Enzyme-linked immunosorbent assays for the sensitive analysis of 2,4-dinitroaniline and 2,6-dinitroaniline in water and soil

The development and characterization of one rat monoclonal antibody (mAb) for 2,4-dinitroaniline and of two rat mAbs for 2,6-dinitroaniline are described. With the immunization of rats with 2,4,6-trinitrophenyl-glycylglycine–keyhole limpet hemocyanine (KLH) conjugate one mAb (PK 5H6) has been developed and formatted into a competitive enzyme-linked immunosorbent assay (ELISA). This assay no. 1 is very sensitive for 2,4-dinitroaniline with a test midpoint of 0.24 ± 0.06 μg L⁻¹ (n = 19) in 40 mM phosphate-buffered saline (PBS). A second hapten, 3-(4-amino-2,6-dinitrophenyl)propionic acid, which was also conjugated to KLH and used for the immunization of rats, led to two sensitive ELISAs for 2,6-dinitroaniline in 40 mM PBS with test midpoints of 0.61 ± 0.08 μg L⁻¹ (n = 15; mAb DNT4 3C6; assay no. 2) and 0.94 ± 0.29 μg L⁻¹ (n = 17; mAb DNT4 1A7, assay no. 3). Selectivities of all mAbs were checked with more than 20 compounds, including nitroaromatic compounds, 2,6-dinitroaniline pesticides, and other substituted derivatives of aniline. As very noticeable cross-reactivities, all mAbs recognize 2-chloro-4,6-dinitroaniline, 4-chloro-2,6-dinitroaniline and 2-bromo-4,6-dinitroaniline, the last of these being a major metabolite of the azo dye Disperse Blue 79. As first demonstrations of applications, two ELISAs (assays no. 1 and 2) were used for the analysis of 2,4- or 2,6-dinitroaniline in spiked water and soil samples. Recovery data were determined and the majority of these data were in the range of 90–120%. These assays can contribute to a very cost-effective and environmentally friendly immunochemical surveillance monitoring of environmental samples for contaminations with these compounds. To the best of the authors’ knowledge, these are the first antibodies described for 2,4-dinitroaniline and for 2,6-dinitroaniline.     

Thermodynamics of complexation of lanthanides and some of transition metal ions by 5,5-dimethyl-cyclohexane-2-(2-hydroxyphenyl)-hydrazono-1,3-dione (DCPHD) and its derivatives

Summary Equilibrium betweenDCPHD,DC-4-Cl-PHD, andDC-4-Me-PHD and protons, transition, and lanthanide ions have been investigated at 30 °C by means of potentiometric titration in 75% (v/v) methanol-water mixture containing 0.10M KNO₃ as a constant ionic medium. Thermodynamic parameters (G, H and S) referring to the formation of species HL ^–,L ^––,ML ^+n–2 andML ₂ ^+n–4 (L ^–– denotes the ligand anion) have been determined in solutions. The solvent effects on the thermodynamic parameters of the complex formation are discussed in terms of differences in the donor ability of methanol and water solvents. The plots of thermodynamic parameters versus ionic potential (Z ²/r) of the lanthanide elements is not linear as expected from ionic theory. The obtained curve can be resolved in an initial group (the lighter lanthanides), an intermediate group (Sm-Dy), and a final group (the heavier ones, Tb-Lu). This behavior was explained in terms of differences in the dehydration of lighter lanthanide(III) from that of heavier ones.

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Thermodynamik der Komplexierung von Lanthaniden und einigen Übergangsmetall-Ionen mit 5,5-Dimethylcyclohexyl-2-(2-hydroxyphenyl)-hydrazono-1,3-dion (DCPHD) und seinen Derivaten

Zusammenfassung Die Gleichgewichte zwischenDCPHD,DC-4-Cl-PHD undDC-4-Me-PHD mit Protonen, Übergangsmetall- und Lanthaniden-Ionen wurden bei 30 °C mittels potentiometrischer Titration in 75% (v/v) Methanol-Wasser mit einem Gehalt an 0.10M KNO₃ als konstantem ionischem Medium untersucht. Die thermodynamischen Parameter G, H und S zur Bildung der Spezies HL ^–,L ^––,ML ^+n–2 undML ₂ ^+n–4 (L ^–– steht für das Ligandenanion) wurden in Lösung bestimmt. Die Lösungsmitteleffekte auf diese Komplexbildungsparameter werden auf Basis der Differenz im Donorvermögen von Methanol und Wasser als Solventien diskutiert. Die Diagramme der thermodynamischen Parameter gegen die ionischen Potentiale (Z ²/r) der Lanthaniden sind, wie nach der Ionentheorie zu erwarten, nicht linear. Die erhaltene Kurve läßt eine Anfangsgruppe (die leichteren Lanthaniden), eine mittlere Gruppe (Sm-Dy) und eine Endgruppe (die schwereren Lanthaniden. Tb-Lu) erkennen. Dieses Verhalten kann aus dem Unterschied im Dehydratationsverhalten erklärt werden.

     

Synthesis and Molecular and Crystal Structure of K4.5{[Mo3(μ3-Te)(μ2-Te2)3(CN)6]I}I1.5·3H2O and Cs3{[Mo3(μ3-Te)(μ2-Te2)3(CN)6]I}·2H2O

Crystal structures of two new compounds containing trigonal tellurium-bridged cluster fragments [Mo₃(₃-Te)(₂-Te₂)₃]⁴⁺ were investigated. Crystal data for K_4.5{[Mo₃(₃-Te)(₂-Te₂)₃(CN)₆]I}I_1.5·3H₂O: space group , Z = 4, a = 13.280(1), c = 23.800(3) , V = 3635.0(6) ³, d _calc = 3.432 g/cm³, R ₁ = 0.0335, wR2 = 0.0912 for 1378 I _hkl > 2 _I from 3545 measured I _hkl ; for Cs₃{[Mo₃(₃-Te)(₂-Te₂)₃(CN)₆]I}·2H₂O: space group P2 ₁ /n, Z = 2, a= 9.650(2) , b = 22.297(5), c = 27.446(7) , = 94.10(2)°, V = 5890(2) ³, d _calc = 4.273 g/cm ³, R ₁ = 0.0384, wR ₂ = 0.0744 for 957 I _hkl > 2 _I from 3758 measured I _hkl (Enraf-Nonius CAD-4 diffractometer, MoK , graphite monochromator). In both compounds, ionic pairs {[Mo₃Te₇(CN)₆]I}^3– with Te_ax...I^– distances of 3.358-3.676 are formed. In the potassium salt, the {[Mo₃Te₇(CN)₆]I}^3– anion pairs are linked by the additional Te_eqI^– short contacts of 3.460 into two-dimensional corrugated layers perpendicular to the c axis of the unit cell. The structure of the cesium salt is ionic with interstitial H₂O molecules and double-layer closest packing of anions.     

Determination of Triphenyltin and Its Metabolite Diphenyltin in Culture Medium by High-Performance Liquid Chromatography with UV detection

A method for the determination of triphenyltin and diphenyltin was developed by reversed-phase high-performance liquid chromatography with UV detection. Triphenyltin and diphenyltin were separated using a reversed-phase Symmetry C₁₈ column (150 × 3.9 mm, 5 m) with tetrahydrofuran-water-acetonitrile-glacial acetic acid (13:25:5:7, v/v) containing 0.05% triethylamine and 1.0% sodium acetate as mobile phase at 0.50 mL min^–1 and detection at 257 nm. The calibration curves were linear from 0.26 mol L^–1 to 1100 mol L^–1 for triphenyltin with a correlation coefficient of 0.9999 (n=12) and from 0.60 mol L^–1 to 1200 mol L^–1 for diphenyltin with a correlation coefficient of 0.9991 (n=12), respectively. The detection limits of triphenyltin and diphenyltin were 0.2 mol L^–1 and 0.4 mol L^–1, respectively. The method was successfully applied to the determination of triphenyltin and its metabolite diphenyltin in culture medium. The recoveries of triphenyltin and diphenyltin were in the ranges of 97.7% to 103.3% and 85.5% to 91.6%, respectively.     

Chromotropic acid,a fluorogenic chelating agent for aluminium(III)

Complexation of aluminium(III) with the fluorogenic ligand chromotropic acid (4,5-dihydroxynaphthalene-2,7-disulfonic acid) has been revisited with the aim of using enhancement of the fluorescence intensity as an analytical tool. Complexation at the optimum pH4 was shown to lead to a 1:1 complex with a stability constant log ₁₁₀=18.4±0.7. The fluorogenic effect was thoroughly investigated. Nearly selective excitation of the chelate rather than the ligand could be achieved at wavelengths longer than 360 nm. For analytical purposes the main interfering ion was Ga³⁺. The strongest competing ligand was shown to be citric acid. Competitive complexation by acetate or formate ions can also make their use in a buffer at the usual concentration, 0.2 mol L^–1, questionable, whereas a 10^–2 mol L^–1 formic acid buffer was shown to be a good alternative. The calibration plot showed that the dependence of response on Al(III) concentration was linear up to 500 g L^–1; the detection limit was 0.65 g L^–1 (3SD _blank, n=10, SD=±1.4% at 10 g L^–1 and ±0.8% at 100 g L^–1). The analytical procedure was successfully applied to several samples of tap water and the results were in good agreement with those from AAS determination.     

Microwave Spectrum and Hindered Pseudorotation of Tetrahydrofuran

The microwave spectrum of the tetrahydrofuran (C₄H₈O) molecule in the ground state and eight excited states of hindered pseudorotation has been studied. A strong perturbation of rotational spectra has been found for three pairs of pseudorotational states, which is due to the vibrational-rotational interaction. To analyze the nonrigid spectra of these states we used the double resonance technique. Two hundred and sixty nine rotational and vibrational-rotational transitions corresponding to the _a and _c components of the dipole moment have been identified. The rotational constants have been determined along with the quartic constants of centrifugal distortion and the spectroscopic parameters of the interaction between the overall rotation and hindered pseudorotation. The splittings of three pairs of quasidegenerate vibrational levels have been calculated: ₀₁ = 21,308.17 MHz, ₂₃ = 61,205.28 MHz, ₅₆ = 68,183 MHz. The potential function of hindered pseudorotation V()=- 7.84(1-cos2)/2+36.10(1-cos4)/2 (cm^–1) was found from the splittings. It is concluded that the molecule has a twisted conformation (C₂ symmetry) in the states =0 and =1 of hindered pseudorotation and a bent conformation (C_s symmetry) in the states = 2 and = 3. The component of the dipole moment of the transition ‹ = 2 |_c | = 3› = 0.57± 0.01D was determined from the Stark effect of the rotational transitions in the = 2, = 3 states.     

Study of Cr(VI)-2-oximinodimedone dithiosemicarbazone reaction and simultaneous determination of Cr(VI) and Fe(III)

Summary 2-Oximinodimedone dithiosemicarbazone reacts with Cr(VI) in strongly acid medium. The orange colour obtained has been used to propose a spectrophotometric method of Cr(VI) determination in the concentration range 0.40–9.5g ml^–1 (=5600 mole^–1-cm^–1 at 485 nm). The stoichiometry of the reaction is 32 (reagentCr(VI)) which is in accordance with the oxidation reaction of the reagent by Cr(VI). The method has been applied to the determination of Cr(VI) and Fe(III) in ceramic materials.

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Eine Studie zur Cr(VI)-2-oximinodimedondithiosemicarbazon-Reaktion und die simultane Bestimmung von Cr(VI) und Fe(III)

Zusammenfassung 2-Oximinodimedonedithiosemicarbazon reagiert in stark saurem Milieu mit Cr(VI). Die orange Farbe kann im Konzentrationsbereich von 0.4–9,5g/ml zur spektrophotometrischen Cr(VI)-Bestimmung verwendet werden (=5600 1 mol^–1cm^–1bei 485 nm). Die Stöchiometrie der Reaktion ist 32 (Reagens: Cr(VI)) und entspricht der Oxidation des Reagens durch Cr(VI). Die Methode wurde zur Bestimmung von Cr(VI) und Fe(III) in keramischen Materialien eingesetzt.

     

Development and application of a simple routine method for the determination of selenium in serum by octopole reaction system ICPMS

The aim of the study was to develop an inductively coupled plasma mass spectrometry (ICPMS) method for robust and simple routine determination of selenium in serum. Polyatomic interferences on ⁷⁶Se, ⁷⁷Se, and ⁷⁸Se were removed by applying an octopole reaction system ICPMS with the reaction cell pressurized with H₂ gas. We developed a novel simple optimization routine for the H₂ gas flow based on a signal-to-noise ratio (SNR) calculation of the selenium signal measured in a single selenium standard. The optimum H₂ flow was 2.9 mL min^–1. The selenium content in serum was determined after a 50-fold dilution with 0.16 M HNO₃ and quantified by using addition calibration and gallium as an internal standard. The method detection limit was 0.10 g L^–1 for ⁷⁶Se and ⁷⁸Se and 0.13 g L^–1 for ⁷⁷Se. Human serum samples from a case-control study investigating if selenium was associated with risk of colorectal adenoma were analyzed. The average selenium concentration for the control group (n=768) was 137.1 g L^–1 and the range was 73.4–305.5 g L^–1. The within-batch repeatability (a batch is ten samples) estimated from 182 replicate analyses was 6.3% coefficient of variation (CV), whereas the between-batch repeatability was 7.4% CV estimated from 361 replicates between batches. The method accuracy was evaluated by analysis of a human serum certified reference material (Seronorm Serum level II, Sero A/S, Norway). There was a fairly good agreement between the measured average of 145±3 g L^–1 (n=36) and the certified value of 136±9 g L^–1. In addition the method was successfully applied for analysis of zinc serum concentrations without further optimization. For the Seronorm certified reference material a value of 911±75 g L^–1 (n=31) for zinc was obtained, which corresponds well to the certified zinc value of 920±60 g L^–1.     

Development and Validation of an HPTLC–Densitometric Method for Determination of ACE Inhibitors

A high-performance thin layer chromatographic method coupled with densitometric analysis has been developed for measurement of benazepril and cilazapril, both pure and in their commercial dosage forms. The active substances were extracted from tablets with methanol (mean recovery 102%) and chromatographed on silica gel 60 F₂₅₄ HPTLC plates in horizontal chambers with ethyl acetate–acetone–acetic acid–water, 8:2:0.5:0.5 (v/v), as mobile phase. Chromatographic separation of these ACE inhibitors was followed by UV densitometric quantitation at 215 nm. Calibration plots were constructed in the range 0.4 to 2.0 g L^–1 for benazepril (2.0–10.0 g spot^–1) and from 0.5 to 1.5 g L^–1 for cilazapril (4.0–12.0 g spot^–1) with good correlation coefficients (r 0.990). The method was used to determine benazepril and cilazapril in pharmaceutical preparations with satisfactory precision (1.4% < RSD < 5.6%) and accuracy (1.7 < RE < 5.1).     

Reaction of sulphur dioxide with chlorocarbonyls of ruthenium,rhodium and iridium

Summary The reactions of SO₂ with chlorocarbonyls of rhodium and iridium ([M(CO)₂Cl₂]^– and ruthenium ([Ru(CO)_2–Cl₂]_n) ions were studied. Addition of either the Ph₄As⁺ cation or the nitrogen-donor ligands 2,2-bipyridine (bipy),o-phenylenediamine (opd), 1,10-phenanthroline (phen), 2,2,6,2-terpyridine (terpy) or 6,7-dihydro-1,4-di(2-pyridyl)-5H-cyclopenta {d}-pyridazine (5-dppn) to the SO_2– treated chlorocarbonyl solutions resulted in the formation of various complexes according to the nature of metal and ligand. The products have been characterized by physicochemical methods.     

2,3-Dihydroxypyridine-loaded cellulose: a new macromolecular chelator for metal enrichment prior to their determination by atomic absorption spectrometry

New macromolecular chelators have been synthesized, by loading 2,3-dihydroxypyridine (DHP) on cellulose via linkers -NH-CH₂-CH₂-NH-SO₂-C₆H₄-N=N- and -SO₂-C₆H₄-N=N-, and characterized by elemental analysis, TGA, IR, and CPMAS ¹³C NMR spectra. The cellulose with DHP anchored by the shorter linker had better sorption capacity (between 69.7 and 431.1 mol g^–1) for Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Pb(II), and Fe(III)) than the other (51.9–378.1 mol g^–1); the former was therefore studied in detail as a solid extractant for these metal ions. The optimum pH ranges for quantitative sorption (recovery 97.6–99.8%) on this matrix were: 7.0–9.0, 6.0–9.0, 3.0–8.0, 6.0–8.0, 6.0–9.0, 6.0–7.0, and 2.0–6.0 respectively. Desorption was quantitative with 0.5 mol L^–1 HCl and 0.5 mol L^–1 HNO₃ (for Pb). Simultaneous sorption (at pH 7.0) of all metal ions other than Fe(III) was possible if their total concentration did not exceed the sorption capacity (lowest value). The recovery of seven metal ions from their mixture at pH 6.0 was nearly quantitative when the concentration level of each metal ion was 0.2 g mL^–1. The optimum flow rate of metal ion solutions for quantitative sorption of metal onto a column packed with DHP-modified cellulose was 2–7 mL min^–1, whereas for desorption the optimum flow rate for the acid solution was 2–4 mL min^–1. The time needed to reach 50% of the total loading capacity (t_1/2) was <5 min for all the metal ions except Ni and Pb. The limit of detection (blank+3s) was from 0.70 to 4.75 g L^–1 and the limit of quantification (blank+10s) was between 0.79 and 4.86 g L^–1. The tolerance limits for NaCl, NaBr, NaI, NaNO₃, Na₂SO₄, Na₃PO_4, humic acid, EDTA, Ca(II), and Mg(II) for sorption of all metal ions are reported. The column packed with DHP-anchored cellulose can be reused at least 20 times for enrichment of metal ions in water sample. It has been used to enrich all the metal ions in pharmaceutical and water samples before their determination by flame AAS. RSD for these determinations was between 1.1 and 6.9%.     

Structural diversity in the self-assembly of Ag(I) complexes containing 2-amino-5-halopyrimidine

A series of Ag(I) complexes containing the 2-amino-5-halopyrimidine ligands have been synthesized and their structures characterized by X-ray crystallography. The isomorphous complexes Ag(L-Cl)₂(CF₃SO₃) (L-Cl = 2-amino-5-chloropyrimidine), 1, and Ag(L-Br)₂(CF₃SO₃) (L-Br = 2-amino-5-bromopyrimidine), 2, are mononuclear, while [Ag(L-Br)(CF₃SO₃)]₆·6C₄H₁₀O, 3, and [Ag(L-I)(CF₃SO₃)]₆ (L-I = 2-amino-5-iodopyrimidine), 4, show cyclic self-assembly of six Ag(Ι) atoms and six L-X ligands, resulting in 24-membered metallocycles. The complex [Ag(L-I)(CF₃SO₃)]_∞, 5, forms 1D zigzag chains which are linked through C-I?Ag and Ag?O interactions to form a 3D structure. The tetranuclear complexes [Ag(L-X)(NO₃)]₄ [X = Cl, 6; Br, 7] form 16-membered metallocycles, while [Ag(L-X)(ClO₄)]_∞ [X = Cl, 8; Br, 9] exhibit helical chains. The different structure of 5 from 1 and 2 appears to be due to the stronger nucleophilic character of the iodine atom. In these complexes, the relatively smaller NO₃⁻ anions lead to the formation of tetranuclear metallocycles and the larger CF₃SO₃⁻ anions support the hexanuclear metallocycles, whereas the ClO₄⁻ anions induce the helical chains.     

Multicentered bonding and quasi-aromaticity in metal-chalcogenide cluster chemistry

On the basis of the localized molecular orbital (LMO) theory, the bonding schemes for the following types of cluster compounds are briefly reviewed in this paper; the linear [Et₄N][Cl₂FeS₂MoS₂Cu(PPh₃)₂] cluster, triangular trinuclear [M ₃(₃–X)(–Y ₃]⁴⁺ (M = Mo, W;X = O, S;Y = O, S, Se) clusters, triangulated polyhedral clusters: closo-boranes B _n H _n ^2–, octahedral [Co₆(CO)₁₄]^4–, [Ni₂Co₄(CO)₁₄]^2– and [Co₆(₃ –X ₈ ·L ₆ ⁿ⁺ (X = S, Se;L = PPh₃, PEt₃, CO;n = 0,1) as well as quasi-aromatic cluster ligands in cubane-type [Mo₃S₄ ·ML _n ^{(4 +q) +} (M = Mo, W, Fe, Ni, Cu, Sn, Sb;L = Ligand and sandwich-type [Mo₃S₄ ·M · S₄Mo₃]⁸⁺ (M = Mo, Sn, Hg). We put emphasis upon the characteristics of multicentered bonding in these cluster molecules, and, especially, point out existence of a novel species of quasi-aromatic cluster compounds.     

A selective and sensitive spot-test for gold

Summary A new spot test for gold has been developed, based on the oxidation of colourless phenolphthalin to red phenolphthalein in alkaline medium. The sensitivity is 0.2g of gold on a spot-plate and 0.15g on filter paper. Ce(IV) interferes seriously, and Pt(IV) at high concentrations, but Pd(II), Cu(II), Fe(III), Cr(III), Ni(II), UO₂(II), ClO₄ ^–, CrO₄ ^2–, BrO₃ ^–, IO₃ ^–, MoO₄ ^2–, and WO₄ ^2– do not.

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Zusammenfassung Eine neue Tüpfelreaktion für Gold wurde entwickelt, die auf der Oxydation des farblosen Phenolphthalins zu rotem Phenolphthalein in alkalischem Milieu beruht. Die Empfindlichkeit beträgt auf der Tüpfelplatte 0,2g Gold, auf Filterpapier 0,15g. Cer(IV) stört stark, Pt(IV) in hoher Konzentration; hingegen stören Pd(II), Cu(II), Fe(III), Cr(III), Ni(II), UO₂(II), ClO₄ ^–, CrO₄ ^2–, BrO₃ ^–, JO₃ ^–, MoO₄ ^2– und WO₄ ^2– nicht.

     

Ion-pair adsorption film colorimetry — A new simple method for ppb level of aluminum ion in water sample

A new, highly sensitive and simple colorimetric method for trace aluminum(III) with 2,2-dihydroxyazobenzene, H₂L, is described, based on the ion-pair adsorption of the anionic Al chelate, [A1L₂ ^–, with crystal violet cation, CV⁺, on the surface of Polyvinylchloride film plasticized with dioctylphthalate. The blue violet species, CV⁺[A1L₂]^–, is enriched onto the transparent film, leading to a remarkable enhancement of the sensitivity, and the detection limits are 3 ng/ml by spectrophotometry and 5 ng/ml by visual colorimetry, respectively. Using spectrophotometer, a linear calibration curve is obtained over the concentration range of 0 to 50 ng/ml of Al. Further, the color system, consisting of red ([A1L₂]^–), yellow (H₂L), and blue violet (CV⁺), gave clear color changes suitable for visual determination of aluminum with an applicable range of 0 to above 3000 ng/ml. The four different color zones are khaki for 0–5 ng/ml, reddish-brown for 5–200 ng/ml, blue violet for 200 ng/ml-3g/ml, and colorless for more than 3g/ml. The proposed method has been successfully applied for the determination of aluminum in tap waters.     

Integrated procedure for determination of endocrine-disrupting activity in surface waters and sediments by use of the biological technique recombinant yeast assay and chemical analysis by LC–ESI-MS

An integrated procedure using mass spectrometry and molecular biology for determination of estrogenicity in natural waters and sediments is reported. Solid-phase extraction (SPE) and pressurized-liquid extraction (PLE), respectively, were used for isolation of endocrine-disrupting compounds (EDC) from surface waters and sediments, followed by liquid chromatography–mass spectrometry using an electrospray interface (LC–ESI-MS). Twenty seven EDC were determined: non-ionic surfactants (nonylphenol ethoxylate), alkylphenols (e.g. nonylphenol and octylphenol), bisphenol A, phthalates, and natural and synthetic steroid sex hormones. Limits of detection varied from 0.02 to 0.22 g L^–1 and from 1 to 10 g kg^–1 in water and sediments, respectively. Recoveries ranged from 65 to 125% and 73 to 97% for waters and sediments, respectively. In addition to LC–ESI-MS determination, extracts obtained by SPE and PLE were analyzed by the recombinant yeast assay (RYA) to assess total estrogenic activity. This bioassay detects natural estrogens and xenoestrogens, producing a quantitative measurement of EDC irrespective of the identity of the chemical responsible for the activity. As a novelty, a relative estrogenicity factor was determined for 19 analytes with EC ₅₀ values ranging from 10^–10 to 10^–9 mol L^–1 for synthetic estrogens, from 10^–7 to 10^–5 mol L^–1 for alkylphenol derivatives, and from 10^–5 to 10^–4 mol L^–1 for phthalates and benzothiazoles. By use of this integrated chemical–ecotoxicological approach good correlation was usually established between chemical composition and estrogenic effects for surface water and sediment samples from Portugal. Estrogenic activity observed was mainly attributed to the presence of nonylphenolic compounds (with concentrations of NP ranging from 0.1 up to 44 g L^–1 in waters and up to 1172 g kg^–1 in sediments), and to the sporadic presence of estrogens, detected at ng L^–1 levels.     

Time-based on-line preconcentration cold vapour generation procedure for ultra-trace mercury determination with inductively coupled plasma atomic emission spectrometry

A time-based sequential dispensing on-line column preconcentration procedure for mercury determination at trace levels by cold vapour generation inductively coupled plasma atomic emission spectrometry (CV-ICP-AES), by means of a unified module of a preconcentration column and a gas–liquid separator (PCGLS) is described. The complex of mercury formed on-line with ammonium pyrrolidine dithiocarbamate (APDC) is retained on the surface of the hydrophobic poly(tetrafluoroethylene) (PTFE) turnings, which are packed into the lower compartment of the PCGLS. Subsequently, mercury vapour is generated directly on the PTFE turnings by reductant SnCl₂ and separated from the liquid mixture via the PCGLS by argon purge gas. The outlet of the PCGLS is connected directly to the torch adapter of the plasma without the normal spray chamber and nebulizer. With 60-s preconcentration time and 12.0 mL min^–1 sample flow rate, the sampling frequency is 30 h^–1. The calibration curve is linear over the concentration range 0.02–5.0 g L^–1, the detection limit (c_L) is 0.01 g L^–1 and the relative standard deviation (s_r) is 3.1% at the 1.0 g L^–1 level. The proposed method was evaluated by analysis of BCR CRM 278 (Mytilus Edulis) reference material and applied to the determination of total mercury in digested urine, blood and hair samples.     

Reactivity of the carbocation generated in the photolysis of 1,2,2,4,6-pentamethyl-1,2-dihydroquinoline toward azide ion

The reaction of the azide ion with the carbocation generated in the photolysis of 1,2,2,4,6-pentamethyl-1,2-dihydroquinoline in methanol was studied by pulse (conventional and laser) and steady-state photolysis techniques. The adduct of the azide ion was characterized by ¹H NMR spectrum. Experimental results were interpreted taking into account a competition between the addition of methanol and azide ion to the carbocation. The rate constants for the reaction of the azide ion with the carbocation (k _Az) were measured at 2—48 °C in a wide range of [N₃ ^–]₀ concentrations from 2·10^–7 to 0.1 mol L^–1 at different ionic strengths () of the solution. The resulting k _Az values are more than an order of magnitude lower than those for diffusional-controlled reactions and vary from 3.2·10⁸ ( = 0) to 4.5·10⁶ L mol^–1 s^–1 ( = 0.8 mol L^–1) in the presence of NaClO₄ (18 °C). The activation energy of addition of the azide ion to the carbocation is 21 kJ mol^–1, which is by 12 kJ mol^–1 lower than the activation energy of the reaction of the carbocation with methanol. The features of the reaction under study are discussed from the viewpoint of the structures of carbocations generated in the photolysis of dihydroquinolines.     

Properties of N,N-Dimethyl-N′-(2-Hydroxybenzyl)ethylenediamine as a Ligand to Copper(II)

The acid-basic and complexing properties of N,N-dimethyl-N-(2-hydroxybenzyl)ethylenediamine (HL) in aqueous propan-2-ol were characterized by spectrophotometry, pH-metry, and mathematical simulation of equilibria in solutions (T = 25 ± 0.1°C, = 0.1 M KNO₃). Dimer H₂L₂ was found to predominate in solution at c _HL = 0.01 mol/l. Three protonated dimeric (H₃L₂ ⁺, H₄L₂ ²⁺, and H₅L₂ ³⁺), diprotonated monomeric (H₃L²⁺), and triprotonated tetrameric forms (H₇L₄ ³⁺) were detected in the system, depending on pH. At lower ligand concentrations (c _HL = 0.0015 mol/l), the solution contains both dimers and monomers of this compound. The higher dentate number of HL compared to 2-alkylaminomethylphenols allows it to form more number of both mono- and binuclear complexes ([Cu(HL)]²⁺, [Cu(HL)₂]²⁺, [CuL₂], [CuL₂OH]^–, [Cu₂(HL)₂]⁴⁺, and [Cu₂(HL)₂L₂]²⁺), making them more stable.     

Di-μ-hydroxo bridge-cleavage reactions between [Co(nta)(μ-OH)]2 2− and different monodentate ligands

The cleavage of the di--hydroxo bridges of [Co(nta)(-OH)]₂ ^2– by dimethylaminopyridine (dmap) and pyridine (py) has been investigated. [Co(nta)(-OH)]₂ ^2– equilibrates rapidly in aqueous basic solutions with a mono--hydroxo bridged Co^III species [pK _OH = 3.26(2)] and both these species react with the incoming ligand to form different ion associated species which react in the subsequent rate-determining steps (k ₁ and k ₂) to form presumably a ligand-substituted, mono-bridged species, [(nta)(OH)Co--OH-Co(nta)(L)]^2–. Values for k ₂, the preferred mono--hydroxo bridged substitution pathway for these reactions, vary between 6.8(2) × 10^–4 s^–1 (py) and 8.5(4) × 10^–2 s^–1 (dmap).