Effects of nanoparticles on the ultrafiltration of surface water

The effects of nanoparticles on the fouling behavior of UF membranes were investigated by filtering river water containing natural organic matter (NOM). Self-dispersible carbon black (70–200 nm) was employed to model nanoparticles in natural water. The presence of nanoparticles transformed the mode of initial fouling from internal pore adsorption of NOM to intermediate pore blocking, which caused a significant flux reduction. The use of powdered activated carbon to adsorb organic micromolecules reduced internal pore fouling, but this effect on initial fouling mode did not much mitigate the overall flux decline. As filtration proceeded, cake filtration became the dominant fouling mode. The resistance-in-series model revealed that boundary-layer resistance contributed significantly to increased filtration resistance in the filtration of river water. The nanoparticles nullified boundary-layer resistance plausibly by removing organic macromolecules from river water, but aggravated cake resistance, which required chemical cleaning. Addition of calcium significantly increased the aggregate size of nanoparticles from 0.18–0.35 μm to 3.4 μm, and thus reduced pore blocking and total cake resistance.     

Preparation and application of zeolite/ceramic microfiltration membranes for treatment of oil contaminated water

NaA zeolite microfiltration (MF) membranes were prepared on α-Al₂O₃ tube by in situ hydrothermal synthesis method and investigated for water separation and recovery from oily water. NaA/α-Al₂O₃ MF membranes with average inter-particle pore sizes of 1.2 μm, 0.4 μm and 0.2 μm were prepared. The membranes were characterized by scanning electron microscope (SEM) and the inter-particle pore size distribution (PSD) was determined by gas bubble pressure method. Membranes with pore sizes of 1.2 μm (NaA1) and 0.4 μm (NaA2) were used to treat an oil-in-water emulsion containing 100 mg/L oil. Better than 99% oil rejection was obtained and water containing less than 1 mg/L oil was produced at 85 L m⁻² h⁻¹ by NaA1 at a membrane pressure of 50 kPa. Consistent membrane performance was maintained by a regeneration regime consisting of frequent backwash with hot water and alkali solution.     

Bare gold nanoparticles mediated surface-enhanced Raman spectroscopic determination and quantification of carboxylated single-walled carbon nanotubes

The paper proposes a simple and portable approach for the surface enhanced Raman scattering (SERS) spectroscopy in situ determination of carboxylated single walled carbon nanotubes (SWNTs) in river water samples. The method is based on the subsequent microfiltration of a bare gold nanoparticles solution and the water sample containing soluble carbon nanotubes by using a home-made filtration device with a small filtration diameter. An acetate cellulose membrane with a pore size of 0.2 μm first traps gold nanoparticles to form the SERS-active substrate and then concentrates the carbon nanotubes. The measured SERS intensity data were closely fit with a Langmuir isotherm. A portable Raman spectrometer was employed to measure SERS spectra, which enables in situ determination of SWNTs in river waters. The limit of detection was 10 μg L⁻¹. The precision, for a 10 mg L⁻¹ concentration of carbon nanotubes, is 1.19% intra-membrane and 10.5% inter-membrane.     

Carboxymethylation of corn starch and characterization using asymmetrical flow field-flow fractionation coupled with multiangle light scattering

Asymmetrical flow field-flow fractionation (AsFlFFF) was coupled online with multiangle light scattering (MALS) to study the changes in the molecular weight and the size distribution of the corn starch during carboxymethylation. A corn starch was derivatized with sodium chloroacetate in alcoholic medium under alkaline condition to produce carboxymethyl starches (CMS) having various degrees of substitution (DS). The change in thermal characteristics and granule structure of the native corn starch and CMS were compared using Thermogravimetric analysis and scanning electron microscope. The ionic strength of the carrier liquid (water with 0.02% NaN₃) was optimized by adding 50 mM NaNO₃ to minimize the interactions among the starch molecules and between the starch molecules and the AsFlFFF membrane. A field-programmed AsFlFFF allowed determination of the molecular weight distribution (MWD) of starches within about 25 min. It was found that carboxymethylation of starch results in reduction in the molecular weight due to molecular degradation by the alkaline treatment. The weight-average molecular weight (M_w) was reduced down to about 4.4 × 10⁵ from about 7.2 × 10⁶ when DS was 0.14. It seems AsFlFFF coupled with MALS (AsFlFFF/MALS) is a useful tool for monitoring the changes taking place in the molecular weight and the size of starch during derivatization.     

Size fractionation of aquatic colloids and particles by cross-flow filtration: analysis by scanning electron and atomic force microscopy

The suitability of the combined application of environmental scanning electron microscopy (ESEM), scanning electron microscopy (SEM) and atomic force microscopy (AFM) for the evaluation of the ability of cross-flow filtration (CFF) to perform adequate size fractionation of freshwater colloids and particles was examined. ESEM and SEM imaging provided reference images of the CFF-generated fractions and, in estimating the experimental cut-off diameter of the membrane, provided evidence that separation was not consistent with nominal pore sizes of the membranes. However, analysis of the images showed that size distribution of CFF-generated fractions and the estimated cut-off diameter of the membranes were dependent on the advantages and limitations of the two imaging techniques. With both ESEM and SEM, best estimates of size cut-offs were lower than the nominal pore size of the membrane in the case of 0.45 μm membranes, but roughly accurate in the case of 0.1 μm pore size membranes. The results also suggested that the effectiveness of CFF may benefit from a pre-separation step using a minimally perturbing technique such as split thin-flow fractionation. AFM demonstrated the presence of colloids smaller than 50 nm in all fractions including the retentates, showing that CFF fractionation is not fully quantitative and not based on size alone. The results indicate that previous studies investigating trace element partitioning using CFF may need re-evaluation as the importance of particles and large colloids may be over-estimated.     

Effect of poly(hydroxybutyrate-co-hydroxyhexanoate) microparticles on growth of murine fibroblast L929 cells

Poly(hydroxybutyrate-co-hydroxyhexanoate) (PHBHHx) microparticles were successfully prepared and their proliferative effects on cultured fibroblasts were studied. PHBHHx microparticles (0.005-0.1 g/L) promoted cell proliferation in murine fibroblast L929 and elevated intracellular calcium concentrations ([Ca²⁺]_i). EGTA (ethylene glycol-bis(2-aminoethylether)-N,N,N′,N′-tetraacetic acid) inhibited PHBHHx microparticle-induced cell proliferation by chelating the extracellular Ca²⁺ and blocking the PHBHHx particle-induced [Ca²⁺]_i increase. Transwell experiments demonstrated that PHBHHx microparticles stimulated fibroblast proliferation when separated from cells by a 0.4 μm filter as effectively as when applied directly to cells. Since PHBHHx microparticles had a diameter of 75 μm, the stimulatory effect of PHBHHx particles on cell growth was attributed to degradation products smaller than 0.4 μm in diameter. The trophic effect of these microparticles is consistent with our previous reports demonstrating good biocompatibility for PHBHHx.     

Microwave assisted synthesis of manganese mixed oxide nanostructures using plastic templates

The synthesis method for obtaining sub-micrometric structures of rare earth manganese-based mixed oxide compounds is described. Pore wetting of porous polycarbonate templates with the liquid precursor was followed by a two-stage thermal treatment to obtain single phase La_0.325Pr_0.300Ca_0.375MnO₃ hollow and solid structures, with external diameter determined by the sacrificial template pore size. The first thermal stage, a microwave assisted denitration process, determines the shape of the structures. The second treatment, performed at 1073 K, allows to obtain the crystallographic structure of the compound. A variety of techniques (scanning and transmission electron microscopy, scanning probe microscopy) allowed to fully characterize the microstructure and morphology of these self-standing manganite nanostructures. For 1 μm pore size templates we obtained tubes, with external diameter around 800 nm and wall thickness around 150 nm; densely packed nanoparticles sized 20-50 nm are the building blocks of the walls. For pore size below 0.1 μm, solid nanowires were obtained, the size of constituent crystallites being around 10 nm. Overall obtained material exhibits ferromagnetic ordering below 200 K.     

On-line coupling of automatic solid-phase extraction and HPLC for determination of carotenoids in serum

The automated method developed for the determination of carotenoids uses 200 μL of serum, which was mixed with 400 μL of tetrahydrofuran, vortexed for 1 min, settled for 10 min, centrifuged for 6 min and the supernatant injected into an automatic solid-phase extraction (SPE) system for cleanup-preconcentration. A 10% water-acetonitrile mobile phase at 1.5 mL min⁻¹ eluted the retained compounds and transferred them on-line to a reversed-phase analytical column for individual separation of the target analytes. Visible detection was performed at 450 and 460 nm. The detection limits for the target analytes were between 3 and 30 ng mL⁻¹; the precision (expressed as relative standard deviation) ranged between 2.83 and 5.06% for repeatability and between 3.80 and 7.40% for within laboratory reproducibility. The total analysis time was 18 min. The proposed method is reliable, robust, and has an excellent potential for high-throughput use in both clinical and research laboratories.     

The performance of hybrid monolithic silica capillary columns prepared by changing feed ratios of tetramethoxysilane and methyltrimethoxysilane

The effect of a feed ratio of methyltrimethoxysilane (MTMS) to tetramethoxysilane (TMOS) was studied to improve the performance of a hybrid monolithic silica capillary column with 100-μm i.d. in HPLC in a range MTMS/TMOS (v/v) = 10/90–25/75. The domain size was also varied by adjusting the amount of PEG to control permeability (K = 2.8 × 10⁻¹⁴–6.9 × 10⁻¹⁴ m²). Evaluation of the performance for those capillary columns following octadecylsilylation proved an increase in retention factor (k) and a decrease in steric selectivity α(triphenylene/ortho-terphenyl) with the increase in MTMS content in the feed. The effect of the feed ratio was also observed in porosity and hydrophobic property of the C18 stationary phase from the results of size exclusion chromatography (SEC) and reversed phase characterization. The monolithic silica capillary columns prepared under new preparation conditions were able to produce a plate height of 4.6–6.0 μm for hexylbenzene in a mobile phase acetonitrile/water = 80/20 at a linear velocity of 2 mm/s. Consequently, it was possible to prepare hybrid monolithic silica capillary columns with higher performance than those reported previously while maintaining the retention factors in a similar range by reducing the MTMS/TMOS ratio and increasing the total silane concentration in feed.     

Dispersive liquid–liquid–liquid microextraction combined with liquid chromatography for the determination of chlorophenoxy acid herbicides in aqueous samples

A novel sample preparation method “Dispersive liquid–liquid–liquid microextraction” (DLLLME) was developed in this study. DLLLME was combined with liquid chromatography system to determine chlorophenoxy acid herbicide in aqueous samples. DLLLME is a rapid and environmentally friendly sample pretreatment method. In this study, 25 μL of 1,1,2,2-tetrachloroethane was added to the sample solution and the targeted analytes were extracted from the donor phase by manually shaking for 90 s. The organic phase was separated from the donor phase by centrifugation and was transferred into an insert. Acceptor phase was added to this insert. The analytes were then back-extracted into the acceptor phase by mixing the organic and acceptor phases by pumping those two solutions with a syringe plunger. After centrifugation, the organic phase was settled and removed with a microsyringe. The acceptor phase was injected into the UPLC system by auto sampler. Fine droplets were formed by shaking and pumping with the syringe plunger in DLLLME. The large interfacial area provided good extraction efficiency and shortened the extraction time needed. Conventional LLLME requires an extraction time of 40–60 min; an extraction time of approximately 2 min is sufficient with DLLLME. The DLLLME technique shows good linearity (r² ≥ 0.999), good repeatability (RSD: 4.0–12.2% for tap water; 5.7–8.5% for river water) and high sensitivity (LODs: 0.10–0.60 μg/L for tap water; 0.11–0.95 μg/L for river water).     

Automated polyvinylidene difluoride hollow fiber liquid-phase microextraction of flunitrazepam in plasma and urine samples for gas chromatography/tandem mass spectrometry

A new polyvinylidene difluoride (PVDF) hollow fiber (200 μm wall thickness, 1.2 mm internal diameter, 0.2 μm pore size) was compared with two other polypropylene (PP) hollow fibers (200, 300 μm wall thickness, 1.2 mm internal diameter, 0.2 μm pore size) in the automated hollow fiber liquid-phase microextraction (HF-LPME) of flunitrazepam (FLNZ) in biological samples. With higher porosity and better solvent compatibility, the PVDF hollow fiber showed advantages with faster extraction efficiency and operational accuracy. Parameters of the CTC autosampler program for HF-LPME in plasma and urine samples were carefully investigated to ensure accuracy and reproducibility. Several parameters influencing the efficiency of HF-LPME of FLNZ in plasma and urine samples were optimized, including type of porous hollow fiber, organic solvent, agitation rate, extraction time, salt concentration, organic modifier, and pH. Under optimal conditions, extraction recoveries of FLNZ in plasma and urine samples were 6.5% and 83.5%, respectively, corresponding to the enrichment factor of 13 in plasma matrix and 167 in urine matrix. Excellent sample clean-up was observed and good linearities (r² = 0.9979 for plasma sample and 0.9995 for urine sample) were obtained in the range of 0.1–1000 ng/mL (plasma sample) and 0.01–1000 ng/mL (urine sample). The limits of detection (S/N = 3) were 0.025 ng/mL in plasma matrix and 0.001 ng/mL in urine matrix by gas chromatography/mass spectrometry/mass spectrometry.     

Behavior of polysaccharide assemblies in field-flow fractionation and size-exclusion chromatography

Asymmetric flow field-flow fractionation (AsFlFFF) and high-performance size-exclusion chromatography (HPSEC) are techniques for separating and characterizing macromolecules; until now the latter is more utilized for analyzing polysaccharides. The demand for characterizing complex, high-molar-mass polysaccharides has raised interest in the use of AsFlFFF in analyzing polymeric carbohydrates in addition to HPSEC. In this paper, we compare the behavior of arabinoxylan aggregates present in aqueous solution in AsFlFFF and HPSEC and their effect on the obtained molecular characteristics (molar mass averages and size). Although the amount of aggregates in aqueous arabinoxylan solutions may be low, their role needs to be understood to avoid erroneous interpretations of AsFlFFF and HPSEC data. When these two separation systems were compared, AsFlFFF seemed to possess more separation power for the differentiation of aggregates from individual chains than HPSEC. To our knowledge, this is the first report on the characterization of xylans with AsFlFFF.     

Facilitated transport of Am(III) through a flat-sheet supported liquid membrane (FSSLM) containing tetra(2-ethyl hexyl) diglycolamide (TEHDGA) as carrier

Facilitated transport of Am(III) in nitric acid medium using tetra(2-ethyl hexyl) diglycolamide (TEHDGA) in n-dodecane as carrier was studied. It was aimed at finding out the physico-chemical model for the transport of Am(III) using TEHDGA/n-dodecane as carrier under various experimental parameters like feed acidity, carrier concentration, varying strippant, varying membrane pore size, etc. The feed acidity and carrier concentrations were varied from 1 M to 6 M HNO₃ and 0.1 M to 0.3 M TEHDGA/n-dodecane, respectively. The transport of Am(III) increased with increase in feed acidity and carrier concentration reaching maximum at 3 M HNO₃ and 0.2 M TEHDGA/n-dodecane, respectively. Several stripping agents were tested and 0.1 M HNO₃ was found to be the most suitable stripping agent for this system. Almost quantitative transport of Am(III) was observed at about 180 min with feed acidity of 3 M HNO₃, 0.1 M HNO₃ as strippant and 0.2 M TEHDGA/n-dodecane as carrier. The pore size of the membrane support was varied from 0.20 μm to 5 μm and the permeation coefficient increased with increase in pore size up to 0.45 μm (2.43 × 10⁻³ cm/s), and then decreased with further increase in pore size. The plot between permeation coefficient vs. (membrane thickness)⁻¹ was linear which showed that the Am(III) transport was membrane diffusion limited. The membrane diffusion coefficient calculated from the graph was found to be 1.27 × 10⁻⁶ cm²/s and its theoretical value was 1.22 × 10⁻⁶ cm²/s. The stability of the carrier against leaching out of the membrane support as well as the integrity of membrane support was studied over a period of 30 days and was found to be satisfactory within the studied time period.     

Facile preparation of ferromagnetic alginate-g-poly(vinyl alcohol) microparticles

Alginate-g-poly(vinyl alcohol) was physically cross-linked with Fe(II) ion in a surfactant-free emulsion system to form microparticles via in situ precipitation. The microparticles were subjected to oxidation in aqueous of pH 13 at ambient temperature and transformed into magnetic ones within minutes. X-ray diffractometry showed that magnetic Fe₃O₄ was formed and it was further confirmed with a vibrating sample magnetometer measurement. Scanning electron microscopy examinations indicated that the iron oxide was well embedded into ferrous alginate and the size of particles was around 0.2-1.2 μm.     

Membrane emulsification using membranes of regular pore spacing: Droplet size and uniformity in the presence of surface shear

During membrane emulsification it is shown that the size of the drops formed at the membrane surface may increase with increasing dispersed phase injection rate through the membrane, or it may decrease, depending on the prevailing conditions. This is illustrated using a paddle stirrer positioned above flat disc membranes with regular arrays of pores of 20 μm diameter and spacing between the pores of 80 and 200 μm. In the former case an additional mechanism for drop detachment is the push-off force, which is determined by the geometry of the drops as they deform at the membrane surface. When dispersing sunflower oil in to aqueous solutions containing Tween 20, drop sizes between 60 and 200 μm were produced, and in the case of the membrane when the push-off force was working the Coefficient of Variation of the drops formed was below 10%. The push-off force may be added to the shear-drag force to predict drop detachment. For the 200 μm pore spaced membrane this force is much less prominent than the 80 μm spaced membrane. The capillary-shear model has been modified to include this push-off force. The experimental study required the use of very low dispersed phase injection rates as well as very high rates. Hence, two different types of pumps were used to provide these: a peristaltic and syringe pumps. A small study comparing the drop size, and size distributions, showed that the pump type did not influence the drops produced by the membrane emulsification process.     

Simple capillary flow porometer for characterization of capillary columns containing packed and monolithic beds

A simple capillary flow porometer (CFP) was assembled for through-pore structure characterization of monolithic capillary liquid chromatography columns in their original chromatographic forms. Determination of differential pressures and flow rates through dry and wet short capillary segments provided necessary information to determine the mean diameters and size distributions of the through-pores. The mean through-pore diameters of three capillary columns packed with 3, 5, and 7 μm spherical silica particles were determined to be 0.5, 1.0 and 1.4 μm, with distributions ranging from 0.1 to 0.7, 0.3 to 1.1 and 0.4 to 2.6 μm, respectively. Similarly, the mean through-pore diameters and size distributions of silica monoliths fabricated via phase separation by polymerization of tetramethoxysilane (TMOS) in the presence of poly(ethylene glycol) (PEG) verified that a greater number of through-pores with small diameters were prepared in columns with higher PEG content in the prepolymer mixture. The CFP system was also used to study the effects of column inner diameter and length on through-pore properties of polymeric monolithic columns. Typical monoliths based on butyl methacrylate (BMA) and poly(ethylene glycol) diacrylate (PEGDA) in capillary columns with different inner diameters (i.e., 50–250 μm) and lengths (i.e., 1.5–3.0 cm) were characterized. The results indicate that varying the inner diameter and/or the length of the column had little effect on the through-pore properties. Therefore, the through-pores are highly interconnected and their determination by CFP is independent of capillary length.     

Carbon nanotube reinforced hollow fiber solid/liquid phase microextraction: A novel extraction technique for the measurement of caffeic acid in Echinacea purpurea herbal extracts combined with high-performance liquid chromatography

A new design of hollow fiber solid–liquid phase microextraction (HF-SLPME) was developed for the determination of caffeic acid in medicinal plants samples as Echinacea purpure. The membrane extraction with sorbent interface used in this research is a three-phase supported liquid membrane consisting of an aqueous (donor phase), organic solvent/nano sorbent (membrane) and aqueous (acceptor phase) system operated in direct immersion sampling mode. The multi-walled carbon nanotube dispersed in the organic solvent is held in the pores of a porous membrane supported by capillary forces and sonification. It is in contact with two aqueous phases: the donor phase, which is the aqueous sample, and the acceptor phase, usually an aqueous buffer. All microextraction experiments were supported using an Accurel Q3/2 polypropylene hollow fiber membrane (600 μm I.D., 200 μm wall thicknesses, and 0.2 μm pore size). The experimental setup is very simple and highly affordable. The hollow fiber is disposable, so single use of the fiber reduces the risk of cross-contamination and carry-over problems. The proposed method allows the very effective and enriched recuperation of an acidic analyte into one single extract. In order to obtain high enrichment and extraction efficiency of the analyte using this novel technique, the main parameters were optimized. Under the optimized extraction conditions, the method showed good linearity (0.0001–50 μg/L), repeatability, low limits of detection (0.00005 μg/L) and excellent enrichment (EF = 2108).     

Development and validation of a simple stability-indicating high performance liquid chromatographic method for the determination of miconazole nitrate in bulk and cream formulations

A simple and stability-indicating high performance liquid chromatographic method was developed and validated for the determination of miconazole nitrate in bulk and cream preparations. The extraction step for cream samples consisted in a warming, cooling and centrifugation procedure that assures the elimination of the lipophilic matrix component, in order to avoid further precipitation in the chromatographic system. Separation was achieved on a ZORBAX Eclipse XDB - C18 (4.6 mm × 150 mm, 5 μm particle size) column, using a mobile phase consisting of water, methanol and acetonitrile, in a flow and solvent gradient elution for 15 min. The column was maintained at 25 °C and 10 μL of solutions were injected. UV detection was performed at 232 nm, although employment of a diode array detector allowed selectivity confirmation by peak purity evaluation. The method was validated reaching satisfactory results for selectivity, precision and accuracy. Degradation products in naturally aged samples could be simultaneously evaluated, without interferences in the quantitative analysis.     

A new simple,low-cost approach for generation of the PM10 fraction from soil and related materials: Application to human health risk assessment

A new simple, robust and low-cost wet laboratory method for the generation of the <10 μm (PM₁₀) particle size fraction is reported. A sedimentation method is directly compared with a centrifugation method for generation of the PM₁₀ fraction. Both approaches are based on an integrated form of Stokes’ law. Subsequently the sedimentation method was adopted. The results from the sedimentation method were corroborated using particle size distribution measurements. This approach for the generation of the PM₁₀ fraction was applied to soil and mine waste samples from Mitrovica, Kosovo as part of an investigation in to the human risk assessment from inhalation of the PM₁₀ fraction containing potentially harmful elements (PHEs). The average daily dose for Cd from the inhalation of suspended soil particles was calculated to be 0.021 and 0.010 μg kg⁻¹_BW d⁻¹ for a child and an adult, respectively. This corresponded to an inhalation dose of 0.50 and 0.70 μg Cd d⁻¹ for a child (20 kg) and an adult (70 kg), respectively.     

Comparison of particle size and flow rate optimization for chromatography using one-monomer molecularly imprinted polymers versus traditional non-covalent molecularly imprinted polymers

The dependence of enantio-selective chromatographic performance on particle size, as measured by separation factor, was investigated for one-monomer molecularly imprinted polymers (OMNiMIPs) compared to traditionally formed EGDMA/MAA molecularly imprinted polymers (MIPs). Five particle size ranges were compared (<20 μm, 20-25 μm, 25-38 μm, 38-45 μm, and 45-63 μm), revealing that the particle sizes above 25 μm provided the highest separation factor, and thus the best enantiomer separation, for both imprinted polymers. Other chromatographic parameters such as the number of theoretical plates and resolution exhibited only minor changes for the OMNiMIPs as the particle size changed, except for particles 20 μm and below. However, the number of theoretical plates and resolution for EGDMA/MAA are higher for particles in the 20-25 μm range. Thus, chromatographic factors for the EGDMA/MAA polymers are better in this range, despite better enantioselectivity for particle sizes above 25 μm. In contrast, OMNiMIPs generally show the most favorable performance for particle sizes in the 38-45 μm range. It was also found that decreasing flow rate resulted in improved enantioselectivity for both MIPs for all particle sizes.