1. Analytica Chimica Acta 813 (2014) 56–62
Contents lists available at ScienceDirect
Analytica Chimica Acta
journal homepage: www.elsevier.com/locate/aca
Solid phase extraction of trace amount of mercury from natural
waters on silver and gold nanoparticles
N. Panichev, M.M. Kalumba∗
, K.L. Mandiwana
Department of Chemistry, Tshwane University of Technology, P.O. Box 56208, Arcadia 0007, Pretoria, South Africa
h i g h l i g h t s
• Ag/Au nanoparticle membrane filters
were used to extract Hg extraction
from natural water.
• The LOD of Hg determination was
lower (0.4 ng L−1
) than the traditional
method of cold vapour generation
(200 ng L−1
).
• Sample contamination was mini-
mized by thermal desorption of Hg
determination.
• Hg collected on nanoparticle mem-
brane filters were kept for at least 5
months without Hg loss.
g r a p h i c a l a b s t r a c t
a r t i c l e i n f o
Article history:
Received 19 March 2013
Received in revised form 5 December 2013
Accepted 5 January 2014
Available online 13 January 2014
Keywords:
Mercury
Nanoparticles
Thermal evaporation
Hg analyzer
a b s t r a c t
Silver (Ag) and gold (Au) nanoparticles impregnated in nylon membrane filters have been proposed as
a new solid phase for preconcentration of mercury from natural waters. Water samples were treated
with KMnO4 to convert all mercury species to inorganic Hg2+
and this was followed by the reduction of
Hg2+
with NaBH4 to elemental Hg0
. The determination of Hg was carried out by thermal evaporation of
mercury from membrane filters using Zeeman mercury analyzer RA–915+ (Lumex, Russia). This process
does not involve any additional sample treatment and sharply reduces risk of samples contamination. The
limit of detection (LOD) was found to be 0.04 ng (absolute mass). Relative LOD was 0.4 ng L−1
for 100 mL of
water. The method was validated through the analysis of CRM NRCC Tort–2 (Lobster hepatopancreas) and
the found value (0.30 ± 0.07 ␮g g−1
) was in good agreement with the certified value (0.27 ± 0.06 ␮g g−1
).
High efficiency of Hg accumulation from aqueous phase to membrane filters can be attributed to a large
surface area of nanoparticles.
© 2014 Elsevier B.V. All rights reserved.
1. Introduction
The determination of mercury (Hg) in natural waters using
cold vapour (CV) generation technique became a routine method
of trace analysis for several decades [1]. The advantages of this
method lie in the minimisation of interferences from matrix due to
∗ Corresponding author. Tel.: +27 12 382 6233/+27 73 661 6061 (mobile);
fax: +27 12 382 6286.
E-mail addresses: Kalumba.merime1@gmail.com, panichevn@tut.ac.za
(M.M. Kalumba).
complete separation of the analyte (Hg) from the matrix in gaseous
state [2]. The detection of Hg is carried out at room temperature
in atomic absorption or atomic fluorescent mode at a wavelength
of 253.7 nm [3]. Generally, before Hg measurements by CV, water
samples should be chemically treated. The first step of sample treat-
ment is the oxidation of all Hg species present in the sample to
one chemical form (Hg2+) [4]. In the second step, Hg2+ is reduced
to its elemental form either by the addition of mild reducing agent
(SnCl2) or more reactive substance (NaBH4). The elemental mercury
(Hg0) is purged from the solution by the carrier gas and transported
to a measurement cell. The limit of detection (LOD) of Hg deter-
mination in natural waters using CV is approximately 0.2 ␮g L−1
0003-2670/$ – see front matter © 2014 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.aca.2014.01.011

2. N. Panichev et al. / Analytica Chimica Acta 813 (2014) 56–62 57
[5–7]. This LOD is not low enough for Hg to be determined at the
natural environmental level. The determination of Hg at trace lev-
els would be possible by analytical methods in which a step of Hg
preconcentration is involved [8–10].
Solid phase preconcentration of Hg on thin films of noble metals
including gold, palladium and silver are favourable solid sorbents
for trapping mercury vapour due to their high affinity towards the
Hg. At present, two methods of Hg preconcentration have been
developed. One of them is to trap Hg0 which was formed during cold
vapour generation on electrothermal atomizers covered with thin
films of noble metals, like Au, Pd or Rh [11–14]. The main advantage
of trapping Hg0 on thin layers of noble metals is the reduction of
LOD. The disadvantages of Hg preconcentration from gaseous state
on thin films of noble metals are higher risk of contamination and
longer cycle time [15].
The other novel solid-phase preconcentration of Hg is based
on the sorption of Hg0 on gold nanoparticles directly from natural
waters. In this case, the stage of cold vapour generation is avoided
because Hg from the aqueous phase is collected on the solid sor-
bent, which consists of silica coated with gold nanoparticles. The
determination of Hg is carried out by atomic fluorescent spectrom-
etry (AFS) after thermal desorption of Hg from the sorbent. Leopold
et al. [16–19] found that all Hg species can be preconcentrated by
amalgamation of Hg0 on the surface of silica due to catalytic activ-
ity of the nano–gold particles, which provides decomposition of
mercury species and some complexes in aqueous sample at room
temperature. Subsequently, the liberation of trapped mercury was
carried out by Hg analyzer after thermal desorption and as a result,
no reagents were needed for species conversion, preconcentration,
sample storage and desorption, resulting in reduced contamination
and lower blank signal. Consequently, a very impressive LOD for Hg
(180 pg L−1) have been achieved [19].
In the present work, the method of solid phase extraction and
preconcentration of mercury from natural waters with low con-
centration of Hg is described. It is based on the sorption of Hg0 on
Ag or Au nanoparticles impregnated into membrane filters during
filtration of water samples. To avoid the problems connected with
additional experiments to prove that gold nanoparticles are capa-
ble of converting different Hg species in acidified waters without
additional reagents, all water samples were treated with KMnO4
according to “classical” procedure of water samples preparation
for Hg determination [5,6]. The measurements were carried out by
mercury analyzer after thermal desorption of Hg0 from filters.
2. Experimental
2.1. Instrumentation
All mercury measurements were carried out with a Model
RA–915+ Zeeman Mercury analyzer (Lumex, St. Petersburg, Rus-
sia) fitted with PYRO–915+ attachment. The working principal of
the instrument is based on the thermal desorption of Hg from sam-
ples placed in pyrolysis tubes, which can be heated from 300 ◦C to
700 ◦C. The measurements of Hg concentration are carried out in an
analytical cell, constantly heated at 800 ◦C. In this work the temper-
ature of preheated tube was set at 700 ◦C. When known amount of
solid sample placed in the sampling boat is inserted in preheated
tube, Hg vapour and smoke formed after combustion of matrix’s
organic materials are transported into analytical cell. Background
absorption in the analytical cell is eliminated by the high-frequency
Zeeman correction system. The high total multi-path optical length
of analytical cell (0.4 m) allows detecting Hg on picogram level.
The concentration of Hg in a sample is determined from integrated
analytical signals, using calibration graph, plotted with different
certified reference materials (CRMs). The PYRO–915+ enables Hg
determination in samples with complex–matrices, such as soils,
sediments, oil products and foodstuffes using pyrolysis technique
without samples pretreatment [20,21]. With no chemical sample
pretreatment and without addition of chemical modifiers, the risk
of contamination is minimized.
The distribution of Ag and Au nanoparticles on membrane filters
have been studied with JSM 7500 F Scanning Electron Microscope
(JEOL, Ltd., Tokyo, Japan). The size of the AuNPs and AgNPs prepared
were investigated using a JEM-2100 (HR) transmission electron
microscopy (JEOL, Ltd., Tokyo, Japan) operated at an accelerating
voltage of 200 kV. The concentration of Ag and Au in solutions with
nanoparticles and the amount of adsorbed Ag and Au on filters
were determined by electrothermal atomic absorption spectrome-
try (ETAAS), using Perkin Elmer Model AAnalyst 600 spectrometer
(Perkin Elmer, USA).
2.2. Reagents and reference materials
All solutions were prepared using ultra-pure water with a
resistivity of 18.2 M cm, obtained from Milli-Q Plus water purifi-
cation system (Millipore, Bedford, MA, USA). Mercury standard
solutions in the range of 0.10–2.0 ␮g L−1 were prepared by sequen-
tial dilution of 1000 mg L−1 Hg stock solution (Merck, Darmstadt,
Germany). Silver nitrate, AgNO3 (Saarchem, Merck, Germany) and
gold as HAuCl4 stock standard solution of 1000 ␮g L−1, (Spec-
troscan, Teknolab, Norway) were used for preparation of Ag and
Au nanoparticles. Sodium borohydride, NaBH4 3% (m/v) solution
in 0.3% (m/v) NaOH was used as a reducing agent and glucose as
the stabilizer were prepared from analytical grade reagents (Merck,
Darmstadt, Germany). After dissolution of the reagents, the solu-
tions were filtrated through Millipore hydrophilic PVDF 0.45 ␮m
filters to remove undissolved solids.
The following CRMs were used in this study to calibrate RA–915+
Zeeman Mercury analyzer: SRM 1515, Apple leaves–Trace elements
(National institute of Standards and Technology, USA), certified
value Hg 0.044 ␮g g−1, CMI 7002 Light Sandy soil–Trace elements,
(Analytika Co Ltd., Czech Republic, certified value Hg 0.090 ␮g g−1
and CRM NCS DC 73308 Stream sediment (China National Analysis
Center for Iron and Steel, China), certified value: Hg 0.28 ␮g g−1.
2.3. Preparation of silver and gold nanoparticles
The preparation of Ag nanoparticles was carried out according
to the procedure recommended by A. Zielinska et al. [22]. For this
purpose, 2.0 mL of 0.005 M AgNO3 was added to 500 mL deionized
water. The calculated concentration of Ag ions in obtained solu-
tion was 2000 ␮g L−1 but the actual concentration using ETAAS
was found to be 2220 ± 60 ␮g L−1. After addition of 10 mL of 5 g L−1
NaBH4 and 0.05 g of glucose, the colourless mixture was slowly
turned pale yellow, indicating that Ag-nanoparticles were formed.
Nanoparticles of Au were prepared by the addition of 6 mL of lemon
juice to 50 mL of hydrogen tetrachloroaurate solution (HAuCl4)
[23]. The mixture was brought to a boil with vigorous stirring. The
colour of the solution changed from colourless to purple to ruby red
within 10 min. The colloidal solution was stirred for an additional
20 min, cooled at room temperature, transferred to an amber bottle
and stored at room temperature. The colour of the solution changed
from yellowish to ruby red, indicating that gold nanoparticles have
formed. The concentration of Au nanoparticles in obtained solution
was found to be 1980 ± 30 ␮g L−1, which corresponds to predicted
value of 2000 ␮g L−1. The last step to impregnate nanoparticles into
membrane filters have been done by filtration of solutions with Ag
or Au nanoparticles. The mass of Ag and Au nanoparticles anchored
on filters was determined by ET AAS.

3. 58 N. Panichev et al. / Analytica Chimica Acta 813 (2014) 56–62
3500
3550
3600
3650
3700
3750
3800
0 2 4 6 8 10 12 14 16
Peakarea(Arbitraryunit)
NaBH4 concentration, % (m/v)
Fig. 1. Effect of NaBH4 concentration on 5 ng Hg peak area.
2.4. Samples preparation for the determination of total Hg
concentration
For sample collection, all glassware used were cleaned with
detergent, thoroughly rinsed with tap water, soaked in a 5% (v/v)
HNO3 solution overnight and finally rinsed with Milli-Q water.
Glass bottles were rinsed three times with the river water before
being filled. Samples were drawn through by vacuum suction, by
force of a pump, or simply rely on gravity to pass through the
solid sorbent. Organic and inorganic Hg compounds in water sam-
ples were decomposed with 2% (m/v) KMnO4. The excess oxidant
(permanganate) was destroyed by the addition of few drops of
hydroxylammonium chloride until the solution was colourless.
Before filtration, Hg2+ was reduced to Hg0 by the addition of 1 mL
of 0.001 M NaBH4 per each 100 mL of water sample. In all cases it
is imperative that sufficient contact time of 1 min was allowed for
analytes to be adsorbed onto the membrane filters, without being
prolonged to the extent of taking several hours simply to pass the
sample through [24].
3. Results and discussions
3.1. Effect of NaBH4 concentration
The first parameter to be examined was the effect of NaBH4
concentration on the production of the mercury vapour. Fig. 1
demonstrates the effect of increasing concentration of NaBH4 from
1 to 15% on the peak area of 5 ng Hg. The results showed the analyt-
ical signal of Hg was constant after addition of 3–15% (m/v) NaBH4
solutions. Hence, 3% (m/v) NaBH4 was used throughout the study
to minimize deterioration of NaBH4 concentration in solution. This
concentration was also thought to be the optimum in terms of
cost-effectiveness.
3.2. Effect of volume of NaBH4
In order to determine the appropriate volume of NaBH4 required
to achieve optimum peak area of Hg, various volumes of 3% (m/v)
NaBH4 were added to the solution containing an absolute amount
of 5 ng Hg2+. It was found that 1–15 mL of NaBH4 are capable to
3500
3550
3600
3650
3700
3750
3800
0 2 4 6 8 10 12 14 16
Peakarea(Arbitraryunit)
Volume of NaBH4 (mL)
Fig. 2. Effect of the volume of NaBH4 3% (m/v) on 5 ng Hg peak area.
produce the absorption signals of Hg with constant peak area
(Fig. 2). On the base of these studies, an addition of 5 mL of NaBH4
was chosen as an optimal volume.
3.3. Adsorption capacity of membrane filters for Ag and Au
nanoparticles
The amount of Ag or Au nanoparticles adsorbed by membrane
filters and their total sorption capacity were determined after the
filtration of different volumes of solutions with known concentra-
tion of Ag and Au as quantified by ETAAS analysis of filters. For
this purpose, filters were dissolved in 1.0 mL of freshly prepared
aqua regia, and diluted to 50 mL with deionized water. The results
of ETAAS determination (Fig. 3) showed that after filtration of dif-
ferent volumes of AuNPs and AgNPs solutions, membrane filters
accumulated stable amount of Ag (11 ± 1 ␮g) and Au (20 ± 0.7 ␮g)
nanoparticles. These amounts could be considered as the total sorp-
tion capacity of membrane filters.
An estimate of particle size had been performed using the TEM
images of AuNPs and AgNPs on the membrane surfaces (Fig. 4) were
0
5
10
15
20
25
0 20 40 60 80 100 120
MassofAgandAuonfilter(µg)
Volumes of Ag ( ) and Au ( ) nanoparticles solution (mL)
Fig. 3. Sorption of Ag ( ) and Au ( ) nanoparticles on 0.20 ␮m membrane filters.

4. N. Panichev et al. / Analytica Chimica Acta 813 (2014) 56–62 59
Fig. 4. TEM images of seed nanoparticles of Au (A and C) and Ag (B and D).
found to be approximately 20 nm. Clearly, the fact that they are
some 10 fold smaller than the membrane filter pore size means that
their presence on the membrane is not due to a filtering action but
rather adsorption onto the surface where they appear to be quite
strongly retained, as evidenced by the fact that once prepared, these
membranes can be used for months with good efficiency.
The different loadings pertain to mass can be accounted for by
the relative atomic weight differences for Au and Ag. In point of fact,
approximately the same molar loadings are achieved with both
metals and since the resultant nanoparticles are approximately
the same size, then the surface areas presented are approximately
equal, thus accounting for the nearly identical sorption kinetics and
capacities for mercury uptake [25]. It was concluded that for the
preparation of membrane filters for Hg sorption, 50 mL of stock
solution with concentration of Ag or Au nanoparticles of approxi-
mately 2000 ␮g L−1 could be taken.
3.4. Adsorption of Hg on membrane filters
The kinetics of adsorption that describes the solute uptake rate
governing the contact time of the adsorption reaction was one of
the important characteristics that define the efficiency of adsorp-
tion. Hence, in the present study, the kinetics of Hg adsorption on
blank nylon membrane filters and filters impregnated with AuNPs
and AgNPs was studied. The results, presented in Fig. 5 showed that
the effect of contact time of Hg solutions with concentrations of
1500 ng L−1 (A) and 2500 ng L−1 (B) on Hg sorption by nanoparticles
on membrane filters. From these data follows that the adsorption
reaches its maximum value in 60 s, which corresponds to 100% of Hg
sorption and remains stable up to 240 s, while only 7.9% of Hg has
been absorbed by the blank membrane filter. The process observed
is a heterogeneous phase separation of the mercury from the solu-
tion to the surface of the nanoparticle. Assuming that “intimate”
mixing was achieved throughout the filtering process, wherein the
solution flows past the immobilized particles, it was clear that the
degree of interaction of the solution with the adsorbent was the
same whether the sample volume is 1 mL or 500 mL. It was only
the time of interaction that was important.
3.5. Adsorption of Hg on filters with Ag and Au nanoparticles
The study of Hg adsorption on filters impregnated with Ag
nanoparticles has been carried out after filtration of different vol-
umes of 1 ng mL−1 Hg standard. The tested volumes varied between
5 and 300 mL, which correspond to the range between 5 and 300 ng
(absolute mass) of Hg. The results showed that filters with pore
size of 0.2 and 0.22 ␮m have the same efficiency for Hg sorption,
because no statistical difference between amounts of Hg adsorbed
have been found at 95% level of confidence (Fig. 6A).
The adsorption of Hg on filters with Ag and AuNPs was car-
ried out by filtration of 50–300 mL of 0.1 ng mL−1 Hg standard
solutions. The results indicated that both kinds of nanoparticles
adsorb Hg with the same efficiency in the range of 0.5–50 ng
(Fig. 6B). The mechanism of Hg interaction with AuNPs and AgNPs
and thus their effect of the adsorption of mercury is possibly due
to the 5d10(Hg2+)–4d10(Ag+) high metallophilic interaction which
allowed Hg amalgamation on Ag [26], and due to the big surface
area of AgNPs and AuNPs [27].
The recovery of Hg adsorbed on filters with impregnated Ag
(Au) NPs (Fig. 6C) had been studied after filtration of 50 mL of

5. 60 N. Panichev et al. / Analytica Chimica Acta 813 (2014) 56–62
A
B
0
200
400
600
800
1000
1200
1400
1600
0 50 100 150 200 250
Concentration,ng/g
Time, sec
0
500
1000
1500
2000
2500
3000
0 50 100 150 200 250
Concentration,ng/g
Time, sec
Fig. 5. Adsorption kinetics of Hg onto blank membrane filter ( ) and filters impreg-
nated with Au ( ) and Ag ( ) nanoparticles from Hg solutions 1500 ␮g L−1
(A) and
2500 ␮g L−1
(B).
solutions with nanoparticles concentration from 100 to
5000 ␮g L−1. It was found that complete adsorption of Hg
(100 ± 2%) was achieved with solutions Ag (Au)NPs concentrations
from 2000 ␮g L−1 to 5000 ␮g L−1. For practical application, the
solutions of Ag (Au)NPs 2000 ␮g L−1 was used.
3.6. Distribution of Ag, Au nanoparticles and Hg on membrane
filters
The scanning electron microscope (SEM) and energy dispersive
spectroscopy (EDS) images of the surface of the membrane are
shown in Fig. 7, where (A) is a view of the blank nylon, (B) modified
membranes with AuNPs, (C) modified membranes with AuNPs + Hg,
(D) modified membranes with AgNPs and (E) modified membranes
with AgNPs + Hg. The maps of Hg distribution demonstrate that it
was attached to specific sites, to individual Ag or Au nanoparticles.
The bond between Hg and nanoparticles of both elements was
stable because the amount of Hg on the filters did not change
even after 6 months of filter storage at room temperature. Typical
cross-sectional areas of the blank membrane were viewed using
SEM as shown by the porous structures (Fig. 7A), however, the
macrovoids do not span the entire width of the membrane as the
adsorbent–adsorbate interactions depend both on diffusion and
interactive parameters [28]. The presence of porous structure in the
membrane indicates that there is uniform distribution of the pores
over the surface. The presence of AuNPs and AgNPs in the filters
was confirmed by ETAAS analysis and EDS measurements which
confirmed the peaks of Au (Fig. 7B), amalgamation of Au with Hg
(Fig. 7C), Ag (Fig. 7D) and Ag (Fig. 7E).
C
0
20
40
60
80
100
120
100 500 1000 2000 3000 4000 5000
Recoveryofmercury(%)
Concentration of nanoparticles solution, µg L-1
A
B
Ag: 0.22 µm : y = 618.1x + 650.4
R² = 0.993
Ag: 0.2 µm: y = 604.4x + 347.5
R² = 0.992
0
40000
80000
120000
160000
200000
0 100 200 300 400
Peakarea(arbitraryunits)
Absolute mass of mercury (ng) on 0.2 µm ( ) and 0.22 µm ( )
membrane filters
Ag: y = 600.7x + 316.6
R² = 0.9989
Au: y = 581.4x + 275.8
R² = 0.9984
0
10000
20000
30000
40000
0 10 20 30 40 50 60
Peakarea(Arbitrayunits)
Absolute mass of collected Hg (ng)
Fig. 6. Absolute mass of Hg (ng) collected on 0.20 ␮m ( ) and 0.22 ␮m ( ) fil-
ters impregnated with Ag nanoparticles (A); Absolue mass of Hg (ng) collected
on 0.20 ␮m membrane filters impregnated with Ag ( ) and Au ( ) nanoparticles
(B); Comparison of the efficiency of Hg adsorption on 0.20 ␮m filters from different
concentrations of Au ( ) and Ag ( ) nanoparticles solutions (C).
3.7. Analytical characteristics of the method
The analytical parameters of the method of Hg determination in
natural water based on the adsorption of Hg on Ag or Au nanoparti-
cles impregnated in membrane filters were carefully investigated.
It was found that the preconcentration of Hg can be carried out
either on Ag or on Au nanoparticles with the same efficiency as
the slope of the calibration curves of Hg standards in Au and Ag

6. N. Panichev et al. / Analytica Chimica Acta 813 (2014) 56–62 61
Fig. 7. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) spectra of products: (A); Blank membrane, (B), modified membranes with AuNPs; (C),
modified membranes with AuNPs + Hg; (D), modified membranes with AgNPs and (E), modified membranes with AgNPs + Hg
nanoparticles were equal at 95% level of confidence. The calibra-
tion curve plotted for small concentrations of Hg in the range of
0.5–50 ng (absolute mass) or 5–500 ng L−1 is linear with regression
coefficients of R2 = 0.9989.
The LOD is defined as the analyte concentration correspond-
ing to three (3) standard deviations of integrated absorbance for
the blank solution divided by the slope of the calibration function.
When blank signal cannot be measured, the calibration data and
regression statistics can be used instead [29]. The limit of detection
(LOD) was calculated from the equation of the calibration curve due
to the absence of samples of water free of Hg that could be used as
blanks [29].
For this purpose, ten (10) different masses of Hg were loaded
on filters after filtration of different volumes of 0.1 ng mL−1 Hg.
The calibration curve was plotted as absolute mass of Hg (ng)
versus peak area (arbitrary units) and was defined by simple

7. 62 N. Panichev et al. / Analytica Chimica Acta 813 (2014) 56–62
Table 1
Analytical results for the determination of trace mercury in natural water samples
collected in Apies river.
Samples Unspiked
(ng L−1
)
Spiked
(ng L−1
)
Found (ng L−1
) Recovery (%)
Location 1 7.5 ± 1.3 2.0 9.5 ± 1.5 98.8
Location 2 15 ± 2.5 2.0 16.9 ± 1.8 99.0
Location 3 120 ± 5 2.0 122 ± 8 100.2
Location 4 35 ± 3 2.0 37 ± 1.3 100.1
Location 5 19 ± 1 2.0 20.9 ± 2.4 99.1
Location 6 14 ± 1 2.0 15.9 ± 1.4 98.7
linear regression equation, y = 490.8x + 10.9, R2 = 0.9987, resulting
in the absolute LOD of 0.040 ng. This value is slightly higher than
the LOD for Hg determination in solid sediments (0.013 ng), which
was obtained using the same RA–915+ mercury analyzer [30]. It
should be noted that the LOD in concentration units is inversely
proportional to the sample volume processed. Because in this study
the typical volume of water sample used for Hg determination was
0.1 L, the LOD in concentration unit was found to be 0.4 ng L−1.
The method was validated by analysis of dissolved CRM NRCC
Tort–2 (Lobster hepatopancreas) with good agreement between
the found Hg concentration (0.30 ± 0.07 ␮g g−1) and the certified
value (0.27 ± 0.06 ␮g g−1).
To check the performance of the mercury analyzer, three repli-
cates of CRM CMI 7002 Light Sandy soil were analyzed daily. The
results of Hg determination were within the confidence interval of
certified value of 0.090 ± 0.012 ␮g g−1.
3.8. Analysis of natural water samples
The developed method was applied for the determination of Hg
in natural waters from Apies River in Pretoria. Water samples were
taken on six (6) different sampling sites in the central part of the
city. Samples were treated with KMnO4 in acid media and Hg was
restored to Hg0 with NaBH4. The results showed that the concen-
tration of Hg in Apies River is relatively low, but varied from one
sampling site to the other (Table 1). The variability of Hg concen-
tration on different sampling location could be connected with the
flow of effluent from numerous drain pipes into river.
4. Conclusions
It was shown that silver (Ag) and gold (Au) nanoparticles
impregnated in nylon membrane filters can be used as a new solid
phase for preconcentration of small amounts of Hg from natural
waters. High efficiency of adsorption of Hg from aqueous phase
to membrane filters can be attributed to the large surface area of
nanoparticles. The additional advantage of the proposed method is
the thermal desorption of Hg from membrane filters using Zeeman
mercury analyzer RA–915+ which eliminate the sample prepara-
tion step thereby sharply reducing the risk of contamination. The
LOD for the determination of Hg in water was 0.4 ng L−1 much lower
than 200 ng L−1 achieved by cold vapour generation technique. The
results of this study clearly show the potential of this method which
could be applied to monitor Hg in water with trace levels of Hg.
Furthermore, water samples can be sampled directly to the impreg-
nated filters from water bodies thereby minimizing contamination
during transport and storage.
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