Catalytic Thermometric Titrations of Various Mixtures of Nitrogen Bases

The reactions of acetylation of hydroquinone and quinhydrone with acetic anhydride, catalysed by perchloric acid, were used to determine the end point of catalytic thermometric titrations of a number of different amines and amides dissolved either in acetic anhydride or in acetic acid-acetic anhydride (10+1) mixture. In the majority of cases primary and secondary amines could be successfully determined if pKb_b≤9.3, tertiary amines if pK_b≤14, and amides if pK_b≤l5. Thanks to the difference in behaviour of organic bases in acety lation reaction, it was possible in some instances to determine selectively the individual bases in their mixtures. Catalytic titrations appeared to be especially suitable for the determination of extremely weak bases, even in the case of using mixtures of organic solvents, when Potentiometrie titrations could not be employed. Amounts of 2.5·10^?6-8·10^?5 mole of bases were determined with a maximal relative standard deviation less then 2%.     

Resolution and Trace Determination of Selected Oxyanions in Binary and Ternary Mixtures by Differential Pulse Polarography

Abstract

Resolution and trace determination of selected oxyanions in binary and ternary mixtures were studied by differential pulse polarography (DPP) at the dropping mercury electrode. The applicability of DPP for the simultaneous determination of the investigated oxyanions (TeO^{2- 4}, VO^? ₃, IO^? ₃, IO^? ₄, and BrO^? ₃) in the binary and ternary mixtures was also examined with regard to the dependence of the DP current on various parameters such as pH, pulse amplitude, scan rate and drop time. Statistical analysis is included on t h e observed concentrations for each of the oxyanions in the mixture and compared with that obtained by the calibration curves. Limits of detection and quantitat - ion have been calculated for the DPP determination of binary and ternary mixtures of these lected oxyanions.     

Spectrophotometric determination of aromatic primary amines and nitrite by flow injection analysis

Aromatic primary amines are determined by injection into dilute hydrochloric acid carrier which merges sequentially with 4-N-methylaminophenol and dichromate. The purple-red color formed by oxidative coupling of amines with 4-N-methylaminophenol is measured at 530 nm. In contrast to the manual procedure, the flow-injection procedure avoided errors arising from the instability of the coupling intermediate, oxidation of the amine, and too great an excess of the oxidant. The method improves the selectivity for certain amines in the presence of those which are sterically hindered or have an electron-deficient aromatic nucleus. Nitrite is determined by diazotization of sulfanilamide and quantifying the residual sulfanilamide by oxidative coupling. The sample thourghout for the assay of amines (0.05–20 μg ml^?1 NH₂-N) and nitrite (1–10 μg ml^?1 NO₂^--N) was 120 h^?1. A system for the consecutive determination of aromatic primary amines and nitrite is decribed.     

Simultaneous Voltammetric Determination of Benzene,Toluene and Xylenes (BTX) in Water Using a Cathodically Pre‐treated Boron‐doped Diamond Electrode

An electrochemical method for the simultaneous determination of benzene, toluene and xylenes (BTX) in water was developed using square‐wave voltammetry (SWV). The determination of BTX was carried out using a cathodically pre‐treated boron‐doped diamond electrode (BDD) using 0.1 mol L^?1 H₂SO₄ as supporting electrolyte. In the SWV measurements using the BDD, the oxidation peak potentials of the total xylenes‐toluene and toluene‐benzene couples, present in ternary mixtures, display separations of about 100 and 200 mV, respectively. The attained detection limits for the simultaneous determination of benzene, toluene and total xylenes were 3.0×10^?7, 8.0×10^?7 and 9.1×10^?7 mol L^?1, respectively. The recovery values taken in ternary mixtures of benzene, toluene and total xylenes in aqueous solutions are 98.9 %, 99.2 % and 99.4 %, respectively.     

Gas-chromatographic determination of aliphatic amines in natural surface water and wastewater

A procedure was developed for the gas-chromatographic determination of aliphatic amines C₇–C₂₀ with prederivatization by N-methyl-bis(trifluoroacetamide), in the concentration range of natural surface water, to 10^?4-1 mg/L, and wastewater, to 10^?3-1 mg/L. The conditions were optimized for the extraction preconcentration of aliphatic amines with toluene from natural surface water and wastewater. The detection limit for aliphatic amines at a signal-to-noise ratio of 3: 1 was 50 ng/L.     

Voltammetric Determination of Selected Aminoquinolines Using Carbon Paste Electrode

Optimum conditions have been found for voltammetric determination of mutagenic 5‐aminoquinoline, 6‐aminoquinoline and 3‐aminoquinoline by differential pulse voltammetry and adsorptive stripping differential pulse voltammetry on carbon paste electrode. The lowest limits of determination were found for adsorptive stripping differential pulse voltammetry in 0.1 mol dm^?3 H₃PO₄ (5×10^?7 mol dm^?3 , 1×10^?7 mol dm^?3, and 1×10^?7 mol dm^?3 for 5‐aminoquinoline, 6‐aminoquinoline and 3‐aminoquinoline, respectively). The possibility to determine mixtures of 8‐aminoquinoline with 3‐aminoquinoline or 5‐aminoquinoline or 6‐aminoquinoline, and mixtures of 5‐aminoquinoline with 3‐aminoquinoline or 6‐aminoquinoline by differential pulse voltammetry was verified. Binary mixtures of 8‐aminoquinoline with 3‐aminoquinoline or 6‐aminoquinoline, and of 3‐aminoquinoline with 5‐aminoquinoline could be successfully analyzed.     

Speciation Analysis of Osmium(VIII) and Osmium(IV) by UV‐VIS Spectrophotometry Using Quercetin as the Reagent

Abstract

The UV‐VIS spectrophotometric methods for the determination of Os(VIII) (as OsO₄) and Os(IV) (as OsCl₆ ^2? complex) in their mixtures were developed. Quercetin (Q), a flavonoid compound, was used as a chromogenic reagent. Both direct and derivative spectrophotometry can be employed for the determination of Os(VIII). The calculation of the first‐derivative spectrum of the examined mixture and the use of the signal at 285.1 nm allows reaching a better detection limit (0.01 µg mL^?1 Os) as compared with direct spectrophotometry (0.1 µg mL^?1 Os). Relative standard deviations of the results are in the range of 0.87%–4.65% and 0.45%–1.15% for direct and derivative mode, respectively. Selective redox reaction of OsO₄ with Q under the conditions used (0.05 M HCl, 1×10^?4 M Q, 15 min heating at 70°C) makes the basis of its determination in mixtures with the OsCl₆ ^2? complex. Quercetin does not react with the OsCl₆ ^2? complex. The signals of the OsCl₆ ^2? complex can be isolated from the examined mixtures by the calculation of the third‐order derivative spectra and the use of the values at 340.0 nm. The effectiveness of the reduction of OsO₄ in chloride solutions has been studied by the developed method.     

Application of H-Point standard addition method and multivariate calibration methods to the simultaneous kinetic-potentiometric determination of permanganate and dichromate

Simultaneous kinetic-potentiometric determination of binary mixture of permanganate (MnO₄ ^?) and dichromate (Cr₂O₇ ^2?) by H-point standard addition method (HPSAM), partial least squares (PLS) and principal component regression (PCR) is described. In this work, the difference between the rate of the oxidation reaction of Fe(II) to Fe(III) in the presence of MnO₄ ^? and Cr₂O₇ ^2? formed the basis of the method. The rate of the consumed fluoride ion for making the complex was detected by a fluoride ion selective electrode (FISE). The results show that the simultaneous determination of MnO₄ ^? and Cr₂O₇ ^2? could be conducted in their concentration ranges of 0.5?C10.0 and 0.1?C20.0 ??g ml^?1, respectively. The total relative standard error (RSE) for applying the PLS and PCR methods to 9 synthetic samples was 5.30 and 3.17, respectively in the concentration range of MnO₄ ^?, and 3.30 and 2.04, respectively, in the concentration range of Cr₂O₇ ^2?. In order for the selectivity of the method to be assessed, we evaluated the effects of certain foreign ions upon the reaction rate. The proposed methods (HPSAM, PLS and PCR) were evaluated using a set of synthetic sample mixtures and then applied to the simultaneous determination of MnO₄ ^? and Cr₂O₇ ^2? in different water samples.     

Spectral and kinetic evidence for attack at coordinated phenanthroline in the reaction between aliphatic amines and transition metal complexes of 5-nitro-1,10-phenanthroline

Various transition metal complexes of 5-nitro-1,10-phenanthroline react with aliphatic amines in dipolar aprotic solvents to give deeply coloured species. The spectral changes, which can be reversed upon addition of acid or of the appropriate protonated amine, do not depend either on the nature of the metal and the ancillary ligands or on the geometry of the complexes; this has been taken as evidence that the colour forming process is due to a specific interaction of aliphatic amines with coordinated phenanthroline. While the rate of reaction of [Pt(5-NO₂phen)Cl₂] and [Pd(5-NO₂phen)Cl₂] with Br^?, which is known to displace Cl^? in the substrates, depends strongly on the nature of the central atom, the second order rate constant at 25°C being 3.2 × 10^?4 dm³mol^?1s^?1 and 1.35 dm³mol^?1s^?1 for the platinum and the palladium derivative respectively, the rate of reaction with n-propylamine has a comparable value for both substrates. This is further evidence that amines attack the coordinated phenanthroline, rather than the central atom. On the basis of the spectral features and the reaction stoicheiometry, the adducts of metal complexes of 5-NO₂phen and aliphatic amines are presumably Meisenheimer-like complexes.     

CURING AND RHEOLOGICAL BEHAVIOR OF VINYL ESTER RESINS PREPARED IN THE PRESENCE OF TERTIARY AMINES

Vinyl ester resins V₁, V₂ & V₃ of acid value (～6 mg KOH g^?1 solid) were synthesized using bisphenol-A epoxy and acrylic acid in the presence of triethyl-, tripropyl- and tributyl-, amines in 210, 270 and 340 minutes, respectively. The synthesized resins were characterized by FTIR spectroscopy and a new peak at 2360 cm^?1 was observed which is due to attachment of amines to resin structure by hydrogen bond. The curing behavior of synthesized resin containing 40% styrene (w/w) and 2% benzoyl peroxide was studied using DSC technique and found to be affected by presence of amines. Activation energy and frequency factor for the curing reaction increases from 14 Kcal mol^?1 to 23 Kcal mol^?1. Rheological behavior of resins containing 40% styrene was studied using a Haake Rotovisco RV20 viscometer, and viscosity was found to increase with shear rate up to 200 sec^?1. The average values of activation energy at constant shear stress (6-15 Pa) were 12.94, 13.20, 13.70 Kcal mol^?1 for V₁, V₂ and V₃, respectively. The activation energy at constant shear rate decreases with an increase in the shear rate.     

Selective extraction-photometric redox determination of low concentrations of sulfur(IV), selenium(IV), tellurium(IV), and arsenic(III)

A procedure is proposed for the selective extraction-photometric determination of the acid-forming elements S(IV), Se(IV), Te(IV), and As(III) in their mixtures containing molecular forms or anions with different electron densities on donor atoms. The procedure is based on the difference in the oxidizability of analytes with the [SbCl₆]^? complex. The analytical ranges are found at different pHs of the medium, affecting the potential of the two-phase redox systems. The detection limits for sulfite, selenite, tellurite, and arsenite are 1 × 10^?3, 5 × 10^?5, 7 × 10^?5, and 1 μg/mL, respectively. The procedure is applied to the determination of selenium in H₂SO₄ of high-purity grade, which is used in the production of microelectronics items and in some agricultural samples. The error of analysis is no worse than 20%.     

Analysis of Aromatic Amines in Surface Waters Receiving Wastewater from a Textile Industry by Liquid Chromatographic with Electrochemical Detection

Abstract

A high performance liquid chromatography (HPLC) method with electrochemical detection (ED) was developed for the determination of benzidine, 3,3‐dimethylbenzidine, o‐toluidine and 3,3‐dichlorobenzidine in the wastewater of the textile industry. The aromatic amines were eluted on a reversed phase column Shimadzu Shimpack C₁₈ using acetonitrile+ammonium acetate (1×10^?4 mol L^?1) at a ratio 46:54 v/v as mobile phase, pumped at a flow rate of 1.0 mL min^?1. The electrochemical oxidation of the aromatic amines exhibits well‐defined peaks at a potential range of +0.45 to +0.78 V on a glassy carbon electrode. Optimum working potentials for amperometric detection were from 0.70 V to +1.0 V vs. Ag/AgCl. Analytical curves for all the aromatic amines studied using the best experimental conditions present linear relationship from 1×10^?8 mol L^?1 to 1.5×10^?5 mol L^?1, r=0.99965, n=15. Detection limits of 4.5 nM (benzidine), 1.94 nM (o‐toluidine), 7.69 nM (3,3‐dimethylbenzidine), and 5.15 nM (3,3‐dichlorobenzidine) were achieved, respectively. The detection limits were around 10 times lower than that verified for HPLC with ultra violet detection. The applicability of the method was demonstrated by the determination of benzidine in wastewater from the textile industry dealing with an azo dye processing plant.     

Processing of signals from an ion-elective electrode array by a neural network

Neural network software is described for processing the signals of arrays of ion-selective electrodes. The performance of the software was tested in the simultaneous determination of calcium and copper(II) ions in binary mixtures of copper(II) nitrate and calcium chloride and the simultaneous determination of potassium, calcium, nitrate and chloride in mixtures of potassium and calcium chlorides and ammonium nitrate. The measurements for the Ca²⁺/Cu²⁺ determinations were done with a pH-glass electrode and calcium and copper ion-selective electrodes; results were accurate to ±8%. For the K⁺/Ca²⁺NO^?₃/Cl^? determinations, the measurements were made with the relevant ion-selective electrodes and a glass electrode; the mean relative error was ±6%, and for the worst cases the error did not exceed 20%.     

Proton-transfer effect in hydrogen-bonded complexes of phospho-diester groups with amines in non-aqueous solvents

The proton transfer in 1 : 1 mixtures of phosphoric acid-di-n-butylester with various aromatic amines has been studied in deutero-chloroform and DMSO-d₆ by ¹H NMR spectroscopy. The 50% equilibrium was found for both solvents at ΔpK_a(50%)-values from 4.4 to 5.2, i.e. the strength of the base is 4.4 to 5.2 higher than that of the acid. The titration curves are steeper in DMSO than in chloroform, indicating a higher potential barrier in POH … N ? PO^? … H⁺N hydrogen bonds in the more polar solvent.     

Separation of Free Amiimo Acids on Reverse Stationary Phases Using an Alkyl Sulfonate Salt as a Mobile Phase Additive

Abstract

Alkylsulfonate (RSO₃ ^?) salts were evaluated as mobile phase additives for the separation of free amino acids on reverse stationary phases using an acidic mobile phase where the amino acids are cations. The enhanced amino acid retention is the result of two major interactions, one being retention of the RSO₃ ^? salt on the stationary phase and the other an ion exchange selectivity between the amino acid analyte cation and the RSO₃ ^? countercation, or other countercations in the mobile phase. Major mobile phase variables are: type and concentration of RSO₃ ^? salt (the studies focused on C₈SO₃ ^? salts), presence of organic modifier, type of countercation present, and mobile phase pH and ionic strength. Alkyl modified silica and polystyrenedivinyl-benzene copolymeric reverse stationary phases were compared. A mobile phase gradient, increasing per cent organic modifier was shown to be best, is necessary for separating complex mixtures of polar and nonpolar or basic amino acids. The procedure is applicable to the identification and/or determination of amino acids in mixtures or in peptides after hydrolysis.     

Exploiting the Brønsted Acidity of Phosphinecarboxamides for the Synthesis of New Phosphides and Phosphines

We demonstrate that the synthesis of new N‐functionalized phosphinecarboxamides is possible by reaction of primary and secondary amines with PCO^? in the presence of a proton source. These reactions proceed with varying degrees of success, and although primary amines generally afford the corresponding phosphinecarboxamides in good yields, secondary amines react more sluggishly and often give rise to significant decomposition of the 2‐phosphaethynolate precursor. Of the new N‐derivatized phosphinecarboxamides available, PH₂C(O)NHCy (Cy=cyclohexyl) can be obtained in sufficiently high yields to allow for the exploration of its Brønsted acidity. Thus, deprotonating PH₂C(O)NHCy with one equivalent of potassium bis(trimethylsilyl)amide (KHMDS) gave the new phosphide [PHC(O)NHCy]^?. In contrast, deprotonation with half of an equivalent gives rise to [P{C(O)NHCy}₂]^? and PH₃. These phosphides can be employed to give new phosphines by reactions with electrophiles, thus demonstrating their enormous potential as chemical building blocks.     

Electrochemiluminescence of SDBS‐Ru(bpy)32+‐CPM System and Its Application

When the concentration of dodecyl benzene sulfonic acid sodium salt (SDBS) is 0.7 mmol·L^?1, the electrochemical and electrochemiluminescence (ECL) intensity of Ru(bpy)₃²⁺‐chlorpheniramine maleate (CPM) system at the Au electrode were studied. The results showed that compared with the absence of SDBS, enhancement of the ECL intensity was 14‐fold at Au electrode. Base on this, an ECL method was established for efficient and simple determination of CPM at Au electrode. Under the optimum experimental condition, the enhanced ECL intensities had good linear relationship with the concentration of CPM in the range of 1.0×10^?4–1.0×10^?7 mol·L^?1, and a linear regression equation was obtained as follows: I (counts)=48.805×10⁶c+394.03 (r=0.9975), the detection limit for CPM was 1.4×10^?8 mol·L^?1. The RSD for 5 times determinations of 1.0×10^?5 mol·L^?1 CPM was 3.2%. The results of recovery test were between 96.3%–102.5%, and the RSD of recovery test (n=5) was 2.7%. In addition, eleven kinds of tertiary amines‐Ru(bpy)₃²⁺ systems were investigated in the absence and presence of SDBS. The results showed that the enhancement of SDBS on ECL intensity of tertiary amines‐Ru(bpy)₃²⁺ systems was universal.     

Trans ligand influence in cobalt(III) Schiff base complexes: Electronic and steric effects on the kinetics of hydrolysis

Rate constants for the hydrolysis (k_h) of six different amines in trans‐[Co((BA)₂en)(amine)₂]ClO₄ complexes (amine = aniline 1a , para‐toluidine 1b , benzylamine 1c (primary amines), pyrrolidine 2a , piperidine 2b , morpholine 2c (secondary amines), and (BA)₂en = Bisbenzoylacetoneethylenediiminato) in mixed methanol/water (1:1) solvent have been determined between 30 and 55°C. The hydrolysis product of 2c , trans‐[Co((BA)₂en)(morpholine)(H₂O)]ClO₄, has been separately prepared and characterized by UV–vis and ¹H NMR spectroscopy. Depending on the nature of the axial amine ligand the limiting first‐order rate constants for the amine hydrolysis at 40°C range from (3.42 ± 0.10) × 10^?5 to (5.32 ± 0.13) × 10^?5 s^?1. At the first glance, a reasonable trend cannot be established between k_h and the basicity or the inductive trans effect of the amine ligands. However, when the complexes are classified into two groups, based on the type of the amine (primary and secondary), the values of k_h correlate well with the basicity or inductive effect of the amine in each group. The observed trend in k_h values for the complexes with primary amines is 1a (5.32 ± 0.13) × 10^?5 s^?1 > 1b (3.51 ± 0.14) × 10^?5 > 1c (1.72 ± 0.03) × 10^?5 (40°C), which is opposite to the amine basicity strength. In the case of the complexes with secondary amines, the observed trend in k_h values is in accord with amine basicity (or inductive trans effect), i.e. 2a (5.02 ± 0.22) × 10^?5 > 2b (4.18 ± 0.10) × 10^?5 > 2c (3.42 ± 0.10) × 10^?5 s^?1 (40°C). © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 387–393, 2002     

Charge transfer initiation of methylmethacrylate by isopropylamine

Methylmethacrylate (MMA) can be initiated by charge transfer complexes (i) formed by the interaction of aliphatic amines and MMA and (ii) formed by the interaction of aliphatic amines and carbon tetrachloride in a solvent like N-N dimethylformamide (DMF), dimethyl sulphoxide (DMSO) or chloroform. This paper reports the polymerization of MMA by isopropylamine (IPA) in the presence of CCl₄ in DMSO at 30. The rate of polymerization, R_p increases rapidly with CCl₄ up to a concentration of 0.25 mol l^?1 but, for a higher concentration, it is practically independent of the CCl₄ concentration. R_p is proportional to (IPA concentration)^{1 2} and to power of (MMA concentration)^1.30 when [CCl₄] ? [IPA]. The average rate constant, k, is 2.1 × 10^?6 l mol^{· 1} sec^{? 1}.     

Determination of Tetracyclines in Water Samples Using Liquid Chromatography with Fluorimetric Detection

A liquid chromatographic method with fluorimetric detection is proposed for the determination of trace levels of oxytetracycline, tetracycline, chlortetracycline and doxycycline in water samples. The analytes are preconcentrated by solid phase extraction using reversed phase polymeric cartridges and acetonitrile as eluent. Preconcentration factors up to 125 can be obtained. The chromatographic separation is performed on a polymeric column with a gradient elution program using mobile phases based on mixtures of acetonitrile and 0.01 mol L^?1 oxalic acid aqueous solution at a flow rate of 1.2 mL min^?1. Tetracyclines are post-column derivatized with a reagent solution consisting of 0.1 mol L^?1 Mg(II) at pH 9 at a flow rate of 0.6 mL min^?1. The highly fluorescent Mg(II) chelates are detected at λ _ex = 374 nm and λ _em = 499 nm. The detection limits of the whole process are in the low μg L^?1 level. The proposed method has been applied to the analysis of spiked natural water samples, and recovery rates higher than 80% have been obtained.