ROZDZIAŁ 20a SEPARATION AND ELEMENTAL CHARACTERIZATION

OF WATER BORN PARTICLES

Gabriella Blo, Catia Contado, Chiara Conato, Francesco Dondi Department of Chemistry, University of Ferrara

Via L. Borsari 46 – 44100 Ferrara, Italy

ABSTRACT The study on the metal load in the Po River of suspended particulate matter, as a function of particle size, is presented. A strategy of hyphenation of separation methods - Field Flow Fractionation (FFF) techniques and Split-Flow Thin (SPLITT) cells – with elemental characterization by spectroscopic techniques, permits the separation, at both analytical and preparative scale, of a complex colloidal system in the liquid phase and their metal load characterization. 1. WATER BORN PARTICLES: GEOCHEMICAL AND ENVIRONMENTAL RELEVANCE

The dispersed solid phase is a very important component of the natural body of water, most chemical reactions occurring in natural water take place at the solid-solution interface. The suspended solid phase consists predominantly of inorganic colloids, such as clays, metal oxides, metal hydroxides and metal carbonates, and of organic matter of detrital origin, as well as living microorganisms.

The importance of suspended particulate matter (SPM) in pollutant transport in rivers is widely reported in environmental literature [1-8] and its role in metal speciation in natural waters is well known. Pollutants transport depends on the characteristics of the particles, especially their nature, composition and size, which define the particle adsorption and physico-chemical properties. In particular it has been suggested that surface composition and size play a fundamental role in defining their pollutant uptake and aggregation properties. In fact, in rivers the behavior of SPM depends on particle dimensions. Two main fractions can be distinguished in the SPM phase in aquatic systems: i) the particulate fraction (diameter > 1 µm) which quite quickly settles and transports metals to the sediments, and ii) the colloidal fraction (diameter < 1 µm - IUPAC) which remains suspended longer and may facilitate the transport of adsorbed species over appreciable distances. Water colloids include small inorganic particles (e.g. clays, oxides, metals), organic particles (e.g. particulate organic carbon, soot, polymers), organic macromolecules as e.g. macromolecules/polymers, humic acids and proteins and biological entities such as viruses and bacteria. The colloidal fraction of SPM has been targeted because of its large specific surface area and hence high potential for the adsorption of organic contaminants and trace metal ions. Some interesting studies have been recently performed regarding the heavy metal distribution among different dimensional SPM fractions [9,10].Although these colloidal particles do not settle in river systems, under suitable agglomerate size and flow velocity they can aggregate and then settle to the bottom. It is thus most important to distinguish between dissolved species and pollutants associated with colloidal and particulate phases of SPM.

Increasing attention is devoted to the SPM behavior in pollutant transport as a function of particle dimension. In particular, since environmental/natural colloids are

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ubiquitous and can show strong interaction with pollutants, there is an increasing concern about the role of colloids (e.g. clays, oxides, organic macromolecules, bacteria) in the transport, fate and bio-availability of virtually all known pollutants. The behaviour of colloidal or particulate bound pollutants is governed by far different parameters than established for truly dissolved pollutants. Since the research on the mobility, formation, degradation, behaviour and general contribution of those natural nanophases to transport processes and the role for contaminant bio-availability is still in its infancy, recent models for the long-term behaviour of pollutants in the subsurface and freshwater systems may fail in the long run or pollutant impact may be overestimated.

The authors investigations are directed to the study of trace heavy metal uptake by colloidal matter in the Po River. Such investigations can not prescind from a comparison with the so-called “zero level” (i.e. natural metal content in SPM) necessary to understand the entity of the anthropic contribute to SPM metal load and to assess the actual pollution status of the Po River [9].

2. ANALYTICAL GENERAL STRATEGY Classical methods of analysis of colloids are either destructive, time consuming, expensive or strongly affect the integrity of the sample. Methods originating from polymer, particle and separation science are often used but poorly adapted to environmental samples.

For the investigation of colloid impact on bio-availability, eco-toxicology and environmental processes, for quantification and model development suitable analytical methods are a key issue. A crucial issue is the size separation and subsequent analysis of size intervals to gain knowledge about the distribution of pollutants across the different potential carriers.

It appears that the new frontier in colloidal world characterization is to make an intelligent synergism between separation techniques and detection development, i.e. by using the well established strategy of hyphenation, which was so winning in the case of chromatography and electrophoresis.

Separation methods were firmly established in the past thirty years - the Field Flow Fractionation (FFF) techniques and the Split-Flow Thin (SPLITT) cells - being able to separate at both analytical and preparative scale, complex colloidal systems in the liquid phase.

The study of metal distribution among different size fractions of SPM is performed by following the analytical procedure schematically represented in Figure 1.

Since the concentration of SPM in the river system is quite low, large volumes of river water (10-50 L) have to be collected in order to have enough SPM on which to perform the analyses.

The sampling step is then followed by a filtration procedure which remove the largest particles (greater than 20-25 µm). During this phase, colloidal particles could be lost because of their aggregation with the biggest particles.

After the largest particles have been removed, ultrafiltration is used to concentrate SPM in the 0.2 – 20 µm diameter size range.

SPLITT cell separation technique is successively employed to fractionate the SPM slurry into two different size fractions. Besides, the SdFFF technique is utilised for sizing and separating colloidal matter into different size fractions.

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Fig. 1. Analytical strategy employed for separation and elemental characterization of fresh water suspended matter.

Information about the effective size of the obtained particle fractions can be

obtained by examination with scanning electron microscope (SEM), while EDAX analysis can be used to identify individual particles and X-ray diffraction to identify their mineralogy. Moreover, elemental composition of the separated fractions and so the heavy metal load, on each selected size dimension range, is obtained by means of spectroscopic techniques, such as AAS, ICP-AES or ICP-MS.

The single steps of this analysis are illustrated in the following paragraphs. The applications of this strategy are reported in the Examples section. 3. SPM CONCENTRATION METHOD

The analysis of a real sample of river SPM generally consists of a separation of suspended material by 0.45 µm filtration, followed by grinding and/or digestion and then spectroscopic elemental determinations. However, there are limitations to this procedure. The colloidal fraction, defined as any organic and inorganic entity within the 1 nm – 1 µm size range, is partially included in the dissolved phase (< 0.45 µm) and not individually characterized. This oversight, plus destructive handling procedures, causes a loss of information regarding the natural colloids which, because of their high reactivity, constitute the most interesting part of the suspended particulate.

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Many problems have been identified with filtration. The pore size may not be precise, clogging and aggregation leads to changes in the effective size during the operation and irreversible retention on the membrane can lead to significant sample loss [11]. Moreover, using membrane filtration, a number of factors can lead to variations in metal concentration in the dissolved phase [12,13]. It is usually difficult to process more than a few hundred millilitres of sample with conventional filtration even when pressure or a vacuum is employed.

In an attempt to minimise the effect of clogging and irreversible sample loss, tangential flow filtration systems were introduced where the water is pumped across the membrane surface with only a small fraction of the water flow being drawn through the filter [14,15]. The water sample is recirculated through the system until the desired degree of filtration and SPM concentration is achieved. Despite the substantial improvement in sample throughput achieved with TFF, it is not without its anomalies. For example membrane rejection of dissolved cations increases during SPM concentration [16].

As represented in Figure 1 and previously written, the authors’ procedure consists of the following: water is filtered on Whatmann 541 filter paper (nominal pore size 20-25 µm) and the filtrate is concentrated by tangential filtration through a 0.2 µm Durapore membrane filter in a Minitan Apparatus (Millipore Co., Bedford, MA). A concentrated slurry is so obtained, in the size range 0.2 – 20 µm [17-20].

The Minitan apparatus is a soft concentration system in that it does not stress sample particles and therefore does not suffer from any serious problems of particle coagulation and pore occlusion, producing artefacts peculiar to classic filtering. 4. PREPARATIVE FRACTIONATION OF WATER BORN PARTICLES: SPLITT CELL PRINCIPLES AND MODES.

Split-flow thin (SPLITT) fractionation is a new family of separation techniques. SPLITT channels are ribbonlike, unpacked, thin flow channels with splitters at the outlet or both inlet and outlet. The inlet splitter allows smooth merging of two inlet flows, and the outlet splitter allows smooth collection of fractionated samples into different outlets without remixing.

Figure 2 shows the scheme of a gravitational SPLITT cell device used for micronic particles and operated in the conventional way (CSF). The channel thickness is defined by the combined thickness of two spacers made of Mylar and one made of stainless steel sheet. These are used to define the effective channel and to form the splitter elements. All these components are sandwiched between two pieces of glass which serve as the upper and lower wall of the channel. Two Plexiglas blocks bolt the assorted previous layers together – two sheet of Teflon are inserted between the Plexiglas and the glass blocks to prevent the glass blocks from breaking.

The SPLITT utilizes the lateral separation or enrichment directly. The separation is generated by taking advantage of the different distributions of different particles across the thinner dimension of the cell. The different particles components, each contained in its own flow stratum, are then divided by one or more flow splitters at the end of the cell and collected in different outlet substreams. One of the most relevant advantages offered by this separation system is to use an open channel, virtually uncloggable by complex material.

Inlet b’

Inlet a’ Outlet a

Outlet bCarrier solution

reservoir(optional in FFD)

Sample suspension reservoir A + B

Fraction collection

a

b

Pump B’

SPLITT cell

Field

Pump A’

Inlet b’

Inlet a’ Outlet a

Outlet bCarrier solution

reservoir(optional in FFD)

Sample suspension reservoir A + B

Fraction collection

a

b

Pump B’Pump B’

SPLITT cell

Field

Pump A’Pump A’

Fig. 2. SPLITT cell operative system.

The theory of the SPLITT cell is well described in a number of publications [21-

23], therefore, for the sake of brevity, only some aspects of theory are reported, here. The suspended natural particles are extremely heterogeneous in chemical

composition (density) and shape, but even when irregular in shape, the particles can likened to a sphere so that their dimension can be described in terms of some specific diameter [19].

Separation occurs with respect to this real or agreed diameter. The nominal cut-off diameter dc is established by setting the volumetric flow rate )(aV& at the upper outlet, through which the smallest (lightest) particles exit, and the flow rate )'(aV& , with which the sample is introduced inside the channel:

[ ]

ρη

ρη

∆∆

=∆

−=

bLGV

bLGaVaVdc

&&& 18)'(5.0)(18 (1)

where b and L are respectively the breadth and the length of the cell, G the gravity acceleration, ∆ρ the difference between sample and carrier densities and η the carrier viscosity.

With different operating procedures it is possible to vary the particle migration mode. The two most common modes for continuous separations are: transport mode and equilibrium mode.

In the transport mode of operation, different kind of particles generally have the same final equilibrium distributions (or at least seriously overlapping distributions) across the channel but advantage is taken of the unequal rate of approaching the equilibrium distributions after the particles are released into the cell from the splitter region.

In the equilibrium mode a sufficient time elapses for the species to be driven to each side of an outlet splitting plane then separation will be complete, the species exiting via opposite outlet streams. This operation mode therefore strictly requires an outlet splitter only.

An alternative separation procedure to the conventional CSF is the Full Feed Depletion fractionation, for which a single cell inlet is used.

The FFD mode has some advantages over the conventional mode. First of all the flow in the cell is hydrodynamically stable, so a relatively high feed concentration can be applied. Secondly the particle suspensions are not further diluted, thus eliminating the inconvenience of re-concentrating the separated particles. Thirdly, the throughput

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system is increased. Fourthly all the experimental apparatus is simpler: only one pump is used, only a single inlet flow need to be adjusted.

The experimental parameters used for measuring the separation efficiency are the retrieval factors Fa and Fb, which measure the mass fractional recovery of the analyte exiting outlet a or b. The analyte retrieval factor, Fa at outlet A is generically defined as [24]

ba

aa MM

MF+

= (2)

where Ma and Mb are the mass amounts of sample exiting outlet a or b, respectively, at a given particle size. Fa is thus the quantile of the mass distribution corresponding to the value of dc.

Theoretically, one should have Fa+Fb=1, but in practice, one has

Fa + Fb + Fw =1 (3) where Fw is the particle fraction lost inside the SPLITT cell along the accumulation wall and/or extra column connections.

The resolution of SF is proportional to the ratio between the two inlet flow rates

for sample introduced at inlet a’ ( )( )'

'aVbVR

&

&∝ (4)

and can be expressed as

01

1

sssR−

= (5)

where s1 and s0 are the sedimentation coefficient for retrievals equal to 1 and 0, respectively.

Resolution can be improved by finite, particle size effects, the influence of hydrodynamic lift forces, and transport effects in the splitter region. 5. FIELD FLOW FRACTIONATION (FFF) TECHNIQUES

Field-Flow Fractionation is able to fractionate colloids/particles between 1nm and 100µm. Fractionation depends on particle properties like diffusion coefficient, size, density and others. Apart from its similar layout, it has to be clearly distinguished from separation methods like chromatography where separation mostly is related to chemical properties of the analytes. Due to the absence of a stationary phase the method is gentle and has a much wider operational size range compared to size exclusion chromatography. Depending on the detectors applied (on-line or off-line), characteristics of the colloids/particles can be determined with an outstanding size-resolution.

SdFFF is a set of high resolution liquid chromatography-like elution methods used for sizing and separating colloidal matter into size fractions. SdFFF separations are performed within a flat open channel, usually having a rectangular cross-section and triangular end pieces where the sample and carrier fluid enters and leaves. SdFFF has excellent resolution but can only process small quantities (<1 mg) of sample in a single run [25-30].

The mechanism for particle separation involves only physical interactions [27]. The sample is introduced into the channel through a septum or injection valve, and then

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the flow is turned off. A centrifugal field is then applied at right angles to the flat face of the ribbon-like channel. This flat channel sits within a centrifuge basket and the centrifugal field drives the particles towards the accumulation wall. There, they form equilibrium clouds whose average thickness or elevation (l) above the accumulation wall depends on how strongly the particles interact with the field and also their diffusivity [25-27,29] (see Figure 3).

Data acquisitioneluent

pump detector

Fraction collectorSdFFF channel

control

Channel details

flow

field

components

Accumulation wall

Data acquisitioneluent

pump detector

Fraction collectorSdFFF channel

control

eluenteluent

pumppump detector

Fraction collectorSdFFF channel

control

Channel details

flow

field

components

Accumulation wall

Channel details

flow

field

components

Channel details

flow

field

components

Accumulation wall

Fig. 3. Schematic diagram of the SdFFF instrumentation and section of the channel, illustrating the laminar parabolic flow profile and sample “clouds” separation mechanism.

When the carrier liquid flow is turned on at the end of the stop flow (relaxation)

period, the run begins. The carrier flow in the thin flat channel is laminar with the linear fluid velocity being zero at the channel walls and increasing with distance away from each wall, thus approaching a maximum at the centre of the channel. The particles with a larger effective mass will have more compressed sample clouds (i.e. a smaller l) and will consequently be swept down the channel by the flow at a lower average velocity than the smaller particles. In this normal mode of SdFFF the smallest particles will elute first [28].

The retention ratio R, for a constant field normal mode FFF run is obtained from the measured elution volume Vr and channel void volume V0 according to the expression:

−== λ

λλ 2

21coth6

VrVoR (6)

where λ is the ratio between l, the cloud thickness, and w the channel thickness and is termed the retention parameter. The force F exerted on an analyte by the external field is related to λ by

FwkT

=λ (7)

where k is Boltzmann’s constant and T absolute temperature.

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In Sedimentation FFF the analyte is under a centrifugal force rmF e

2ω= (8) where me is the buoyant mass, ω the angular rotation frequency and r the radius of curvature of the rotor. By insertion of the centrifugal force into equation (7) we obtain

rwmkT

e2ω

λ = (9)

For a colloidal sphere of diameter d, the volume of the sphere is πd3/6. Since m is the product of particle volume and particle density, the equivalent spherical particle diameter, d, can be calculated from λ provided the density difference between the particle and the carrier liquid ∆ρ is known. The expression used is

ρωπλ

∆=

rwdkT23

6 (10)

For samples which contain a broad size distribution the field decay program strategy of Williams and Giddings can be used [31,32]. This program uses an initial constant centrifugal field for a period t1, after which the centrifugal field decays according to the power equation:

( )p

a

a

ttttStS

−−

= 10 (11)

where ta is a constant that controls the rate of decay and t is the run time. This enables the smaller particles to be adequately resolved from the void peak utilizing the higher field strength period while avoiding excessively long retention times for the larger particles. The run can be optimised to achieve a desired level of resolving power across the size range if suitable values of wo, t1, ta and flow rate are used [28]. 6. DETECTION SYSTEMS: AAS, ICP (COUPLING OFF-LINE AND ON-LINE) Distribution of the number of particles, total mass, specific element content etc. as a function of the particle size, provides useful information to characterize the river SPM sample.

SdFFF can be combined with specific detection system to produce what are called hyphenated instruments. Spectroscopic techniques—e.g. Absorption Atomic Spectroscopy (AAS) and Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES and ICP-MS)— are the ideal candidates for compositional investigations and so to obtain the various distribution mentioned above. Coupling of fractionation systems and spectroscopic techniques in SPM characterization is an analytical approach able to provide interesting results, supporting environmental studies on the behavior of metals in natural waters; this is particularly true if the entire procedure is applied under quantitative controls.

UV detection has long been employed for determining the relative amount of mass in separated fractions. However, it is well known that the UV signal gives only approximate estimates because light attenuation is also dependent on shape, size, and the optical properties of the particles. Exact mass calibration of the UV detector is possible only for well-characterised homogeneous samples, whose optical constants are known.

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Regarding the coupling with spectroscopic techniques, the authors have suggested the coupling of both the Sedimentation Field-Flow Fractionation (SdFFF) and the SPLITT cell techniques with the AAS techniques, for a dimensional and elemental characterization of natural particle samples in the particulate and in the colloidal range [18,33]. GFAAS was employed as detection system for SdFFF, because the high temperature of graphite furnace introduction system is able to completely atomise the particulate sample (slurry introduction, [34]), avoiding in such a way the complex and lengthy sample digestion steps. The advantage of this detection system is the wide availability of GFAAS and the possibility of performing repeated analyses on the same fractions, thus improving the response accuracy. The combination of the high SdFFF fractionation power with the sensitivity of the specific AAS detector has shown very interesting quantification performances. This analytical approach can really become an adequate methodology for direct natural slurry particle sample analysis, it has in fact provided that the slurry sampling is accurate and the atomization efficiency in electrothermal atomizer (ETA) is quantitative [20]. The slurry AAS analysis has been so validated in the colloidal range (i.e. the operative range of SdFFF).

Moreover, the evaluation of the effects of particle dimension was made by the authors, on the coupled SPLITT-AAS technique, which permits extension of the dimensional and the elemental characterization to a broader size range (up to 10 µm). The technique has been applied to a real sample of SPM from the Po River, where trace elements of environmental interest have been determined for the whole fraction in the dimensional range 0.2 - 25 µm, and for some sub-fractions obtained by SPLITT fractionation. In general, element values of global and fractionated samples are with each other consistent since the formers lie within the range of the latter [20]. The SPLITT cell coupling with the direct slurry ETAAS identification, has shown to be a reliable method for SPM size-elemental characterization of both the submicronic and micronic fractions. The present approach can thus be applied in both geological end environmental study and monitoring.

Inductively coupled plasma-mass spectrometry is a useful detection system because of its unique capabilities for simultaneous determination of many elements which may be used to compute the molar ratio of elements [28,35-38].

ICP-AES application has permitted evaluation in a simple manner of the metal balance for SPLITT fractionation [20]. The ICP-AES technique coupled with SPLITT fractionation, perform accurate determinations in colloidal SPM fraction (φ <1-2 µm), of greater environmental interest, while the ICP-AES analysis of the higher fractions (φ > 2 µm ) and of the total SPM slurry can be invalidated by bias, because of an incomplete atomization and an analyte transport efficiency into plasma. The suggested SPLITT/ICP-AES procedure permit a reduction in both analysis time and sample size to levels which are acceptable for routine applications. Moreover, direct hyphenation of the SF technique to the pertinent spectroscopic technique is also conceivable. This solution appears simpler, cheaper and more economic in terms of instrumentation cost and gas consumption.

Both SdFFF-ICPMS and SdFFF-GFAAS procedures were utilized to analyse a reference standard of kaolin and a sample of the Po River colloidal matter [18]. The results obtained by the two systems were compared also with results obtained on the same digested samples, assessing so the atomisation efficiency of the two methods. The elemental analysis, both by ICP-MS and GFAAS, performed on the fractionated Po River colloidal sample, has permitted the reporting of elemental size distribution for the detected metals (i.e. the metal concentration as a function of the particle spherical

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diameter) and to understand the mineralogical composition of the submicronic fraction, as a function of the particle size (see examples section).

The illustrated hyphenated techniques have been, till now, employed off-line. Some work has been done in coupling on-line SdFFF with ICP-MS [28,37,38]. Recently, a first approach to on-line coupling of SdFFF with ICP-AES has been undertaken [unpublished results].

PUMP

FLOW UV Detector

Fractioncollector

ICP

SdFFF/SPLITT

off-line coupling

on-line coupling

PUMPPUMP

FLOW UV DetectorUV Detector

FractioncollectorFractioncollector

ICPICP

SdFFF/SPLITT

off-line coupling

on-line coupling

Fig. 4. Block diagram of fractionation instrumentation coupled with ICP determination. Dotted line represents off-line coupling. 7. EXAMPLES The performances of two modes of SPLITT cell operation (SF and FFDSF) have been discussed [19], using a polydisperse silica sample. This sample was chosen because of its physical-chemical similarity to the particles contained in natural river sample (alumino-silicate and silica particles). This study shows the capacity of FFDSF mode to give resolution and quantitative cut-offs without dilution effects. This SPLITT operation mode was so applied to a River Po SPM sample, concentrated following the procedure described in section 3, choosing particle diameter of 1 µm as cut-off. The so separated fraction < 1 µm was then subjected to an SdFFF fractionation and each fraction content was checked with SEM (Scanning Electron Microscopy). The efficiency of FFDSF pre-separation in handling an environmental sample prior to SdFFF characterization was in this study confirmed.

A procedure for elemental composition determination of water-born Po river particles on both size-fractionated and unfractionated submicron particles (0.1 – 1 µm) by GFAAS and ICP-MS is reported in ref. 18. Sample fractionation was performed using SdFFF and the distribution of relative mass as a function of particle size was determined using UV detection. Fractions were collected over a narrow size range for SEM. With the combination of these techniques, the mass, elemental composition and shape distributions were obtained across the size spectrum of the sample.

The size distribution of the major element (Al, Fe) was determined by coupling both GFAAS and ICP-MS techniques to SdFFF and the procedure was validated using a reference clay sample.

Trace metal content on unfractionated Po river samples was determined both by GFAAS and ICP-MS, showing a good agreement between the obtained results. The data

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are reported in Tab. I, with metal concentrations in some natural systems as a comparison [from ref. 18].

This study has demonstrated that SdFFF can be directly interfaced with GFAAS to produce element composition data across the size distribution of colloidal samples, as was already demonstrated for the coupling with ICP-MS [28,36]. Both GFAAS and ICP-MS are ideal qualitative and quantitative element detectors for the SdFFF system. Table 1. Metal concentrations in natural systems (data are reported in ppm).

Metal Determination in Po River SPM

GFAAS ICPMS

Max. metal content accepted

in irrigation watera(µg/L)

Natural background

metal content in soilsa (µg/g)

Max. metal content accepted

in irrigation agricultural

soilsb

Al 287000 258000

Fe 55000 62500

Mg 35000 41700

Cu 600 580 1000 – 1750 2 – 6 100

Pb 500 510 750 – 1200- 0.1 – 150 100

Cr 400 460 5 – 100 53

Cd 3 2.3 20 - 40 < 0.5 3 aEEC directive, 1986 bItalian Minister of Agriculture Directive, 1984.

The application of SPLITT cell for the separation of particulate matter of environmental interest has been investigated [39] and the effects of the particle porosity, dimension, shape and density have been considered, by studying suspensions of porous silica, kaolin and montmorillonite in the submicron to micron diameter range. Major critical aspects of SPLITT operation stem from the shape of the separated particles, their porosity and shrinking or swelling within the employed carrier. The three typologies of particles employed in this study have different properties and the data presented show that SPLITT cell operation can be coherently interpreted, if pertinent expression is employed. SPLITT separations results were compared with classical static sedimentation procedure and the agreement obtained between the two techniques was generally satisfactory.

An analytical methodology for characterizing natural water SPM, by using the coupling between the SPLITT cell separation and elemental ETAAS (Electrothermal Absorption Atomic Spectroscopy) identification, has been presented by the authors [20]. Validation of the direct slurry elemental analysis are there reported for Al and Fe determination in clay - like particle materials, considered as representative models of the real SPM, showing that results are accurate in the particle size range up to 25 µm. The evaluation of the coupled SPLITT-ETAAS technique is then considered for the dimensional and elemental characterization of the same samples.

The developed procedure was applied to a real sample of SPM from the Po river, where trace elements of environmental interest were determined for the whole fraction

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in the dimensional range 0.2 - 25 µm, and for some sub-fractions obtained by SPLITT fractionation.

In order to evaluate the particle size effects on the ETAAS slurry analysis, a fractionation procedure by SPLITT cell was employed and each obtained fraction was analysed both as a slurry and digest sample by ETAAS. It was observed that, in general, element values of global and fractionated samples are consistent with each other . Some drawbacks in the SPLITT cell application for real SPM sample have been focused by the authors. However, for FFDSF mode, the only drawback comes from the residual quantity retained inside the cell at the end of the fractionation. Since this amount can be recovered, it does not affect the mass balance results both in term of size and elemental composition.

The quantitative aspects of the analytical procedure described previously (for the single steps see section 2. analytical strategy) for the trace element characterization of SPM are reported in ref. 17. SPLITT cell fractionation into different micronic-submicronic dimensional ranges have been coupled with ICP-AES elemental determination on both the separated fractions and the bulk phase. The investigation was performed on a Po river SPM sample. Quantitative aspects of the tangential flow filtration step recovery and of the CSF and FFDSF modes were investigated in terms of total mass balance, proving that only the FFDSF mode is currently satisfactory for quantitative purposes. Mass balance for some elements of environmental interest was performed using ICP-AES over the FFDSF SPM fractions, proving that the employed analytical procedure is consistent and useful in the investigation of trace element distribution in different SPM dimensional ranges vs. that of the bulk phase. BIBLIOGRAPHY [1.] Beckett R., in The Role of Particulate Matter in the Transport and Fate of Pollutants, B.T.Hart

(ed.), Water Studies Centre, Chisholm Institute of Technology, Melbourne, Australia, 1986. [2.] Salomons W. and Forstner U., Metals in the Hydrocyle, Springer-Verlag (ed.), Berlin, 1984. [3.] Stumm W., Chemistry of the Solid-Water Interface, Wiley (ed.), New York, 1992 [4.] Eisma D., Suspended matter in the Aquatic Environment, Springer-Verlag (ed.), Berlin, 1993. [5.] Millward G.E., Analyst, 120, 609 (1995). [6.] Muller B. and Sigg L., Aquat. Sci., 52, 75 (1990). [7.] Sung W., Environ. Sci.Technol., 29, 1303 (1995). [8.] Luoma S.N. and Davis J.A., Mar. Chem., 12, 159 (1983). [9.] Blo G., Conato C., Contado C., Fagioli F. and Dondi F., submitted to Annali di Chimica, Rome. [10.] C. Contado, G. Blo, C. Conato, F. Dondi and R. Beckett, submitted to J. Environ. Monitor. [11.] Droppo I.G., Krishnappan B.G., Rao S.S., Ongley E.D., Environ. Sci. Technol., 29, 546 (1995). [12.] Horowitz A.J., Lum K.R., Garbarino J.R., Hall Gem, Lemieux C. and Demas C.R., Water Air Soil

Poll., 90, 281 (1996). [13.] Horowitz A.J., Lum K.R., Garbarino J.R., Hall Gem, Lemieux C. and Demas C.R., Environ. Sci.

Technol., 30, 954 (1996). [14.] Horowitz A.J.,. Elrick K.A and Hooper R.C., Hydrol. Process, 2, 163 (1988). [15.] Buffle J., Perret D. and Newman M., Environ. Part., 1, 171 (1992). [16.] Douglas G.B., Beckett R. and Hart T.B., Hydrol. Process, 7, 17 (1993). [17.] Blo G., Contado C., Grandi D., Fagioli F. and Dondi F., Anal. Chim. Acta, 470, 253 (2002). [18.] Contado C., Blo G., Fagioli F., Dondi F. and Beckett R., Colloid Surface A, 120, 47 (1997). [19.] Contado C., Dondi F., Beckett R. and Giddings J.C., Anal. Chim. Acta, 345, 99 (1997). [20.] Blo G., Contado C., Fagioli F., and Dondi F., Analyst, 125, 1335 (2000). [21.] Giddings J. C., Sep. Sci. Technol., 20, 749 (1985).

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[22.] Giddings J.C., Chemical Separation, in: J.D. Navratil, C.J. King (eds), vol. I, Litavran, Denver, 1986, 3.

[23.] Levin S. and Giddings J.C., J. Chem. Tech. Biotechnol., 50, 43 (1991). [24.] C.B. Fuh, S. Levin, L.C. Giddings, Anal Biochem. 1993, 208, 80-87. [25.] Beckett R., Hotchin D.M. and Hart B.T., J. Chromatogr., 517, 435 (1990). [26.] Beckett R., Nicholson G., Hotchin D.M. and Hart B.T., Hydrobiologia, 235/236, 697 (1992). [27.] Beckett R. and Hart B.T., Environmental Particles, vol. 2, Lewis Publishers, 1993, 165. [28.] Murphy D.M., Garbarino J.R., Taylor H.E., Hart B.T. and Beckett R., J. Chromatogr., 642, 459

(1993). [29.] Giddings J.C., Chem. Eng. News, 66, 34 (1988). [30.] Dondi F., Blo G. and Martin M., Annali di Chimica, 87, 113 (1997). [31.] Giddings J.C., Williams P.S. and Beckett R., Anal. Chem, 59, 28 (1987). [32.] Williams P.S. and Giddings J.C., Anal. Chem, 59, 2038 (1987). [33.] Blo G., Contado C., Fagioli F., Bollain Rodriguez M. H. and Dondi F., Chromatographia, 41

(11/12), 715 (1995). [34.] Hoening M., Regnier P. and Wollast R., J. Anal. Atom. Spectrom., 4, 631 (1989). [35.] Taylor H.E., Garbarino J.R., Murphy D.M. and Beckett R., Anal. Chem., 64, 2036 (1992). [36.] Brenner I.B. and Taylor H.E., Crit. Rev. Anal. Chem., 23(5), 335 (1992). [37.] Hassellov M., Lyven B. and Beckett R., Environ. Sci. Technol., 33, 4528 (1999). [38.] Hassellov M., Lyven B., Haraldsson C. and Sirinawin W., Anal. Chem., 71, 3497 (1999). [39.] Dondi F., Contado C., Blo G. and Garcia Martin S., Chromatographia, 48, 643 (1998).