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Review of Preconcentration and Solid Phase Extraction for the
determination of trace lead
Ali MOGHIMI* Department of Chemistry, Varamin(Pishva) Branch
Islamic Azad University, Varamin, Iran * Corresponding author. e-
mail: [email protected]
Abstract Spectrometric techniques for the analysis of trace lead
have developed rapidly due to the increasing need for accurate
measurements at extremely low levels of this element in diverse
matrices. This review covers separation and preconcentration
procedures, and consider the features of the their application with
several spectrometric techniques. The use of an appropriate sample
handling technique is a must in an analysis of trace lead in water.
The efforts to use a solid phase for the recovery of analytes from
a water matrix prior to their detection have a long history. The
initial experimental applications of SPE resulted in widespread use
of this technique in current water analysis and also to adoption of
SPE into standardized analytical methods. Lead is recognized
worldwide as a poisonous metal. Thus, the determination of this
element is often required in environmental, biological, food and
geological samples. However, these analyses are difficult because
such samples contain relatively low concentrations of lead, which
fall below the detection limit of conventional analytical
techniques such as flame atomic absorption spectrometry and
inductively coupled plasma optical emission spectrometry. Several
preconcentration procedures to determine lead have therefore been
devised, involving separation techniques such as liquidliquid
extraction, solid phase extraction, coprecipitation and cloud point
extraction. review of preconcentration procedures for determining
lead using spectroanalytical techniques. A brief overview of the
history of the use of SPE in trace lead analysis of water is given
in presented paper.
Keywords : Reviews; Solid-phase extraction; Preconcentration;
Water analysis; Trace lead
Contents 1. Introduction 2. The age of technical developments in
trace lead analysis 3. Present status the modern age of solid-phase
extraction in trace lead analysis 4. Conclusions References
1. Introduction Despite the selectivity and sensitivity of
analytical techniques such as atomic absorption spectrometry, there
is a crucial need for the preconcentration of trace lead before
their analysis due to their frequent low concentrations in numerous
samples (especially water samples). Additionally, since high levels
of non-toxic components usually accompany analytes, a clean-up step
is often required. Liquidliquid extraction is a classical method
for preconcentrating metal ions andyor matrix removal. Solid phase
extraction (SPE) is another approach that offers a number of
important benefits. It reduces solvent usage and exposure, disposal
costs and extraction time for sample preparation. Consequently, in
recent years SPE has been successfully used for the separation and
sensitive determination of metal ions, mainly in water samples.
After outlining the theory of this technique, guidelines are given
for the development of SPE-based methods for preconcentration of
many trace lead. Finally, examples of applications are presented.
From the analytical tools above listed, FAAS presents low costs,
operational facility and high sample throughput. The determination
of cadmium by flame atomic spectrometry is free of interference and
this can be easily atomized in air-acetylene flame. In the
resonance line 228 nm, the characteristic concentration is 0.02 mg
L1. The analytical line at 326.1 nm is suitable for determining
higher Cd
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concentrations and the characteristic concentration is about 6mg
L1, so that excessive dilution can be avoided [15]. Cadmium can be
determined by CV AAS where atomic Cd vapor is measured by AAS in an
unheated quartz cell. LOD of 80 ng L1 was obtained which can be
further improved by working at low temperature. The sensitivity can
be increased collecting the atomic Cd vapor in a graphite tube
pre-treated with palladium at 150 C and then reatomizing at 1600 C
[14]. Cold vapor generation coupled to atomic absorption
spectrometry with flow injection (FI-CV AAS) was evaluated as a
rapid and simple method for the determination of cadmium [16]. The
determination of cadmium by ETAAS was, for a long period,
difficulty because the cadmium is an element with high volatility
[17]. The principle of SPE is similar to that of liquid liquid
extraction (LLE), involving a partitioning of solutes between two
phases. However, instead of two immiscible liquid phases, as in
LLE, SPE involves partitioning between a liquid (sample matrix) and
a solid (sorbent) phase. This sample treatment technique enables
the concentration and purification of analytes from solution by
sorption on a solid sorbent. The basic approach involves passing
the liquid sample through a column, a cartridge, a tube or a disk
containing an adsorbent that retains the analytes. After all of the
sample has been passed through the sorbent, retained analytes are
subsequently recovered upon elution with an appropriate solvent.
The first experimental applications of SPE started fifty years ago
[1,2,3]. However, numerous studies have also shown the great
potential of this technique for speciation studies.[18,161-177]
1.1. Basic principles An SPE method always consists of three to
four successive steps, as illustrated in Fig. 1. First, the solid
sorbent should be conditioned using an appropriate solvent,
followed by the same solvent as the sample solvent. This step is
crucial, as it enables the wetting of the packing material and the
solvation of the functional groups. In addition, it removes
possible impurities initially contained in the sorbent or the
packaging. Also, this step removes the air present in the column
and fills the void volume with solvent. The nature of the
conditioning solvent depends on the nature of the solid sorbent.
Typically, for reversed phase sorbent (such as octadecyl-bonded
silica), methanol is frequently used, followed with water or
aqueous buffer whose pH and ionic strength are similar to that of
the sample. Care must be taken not to allow the solid sorbent to
dry between the conditioning and the sample treatment steps,
otherwise the analytes will not be efficiently retained and poor
recoveries will be obtained. If the sorbent dries for more than
several minutes, it must be reconditioned. The second step is the
percolation of the sample through the solid sorbent. Depending on
the system used, volumes can range from 1 ml to 1 l. The sample may
be applied to the column by gravity, pumping, aspirated by vacuum
or by an automated system. The sample flow-rate through the sorbent
should be low enough to enable efficient retention of the analytes,
and high enough to avoid excessive duration. During this step, the
analytes are concentrated on the sorbent. Even though matrix
components may also be retained by the solid sorbent, some of them
pass through, thus enabling some purification (matrix separation)
of the sample. The third step (which is optional) may be the
washing of the solid sorbent with an appropriate solvent, having a
low elution strength, to eliminate matrix components that have been
retained by the solid sorbent, without displacing the analytes.
Fig. 1. SPE operation steps.
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A drying step may also be advisable, especially for aqueous
matrices, to remove traces of water from the solid sorbent. This
will eliminate the presence of water in the final extract, which,
in some cases, may hinder the subsequent concentration of the
extract andyor the analysis. The final step consists in the elution
of the analytes of interest by an appropriate solvent, without
removing retained matrix components. The solvent volume should be
adjusted so that quantitative recovery of the analytes is achieved
with subsequent low dilution. In addition, the flow-rate should be
correctly adjusted to ensure efficient elution. It is often
recommended that the solvent volume be fractionated into two
aliquots, and before the elution to let the solvent soak the solid
sorbent. 1.2. Retention of trace lead on the sorbent Adsorption of
trace lead on the solid sorbent is required for preconcentration
(see Fig. 2). The mechanism of retention depends on the nature of
the sorbent, and may include simple adsorption, chelation or
ion-exchange. Also, for trace lead, ion-pair solid phase extraction
may be used. 1.2.1. Adsorption. Trace lead are usually adsorbed on
solid phases through van der Waals forces or hydrophobic
interaction. Hydrophobic interaction occurs when the solid sorbent
is highly non-polar (reversed phase). The most common sorbent of
this type is octadecyl-bonded silica (C18 -silica). More recently,
reversed polymeric phases have appeared, especially the
styrene-divinylbenzene copolymer that provides additional pp
interaction when p-electrons are present in the analyte w4x.
Elution is usually performed with organic solvents, such as
methanol or acetonitrile. Such interactions are usually preferred
with online systems, as they are not too strong and thus they can
be rapidly disrupted. However, because most trace element species
are ionic, they will not be retained by such sorbents. 1.2.2.
Chelation. Several functional group atoms are capable of chelating
trace lead. The atoms most frequently used are nitrogen (e.g. N
present in amines, azo groups, amides, nitriles), oxygen (e.g. O
present in carboxylic, hydroxyl, phenolic, ether, carbonyl,
phosphoryl groups) and sulfur (e.g. S present in thiols,
thiocarbamates, thioethers). The nature of the functional group
will give an idea of the selectivity of the ligand towards trace
lead. In practice, inorganic cations may be divided into 3 groups:
group I-hard cations: these preferentially react via electrostatic
interactions (due to a gain in entropy caused by changes in
orientation of hydration water molecules); this group includes
alkaline and alkaline-earth metals (Ca2+ , Mg2+ , Na+ ) that form
rather weak outer-sphere complexes with only hard oxygen ligands.
group II-borderline cations: these have an intermediate character;
this group contains Fe , Co2+ Ni2+ Cu2+ Zn2+ Pb2+ Mn2+ . They
possess affinity for both hard and soft ligands. group III-soft
cations: these tend to form covalent bonds. Hence, Cd2+ and Hg2+
possess strong affinity for intermediate (N) and soft (S) ligands.
For soft metals, the following order of donor atom affinity is
observed: 0-N-S. A reversed order is observed for hard cations. For
a bidentate ligand, affinity for a soft metal increases with the
overall softness of the donor atoms: (0, 0)-(0, N)-(N, N)-(N, S).
The order is reversed for hard metals. In general, the competition
for a given ligand essentially involves Group I and Group II metals
for O sites, and metals of Group II and Group III for N and S
sites. The competition between metals of Group I and Group III is
weak. Chelating agents may be directly added to the sample for
chelating trace lead, the chelates being further retained on an
appropriate sorbent. An alternative is to introduce the functional
chelating group into the sorbent. For that purpose, three different
means are available: (1) the synthesis of new sorbents containing
such groups (new sorbents); (2) the chemical bonding of such groups
on existing sorbents (functionalized sorbents); and (3) the
physical binding of the groups on the sorbent by impregnating the
solid matrix with a solution containing the chelating ligand
(impregnated, coated or loaded sorbents). The latter remains the
most simple to be used in practice. Its main drawback is the
possible flush of the chelating agent out of the solid sorbent
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during sample percolation or elution that reduces the lifetime
of the impregnated sorbent. Different ligands immobilized on a
variety of solid matrices have been successfully used for the
preconcentration, separation and determination of trace metal ions.
Chelating agents with an hydrophobic group are retained on
hydrophobic sorbents (such as C18 -silica). Similarly, ion-exchange
resins are treated with chelating agents containing an ionexchange
group, such as a sulfonic acid derivative of dithizone (i.e.
diphenylthiocarbazone) (DzS), 5-sulfo-8-quinolinol,
5-sulfosalicylic acid, thiosalicylic acid, chromotropic acid, or
carboxyphenylporphyrin (TCPP) [58]. Binding of metal ions to the
chelate functionality is dependent on several factors: (1) nature,
charge and size of the metal ion; (2) nature of the donor atoms
present in the ligand; (3) buffering conditions which favor certain
metal extraction and binding to active donor or groups; and (4)
nature of the solid support (e.g. degree of cross-linkage for a
polymer). In some cases, the behavior of immobilized chelating
sorbents towards metal preconcentration may be predicted using the
known values of the formation constants of the metals with the
investigated chelating agent [9]. However, the presence of the
solid sorbent may also have an effect and lead to the formation of
a complex with a different stoichiometry than the one observed in a
homogeneous reaction [10,11]. In fact, several characteristics of
the sorbent should be taken into account, namely the number of
active groups available in the resin phase [7,10], the length of
the spacer arm between the resin and the bound ligand [12], and the
pore dimensions of the resin [13].
Fig. 2. Interactions occurring at the surface of the solid
sorbent. F, functional group; TE, trace element; MS, matrix
solvent; MI, matrix ions; ES, elution solvent.
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2. Lead determination 2.1. Atomic absorption spectrometry (AAS)
The determination of lead by flame atomic absorption spectrometry
(FAAS) is practically free of interference and requires an
airacetylene flame [13]. The interference caused by aluminum and
iron can be overcome by the addition of ascorbic acid, citric acid
and EDTA [13]. The threshold of sensitivity of this technique is
very low (LOD 0.01 mg L1) and is often unsuitable for trace
analysis [13]. In this sense, many preconcentration procedures must
be performed to determine trace amounts of lead, as indicated in
the tables shown here. The most important analytical lines of lead
are 217.00 and 283.31 nm. The 217.00 nm line is more sensitive,
notwithstanding the greater amount of background absorption effects
[13]. Electrothermal atomic absorption spectrometry (ETAAS) is a
good alternative for determining trace amounts of lead in several
types of samples in view of its good sensitivity [13]. However, in
some cases, previous preconcentration and separation steps are
carried out before analytical measurements by ETAAS. The use of a
modifier stabilizes lead, allowing for its determination without
causing matrix effects. The PdMg modifier is the one most commonly
used, since it produces the best results. This modifier allows for
the application of pyrolysis temperatures ranging from 1200 to 1400
C, which enables the separation of most interfering elements
[1317]. The stabilizing effect of this modifier also raises the
atomization temperature to 2000 C, which allows a characteristic
mass of about 16 pg [13]. Ammonium phosphate is another modifier
frequently used for determining lead by ETAAS, allowing for an
atomization temperature of 1600 C and enabling a low characteristic
mass of 12 pg [13,18].
2.2. Inductively coupled plasma optical emission spectrometry
(ICP OES) Inductively coupled plasma optical emission spectrometry
is an analytical technique often employed to determine lead in
various types of samples [19]. The main emission lines are: Pb II
220.353 nm, Pb I 216.999 nm and Pb I 283.306 nm, with 220.353 nm
being the most sensitive. However, the low level of lead in many
samples lies below the detection limit of this technique. Moreover,
several types of spectral interference have been reported in the
determination of lead by ICP OES. Virtually all
photomultiplier-based ICP spectrometers use the Pb 220.353 nm
analytical line, despite its severe background continuum and
inter-element interference from Al 220.4 nm and background shift
due to iron (Fe). Direct spectral overlap interference due to iron
has also been found in the 216.9 and 283.9 nm analytical lines
[20,21]. Thus, preconcentration and separation procedures have been
devised to allow trace amounts of lead to be determined in complex
matrices using ICP OES. Several tables shown in this paper
summarize the use of separation techniques such as liquidliquid
extraction, solid phase extraction, cloud point extraction and
others, as pre-steps in determining lead using ICP OES.
3. Lead separation and preconcentration Separation techniques
such as coprecipitation [23,50], liquidliquid extraction [5760],
solid phase extraction [69134] and more recently, cloud point
extraction [139146,150] and on-line coprecipitation using a knotted
reactor [150160] have been successfully employed to determine trace
levels of lead. Each technique has its pros and cons and should be
chosen according to the analytical problem.
3.1. Coprecipitation
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Coprecipitation is one of the most efficient separation/
enrichment techniques for trace heavy metal ions. The main
requirement for this technique is that the collector should
separate easily from the matrix solution. This can be done by
filtering, centrifuging and washing of the precipitate. In
addition, it is desirable that the collector should be a pure and
readily available substance. The advantages of this technique are
its simplicity and the fact that various analyte ions can be
preconcentrated and separated simultaneously from the matrix.
Inorganic or organic coprecipitants have been used as efficient
collectors of trace elements. However, this process is slow and
samples sometimes have to be kept over-night for complete
coprecipitation [22]. This technique has been widely applied in
preconcentration procedures for determining lead inwater samples.
Inorganic coprecipitants such as manganese dioxide and aluminum,
gallium, cerium(IV), erbium, iron(III), magnesium, samarium and
zirconium hydroxides have been widely and successfully used for
preconcentrating trace lead ions from different mediums [23,50]. A
fast procedure for separation and preconcentration using
ultrasound-assisted coprecipitation with manganese dioxide has
recently been proposed for determining lead in environmental
samples by ICP OES [18]. Coprecipitation parameters, including
concentration of oxidizing agentKMnO4, concentration of MnSO4 and
exposure time to ultrasound irradiation, are discussed. The time
required for coprecipitation is about 60 s. Another paper proposed
an aluminum hydroxide coprecipitation method for the determination
of trace amounts of Cu, Cd and Pb by FAAS in seawater and mineral
water after a 125-fold preconcentration [19]. Table 1 lists several
methods for determining lead in many samples, using coprecipitation
as the separation and preconcentration technique
3.2. Liquidliquid extraction Solvent extraction has been one of
the most extensively studied and widely applied methods in
preconcentration and separation procedures for the determination of
trace elements due to its simplicity, convenience, wide scope, etc.
In this technique, the metal is distributed between two immiscible
liquid phases (usually an aqueous and an organic phase). Metal ion
stripping from aqueous solution to organic phase takes place after
a complexation reaction. For the analytical measurement, the
extracted metal ion can be directly measured in organic extract or
a backextraction step is carried out in an aqueous medium, usually
acid [5153]. Separation and preconcentration procedures using
solvent extraction generally result in a high enrichment factor due
to the difference between the volumes of aqueous and organic
phases. Although this procedure is operated in batch mode, it is
time-consuming and produces large amounts of potentially toxic
organic solvents as waste. The implementation of methods in
continuous mode overcomes these drawbacks. Such unit operations
are, instead, carried out in flow injection (FI) and/or sequential
injection (SI) systems, which, besides reducing sample and reagent
consumption, allow all manipulations to be done automatically in an
enclosed environment, thus minimizing the risk of sample
contamination. Analytical procedures for lead separation and
preconcentration by solvent extraction and determination by atomic
spectrometric techniques have been widely applied since these
techniques were invented [54].
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Table 1 Preconcentration procedures using coprecipitation for
the determination of lead
Table 2 Procedures for lead preconcentration based on solvent
extraction
Procedures in flow injection systems for separation and
preconcentration with the application of solvent extraction to
determine metals, including lead, are extensively discussed in the
literature [55,56]. Table 2 lists several analytical systems
proposed for lead separation and preconcentration by solvent
extraction and lead determination using atomic spectrometric
techniques.
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3.3. Solid phase extraction Solid phase extraction is based on
the partition between a liquid (sample matrix) and a solid phase
(sorbent). Several sorbents coupled to detection systems have been
used for lead preconcentration and determination. The basic
approach is the contact of a liquid sample through a column, a
flask, a cartridge, a tube or a disk containing an adsorbent that
retains lead ions. After this first step, the retained lead is
recovered upon elution with an appropriate solvent [68]. Sorbents
used in preconcentration systems for lead determination can be
unloaded, loaded or chemically modified with the help of complexing
reagents. Unloaded supports are potential collectors of analytes in
the form of a single ion or associated with other species such as
complexes. The sorbents in this class include activated carbon
[69], natural adsorbents [70], Amberlite XAD resins [7175],
polyethylene [76] and others [77]. Lead can also be complexed with
ligands loaded in several supports, such as polyurethane foam
[7880], activated carbon [81] and polymeric materials [8284], which
make for efficient preconcentration procedures. Many reagents have
been used to load these supports and to retain lead ions by
complexation. These include: 2-(2_-thiazolylazo)-pcresol (TAC)
[85], 2-propylpiperidine-1-carbodithioate [86],
2-(2-benzothiazolylazo)-2-p-cresol (BTAC) [80,87], pyrogallol red
[81], 1-(2-pyridylazo)-2-naphthol (PAN) [88], dithizone [89,90] and
2-(5-bromo-2-pyridylazo)-5-diethyl-aminophenol (5-Br-PADAP) [91].
Supports can also be functionalized with chelating reagents, which
render them powerful absorbents for lead preconcentration. Supports
such as Amberlite XAD series [92,93], silica gel [9496] and
cellulose [97,84] have been modified with reagents by several
routes. Several methods have been proposed for preconcentrating
lead using the solid phase batch extraction procedure (Table
3).
3.4. Automation and possible on-line coupling toanalysis
techniques SPE can be easily automated, and several commercially
available systems have been recently reviewed [123]. Home-made
systems have also been reported [124]. In addition, all the sample
volume is further analyzed, which enables smaller sample volume to
be used. However, in the case of complex samples, off-line SPE
should be preferred due to its greater flexibility, and the
opportunity to analyze the same extract using various
techniques.
3.4.1. On-line coupling to liquid chromatography. On-line
systems mainly use a micro-column. The sorbent is chosen not only
for its efficiency in trapping analytes, but also for its
compatibility with the stationary phase packed into the
chromatographic column. Indeed, it is highly recommended to use the
same packing in the precolumn and the chromatographic column to
prevent losses in efficacy upon analysis. For the case of two
different sorbents being used, the retention of the analytes in the
precolumn should be lower than in the analytical column to ensure
band refocusing at the head of the chromatographic column. On-line
systems with several detectors have been reported, such as
ultraviolet (UV) detector or inductively coupled plasma mass
spectrometer (ICP MS), with detection limits in the 0.0550 mgyl
range. Detection limits as low as 0.5 ngyl could even be achieved
by detection at the maximum absorption wavelength using a
photodiode array UV detector [125].
3.4.2. On-line coupling to atomic absorption
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spectrometry. Olsen et al. [126] and Fang et al .[127,128] were
the first to describe an on-line flowinjection (FI) sorbent
extraction preconcentration system for flame AAS (F-AAS) using
microcolumns packed with a cation-exchanger. Later, they also
proposed a system for on-line flowinjection sorbent extraction
preconcentration with electrothermal vaporization AAS (ET-AAS)
using lead as a model trace element[129]. Since then, numerous
papers reported FI with on-line preconcentration followed by AAS,
as exemplified by determination of Pb [129]. Selected applications
are reported in Table 4. The sorbent should provide for rapid
sorption and desorption of the analytes to be used in FI systems
[130]. In addition, it should be provided for a high selectivity.
In practice, C18-silica is very frequently used as organic solvents
(such as methanol) can be used as eluting solvents leading to a
high sensitivity in flame AAS. Complexing reagents are, therefore,
added for efficient retention of trace metals. Their choice is
based on their fast reaction with metals, such as
diethyldithiocarbamate (DDTC) and ammonium pyrrolidine
dithiocarbamate (APDC) [131,132]. In addition, both reagents are
water soluble and do not adsorb on C18-silica so that it does not
overload with the reagent itself. However, these reagents lack
selectivity, so that other reagents have been used for particular
applications, like 1-10-phenanthroline [135s],
0,0-diethyl-dithiophosphate (DDTP) [134]. The micro column can be
inserted into the tip of the PTFE capillary in the autosampler arm
of a graphite furnace atomic absorption spectrometer [131]. Even
though C18-silica has been the most frequently used sorbent for FI
preconcentration, other sorbents were found satisfactory for some
applications as shown in Table 4, such as functionalized activated
carbon [134], polyurethane foam (PUF) [134], or PTFE turnings
[133]. A particular knotted reactor (KR) has been recently
developed, which consists of a long tube properly knotted usually
made of PTFE.
3.4.3. On-line coupling to ICPAES or ICP MS. The first report of
FI on-line preconcentration coupled to ICP-atomic emission
spectrometry (AES) appeared nearly twenty years ago [130]. Since
then, several studies have used this coupling with different
sorbents such as ZrO2 or functionalized silica gel for example
[136].
3.4.4. On-line coupling to spectrophotometry. Spectrophotometry
offers the advantage of requiring inexpensive and very common
instrumentation. In addition, by choosing a non-selective
chromogenic reagent, multi-metal determinations may be
possible[123]. Its coupling to FI analysis is well suited for
monitoring purposes and a few studies present such systems as
indicated in Table 4 [123]. Solid-phase spectrophotometry (SPS) has
also been reported with FI systems due to its simplicity and low
detection limits. The solid sorbent is packed in either
commercially available or customized flow cells. On-line FI sorbent
extraction procedures have several advantages over the
corresponding off-line methods: higher sample throughput (increased
by 1 to 2 orders of magnitude), lower consumption of sample and
reagent (also reduced by 1 to 2 orders of magnitude), better
precision (with relative standard deviations approx. 12%), lower
risk of loss or contamination and easy automation.
3.5. Cloud point extraction (CPE) The cloud point phenomenon
occurs when a nonionic or amphoteric surfactant above its critical
micellar concentration (CMC) causes the separation of the original
solution into two phases when heated at a characteristic
temperature called cloud point temperature. Above the cloud point,
micelles formed from surfactant molecules act as an organic solvent
in liquidliquid
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extraction and the analytes are partitioned between the micellar
and aqueous phases [135137]. Thus, metallic elements can be
extracted to a surfactant-rich phase, trapped in the hydrophobic
micellar core, in the form of hydrophobic complexes that are formed
between the metal ion and an appropriate chelating agent under
adequate conditions. An evaluation of the partition coefficients of
ligands and complexes involved is, therefore,
Table 3 Off-line procedures for lead preconcentration using
solid phase extraction
Table 4
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Applications of SPE to FI on-line preconcentration systems
Table 5 CPE applications for lead preconcentration and
determination
TAN: 1-(2-Thiazolylazo)-2-naphthol; Br-PADAP:
2-(5-bromo-2-pyridylazo)-5-(diethylamino)-phenol; DDTP:
O,O-diethyldithiophosphate
Table 6 Separation and preconcentration of lead using knotted
reactors.
a
ng L1.
Matrix Sorbent Eluent Analysis method Recovery% Preconcentration
factor
LOD(ng/l) Ref.
Certified biological, vegetable samples
C18-silica IBMK F-AAS 99.2101% 60189 3000 [132]
Standard solutions
C18-silica EtOH F-AAS -- 41000 3003000 [134]
Standard solutions
C18-silica MeOH F-AAS -- 1460 4000-10000 [130]
Tap, river and coastalwaters, marine sediment, fish and mussel
tissues
PTFE turnings
IBMK F-AAS 95102 330 800 [133]
Standard solutions
PUF EtOH F-AAS -- 41000 3003000 [134]
River, ground waters
Lewatit TP80784 PAPhA
HCl Spectrophotometry 80120 50 2000-5500 [123]
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Surfactant solutions provide a medium that modifies the reaction
ratio, equilibrium position and spectral and analytical parameters.
However, the micellar phase obtained after a CPE has physical and
chemical characteristics that must be taken into account in the
development of an analytical procedure. Borges et al. [140], for
example, determined lead by preconcentration in a micellar phase of
Triton X-114 and determination by ETAAS using Ir and Ru as
permanent modifiers. This enabled them to reach a higher pyrolysis
temperature and thus, eliminate the surfactant matrix before the
atomization step without risk of analyte loss, as well as to avoid
high background absorption. Table 5 shows some recent CPE
applications for lead determination and some analytical
characteristics.
4. Conclusions Considering the poisonous nature of lead and the
low concentration of this element in samples, preconcentration
procedures have been devised involving separation techniques such
as liquidliquid extraction, solid phase extraction, coprecipitation
and cloud point extraction. Nevertheless, each technique has its
pros and cons and should therefore be chosen according to the
analytical problem. Most of the proposed methods were established
using solid phase extraction. In recent years, on-line systems have
been preferred.
Acknowledgements The author gratefully acknowledge department of
chemistry, Varamin(Pishva) branch Islamic Azad University,
Varamin.
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