Gravitational field-flow fractionation in combination with flow injection analysis or electrothermal AAS for size based iron speciation of particles

A simple gravitational field-flow fractionation (GrFFF) system was used for size separation of micron sized silica particles coated with hydrous iron oxide (geothite). The amount of iron on the particles was monitored either on-line by reverse-flow injection analysis (r-FIA) with chemiluminescence detection using luminol or off-line by electrothermal atomic absorption spectrophotometry (ETAAS). The combination of GrFFF with reverse FIA or with ETAAS has been demonstrated to be a cost-effective tool for size based iron speciation of particles.     

Development of an SdFFF–ETAAS hyphenated technique for dimensional and elemental characterization of colloids

Direct hyphenation of electrothermal atomic-absorption spectroscopy (ETAAS) to sedimentation field-flow fractionation (SdFFF) has been developed to enable elemental characterization of submicron particles as a function of size. This hyphenation is particularly suitable for characterizing colloidal particles of environmental interest, for example water-borne particles. The interface is an automatic capillary injection device (CID) which enables direct introduction of large and variable volumes of colloidal particle suspensions into a hot graphite furnace, thus preconcentrating the colloidal particles on the furnace walls. The method was validated by determination of Fe in certified submicron Fe₂O₃. The procedure was set up by first optimizing the SdFFF fractionation under programmed field conditions, thus enabling optimum fractionation of particle size. The ETAAS procedure was then tested to determine whether it could be used for direct analysis of Fe₂O₃ slurries without the need for a mineralization step. CID coupled to ETAAS was subsequently exploited for its ability to enhance the sensitivity, because of the increased injection volume. Statistical tests and data handling were conducted to prove the suitability of the ETAAS-CID module. Finally, off-line and on-line ETAAS-CID-SdFFF hyphenation were investigated. These experiments emphasized the advantages of the on-line coupling, because it enables synchronized sampling, enrichment, and elemental analysis of the flowing eluate. The benefits of the proposed hyphenation are the high specificity of analytical detection, increased sensitivity, reduction of analysis time, and minimum sample handling and contamination.      

Development of a new microelectrolysis system for in-situ electrodeposition of ultra-traces of gold prior to measurement by ETAAS

Electrodeposition is known to be suitable for separation and preconcentration of extremely low concentrations of analyte from bulk samples and is instrumentally is very simple. In this approach a new combined system was designed for in-situ electrodeposition of ultratrace levels of gold from micro samples on to a graphite furnace prior to determination by electrothermal atomic absorption spectrometry (ETAAS). Sediment samples were digested and traces of the gold content were extracted with boiling aqua regia. To prevent the highly corrosive effect of aqua regia media, the graphite tube surface was pre-coated by electrodeposition of ppm amounts of Pd prior to sample introduction. Separation of the analyte from the matrix was achieved by electrodeposition of the analyte in situ on the Pd/C surface of the furnace tube. Vanadium was also used as a modifier to stabilize the analyte from decomposition at charring temperatures. By using the proposed microelectrolysis preconcentration technique a considerable improvement in sensitivity and detection limit was achieved compared with conventional ETAAS. Characteristic masses for ED-ETAAS techniques in both nitric acid and aqua regia were reported to be m(o)=4.1 pg, with %RSD=2.9; the calculated LOD was 0.105 ppb, and typical calibration graphs for this element in nitric acid and aqua regia for both techniques were linear up to 70 microg L(-1) with about 99% recovery. Six reference sediments samples were tested by the proposed technique and by the Conv-ETAAS method. The results were in agreement with recommended values (reported by a reference laboratory using UV-visible spectrometry), demonstrating the efficiency of extraction and preconcentration of ultratrace levels of gold.     

Coulter particle analysis used for studying the effect of sample treatment in slurry sampling electrothermal atomic absorption spectrometry

This work focuses on the potential of using a Coulter particle analyzer for method development in slurry sampling ETAAS. Plant materials were used as an example; the particle size distributions obtained after grinding in a mixer mill were measured for ground material and slurries prepared from flowers, leaves, stem and roots of the same plant material. Normally the particle size distribution is reported either as number of particles versus size or volume of particles versus size. The advantage of using the latter mode of reporting is demonstrated. It is shown that detailed information about the larger particles is lost when the distribution is reported in terms of the number-percentage. In the present case, 60 min of grinding gave similar size distribution for all the plant materials. All particles had diameters less than 50 μm and the calculated number of particles per mg was 6–8 × 10⁷. It is shown that the ultrasonic agitation used to homogenize the slurries, prior to injection of the sample, also had an effect on the particle size distribution.     

Concentration and characterization of dilute colloidal samples by potential-barrier field-flow fractionation

Summary Potential-barrier field-flow fractionation, which is a combination of potential-barrier chromatography and sedimentation field-flow fractionation, is shown to be a convenient and accurate method for the concentration and analysis (separation and characterization) ofdilute colloidal samples. Two sizes (0.158 and 0.271 μm) of haematite (α-Fe₂O₃) monodisperse colloidal samples diluted in volumes of up to 20 cm³ are used as model colloids. The particle diameters found by the present concentration procedure under various experimental conditions are in good agreement with those determined by conventional sedimentation field-flow fractionation, in which a small concentrated sample volume was injected directly into the column.     

场流分级的机内浓缩和再进样方法

<正> 除制备色谱外,一般色谱和场流分级的进样量都是很小的,而溶质层在经过色谱柱或场流分级柱槽后由于分离以及加宽效应浓度又要大大降低,因此,所得级分中溶质的含量极少。如需把所得级分做再进样,则必须在同一条件下重复收集同一集分,经浓缩后再进     

Coulter particle analysis used for studying the effect of sample treatment in slurry sampling electrothermal atomic absorption spectrometry

This work focuses on the potential of using a Coulter particle analyzer for method development in slurry sampling ETAAS. Plant materials were used as an example; the particle size distributions obtained after grinding in a mixer mill were measured for ground material and slurries prepared from flowers, leaves, stem and roots of the same plant material. Normally the particle size distribution is reported either as number of particles versus size or volume of particles versus size. The advantage of using the latter mode of reporting is demonstrated. It is shown that detailed information about the larger particles is lost when the distribution is reported in terms of the number-percentage. In the present case, 60 min of grinding gave similar size distribution for all the plant materials. All particles had diameters less than 50 μm and the calculated number of particles per mg was 6–8 × 10⁷. It is shown that the ultrasonic agitation used to homogenize the slurries, prior to injection of the sample, also had an effect on the particle size distribution. Received: 16 February 1998 / Revised: 20 July 1998 / Accepted: 26 July 1998     

On the effect of thermophoretic force,gravitational force,and particle–particle interactions in field-flow fractionation

The theoretical calculations confirmed that the gravitational force cannot be neglected in all field-flow fractionation techniques separating nanometer-sized colloidal particles whenever particle diameter is approximately 200?nm and larger. Particle–particle repulsive interactions, mostly electrostatic repulsions, influence substantially concentration distribution established by any effective field acting across the fractionation channel, as confirmed explicitly for thermophoretic force generated by temperature gradient in microthermal field-flow fractionation. The ionic strength of the carrier liquid causes the screening of the electrostatic double layer around the dispersed particles and thus influences the retention. The attractive particle–particle forces occur when the zeta potential of the particles approaches to 0?mV, the electrostatic repulsions are screened, and the aggregation of the particles is observed. The pH influences differently the size and zeta potential of the plain polystyrene latex particles and of the particles modified on the surface by the groups –COOH and –NH₂. The role of a detergent in carrier liquid is non-negligible, as demonstrated by its presence or absence in carrier liquid.     

Determination of particle size distribution by gravitational field-flow fractionation: Dimensional characterization of silica particles

Summary Gravitational field-flow fractionation (GFFF) is the simplest and cheapest of field-flow fractionation (FFF) techniques, although it is still at an early development stage. The application of GFFF to the determination of particle size distribution (PSD) of silica particles used as chromatographic supports is described. The accuracy of the method is evaluated by comparing PSDs obtained by GFFF with those obtained by laser diffraction, a non-separative technique widely applied to particle characterization. It is ultimately demonstrated that a low-cost GFFF channel can simply replace the column of a standard HPLC system, allowing laboratories that are not specialized in size analysis to perform accurate PSD studies with standard HPLC expertise.     

Characterization of particle size and size distribution of multi-sized polymer lattices by centrifugation plus quasielastic light scattering

 A method for characterizing the particle size and size distribution of multi-sized polymer lattices was developed by combining quasielastic light scattering (QELS) with a centrifuge. Lattices were first fractionated by centrifugation and the different populations of particles were separated in successive steps. The size of these particles was measured by QELS, and the mass fraction of the particles was determined gravimetrically. The particle size and size distribution of several blends of monodisperse lattices and two industrial multi-sized lattices have been measured by this method. The results show that the particle sizes obtained using this method are in good agreement with the expected particle diameters, and that the relative amounts of the different groups of particles in the blends can be accurately determined. The efficiency of centrifuge-QELS was also confirmed by comparison with other techniques such as transmission electron microscopy (TEM), QELS, field-flow fractionation (FFF) and capillary hydrodynamic fractionation (CHDF). However, this method is not suited for the analysis of continuous, broad distributions or mixtures with a high number of different populations. It is better suited for distributions with a small number of families of particles, and then can be used for preparative propose on a laboratory scale. Received: 9 October 1996 Accepted: 7 July 1997     

A quantitative approach to the analysis of supermicron dispersions by field-flow fractionation with UV-vis detectors. The application of an absolute method

Summary Quantitative analysis in field-flow fractionation is becoming a necessary requirement for routine applications, instrumental optimization and scale-up to preparative separations. The use of detection systems which show complex dependence on sample characteristics (i.e. UV spectrometry) has hindered the application of quantitative methods of analysis in field-flow fractionation. A standardless model, shown valid in flow-through, homogeneous systems, is applied here to a heterogeneous system (dispersed supermicron particles) in field-flow fractionation by single peak area measurements. Absolute analysis in the fractionation of spherical silica particles for high-performance liquid chromatography column packing by gravitational field-flow fractionation with UV-Vis detectors is presented. It has been shown that for such samples extinction coefficients are independent of sample concentration and are determined by the size and density of the particles. The accuracy of such an approach to absolute analysis is discussed. In memory of J. C. Giddings Presented at FFF'95-Fifth International Symposium on Field-Flow Fractionation, Park City, UT, USA, July 10–12 1995.     

Characterization of Diamond Nanoparticles by High-Speed Micro-Thermal Field-Flow Fractionation

Micro-thermal field-flow fractionation was used to characterize the particle size distribution of nanometer-sized diamond nanoparticles. Although the experimental conditions were chosen to perform high-speed separation, and, consequently, the resolution achieved experimentally was not very high, the application of the original correction method for the zone spreading allowed for obtaining of very good calculated particle size distribution or, explicitly, a true polydispersity index of the diamond nanoparticle sample. The future use of several samples of diamond nanoparticles of different average sizes and different surface chemistries should allow deeper insight into the effect of these particulate characteristics on the retention in micro-thermal field-flow fractionation.     

Newly designed flow field-flow fractionation channel for macromolecules and particles in the submicrometer and micrometer range

The flow field-flow fractionation (FIFFF) technique is a promising method for separating and analysing particles and large size macromolecules from a few nanometers to approximately 50 μm. A new fractionation channel is described featuring well defined flow conditions even for low channel heights with convenient assembling and operations features. The application of the new flow field-flow fractionation channel is proved by the analysis of pigments and other small particles of technical interest in the submicrometer range. The experimental results including multimodal size distributions are presented and discussed.     

Hollow-fiber flow/hyperlayer field-flow fractionation for the size characterization of airborne particle fractions obtained by SPLITT fractionation

Hollow-fiber flow field-flow fractionation (HF FlFFF) was applied for the separation and size characterization of airborne particles which were collected in a municipal area and prefractionated into four different-diameter intervals >5.0, 2.5-5.0, 1.5-2.5, <1.5 microm) by continuous split-flow thin (SPLIIT) fractionation. Experiments demonstrated the possibility of utilizing a hollow-fiber module for the high-performance separation of supramicron-sized airborne particles at steric/hyperlayer operating mode of HF FlFFF. Eluting particles during HF FlFFF separation were collected at short time intervals (approximately 10 s) for the microscopic examination. It showed that particle size and size distributions of all SPLITT fractions of airborne particles can be readily obtained using a calibration and that HF FlFFF can be utilized for the size confirmation of the sorted particle fraction during SPLITT fractionation.     

Standardless method for quantitative particle-size distribution studies by gravitational field-flow fractionation. Application to silica particles

Summary Gravitational field-flow fractionation is a separative analytical technique which has already proved suitable for quantitative particle-size distribution analysis. One of the most attractive aspects of the technique is that it can allow for direct conversion of fractograms into size distributions of the samples, although retention exhibits substantial dependence on flow rate, compared to other field-flow fractionation methods. It is shown here that conversion of fractograms into quantitative, size-distribution profiles of micron-sized silica particles is possible through gravitational field-flow fractionation in standardless mode. Standardless means that the conversion of fractograms is performed by single-run analysis because all the parameters necessary for the calculations can be obtained, from sample specifications and previous instrumental calibration, by means of semiempirical models. Work partially presented at FFF’98-7^th International Symposium on Field-Flow Fractionation, Salt Lake City, Utah (USA), February 8–11, 1998     

Newly designed flow field-flow fractionation channel for macromolecules and particles in the submicrometer and micrometer range

The flow field-flow fractionation (FIFFF) technique is a promising method for separating and analysing particles and large size macromolecules from a few nanometers to approximately 50 μm. A new fractionation channel is described featuring well defined flow conditions even for low channel heights with convenient assembling and operations features. The application of the new flow field-flow fractionation channel is proved by the analysis of pigments and other small particles of technical interest in the submicrometer range. The experimental results including multimodal size distributions are presented and discussed.     

Characterisation of River Po particles by sedimentation field-flow fractionation coupled to GFAAS and ICP-MS

A procedure for elemental composition determination of water-borne river particles (Po River) on both size-fractionated and unfractionated submicron particles (0.1–1 μm) by graphite furnace atomic absorption spectroscopy (GFAAS) and inductively coupled plasma-mass spectrometry (ICP-MS) is reported. Sample fractionation was performed using sedimentation field-flow fractionation (SdFFF). The distribution of relative mass vs. particle size was determined using UV detection. Fractions were collected over a narrow size range for scanning electron microscopy. With this combination of techniques the mass, elemental composition, and shape distributions can be obtained across the size spectrum of the sample.

The size distributions of the major elements (Al, Fe) were determined by coupling both GFAAS and ICP-MS techniques to the SdFFF. The procedure was validated using a reference clay sample. Satisfactory agreement was found between both the GFAAS and ICP-MS aluminium signal and the UV detector signal. Some discrepancies were observed in the Fe/Al ratios when comparing GFAAS and ICP-MS. Thus further investigation is in order to fully assess the role of SdFFF-ICP-MS and SdFFF-GFAAS techniques for elemental characterisation of aquatic colloids. Both GFAAS and ICP-MS signals unambiguously indicate a significantly higher Fe content in the lower size range, which is consistent with previous investigations.

Trace element levels in unfractionated Po River particles, determined by both GFAAS and ICP-MS, show good agreement. The high levels of Cu, Pb, Cr and Cd found associated with the colloidal particles underlines the significance of the environmental role played by the suspended matter in rivers in both highly industrialised and intensively cultivated areas.     

重力场流分离系统中载液及流速条件对分离的影响

重力场流分离作为最简单的一种场流分离技术,常用于分离微米级颗粒。选择两种不同粒径(20 μ m和6 μ m)的聚苯乙烯(PS)颗粒作为样品,通过改变载液中叠氮化钠浓度、混合表面活性剂的比例及载液流速,利用自行设计生产的重力场流分离(gravitational flow field-flow fractionation, GrFFF)仪器,对颗粒混合样品进行分离,得到了相关谱图与数据,考察了这3种因素对分离效果(保留比(R)、塔板高度(H))的影响。结果表明:20 μ m PS颗粒的R值均大于6 μ m PS颗粒的R值,H值均小于6 μ m颗粒的H值;PS颗粒的R值与H值均随着载液中叠氮化钠浓度的增加而增加;但随着载液流速的增加,R值增加,H值减小。该研究为GrFFF系统的开发及应用提供了重要的参考价值。     

Gravitational field-flow fractionation for the characterisation of active dry wine yeast.

Gravitational field-flow fractionation (GrFFF) is applied to the fractionation of active dry wine yeast. An experimental approach to the analysis of the effects that field variation by changing mobile phase composition and flow-rate have on the fractionation process of standard particles (polystyrene) was first developed to further obtain effective fractionation of wine yeast by GrFFF. Scanning electron microscopy and Coulter counter particle size measurements were used to monitor the fractionation extent and capabilities of GrFFF to describe the distribution of yeast cells populations.     

Laser-induced breakdown detection combined with asymmetrical flow field-flow fractionation: application to iron oxi/hydroxide colloid characterization

The combination of asymmetrical flow field-flow fractionation (AsFlFFF) with the laser-induced breakdown detection (LIBD) is presented as a powerful tool for the determination of colloid size distribution at trace particle concentrations. Detection limits (D1) of 1, 4, and 20 microg/L have been determined for a mixture of polystyrene reference particles with 20, 50, and 100 nm in size, respectively. This corresponds to injected masses of 1, 4, and 20 pg, which is lower than found in a previous study with the symmetrical FlFFF (SyFlFFF). The improvement is mainly due to the lower colloid background discharged from the AsFlFFF channel. The combined method of AsFlFFF-LIBD is then applied to the analysis of iron oxi/hydroxide colloids being considered as potential carriers for the radionuclide migration from a nuclear waste repository. Our LIBD arrangement is less sensitive for iron colloid detection as compared to reference polystyrene particles which results in a detection limit of approximately 240 microg/L FeOOH for the AsFlFFF-LIBD analysis. This is superior to the detection via UV-Vis absorbance and comparable to ICP-MS detection. Size information (mean size 11-18 nm) for different iron oxi/hydroxide colloids supplied by the present method is comparable to that obtained by sequential ultrafiltration and dynamic light scattering. A combined on-line ICP-MS detection is used to gain insight into the colloid-borne main and trace elements.