Flow-through Apparatus Research Articles

Amphiphilic porphyrin film on glass as a simple and selective solid-state chemosensor for aqueous Hg2+

Deposition of amphiphilic porphyrin derivatives occurs spontaneously on silanised glass surfaces, in a controlled fashion. The resulting porphyrin films show appreciable fluorescence emission. This emission can be effectively quenched by immersion of the slides into a diluted solution of Hg(2+) (microM concentration). The initial intensity can be restored by washings with a solution of N,N,N',N'-tetrakis(2-pyridilmethyl)ethylenediammine with no loss of efficiency. A remarkable selectivity is featured toward the detection of Hg(2+) over Cu(2+), Cd(2+), Pb(2+) and Zn(2+) counterparts. This protocol can be extended to a flow-through apparatus. The presented results are of importance for the achievement of a solid-state chemosensor for mercuric ions, at micromolar concentration, in water.

Intestinal permeability and excretion into bile control the arrival of amlodipine into the systemic circulation after oral administration

The objective of this study was to identify the factors controlling the arrival of amlodipine into the systemic circulation after oral administration in the fasting state. Dissolution data were collected with the rotating paddle and the flow-through apparatus. Caco-2 cell lines were used to assess the intestinal permeability characteristics. Actual in-vivo data were collected in 24 fasted healthy subjects after single-dose administration of the same amlodipine besylate tablet formulation used in the in-vitro dissolution studies. Regardless of the hydrodynamics, dissolution of amlodipine besylate tablets was rapid and complete in media simulating the contents of the upper gastrointestinal tract in the fasting state. Permeability of amlodipine through Caco-2 cell lines was lower than propranolol's and higher than ranitidine's, indicating that transport through the intestinal mucosa may be one process that limits the arrival into the systemic circulation. Indeed, the de-convoluted profile indicated that arrival into portal blood occurs at rates much slower than gastric emptying or dissolution rates. However, prediction of amlodipine's mean plasma profile after oral administration became possible only after additionally assuming excretion of amlodipine into the bile and a reasonable gastrointestinal residence time. Interestingly, in-vitro permeability data collected in this or in previous studies were inappropriate for simulating the mean actual plasma profile.

Batch and Tubular-Batch Crystallization of Paracetamol: Crystal Size Distribution and Polymorph Formation

The crystallization of paracetamol from ethanol and methanol solutions was used to examine the possibility of using rapid cooling in a tubular flow-through apparatus to manipulate crystal size distribution and morphology. Flow through the tubular portion of the apparatus was laminar, and hence, the device, including a receiving vessel, is referred to as a laminar-flow tubular crystallizer (LFTC). Undersaturated solution entered the tubular portion of the LFTC and was rapidly cooled to temperatures far below solubility conditions. Experimental results were also obtained using a typical batch configuration with the same solute and solvents, but with significantly lower cooling rates than in the LFTC. The crystals produced in the flow-through apparatus were of smaller mean size than those obtained from batch crystallizations, and evidence was found that using the rapid-cooling technique could lead to the generation of kinetically stable polymorphs. Moreover, the total run time required to relieve all of the ...

超臨界水・メタノール中での酸塩基平衡の分光測定

Acid-base equilibria in supercritical water and alcohols are of great importance in controlling chemical processes in the high-temperature and high-pressure media. Recent advances in spectroscopic measurement of acid-base equilibria in supercritical water are reviewed together with those in conductmetric and potentiometric methods. I also present our recent study of acid-base equilibria in supercritical methanol using a flow-through apparatus and 2,5-dichlorophenol (DCP) as an indicator. It is explained how to determine the degree of dissociation of DCP in ambient to supercritical methanol from the absorption spectra at various concentrations of base.

Effects of Soil Storage on the Microbial Community and Degradation of Metsulfuron-methyl

The effect storage had on the microbial biomass in two soils (Trevino and Fargo) was compared to the effect storage had on each soil's capacity to degrade metsulfuron-methyl. Soils were collected from the field and used fresh (<3 weeks old) or stored at 20 and 4 degrees C for 3 or 6 months. The phospholipid fatty acid content of the soils was used to monitor changes in the microbial biomass during storage and incubation in a flow-through apparatus. In both soils, [phenyl-U-14C]metsulfuron-methyl was used to monitor changes in the route and rate of degradation along with 14CO2 evolution (mineralization). Total microbial biomasses in both soils were significantly reduced for soils incubated in the flow-through apparatus, whereas only the Trevino soil's microbial biomass was significantly reduced as a result of storage. The microbial communities of both soils were significantly different as a result of storage as shown by discriminant analysis. In both soils, degradation rate, pathway of degradation, and mineralization of metsulfuron-methyl were significantly affected by storage compared to fresh soil. The half-life of metsulfuron-methyl increased significantly (P < 0.05) in the Trevino soil from 45 days (fresh) to 63 days (stored soil), whereas in the Fargo soil half-lives increased significantly (P < 0.05) from 23 days (fresh) to 29 days (soils stored for 6 months). In both soils, mineralization of [14C]metsulfuron-methyl was significantly (P < 0.05) higher in fresh soils compared to stored soils. The degradation pathways of metsulfuron-methyl changed with storage as evidenced by the loss of formation of one biologically derived metabolite (degradate) in stored soils compared to fresh soils.

Nitric oxide gas stimulates germination of dormant Arabidopsis seeds: use of a flow-through apparatus for delivery of nitric oxide

Nitric oxide (NO) is a gaseous free radical that reacts with O(2) in air and aqueous solution. NO donors have been widely used to circumvent the difficulties inherent in working with a reactive gas, but NO donors do not deliver NO at a constant rate for prolonged periods of time. Furthermore, some of the most commonly used NO donors produce additional, bioactive decomposition products. We designed and built an apparatus that allowed for the precise mixing of gaseous NO with air and the delivery of gas through sample vials at fixed rates. This experimental setup has the added advantage that continuous flow of gas over the sample reduces the buildup of volatile breakdown products. To show that this experimental setup was suitable for studies on the dormancy and germination of Arabidopsis thaliana seeds, we introduced vapors from water or sodium nitroprusside (SNP) into the gas stream. Seeds remained dormant when treated with water vapor, but gases generated by SNP increased germination to 90%. When pure NO was mixed with air and passed over dormant seeds, approximately approximately 30% of the seeds germinated. Because nitrite accumulates in aqueous solutions exposed to NO gas, we measured the accumulation of nitrite under our experimental conditions and found that it did not exceed 100 microM. Nitrite or nitrate at concentrations of up to 500 microM did not increase germination of C24 ecotype Arabidopsis seeds to more than 10%. These data support the hypothesis that NO participates in the loss of Arabidopsis seed dormancy, and they show that for some dormant seeds, exposure to exogenous NO is sufficient to trigger germination.

New Developments in Flow-Through Apparatus for Measurement of Adsorption Mass-Transfer Rates by Frequency Response Method

A new flow-through frequency response method based on a sinusoidal modulation of pressure is developed to measure gas adsorption equilibria and kinetics simultaneously. The transfer phenomena of pure N2 and O2 gases in carbon molecular sieve are investigated for different pressures and particle sizes by this method. Also, this apparatus has been extended to measure data for mixtures at different compositions at atmospheric pressure and room temperature. This is the first application of the flow FR system for a mixture. A negative cross-term diffusivity is reported. It shows that for co-diffusion, the fast diffusing molecule O2 is decelerated by the slow diffusing molecule N2, and the slower moving molecule N2 is sped up by the faster moving O2. The main-term diffusivities agree with the pure component diffusivities.

Hydrothermal synthesis of ZnO nanocrystals using microreactor

Hydrothermal synthesis of ZnO nanocrystals from 10 −3 mol/kg ZnSO 4 and 4×10 −3 mol/kg KOH solutions was carried out with a microreactor and a flow-through apparatus for a rapid heating of the starting solution to reaction temperature and for a rapid cooling after reaction to room temperature. Effect of inner diameter of the microreactor on particle size was examined at 673 K and 30 MPa. Nanocrystals having an average diameter of 9 nm was produced using the microreactor with inner diameter of 0.3 mm.

Effect of cations and anions on properties of zinc oxide particles synthesized in supercritical water

Hydrothermal synthesis of zinc oxide fine particles from zinc salt (Zn(CH 3COO) 2, ZnSO 4, Zn(NO 3) 2) and alkali metal hydroxide (LiOH, KOH) aqueous solution was carried out with a Ti alloy batch reactor in supercritical water. Particle size synthesized in LiOH solution was relatively smaller than that in KOH. Emission spectra of the particle produced from ZnSO 4 and LiOH aqueous solution shows the highest intensity among these systems. Hydrothermal synthesis of zinc oxide fine particles from Zn(NO 3) 2 and LiOH solution was also carried out with a flow-through apparatus for continuous production and rapid heating of the starting solution to supercritical states. Nanoparticles having an average particle diameter of 16 nm was produced at 659 K and 30 MPa.

A Study of Radial Mixing in a Continuous Flow-through Apparatus

The structure of flows was studied experimentally in continuous flow-through apparatus in various flow modes.

Experimental determination of sorption in fractured flow systems

Fracture “skins” are alteration zones on fracture surfaces created by a variety of biological, chemical, and physical processes. Skins increase surface area, where sorption occurs, compared to the unaltered rock matrix. This study examines the sorption of organic solutes on altered fracture surfaces in an experimental fracture-flow apparatus. Fracture skins containing abundant metal oxides, clays, and organic material from the Breathitt Formation (Kentucky, USA) were collected in a manner such that skin surface integrity was maintained. The samples were reassembled in the lab in a flow-through apparatus that simulated ∼2.7 m of a linear fracture “conduit.” A dual-tracer injection scheme was utilized with the sorbing or reactive tracer compared to a non-reactive tracer (chloride) injected simultaneously. Sorption was assessed from the ratio of the first temporal moments of the breakthrough curves and from the loss of reactive tracer mass and evaluated as a function of flow velocity and solute type. The breakthrough curves suggest dual-flow regimes in the fracture with both sorbing and non-sorbing flow fields. Significant sorption occurs for the reactive components, and sorption increased with decreasing flow rate and decreasing compound solubility. Based on moment analysis, however, there was little retardation of the center of solute mass. These data suggest that non-equilibrium sorption processes dominate and that slow desorption and boundary layer diffusion cause extensive tailing in the breakthrough curves.

Influence of aminoacid anions on the absorption process of Mg2+ ions in vitro

Influence of aminoacid anions on the absorption process of Mg2+ ions in vitro - The results of the research on influence of modification in the structure of magnesium salts with glycine on the process of Mg (11) ions absorption were presented in this paper. A flow-through apparatus containing a piece of small intestine of a rat was used for the absorption rate measurement of selected organic magnesium salts. The results of the investigations showed the positive influence of modification of the structure on the absorption process. A correlation was established between quantity of absorbed magnesium and the partition coefficient values (log P).

Experimental Determination of Dissolution Kinetics of Zr-Substituted Gd-Ti Pyrochlore Ceramics: Influence of Chemistry on Corrosion Resistance

ABSTRACTThe corrosion resistance of a series of zirconium-substituted gadolinium pyrochlore, Gd2(Ti1-x Zrx)2O7, where x = 0.0, 0.25, 0.50, 0.75, and 1.00, were evaluated using single-pass flow-through (SPFT) apparatus at 90°C and pH = 2. The zirconate end-member, Gd2Zr2O7, has a defect fluorite structure, which distinguishes it from the face-centered cubic structure of the true pyrochlore specimens. In addition to the chemical variation, the samples include annealed, un-annealed, and ion-bombarded monoliths. In the case of the titanate end-member, Gd2Ti2O7, the annealed specimen exhibited the least reactivity, followed by the un-annealed and ion-bombarded samples (2.39×10-3, 1.57×10-2, and 1.12×10-1 g m-2 d-1, respectively). With increasing zirconium content, the samples displayed less sensitivity to processing or surface modification with the zirconate end-member exhibiting no difference in reactivity between annealed, un-annealed, and ion-bombarded specimens (rate = 4.0×10-3 g m-2 d-1). In all cases, the dissolution rate decreased with increasing zirconium content to the Gd2(Ti0.25Zr0.75)2O7 composition (1.33x10-4 g m-2 d-1), but the zirconate end-member yielded rates nearly equal to that of the titanate end-member. These results demonstrate that to achieve the greatest radiation and corrosion resistance in this series, the Gd2(Ti0.25Zr0.75)2O7 composition should be considered.

Results of Vertical Scanning Interferometry (VSI) of Dissolved Borosilicate Glass: Evidence for Variable Surface Features and Global Surface Retreat

ABSTRACTTwo disparate reaction mechanisms have been invoked to explain the reactivity of glass in contact with aqueous solution. One model is based on arguments from Transition State Theory (TST), which postulates that glass dissolution rates are surface reaction controlled. Alternatively, the second model argues that release of elements from glass to solution is governed by diffusion through an altered layer that forms on the surface of glass. Vertical Scanning Interferometry (VSI) is a new technique that allows one to observe surface features of specimens exposed to solution and may, potentially, be used to distinguish between competing models. We performed a series of dissolution experiments with a suite of glass compositions from chemically simple (sodium borosilicate) to complex (sixteen component borosilicate). Dissolution rates were determined using single-pass flow-through (SPFT) apparatus at 90°C and pH = 9 and over a solution saturation interval. Upon termination of the experiments, glass coupons were examined by VSI techniques. Effluent chemistry and VSI measurements indicate a nearly constant rate of 2.2 to 3.4 g m-2 d-1 over the solution interval; rates calculated from both methods are identical within experimental uncertainty. We argue that this glass is phase separated, and propose a model for dissolution based on the relative rates of dissolution of the two glass compositions. The data are consistent with a modified version of TST and indicate the potency of VSI methods to elucidate glass reaction mechanisms.

Photic regulation of melatonin in rat retina and the role of proteasomal proteolysis.

Several investigations have shown that illumination at night reduces melatonin level in the mammalian pineal, but the effect of night illumination on the retina is not known. In this study retinas were cultured in a flow-through apparatus and then were exposed to light at ZT 18. Light exposure reduced melatonin levels to the daytime level within 30 min. The reduction of melatonin levels was due to a rapid decrease in the activity of the enzyme AA-NAT; AA-NAT mRNA levels were not affected by illumination. Pre-incubation with lactacystin (25 microM) prevented light-induced reduction of AA-NAT activity and melatonin levels. These results demonstrate that melatonin levels in the mammalian retina are affected by light exposure at night, via proteosomal proteolysis of AA-NAT.

Areca nut extract lowers the permeability of vaginal mucosa to reduced arecoline and arecaidine.

Areca nut chewing has been implicated in the development of oral cancer and oral submucous fibrosis. Arecoline and arecaidine, which are alkaloids present in the areca nut, are thought to play a major role in the development of adverse effects resulting from this chewing habit. Because these alkaloids appear to be associated with the development of the above diseases, we determined their diffusion kinetics through human vaginal mucosa in the presence and absence of a 1% areca nut extract. Seven clinically healthy vaginal mucosa specimens (mean patient age+/-standard deviation, 52+/-13 years; age range, 38-74 years) were obtained during surgery. In vitro flux values of reduced arecoline and arecaidine (r-arecoline and r-arecaidine) were determined through use of a flow-through diffusion apparatus. Analysis of variance, a Duncan multiple range test, and an unpaired t-test were used to determine steady state kinetics and flux differences over time intervals. The flux values across vaginal mucosa of r-arecoline and r-arecaidine were decreased in the presence of 1% areca nut extract. For r-arecoline, these flux values were significantly lower statistically when compared to those obtained in the absence of areca nut extract. These findings concur with results previously obtained for water, where the astringent action of the tannins present in the areca nut extract was thought to alter the barrier properties of the epithelium, resulting in decreased permeability.

Influence of Dissolution Medium Agitation on Release Profiles of Sustained-Release Tablets

Reaching nearly perfect sink conditions is very important in the determination of drug dissolution rates. Many times, the only factor that is taken into consideration in achieving sink conditions is the relation between the drug concentration and its solubility. The analytical conditions of the dissolution assay, as well as the dissolution apparatus, stirring speed, and nature and volume of the dissolution fluid may also influence the dissolution results. The main objective of this work was to study the influence of the stirring rate conditions and of the dissolution apparatus in the diltiazem hydrochloride release from tablets. Diltiazem hydrochloride sustained-release (SR) tablets were tested and the following dissolution parameters were evaluated: t10%, t25%, t50%, dissolution time, mean dissolution time (MDT), and dissolution efficiency (DE) at t120, and at t360. To analyze the release mechanism, several release models were tested, such as Higuchi, zero order, first order, Baker-Lonsdale, Hixson-Crowell, Weibull, and Korsmeyer-Peppas. The similarities between two in vitro dissolution profiles were assessed by the similarity factor f2. The in vitro release kinetics of diltiazem hydrochloride sustained-release tablets were evaluated using the USP 2 (paddle) and USP 4 (flow-through) apparatus.

Relationships of ultraviolet radiation dose and inactivation of pathogen propagules in water and hydroponic nutrient solutions

Conidia of Fusarium oxysporum f. sp. cyclaminis and zoospores of Pythium aphanidermatum were suspended in water and hydroponic nutrient solutions and treated with various doses of UV radiation (253.7 nm) by means of a collimated-beam apparatus and a flow-through apparatus. Germination and colony-forming ability of spores from treated suspensions were estimated on agar media. Colony-forming ability of F. oxysporum f. sp. cyclaminis decreased logarithmically, with increase in applied dose of UV radiation, and in curves that were 3 to 10 times steeper for conidia in water compared to crop nutrient solutions. In tests in the flow-through apparatus, applied doses required to inactivate 99.90% of conidia in water, in fresh nutrient solution, and in nutrient solutions from pepper and tomato crops were 20, 93, 104, and 254 mW·s·cm−2, respectively. In the collimated-beam apparatus, applied doses to inactivate 99.90% of conidia were two to three times higher. Colony-forming ability of P. aphanidermatum zoospores decreased logarithmically, with UV radiation dose, in curves that ranged from similar to twice as steep for zoospores in water compared to plant nutrient solutions. Inactivation of 99.99% of zoospores in water, fresh plant nutrient solution, and pepper crop nutrient solution, respectively, required doses of 12, 17, and 38 mW·s·cm−2 as estimated in the flowthrough apparatus, and 34, 46, and 213 mW·s·cm−2 as estimated in the collimated-beam apparatus. Colony-producing ability of zoospores of P. aphanidermatum and an unidentified species of Pythium from hydroponic lettuce declined more rapidly than did germination incidence as UV dose was increased. In conclusion, UV radiation doses of 30-40 and 20-30 mW·s·cm−2 inactivated most conidia of F. oxysporum f. sp. cyclaminis and zoospores of P. aphanidermatum, respectively, when applied to suspensions of the spores in water. For spores in plant nutrient solutions, the applied dose must be increased to compensate for absorbance of UV radiation in the solution

NMR imaging investigations of drug delivery devices using a flow-through USP dissolution apparatus

A system for performing NMR imaging experiments on drug delivery devices within a flow-through dissolution apparatus, USP Apparatus 4, has been developed. The system was used to image the physical changes that occur in solid dosage forms during dissolution in the flow-through apparatus. Simultaneous cumulative drug release measurements were also made. The NMR images obtained under these conditions and the drug release data provide a better understanding of the processes involved in the release of drugs from drug delivery systems based on diffusion, dissolution and osmosis mechanisms.

Dopamine inhibits melatonin release in the mammalian retina: in vitro evidence

A circadian oscillator located within the retina controls melatonin synthesis in the retina of mammals. In non-mammalian vertebrates retinal melatonin and dopamine appear to act as mutually inhibitory paracrine signals for night and day, respectively; while in mammals this mutually inhibitory capability has now been fully demonstrated. In this study using a flow-through culture apparatus we investigated melatonin release from cultured retinas of golden hamster ( Mesocricetus auratus) in the presence of dopamine or dopaminergic agonists and antagonists. Neural retinas were cultured with medium 199 for 24 h in a flow-through apparatus at the temperature 33°C. During the subjective night the culturing medium was supplemented with dopamine, dopamine receptor antagonists or agonists. At the concentration of 0.1 μM dopamine did not inhibit melatonin release, while at higher dopamine concentration (1 to 1000 μM) melatonin release was inhibited in a dose-dependant manner. These effects appeared to be mediated by a D 2/D 4 receptor, because D 2 and D 4 receptor agonists (100 μM), but not D 1/D 5 receptor agonists (100 μM), inhibited melatonin release. Furthermore, D 2/D 4 selective receptor antagonists (100 μM) in conjunction with 100 μM dopamine blocked melatonin suppression, whereas a D 1/D 5 selective receptors antagonist was completely ineffective. Taken together, these results directly demonstrate for the first time that in the retina of mammals dopamine may suppress melatonin, and that suppression is mediated by D 2D 4 dopaminergic receptors.