Single Hollow Fiber Research Articles

Headspace single drop and hollow fiber liquid phase microextractions for HPLC determination of phenols

Two methods based on headspace single drop microextraction (HS-SDME) and headspace hollow fiber liquid phase microextraction (HS-HF-LPME) were developed and critically compared with HPLC-UV determination of phenols (including phenol (Ph), 2-chlorophenol (CP), 2,4-dichlorophenol (DCP) and 2,4,6-trichlorophenol (TCP)) in this paper. The significant parameters affecting the extraction efficiency of the target analytes in both extraction modes were studied and the optimal extraction conditions were established. Under the optimal conditions, the detection limits (S/N = 3) for Ph, CP, DCP and TCP obtained by HS-SDME-HPLC-UV and HS-HF-LPME-HPLC-UV were 2.1, 0.2, 0.8,1.1 ng/mL and 4.2, 0.4, 0.4, 0.4 ng/mL with enrichment factors of 15.8, 198.9, 159.7, 194.8 and 9.2, 149.9, 301.9, 411.1, respectively. The RSDs obtained by HS-SDME-HPLC-UV and HS-HF-LPME-HPLC-UV were 3.7, 4.0, 9.8, 6.7% and 6.3, 3.6, 3.1, 4.8% for Ph, CP, DCP and TCP, respectively. Both extraction modes have a comparable analytical performance, but HS-HF-LPME was more robust than HS-SDME, while HS-SDME was simpler than HS-HF-LPME. The two headspace microextraction modes were applied for HPLC-UV determination of target phenols in water, honey and toner samples, and the determined values obtained by both techniques were in good agreement with each other.

Non-invasive monitoring of fouling in hollow fiber membrane via UTDR

Fouling is the most critical problem associated with membrane separations in liquid media. But it is difficult to control the inevitable membrane fouling because of its invisibility, especially on the inside surface of hollow fiber membranes. This study describes the extension of ultrasonic time-domain reflectometry (UTDR) for the real-time measurement of particle deposition in a single hollow fiber membrane. A transducer with a frequency of 10 MHz and polyethersulfone hollow fiber membranes with 0.8 mm inside diameter (ID) and 1.2 mm outside diameter (OD) were used in this study. The fouling experiments were carried out with 1.8 g/L kaolin suspension at flow rates 16.7 and 10.0 cm/s. The results show that UTDR technique is able to distinguish and recognize the acoustic response signals generated from the interfaces water/upper outside surface of the hollow fiber, lumen upside surface/water, water/lumen underside surface and lower outside surface/water in the single hollow fiber membrane module in pure water phase. The systemic changes of acoustic responses from the inside surfaces of the hollow fiber in the time- and amplitude-domain with operation time during the fouling experiments were detected by UTDR. It is associated with the deposition and formation of the kaolin layer on the inside surfaces. Further, the acoustic measurement indicates that the deposited fouling layer is denser on the lumen underside surface of the hollow fiber than that on the lumen upside surface as a result of weight. Moreover, it is found that the fouling layer grows faster on the inside surface of the hollow fiber at a flow rate of 10.0 cm/s than that at 16.7 cm/s due to the lower shear stress. The fouling layer formed is thicker at a flow rate of 10.0 cm/s than that at 16.7 cm/s. The flux decline data and SEM analysis corroborate the ultrasonic measurement. Overall, this study confirms that UTDR measurement will provide not only a new protocol for the observation of hollow fiber membrane fouling and cleaning, but also a quantitative approach to the optimization of the membrane bioreactor system.

Robustly single mode hollow core photonic bandgap fiber

We report the fabrication of a novel type of hollow core photonic bandgap fiber (PBGF) with a small core formed by 3 omitted unit cells in a triangular array of holes. The transmission properties of fibers designed for operation at 1500nm wavelength are investigated both experimentally and through extensive modeling. The novel PBGF structure provides robust single mode guidance and is of particular interest for device applications which require low index bandgap guidance and short device lengths.

Micro-scale membrane extraction of glyphosate and aminomethylphosphonic acid in water followed by high-performance liquid chromatography and post-column derivatization with fluorescence detector

A carrier-mediated supported liquid membrane micro-extraction using single hollow fiber membrane suitable for the determination of the herbicide glyphosate and its main metabolite aminomethylphosphonic acid in water is reported. A solution of 0.20 M Aliquat-336, a cationic carrier, in di- n-hexyl ether was selected as the supported liquid. A 20 μL of 1.0 M potassium chloride as the acceptor phase was filled in the membrane lumen. The membrane was immersed in a 20 mL of pH 9.0 sample solution. After 60-min extraction, the acceptor phase was analyzed by high-performance liquid chromatography with post-column derivatization. The enrichment factors were found to be 853 and 136 for glyphosate and aminomethylphosphonic acid, respectively. The method detection limits are 0.22 μg/L for glyphosate and 3.40 μg/L for aminomethylphosphonic acid. The procedure was validated and showed good accuracy and precision over a large linear dynamic range. The validated method was tested for the analysis of both analytes in spiked groundwater with good success.

Single hollow fiber SLM extraction of polyamines followed by tosyl chloride derivatization and HPLC determination

Determination of polyamines in biological fluids possesses medical diagnostic relevance. Despite the vast panel of analytical methods developed for polyamines they are not applied in routine clinical usage, mainly due to the time and labor consuming sample preparation step and complicated derivatization procedures. Thus, new simpler methods are needed. This paper describes a single hollow fiber SLM extraction method of polyamines followed by simple pre-column derivatization with tosyl chloride and HPLC-UV analysis. The influence of different parameters such as the extraction time, organic phase composition, acceptor pH, donor pH, acceptor volume, donor volume and stirring speed on the transport parameters and enrichment was studied and discussed. The optimized method was applied to real matrices such as urine and plasma.

Few-cycle laser pulses tested with double ionization of H2

Different compression schemes for the production of sub-10 fs laser pulses are tested using double ionization of H2. Compression schemes differ in the laser beam guiding modes which are necessary in order to get a spatially-homogeneous spectral broadening through self-phase modulation in argon. Guiding may take place in a hollow fibre waveguide or may be self-induced in a filament. We tested four set-ups: a single hollow fibre, two hollow fibres, a hollow fibre then a filament, and two filaments. The shortest pulses around 8 fs were recorded with the set-ups involving one or two filaments. Double ionization of H2 and the associated proton spectra give results in good agreement with the spectral and interferometric autocorrelation measurements. The two-filament set-up gives the shortest pulses. In addition, the H2 experiment reveals that the spectral phase induced with two filaments cannot be fully compensated with second-order chirped mirrors as for the other tested set-ups.

Unstable filtration behavior with submerged hollow fiber membranes

Freshly wetted, submerged hollow fiber polypropylene membranes have been observed to exhibit unstable behavior characterized by fluctuating suction pressure–time profiles on filtration of MilliQ water. Filtration results with single hollow fibers reveal that the observed suction pressure fluctuation could be caused by an unstable local resistance at some location inside the fiber lumen. The evidence from X-ray microimaging of the fiber lumen suggests that abnormal local flow conditions were induced by the presence of stagnant bubbles firmly attached to the internal wall of the hollow fiber membranes. The formation of these stagnant bubbles is attributed to some ‘dry’ points existing on the internal surface of the hollow fiber membrane. It appears that these ‘dry’ points cause significant and unstable local resistances for the permeate flow inside the fiber lumen. For a fixed average flux the high local resistance results in increased suction pressure in the lumen region downstream of the ‘dry point’ and this shifts an additional flux load to this region. The resultant maldistribution of local fluxes caused by abnormal local flow resistances can markedly affect the filtration behavior of the hollow fiber membrane. Interestingly the effect was not observed for all fibers and appears to require local ‘dry point’ existence within the lumen. The filtration of latex particle suspensions under different conditions showed that those fresh fibers with fluctuating suction pressure–time profiles also exhibited a sharp increase in the suction pressure and had limited run times for filtration. A pre-treatment protocol using pressurized water (PW) applied to the freshly ethanol-wetted fibers was found to result in marked improvement in the stability of the hollow fiber membranes tested.

Modelling nutrient transport in hollow fibre membrane bioreactor for growing bone tissue with consideration of multi-component interactions

Current work in bone tissue engineering (BTE) suggests that hollow fibre membrane bioreactors (HFMBs) can be used to grow artificial bone tissue which may then be implanted in humans to treat various bone defects. The HFMBs mimic the blood capillary networks in human bones and are able to maintain high concentrations of nutrients by minimising mass transfer distance. To further establish this method and to develop effective BTE protocols, nutrient transport behaviour in the HFMB must be characterised. By doing so, the quantitative relationships between the cell environments and, bioreactor operating conditions and designs can be elucidated. This also paves the way for possible improvement and optimisation of the HFMB performance. However, characterising the nutrients transport properties in HFMB are not straightforward as online measurements of key parameters are almost impossible at the moment. This is due to the very small size and the stringent operating conditions of the bioreactors. Hence, much work is needed on mathematical modelling of mass transport in these bioreactors. In this paper, we present a rigorous framework for modelling mass transport in HFMB for growing bone tissue. In particular, we consider the effects of hydrodynamics and multi-component interactions on nutrient transport profiles. The developed framework is then used to study the behaviour of nutrient transport in HFMB for bone tissue growth for various operating conditions with a view to generalise their effects as far as possible. Maxwell–Stefan, Navier–Stokes and reaction kinetic equations are combined to quantify the multi-component nutrient transport behaviour in the bioreactor. The framework also relies on the use of a single hollow fibre (Krogh cylinder assumption), which is representative of the whole fibre bundle. The numerical solutions of the governing model equations are obtained using finite element method. The effects of different bioreactor designs (e.g., fibre length, lumen thickness, etc.) and process parameters (e.g., nutrient inlet concentration, fluid velocity, etc.) on multi-component nutrient concentration profiles (e.g., glucose and oxygen) are simulated. The results show that the HFMB designs and process parameters may be optimised to further enhance mass transport for growing bone tissues.

Facile and versatile preparation of silicalite-1 hollow structures using cotton threads as templates

In situ hydrothermal synthesis of various silicalite-1 hollow structures with different morphologies by using cotton threads as the templates was presented. It was found that the cotton thread was composed of many cotton fibers twisted together. By using loosely cotton thread, bunchy silicalite-1 hollow fibers with inner diameter close to the cotton fibers composed of the cotton thread were formed after burn-off of the template. Honeycomb silicalite-1 structure was prepared after three cycles of hydrothermal syntheses of the above bunchy silicalite-1 fibers. When tightly stretched single cotton thread was used, single silicalite-1 hollow fiber with inner diameter smaller than the outer diameter of the thread could be produced. Monolithic silicalite-1 structures were also prepared when the cotton threads were tightly stretched and also closely contacted in parallel with each other after three cycles of synthesis. Therefore, various silicalite-1 hollow structures could be easily and readily prepared by controlling the status of the cotton thread and the hydrothermal synthesis cycles.

Chimeric protein for selective cell attachment onto cellulosic substrates

We have developed a fusion protein (CBD-LG) incorporating a cellulose-binding domain and an antibody binding domain, protein LG, to provide an adaptor molecule for cell separation with regenerated cellulose hollow fiber arrays. A single hollow fiber cell adhesion assay utilizing a CD34+ cell line, KG1a, was used to investigate whether ligand affinity interactions were strong enough for cell attachment and separation. CBD-LG efficiently captured CD34+ cells labeled with the mouse IgG2a monoclonal antibody MHCD3400. However, it was not possible to bind CD34+ cells labeled with an IgG1 antibody (HPCA-2). The low affinity of HPCA-2 for LG was overcome by secondary antibodies: KG1a cells that were dual labeled with HPCA-2 followed by rat anti-mouse IgG1 adhered inside hollow fibers coated with CBD-LG. Alternatively, immobilized rabbit polyclonal anti-mouse IgG1 captured cells labeled with HPCA-2. The development of an adaptor molecule to display recombinant domains at the surface of hollow fibers will be an effective tool to investigate cellular ligand-receptor interactions, a necessary step in the development of hollow fiber bioreactors for manufacture of human cellular products.

Bundled hollow optical fibers for transmission of high-peak-power Q-switched Nd:YAG laser pulses

A hollow-fiber bundle was designed and used to deliver high-peak-power pulses from a Q-switched Nd:YAG laser. An 80 cm long bundle with a total diameter of 5.5 mm was composed of 37 glass capillaries with bore diameters of 0.7 mm. Beam-resizing optics with two lenses were used to couple the laser beam into the bundle. The measured coupling loss due to the limited aperture ratio of the bundle was 2.3 dB, and the transmission loss at wavelengths of 1064 and 532 nm was 0.3 dB. When an inert gas flowed through the bores of the capillaries, the maximum output pulse energy was 200 mJ, which was the limit of the laser used in the experiment. Hollow-fiber bundles withstand irradiation better than single hollow fibers and silica-glass optical fibers do. They are suitable for many dermatological applications because they can be used to irradiate a large area.

Bicomponent Hollow Fibers for Pervaporation

Fiber and textile scientists have made great strides in the formation of single and multihole hollow fibers which are of significant practical value to separation science. Pervaporation through bicomponent/composite hollow fibers represents a major potential for the separation of organic and aqueous-organic mixtures. By appropriate selection of the exposed membrane, high throughputs at high selectivities with good chemical and physical stability may be achieved. The article analyzes the transport of isopentane through a composite of silicone rubber and polysulfone asymmetrical hollow fiber membrane. A one parameter mathematical model of the pervaporation process is developed. The parameter is related to the sorption and transport properties of the penetrant through the membrane layers. Pervaporation parameter is a useful tool for membrane characterization and process design.

Hollow fiber liquid phase microextraction combined with electrothermal vaporization ICP-MS for the speciation of inorganic selenium in natural waters

A novel method for the speciation of Se(IV) and Se(VI) in environmental water samples based on liquid-phase microextraction (LPME) methods in conjunction with electrothermal vaporization (ETV) ICP-MS has been developed. Two modes of LPME: single drop microextraction (SDME) and hollow fiber liquid phase microextraction (HF-LPME) were studied comparatively. The organic chelating reagent ammonium pyrrolidine dithiocarbamate (APDC) was used as both the extractant for microextraction and the chemical modifier for ETV-ICP-MS determination. Under the optimal conditions, enrichment factors of 75 and 410 could be achieved for SDME and HF-LPME, respectively. The detection limit of Se in HF-LPME-ETV-ICP-MS and SDME-ETV-ICP-MS were 0.50, 0.56 pg mL−1 and 2.7, 3.0 pg mL−1 for Se(IV) and Se(VI), respectively. HF-LPME was finally selected for the analysis of Se(IV) and Se(VI) in lake water, river water and pool water samples due to its good analytical features and robustness. The proposed method was validated by the determination of total Se with PN-ICP-MS.

Equilibrium sampling through membrane based on a single hollow fibre for determination of drug–protein binding and free drug concentration in plasma

The determination of drug-protein binding and free drug concentration in plasma applying the equilibrium sampling through membrane (ESTM) technique has been studied using supported liquid membrane extraction in a single hollow fibre without any membrane carrier. In the extraction setup, the donor phase (plasma or buffer) was placed in the vial, into which was immersed the hollow fibre with the acceptor phase situated in the lumen. This proposed technique was applied to study the drug-protein binding of five local anaesthetics and two antidepressants as model substances, and the influence of the total drug concentration on the drug-protein binding was investigated. The brief theoretical background for determination of the drug-protein binding under equilibrium conditions is described. The developed method shows a new, improved and simple procedure for determination of free drug concentration in plasma and extent of drug-protein binding.

Analysis of constant permeate flow filtration using dead-end hollow fiber membranes

Dead-end filtration of colloids using hollow fibers has been analysed theoretically and experimentally. A mathematical model for constant flux filtration using dead-end hollow fiber membranes has been developed by combining the Hagen–Poiseuille equation, the (standard) filtration equation, and cake filtration theory of Petsev et al. [D.N. Petsev, V.M. Starov, I.B. Ivanov, Concentrated dispersions of charged colloidal particles: sedimentation, ultrafiltration and diffusion, Colloid Surf. A: Physicochem. Eng. Aspects, 81 (1993) 65–81.] to describe the time dependence of the filtration behavior of hollow fiber membranes experiencing particle deposition on their surface. Instead of using traditional constitutive equations, the resistance of the cake layer formed by the deposited colloids has been directly correlated to the cake structure. This structure is determined by application of a force balance on a particle in the cake layer combined with the assumption that an electrostatically stable cake layer of mono-sized particles would be ordered in a regular packing geometry of minimum energy. The developed model has been used to identify the relationship between the filtration behavior of the hollow fiber membrane and the particle properties, fiber size, and imposed average flux. Filtration experiments using polystyrene latex particles of relatively narrow size distribution with a single dead-end hollow fiber membrane demonstrate good consistency between experimental results and model prediction. The developed model has been used to simulate the distribution of the cake resistance, transmembrane pressure, and flux along the hollow fiber membrane and used to assess the effect of fiber size, particle size, zeta potential, and the average imposed flux on the suction pressure-time profiles, flux, and cake resistance distributions. These results provide new insights into the filtration behavior of the hollow fiber membrane under constant flux conditions.

Impact of geometrical fiber dimensions on dialyzer efficiency

While dialyzer manufacturers only provide information about their products as a black box, this study aimed at optimizing dialyzer geometry by looking in detail at transport processes and fluid properties inside the dialyzer using numerical modeling. A three‐dimensional computer model of a single hollow fiber with its surrounding membrane and dialysate compartment was developed. Different equations govern blood and dialysate flow (Navier‐Stokes), radial filtration flow (Darcy), and solute transport (convection‐diffusion). Blood was modeled as a non‐ Newtonian fluid with a viscosity varying in radial and axial direction because of the influence of local hematocrit, diameter of the capillaries, and local shear rate. Dialysate flow was assumed as an incompressible, laminar Newtonian flow with a constant viscosity. The permeability characteristics of the asymmetrical polysulphone membrane were calculated from laboratory tests for forward and backfiltration. The influence of the oncotic pressure induced by the plasma proteins was implemented as well as the reduction of the overall permeability caused by the adhesion of a protein layer on the membrane. Urea (MW60) was used as a marker to simulate small molecule removal, while middle molecule transport was modeled using vitamin B12 (MW1355) and inulin (MW5200). The corresponding diffusion coefficients were determined by counting for the fluid and membrane characteristics. Fiber diameter and length were changed in a wide range for evaluation of solute removal efficiency. The presented model allowed us to investigate the impact of flow, hematocrit, and capillary dimensions on the presence and localization of backfiltration. Furthermore, mass transfer was found enhanced for increased fiber lengths and/or smaller diameters, most pronounced for the middle molecules compared to urea.

Non-invasive observation of external and internal deposition during membrane filtration by X-ray microimaging (XMI)

This paper describes the application of phase contrast X-ray microimaging (XMI) for the non-invasive observation of membrane filtration processes. Using a single hollow fibre with lumen feed of an iron hydroxide suspension it is shown that the technique can observe the cake layer inside the fibre and fouling deposition within the pores. This technique has the potential to observe real-time fouling phenomena within a membrane at a higher level of resolution than other non-invasive methods.

Air gap membrane distillation: 2. Model validation and hollow fibre module performance analysis

In this paper the experimental results of counter current flow air gap membrane distillation experiments are presented and compared with predictive model calculations. Measurements were carried out with a cylindrical test module containing a single hollow fibre membrane in the centre and a well-defined air gap situated around the fibre. The experimental results show that the previous developed predictive model, with membrane parameters determined from gas permeation experiments, describes correctly the dependence of water vapour flux on temperature level, temperature difference, air gap total pressure, hot water flow and membrane type. At atmospheric air gap pressure, the measured fluxes per saturated water vapour pressure difference between the bulk flows (0.08–0.10 kg/m 2h mbar) are comparable with those presented in literature. A reduction of the total air gap pressure to the saturated water vapour pressure of the hot water feed flow temperature of 65 °C, raises the flux by a factor of three. Next to the water vapour flux, the energy efficiency of the process is very important. The measured energy efficiencies (typically 85–90% for a 3 mm air gap and a hot water feed temperature of 65 °C) are slightly below the theoretical values (95–98%), which could be explained by a small heat loss to the surroundings. For air gaps of 1.5 mm or smaller, the energy efficiency is reduced to less than 70%, due to thermal conduction across product water bridges between the membrane fibre and the condenser surface. An optimal air gap is about 3 mm wide and has a total pressure that is equal to or slightly below the saturated water vapour pressure of the hot water entering the hollow fibre membrane.

Effect of fractionated NOM on low-pressure membrane flux declines

The membrane fouling characteristics of natural organic matter (NOM) were assessed using single polypropylene hollow fibre membranes of pore size 0.2 μm. The membranes were liquid backwashed every 30 minutes and filtration runs of up to 48 hours (≤8 litres) were conducted. The NOM samples were fractionated into different chemical classes based on their adsorption properties. For the two waters investigated, the hydrophobic components were the major foulant for one water, and the hydrophilics were the major foulant for the other. Interaction between the strongly hydrophobic and weakly hydrophobic fractions was significant for one water, but the extent of interaction between these fractions was minor for the other. The long term membrane fouling characteristics could not always be deduced from short term fouling trials.

A study on the fouling phenomena of a microfiltration membrane

The utilization of membrane processes for drinking water treatment has become more popular. However, fouling by source water probably is the major factor prohibits its widespread application. In this research, the fouling phenomena of a microfiltration (MF) membrane were studied. The interactions among colloidal particles, calcium ion, and dissolved organics, such as salicylic acid, humic acid, and alginic acid, on MF fouling were focused. A lab-scale single hollow fiber MF membrane, made of polyvinylidenefluoride (PVDF), module was used. The results show that, for single organic compound, the extent of fouling caused by humic acid was higher that of alginic acid. For the latter, the permeate flux decrease at lower pH was more significant than those at higher pH. For low MW salicylic acid, both rejection and flux decrease were minor. It seems that solubility have strong correlation with fouling rate. The higher the solubility is, the lower the fouling rate. For sole colloidal particle system, latex beads with diameter close to the pore size of MF membrane showed severe fouling. Adding Ca can aggregate the latex beads, and alleviate fouling. However, calcium ion also found to increase fouling of alginic acid on membrane under neutral or alkali pH condition, probably via charge neutralization and/or bridging. In conclusion, MF fouling seems to be strongly related to the type of organics, size of colloidal particles, and the existence of divalent ions, in the feed water.