A new fluorescent ionophore for alkaline earth metal ions, 4′-(9-fluorenecarboxamido)benzo-15-crown-5 (3), was synthesized; its photochemical behavior was investigated using UV, fluorescence, 1H NMR, and 13C NMR spectrometry. In the absence of a metal ion, the fluorene moiety showed weak fluorescence emission (fluorescence “Off” state). However, complexation with metal ions greatly enhanced the fluorescence intensity (fluorescence “On” state).
The spatial distribution analysis of emission signals from a laser-induced plasma can provide information on the excitation mechanism as well as on the optimization of the analytical conditions when it is employed as a sampling and excitation source in optical emission spectrometry. A two-dimensionally imaging spectrometer system was employed to measure spatial variations in the emission intensities of a copper sample and plasma gases when krypton, argon, or helium was employed under various pressure conditions. The emission image of the Cu I 324.75-nm line consists of a breakdown spot and a plasma plume, where the breakdown zone expands toward the surrounding gas. The shape and the intensities of the plasma plume are strongly dependent on the kind and pressure of the plasma gas, while those of the breakdown zone are less influenced by these experimental parameters. This effect can be explained by the difference in the cross-section of collisions between krypton, argon, and helium. The signal-to-background ratio of the Cu I 324.75-nm line was estimated over two-dimensional images to determine the optimum position for analytical applications.
Hydro-membrane gas chromatography (HMGC) is achieved by the annular condensation of water in a capillary column at less than 70°C. The annular membrane of water is formed as a result of the wettability of the stationary phase, which is induced at a water contact angle ranging from 75° to 79°, as derived from a solubility parameter (δ) range of 15.7 ± 0.3 MPa1/2 of the coated resin. The range of the liquid to gas volume ratio (β) required to support the annular membrane should be kept between 0.00005 and 0.0003. In the case of a 0.25-mm i.d. column, the ratio can be set by the combination of a 0.1 to 0.2 µl min-1 water supply rate and helium gas flow rate. Separation by HMGC develops not only a gas-solid partition but also a focusing effect on the water membrane. One feature of HMGC is that it gives a non-adsorption chromatogram based on the blocking effect of pre-adsorbed water; furthermore, despite the presence of a relatively large quantity of water, the electron impact ionization efficiency is kept the same as in the usual GC/MS condition. The detection limit with the injection of 1 µl of aquatic solution was estimated to be less than 0.1 ppb of low-molecular-weight fatty acids with s/n = 5 on a mass chromatogram at m/z 45. The HMGC/EI-MS system can be applied to the trace analysis of C1 to C3 volatile acids, volatile inorganic acids, and halogenated organic acids in water.
We present a method to determine 88Sr/86Sr and 87Sr/86Sr simultaneously. The former variation reflects the mass-dependent isotopic fractionation through the physico-chemical processes, and the latter originates from β--decay of the parent nuclide 87Rb as well as the mass-dependent isotopic fractionation. In order to determine the mass-dependent isotopic fractionation, the mass-discrimination effect on 88Sr/86Sr was externally corrected by an exponential law using Zr. For the radiogenic growth of 87Sr/86Sr, the mass-dependent isotopic fractionation effect on 87Sr/86Sr was corrected by a conventional correction technique using the 88Sr/86Sr ratio. The reproducibility of the 88Sr/86Sr and 87Sr/86Sr measurements for a high-purity Sr chemical reagent was 0.06‰ (2SD, n = 20) and 0.07‰ (2SD, n = 20), respectively. Strontium isotopic ratios (88Sr/86Sr and 87Sr/86Sr) were measured on six geochemical reference materials (igneous rock: JB-1a and JA-2; carbonate mineral: JLs-1, JDo-1, JCp-1 and JCt-1) and one seawater sample. The resulting 87Sr/86Sr ratios obtained here were consistent with previously published data within the analytical uncertainties. The resulting 88Sr/86Sr ratios for igneous rock samples did not vary significantly within the samples, whereas the carbonate samples showed enrichments of the lighter Sr isotopes over the seawater sample. The 88Sr/86Sr ratio of geochemical samples could reflect the physico-chemical processes for the sample formation. Also, a combined discussion of 88Sr/86Sr and 87Sr/86Sr of samples will render multi-dimensional information on geochemical processes.
An immunochromatographic assay was developed to detect chloramphenicol (CAP) residues in aquaculture tissues. The limit of detection (LOD) was 10 ng g-1 for detecting CAP spiked in the aquaculture tissues. The results were confirmed by liquid chromatography tandem mass spectrometry (LC/MS/MS) and indicated that there was a good agreement between the two methods. The linear regression equation was y = 1.19x + 0.539 with R2 = 0.978. The assay time for test was less than 5 min and the method is suitable for rapid testing on-site.
Titanium (Ti) and TiO, Ti2O3, Ti3O5 and TiO1.98 as well as TiO2 have been evaluated as chemo-affinity sorbents for the selective enrichment of organic phosphates. A column-switching high-performance liquid chromatography (HPLC) system, constructed with a precolumn (4.6 mm i.d. × 10 mm) packed with the titanium sorbents, an anion-exchange analytical column and a UV detector (215 nm) was used. When an aqueous 0.015% trifluoroacetic acid (TFA) was used as a sample-loading solution, O-phospho-L-tyrosine (P-Tyr), phenyl phosphate and phenylphosphonic acid were adsorbed onto all of the titanium sorbents with recoveries of 60.9 - 102.9%. Some acidic compounds other than phosphates, such as benzenedicarboxylic acid (BDA) isomers, were also adsorbed onto all of the titanium sorbents. To improve the selectivity to organic phosphates, various sample-loading solutions were examined using a Ti precolumn, two phosphorylated peptides [Ile-Ser(p)-Val-Arg (PP1) and Gln-Ile-Ser(p)-Val-Arg (PP2)], P-Tyr, BDA isomers and diglutamic acid (Glu-Glu) as test compounds. Among the sample-loading solutions tested, such as TFA, HClO4, organic acids, boric acid and NaCl, the use of 100 mM NaCl in 10 mM boric acid was found to be effective. The recoveries of PP1, PP2 and P-Tyr were 73.0, 88.3 and 71.5%, respectively, whereas those of Glu-Glu and BDAs were suppressed to only below 10%.
3-(2-Pyridyl)-5,6-diphenyl-1,2,4-triazine (PDT) was used for the first time as a precolumn derivatizing reagent in the high-performance liquid chromatography (HPLC) method with UV absorbance detection for the Fe(II) determination. The Fe(II) reacts with PDT to form a magenta colored chelate in the presence of sodium dodecyl sulfate (SDS) and acetic acid-sodium acetate buffer solution medium of pH 4.65. The selection of maximum absorbance detection wavelength and the optimum composition of the organic modifier in the mobile phase were investigated in detail for the quantitative determination of Fe(II) using HPLC system. The formed Fe(II)-PDT chelate was satisfactorily separated from PDT on an Agilent Shim-pack ODS column (Eclipse XDB-C8, 4.6 × 150 mm) by isocratic elution with acetonitrile and 0.02 mol L-1 acetic acid-sodium acetate buffer solution (pH 4.65, containing 0.02% of SDS and 60 × 10-3 mol L-1 NaClO4) as mobile phase at a flow rate of 1 mL min-1, and monitored with a multiple wavelength detector. The detection limit (S/N = 3) is 0.35 ng mL-1. Due to the excellent separation ability of HPLC, the innovative introduction of PDT as the precolumn derivatizing reagent, and the proper selection of the detect wavelength, the sensitivity of our newly developed HPLC method was enhanced remarkably compared to those of the common spectrophotometric methods. The developed HPLC method was successfully applied to the determination of Fe(II) in lake water samples.
A new, sensitive method for determining dopamine has been established based on the principle of fluorescence quenching. A linear relationship is obtained between F0/F and the concentration of dopamine in the range of 0.80 - 16.00 µg mL-1. The detection limit was 0.23 µg mL-1 and the relative stand deviation was 1.54%. The mechanism of the fluorescence quenching has been discussed. Effects of pH, foreign ions, and standing time on the determination of dopamine have been examined. This method is simple and can be used for the determination of dopamine in injections solution of dopamine. The results obtained by this method agreed with those obtained by the official method.
A new post-chemiluminescence (PCL) reaction was observed when piroxicam was injected into the reaction mixture after the CL reaction of N-bromosuccinimide (NBS) and luminol. A possible reaction mechanism was proposed based on the studies of the CL kinetic characteristics, the CL spectra, fluorescence spectra and other experiments. A new flow injection CL method for the determination of piroxicam was established based on the PCL reaction. The relative standard deviation (RSD) for the determination of piroxicam was 1.2% (n = 11, c = 2.0 × 10-6 g/ml). The CL intensity responded linearly to the concentration of piroxicam in the range 1.0 × 10-7 - 1.0 × 10-5 g/ml (r = 0.9991). The detection limit was 4.0 × 10-8 g/ml. The method had been applied to the determination of piroxicam in tablets with satisfactory results.
A simple, highly sensitive and dye-less assay for proteins was reported using a resonance light-scattering (RLS) technique based on the enhanced RLS intensity of β-cyclodextrin (β-CD)-sodium dodecylsulfate (SDS)-protein system. Under the optimum conditions, the enhanced RLS intensity is in proportion to the concentration of proteins in the range of 0.01 to 2.3 µg ml-1 for bovine serum albumin (BSA), 0.01 to 2.0 µg ml-1 for human serum albumin (HSA), 0.015 to 5.0 µg ml-1 for γ-globulin (γ-G), 0.02 to 3.5 µg ml-1 for egg albumin (EA), 0.02 to 4.0 µg ml-1 for pepsin (Pep), and 0.02 to 3.6 µg ml-1 for α-chymotrypsin (Chy). Their detection limits (S/N = 3) are 1.1, 1.6, 2.4, 6.7, 5.4 and 4.2 ng ml-1, respectively. Synthetic samples and human serum samples were determined satisfactorily, and the results were in reasonable agreement with those obtained by a documented spectrophotometric (Bradford) method.
Ternary mixtures of thiamin, riboflavin and pyridoxal have been simultaneously determined in synthetic and real samples by applications of spectrophotometric and least-squares support vector machines. The calibration graphs were linear in the ranges of 1.0 - 20.0, 1.0 - 10.0 and 1.0 - 20.0 µg ml-1 with detection limits of 0.6, 0.5 and 0.7 µg ml-1 for thiamin, riboflavin and pyridoxal, respectively. The experimental calibration matrix was designed with 21 mixtures of these chemicals. The concentrations were varied between calibration graph concentrations of vitamins. The simultaneous determination of these vitamin mixtures by using spectrophotometric methods is a difficult problem, due to spectral interferences. The partial least squares (PLS) modeling and least-squares support vector machines were used for the multivariate calibration of the spectrophotometric data. An excellent model was built using LS-SVM, with low prediction errors and superior performance in relation to PLS. The root mean square errors of prediction (RMSEP) for thiamin, riboflavin and pyridoxal with PLS and LS-SVM were 0.6926, 0.3755, 0.4322 and 0.0421, 0.0318, 0.0457, respectively. The proposed method was satisfactorily applied to the rapid simultaneous determination of thiamin, riboflavin and pyridoxal in commercial pharmaceutical preparations and human plasma samples.
The oxidation of N,N′-diphenyl-1,4-phenylenediamine (DPPD) has been studied by cyclic voltammetry at glassy carbon electrodes in propylene carbonate. Next, the reaction between ammonia and DPPD was similarly investigated. It has been shown that ammonia reversibly removes protons from oxidized DPPD molecules, thus facilitating the oxidative process with the emergence of a new wave at less positive potentials. The results suggest a novel methodology for the electrochemical determination of ammonia based on its interaction with DPPD in propylene carbonate. The measurement of the current of the new wave is shown to scale linearly with the ammonia concentration up to ca. 200 ppm and above.
A multi-wall carbon nanotubes (MWNTs)-quantum dots (QDs) composite-modified glassy carbon electrode (GCE) was prepared. The complex was characterized by transmission electron microscopy (TEM). The electrochemical behavior of levodopa at MWNTs and QDs-modified GCEs (MWNTs-QDs/GCE) was studied by cyclic voltammetry (CV) and chronocoulometry (CC). It was found that its electrochemical behavior was a two-charge-two-proton process. The modified electrode had high electrocatalytic activity for levodopa with a standard heterogeneous rate constant of 0.595 cm s-1, which was greatly increased compared with the values for bare GCE and individual MWNTs modified GCE. The better electrocatalytic activity for levodopa at MWNTs-QDs/GCE may due to a synergistic effect between MWNTs and QDs. This result provides a novel way to promote research on biomicromolecules at nano-dimensions.
In this paper, we firstly report the direct voltammetric recognition and determination of dopamine (DA) by using AlIII-DA complexes at the hanging mercury drop electrode (HMDE). A new sensitive cathodic peak of AlIII-DA can be detected at -900 mV (vs. SCE) in 0.1 M NH4Cl-NH3·H2O-0.1 M KCl buffer solution at pH 8.5. This unique -900 mV cathodic peak arises from the specific interaction between AlIII and DA on the HMDE, whereas other substances with similar structures, such as L-dopa, epinephrine (EP), norepinephrine (NE), catechols, caffeic acid (CA), trihydric phenols and tiron, do not yield any new peak on the voltammograms in the potential range from -100 to -1200 mV when AlIII is added. The distinct voltammetric characteristic of the recognition of DA can effectively inhibit the interferences of both ascorbic acid and uric acid in the DA determination by the direct electrochemistry, which is a major difficulty when a solid electrode is used. The proposed method can be anticipated as an effective means for the recognition of DA in the elucidation of the mechanisms of Parkinson's disease (PD) and Alzheimer's disease (AD) in the presence of AlIII.
A new highly selective iodide electrode incorporating a binuclear manganese(III) complex, bis(salicylaldehyde-aminopropanol)dichloroaceticdimanganese(III) [Mn(III)2-BSAPDCA], as a neutral carrier is described. The electrode displays an anti-Hofmeister selectivity sequence: iodide >> perchlorate > salicylate > thiocyanate > nitrate > bromide > nitrite > chloride > sulfate. The excellent selectivity for iodide is related to a direct interaction between the central Mn(III) atom and iodide and a steric effect associated with the structure of the carrier, which is supported by UV spectroscopy and AC impedance techniques. The electrode exhibits a near-Nernstian potentiometric linear response range to iodide from 1.0 × 10-1 to 2.0 × 10-5 mol/L with a detection limit of 8.0 × 10-6 mol/L and a slope of -60.3 mV/decade in pH 3.0 of phosphate buffer solutions at 20°C. From a comparison of the potentiometric response characteristics between a binuclear manganese(III) complex, Mn(III)2-BSAPDCA, and a mononuclear manganese(III) complex, Mn(III)-BSAPB, an enhanced response towards iodide from a binuclear metallic complex-based electrode was observed. The electrode, based on binuclear manganese(III) complex, was successfully applied to the determination of inorganic total iodine in iodized table salt with satisfactory results.
Supercritical fluid extraction (SFE) provides an environmentally green technique to decontaminate chromium species from solid matrices using supercritical fluid carbon dioxide (ScCO2). Methanol and a small amount of water were found to significantly improve the extraction efficiency. The fluorinated chelating agent lithium bis(trifluoroethyl)-dithiocarbamate (LiFDDC) was effective in removing Cr ions in methanol-modified CO2via in situ chelation/SFE technique. This paper indicates that the extraction efficiencies of Cr(III) and Cr(VI) from solid matrices can be greatly increased to more than 92% in the presence of a small amount of water, using 5% methanol-modified CO2 containing LiFDDC as an extractant. Chromium species in a wood waste sample in the form of chromated copper arsenate (CCA) can be extracted, but the extraction efficiency is not as good as expected, possibly due to the complications of the chemistry of Cr species in different oxidation states and to matrix effects.
A very sensitive and simple method is presented for the determination of Se(IV) by Osteryang square-wave cathodic stripping voltammery (OSWCSV). The method is based on the reduction of Se(IV) with Bi(III) onto an edge-plane type of pyrolytic graphite substrate, followed by a cathodic potential scan. OSWCSV studies indicate that the reduced selenium produced a distinct catalytic hydrogen wave at -1150 mV vs. Ag/AgCl. The peak height of the catalytic hydrogen wave was directly proportional to the initial Se(IV) concentration in the ranges of 0.1 - 1.0 and 1.0 - 20.0 µg L-1 (correlation coefficients 0.9800 and 0.9901, respectively) when the optimized parameters were used. A 3σ detection limit of 0.025 µg L-10 Se(IV) was obtained at 30 s deposition time. The relative standard deviation was 4.0% on replicate runs (n = 12) for the determinations of 0.10 µg L-1 Se(IV). Analytical results of natural water samples demonstrate that the proposed method is applicable to speciation analysis of Se(IV) and Se(VI).
A capillary electrophoresis with tris(2,2′-bipyridyl)ruthenium(II)-based electrogenerated chemiluminescence detection method was investigated for the determination of monosaccharides using 2-diethylaminoethanethiol as a derivatizing reagent. Xylose, rhamnose, glucose and glucosamine were selected for the demonstration of the method. Under optimal conditions, the calibration curve of glucose was linear over the range of 1.0 × 10-4 to 1.0 × 10-7 mol/L (R = 0.999) and the detection limit was 6.0 × 10-8 mol/L (S/N = 3). The method was successfully applied for the assay of glucose in angelica.