•Selective ultratrace determination of cyanides by headspace GC-NPD.•Easy sample preparation for the analysis of both available and total cyanides in wastewaters.•Speciation of cyanides through ...different thermal treatment.•Proposal of an equilibrium model for weak acid dissociable cyanide complexes.
A new analytical method for the determination of both available (free and weak acid dissociable, WAD) and total cyanides in industrial wastewaters has been developed. It is based on the static headspace (HS) sampling procedure followed by a GC separation and the selective nitrogen-phosphorous detection (NPD), in which different thermal treatment allows the speciation of total and available cyanides. Detection limits (0.5μg/L), recovery (84.7–114.6% for free and 76.8–121.5% for total cyanides) and precision (5% at 5μg/L), evaluated on both real and synthetic samples, were fit-for-purpose for the legal requirement (5μg/L) enforced in the Venice lagoon, without significant interfering species. In addition, analytical results of the HS-GC-NPD method have been compared with those obtained using the 4500 CN and EN ISO 14403 official methods for the determination of total and free cyanides, respectively. The new method has been successfully applied for the determination of cyanide concentrations in main influent and final effluent to the Venice lagoon to verify the efficiency of the industrial wastewater treatment plant of Porto Marghera (Venice, Italy). The capability of the proposed method to detect the WAD cyanides has been tested by studying the acid dissociation of K2Ni(CN)4. An unexpected speciation picture was obtained for this complex, which suggests that the present definition and analytical strategy of this cyanide class should be reconsidered.
About ninety empirical functions for the representation of chromatographic peaks have been collected and tabulated. The table, based on almost 200 references, reports for every function: (1) the most ...used name; (2) the most convenient equation, with the existence intervals for the adjustable parameters and for the independent variable; (3) the applications; (4) the mathematical properties, in relation to the possible applications. The list includes also equations originally proposed to represent peaks obtained in other analytical techniques (e.g. in spectroscopy), which in many instances have proved useful in representing chromatographic peaks as well; the built-in functions employed in some commercial peak-fitting software packages were included, too. Some of the most important chromatographic functions, i.e. the Exponentially Modified Gaussian, the Poisson, the Log-normal, the Edgeworth/Cramér series and the Gram/Charlier series, have been reviewed and commented in more detail.
4-hydroxy-3,5-pyridinedicarboxylic acid (DQ58) and 4-hydroxy-1-methyl-3,5-pyridinedicarboxylic acid (DQ71508) have been synthesized, and their Fe(III), Al(III), Cu(II), and Zn(II) coordination ...properties have been studied by potentiometry, UV–Vis spectroscopy (in the case of Fe(III), Al(III), Cu(II)),
1
H-NMR (for Al(III)) and EPR (for Cu(II)). The thermodynamic results were used to model the extent of the toxic metal ions decorporation (Fe(III) or Al(III)) in the presence of the essential metal ions (Cu(II) or Zn(II)). DQ58 and DQ71508 were demonstrated to interact with human serum albumin (HSA), which is assumed to be the main serum transporter of the chelators, and binding constants have been obtained by ultrafiltration. IC
50
values of 5.185 × 10
−3
and 1.033 × 10
−3
mol·L
−1
were collected after 24 and 48 h of treatment with DQ71508 towards human embryonic kidney HEK-293 cells, demonstrating the relatively low cytotoxicity of this compound. According to these results, both DQ58 and DQ71508 seem to be potential candidates for Fe chelation therapy, and DQ58 is a better Fe(III) chelator than DQ71508.
The coordination properties of four hydroxypyridinecarboxylates, designed for the treatment of iron‐overloading conditions as bidentate O,O′‐donor ligands, have been studied with ZnII in the solid ...state. The coordination compounds Zn(A1)2(H2O)2 (1), Zn(A2)2(H2O) (2), Zn(A3)2(H2O)·2H2O (3) and Zn2(B1)4(H2O)2·4H2O (4), where the ligands are 1‐methyl‐4‐oxidopyridinium‐3‐carboxylate (A1, C7H6NO3), 1,6‐dimethyl‐4‐oxidopyridinium‐3‐carboxylate (A2, C8H8NO3), 1,5‐dimethyl‐4‐oxido‐pyridinium‐3‐carboxylate (A3, C8H8NO3) and 1‐methyl‐3‐oxidopyridinium‐4‐carboxylate (B1, C7H6NO3), have been synthesized and analysed by single‐crystal X‐ray diffraction. The ligands were chosen to probe (i) the electronic effects of inverting the positions of the O‐atom donor groups (i.e. A1 versus B1) and (ii) the electronic and steric effects of the addition of a second methyl group in different positions on the pyridine ring. Two axially coordinated water molecules resulting in a six‐coordinated symmetrical octahedron complement the bis‐ligand complex of A1. Ligands A2 and A3 form five‐coordinated trigonal bipyramidal complexes with one additional water molecule in the coordination sphere, which is a rarely reported geometry for ZnII complexes. Ligand B1 shows a dimeric structure, where the two Zn2+ dications have slightly distorted octahedral geometry and the pyridinolate O atom of the neighbouring complex bridges them. The coordination spheres of the Zn2+ dications and the supramolecular structures are discussed in detail. The packing arrangements of 1–3 are similar, having alternating hydrophilic and hydrophobic layers, however the similarity is broken in 4. The obtained coordination geometries are compared with their previously determined CuII analogues. The study of the individual complexes is complemented with a comprehensive analysis of ZnII complexes with oxygen donor ligands with data from the Cambridge Structural Database.
The structure‐directing effects of four O,O′‐donor hydroxypyridinecarboxylate derivatives in their complexation with ZnII have been investigated by single‐crystal X‐ray diffraction. One octahedral and two trigonal bipyramidal mononuclear complexes, as well as a pyridinolate‐bridged dinuclear complex with octahedral geometry, were detected.
In this paper we study complete maximal spacelike hypersurfaces in anti-de Sitter space H1n+1 with either constant scalar curvature or constant non-zero Gauss–Kronecker curvature. We characterize the ...hyperbolic cylinders Hm(c1)×Hn−m(c2),1≤m≤n−1, as the only such hypersurfaces with (n−1) principal curvatures with the same sign everywhere. In particular we prove that a complete maximal spacelike hypersurface in H15 with negative constant Gauss–Kronecker curvature is isometric to H1(c1)×H3(c2).
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