The intermolecular interaction between 2-phenoxypropionic acid and β-bromo-cyclodextrin affixed on the stationary phase surface in a chiral HPLC system was studied by the moment analysis method. At first, pulse response and peak parking experiments were conducted to measure some parameters concerning the column geometry, adsorption equilibrium, and mass-transfer kinetics. Then, the first absolute moment (μ1) and second central moment (μ2′) of the elution peaks were analyzed by the moment equations, which were developed by assuming that the reaction kinetics between the solute molecules and the functional ligands can be represented by the Langmuir-type rate equation. Finally, the flow-rate dependence of HETP calculated from μ1 and μ2′ was analyzed by using the values of the parameters to determine the association and dissociation rate constants of the intermolecular interaction. It was demonstrated that the combination of the chromatographic experiments and moment analysis is one of the effective strategies for the kinetic study of intermolecular interactions.
A sensitive and selective chemiluminescence method was developed to determine ethylenediaminetetraacetic acid (EDTA) in water samples. It was observed that gold nanoparticles (AuNPs) catalyzed chemiluminescence (CL) reactions of permanganate-aldehydes which underwent an enhancement effect in the presence of iron(III) ions (Fe3+). This effect is more remarkable in the presence of EDTA, and a highly intensive CL emission is created in proportion to the EDTA concentration. These observations form the basis of the method for the high sensitive determination of EDTA in the 0.83 – 167 nmol L−1 concentration range, with a detection limit of 0.25 nmol L−1. The relative standard deviations for five repeated measurements of 5, 40 and 140 nmol L−1 EDTA were 1.14, 2.48 and 0.65%, respectively. The method has good selectivity toward EDTA, and there are no interferences from other ions. The offered method has good precision, and was satisfactorily used for the sensitive determination of EDTA in water samples.
A dew point meter (DP) and an infrared (IR) CO2 analyzer were assembled in a humid CO2 adsorption/desorption system in series for simultaneous online measurements of H2O and CO2, respectively. The humidifier, by using surface-flushing on a saturated brine solution was self-made for the generation of humid air flow. It was found that by this method it became relatively easy to obtain a low H2O content in air flow and that its fluctuation could be reduced compared to the bubbling method. Water calibration for the DP-IR detector is necessary to be conducted for minimizing the measurement error of H2O. It demonstrated that the relative error (RA) for simultaneous online measurements H2O and CO2 in the desorption process is lower than 0.1%. The high RA in the adsorption of H2O is attributed to H2O adsorption on the transfer pipe and amplification of the measurement error. The high accuracy of simultaneous online measurements of H2O and CO2 is promising for investigating their co-adsorption/desorption behaviors, especially for direct CO2 capture from ambient air.
We investigated the structural transition from liquid silk to silk fibers with vibrational circular dichroism spectroscopy. Liquid silk showed a major right-handed optically active band at around 1650 cm−1 and a minor one at around 1680 cm−1. The former disappeared over time, while the intensity in the latter increased. With the former wavenumber, liquid silk mainly adopted a random-coil structure. In contrast, the latter may reflect an intermediate structure in the transition. Furthermore, two right-handed bands at around 1630 and 1660 cm−1 appeared with the disappearance of the major band, and then the wavenumber of the former shifted to around 1620 cm−1. The shift results from the decrease in the frequency of the CO stretching mode due to the stacking of the β-sheet that comprises fibers. The band at 1660 cm−1 may reflect another intermediate structure due to its strong correlation with that at 1620 cm−1 in terms of their temporal change in intensity.
1,1,5,5-Tetramethylcarbohydrazide (TMCH) is the main precursor of N-nitrosodimethylamine upon ozonation in the Yodo River basin, Japan. This study was performed to develop an analytical method for TMCH using solid-phase extraction with ultra-high performance liquid chromatography–tandem mass spectrometry. TMCH is hydrophilic and a tertiary amine derivative, so Oasis® MCX cartridges were used as solid-phase cartridges. The recoveries of TMCH in tap and river waters as well as secondary effluent from a sewage treatment plant ranged from 75 to 94%. The limit of quantification of TMCH was 4 ng L−1. The source of TMCH in the Yodo River basin was found to be effluent from one sewage treatment plant. The concentrations were < 4 ng L−1 in raw water from water purification plants in regions other than the Yodo River basin, indicating that TMCH was used specifically in the basin.
In this work the electrooxidations of glucose, galactose, mannose, rhamnose, xylose and arabinose are studied at a nickel hydroxide nanoparticle modified boron-doped diamond electrode and compared to an unmodified electrode. These carbohydrates are very important in the second-generation ethanol production process. Nickel hydroxide modified boron-doped diamond was characterized by scanning electron microscopy and energy dispersive X-ray. Electrochemical impedance spectroscopy was employed to study the interface properties of surface-modified electrodes in the absence and presence of the carbohydrates. Limits of detection were 5.3 × 10−5, 6.8 × 10−5, 2.7 × 10−4, 6.9 × 10−5, 8.8 × 10−5 and 2.6 × 10−5 mol L−1 for glucose, galactose, mannose, rhamnose, arabinose, xylose, respectively.
With a view to enhance the sensitivity of analytical instruments used in the measurement of trace elements contained in a single cell, we have now equipped the previously reported micro-droplet injection system (M-DIS) with a desolvation system. This modified M-DIS was coupled to inductively coupled plasma atomic emission spectroscopy (ICP-AES) and evaluated for its ability to measure trace elements. A flow rate of 100 mL/min for the additional gas and a measurement point –7.5 mm above the load coil (ALC) have been determined to be the optimal parameters for recording the emission intensity of the Ca(II) spectral lines. To evaluate the influence of the desolvation system, we recorded the emission intensities of the Ca(I), Ca(II), and H-β spectral lines with and without inclusion of the desolvation system. The emission intensity of the H-β spectral line reduces and the magnitude of the Ca(II)/Ca(I) emission intensity ratio increases four-fold with inclusion of the desolvation system. Finally, the elements Ca, Mg, and Fe present in a single cell of Pseudococcomyxa simplex are simultaneously determined by coupling the M-DIS equipped with the desolvation system to ICP-AES.
Based on the principle of fluorescence enhancing, by the strong and specific interreaction between iodide (I−) ions and nanoAg on the surface of graphene quantum dots/Ag (GQDs/Ag) nanocomposite, we propose a simple label-free and turn-on method for the detection of I− ions with high selectivity and sensitivity by using fluorescent GQDs/Ag nanocomposite in aqueous media.
In this study, electrochemical molecularly imprinted sensors were fabricated and used for the determination of ascorbic acid (AA). Nanofiber membranes of cellulose acetate (CA)/multi-walled carbon nanotubes (MWCNTs)/polyvinylpyrrolidone (PVP) (CA/MWCNTs/PVP) were prepared by electrospinning technique. After being transferred to a glass carbon electrode (GC), the nanofiber interface was further polymerized with pyrrole through electrochemical cyclic voltammetry (CV) technique. Meanwhile, target molecules (such as AA) were embedded into the polypyrrole through the hydrogen bond. The effects of monomer concentration (pyrrole), the number of scan cycles and scan rates of polymerization were optimized. Differential pulse voltammetry (DPV) tests indicated that the oxidation current of AA (the selected target) were higher than that of the structural analogues, which illustrated the selective recognition of AA by molecularly imprinted sensors. Simultaneously, the molecularly imprinted sensors had larger oxidation current of AA than non-imprinted sensors in the processes of rebinding. The electrochemical measurements showed that the molecularly imprinted sensors demonstrated good identification behavior for the detection of AA with a linear range of 10.0 – 1000 μM, a low detection limit down to 3 μM (S/N = 3), and a recovery rate range from 94.0 to 108.8%. Therefore, the electrochemical molecularly imprinted sensors can be used for the recognition and detection of AA without any time-consuming elution. The method presented here demonstrates the great potential for electrospun nanofibers and MWCNTs to construct electrochemical sensors.
A nanocomposite platform built with multi-walled carbon nanotubes (MWCNTs) and nicotinamide adenine dinucleotide (NAD+) via a noncovalent interaction between the large π systems in NAD+ molecules and MWCNTs on a glassy carbon substrate was successfully developed for the sensitive and selective detection of uric acid (UA) in the presence of ascorbic acid (AA), dopamine (DA). NAD+ has an adenine subunit and a nicotinamide subunit, which enabled interaction with the purine subunit of UA through a strong π–π interaction to enhance the specificity of UA. Compared with a bare glassy carbon electrode (GCE) and MWCNTs/GCE, the MWCNTs-NAD+/GCE showed a low background current and a remarkable enhancement of the oxidation peak current of UA. Using differential pulse voltammetry (DPV), a high sensitivity for the determination of UA was explored for the MWCNTs-NAD+ modified electrode. A linear relationship between the DPV peak current of UA and its concentration could be obtained in the range of 0.05 – 10 μM with the detection limit as low as 10 nM (S/N = 3). This present strategy provides a novel and promising platform for the detection of UA in human urine and serum samples.
To ensure the reliability of amino acid analyses, the National Metrology Institute of Japan of the National Institute of Advanced Industrial Science and Technology (NMIJ/AIST) has developed high-purity certified reference materials (CRMs) for 17 proteinogenic amino acids. These CRMs are intended for use as primary reference materials to enable the traceable quantification of amino acids. The purity of the present CRMs was determined based on two traceable methods: nonaqueous acidimetric titration and nitrogen determination by the Kjeldahl method. Since neither method could distinguish compounds with similar structures, such as amino acid-related impurities, impurities were thoroughly quantified by combining several HPLC methods, and subtracted from the obtained purity of each method. The property value of each amino acid was calculated as a weighted mean of the corrected purities by the two methods. The uncertainty of the property value was obtained by combining measurement uncertainties of the two methods, a difference between the two methods, the uncertainty from the contribution of impurities, and the uncertainty derived from inhomogeneity. The uncertainty derived from instability was considered to be negligible based on stability monitoring of some CRMs. The certified value of each amino acid, property value with uncertainty, was given for both with or without enantiomeric separation.
In vitro selection methods allow for isolation of DNAzymes (catalytic DNAs) from random DNA pools. Here we describe a fluorogenic DNAzyme, LYF5, isolated using a double-random selection approach: a random DNA pool was selected against a complex molecular mixture derived from a breast cancer cell line, T47D. LYF5 specifically indicates the T47D breast cancer cell line with high sensitivity. After sequence optimization, the second-generation DNAzyme, 2G-LYF5, exhibited an approximately 2-fold higher cleavage percentage. Finally, we have determined that the intramolecular stem-loop motif plays a crucial role in 2G-LYF5 activity. Our findings underscore the capability of single-stranded DNA molecules to perform highly sophisticated functions that are amenable to the development of diagnostic tests for early identification of breast cancer.
A reliable and cost-effective method for the determination of multiple neonicotinoids was developed using a modified QuEChERS-based extraction procedure in complex matrices, namely Hedyotis diffusa (a representative of the Traditional Chinese herb which contains lots of pigment, saponin and terpene) and Semifluid extract of deer foetus (a representative of the Chinese traditional patent medicine that was produced with several different herbs, and especially containing lots of protein, except for other interference components). Ultra-performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) was used for the quantification and confirmation of five compounds. Except for two transitions obtained by the MRM mode, identification was further carried out by the ion radios. The proposed chemical structure of every selected product ion and the proposed pyrolysis way were presented. The extraction, clean-up, UPLC separation and MS/MS parameters were especially optimized in order to obtain better recoveries. The low limits of detection (LODs) of five insecticides ranged from 0.04 to 0.81 μg kg−1. Matrix matched calibration in the concentration range of 0.05 – 50 μg kg−1 were used to compensate the matrix effect, and reasonable recoveries 80.2 – 105.4% of five compounds were demonstrated in different spiked levels with inter-RSD from 1.7 to 10.6%. The proposed method is an alternative approach to make an analysis of neonicotinoids in Chinese medicine, which is more reliable and promising compared with other detection methods.
In order to analyze trigonelline, caffeine, chlorogenic acid, and their related compounds simultaneously, an HPLC method using an InertSustain C18 column and a mobile phase containing octanesulfonate as an ion-pairing reagent under an acidic condition was developed. The optimum mobile phase conditions were determined to be 0.1% phosphoric acid, 4 mM octanesulfonate, and 15% methanol at 35°C. Using the proposed method, trigonelline, nicotinic acid, caffeine, theophylline, chlorogenic acid, and caffeic acid in ten instant coffee samples were analyzed. These analytes except for theophylline were detected in all samples. An increase in the caffeine content in instant coffee samples tended to decrease in both trigonelline and chlorogenic acid contents, and the trigonelline content was found to be correlated well with the chlorogenic acid content (R2 = 0.887).
The beam deflection method and absorbance spectroscopy were applied to study effects of acid solutions on aquatic plants, and their results were compared. Aquatic plants Egeria densa and Ceratophyllum demersum L were used as model plants. In absorbance experiments, a piece of the plants was put in a beaker with 20 mL HCl solution, and absorbance of the HCl solution was measured every 30 min. In beam deflection experiments, a probe beam from a He-Ne laser was focused to a vicinity of the plants in a culture dish with HCl solution by an objective lens, and deflection signals of the probe beam were monitored by a position sensor. Absorbance spectra of the HCl solutions with immersing of the plants showed absorbance below 410 nm, suggesting that some compounds leaked from the plants into the HCl solutions. Changes of absorbance and deflection signals with immersion time were examined for different pH levels. The changing trends of the absorbance and deflection signals with time were similar, but the absorbance changes were delayed for about 2 – 3 h. The absorbance method could not detect the effect of the pH 5.0 HCl solutions on the aquatic plants, while the deflection method could.
A stationary phase with a dipole interaction was synthesized by immobilizing the 2,4-dibromophenoxy (DBP) group onto a hydrophilic base resin. The chromatographic properties for halogenated benzenes were evaluated on the DBP-resin by reversed phase mode. The separation efficiency of the DBP-resin for p-xylene and 1,4-dihalogenated benzenes was better than that of the column packed with octadecylsilane (ODS). The results suggested that the retention of the solutes on the DBP-resin depends on the Debye interaction in addition to with the dispersion force caused by the DBP group.
Under conditions where carbonate and oceanic parameters such as alkalinity (AT), salinity (Sp), and phosphate (PT) and silicate (SiT) concentrations cannot be obtained, the use of fixed values to calculate total pH (pHT) at 25°C was demonstrated. For temperatures of 20 – 30°C, these values caused a maximum error of ±0.001 in pHT. For temperatures of 0 – 40°C, using fixed values with correct SP values caused a maximum error of approximately +0.0021.
This paper suggests a correction-free calibration method in wavelength dispersive X-ray fluorescence analysis in order to determine tungsten as a major alloyed element in high-speed steels accurately. Matrix effects on fluorescent X-ray intensity of tungsten Lα line were minimized by borate fusion, and the total amount of tungsten in the glassy matrix could be quantified. Glass bead specimens were prepared with 10 to 12 mg of the steel sample and 4.0 g of lithium tetraborate as a flux agent. Without untraceable X-ray intensity correction, a linear calibration curve was obtained by measuring synthesized calibration standards prepared by using standard solutions. As compared with fundamental parameter calculations, the present method gave more accurate results of tungsten in certified reference materials of high-speed steel.
The effect of long-time X-ray irradiation on Cr and Hg in a polypropylene disk certified reference material (PP disk CRM, NMIJ CRM 8136-a) during measurements by X-ray fluorescence (XRF) spectrometry was examined in the present study. The XRF intensities of Cr (Kα), Hg (Lα) and Pb (Lα), obtained by an energy-dispersive (ED)-XRF spectrometer, showed the different intensity trends and the obtained XRF intensity ratios of Cr/Pb and Hg/Pb revealed decreasing and constant ratios, respectively, for long-time X-ray irradiation of up to 430 h. A similar decreasing trend of the Cr/Pb intensity ratio was also observed by wavelength-dispersive (WD)-XRF measurements for 120 h. Moreover, Cr, Hg and Pb in the PP disks obtained after long-time measurements by the WD-XRF spectrometer were measured by an ED-XRF spectrometer, and the loss of Cr was confirmed. From these results, Cr in the PP disk CRM, whose chemical form was an organometallic compound, was considered to be possibly lost during the XRF analysis for long-time or frequent measurements.
On page 481, the footnote, ‡ To whom correspondence should be addressed. E-mail: firstname.lastname@example.org (K. M.); email@example.com (H. I.) should read ‡ To whom correspondence should be addressed. E-mail: firstname.lastname@example.org (K. M.); email@example.com (H. I.) K. M. present address: Department of Chemistry, Faculty of Science, Toho University, 2-2-1 Miyama, Funabashi 274-8510, Japan.