Many environmental organic chemicals have chloride in their structure. Thus, researching the chlorination mechanism of carbon is of interest. Dioxins are typically concentrated in fly ash collected from the post-combustion zone during the operation of municipal solid waste incinerators. In this study, we report the application of Cl-K near-edge X-ray-absorption fine structure (NEXAFS) in determining the chlorination mechanism of carbon in fly ash. The separation of a chloride–carbon (C–Cl) bond was readily recognizable as a peak in the Cl-K NEXAFS spectrum. Chlorination effects could be estimated using Cl K-edge NEXAFS with no dependence on metal species. Analysis of Cl K-edge NEXAFS spectra showed the reduction of copper(II) chloride at 300°C and oxidation of iron(III) chloride at 400°C in connection with the chlorination of carbon.
A novel fire investigation technique using a needle extraction device was studied. Using a polymer particle-packed needle device, air samples containing volatile organic compounds (VOCs) generated from fire accelerants, gasoline and kerosene were extracted effectively, and subsequent gas chromatographic (GC) analyses were successfully carried out. Carpet and wood samples were spiked with gasoline and kerosene, followed by monitoring of the time-variation profiles of emitted VOCs up to 48 h. The fire accelerants were also measured for combusted carpet and wood samples, and the applicability of the proposed method to fire investigations was confirmed. Even at 48 h after spiking, groups of characteristic compounds were clearly observed in the air environments near the combusted sample. This method was further applied to the determination of VOCs in simulated fires, strongly suggesting the applicability of the developed method to real fire investigations.
A sensitive and accurate high-performance liquid-chromatography method was developed and validated for the simultaneous determination of pyrazinamide (PZA), isoniazid (INH), rifampicin (RFP) and acetylisoniazid (AcINH) in human plasma. Separation was performed on a Max-RP C12 column using gradient elution and a flow-rate program. The mobile phase was methanol–acetonitrile–buffer (20 mM of heptanesulfonic acid sodium, pH 2.5) with a ratio of 10:8:82 (v/v/v) at the initial phase. All calibration curves had good linearity (r2 > 0.99) between the test ranges. The intra- and inter-day precision was less than 8.8% in good accuracy (<15%). The limit of detection with a signal-to-noise (S/N) of 3 was 0.014, 0.009, 0.023 and 0.054 μg mL−1 for PZA, AcINH, INH and RFP, respectively. The method was selective, sensitive and reliable, and is a good alternative for routine therapeutic drug monitoring of the four compounds during the treatment of tuberculosis patients.
A micro-free flow electrophoresis (μFFE) analytical system with voltage applied in two dimensions was proposed. Both fluid transport and separation were driven electrokinetically. The Alpha-Imager was applied as an in-situ detector, which could observe, scan and analyze the photometric state of the whole separating area. The mass-transfer process and the range of voltages applied on the chip were simulated and calculated by MATLAB software. Then, the chip design with a separating chamber, which was 12 mm in length, 5 mm in width and 20 μm in depth, was presented. Under the CZE-CZE mode, the operational conditions, such as the EOF, the pH of the buffer and the ratio of the voltage applied in two dimensions, were optimized. Mixed amino acids, including FITC-labeled L-lysine, FITC-labeled L-phenylalanine and FITC-labeled L-aspartic, were successfully separated on the chip when the borate buffer contained 3% glycerol, with pH as 11 and the ratio of field strength in two-dimension was 1:7. The resolution could achieve 2.1 and 1.9, respectively.
In this study, I separated gold nanoparticles (Au NPs) using the reversed electrode polarity stacking mode (REPSM) of a capillary electrophoresis system for on-line enhancement prior to performing micellar electrokinetic chromatography (MEKC). In the first part of this paper, I discuss the effects of several new and important parameters, the nature of the added salt, the pH of the sample matrix, and the size of the injection buffer plug that appears after introducing the samples, on the systems’ on-line concentration and separation performance for a variety of sample compositions. In the second part of this paper, I describe my use of the optimized conditions to monitor the migration of the Au NPs during the concentration and separation processes. The results of these studies suggest that combining REPSM with MEKC is a very good strategy for the on-line concentration and separation of Au NPs at trace concentrations.
The effect of urea as an electrophoretic buffer solution modifier on the ion-association (IA) capillary electrophoresis (CE) separation of four anionic metal complexes of Al(III), Co(III), Cr(III), and Fe(III) with 2,2′-dihydroxyazobenezene-5,5′-disulfonate (DHABS) using a hydrophobic ion-association agent, tetrapentylammonium bromide, was studied. The mutual separation of the four anionic metal-DHABS complexes was not achieved without the addition of urea in the electrophoretic buffer solution. However, the addition of 1.5 M urea in the electrophoretic buffer solution brought about a complete separation of the four metal complexes. The ion-association constants between all metal-DHABS complexes and tetrapentylammonium in an aqueous urea solution were smaller than those in a neat aqueous solution. This indicates the hydrophobic interaction contributing to the ion-association between analytes and ion-association agent during IA-CE separation processes can be controlled with the addition of urea to the electrophoretic buffer solution. Another advantage of adding urea was a substantial enhancement of separation efficiency with a reduction of the half-bandwidth of the peaks. Also, a reduction of the electrophoretic mobility of the electroosmotic flow when urea was added was much less than when organic solvents were used.
A rapid and sensitive method using pressure-assisted electrokinetic injection (PAEKI) as the on-line sample enrichment technique and electrospray–tandem mass spectrometry as the monitor has been developed for the determination of four halogenated phenols, 2,4,6-trichlorophenol, 2,4-dichlorophenol, 2,3,4,6-tetrachlorophenol and tetrabromobisphenol A, in water samples. In 8-min of injection, the four halogenated phenols in water samples were enriched up to several thousand times. With the aid of a solid-phase extraction clean-up procedure, the method achieved a detection limit in the range of 7.4 to 37.1 ng L−1 for the four phenols by multiple reaction monitoring in a negative mode. The overall recoveries for all four halogenated phenols in water samples were in the range of 68 to 114%. The good method repeatability has been demonstrated by the relative standard deviations (RSDs) of less than 10% for water samples spiked with standard mixtures. The four target phenols in all the water samples were below the detection limits.
In this paper, a novel method has been established to determine ethamsylate using potassium ferricyanide as a spectroscopic probe reagent. It has been demonstrated that Fe(III) is reduced to Fe(II) by ethamsylate, and that the formed Fe(II) reacts with potassium ferricyanide to form soluble prussian blue (KFeIII[FeII(CN)6]). Beer’s law is obeyed in the range of 0.16 – 24.00 μg mL−1 with the molar absorption coefficient of 2.1 × 104 L mol−1 cm−1. The detection limit (3 σ/k) is 0.11 μg mL−1. This method has been successfully applied to determine ethamsylate in pharmaceutical and serum samples with satisfactory results, and presented quite satisfactory credibility during method equivalence assessment.
Here, we describe a colorimetric sensor for detecting Hg2+ in aqueous media, which is simply constructed by the self-assembly of thymine acetamidoethanethiol (T-SH) on gold nanoparticles (AuNPs). Based on the specific interaction of Hg2+ with two thymines (T), the T-SH modified AuNPs can be induced to aggregate through the formation of a stable T-Hg-T complex in the presence of Hg2+, resulting in a color change from red to blue-gray. As low as 0.5 μM of Hg2+ can be easily monitored by the naked eye using this sensor. Other metal ions, including Zn2+, Cd2+, Pb2+, Ni2+, Cu2+, Co2+, Mn2+, Ba2+, Fe2+, Ca2+, Mg2+, Al3+, and Fe3+, could not cause any response, even at concentrations 100-fold higher than Hg2+. The high selectivity, high stability and easy operation enable this sensor suitable for the rapid on-site detection of Hg2+ pollution.
Nitrate and nitrite ions were found to be successfully electroreduced at an in situ electrochemically pretreated copper electrode in acidic media, and their reduction peaks of a cyclic voltammogram were found at two distinct electrode potentials. Cyclic voltammetric experiments revealed a highly sensitive behavior of the pretreated copper electrode upon the electroreduction of nitrate and nitrite ions, and showed that a simultaneous voltammetric determination of the ions was achievable. Differential pulse voltammetry (DPV) was applied to the simultaneous determination. As a result, the detection limits were 0.26 and 0.17 μmol dm−3 for nitrate and nitrite ions, respectively. Simultaneous determinations for real samples (river water) were carried out by DPV at the pretreated copper electrode and spectrophotometry (the Griess method). The determination values obtained by both methods were in a good agreement with each other.
A stable composite film composed of 1-butyl-3-methyl-imidazolium tetrafluoroborate, chitosan, zirconia nanoparticles and the hemoglobin (Hb) was cast on the surface of an ionic liquid of an N-butylpyridinium hexafluorophosphate modified carbon paste electrode to fabricate a modified electrode. Scanning electron microscopy images of the modified electrode indicated that there was a dendritic structure on the modified electrode, and UV-Vis and FT-IR spectra showed that Hb in the composite film retained its native structure. Voltammetric experiments at the modified electrode showed that, in a pH 7.0 phosphate buffer solution, a pair of well-defined and quasi-reversible redox voltammetric peaks was obtained with the formal potential located at −0.216 V. The electrochemical parameters of Hb in the composite film were further carefully calculated: the electron-transfer rate constant was 0.52 s−1 and the charge transfer coefficient was 0.34. The catalytic reduction peak current had a linear relationship with the concentration of trichloroacetic acid (TCA) in the range from 0.2 to 10.3 mmol/L with a detection limit of 66.7 μmol/L. Therefore, the composite film as a novel matrix opened up a possibility for further study on the design of enzymatic biosensors with potential applications.
The stability constants and the hydration number of a complex between tris(pivaloyltrifluoroacetonato)lanthanide(III) (LnA3) and 2,2′-bipyridyl (B), LnA3B, and the complexation heat were determined across the Ln series by a solvent-extraction technique, Karl Fischer coulometry, and calorimetry, successively. The number of water molecules released from LnA3 upon the complexation with B as well as the values of the stability constant increased along with increasing Ln atomic number to around Dy(III); via a maximum, it decreased. It is concluded that the largest stability constant of the complex of Ho(III) or this vicinity is derived from the strongest bond energy, due to the fitness between LnA3 and B. This conclusion was supported by the trend of the variation of the entropy change as well as that of the hydration number across the Ln series.
Kinetic analyses of lactate-dehydrogenase (LD)-coupled alanine transaminase (ALT) reaction processes were investigated for measuring ALT by an integration strategy. For measuring ALT by a kinetic analysis of an LD-coupled ALT reaction curve, candidate reaction curves were calculated via iterative numerical integration of the differential velocity equations to execute a weighted nonlinear-least-square-fitting. To realize the integration strategy, the conventional initial-velocity method was used if the ALT activities were below 25 U/L; otherwise, kinetic analyses of the reaction curves were employed. Of the reaction curves recorded at 10-s intervals, kinetic analyses gave ALT activities resistant to deviations in the LD kinetic parameters. The integration strategy yielded a higher value of the lower limit, but an upper limit of over 100 U/L by simulations and over 75 U/L with purified ALT. Also, its intra-run relative standard deviations were below 9% for 0.50 U/L ALT and below 5% for final 1 to 65 U/L ALT. The integration strategy gave consistent ALT activities in clinical sera. Hence, this new approach for kinetic analyses of ALT reaction processes and the integration strategy were effective to measure ALT.
Endocannabinoid 2-arachidonoylglycerol (2-AG) regulates several important physiological processes in the brain. 2-AG is commonly quantified by gas chromatography mass spectrometry after an initial purification step. The most precise and rapid purification utilizes C18 solid-phase extraction, but quantification problems can arise with acyl migration from 2-AG to 1-arachidonoylglycerol. We found that extraction with methanol promoted this migration, but acetone and diethyl ether (Et2O) did not. Acetone and Et2O were used to develop a purification method for the direct determination of 2-AG.
The stability of a Ag/AgCl reference electrode equipped with a gelled ionic liquid, 1-methyl-3-octylimidazolium bis(trifluoromethanesulfonyl)amide (C8mimC1C1N), as a salt bridge, was examined in the potentiometry of pH standard solutions. The variation in the liquid junction potential (LJP) of the ionic liquid (IL)-type reference electrode, measured with respect to a double junction-type KCl reference electrode, was within 1 mV when one standard solution was replaced by another, except for the phthalate standard. The time course of the potential of the IL-type reference electrode showed a standard deviation of ±0.3 mV in all buffer solutions. The reproducible deviation of the potential of the IL-type reference electrode in the phthalate pH standard amounted to 5 mV. The deviation is due to the partition of the hydrogen phthalate in the C8mimC1C1N, influencing the phase boundary potential (PBP) across the interface between C8mimC1C1N and the phthalate standard. If a citrate standard is used instead of the phthalate buffer, the IL salt bridge works satisfactorily as a salt bridge for a reference electrode suitable for potentiometoric pH measurements.