Liquid chromatographic determination of aliphatic amines in water using solid support assisted derivatization with 9-fluorenylmethyl chloroformate

Summary A simple and sensitive method has been developed for the liquid chromatographic determination of short-chain aliphatic amines in water. Analytes are retained in solid-phase extraction (SPE) cartridges, and then derivatized by drawing an aliquot of the fluorogeneic reagent 9-fluorenylmethyl chloroformate (FMOC) through the cartridges. After a certain reaction time the derivatives formed are desorbed with acetonitrile. The collected extracts are then chromatographed on a LiChrospher 100 RP₁₈ 125 mm×4 mm i.d., 5 μm, column using an acetonitrile-water gradient. The influence of experimental conditions (SPE material, volume of sample, concentration of FMOC, time of reaction and pH) has been investigated. Optimal results have been obtained with C₁₈ SPE cartridges using a sample volume of 5.0 mL. For derivatization, 0.25 mL aliquots of 25 mM FMOC have been used, the reaction time being only 2 min. The method has been applied to the quantification of several aliphatic amines: methylamine, ethylamine, dimethylamine,n-butylamine,n-pentylamine andn-hexylamine. Under the proposed conditions the percentages of analytes retained plus derivatized were of about 54–107% compared to those obtained with direct solution derivatization. The method provided good reproducibility, linearity and accuracy within the 0.050–1.0 mg L⁻¹ concentration range. The limits of detection were in the 0.25–5.0 μg L⁻¹ range. The utility of the described approach has been tested by analysing tap water, river water and industrial waste water.     

Comparative Characteristics of Some Physicochemical Properties of Azoles

We have carried out a correlation analysis of some physicochemical characteristics of pyrrole, pyrazole, imidazole, triazole, and tetrazole, calculated by the semiempirical quantum-chemical AM1 method. We have found the linear dependences of the ionization potential, the dipole moment, and the acidity on the -electron excess, and also the dependence of the ionization potential on the enthalpy of formation of the studied azoles.     

Coupling continuous ultrasound-assisted extraction, preconcentration and flame atomic absorption spectrometric detection for the determination of cadmium and lead in mussel samples

Continuous ultrasound-assisted extraction has been coupled with preconcentration and flame atomic absorption spectrometry for the determination of cadmium and lead in mussel samples. Experimental designs were used for the optimisation of the leaching and preconcentration steps. The use of diluted nitric acid as extractant in the continuous mode at a flow rate of 3.5 ml min⁻¹ and room temperature was sufficient for quantitative extraction of these trace metals. A minicolumn containing a chelating resin (Chelite P, with aminomethylphosphoric acid groups) was proved as an excellent material for the quantitative preconcentration of cadmium and lead prior to their flame atomic absorption detection. A flow injection manifold was used as interface for coupling the three analytical steps, which allowed the automation of the whole analytical process. A good precision of the whole procedure (2.0 and 2.3%), high enrichment factors (20.5 and 11.8) and a detection limit of 0.011 and 0.25 μg g⁻¹ for cadmium and lead, respectively, were obtained for 80 mg of sample. The sample throughputs were ca. 16 and 14 samples h⁻¹ for cadmium and lead, respectively. The accuracy of the analytical procedures was verified by using a standard reference material (BCR 278-R, mussel tissue) and the results were in good agreement with the certified values. The method was successfully applied to the determination of trace amounts of cadmium and lead in mussel samples from the coast of Galicia (NW, Spain).     

Metal speciation measurement by diffusive gradients in thin films technique with different binding phases

Since its invention in the mid-1990s, the diffusive gradients in thin films (DGT) technique has rapidly become one of the most promising in situ sampling techniques for trace metal measurement in natural waters. We investigated here the possibility of using DGT devices with different binding phases to determine different DGT labile fractions of Cd and Cu in laboratory solutions and in natural waters. Several binding phases were studied, including conventional Chelex 100 resin imbedded polyacrylamide hydrogel (Chelex) and several recently developed binding phases, poly(acrylamide-co-acrylic acid) (PAM-PAA) gel, poly(acrylamidoglycolic acid-co-acrylamide) (PAAG-PAM) gel, Whatman P81 cellulose phosphate ion-exchange membrane (P81), and poly(4-styrenesulfonate) (PSS) aqueous solution. Laboratory testing in metal solutions spiked with EDTA or humic acid suggested that all the DGT devices measured only free metal ions and inorganic metal complexes. Upon field testing at both freshwater and seawater sites it was found that the DGT labile metal concentrations measured by different binding phases can be significantly different, suggesting that the DGT labile metal fractions were dependent on binding strength of the binding phase. By designing binding phases that can compete with different natural water complexing ligands to varying extents, it is possible to use these different DGT devices to measure metal speciation in natural waters.     

A molecular mechanics and semiempirical conformational analysis of the herbicide diuron inhibitor of photosystem II

The potential energy surface (PES) for the herbicide diuron (DCMU), a photosystem II inhibitor, has been extensively investigated using the quantum-mechanical semiempirical molecular orbital methods AM1 and PM3 and molecular mechanics method. A detailed conformational search has been carried out which revealed the occurrence of four genuine minimum energy structures. The relative stability of the conformers and rotational barriers to conformational interconversion were evaluated using distinct theoretical approaches. The results showed that thetrans form of the diuron molecule is more stable than thecis form in all methods, and so it may possibly be the biologically active isomer.     

Element-selective detection using capillary gas chromatography with atomic emission detection

Capillary GC coupled to an atomic emission detector (AED) provides a powerful new hyphenated technique for the separation and characterization of complex mixtures and compounds. The AED provides simultaneous and truly specific multi-element detection. The specificity of detection reduces the need for the complex sample pretreatment procedures which are necessary to reduce the interference from co-eluted substances which is experienced with detectors such as the FID and the ECD. A range of environmentally significant problems has been studied, including PCB analysis, the characterization of the reaction products of a novel waste treatment process, and the profiling of sulfur-containing species formed by the pyrolysis of various types of coal.     

Significance of Non-isothermal Kinetic Data. A statistical study

Arrhenius parameters values, in non-isothermal kinetic vaporisation processes for a series of compounds with related structures, have been calculated. This was made using a method of calculation that allows to find the most probable vaporisation mechanisms. According to this method DTG curves were compared with some theoretical ones reported in literature, whose shape results to be only a function of the mechanisms. In this way the choice of the mathematical functions which can be inserted in the kinetic equations, was influenced by the shape of the DTG plots and other thermal analysis signals thus allowing to choose the most probable mechanisms. The kinetic parameters derived from these mechanisms were compared, using statistical analysis, with those obtained from another method of calculation based on ‘a priori’ vaporisation mechanism chosen for the investigated liquid–gas transition. The standard deviations of the slope and of the intercept, together with the standard deviation and the square correlation coefficient (r ²) of the linear regression equations related to the mechanisms of the two methods were calculated. Student t-test, Fisher F-test, confidence intervals (c.i.) and residuals valueswere also given. Statistical analysis shows that the mechanisms obtained with the former method (diffusive and geometrical models) and the related Arrhenius parameters result to be more significant (in terms of probability) than the corresponding quantities of the latter for which a first-order model was chosen. This revised version was published online in August 2006 with corrections to the Cover Date.     

Fast-cycle trace analysis of dioxin in flue gas. Monitoring of the incineration of dioxin-containing waste from seveso

The fast trace analysis method used to monitor 2,3,7,8-TCDD in stack gas during the incineration of the waste from Seveso is described. The sampling of volatile organic compounds from flue gases, distributed between all three aggregation states, is based on a micromethod developed for the trace analysis of water using a specially dimensioned adsorptive charcoal filter (1.5 mg charcoal). In conjunction with subsequent GC/MS measurements the rapid “fast cycle trace analysis” ensured specific 2,3,7,8-TCDD detection down to 100 pg per m³ flue gas in cycle times of about 1–2 hours.