Analysis of Relationship Between Microbial and Methanogenic Biomass in Methane Fermentation

To analyze the relationship between biomass of microorganisms and methane production, the total biomass of bacteria and archaea (BA) during methane fermentation was analyzed by the environmental DNA analysis method. In the case of using methanogenic sludge as a seed which is generally used for methane fermentation, the total BA biomass reached to 1.5 × 10⁸ to 3.6 × 10⁸ cells/ml when methane was produced. On the other hand, soil suspension was used as a seed; methane was not produced for 14-day cultivation. However, the total BA biomass reached to above 1.5 × 10⁸ cells/ml. The methanogen biomass was counted by using a fluorescence microscope (coenzyme F₄₂₀), and the methanogen biomass and the ratio of methanogens in the total of BA were analyzed during methane fermentation. At the methane-producing phase, the methanogen biomass reached to 1.3 × 10⁸ cells/ml, and the ratio of methanogens was above 70% of the total BA. When the ratio of methanogens in a seed was changed, the methane-producing phase was moved. However, the relationship between methanogens and other microorganisms at the methane-producing phase was almost similar.     

Novel fabrication of silver-coated glass capillaries for ready SERS-based detection of dissolved chemical species

A novel method to deposit a highly surface-enhanced Raman scattering (SERS) active silver film onto the inside surface of a glass capillary is developed. Firstly, Ag sol was synthesized by the reaction of AgNO₃ with poly-(ethylenimine) (PEI), and then toluene and benzenethiol (BT) were added into the sol. The mixture was flowed through the glass capillary to obtain the SERS-active Ag film-coated glass capillary. The SERS activity of the Ag-coated capillary was dependent on the amount of PEI and BT used. In addition, BT could be easily desorbed from the Ag surface by treating it with a borohydride solution, maintaining the initial SERS activity. The SERS enhancement factor at 632.8-nm excitation was estimated to be on the order of 10⁶. The detection limits of adenine and dipicolinic acid were then as low as 1.0 × 10⁻⁸ and 1.0 × 10⁻⁷ M, respectively, based on an S/N ratio of 3. This clearly suggests that the Ag-coated capillary is an invaluable device for the analysis of effluent chemicals by SERS.     

Flow injection analysis of volatile phenols in environmental water samples using CdTe/ZnSe nanocrystals as a fluorescent probe

On the basis of flow injection analysis technology, a simple, accurate, and sensitive method has been developed for the determination of volatile phenols in environmental water samples by using CdTe/ZnSe nanocrystals as a fluorescent probe. The influences of coexisting metal ions and volatile phenol substitutes were also investigated. The method developed for analysis of volatile phenols displayed very good linearity in the range from 1.0 × 10⁻⁸ to 4.0 × 10⁻⁷ g L⁻¹, with a correlation coefficient greater than 0.995 and a detection limit down to 2.7 × 10⁻⁹ g L⁻¹ (signal-to-noise ratio 3). The proposed method was successfully applied to determine the content of volatile phenols in environmental water samples, and the quantitative recoveries were 93.4–106.1%. A possible reaction mechanism for the quenching of fluorescence is discussed using UV–vis absorption spectra, fluorescence spectra, and time-resolved luminescence spectra of volatile phenols obtained by titrating a CdTe/ZnSe nanocrystal aqueous solution and zeta potential data.     

A compact miniaturized continuous flow system for the determination of urea content in milk

A multicommutation-based flow system with photometric detection was developed, employing an analytical microsystem constructed with low temperature co-fired ceramics (LTCC) technology, a solid-phase reactor containing particles of Canavalia ensiformis DC (urease source) immobilized with glutaraldehyde, and a mini-photometer coupled directly to the microsystem which monolithically integrates a continuous flow cell. The determination of urea in milk was based on the hydrolysis of urea in the solid-phase reactor and the ammonium ions produced were monitored using the Berthelot reaction. The analytical curve was linear in the urea concentration range from 1.0 × 10⁻⁴ to 5.0 × 10⁻³ mol L⁻¹ with a limit of detection of 8.0 × 10⁻⁶ mol L⁻¹. The relative standard deviation (RSD) for a 2.0 × 10⁻³ mol L⁻¹ urea solution was lower than 0.4% (n = 10) and the sample throughput was 13 h⁻¹. To check the reproducibility of the flow system, calibration curves were obtained with freshly prepared solutions on different days and the RSD obtained was 4.7% (n = 6). Accuracy was assessed by comparing the results of the proposed method with those from the official procedure and the data are in close agreement, at a 95% confidence level.     

Microencapsulated Engineered <Emphasis Type="Italic">Lactococcus lactis Cells</Emphasis> for Heterologous Protein Delivery: Preparation and In Vitro Analysis

This article demonstrates the potential of encapsulated, engineered Lactococcus lactis as a vehicle for the oral delivery of therapeutic proteins. Using alginate-poly-l-lysine-alginate membrane-encapsulated L. lactis engineered to secrete the reporter protein Staphylococcal aureus nuclease, we show comparable viability and protein secretion between free and immobilized cells. After 12 h, microcapsules with a cell density of 4.8 × 10⁵ colony forming unit (CFU) ml⁻¹ grew to 2.2 × 10⁸ CFU ml⁻¹ and released 0.24 arbitrary unit (AU) ml⁻¹ of nuclease, producing similar results as free cells, which grew from 3.4 × 10⁵ to 1.9 × 10⁸ CFU ml⁻¹ and secreted 0.21 AU ml⁻¹ of nuclease. Moreover, encapsulated cells at a density of 4.4 × 10⁷ CFU ml⁻¹ grew to 2.2 × 10¹⁰ CFU ml⁻¹ in 12 h and secreted 15.3 AU ml⁻¹ of nuclease although 3.1 × 10⁷ CFU ml⁻¹ of free cells reached only 2.3 × 10⁹ CFU ml⁻¹ and released 5.6 AU ml⁻¹ of nuclease. We also show the sustained stability of the microcapsules during storage at 4°C over 8 weeks.     

A New Differential Pulse Voltammetric Method for the Determination of Nitrate at a Copper Plated Glassy Carbon Electrode

 A differential pulse voltammetric method for the determination of nitrate has been described, which is applicable to the analysis of natural water samples with nitrate levels greater than 2.8 × 10⁻⁶ M. A reduction peak for the nitrate ions at a freshly copper plated glassy carbon electrode was observed at about −0.50 V vs Ag ∣AgCl∣KCl_satd electrode in a solution of 2.0 × 10⁻² M Cu²⁺, 0.5 M H₂SO₄ and 1.0 × 10⁻³ M KCl and exploited for analytical purposes. The working linear range was established by regression analysis and found to extend from 2.8 ×10⁻⁶ M to 8.0 × 10⁻⁵ M. The proposed method was applied for the determination of nitrate in natural waters. The detection limit of the method was 2.8 × 10⁻⁶ M and the sensitivity was 0.9683 A·L/mol. The possible interferences by some ions such as phosphate, nitrite and some halides were determined and found to lead to shifts of the peak position and increasing the peak heights. Received March 15, 1999. Revision July 9, 1999.     

Investigation of calcium antagonist–L-type calcium channel interactions by a vascular smooth muscle cell membrane chromatography method

The dissociation equilibrium constant (K _D) is an important affinity parameter for studying drug–receptor interactions. A vascular smooth muscle (VSM) cell membrane chromatography (CMC) method was developed for determination of the K _D values for calcium antagonist–L-type calcium channel (L-CC) interactions. VSM cells, by means of primary culture with rat thoracic aortas, were used for preparation of the cell membrane stationary phase in the VSM/CMC model. All measurements were performed with spectrophotometric detection (237 nm) at 37 °C. The K _D values obtained using frontal analysis were 3.36 × 10⁻⁶ M for nifedipine, 1.34 × 10⁻⁶ M for nimodipine, 6.83 × 10⁻⁷ M for nitrendipine, 1.23 × 10⁻⁷ M for nicardipine, 1.09 × 10⁻⁷ M for amlodipine, and 8.51 × 10⁻⁸ M for verapamil. This affinity rank order obtained from the VSM/CMC method had a strong positive correlation with that obtained from radioligand binding assay. The location of the binding region was examined by displacement experiments using nitrendipine as a mobile-phase additive. It was found that verapamil occupied a class of binding sites on L-CCs different from those occupied by nitrendipine. In addition, nicardipine, amlodipine, and nitrendipine had direct competition at a single common binding site. The studies showed that CMC can be applied to the investigation of drug–receptor interactions.     

Nucleation and growth processes in the colloidal crystallization of silica spheres in the presence of sodium chloride as studied by reflection spectroscopy

Time-resolved reflection spectroscopic measurements are made for the kinetic analyses of the nucleation and growth processes of soft-type colloidal crystals of silica spheres (110 nm in diameter) in the presence of sodium chloride. Fast-scanning reflection spectra are taken using a continuous circulating-type stopped-flow cell system. The cell system is composed of a peristaltic pump and a quartz flow cell, which are connected with a PharMed tube in a closed circuit. The volume fraction of the spheres is 0.028. Induction periods range from 0.2 to 1.3 s and increase as salt concentration increases. Nucleation rates are 1 × 10⁴ to 7 × 10⁴ spheres/mm³s and decrease as salt concentration increases. The crystallization process has been observed from the sharpening and the increase in intensity of the reflection peaks. The crystal growth rate in the absence of salt is 23 μm/s, and decreases as salt concentration increases. The importance of electrostatic intersphere repulsion through the electrical double layers and the cooperative and synchronous fluctuation of colloidal spheres in the crystallization processes is supported. Received: 15 July 1998 Accepted in revised form: 18 September 1998     

Adsorptive anodic stripping voltammetry of zirconium(IV)-alizarin red S complex at a carbon paste electrode

A sensitive adsorptive anodic stripping procedure for the determination of trace zirconium at a carbon paste electrode (CPE) has been developed. The method is based on adsorptive accumulation of the Zr(IV)-alizarin red S(ARS) complex onto the surface of the CPE, followed by oxidation of adsorbed species. The optimal experimental conditions include the use of 0.10 mol · L⁻¹ ammonium acetate buffer (pH 4.3), ARS, an accumulation potential of 0.20 V (versus SCE), an accumulation time of 2 min, a scan rate of 200 mV · s⁻¹ and a second-order derivative linear scan mode. The oxidation peak for the complex appears at 0.69 V. The peak current is proportional to the concentration of Zr(IV) over the range of 1.0 × 10⁻⁹–2.0 × 10⁻⁷ mol · L⁻¹, and the detection limit is 3 × 10⁻¹⁰ mol · L⁻¹ for a 2 min adsorption time. The relative standard deviations (n = 8) for 5.0 × 10⁻⁸ and 5.0 × 10⁻⁹ mol · L⁻¹ Zr(IV) are 3.3 and 4.8%, respectively. The proposed method was applied to the determination of zirconium in ore samples with satisfactory results.     

Study on the Catalytic Determination of Vanadium (V) Using the Rhodamine 6G-Periodate Redox Reaction and its Analytical Application

 A fluorescence quenching method for the determination of vanadium (V) based on the vanadium- catalyzed oxidation of rhodamine 6G (R6G) with periodate in the presence of ethylenediaminetetraacetic acid disodium salt (EDTA) in sulfuric acid medium is described. The fluorescence was measured with excitation and emission wavelengths of 525 and 555 nm, respectively. The calibration graph for vanadium (V) had linear ranges of 3.0 × 10⁻⁹–1.5 × 10⁻⁸ mol/l and 1.5 × 10⁻⁸–4.0 × 10⁻⁸ mol/l, respectively. The detection limit was 1.7 × 10⁻⁹ mol/l. The proposed method was successfully applied to the determination of vanadium (V) in river water, rain water and cast iron samples. Received June 29, 2001 Revision October 9, 2001     

A solid-contact Pb2+-selective polymeric membrane electrode with Nafion-doped poly(pyrrole) as ion-to-electron transducer

Conducting polymer poly(pyrrole) (PPy) doped with Nafion was successfully used as ion-to-electron transducer in the construction of a solid-contact Pb²⁺-selective polymeric membrane electrode. The Nafion dopant can effectively increase the capacitance of the conducting polymer and improve the mechanical robustness of the coating. The transducer layer, PPy-Nafion, characterized by cyclic voltammetry and electrochemical impedance spectroscopy, exhibits a sufficiently high bulk (redox) capacitance and fast ion and electron transport process. The new Pb²⁺-selective polymeric membrane electrode, based on PPy-Nafion film as solid contact, shows stable Nernstian characteristics in Pb(NO₃)₂ solution within the concentration range of 1.0 × 10⁻⁷–1.0 × 10⁻³ M, and the detection limit is 4.3 × 10⁻⁸ M. The potential stability of the electrode and the influence of the interfacial water layer were also evaluated by chronopotentiometry and potentiometric water layer test, respectively. The results show that the solid-contact Pb²⁺-selective electrode, based on PPy-Nafion film as ion-to-electron transducer, can effectively overcome the potential drift and reduce the water layer between the PPy-Nafion transducer layer and the ion-selective membrane.     

Determination of Tannic Acid by Flow Injection Analysis with Inhibited Chemiluminescence Detection

A novel flow injection procedure has been developed for the determination of tannic acid based on the inhibition of the chemiluminescences in luminol-H₂O₂-Manganese tetrasulfonatophthalocyanine (MnTSPc) system by tannic acid. The method is simple, rapid and sensitive with a detection limit of 8 × 10⁻¹⁰ mol·L⁻¹ and a linear range of 7 × 10⁻⁹–5 × 10⁻⁶ mol·L⁻¹. The relative standard deviation is 1.9% for eleven measurements of 5 × 10⁻⁷ mol·L⁻¹ tannic acid. The method has been successfully applied to the determination of tannic acid in real Chinese gall and hop pellets samples.     

Determination of Periodate by Fluorescence Quenching of Tetraiodofluorescein

 The fluorometric determination of periodate with tetraiodofluorescein has been developed. Under the optimum conditions responses were linear between 4.0×10⁻⁷ ∼ 1.0 × 10⁻⁵ mol/L of periodate. The detection limit was 1.0 × 10⁻⁷ mol/L corresponding to a signal to noise ratio of 2. The proposed method was applied to the determination of periodate in artificial fresh water and kelp sample with good results. Received March 20, 2001 Revision December 19, 2001     

Molecularly imprinted on-line solid-phase extraction combined with chemiluminescence for the determination of pazufloxacin mesilate

A novel molecularly imprinted polymer solid-phase extraction (MISPE) with flow-injection chemiluminescence (CL) was developed for the determination of pazufloxacin mesilate (PZFX). The molecularly imprinted polymer (MIP) was synthesized by using PZFX as the imprinting molecule. A glass tube packed the particles of the MIP was employed as MISPE micro-column, which was connected into the sampling loop of the eight-way injection valve for on-line selective preconcentration and extraction of PZFX. The eluent of acetonitrile:acetic acid (9:1, v:v) was used as carrier for eluting the adsorbed PZFX to react with the mixture of cerium(IV) and sodium sulfite in the flow cell to produce strong CL. The relative intensity of CL was linear to PZFX concentration in the range from 2.5 × 10⁻⁹ to 2.5 × 10⁻⁷ g mL⁻¹. The limit of detection was 7 × 10⁻¹⁰ g mL⁻¹ (3 σ) and the relative standard deviation for 5 × 10⁻⁸ g mL⁻¹of PZFX solution was 3.7% (n = 7). This method has been applied to the determination of PZFX in human urine.     

Microgravity experiments on colloidal crystallization of silica spheres in the presence of sodium chloride

 Rate coefficients (k) in the colloidal crystallization of monodispersed silica spheres in the presence of sodium chloride are studied in microgravity achieved by parabolic flights of an aircraft. Time-resolved reflection spectroscopy is made with a continuous circulating-type stopped-flow cell system. The k values decrease as the salt concentration increases both at 0 and 1 G and those in microgravity are smaller than those in normal gravity by 16% (maximum), especially in water and in the presence of a small amount of the salt lower than 2 × 10⁻⁶ mol/l. The rates in flight at 1 G are larger by 15% (maximum) compared with those at 1 G on the ground. The k values obtained at 0 G, 1 G in flight and 1 G on the ground agree excellently with each other for the suspensions with 3 × 10⁻⁶ and 4 × 10⁻⁶ mol/l sodium chloride. Disappearance of the downward diffusion of spheres and no convection of the suspensions are important for retardation in microgravity. Received: 20 January 2000 Accepted: 9 March 2000     

CO<Subscript>2</Subscript> corrosion inhibition of X-70 pipeline steel by carboxyamido imidazoline

The corrosion inhibition of X-70 pipeline steel in saltwater saturated with CO₂ at 50 °C with carboxyamido imidazoline has been evaluated by using electrochemical techniques. Techniques included polarization curves, linear polarization resistance, electrochemical impedance, and electrochemical noise measurements. Inhibitor concentrations were 0, 1.6 × 10⁻⁵, 3.32 × 10⁻⁵, 8.1 × 10⁻⁵, 1.6 × 10⁻⁴, and 3.32 × 10⁻⁴ mol l⁻¹. All techniques showed that the best corrosion inhibition was obtained by adding 8.1 × 10⁻⁵ mol l⁻¹ of carboxyamido imidazoline. For inhibitor concentrations higher than 8.1 × 10⁻⁵ mol l⁻¹ a desorption process occurs, and an explanation has been given for this phenomenon.     

Flow-injection analysis for the determination of total inorganic carbon and total organic carbon in water using the H2O2–luminol–uranine chemiluminescent reaction

In the presence of carbonate and uranine, the chemiluminescent intensity from the reaction of luminol with hydrogen peroxide was dramatically enhanced in a basic medium. Based on this fact and coupled with the technique of flow-injection analysis, a highly sensitive method was developed for the determination of carbonate with a wide linear range. The method provided the determination of carbonate with a wide linear range of 1.0 × 10⁻¹⁰–5.0 × 10⁻⁶ mol L⁻¹ and a low detection limit (S/N = 3) of carbonate of 1.2 × 10⁻¹¹ mol L⁻¹. The average relative standard deviation for 1.0 × 10⁻⁹–9.0 × 10⁻⁷ mol L⁻¹ of carbonate was 3.7% (n = 11). Combined with the wet oxidation of potassium persulfate, the method was applied to the simultaneous determination of total inorganic carbon (TIC) and total organic carbon (TOC) in water. The linear ranges for TIC and TOC were 1.2 × 10⁻⁶–6.0 × 10⁻² mg L⁻¹ and 0.08–30 mg L⁻¹ carbon, respectively. Recoveries of 97.4–106.4% for TIC and 96.0–98.5% for TOC were obtained by adding 5 or 50 mg L⁻¹ of carbon to the water samples. The relative standard deviations (RSDs) were 2.6–4.8% for TIC and 4.6–6.6% for TOC (n = 5). The mechanism of the chemiluminescent reaction was also explored and a reasonable explanation about chemical energy transfer from luminol to uranine was proposed. Figure Chemiluminescence profiles in batch system. 1, Injection of 100 μL of K₂CO₃ into 1.0 mL luminol-1.0 mL H₂O₂ solution; 2-3 and 4-5, Injection in sequence of 100 μL of K₂CO₃ and 100 μL of uranine into 1.0 ml luminol-1.0 mL H₂O₂ solution; C_luminol = 1.0 × 10⁻⁷ mol/L, C_H2O2 = 1.0 × 10⁻⁵ mol/L, C_uranine = 1.0 × 10⁻⁵ mol/L, C_K2CO3 = 1.0 × 10⁻⁷ mol/L except for 4-5 where C_K2CO3 = 1.0 × 10⁻⁴ mol/L     

An electrochemiluminescence sensor for determination of durabolin based on CdTe QD films by layer-by-layer self-assembly

This work reported for the first time the use of flow injection electrochemiluminescence (FI-ECL) sensor for the determination of durabolin in an aqueous system based on CdTe quantum dot (QD) films. Aqueous CdTe colloidal solutions were prepared using thioglycolic acid as a capping agent. Zetasizer Nano ZS (Malvern, UK) was employed to characterize the size of CdTe QDs. The UV–vis and photoluminescence spectra of samples were systematically characterized. Indium tin oxide (ITO) slide glass was modified with CdTe QDs by layer-by-layer self-assembly. CdTe QD films were packed into a homemade cell and used as a recognizer of the FI-ECL sensor to determine durabolin. The intensive anodic ECL emission was obtained at a starting potential of +1.3 V (vs. Ag/AgCl) in a carbonate bicarbonate buffer solution with a pH of 9.93 at an ITO electrode. The ECL intensity was correlated linearly with the concentration of durabolin over the range of 1.0 × 10⁻⁸–1.0 × 10⁻⁵ g mL⁻¹, and the detection limit was 2.5 × 10⁻⁹ g mL⁻¹. The relative standard deviation for the determination of 1.0 × 10⁻⁶ g mL⁻¹ durabolin was 1.04% (n = 11). This simple and sensitive sensor revealed good reproducibility for ECL analysis. As a result, the new FI-ECL sensor had been successfully applied to the determination of durabolin in food samples. This strategy could be easily realized and opened new avenues for the applications of QDs in ECL biosensing.     

Voltammetric sensor for nitrite determination based on its electrocatalytic reduction at the surface of p-duroquinone modified carbon paste electrode

A p-duroquinone (tetramethyl-p-benzoquinone) modified carbon paste electrode (DMCPE) was employed to study the electrocatalytic reduction of nitrite in aqueous solutions using cyclic voltammetry (CV), double potential-step chronoamperometry, and differential pulse voltammetry (DPV). It has found that under an optimum condition (pH 1.00), the reduction of nitrite at the surface of DMCPE occurs at a potential of about 660 mV less negative than that of an unmodified carbon paste electrode (CPE). The catalytic rate constant, k′_h, based on Andrieux and Saveant theoretical model was calculated as for scan rate 10 mV s^-1. Also, the apparent diffusion coefficient, D _app, was found as 2.5 × 10^–10 and 3.61 × 10^–5 cm² s^-1 for p-duroquinone in carbon paste matrix and nitrite in aqueous buffered solution, respectively. The values for αn_α were estimated to be −0.65 and −0.19 for the reduction of nitrite at the surface of DMCPE and CPE, respectively. The electrocatalytic reduction peak currents showed a linear dependence on the nitrite concentration, and a linear analytical curve was obtained in the ranges of 5.0 × 10^–5 M to 8.0 × 10^–3 M and 6.0 × 10^–6 M to 8.0 × 10^–4 M of nitrite concentration with CV and DPV methods, respectively. The detection limits (2σ) were determined as 2.5 × 10^–5 M and 4.3 × 10^–6 M by CV and DPV methods. This method was also applied as a simple, selective and precise method for determination of nitrite in real samples (the weak liquor from the wood and paper factory of Mazandaran province in Iran) by using a standard addition method.     

Chemiluminescence determination of chromium(III) and total chromium in water samples using the periodate-lucigenin reaction

A new chemiluminescence (CL) method combined with flow injection technique is described for the determination of Cr(III) and total Cr. It is found that a strong CL signal is generated from the reaction of Cr(III), lucigenin and KIO₄ in alkaline condition. The determination of total Cr is performed by pre-reduction of Cr(VI) to Cr(III) by using H₂SO₃. The CL intensity is linearly related to the concentration of Cr in the range 4.0 × 10⁻¹⁰–1.0 × 10⁻⁶ g mL⁻¹. The detection limit (3s _b) is 1 × 10⁻¹⁰ g mL⁻¹ Cr and the relative standard deviation is 1.9% (5.0 × 10⁻⁸ g mL⁻¹ of Cr(III) solution, n = 11). The method was applied to the determination of Cr(III) and total Cr in water samples and compared satisfactorily with the official method.