathode lamp was used for
absorbance measurements at wavelength of 242.8 nm.
The instrumental parameters were adjusted according to
Copyright © 2011 SciRes. AJAC
the manufacturer’s recommendations. Acetylene flow rate
and burner height were adjusted in order to obtain the
maximum absorbance signal, while aspirating the analyte
solution. A Metrohm 692 pH meter (Herisau, Switzer-
land) was used for pH measurements. An ultrasonic bath
with temperature control (FALC instruments S.V.l Tre-
viglio, Italy) model LBS2 was used to assist the emulsi-
fication process of the microextraction technique.
2.2. Reagents and Solutions
All chemicals were analytical-reagent grade (Merck,
Darmstadt, Germany) and were used without previous
purification. The laboratory glassware was kept over-
night in a 1.4 mol·L1 HNO3 solution. Before using, the
glassware was washed with de-ionized water and dried.
Stock solution of gold at a concentration of 1000.0
μg·mL1 was prepared by dissolving an appropriate
amount of HAuCl4·3H2O (Merck) in double distilled
water. The working reference solutions were obtained
daily by stepwise dilution from stock solution. A 0.05%
(w/v) solution of 5-(4-dimethylamino-benzylidene) (Rho-
danine) (Mer- ck) was prepared by dissolving it in etha-
nol. The solutions of alkali metal salt (1% w/v) and var-
ious metal salts (0.1% w/v) were used to study the inter-
ference of anions and cations, respectively.
2.3. USAMEM-SFO Procedure
All standards and samples were prepared for analysis
according to the following procedure. Eight mL of each
sample was placed in a screw cap glass test tube. To each
test tube, 1 mL of 0.1 mol·L1 phosphate buffer (pH 3),
100 µL Rhodanine 0.05% in ethanol and 1 mL of 10%
(w/v) NaCl were added. Then, 25.0 µL 1-dodecanol was
injected into each solution and all samples were soni-
cated for 10 minutes at 42˚C in ultrasonic bath. As a re-
sult, oil-in-water emulsions of 1-dodecanol in water were
formed. After centrifuging at 4000 rpm for 4 min, the
organic solvent droplet was floated on the surface of the
aqueous solution due to low density below water. Then,
the sample vial was put into an ice bath for 5 min, at this
time the floated solvent was solidified because of low
melting point (24˚C). Then, the solidified solvent was
transferred to a conical test tube. The extractant in the
test tube was washed by iced water for 2 times, and the
water in the vial was drawn out by a syringe. The solidi-
fied organic solvent melted quickly at room temperature.
Prior to analysis of gold by FAAS, the extractant was
mixed with 0.5 mL of dimethyleformamid.
2.4. Sample Preparation
In order to test the reliability of the proposed USAMEM-
SFO procedure for extraction and determination of gold
in the real samples, two Canadian Certified Reference
Materials Project (CCRMP) and a silica ore sample
(Muteh gold mine, Isfahan, Iran) were analyzed. For this
purpose, 200.0 mg of CCRMPs and 1.00 g of silica ore
sample were taken and dissolved completely in a mixture
of nitric acid, hydrochloric acid and HF (2:6:1) with
heating. The solutions were cooled, diluted and filtered.
Then, the filtrates were made to 50.0 mL with deionized
water in a volumetric flask.
River water and wastewater samples were collected in
acid leached polyethylene bottles. River water sample
was collected from Shahdad (Kerman, Iran) and waste-
water samples were collected from copper factory in
Sarcheshmeh area (Kerman, Iran) and Bahonar copper
factory in Kerman. The only pretreatment was acidifica-
tion to pH 2 with nitric acid, which was performed im-
mediately after collection, in order to prevent adsorption
of the metal ions on the flask walls. The samples were
filtered before analyses through a cellulose membrane
(Millipore, Bedford, MA, USA).
3. Results and Discussion
3.1. Type and Volume of the Extraction Solvent
Selection of the extraction solvent is important in the
optimization of USAEME-SFO conditions. It should
have low solubility in water, high affinity to analytes,
lower melting point than room temperature and lower
density than water. In this work, 1-undecanol and
1-dodecanol were selected as extraction solvent, and
their extraction efficiency were studied. The results were
shown that both of solvent are suitable for extraction of
gold. 1-undecanol is more expensive than 1-dodecanol
(DOD), therefore DOD was selected as the extraction
solvent in the subsequent experiments. The effect of the
DOD volume on the extraction efficiency was also in-
vestigated. Therefore, some experiments were performed
with different volumes of DOD (15.0 - 50.0 µL) as the
extraction solvent and keeping the other variable con-
stant. The results are shown in Figure 1. It was observed
that the maximum extraction efficiency was obtained at
the volume range of 20.0 to 50.0 µL of DOD. Thereby,
25.0 µL DOD was used as extraction solvent in the sub-
sequent experiments.
3.2. Effect of pH on the USAEME-SFO
The pH plays a unique role on the metal-chelate formation
and the subsequent extraction. Therefore, the effect of pH
on the USAEME-SFO extraction of gold was studied in
Copyright © 2011 SciRes. AJAC
10 2030 40 50
Volume o f extraction solvent (L)
Recovery (%)
Figure 1. Effect of the extraction solvent volume (DOD) on
the USAEME-SFO extraction of gold. Conditions: Au(III),
8.0 g; Buffer with pH 3, 1 mL; NaCl 1% (w/v); Extraction
time, 10 min; Extraction temperature, 42˚C.
the pH range of 1 - 9 and keeping the other variable con-
stant. The results are shown in Figure 2. As can be seen
in Figure 2, the highest extraction efficiency of gold was
obtained at the pH range of 2.5 - 3.5. Therefore, pH 3
was selected for the further experiments.
3.3. Effect of the Extraction Temperature
Temperature affects organic solvent solubility in water as
well as the emulsification phenomenon. Thus, this affects
the mass-transfer process and the extraction efficiency.
To determine the influence of the extraction temperature,
8.0 mL aqueous solution containing 8.0 μg of gold was
extracted at different temperatures ranging from 30˚C to
60˚C. The results are shown in Figure 3. It was observed
that the highest extraction efficiency was obtained at the
range of 40˚C - 45˚C. Hence, 42˚C was used for further
3.4. Effect of the Extraction Time
In USAEME, the extraction time is defined as interval
time between the injection of the extraction solvent and
the starting of centrifuge. Effect of the extraction time
was examined in the range of 5 to 20 min and keeping
the other variable constant. The results are shown in
Figure 4. It was observed that the highest extraction
Recovery (%)
Figure 2. Effect the pH of sample solution on the USAEME-
SFO extraction of gold. Conditions were the same as Figure
1 except to pH.
25 30 35 40 45 50 55 60 65
Extraction temperature (
Recovery (% )
Figure 3. Effect of the extraction temperature on the
USAEME-SFO extraction of gold. Conditions were the same
as Figure 1 except to extraction temperature.
051015 20 25
Ex tr actio n time (min )
Reco v er y (%)
Figure 4. Effect of the extraction time on the USAEME-
SFO extraction of gold. Conditions were the same as Figure
1 except to extraction time.
efficiency was obtained at 7.5 - 12.5 min. Based on these
observations; an extraction time of 10 min was used for
further experiments.
3.5. Effect of Ionic Strength
In the extraction methods, the solubility of many analytes
in aqueous solutions decreases with increasing ionic
strength due to salting out effect. For investigating the
influence of the effect ionic strength on the USAEME-
SFO extraction of Au(III) ion, sodium chloride solution
was used in the concentration range of 0.25% to 2.5%
(w/v). The results were shown that the highest recovery
percent of gold ion was obtained at 0.75% - 1.25% NaCl
concentration. Below or above this concentration range,
a decrease on the extraction efficiency was observed.
Therefore, 1% NaCl concentration was used in the sub-
sequent experiments.
3.6. Interference
The efficiency of the USAEME-SFO procedure in the
extraction and preconcentration of gold ions were also
studied in the presence of various cations and anions. In
order to, interference ions in different interference-to-
analyte ratios were added to a solution containing 8.0 µg
Copyright © 2011 SciRes. AJAC
of Au(III) and were subjected to the USAEME-SFO
procedure. The tolerance limit was set as the amount of
ion required to cause ±5% error in the determination of
gold. The results are given in Table 1. The results were
shown that the presence of large amounts of species
commonly present in water samples have no significant
effect on the extraction of gold.
3.7. Analytical Figures of Merit
Figures of merit of the USAEME-SFO procedure were
obtained by processing of the standard solution of gold.
For a sample volume of 8 mL, the calibration graph ex-
hibited linearity over the range of 8.0 ng·mL1 - 3.0
µg·mL1 with a correlation coefficient of 0.9978 (A=
0.2549C + 0.0026, where A is the absorbance value and
C is the concentration of gold (µg·mL1). The relative
standard deviations (n = 8) at 0.2 and 1.0 g·L1 of gold
were ±2.3% and ±1.5%, respectively. The limit of detec-
tion, based on three times the standard deviation of the
blank signal was 1.5 ng·mL1 of gold. The enrichment
factor was calculated as the ratio of the analytical signal
of Au obtained after and before extraction. The enrich-
ment factor was 14.2 for 8.0 mL sample solution.
Table 1. Tolerance limit of interference ions.
Interference ions Interference/gold ratio Recovery (%)
PO43–, H2PO4, HPO42– >5000 95
K+ 3000 104
Na+ 3500 105
Ca2+ 3000 95
Mg2+ 2500 105
Co2+ 700 95
Mn2+ 500 105
Ni2+ 600 98
Cu2+ 400 105
Pb2+ 500 95
Cd2+ 600 96
Pd2+ 600 104
Rh3+ 800 105
Zn2+ 300 95
Ag+ 200 95
Fe3+ 100 96
Al3+ 50 95
Conditions were the same as Figure 1.
3.8. Accuracy of the Method
The accuracy of the USAEME-SFO procedure was
checked to the determination of gold in CCRMP (MA-1b
and CCU-1b). An aliquot of the sample solution was
taken and gold was determined after the USAEME-SFO
procedure. The results are given in Table 2 and are in
good agreement with the certified value.
3.9. Application
The USAEME-SFO procedure was applied to the deter-
mination of gold in a silica ore, wastewater and river
water samples. The recovery of gold from the silica ore,
wastewater and river water samples spiked with the
known amounts of gold ions was also studied. The ob-
tained results are shown in Table 3. According to these
results the added gold ions spiked to the wastewater and
river water samples can be quantitatively recovered, and
no significant interference was observed.
Furthermore, the ore sample was analysed by induc-
tively coupled mass spectrometry (ICP-MS) technique
for verifying the result obtained by the USAEME-SFO
procedure developed in this paper. As it is obvious from
Table 2. Determination of gold in canadian certified refer-
ence materials project.
Sample Certified value
(g g1)
(g g1)
MA-1b reference
gold ore 17.0 17.1 0.5
CCU-1b copper
flottation concentrate 5.89 ± 0.10 5.86 0.17
aAveragestandard deviation (n = 4).
Table 3. Determination of gold in real samples.
Gold amount (ng·mL–1)
Added Founda
Silica ore (Muteh
gold mine, Isfahan,
41.40 ± 1.80b
51.23 ± 0.5
Shoor river
(Shahdad, Kerman)
9.8 ± 0.3
Wastewater (copper
factory, Sarchashmeh,
10.6 ± 0.4
Wastewater (copper
factory, Shahid
Bahonar, Kerman)
10.4 ± 0.4
aMean ± standard deviation (n = 4).bThe quantitative analysis of gold con-
tent in the silica ore sample by the proposed method and ICP-MS was found
to be 2.07 ± 0.09 µg g1 and 2.11 ± 0.12 µg·g1, respectively. cNot detect.
dBelow of linear range.
Copyright © 2011 SciRes. AJAC
Table 3, there is a satisfactory agreement between the
results obtained by ICP-MS (2.11 ± 0.12 µg·g1) and the
proposed method (2.07 ± 0.09 µg·g1).
4. Conclusions
In this paper, we introduced a USAEME-SFO method
for the analysis of trace amounts of gold in wastewater
and river water samples. The USAEME-SFO procedure
has numerous advantages such as: low cost, low toxic,
simplicity of operation, rapidity and high selectivity. In
addition, it is important to point out that USAEME-SFO
is a low organic solvent consuming extraction technique,
which turns it into a low cost and also an environmen-
tally friendly technique. In this method, the consumption
of the toxic organic solvent (at microlitre level) was
minimized without affecting sensitivity of the method.
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