Analysis of 2-arachidonoylglycerol (2-AG) and N-arachidonoylethanolamide (anandamide) via alkali or alkaline earth metal-adduct high-energy collision-induced dissociation (CID) in fast-atom bombardment (FAB) ionization-mass spectrometry (MS) is described. The CID-MS/MS of the [2-AG+Li]+ or [2-AG+Na]+ ion undergoes charge-remote fragmentation (CRF), which is useful for the determination of the double-bond positions in the hydrocarbon chain, while the CID-MS/MS of the [2-AG-H+Cat]+ (Cat = Mg2+, Ca2+, Ba2+) ion provides an abundant fragment ion of the cationized arachidonic acid species, which is derived from cleaving the ester bond via a McLafferty-type rearrangement in addition to structurally informative CRF ions in small amounts. On the other hand, the CID-MS/MS spectra of anandamide cationized with both alkali metal (Li+ or Na+) and alkaline earth metal (Mg2+, Ca2+, or Ba2+) show CRF patterns: the spectra obtained in lithium or sodium adduct are more clearly visible than those in magnesium, calcium, or barium adduct. The McLafferty rearrangement is not observed with metal-adduct anandamide. The characteristics in each mass spectrum are useful for the detection of these endogenous ligands. m-Nitrobenzyl alcohol (m-NBA) is the most suitable matrix. A lithium-adduct [2-AG+Li]+ or [anandamide+Li]+ ion is observed to be the most abundant in each mass spectrum, since the affinity of lithium for m-NBA is lower than that for other matrices examined.
The diffusion coefficients of C60 in dichloromethane and benzonitrile solutions containing 0.1 M tetrabutylammonium perchlorate were determined by single potential-step chronoamperometry at small disk electrodes. The diffusion coefficients of C60 were obtained by curve fitting of the chronoamperograms to a theoretical equation by Shoup and Szabo. The values were (1.4 ± 0.3) × 10-9 and (4.1 ± 0.3) × 10-10 m2 s-1, respectively (the errors are 95% confidence limits). The diffusion coefficients of C60- in these solutions were measured by double potential-step chronoamperometry. The ratios of the diffusion coefficients of C60 to those of C60- were obtained from theoretical curves of the ratios of the current at the second potential step to the current at the first one. The values of the ratios were 1.2 ± 0.2 and 1.0 ± 0.3, respectively.
In Part 1 of this series (Anal. Sci., 2006, 22, 383), design, fabrication, and optical data acquisition of an array of tiny color changing capsules embedded in a cellulose acetate bar, called the “sliver sensor”, have been described. Capsule colors are read by a CCD camera and translated into blue, red and green Kubelka-Munk variables for quantitative analysis. The respective concentrations are determined using prior calibration. The approach may be adapted to different non-biological analytical problems, as well as in vitro and in vivo applications. To demonstrate this adaptability to potential in vivo use as an example, sensitivity for each target ion was tuned to cover the respective interstitial levels by varying the relative amount of ionophore used in the corresponding microscopic beads. After optimizing the ratio of glucose oxidase (GOX)-containing beads relative to the coupled pH sensing beads and their composition, reversible color response to glucose was obtained in the entire clinically relevant glucose concentration range (10 to 600 mg/dL, 0.55 to 33 mM). Decoupling of pH and glucose sensing from possible variations in interstitial sodium level and buffer capacity is currently being optimized for future in vivo use. In vitro and non-biological applications are also being explored.
A highly La(III) ion-selective PVC membrane sensor based on N′-(1-pyridin-2-ylmethylene)-2-furohydrazide (NPYFH) as an excellent sensing material was successfully developed. The electrode shows a good selectivity for La(III) ion with respect to most common cations including alkali, alkaline earth, transition and heavy metal ions. The proposed sensor exhibits a wide linear response with slope of 19.2 ± 0.6 mV per decade over the concentration range of 1.0 × 10-6 - 1.0 × 10-1 M, and a detection limit of 7.0 × 10-7 M of La(III) ions. The sensor response is independent of pH in the range of 3.5 - 10.0. The proposed electrode was applied as an indicator electrode in potentiometric titration of La(III) ion with EDTA.
A novel high-selective potentiometric sensor for molybdate was prepared with a PVC membrane combining μ-oxo-bis[5,10,15,20-tetra(p-methylphenyl)porphinatomanganese(III)] [[Mn(p-Me)TPP]2O] as an electroactive material and 2-nitrophenyl octyl ether (o-NPOE) as a plasticizer in the percentage ratio of 3:65:32, [Mn(p-Me)TPP]2O:o-NPOE:PVC (w:w). The sensor exhibited a linear response with a Nernstian slope of 30.5 mV per decade within a concentration range of 2.1 × 10-6 to 1.0 × 10-1 M MoO42-, with a working pH range from 5.0 to 12.5, and a fast response time of less than 15 s. The electrode showed improved selectivity toward molybdate with respect to common coexisting anions compared to monometalloporphyrin counterparts. Several electroactive materials and solvent mediators were compared and the experimental conditions were optimized. The sensor is preliminary applied to the assay of MoO42- in corrosion inhibitor samples with satisfactory results.
A novel, sensitive and selective adsorptive stripping procedure for simultaneous determination of copper, bismuth and lead is presented. The method is based on the adsorptive accumulation of thymolphthalexone (TPN) complexes of these elements onto a hanging mercury drop electrode, followed by reduction of adsorbed species by voltammetric scan using differential pulse modulation. The influences of control variables on the sensitivity of the proposed method for the simultaneous determination of copper, lead and bismuth were studied using the Derringer desirability function. The optimum analytical conditions were found to be TPN concentration of 4.0 µM, pH of 9.0, and accumulation potential at -800 mV vs. Ag/AgCl with an accumulation time of 80 s. The peak currents are proportional to the concentration of copper, bismuth and lead over the 0.4 - 300, 1 - 200 and 1 - 100 ng mL-1 ranges with detection limits of 0.4, 0.8 and 0.7 ng mL-1, respectively. The procedure was applied to the simultaneous determination of copper, bismuth and lead in the tap water and some synthetic samples with satisfactory results.
Zeolite NaA-type membranes hydrothermally synthesized on porous alumina tubes, for dehydration process, were characterized by grazing incidence 2 θ scan X-ray diffraction analysis (GIXRD). The fine structure of the membrane was studied fractionally for surface layer and for materials embedded in the porous alumina tube. The thickness of the surface layer on the porous alumina tube in the membranes used in this study was approximately 2 - 3 µm as determined from transmission electron microscopy with focused ion beam thin-layer specimen preparation technique (FIB-TEM). To discuss the effects of the membrane surface morphology on the GIXRD measurements, CaA-type membrane prepared by ion exchange from the NaA-type membrane and surface-damaged NaA-type membrane prepared by water leaching were also studied. For the original NaA-type membrane, 2 θ scan GIXRD patterns could be clearly measured at X-ray incidence angles (α) ranging from 0.1 to 2.0 deg in increments of 0.1 deg. The surface layers of the 2 - 3 µm on the porous alumina tube correspond to the α values up to ca. 0.2 deg. For the CaA-type and the surface-damaged NaA-type membranes, however, diffraction patterns from the surface layer could not be successfully detected and the others were somewhat broad. For all the three samples, diffraction intensities of both zeolite and alumina increased with depth (X-ray incidence angle, α) in the porous alumina tube region. The depth profile analysis of the membranes based on the GIXRD first revealed that amount of zeolite crystal embedded in the porous alumina tube is much larger than that in the surface layer. Thus, the 2 θ scan GIXRD is a useful method to study zeolite crystal growth mechanism around (both inside and outside) the porous alumina support during hydrothermal synthesis and to study water permeation behavior in the dehydration process.
A plant tissue-based chemiluminescence biosensor for ethanol based on using mushroom (Agaricus bisporus) tissue as the recognition element is proposed in this paper. The principle for ethanol sensing relies on the luminol-potassium hexacyanoferrate(III)-hydrogen peroxide transducer reaction, in which hydrogen peroxide is produced from the ethanol enzymatic catalytic oxidation by oxygen under the catalysis of alcohol oxidase in the tissue column. Under optimum conditions, the method allowed the measurement of ethanol in the range of 0.001 - 2 mmol/l with a detection limit (3 σ) of 0.2 µmol/l. The relative standard deviation (RSD) was 4.14% (n = 11) for 0.05 mmol/l ethanol. The proposed method has been applied to the determination of ethanol in biological fluids and beverages with satisfactory results.
A luminol-potassium ferricyanide-perphenazine CL reaction with high sensitivity for the determination of perphenazine was found. A perphenazine molecular imprinted polymer (MIP) was synthesized. Using the perphenazine MIP as a recognition material, a novel molecular imprinting-chemiluminescence (MI-CL) sensor for the determination of perphenazine was made based on the luminol-potassium ferricyanide-perphenazine CL reaction. The sensor displayed good selectivity and high sensitivity. The linear-response range of the sensor was 5.0 × 10-8 - 1.0 × 10-5 g/ml with a linear correlation coefficient of 0.9961. The detection limit was 2 × 10-8 g/ml perphenazine and the relative standard deviation for 1.0 × 10-6 g/ml perphenazine solution was 3.7% (n = 11). The sensor was applied to the determination of perphenazine in urine samples with satisfactory results.
An aminobenzanthrone Schiff base has been synthesized as a new fluorescence carrier for the preparation of an optical chemical sensor for iodine. The response of the sensor is based on fluorescence quenching of the aminobenzanthrone Schiff base by iodine. The sensor shows a linear response toward iodine in the range of 1.0 × 10-5 to 1.0 × 10-3 mol l-1, with a detection limit of 6.0 × 10-6 mol l-1 at pH 8.0. Leaching of the fluorophore from the membrane is effectively hindered by covalent immobilization, resulting in an enhanced sensor lifetime. In addition to satisfactory reproducibility and reversibility, the prepared sensor exhibits sufficient selectivity toward iodine with respect to other coexisting ions. The sensor has been applied to the determination of iodine in common salt samples.
A kinetic spectrophotometric method has been developed which is based on the oxidation of pantoprazole with Fe(III) in sulfuric acid medium. Fe(III) subsequently reduces to Fe(II), which is coupled with potassium ferricyanide to form Prussian blue. The reaction is followed spectrophotometrically by measuring the increase in absorbance with time (1 - 8 min) at 725 nm. The initial rate method is adopted for constructing the calibration graph, which is linear in the concentration range of 5 - 90 µg ml-1. The regression analysis yields the calibration equation, ν = 3.467 × 10-6 + 4.356 × 10-5C. The limits of detection and quantitation are 1.46 and 4.43 µg ml-1, respectively. The proposed method was optimized and validated both statistically and through recovery studies. The experimental true bias of all samples is < ±2.0%. The method has been successfully applied to the determination of pantoprazole in pharmaceutical preparations.
A new chromogenic reagent, N-o-methylphenyl-N′-(sodium p-aminobenzenesulfonate)thiourea (MSAT), has been synthesized and characterized by elemental analysis, 1H-NMR, FT-IR and UV-Vis spectra. Based on the absorption spectrum of the colored complex of MSAT with palladium(II), a novel spectrophotometric method for the determination of palladium has been developed. In a pH 4.0 - 5.5 HAc-NaAc buffer solution, palladium(II) reacted with MSAT to form a stable yellow water-soluble complex with an apparent molar absorptivity of ε = 2.04 × 105 L mol-1 cm-1 at the maximum absorption of 318.0 nm. Beer's law was obeyed in the concentration range of 1.2 - 11.8 µg per 25 mL for palladium(II) with a correlation coefficient of 0.9997. The probable interfering ions and their tolerable limits have also been investigated in detail. The proposed method is simple, rapid, and sensitive, and has been applied to the determination of palladium in anode mud and ore samples with satisfactory results.
The evaluation of a badge-type diffusive sampler for measuring formaldehyde using 3-methyl-2-benzothiazolinone hydrazone (MBTH) was investigated. On average, the formaldehyde concentration in blanks was reduced by approximately 31% by cleaning procedures. The cleaning techniques did not significantly differ in effectiveness. The maximum sampling rate was 22.4 ± 3.5 mL min-1 at MBTH concentrations of 0.05%. The formaldehyde concentration in blanks did not appreciably increase over a period of about 1 month at room temperature, and was 0.36 ± 0.03 µg, with a relative standard deviation of 8%. The diffusive sampler had good precision and accuracy for measuring formaldehyde in indoor environments. For a 24-h exposure time, the limits of detection and quantification calculated with the field blanks were 9.7 and 13.8 ppb, respectively. The minimum exposure times were calculated based on the measured and calculated limits of quantification, the sampling rate, and the atmospheric formaldehyde concentration. The capacity of the diffusive sampler with 0.5% MBTH was 3 ppm h-1, approximately 1.5-times the capacity when the MBTH concentrations were 0.05%.
Tris(2,2′-bipyridyl)ruthenium(II) electrochemiluminescence (ECL) detection in a capillary electrophoresis separation system was used for the determination of chlorpheniramine (CPM). The experimental conditions, such as the applied potential, separation voltage, injection voltage, injection time and the pH of the separation buffer were considered in detail. The ECL intensity showed two linear responses to CPM, i.e., from 15 µM to 1 mM and from 0.8 µM to 15 µM with a detection limit of 0.5 µM. The binding of CPM with human serum albumin was also monitored using this method and the binding constant was estimated to be 4.1 × 103 M-1.
An electroless plating method was applied to deposit Au onto the surfaces and the walls of pores of polycarbonate membranes to prepare gold nanotubules. The nanotubules were modified with cysteine (Cys) or with carbamidine thiocyante (Gua). The effects of modifiers and of the fine structure of organic molecules on the transport properties of those molecules through the gold nanotubules were investigated. Studies show that the hydrophilicity of modifiers and the planar structure of permeating molecules clearly affect the transport of small organic molecules in gold nanotubules. Tryptophan (Try) and vitamin B2 (VB2) was cleanly separated at pH 6.8.
A laser-induced plasma generated with a pulsed Nd:YAG laser under evacuated conditions has complicated structures both temporally and spatially. The time-resolved spectra of copper in three different wavelength regions were observed in detail for elucidating the excitation mechanisms of many atomic/ionic copper emission lines. The emission intensities of copper emission lines, measured in a time-resolved mode, were strongly dependent on the kind of copper lines: ionic or atomic lines, and their excitation energies. Generally, copper ionic lines were rapidly decayed and dominantly emitted from the initial breakdown zone, because the copper ions requiring larger excitation energies were produced mainly in the hot breakdown zone. On the other hand, the atomic lines were emitted during prolonged periods, implying that they could also be excited in the expanded plasma zone. The excitation phenomena occurring in the laser-induced plasma could be better understood by analyzing the time-resolved copper spectra.
A flow injection analysis system was built with a liquid core waveguide spectrophotometric detector using an 80 cm Teflon AF-1600 capillary tube (2,2-bistrifluoromethyl-4,5-difluoro-1,3-dioxole/tetrafluoroethylene). The system was applied to determine nitrite ion in river water samples. The lower limit of detection for nitrite was 2.1 nmol dm-3 (0.1 ng dm-3 as NO2-) and the relative standard deviation of measurements was typically 0.56% (n = 5) at 0.21 µmol dm-3.
We present a new multielement masking method using magnesium hydroxide coprecipitation for the selective determination of Pb by differential pulse anodic stripping voltammetry (DPASV). The recovery of Pb in the masking method was over 95%, while interfering ions (Cd2+, Co2+, Cu2+, Fe3+, Mn2+, and Ni2+) could be removed at 100% from the analytical sample. A linear regression was obtained in the Pb concentration from 10 to 1000 µg kg-1 in the existence of 100 µg kg-1 of the interfering ions. When this method was applied to the determination of Pb in a natural water-standard reference material (NIST 1640), the determined value for Pb in this work (25.4 ± 4.1 µg kg-1) almost agreed with the certified value (27.89 ± 0.14 µg kg-1).
A simple and sensitive preconcentration analysis-atomic absorption spectrometric procedure is described for the determination of lead, cadmium and nickel. The method is based upon on-line preconcentration of metal ions on a minicolumn of Cibacron Blue F3-GA immobilized on poly(hydroxyethylmethacrylate), poly(HEMA). The enrichment factors obtained were 42 for lead, 52 for cadmium and 63 for nickel (sample volume 10 mL and sample flow rate 5 mL/min). The relative standard deviations (n = 10), in 10 mL sample solutions containing 100 µg/L Pb2+, 10 µg/L Cd2+ and 100 µg/L Ni2+ were 8.9, 3.7 and 3.5%, respectively. The limits of detection (blank + 3s) (n = 10), were found to be 12.01 µg/L for Pb2+, 1.34 µg/L for Cd2+ and 28.73 µg/L for Ni2+. The accuracy of the system was checked with certified and tap water samples spiked with known amounts of metal ions. No significant difference was found between the achieved results and the certified values.
A zeolite NaA (LTA) membrane supported by an alumina porous support tube for pervaporation (PV) dehydration of ethanol was characterized by transmission electron microscopy (TEM) using a focused ion beam (FIB) thin-layer specimen preparation technique and by Fourier transform infrared attenuated total reflectance method (FTIR-ATR) using a diamond prism as the waveguide. FIB-TEM clearly presented cross-section images up to about 15 µm depth from the membrane surface. FTIR-ATR monitored the Si-O asymmetric stretching vibration spectrum. The Si-O spectrum was compared with the TEM image and their relationships were discussed. By combining the two methods, we could study the thickness of surface LTA crystals, the grain boundary, the LTA/alumina interface structure and the crystallinity and density of materials inside of the alumina porous support. Consequently, fine structure changes of the LTA membrane corresponding to the hydrothermal synthesis condition could be sensitively detected.
The effect of the central metal of columns packed with silica gels binding Ni2+- and Cu2+-phthalocyanine derivatives (Ni-and Cu-PCSDs) on the retention behavior of poly-aromatic-hydrocarbons (PAHs) thereof in a polar eluent was examined. The retention factors of PAHs on the Ni- and Cu-PCSDs in 80% methanol showed a good linear correlation. The Cu-PCSD column exhibited the π-π interactions for PAHs, while the Ni-PCSD column exhibited the π-d interactions for PAHs in addition to the π-π interaction for PAHs. Further, an investigation of the retention behavior of anthracene derivatives having different substituents revealed that the Ni- and Cu-PCSD columns could recognize the differences of substituents only in a polar eluent.
An improvement has been made to couple isoelectric focusing (IEF) sample injection and capillary zone electrophoresis in an untreated fused silica capillary. Electroosmotic flow is efficiently prevented by simply using a rubber block at the outlet end of the capillary during IEF sample injection. The experimental conditions that affect the concentration effect are discussed. A concentration enhancement factor of over 100-fold can be easily obtained for two model proteins: lysozyme and ribonuclease A.
A Raman microprobe spectrometer that could be installed in the bore of a cryogen free super-conducting magnet (10 T) was designed and constructed for the investigation of the external magnetic field effect on the Raman spectra of molecular aggregates in solutions and at interfaces. The performance of the present instrument was demonstrated by measuring the magnetic field effect (0 - 10 T) on the resonance Raman spectra of diprotonated meso-tetra-(sulfonatophenyl)porphine aggregates in an acidic solution. The Raman shifts of the aggregates were not significantly influenced even in 10 T. However, the relative intensity of 1123 cm-1 peak (ν(Ca-N)) was interestingly enhanced about 20% under the magnetic fields higher than 2.5 T.