A computational method for determination of the mass-transfer coefficient in packed-bed immobilized enzyme reactors

A computational method was developed that determined the mass-transfer coefficient k_L or the volumetric mass-transfer coefficient k_La in packed-bed immobilized enzyme (IME) reactors. To study the performance of this method, two experimental systems were considered where an enzyme was immobilized on a non-porous support surface (surface-IME system) or within a porous support (pore-IME system). The values of k_L and k_La determined in these packed-bed IME reactor systems were successfully expressed in terms of the substrate concentration at the reactor inlet and the liquid flow rate. Furthermore, the correlations obtained for k_L and k_La were used to calculate the unconverted fractions of substrate at the reactor outlet. Comparison showed that the calculated results were in satisfactory agreement with the experimental values.     

A novel method for continuous production of cyclodextrins using an immobilized enzyme system

Selected specific α-amylase and glucoamylase enzymes were immobilized and combined with immobilized cyclodextrin glycosyltransferase to continuously produce cyclodextrin (CD). The liquefied starch was cyclized to CD by ICGTase and then treated by immobilized α-amylase and glucoamylase to contain CD and glucose only. β-CD and soluble CD (α- and γ-CD) in the final CD solution could be easily separated. The pH-activity curve, temperature-activity curve, batch re-usability and continuous operation stability of immobilized enzymes were discussed. The continuous production of CD by an immobilized enzyme system was also reported. The optimal conditions for using immobilized α-amylase and glucoamylase simultaneously were 40°C and pH 4.5 adjusted by 1 mol dm^?3 HCl/NaOH. A 70% yield of CD could be obtained from 1% (w/v) of liquefied starch under continuous operation at 0.055 h^?1 space velocity, and almost all the oligosaccharides (β 98%) were converted to glucose. In this study, the separation of α-CD, γ-CD and glucose, using organic solvent from the final product after precipitating β-CD, was also investigated.     

A simple method for accurate determination of porosity using ideal gas law

We suggest a simple method for experimental determination of porosity of a material. This technique, which is similar to the variable-volume gas pycnometry, is very inexpensive and extremely simple yet produces accuracies that are comparable to the existing methods. Some of the advantages of the technique as well as the effect of material compressibility are also discussed.     

Design and operation of an autosampler controlled flow-injection preconcentration system for lead determination by flame atomic absorption spectrometry

Flow-injection manifolds are described which allow the preconcentration of lead for flame atomic absorption determinations, using columns contained within the sample loop of an injection valve. An interface was designed which allowed the valves and pump in the system to be controlled by an autosampler which enabled precise timing of preconcentration and elution steps. The effects of sample flow rate, buffer pH and buffer type for preconcentration and eluent concentration and flow rate were investigated in order to obtain optimum performance of the system. A 50-times improvement in detection limits over conventional sample introduction was obtained for a sample volume of approximately 12 ml, preconcentrated for 150 s. The injection of eluent, as opposed to the use of a continuously flowing eluent stream, enabled this reagent to be conserved.     

Degradation of pentachlorophenol by an electroenzymatic method using immobilized peroxidase enzyme

In this study, pentachlorophenol (PCP) was degraded by the electroenzymatic method, which combines the enzymatic catalysis and the electrogeneration of hydrogen peroxide (H₂O₂). The experiments were conducted in a two-compartment packed-bed reactor using horseradish peroxidase (HRP) immobilized electrode. The highest production of H₂O₂ and the current efficiency were observed at −0.4 V vs. Ag/AgCl and a flow rate of 1 mL/min. The highest initial degradation rate and degradation efficiency of PCP were achieved at pH 5 and 25 °C. Under the conditions, the electrolysis was compared with an electrochemical method. The presence of chloride ion indicates that PCP was dechlorinated at the initial period of degradation. According to the proposed breakdown pathway and the intermediates, the electroenzymatic method showed an improved degradation ability compared to an electrochemical method.     

A simple and precise method for the routine determination of platelet-activating factor in blood and urine

A simple and precise method is described for the measurement of platelet-activating factor (PAF) in blood and urine. The method involves the isolation of PAF from blood samples by two successive steps. In the first step, blood proteins are precipitated with ethanol and the “free” PAF, i.e. the PAF which is extractable with ethanol, is recovered. In the second step, “bound” PAF, i.e., PAF not extractable with ethanol, is extracted from the protein precipitate with chloroform/methanol/water. The extraction of PAF from urine samples requires only the ethanol extraction step. “Free” and “bound” PAF are then each fractionated by silicic acid column chromatography, and the methanol/water eluent containing PAF is then further fractionated by high-performance liquid chromatography using an isocratic solvent system of acetonitrile/methanol/water. PAF is then quantitated by measuring its ability to induce platelet aggregation in an aggregometer. Application of the method to blood and urine samples from twenty-three healthy volunteers revealed PAF levels in blood of 140–480 pg/mL (630–254.4 pg “free” PAF/mL and 64–225.6 pg “bound” PAF/mL), and of 1.2–4.0 pg PAF/mL in urine. The method overcomes various technical problems and was shown to be very precise. It should prove useful for monitoring PAF levels in various disease conditions.     

Automation of flow injection gas diffusion-ion chromatography for the nanomolar determination of methylamines and ammonia in seawater and atmospheric samples

The automation and improved design and performance of Flow Injection Gas Diffusion-Ion Chromatography (FIGD-IC), a novel technique for the simultaneous analysis of trace ammonia (NH₃) and methylamines (MAs) in aqueous media, is presented. Automated Flow Injection Gas Diffusion (FIGD) promotes the selective transmembrane diffusion of MAs and NH₃ from aqueous sample under strongly alkaline (pH > 12, NaOH), chelated (EDTA) conditions into a recycled acidic acceptor stream. The acceptor is then injected onto an ion chromatograph where NH₃ and the MAs are fully resolved as their cations and detected conductimetrically. A versatile PC interfaced control unit and data capture unit (DCU) are employed in series to direct the selonoid valve switching sequence, IC operation and collection of data. Automation, together with other modifications improved both linearily (R² > 0.99 MAs 0-100 nM, NH₃ 0-1000 nM) and precision (<8%) of FIGD-IC at nanomolar concentrations, compared with the manual procedure. The system was successfully applied to the determination of MAs and NH₃ in seawater and in trapped particulate and gaseous atmospheric samples during an oceanographic research cruise.