Sorbent Membrane Research Articles

Sampling Rate of Polar Organic Chemical Integrative Sampler (POCIS): Influence Factors and Calibration Methods

As a passive sampling device, the polar organic chemical integrative sampler (POCIS) has the characteristics of simple operation, safety, and reliability for assessing the occurrence and risk of persistent and emerging trace organic pollutants. The POCIS, allowing for the determination of time-weighted average (TWA) concentration of polar organic chemicals, exhibits good application prospects in aquatic environments. Before deploying the device in water, the sampling rate (Rs), which is a key parameter for characterizing pollutant enrichment, should be determined and calibrated accurately. However, the Rs values strongly depend on experimental hydrodynamic conditions. This paper provides an overview of the current situation of the POCIS for environmental monitoring of organic pollutants in an aquatic system. The principle and theory of the POCIS are outlined. In particular, the effect factors such as the ambient conditions, pollutant properties, and device features on the Rs are analyzed in detail from aspects of impact dependence and mechanisms. The calibration methods of the Rs under laboratory and in situ conditions are summarized. This review offers supplementary information on comprehensive understanding of mechanism and application of the POCIS. Nevertheless, the Rs were impacted by a combined effect of solute–sorbent–membrane–solution, and the influence extent of each variable was still unclear. On this basis, the ongoing challenges are proposed for the future application of the POCIS in the actual environment, for instance, the need for this device to be improved in terms of quantitative methods for more accurate measurement of the Rs.

Multi-residue determination of organic micro-pollutants in river sediment by stir-disc solid phase extraction based on oxidized buckypaper

This paper describes a procedure for the isolation of 20 organic micro-pollutants among pesticides, drugs, recreational drugs, flame retardants from river sediments. After a solid-liquid extraction with a methanol:water (50:50, v/v) solution, the supernatant was diluted with water and cleaned up by stir-disc solid-phase extraction (SPE). The disc was made of buckypaper, a self-supporting entangled assembly of carbon nanotubes, which was used as a highly porous, two-sided, sorbent membrane. In the preliminary activation step, the membrane was oxidised for 2-hours with nitric acid to extend its extraction capability also to more polar compounds. All extracts were analysed by ultra-high-performance liquid chromatography-tandem mass spectrometry. A comparative investigation with commercial Strata-X Polymeric Reversed Phase SPE cartridges proved the effectiveness of the lab-made device. On the average, the analytes were recovered with yields around 69% (low spike level) and 80% (medium and high spike level), while only a couple of analytes exhibited values less than 50%. The relative standard deviation was always less than 20%. Limits of detections were in the range 0.02–9.9 ng g−1. The validated method was then applied for the analysis of sediment samples from different sites of the River Turia basin in the area of Valencia (Spain), finding tris(2-chloroisopropyl)-phosphate in all sediments at a level ranging from 6.9 to 387.9 ng g−1. Other compounds, such as pesticides and pharmaceuticals were more sporadically in these samples.

Nano-liquid chromatography for enantiomers separation of baclofen by using vancomycin silica stationary phase

The chiral separation of baclofen (Bac) was obtained by nano-liquid chromatography tandem mass spectrometry (nano-LC–MS/MS) using a 100 μm I.D. fused silica capillary column packed with silica particles chemically modified with vancomycin. Various experimental parameters, such as composition (buffer concentration, water content, organic modifier) and pH of the mobile phase and sample solvent were investigated for method optimization. In order to increase the sensitivity an on-column focusing procedure was applied. Acceptable separation of Bac enantiomers was obtained in less than 11 min eluting in isocratic mode, with 90:10 MeOH/water (v/v) containing 10 mM ammonium acetate at pH 4.5. These optimized experimental conditions were applied to the analysis of human plasma samples spiked with racemic mixture of Bac. The use of a Buckypaper disc as sorbent membrane allows one to recover both enantiomers with yields ≥ 65%. The method was fully validated, following the identification criteria of the European Commission Decision 2002/657/EC.

Rotating-disc micro-solid phase extraction of F2-isoprostanes from maternal and cord plasma by using oxidized buckypaper as sorbent membrane

This paper describes the development of an original micro-solid phase extraction device and its evaluation for the isolation of F2-isoprostanes (F2-IsoPs) from cord and maternal plasma samples. The unit is very simple and consists in a rotating disc (1.8 cm diameter) of oxidized buckypaper (BP), enwrapped in a polypropylene mesh pouch. Even if the selected F2-IsoPs have logP and pKa values that make them suitable candidates for their sorption on BP, several parameters were optimized to maximize recoveries: time of adsorption and desorption; stirring speed; volume, pH and ionic strength of the sample; type, volume, and fractions of the elution solvent; oxidation grade of BP. Among all, the last one was crucial in affecting extraction yields because of the analyte interactions with polar functionalities, introduced by a preliminary oxidative acid treatment. The investigation established the optimal oxidation time and highlighted the pros and cons of the acid activation step. All extracts were analyzed by means of liquid chromatography-tandem mass spectrometry (LC–MS/MS). Validation was performed according to the main FDA guidelines for bioanalytical methods. Depending on the spike level and analyte, recoveries ranged between 30 and 120% with precision and accuracy values lower than 20%. Quantitative analysis was accomplished by matrix-matched calibration curves whose determination coefficients were higher than 0.95. Lower limit of quantitation (LLOQ) spanned the range 2.45–6.77 μg L−1. The validated method was applied to the analysis of eight pairs of mother/child plasma samples, revealing the presence of 8-iso-15-keto-PGF2α and 8-iso-PGE2 at a concentration of about 10 μg L−1 in most cord plasma samples of preterm newborns.

On-Chip Fabrication of Carbon Nanoparticle–Chitosan Composite Membrane

The on-chip fabrication of a carbon nanoparticle–chitosan composite membrane (i.e. a sorbent membrane or a mixed matrix membrane) using laminar flow-based interfacial deprotonation technology was presented in this paper. In addition, the effects of carbon nanoparticles and reactant flow rates on membrane formation were investigated. Finally, the permeability and adsorption capacities of the membrane were discussed. During fabrication, an acidic chitosan solution and a basic buffer solution that contained carbon nanoparticles were introduced into a microchannel. At the flow interface, a freestanding composite membrane with embedded carbon nanoparticles was formed due to the deprotonation of the chitosan molecules. The membrane growth gradually stopped with time from upstream to downstream and the thickness of the membrane increased rapidly and then slowly along the reactant flow direction. The formation of the membrane was divided into two stages. The average growth rate in the first stage was significantly larger than the average growth rate in the second stage. Carbon nanoparticles in the basic solution acted as nucleating agents and made the membrane formation much easier. As the flow rate of the chitosan solution increased, the averaged membrane thickness and the membrane hydraulic permeability initially increased and then decreased. Because of the addition of carbon nanoparticles, the formed membrane had adsorption abilities. The carbon nanoparticle–chitosan composite membrane that was fabricated in this study could be employed for simultaneous adsorption and dialysis in microdevices in the future.

Development of miniaturized sorbent membrane funnel-based spray platform for biological analysis.

In this work, a miniaturized solid-phase extraction (SPE) platform, called sorbent membrane funnel, which permits in situ cleanup prior to membrane funnel-based spray analysis was developed. The fabrication of funnel and the mounting of SPE sorbent were simple and straightforward by a homemade punching system. Using different sorbents, the SPE sorbent funnel has been successfully applied in spray analysis of drug molecules spiked in human plasma, trypsin digested solution of bovine serum albumin in the presence of high concentration of chaotropic reagents, and phosphopeptides in the tryptic digested solution of casein. The results demonstrated that SPE sorbent attached membrane funnels can be a useful tool in common metabolomic and proteomic applications.

Combination of New Solid/Liquid Phase Microextraction Technique Based on Functionalized Multiwalled Carbon Nanotubes with Flame Atomic Absorption Spectroscopy for the Extraction and Determination of Zn(II) in the Environmental Samples

A new design of equilibrium hollow fiber solid-liquid phase micro-extraction (HF–SLPME) was developed for the determination of Zn(II) in environmental water samples. Membrane extraction with sorbent interface which we used in this research is a two-phase supported liquid membrane consisting of aqueous (donor phase), organic solvent/nano sorbent membrane (acceptor phase) system operated in direct immersion sampling modes. Where the multiwalled carbon nanotube dispersed in the organic solvent is held in the pores of a porous membrane supported by capillary forces and sonification. All microextraction experiments were supported using an Accurel Q3/2 polypropylene hollow fiber membrane (600 μm I.D., 200 μm wall thicknesses, 0.2μm pore size). The experimental setup is very simple and highly affordable. Among most of micro-extraction techniques reported, it is the most effective sample preparation/preconcentration technique. The hollow fiber is disposable, so single use of the fiber reduces risk of crosscontamination and carry-over problems. The proposed method allows the very effective and enriched recuperation of ionic analyte into MWCNTs/organic phase. 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, repeatability, low limits of detection and very excellent enrichment factor (EF = 950).

New capabilities for optimizing SAW gas sensors.

It is shown how the performances of SAW gas sensors can be optimized based on pure acoustic peculiarities of SAW propagation in anisotropic single crystals. For a given gas and sensitive membrane, the calibration curve (dependence of the response R versus gas concentration n), the sensitivity S (slope of the calibration curve: S = dR/dn), the detection limit nth, (cut-off of the curve at the threshold Pthr), and the resolution deltan of the sensor (recognition of two close concentrations) can be controlled by a proper choice of the substrate material and its crystallographic orientation (cut and direction of the SAW propagation). An experimental test of this property is performed on SAW devices implemented on different substrate materials and crystallographic orientations, both uncoated or coated, with a sorbent membrane of polycrystalline Pd or Pd:Ni film, upon exposure to humid air as a test analyte.

Application of a Novel Form of Solid-Phase Sorbent (Empore(R) Membrane) to the Isolation of Tricyclic Antidepressant Drugs from Blood

We employed a new form of solid-phase material, the Empore octyl (C8) extraction membrane (SPEM), for the efficient extraction of tricyclic drugs from patients' serum specimens. Both extraction and companion high-performance liquid chromatographic (HPLC) assay of doxepin (DOX), desmethyldoxepin (DDOX), imipramine (IMI), desmethylimipramine (DESI), amitriptyline (AMI), nortriptyline (NOR), clomipramine (CLO), and desmethylchlomipramine (DCLO) are presented here. Routinely, serum (1.0 mL or less) adjusted to pH 5.5 with phosphate buffer is passed through the SPEM secured in a MF-1 microfilter unit. Proteins and potential interferences retained on SPEM are removed with an acetonitrile-water wash. The tricyclic drugs are eluted with HPLC mobile phase and the eluate is injected directly on a Zorbax cyanopropyl (CN) HPLC column, thereby avoiding time consuming evaporation-concentration steps that can affect drug stability. Recovery for all drugs exceeds 90% and analytical responses are linear from a lower limit of sensitivity of 8 micrograms/L up to at least 1000 micrograms/L. Between-run coefficients of variation (CV) range from 2.9 to 8.3% through the concentration range of 75 to 300 micrograms/L. Performance characteristics of the SPEM are compared to those of conventional large particle silica- and polymeric-based sorbents. Within the requirements of this assay, the SPEM extraction requires less sample volume and reduces elution and solvent volumes.

Theory of diffusion through, and sorption in, a biporous sorbent membrane with a constant difference in concentration at the membrane faces and linear sorption isotherm 3. Sorption in the transport pore system

1. The problem of saturating the biporous membrane is discussed for the special case in which a constant difference in concentration is maintained between the membrane faces. 2. Analytical expressions for the concentration profile of the diffusing material within the membrane, the degree of approach to the stationary state, and total flux of diffusing material, have been obtained. 3. The effect of the various model parameters on the progress of the saturation process is analyzed.

Sorbent membrane dialysis in uremia.

The inclusion of activated charcoal within hemodialysis membranes offers potentially improved plasma clearance of creatinine and middle molecules. However, the carbon becomes saturated with continued use and beyond 1 h removal of solutes is by dialysis alone. Two independently conducted crossover studies, to assess the efficacy of sorbent membrane dialysis (SMD) in the treatment of uremia, found predialysis urea levels increased by approximately 15%, creatinine by 10-15%, and inorganic phosphate levels by 10-18% on SMD compared to conventional hemodialysis. One study also observed "middle molecule' (peak "b') levels elevated. No differences were observable in the clinical status of patients. The results suggest that the charcoal content of the SMD device is too small to effect any advantages over conventional dialysis.

Theory of the diffusion and sorption of various substances through a biporous sorbent membrane with constant concentration difference at its boundaries

1. We have considered the determination of the transfer coefficients in transport pores and micropores during the diffusion and sorption of various substances through a biporous sorbent membrane, when there is a constant concentration difference of diffusing substance at the boundaries. 2. We have obtained simple formulas for the separate determination of diffusion relaxation times in transport pores and micropores from the experimentally determined dependence of the amount of substance carried away from the back side of the membrane on time.

Sorbent Membranes: Determination of Sorption Capacity and True Membrane Permeability

ABSTRACTSorbent membranes are designed to meet the requirements for extracorporeal treatment of body fluids. These membranes offer the possibility of combining hemodialysis and hemoperfusion in a single device. Transport of solutes with both sorption and dialysis occurs simultaneously in a sorbent membrane dialyzer. In an effort to determine the sorption capacity and true membrane permeability (by dialysis only) of sorbent membranes, in vitro data were obtained for creatinine. The individual effects of dialysis and sorption on the rate of removal of solutes and their dependence upon flow rate in a sorbent membrane dialyzer were determined from the data of solute vessel concentration vs time. Experiments were carried out with a continuous flow, flat‐plate dialyzer and Enka AG sorbent membranes have been selected for evaluation. It was found that sorption plays an important role in the creatinine removal. However, as the time increases, sorption becomes relatively less important and the creatinine removal becomes dominated by dialysis.

Theory of diffusion and sorption of various substances through a biporous sorbent membrane for the case of a constant concentration difference at its boundaries and a linear sorption isotherm. I. Case of an exponential kinetic function for the microporous zones

1. An analytical solution has been obtained for the passage of the sorbed substance through a membrane of a biporous sorbent for the case of constant concentration differences of the sorptive on its boundaries and a linear sorption isotherm. 2. The distribution of the sorptive concentration in the membrane in different moments of time has been calculated as an example, for the case of equal characteristics of diffusion relaxation times in the transporting porous system and in the microporous zones.