A rapid determination of decabromodiphenyl ether (DeBDE) in polystyrene (PS) by thermal desorption (TD)-GC/MS was studied. The TD-GC/MS method using a pyrolysis-GC/MS system allowed the quick quantification of DeBDE in a waste TV back plate composing of a PS flame-retarded with polybrominated diphenyl ethers on the basis of the resulting chromatogram with a ca. 4% relative standard deviation without using any tedious sample pretreatment, such as solvent extraction.
2,10-Disubstituted phenothiazines are the best drugs in psychiatry. Several methods for their analysis have been reported in the literature. The official methods are based on non-aqueous titration or spectrophotometry. Various oxidizing agents have been used for the spectrophotometric determination of 2,10-disubstituted phenothiazines, e.g. Ce(SO4)2, NH4VO3, K2S2O8, KIO4, KIO3, KBrO3, FeCl3, NaNO2, H2O2, chloramine T, p-benzoquinone, N-bromosuccinimide. Oxidation reactions of phenothiazines were also used for their determination by flow-injection methods.
The Rotating Sample System (RSS) has been conceived in the authors' laboratory as a convection platform for microliter-sized solution volumes. Convection is achieved by rotating a small drop of sample on a stationary substrate by humidified gas jets directed tangentially at the drop base with the working electrode and a liquid junction embedded in it. Simplicity and portability of the device, and substrates complete with microfabricated electrode and junction made potentially disposable, are further competitive advantages with respect to competing, conventional analytical systems. In this work the RSS' performance with variation of system parameters such as the position and size of gas jets used for sample rotation, and position of the working electrode in the substrate are studied. Trace levels of Pb could be detected with this system and is reported here.
Capillary electrophoresis with electrochemical detection has been employed for the separation and determination of the three active constituents (paeonol, benzoyloxypaeoniflorin, and oxypaeoniflorin) in traditional Chinese medicine, Moutan Cortex (root cortex of Paeonia suffruticosa Andrews). The effects of several important factors, such as the concentration of running buffer, the separation voltage, the injection time, and the detection potential, were investigated to determine the optimum conditions. The detection electrode was a 300 µm diameter carbon-disc electrode at a working potential of +0.90 V (versus SCE). The three analytes could be well separated within 7 min in a 40 cm length fused-silica capillary at a separation voltage of 12 kV in a 50 mM borate buffer (pH 9.2). The relation between the peak current and the analyte concentration was linear over 3 orders of magnitude with detection limits (S/N = 3) ranging from 0.4 to 0.7 µM for all analytes. The proposed method has been successfully applied to the determination of paeonol, benzoyloxypaeoniflorin, and oxypaeoniflorin in real plant samples with satisfactory assay results.
The performance of an open-tubular capillary column coated with a modified silica-gel thin layer was investigated, particularly concerning the effect of the silanization process on it. Although the increase in the octadecyltriethoxysilane (ODTES) concentration in the silanization process could enhance the retention factor of naphthalene, its theoretical plate number was significantly reduced (ODTES, 5 to 50%; k, 0.2 to 4.3; N, 79600 to 2600 m-1). Namely, the increase in the retention factor was accompanied by a decrease in the theoretical plate number. A similar phenomenon was also observed when octadecyldimethylchlorosilane (ODCS) was used as the silanization regent. However, increases in both the retention factor and the theoretical plate number could be achieved (sample, naphthalene; k, 0.05 to 0.09; N, 149000 to 220000 m-1) by a NaOH treatment to the fabricated thin porous silica-gel layer before silanization with ODCS. The electrochromatographic separation of proteins and peptides by using the NaOH-treated column could obtain more peaks than electrophoretic separation.
In order to evaluate the extraction property of new extractants, diglycolamide (DGA) compounds, we investigated the maximum extraction of di-, tri-, and tetravalent metal ions using nitric acid and n-dodecane. The limits of metal concentration (LOC) for Ca(II), Nd(III) and Zr(IV) in the organic phase are strongly influenced by HNO3 and the extractant concentration. For the purpose of enhancing the LOC value, we employed a modifier of the solvent, N,N-dihexyl-octanamide (DHOA) and DGA with a long alkyl chain, and examined the results. It was evident that LOC increased with the DHOA concentration and the length of the alkyl chain attached to the N atom of DGA. The stoichiometric values of LOC(Zr) estimated from the extraction reaction were confirmed by using the extraction condition: tetraoctyl-DGA/1 M DHOA + n-dodecane and 3 M HNO3.
An analytical method of on-line high performance liquid chromatography (HLPC) was developed to simultaneously separate and identify the monosaccharide composition of three Angelica polysaccharide fractions (APF), named APF1, APF2 and APF3. In this method, APF were hydrolyzed into component monosaccharides and subsequently labeled with 1-phenyl-3-methyl-5-pyrazolone (PMP), and then the labeled monosaccharide derivatives were separated by a reverse-phase C18 column and monitored by UV absorbance at 250 nm. The results showed that nine monosaccharide derivatives have been well separated by HPLC under optimized conditions and the composition analysis of monosaccharides from APF samples could be achieved using acid hydrolysis and a set of monosaccharide standards. With this method, the within-day and day to day precisions of the composition determinations were 3.41 - 4.87% and 3.12 - 4.93% (RSD), respectively. The method was successfully applied to the determination of the component monosaccharides of Angelica polysaccharides.
Sediments as a tool for monitoring contamination by heavy metals in the environment has long been considered. It is therefore a necessity to produce reliable data for such purposes. Microwave-assisted acid dissolution has proved to be a suitable method for digesting complex matrices, such as sediments. However, due to the infancy of the technique, the procedures are numerous and varied in both the reagents used and microwave conditions. In this study, the efficiency of two recommended acid mixtures, a HNO3-HF mixture and an aqua regia-HF mixture, under the same microwave digestion conditions were compared using certified reference materials. It was observed that the HNO3-HF mixture showed better efficiency than the aqua regia-HF mixture in most of the heavy metals analyzed in all certified reference materials used.
A new chelating resin, silica gel loaded with 1-phenyl-3-methyl-4-benzoylpyrazol-5-one (PMBP), was prepared and used for the preconcentration of trace amounts of rare earth elements (REEs) in water samples prior to their determination by inductively coupled plasma atomic emission spectrometry (ICP-AES). REEs (La, Eu, Yb and Y) were quantitatively retained on the column packed with modified silica gel in the pH range 5 - 8 and separated from the matrix, and then recovered by eluting with 2.0 mol L-1 HNO3. The adsorption capacity of modified silica gel for La, Eu, Yb and Y was 0.208, 0.249, 0.239 and 0.224 mmol g-1, respectively. The method has been successfully applied for the determination of La, Eu, Yb and Y in geological and environmental samples with satisfactory results.
A simple spectrophotometric system, based on a prolonged pseudo-liquid drop device as an optical cell and a handheld charge coupled device (CCD) as a detector, was constructed for automatic liquid-liquid extraction and spectrophotometric speciation of trace Cr(VI) and Cr(III) in water samples. A tungsten halogen lamp was used as the light source, and a laboratory-constructed T-tube with two open ends was used to form the prolonged pseudo-liquid drop inside the tube. In the medium of perchloric acid solution, Cr(VI) reacted with 1,5-diphenylcarbazide (DPC); the formed complex was automatically extracted into n-pentanol, with a preconcentration ratio of about 5. The organic phase with extracted chromium complex was then pumped through the optical cell for absorbance measurement at 548 nm. Under optimal conditions, the calibration curve was linear in the range of 7.5 - 350 µg L-1, with a correlation coefficient of 0.9993. The limit of detection (3 σ) was 7.5 µg L-1. That Cr(III) species cannot react with DPC, but can be oxidized to Cr(VI) prior to determination, is the basis of the speciation analysis. The proposed speciation analysis was sensitive, yet simple, labor-effective, and cost-effective. It has been preliminarily applied for the speciation of Cr(VI) and Cr(III) in spiked river and tap water samples. It can also be used for other automatic liquid-liquid extraction-spectrophotometric determinations.
We have developed an on-line sensing method for the detection of volatile organic compounds (VOCs) in contaminated aqueous solutions by combining a microporous hollow fiber membrane with an infrared (IR) sensing system. Polypropylene microporous hollow fibers were used to separate the VOCs from the aqueous solution into the hollow fibers, which were purged countercurrently for detection by the IR sensing systems. An evanescent-wave-type IR sensing system was used to detect the VOCs that were purged from the hollow fibers. The sensing element was coated with polyisobutylene (PIB) to concentrate the VOCs for their detection. To study the performance of this system, we examined a number of factors, such as the purging flow rate, the sample flow rate, and the volatilities of the VOCs. The results indicate that an increase in the purging flow rate reduces the analytical signal significantly, especially for purging flow rates >2 mL/min. The pumping flow rate for the aqueous sample also influenced the analytical signals, but far less sensitively. The volatilities of the examined compounds also affected the analytical signals: the higher the volatility of the compound, the lower the intensity of the analytical signals and the shorter the time required to reach the equilibrium signal. From an examination of the dynamic range of this proposed method, a regression coefficient >0.994 was obtained for concentrations below 250 mg/L, even under non-equilibrium conditions. The response time of the system was studied in an effort to examine the suitability of using this sensing method for automatic detection. The results indicate that new equilibrium conditions were established within 3 min for highly volatile compounds, which suggests that on-line monitoring of the levels of VOCs can be performed in the field.
A method capable of determining 13 PAHs (acenaphthene, anthracene, benzo[a]anthracene, benzo[a]pyrene, benzo[b]fluoranthene, benzo[k]fluoranthene, chrysene, dibenzo[ah]anthracene, fluoranthene, fluorene, indene[1,2,3-cd]pyrene, phenanthrene and pyrene) in a mixture of 16 EPA PAHs by second derivative synchronous spectrofluorometry in the constant wavelength mode was developed. It has not been possible to determine the following PAHs in the mixture: acenaphthylene, benzo[ghi]perylene and naphthalene. The approach studied allows the sensitive, rapid and inexpensive identification and quantitation of 13 PAHs in a solution of hexane. The detection limits are <1 µg L-1 (except for chrysene and phenanthrene).
A new spectrofluorometric method was developed for the determination of trace amounts of heparin (Hep). Using ciprofloxacin (CIP)-terbium (Tb3+) as a fluorescent probe, in a buffer solution of pH 7.20, Hep can remarkably enhance the fluorescence intensity of the CIP-Tb3+ complex at λ = 545 nm; also, the enhanced fluorescence intensity the Tb3+ ion is proportional to the concentration of Hep. The optimum conditions for the determination of Hep were also investigated. The dynamic range for the determination of Hep is 0.1 - 1.2 µg ml-1 with a detection limit of 6.89 ng ml-1. This method is simple, practical and relatively free of interference from coexisting substances, and can be successfully applied to assess Hep in biological samples. By the Rosenthanl graphic method, the association constant and binding numbers of heparin with the probe are 2.44 × 105 l mol-1 and 19.7. Moreover, the enhancement mechanisms of the fluorescence intensity in the CIP-Tb3+ system and the CIP-Tb3+-Hep system have also been considered.
This study reports a sensitive kinetic spectrophotometric method for the determination of trace amounts of thiocyanate. In acidic solution, Methylene Blue (MB) is oxidized by bromate to form a colorless compound. The reaction is accelerated by trace amounts of thiocyanate and can be followed by measuring the absorbance at 664 nm. The absorbance of the reaction decreased with an increase in the reaction time. Under the optimum experimental conditions (0.56 M of sulfuric acid, 3.9 × 10-5 M of MB, 3.0 × 10-3 M of bromate, 180 s, 25°C), thiocyanate can be determined in the range 5.0 - 180 ng/ml. The relative standard deviations (n = 8) are 2.81 and 1.43% for 10.0 and 150 ng/ml thiocyanate, respectively. The detection limit of this method is (3 σ) 3.8 ng/ml. This method was successfully applied to the determination of thiocyanate in real samples.
A novel herbicide biosensor with a thylakoid modified membrane electrode is presented. Thylakoid, isolated from spinach leaves, was entrapped in a membrane of poly (vinylalcohol) with the styrylpyridinium group (PVA-SbQ). The thylakoid membrane was fixed on the surface of a platinum electrode. It was found that the enzymes in thylakoid kept their activity for several months in the membrane. The oxidative current of hydrogen peroxide in a Tris-HCl buffer solution (pH 7.4) was detected at the modified electrode by a differential pulse voltammetric method. In the presence of herbicides, the oxidation current from the hydrogen peroxide decreased due to an inhibitor effect on the enzymes in thylakoid compared with that in the absence of the herbicides. The changes in the oxidation current at the electrode were proportional to the herbicide concentrations. The sensor could be used to detect herbicides in concentration ranges of 3 × 10-9 - 1.5 × 10-7 M for paraquat, 1 × 10-8 - 3 × 10-7 M for diuron, 4 × 10-8 - 3 × 10-6 M for prometryn, 5 × 10-8 - 5 × 10-6 M for atrazine and 1 × 10-7 - 5 × 10-6 M for ametryn, respectively. The enzyme activity on scavenging hydrogen peroxide in the modified PVA-SbQ membrane was examined.
The electrochemical behavior of 6-benzyl adenine (6-BA) has been studied in 0.1 mol L-1 HAc-NaAc solution (pH 3.8). Cyclic voltammetry, single-sweep polarography and direct current polarography were employed to clarify the mechanism of the electrode process; the kinetic parameters of the rate-determining step were determined. Reduction of 6-BA involves two pH-dependent processes, corresponding to the overall irreversible reduction of the 1,6 and 3,2 N=C bonds. Each reduction stage consists a preprotonation of the nitrogen atom at the electroactive site and a rapid two-electron transfer. In the presence of 6-BA, the reduction potentials of some ions were shifted. Under the given conditions, 6-BA displays one irreversible reduction peak controlled by adsorption. Two linear response were observed in the range 2.0 × 10-8 - 8.0 × 10-7 mol L-1 and the range 1.0 × 10-6 - 8.0 × 10-6 mol L-1, with correlation coefficients of 0.9995 and 0.9998, respectively. The detection limit is 7.1 × 10-9 mol L-1. The method had been applied to the determination of 6-BA in bean sprout samples with satisfactory results.
The adsorption of cobalt nanoparticles on a carbon microfiber surface has been electrochemicaly detected. The redox processes observed in an electrochemical cell filled with redistilled water and equipped with the carbon fiber microelectrode modified by cobalt nanoparticles have been compared to those observed in an aqueous solution of Co2+ cations. The movement of the adsorbed nanoparticles has been demonstrated by the feedback capacitance-potential method.
Photo-modulation voltammetry was applied to detecting the photolysis of tetraphenylborate (TPhB-) at a water/1,2-dichloroethane (DCE) interface by using a He-Cd laser emitting a beam with a major 325-nm line and minor lines of shorter wavelengths. When the interface was irradiated from the water-phase side, a new wave appeared in the photo-modulation voltammogram, suggesting that TPhB- was photolyzed and the anionic product was transferred across the interface. The concentration dependence of the photocurrents was successfully explained by a theory based on the photolytic process at the interface.
A simple and sensitive spectrophotometric method for the determination of human serum albumin (HSA) was established based on the ternary complex-formation reaction of HSA with o-sulfophenylfluorone (SPF) as a xanthene dye and metal ion (niobium(V) and bismuth(III)) in the presence of a dispersion agent. This new method enabled the determination of HSA in the range of 1 - 15 µg/ml HSA by measuring the difference of the absorbance at 530 nm between HSA-SPF-metal ion and SPF-metal ion solutions. In the determination of HSA, this method is about 2-times more sensitive than the Pyrogallol Red-molybdenum(VI) method (PR method), which accounts for more than 80% of the quantification methods for urinary protein assays in Japan. There was no significant difference between the results obtained by the present method and the PR method for human urine samples. The binding process between the SPF-metal complex and HSA was studied by determining the binding parameters and the thermodynamic parameters.
A determination method for steroid 5 α-reductase activity using liquid chromatography/atmospheric pressure chemical ionization-mass spectrometry (LC/APCI-MS) in the positive-ion mode has been developed. The rat prostatic enzyme source was used and the enzymatically formed 5 α-dihydrotestosterone and 5 α-androstane-3 α,17 β-diol were determined by LC/APCI-MS using absolute calibration curve method. The sum of the formed products was used as a measurement of the enzyme activity. This method was applied to kinetic study of this enzyme and inhibitory experiments using Finasteride® as a model inhibitor.
A complex of 1,6-anhydro-β-maltose with rubidium and that of 1,6-anhydro-β-D-glucopyranose with rubidium were characterized using 87Rb NMR spectroscopy, diffusion-ordered NMR spectroscopy (DOSY) and electrospray ionization mass spectrometry (ESI-MS). Although subtle differences were observed in the 1H chemical shifts of 1,6-anhydro-β-maltose in between the presence and absence of rubidium in deuterium oxide, measurements of the spin-lattice relaxation time (T1) of the 87Rb nucleus, the diffusion coefficients of 1,6-anhydro-β-maltose using 1H DOSY and ESI-MS indicated the complex formation of 1,6-anhydro-β-maltose with rubidium. The complex formation with rubidium was also identified for 1,6-anhydro-β-D-glucopyranose using NMR and ESI-MS techniques.
Cyclic voltammetry and differential pulse voltammetry were used to explore the adsorption behavior of three antibacterial agents at a carbon paste electrode. The drugs were accumulated on a carbon paste electrode, and a well-defined oxidation peak was obtained in acetate buffer (pH 5.0). The adsorptive stripping response was evaluated as a function of some variables such as the scan rate, pH and accumulation time. A simple, precise, inexpensive and sensitive voltammetric method has been developed for the determination of the cited drugs (Lomefloxacin (LFX), Sparfloxacin hydrochloride (SFX), and Gatifloxacin (GFX)). A linear calibration was obtained from 2 × 10-7 M to 4 × 10-5 M for LFX, 2 × 10-7 M to 6 × 10-5 M for SFX, and GFX. The limits of detection (LOD) were 4.2 × 10-7, 7 × 10-7 and 6.6 × 10-7 M, while the limits of quantification (LOQ) were 1.4 × 10-6, 2.3 × 10-6 and 2.2 × 10-6 M for LFX, SFX, and GFX, respectively. The R. S. D. of five measurements at the 1 × 10-6 M level were 0.4, 0.5 and 0.3 for LFX, SFX and GFX, respectively. The method was applied to the determination of LFX, SFX and GFX in dilute urine samples and dosage forms, and compared with the HPLC method.