Coordination polymer (CP) formation is an unexplored area in weak-interaction chemistry due to the difficulty of monitoring the coordination process. By using cold-spray ionization mass spectrometry (CSI-MS), several kinds of coordination compounds were detected when CuI metal and the 4,7-phenanthroline organic bridged ligand were mixed in solution. The observed ion peaks could be reasonably and simply assigned to various combinations of the metal and the ligand without any fragmentation.
The behavior of hydrated Ag+ ions in a 1.5 mol dm−3 AgNO3 aqueous solution confined in mesoporous silica MCM-41 with different pore sizes was characterized by synchrotron X-ray absorption spectroscopy. The hydrated Ag+ ions are stabilized in 4-fold coordination down to 195 K in the pores (21 Å in diameter), whereas in the larger pores (28 Å) the hydrated Ag+ ions are reduced to Ag0 to form nano clusters with the Ag–Ag interactions of 2.80 Å.
An electrochemical DNA detection format has been developed to allow simple and rapid assays with downsized instruments. Since naphthalene diimide derivatives are known to bind to double stranded DNA (dsDNA) with threading intercalation, they are stabilized by pseudo-catenane formation. For example, ferrocenylnaphthalene diimide (FND) can be efficiently concentrated on dsDNA, thus enabling its electrochemical detection. Since dsDNA is formed between single stranded target DNA and DNA probe, the target DNA can be detected electrochemically, using DNA probe-immobilized on the electrode. Further stabilization of naphthalene diimide derivatives as a complex with dsDNA on the electrode is expected to lead to more precise and selective detection of target DNA. This approach was realized by the formation of inclusion complexes of ferrocene with β-cyclodextrin (β-CD) for the FND-dsDNA complexes on the electrode. Combination of adamantylnaphthalene diimide (AND) and ferrocenyl-β-CD (Fc-CD) gave new supramolecular DNA detection assays coupled with DNA probe-immobilized electrodes. The electrochemical signal increased only upon formation of the Fc-CD/AND complex bound to dsDNA on the electrode. Naphthalene diimide carrying ferrocene and β-CD realized “signal on” type detection of dsDNA in homogenous solution. Naphthalene diimide carrying two dithiolene termini provided a new method to immobilize dsDNA on the gold electrode that may be suitable for the electrochemical detection of target DNA.
A simple and inexpensive method for fabricating a microfluidic platform was developed. A printed circuit board (PCB) was used to make a master mold for replicating a polydimethylsiloxane (PDMS) microchannel. The master mold was fabricated by a simple photolithographic method, employing a photoresist dry film. The process did not use hazardous chemicals, a clean room or any expensive instrument. The PDMS microchannel was clamped with polymethylmethacrylate (PMMA) plates, where a light emitting diode (LED) as a light source and a light dependent resistor (LDR) as a light sensor were attached to form a simple optical sensor. The system was successfully employed as a micro flow injection analysis for the determination of glutathione in dietary supplement samples. A linear calibration graph in the range of 5.0 – 60.0 mg L−1 glutathione was obtained with a detection limit of 0.01 mg L−1. The system provided a sample throughput of 48 h−1, with microliter consumption of the reagent.
An enzymatic reaction rate of glucose oxidase (GOD) using ferricyanide ion ([Fe(CN)6]3−) as an oxidant significantly increased by the addition of ε-poly-L-lysine (ε-PL). The bimolecular rate constant between GOD and [Fe(CN)6]3− in the presence of ε-PL reached about 10000-fold relative to what it was measured without the ε-PL, and the Michaelis constant decreased. The reaction rate reached a maximum at around pH 6, where ε-PL and GOD possess highly positive and negative charges, respectively. The increment of the reaction rate by ε-PL can be attributed to the electrostatic association of the polycationic ε-PL with the negatively charged GOD to form a polyion complex soluble in the aqueous medium. The adduction of the cationic polymer may relieve the electrostatic repulsion between GOD and [Fe(CN)6]3−, so that the electron transfer effectively occurs between them.
The channel activity of gramicidin A in free-standing planar lipid bilayers with different charges of polar head groups and various lengths of hydrocarbon tails were analyzed in terms of the channel conductance, the lifetime of channel events and the magnitude of integrated currents. The channel activity of gramicidin A in lipid bilayers is tunable by adjusting the membrane composition. The in situ coupling of the anti-BSA antibody as a model protein to the amine moiety of phosphatidylethanolamine (PE) in a lipid bilayer by the amine coupling method allowed us to design an antigen (BSA)-sensitive interface, in which the integrated current, rather than the frequency of channel event, can be used as an analytical signal. The potential of the present system for highly sensitive and selective detection of BSA at 10−9 g/mL level is demonstrated.
Fenthion, fenthion sulfoxide, fenthion oxon sulfoxide and fensulfothion showed two different mass spectra in GC/MS, depending on their concentrations. The base peaks shifted to lower levels by 1 m/z at lower concentration, and no retention time shifts were observed. The “shifted base peaks” were not obtained by a general EI fragmentation. The product ion scan spectra of the “shifted base peaks” were coincident with those of molecular ions of their corresponding sulfides. These phenomena can be ascribed to the conversion of sulfoxide into sulfide by the dominant deoxidation reaction than EI fragmentation in an ion source. Adding polyethylene glycol 300 (PEG300) into a test solution prevented sulfoxide deoxidation.
The biodegradation study of algal dissolved organic matter (DOM) released from Microcystis aeruginosa, Staurastrum dorsidentiferum and Cryptomonas ovata was carried out. The algal DOM released from Microcystis aeruginosa and Staurastrum dorsidentiferum is relatively stable, while a part of the algal DOM released from Cryptomonas ovata may be easily decomposed. Before biodegradation, two fulvic-like fluorescence peaks (A and B) and a protein-like fluorescence peak (C) and another peak with Ex/Em values of 320 – 330/390 nm (peak D) were observed in the algal DOM released from three kinds of phytoplankton. The fulvic-like fluorophores may be refractory regardless of the kinds of phytoplankton, while protein-like fluorophores released from Microcystis aeruginosa and Staurastrum dorsidentiferum may be relatively refractory and those from Cryptomonas ovata may be unstable. Peak D in the surface water of Lake Biwa may be attributed to low-molecular-weight substances produced during cultivation and/or biodegradation of several kinds of phytoplankton. The ratios of the fluorescence intensities (RFI/DOC) of peak A to peak B in algal DOM (< 1.0) were lower than those in soil Dando FA (1.8). On the other hand, no relationships between peak A and peak C were observed for three kinds of phytoplankton.
A time-of-flight mass spectrometer was constructed for use in detecting negatively charged species induced by laser multiphoton ionization. Mass spectra, collected for a variety of compounds, contained several signal peaks. Their flight times were, however, an order of magnitude shorter than the values predicted based on the length of the flight region. To clarify this curious phenomenon, a simple molecule, namely, nitric oxide was measured for calibration of the flight times and for assignment of the signal peaks. A careful investigation led to a possible mechanism, in which the signals do not arise from negative ions but arise from electrons generated at the surface of the repeller electrode by collisions of positive ions that are formed by multiphoton ionization of the analyte in a molecular beam.
This study reports on a headspace gas chromatographic method (HS-GC) for the determination of formaldehyde in sanitary napkin samples. The method is based on the reaction of formaldehyde and sodium borohydride in a concentrated potassium carbonate solution (824 g/L), in which formaldehyde is quantitatively converted to methanol at 105°C in 45 min. The methanol from the conversion is determined by HS-GC. The repeatability of the method had a relative standard deviation of less than 4.5%; the limit of quantification (LOQ) was 1.17 μg, and the recovery ranged from 96.8 – 106%. The present method is simple, rapid, and accurate. It is suitable for use in the batch testing for product quality control of tissue papers during the manufacturing process and in analysis of point-of-sale samples from commercial markets.
A simple, sensitive and inexpensive electrochemical method was developed for the determination of metoclopramide (MCP) with a multi-wall carbon nanotube (MWNT) modified glassy carbon electrode (GCE). MWNT was dispersed into polyacrylic acid (PAA); the aqueous suspension was then cast on GCE electrodes, forming MWNT-PAA films after evaporation of the solvent. The electrochemical behavior of MCP at the MWNT-modified electrode was investigated in detail. Compared with the bare GCE, the MWNT-modified electrode exhibits electrocatalytic activity to the oxidation of MCP because of the significant oxidation peak-current enhancement. Furthermore, various experimental parameters, such as the solution pH value, the amount of MWNT-PAA suspension and accumulation conditions were optimized for the determination of MCP. Based on the electrocatalytic effect of the MWNT-modified electrode, linear sweep voltammetry (LSV) was developed for the determination of MCP with the linear response in the range from 1.0 × 10−7 to 1.0 × 10−5 mol L−1 and a detection limit of 5.0 × 10−8 mol L−1. The method has been successfully applied to the determination of MCP in commercial MCP tablets.
A flexible, transparent, single-walled carbon nanotube (SWCNT) film electrode was prepared by vacuum filtering methods, followed by photolithographic patterning of a photoresist polymer on the SWCNT surface. The morphology of the SWCNT film electrode surface was characterized using a field-emission scanning electron microscope coupled to an energy-dispersive X-ray spectrophotometer. The electrodes were successfully used as a mercury-free electrochemical sensor for individual and simultaneous detection of cadmium (Cd2+) and lead (Pb2+) in 0.02 M HCl by square-wave stripping voltammetry. Some important operational parameters, including deposition time, deposition potential, square-wave amplitude, and square wave-frequency were optimized for the detection of Cd2+ and Pb2+. The newly developed sensor showed good linear behavior in the examined concentration. For individual Cd2+ and Pb2+ ion detection, the linear range was found from 0.033 to 0.228 ppm with detection limits of 0.7 ppb (R2 = 0.985) for Cd2+ and 0.8 ppb (R2 = 0.999) for Pb2+. For simultaneous detection, the linear range was found from 0.033 to 0.280 ppm with a limit of detection of 2.2 ppb (R2 = 0.976) and 0.6 ppb (R2 = 0.996) for Cd2+ and Pb2+, respectively. SWCNT film electrodes offered favorable reproducibility of ± 5.4% and 4.3% for Cd2+ and Pb2+, respectively. The experiments demonstrated the applicability of carbon nanotubes, specifically in the preparation of SWCNT films. The results suggest that the proposed flexible SWCNT film electrodes can be applied as simple, efficient, cost-effective, and/or disposable electrodes for simultaneous detection of heavy metal ions.
A new sensor containing MgFe2O4 nanoparticles in modified multiwall carbon nanotubes (MgFe2O4-MWCNTs) was prepared, and its electrochemical behavior was investigated. MgFe2O4-MWCNTs were used as a voltammetric sensor for the electrocatalytic determination of ciprofloxacin. The synthesized materials were characterized by different methods such as transmission electron microscopy (TEM), X-ray diffraction (XRD), cyclic voltammetry, and electrochemical impedance spectroscopy. The MgFe2O4-MWCNTs electrode showed an oxidation peak potential at around 250 mV. The immobilized composite films facilitate interfacial electron transfer and electrocatalytic activity on the oxidation of ciprofloxacin. The oxidation peak current was dependent on the ciprofloxacin concentration, which was linear over the range of 0.10 – 1000 μmol L−1 with a detection limit and quantification limit of 0.01 and 0.08 μmol L−1, respectively. The relative standard deviation for the determination of 1.0 μmol L−1 ciprofloxacin was 1.1%. The repeatability of the sensor was investigated by preparing nine similar electrodes. The proposed sensor is a selective and fast tool for the determination of ciprofloxacin in tablet, plasma, and urine samples.
A nano-cluster with highly efficient peroxide activity was constructed based on nafion (NF) and cytochrome c (Cyt c). UV-Vis spectrometry and transmission electron microscopy (TEM) methods were utilized for characterization of the nano-structured enzyme or artificial peroxidase (AP). The nano-cluster was composed of a Chain-Ball structure, with an average ball size of about 40 nm. The Michaelis–Menten (Km) and catalytic rate (kcat) constants of the AP were determined to be 2.5 ± 0.4 μM and 0.069 ± 0.001 s−1, respectively, in 50 mM PBS at pH 7.0. The catalytic efficiency of the AP was evaluated to be 0.028 ± 0.005 μM−1 s−1, which was 39 ± 5% as efficient as the native horseradish peroxidase (HRP). The AP was also immobilized on a functional multi-wall carbon nanotube (MWNCTs)-gold colloid nanoparticles (AuNPs) nano-complex modified glassy carbon (GC) electrode. The cyclic voltammetry of AP on the nano complex modified GC electrode showed a pair of well-defined redox peaks with a formal potential (E°′) of –45 ± 2 mV (vs. Ag/AgCl) at a scan rate of 0.05 V/s. The heterogeneous electron transfer rate constant (ks) was evaluated to be 0.65 s−1. The surface concentration of electroactive AP on GC electrode (Γ) was 7 × 10−10 mol cm−2. The apparent Michaelis–Menten constant (Kmapp) was 0.23 nM.
Electrochemical hydride generation (EcHG) as a sample introduction system for determination of zinc was developed. It was directly coupled to an electrically heated quartz tube atomizer (QTA) atomic absorption spectrometry (AAS) system. The hydride generator is a laboratory-made semi-batch electrolytic cell that consists of a lead-tin alloy cathode and a platinum anode. The effects of typical parameters on the generation efficiency of the technique, such as types of cathode material and catholyte and anolyte solutions, were studied. The influences of numerical experimental operating parameters on the analytical signal were evaluated in detail and optimum conditions were obtained. The analytical figures of merit for the developed method were determined. The calibration curve was linear up to 300 ng mL−1 of Zn. A concentration detection limit (3σ, n = 9) of 11 ng mL−1 Zn and a relative standard deviation of 5.0% (RSD, n = 9) for 200 ng mL−1 Zn were accessed. In addition, the susceptibility of interference from various ions was evaluated. The accuracy of the method was verified by determination of Zn in a certified reference material and in tap water. The achieved concentrations were found to be in good agreement with both the certified value and the data obtained using flame AAS.
A mass-spectrometric method for a de novo determination of O-glycosylation heterogeneity was developed. We used a mild fragmentation technique, electron capture dissociation (ECD), which enables the determination of glycosylation sites as well as peptide sequencing. To demonstrate the correct identification of glycopeptides, we prepared a series of glycopeptides with the same peptide sequence and 6 different glycan modifications. ECD spectra were obtained at various electron energies, and were analyzed with the Mascot database-search engine. The obtained candidate glycopeptides were further validated by confirming the spectral overlap of ECD fragment peaks with the theoretical peaks. The results indicate that all glycopeptides were unambiguously identified, including glycosylation sites by combining ECD results with different electron energies for each glycopeptide.
Wavelet transformation was applied as a noise elimination method of an amperometric algal biosensor. The drift of the baseline current was clearly removed by using the wavelet transformation. The S/N ratio, calculated by the power spectrum density, is about 3-times larger than that calculated by the current response. The response to a herbicide, atrazine, calculated from the power spectrum density in high-noise circumstance, was the same as that calculated from the current response in a low-noise circumstance.