Bis-dimethylaminobenzaldehyde Schiff-base cobalt(II) complex as a neutral carrier for a highly selective iodide electrode.

A new solvent polymeric membrane electrode based on N,N'-bis-(dimethylaminobenzaldehyde)-glycine cobalt(II) [Co(II)-BDMABG] as a neutral carrier is described, which displays a preferential potentiometric response to iodide ion and an anti-Hofmeister selectivity sequence in the following order: I- > ClO4- > Sal- > SCN- > NO2- > Br- > NO3- > Cl- > SO3(2-) > SO4(2-). The electrode exhibits a near-Nernstian potential linear range of 9.0 x 10(-7)-1.0 x 10(-1) M with a detection limit of 6.8 x 10(-7) M and a slope of -53.0 mV/decade in pH 2.0 of a phosphate buffer solution at 20 degrees C. The response mechanism is discussed in view of the A.C. impedance technique and the UV spectroscopy technique. The electrode was successfully applied to the determination of iodide in Jialing River and Spring in Jinyun Mountains with satisfactory results.     

Electrochemical adsorptive behavior of some fluoroquinolones at carbon paste electrode.

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 x 10(-7) M to 4 x 10(-5) M for LFX, 2 x 10(-7) M to 6 x 10(-5) M for SFX, and GFX. The limits of detection (LOD) were 4.2 x 10(-7), 7 x 10(-7) and 6.6 x 10(-7) M, while the limits of quantification (LOQ) were 1.4 x 10(-6), 2.3 x 10(-6) and 2.2 x 10(-6) M for LFX, SFX, and GFX, respectively. The R. S. D. of five measurements at the 1 x 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.     

Simultaneous determination of ethamsylate, tramadol and lidocaine in human urine by capillary electrophoresis with electrochemiluminescence detection

Ethamsylate, tramadol and lidocaine, partly excreted by the kidney, are generally used as hemostatic, analgesic and local anesthetic in surgery. We developed a simple and sensitive method for their simultaneous monitoring in human urine based on CE coupled with electrochemiluminescence detection by end-column mode. Under optimized conditions the proposed method yielded linear ranges from 5.0 x 10(-8) to 5.0 x 10(-5), 1.0 x 10(-7) to 1.0 x 10(-4) and 1.0 x 10(-7) to 1.0 x 10(-4) M with LODs of 8.0 x 10(-9) M (36 amol), 1.6 x 10(-8) M (72 amol) and 1.0 x 10(-8) M (45 amol) (S/N = 3) for ethamsylate, tramadol and lidocaine, respectively. The RSD for their simultaneous detection at 1.0 x 10(-6) M was 2.1, 2.8 and 3.2% (n = 7), respectively. For practical application an extraction step with ethyl acetate at pH 11 was performed to eliminate the influence of the sample ionic strength. The recoveries of ethamsylate, tramadol and lidocaine at different levels in human urine were between 87 and 95%. This method was used for simultaneous detection of ethamsylate, tramadol and lidocaine in clinic urine samples from two medicated patients. It was valuable in clinical and biochemical laboratories for monitoring these drugs for various purposes.     

Voltammetric detection of sulfonamides at a poly(3-methylthiophene) electrode

Detection of sulfonamide compounds in a mixture of standards at a poly(3-methylthiophene) coated on glassy carbon (GC) electrode is reported. The polymer, poly(3-methylthiophene), was electrochemically synthesized at a GC rotating disk-working electrode versus Ag/AgCl using cyclic voltammetry (+0.5 to +2.0 V). Square wave voltammetry (SQWV) with cathodic reduction (0 to -4.0 V) was used for the detection of seven sulfonamide compounds in a mixture. The working concentration ranges (curvilinear) established for different compounds in Britton-Robinson (BR) buffer (pH 6.26), were: 5.0x10(-6)-3.2x10(-3) M sulfamerazine, 5.0x10(-6)-3.2x10(-3) M sulfadiazine, 7.5x10(-7)-3.2x10(-4) M sulfasalazine, 9.0x10(-7)-5.0x10(-4) M sulfamethazine, 6.5x10(-8)-3.5.0x10(-5) M sulfamethoxazole, 9.7x10(-8)-5.0x10(-5) M sulfathiazole, and 9.0x10(-8)-3.2x10(-5) M 5-sulfaminouracil. Detection limits were calculated as: 3.9x10(-6) M for sulfamerazine; 4.0x10(-6) M sulfadiazine; 2.5x10(-7) M sulfasalazine; 3.7x10(-7) M sulfamethazine; 4.0x10(-8) M sulfamethoxazole; 6.4x10(-8) M sulfathiazole and 6.0x10(-9) M 5-sulfaminouracil. The data suggests a potential application of the poly(3-methylthiophene) (P3MT) electrode for determination of sulfonamides in veterinary and other applications.     

Catalytic effect of some inorganic ligands on a ligand substitution reaction involving mercury(II) and its application as a differential kinetic method of analysis

To design a sensitive and selective kinetic method for determining a catalyst, the kinetics of the ligand substitution reaction between the mercury(II)-4-(2-pyridylazo)resorcinol complex and 1,2-cyclohexanediamine-N,N,N',N'-tetraacetic acid together with the catalytic effect of some inorganic ligands on this reaction were studied. The rate constant for a catalyzed reaction path was found to be linearly correlated with the electron donor constant of the catalyst. From this correlation, the difference in reactivity between sulfite or thiosulfate and sulfate was established. Under the selected conditions, sulfite up to 1.5 x 10(-6) M and thiosulfate up to 7 x 10(-7) M could be determined with detection limits of 3 x 10(-8) and 2 x 10(-8) M in the presence of 10 000 and 25 000-fold molar amounts of sulfate, respectively. The tolerance level in the determination of 1 x 10(-6) M of sulfite and 4 x 10(-7) M of thiosulfate was studied for 15 inorganic anions and 44 metal ions.     

Differential pulse adsorptive stripping voltammetric determination of dinoseb and dinoterb at a modified electrode.

A sensitive adsorptive stripping voltammetric method for the determination of dinitrophenolic herbicides, dinoseb (DSB) and dinoterb (DTB) at a bare carbon paste electrode (CPE) and a clay modified carbon paste electrode (CMCPE) was developed. A systematic study of various experimental conditions, such as the pH, accumulation variables and composition of a modifier on the adsorptive stripping response, were examined by using differential pulse voltammetry. A significant improvement was observed in the sensitivity by using the present method with CMCPE. When CMCPE was used, a linear response was obtained over the concentration range 2 x 10(-10) to 3 x 10(-7) M and 6 x 10(-10) to 6 x 10(-7) M with lower detection limits of 1 x 10(-10) M and 5.4 x 10(-10) M for dinoseb and dinoterb, respectively, at an accumulation time of 100 s. The interference from other herbicides and ions on the stripping signals of both compounds was also evaluated. The described method was applied to estimate of the dinoseb and dinoterb in environmental samples.     

Catalysis of the beta-elimination of HF from isomeric 2-fluoroethylpyridines and 1-methyl-2-fluoroethylpyridinium salts. Proton-activating factors and methyl-activating factors as a mechanistic test to distinguish between concerted E2 and E1cb irreversible mechanisms

Second-order rate constants, k(OH)(N), M(-)(1) s(-)(1), for the beta-elimination reactions of HF with 2-(2-fluoroethyl)pyridine (2), 3-(2-fluoroethyl)pyridine (3), and 4-(2-fluoroethyl)pyridine (4) in OH(-)/H(2)O, at 50 degrees C and mu = 1 M KCl, are = 0.646 x 10(-)(4) M(-)(1) s(-)(1), = 2.97 x 10(-)(6) M(-)(1) s(-)(1), and = 5.28 x 10(-)(4) M(-)(1) s(-)(1), respectively. When compared with the second-order rate constants for the same processes with the nitrogen-methylated substrates 1-methyl-2-(2-fluoroethyl)pyridinium iodide (5), 1-methyl-3-(2-fluoroethyl)pyridinium iodide (6), and 1-methyl-4-(2-fluoroethyl)pyridinium iodide (7), the methyl-activating factor (MethylAF) can be calculated from the ratio k(OH)(NCH)3/, and a value of 8.7 x 10(5) is obtained with substrates 5/2, a value of 1.6 x 10(3) with 6/3, and a value of 2.1 x 10(4) with 7/4. The high values of MethylAF are in agreement with an irreversible E1cb mechanism (A(N)D(E) + D(N)) for substrates 5 and 7 and with the high stability of the intermediate carbanion related to its enamine-type structure. In acetohydroxamate/acetohydroxamic acid buffers (pH 8.45-9.42) and acetate/acetic acid buffers (pH 4.13-5.13), the beta-elimination reactions of HF, with substrates 2 and 4, occur at NH(+), the substrates protonated at the nitrogen atom of the pyridine ring, even when the [NH(+)] is much lower than the [N], the unprotonated substrate, due to the high proton-activating factor (PAF) value observed: 3.6 x 10(5) for 2 and 6.5 x 10(4) for 4 with acetohydroxamate base. These high PAF values are indicative of an irreversible E1cb mechanism rather than a concerted E2 (A(N)D(E)D(N)) mechanism. Finally, the rate constant for carbanion formation from NH(+) with 2 is k(B)(NH)+ = 0.35 M(-)(1) s(-)(1), which is lower than when chlorine is the leaving group ( = 1.05 M(-)(1) s(-)(1); Alunni, S.; Busti, A. J. Chem. Soc., Perkin Trans. 2 2001, 778). This is direct experimental evidence that some lengthening of the carbon-leaving group bond can occur in the intermediate carbanion. This is a point of interest for interpreting a heavy-atom isotope effect.     

Falloff curves for the Reaction CH3 + O2 (+ M) --> CH3O2 (+ M) in the pressure range 2-1000 bar and the temperature range 300-700 K

The reaction CH(3) + O(2) (+M) --> CH(3)O(2) (+M) was studied in the bath gases Ar and N(2) in a high-temperature/high-pressure flow cell at pressures ranging from 2 to 1000 bar and at temperatures between 300 and 700 K. Methyl radicals were generated by laser flash photolysis of azomethane or acetone. Methylperoxy radicals were monitored by UV absorption at 240 nm. The falloff curves of the rate constants are represented by the simplified expression k/k(infinity) approximately [x/(1 + x)]F(cent)(1/{1+[(log)(x)/)(N)(]2}) with x = k(0)/k(infinity) F(cent) approximately 0.33, and N approximately 1.47, where k(0) and k(infinity) denote the limiting low and high-pressure rate constants, respectively. At low temperatures, 300-400 K, and pressures >300 bar, a fairly abrupt increase of the rate constants beyond the values given by the falloff expressions was observed. This effect is attributed to a contribution from the radical complex mechanism as was also observed in other recombination reactions of larger radicals. Equal limiting low-pressure rate constants k(0) = [M]7 x 10(-31)(T/300 K)(-3.0) cm(6) molecule(-2) s(-1) were fitted for M = Ar and N(2) whereas limiting high-pressure rate constants k(infinity) = 2.2 x 10(-12)(T/300 K)(0.9) cm(3) molecule(-1) s(-1) were approached. These values are discussed in terms of unimolecular rate theory. It is concluded that a theoretical interpretation of the derived rate constants has to be postponed until better information of the potential energy surface is available. Preliminary theoretical evaluation suggests that there is an "anisotropy bottleneck" in the otherwise barrierless interaction potential between CH(3) and O(2).     

Sulfate-selective electrode based on a complex of copper.

A new sulfate-selective electrode based on the complex N,N'-bis(2-amino-1-oxo-phenelenyl)phenylenediamine copper(II) (CuL) as the membrane carrier was developed. The electrode exhibited a good Nernstian slope of -29.5 +/- 0.5 mV/decade and a linear range of 1.0 x 10(-7) - 1.0 x 10(-1) M for sulfate. The limit of detection was 1.0 x 10(-8) M. It has a fast response time of 10 s and can be used for more than three months. The selective coefficients were determined by the fixed interference method (FIM). The electrode could be used in the pH range 3.5 - 8.0. It was employed as an indicator electrode for direct determination of sulfate in pharmacy and cement samples.     

Simultaneous determination of Cl(-), Br(-), I(-) and F(-) with flow-injection/ion-selective electrode systems

Flow-through ion-selective electrodes were constructed from compressed pellets (8-10 mm thick, 13 mm diameter, 10 tons/cm(2) pressure) of Ag(2)S/AgX (X = Cl(-), Br(-) or I(-)) drilled longitudinally (1.5 mm diameter hole) to be suitable for use in flow-injection analysis. A column of AgCl (5.5 cm long, 2-3 mm i.d.) was included in the Cl(-)-electrode manifold to remove interferences from 10(-4)M Br(-) and 3 x 10(-5)M I(-) and S(2-). A column of amalgamated lead (2-3 cm long, 2-3 mm i.d.) was used in the Br(-) electrode manifold to remove interference from 2 x 10(-5)M I(-), 3 x 10(-5)M S(2-) and 7 x 10(-4)M Cl(-). These columns and the addition of ascorbic acid were not required when I(-) was determined with the iodide electrode. The carrier stream was 0.1M sodium perchlorate (pH 4) at a flow-rate of 0.5 ml/min. The sample pH could be 4-7. Simultaneous determination of Cl(-) and I(-), Cl(-), I(-) and Br(-) and Cl(-), I(-), Br(-) and F(-) ions was possible with combinations of the corresponding electrodes and columns in series and/or parallel in specially designed manifolds. Calibration plots were linear, with almost theoretical slopes, down to 10(-6)M I(-), 5 x 10(-6)M Br(-), 10(-4)M Cl(-) and 5 x 10(-6)M F(-), with precision better than 1%. Sampling rates for single-ion determinations were 72, 102, 90 and 80 per hr for the one-, two-, three- and four-electrode systems respectively. Determinations of these ions in water samples by the recommended procedure and by established batch methods showed no significant difference at the 95% confidence limits in a paired comparison t-test.     

Carbazole as fluorescence carrier for preparation of doxycycline sensor.

Carbazole is a promising pharmaceutical species. A novel optical sensor for determining doxycycline based on the fluorescence quenching of N-allylcarbazole immobilized on an quartz glass plate surface by covalent bonding has been described. The sensor shows satisfactory virtues in reversibility, repeatability, selectivity and sufficient lifetime resulting from its excellent optode membrane. Its response time is less than 60 s. The determination range and detection limit of the sensor are 6.0 x 10(-7)-2.0 x 10(-3) M and 2.0 x 10(-7) M, respectively. The lifetime of each sensor is at least three to four months. The sensor can be used for direct determination of doxycycline in pharmaceutical preparations and urine samples.     

用分子子图对烷烃摩尔响应值的估计与预测

提出了一种新的烷烃拓扑子图表示方法,并结合多元线性回归算法和反传神经网络算法,对烷烃摩尔响应值进行处理,获得了比文献更佳的预测效果,交互校验的相关系数ｒ＝０．９８９。     

Capillary electrophoresis with inductively coupled plasma-mass spectrometric and electrospray time of flight mass spectrometric detection for the determination of arsenic species in fish samples

CE was coupled to inductively coupled plasma MS (ICP-MS) and ESI-MS to identify and quantify the arsenic species arsenobetaine (AsB), arsenite (As(III)), arsenate (As(V)), and dimethylarsinic acid (DMA). A GC-flame ionization detector (FID)-based German standard method and ICP-MS were used for validation of the data obtained for arsenobetaine and total arsenic, respectively. LODs obtained with the CE-ESI-TOF-MS method were 1.0x10(-7) M for AsB, 5.0x10(-7) M for DMA, and 1.0x10(-6) M for As(III) and As(V). For the CE-ICP-MS method, LODs were 8.5x10(-8) M for AsB, 9.5x10(-8) M for DMA, 9.3x10(-8) M for As(III), and 6.2x10(-8) M for As(V). While CE-ICP-MS provided high sensitivity and better reproducibility for quantitative measurements, CE-ESI-MS with a TOF mass analyzer proved to be valuable for species identification. With this setup, fish samples were prepared and analyzed and the obtained data were successfully validated with the independent methods.     

Synthesis of a heptacontapeptide corresponding to the entire amino acid sequence of eglin C

A heptacontapeptide corresponding to the entire amino acid sequence of eglin c was synthesized by the conventional solution method using a minimal protecting method. The synthetic eglin c exhibited a symmetrical single peak on HPLC at the same retention time as an authentic eglin c, and had the same inhibitory activity against human leukocyte elastase, cathepsin G and alpha-chymotrypsin (Ki = 6.0 x 10(-9) M, 5.5 x 10(-9) M and 2.5 x 10(-9) M, respectively) as N alpha-acetyl-eglin c synthesized genetically (Ki = 5.1 x 10(-9) M, 1.5 x 10(-8) M and 2.2 x 10(-9) M, respectively).     

Determination of arsenate by sorption pre-concentration on polystyrene beads packed in a microfluidic device with chemiluminescence detection

A highly sensitive chemiluminescence (CL) method for the determination of arsenate in water based on a simple microfluidic device was developed. The method was based on sorption pre-concentration of arsenate as a form of vanadomolybdoarsenate heteropoly acid (VMoAs-HPA) ion-paired with hexadecyltrimethylammonium bromide on the surface of polystyrene beads packed in a microfluidic device monitored by chemiluminescence detection. The composition of the VMoAs-HPA complex was studied by varying the concentrations of ammonium molybdate, ammonium vanadate and sulfuric acid with a variable-size simplex optimization process, of which the optimum concentrations were 6.3 x 10(-5), 5.0 x 10(-6) and 1.0 x 10(-2) M, respectively. In this work, 1.0 x 10(-3) M ethylenediaminetetraacetic acid was added to all work solutions to remove the interferences of the other metal ions on the CL detection. The integration of sorption pre-concentration not only increased the detection sensitivity but also eliminated the interference from phosphate and chromate. The calibration plot was linear from 1.0 x 10(-7) to 5.0 x 10(-5) M As(v). The limit of detection was 8.9 x 10(-8) M As(v) (S/N = 3). The time required for one analysis run was as short as 5 min. The relative standard deviation was 5.9% (n = 9). This method was successfully applied to the determination of arsenate in mineral-, drinking- and tap-water samples.     

Generation of a peroxynitrato metal complex from nitrogen dioxide and coordinated superoxide

The reaction between photogenerated NO(2) radicals and a superoxochromium(III) complex, Cr(aq)OO(2+), occurs with rate constants k(Cr)(20) = (2.8 +/- 0.2) x 10(8) M(-)(1) s(-)(1) (20 vol % acetonitrile in water) and k(Cr)(40) = (2.6 +/- 0.5) x 10(8) M(-)(1) s(-)(1) (40 vol % acetonitrile) in aerated acidic solutions and ambient temperature. The product was deduced to be a peroxynitrato complex, Cr(aq)OONO(2)(2+), which undergoes homolytic cleavage of an N-O bond to return to the starting materials, the rate constants in the two solvent mixtures being k(H)(20) = 172 +/- 4 s(-)(1) and k(H)(40) = 197 +/- 7 s(-)(1). NO(2) reacts rapidly with 10-methyl-9,10-dihydroacridine, k(A)(20) = 2.2 x 10(7) M(-)(1) s(-)(1), k(A)(40) = (9.4 +/- 0.2) x 10(6) M(-)(1) s(-)(1), and with N,N,N',N'-tetramethylphenylenediamine, k(T)(40) = (1.84 +/- 0.03) x 10(8) M(-)(1) s(-)(1).     

Chemiluminescence determination of nitrate with photochemical activation in a flow injection system

A chemiluminescence flow injection system is described for the determination of nitrate, involving use of a laboratory-built flow-through photochemical reactor. Optimum analytical conditions were established. The linear range for nitrate is 7 x 10(-8)-1 x 10(-4)M. The sampling frequency is 60 samples per hour. The relative standard deviation for 1 x 10(-7), 1 x 10(-6) and 1 x 10(-5)M nitrate is 0.97, 0.84 and 0.76%, respectively. The method has been applied to the determination of nitrate in natural water samples, and recoveries of 96-103% have been attained.     

Highly selective iodide electrode based on the copper(II)-N,N'-bis(salicylidene)-1,2-bis(p-aminophenoxy)ethane tetradentate complex.

In this paper, a new PVC-based liquid-membrane anion-selective electrode based on a copper(II) of N,N'-bis(salicylidene)-1,2-bis(p-aminophenoxy)ethane tetradentate complex (Cu(II)BBAP) is described, which displays a preferential potentiometric response to iodide ion at pH 2.0 and an anti-Hofmeister selectivity sequence: I->SCN->ClO4->NO2->H2PO4->NO3->SO4(2-)>Br->Cl-. The electrode exhibits a near-Nernstian potential linear range of 8.2x10(-7)-1.0x10(-1) M with a detection limit of 5.3x10(-7) M and a slope of -58.8 mV per decade. The A.C. impedance technique and the UV/Vis spectroscopy technique were used to analyze the response mechanism. The electrode could be applied to determine iodide in medicine analysis, and the obtained results were fairly satisfactory.     

Enhanced spectrophotometric determination of nicotinic acid in a sodium dodecyl sulphate micellar medium

The spectrophotometric determination of pyridine and pyridine derivatives by means of the K?nig reaction was studied in micellar media of sodium dodecyl sulphate (SDS), N-cetylpyridinium chloride and Triton X-100. The sensitivity was largely increased in SDS micellar medium. The attack of the pyridine ring with cyanogen bromide to produce a glutaconic aldehyde was not affected by the presence of SDS, but the yield of the coupling reaction with an arylamine to produce a polymethine dye was largely increased. In the SDS micellar medium, aniline was superior to other coupling reagents. The limits of detection (LODs) were 6 x 10(-7), 1 x 10(-6) and 5 x 10(-7)M for pyridine, pyrrol-ylmethylpyridine and nicotinic acid, respectively, and the reproducibility for 2 x 10(-5)M solutions was ca. 2%. In the absence of SDS, the LODs were 3 x 10(-6), 3 x 10(-6) and 9 x 10(-6)M, respectively, and the reproducibility was ca. 3.5%. Application was made to the determination of nicotinic acid in pharmaceuticals.