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Trace metals in the environment occur in a variety of forms in solution, in colloids and particulates. Speciation studies try to distinguish between different dissolved forms (valence state, ionic, (in)organic complexed). Speciation has become important in studies concerning transport processes and the fate of trace elements. The toxic effects of trace elements are very much related to their form in the environment (see eg. Langston & Bryan, this volume).

Preparative paper chromatography is proposed as a suitable method for purification of Xylenol Orange (XO). The last three dissociation constants of pure XO have been determined with the aid of the program SPEKTFOT, the values found being p K 9 = 12.34; p K 8 = 10.66; p K 7 = 6.69 (0.1 M KNO 3 , 20 ± 0.5°). The complexation of zirconium with the purified reagent has been studied and the co-existence of ML and M 2 L complexes proved by use of the program DALSFEK. The following conditional stability constants of the complexes and their molar absorptivities were computed: log β' ml 4.58; log β' M 2 L 11.59; ϵ ML 2.00 × 10 4 ; ϵ M 2 L 9.40× 10 4 l.mole −1 .cm −1 at 550 nm.

A numerical method for treating two-phase flow in pipes is presented which incorporates the use of a partially implicit scheme in regions of relatively low flow velocity and a fully implicit treatment in regions of high velocity. This method takes advantage of the lower cost per iteration of the partially implicit scheme, without being limited by its conditional stability. Applications of this approach to water reactor blowdown calculations produce reductions in computer time by factors of 2-4 without a significant loss of accuracy.

Kramer, C. J. M., 1986. Approaches in chemical speciation studies in marine waters. In: P. Lasserre and J. M. Martin (eds), Biogeochemical Processes at the Land-Sea Boundary. Elsevier, Amsterdam. After a brief introduction on terminology, this overview summarizes the experimental and theoretical modelling methods applied in trace metal speciation studies, emphasizing the dissolved fraction as defined by 0.45 μn filtration. The experimental approach comprises interactions with organic – and inorganic ligands, speciation schemes, biological experiments and interactions with particles and colloids. To illustrate one type of speciation research, i.e. the determination of the apparent complexation capacity for copper (CC Cu ) and the conditional stability constant (K′), examples are given for three marine areas, viz. the Scheldt estuary, the Southern Bight of the North Sea and the open north Atlantic Ocean. A hypothetical model is presented giving the complexation capacity across the land-sea boundery : from river to ocean.

It has been established that 1-(2-phenyl-2-hydroxyiminoethyl)-1-quinolinium chloride, 1-(2-phenyl-2-hydroxyiminoethyl)-1-isoqui-nolinium chloride, 1-(2-phenyl-2-hydroxyiminoethyl)-1-(4′-methyl)-quinolinium chloride and 1-(2-phenyl-2-hydroxyiminoethyl)-1-(6′-methyl)quinolinium chloride react with palladium(II) chloride in the pH range 3.3–7.1 and form yellow water-soluble 1∶1 complexes with maximum absorbance at 413 nm. The conditional stability constants of the complexes at the optimum pH of 6.5 are all about 104.7, and the molar absorptivities are in the range 2.2–2.6×103 l·l mole−1·cm−1 at pH 6.5 and 413 nm. Beer's law is obeyed up to 3–4×10−4M oxime concentration, depending on the oxime determined.

The nonlinear stability of the rotating Benard problem for a binary mixture is investigated through the Lyapunov direct method. It is showen that the stability conditions obtained for a homogeneous fluid are sufficient for the nonlinear stability in the case of a mixture. It is also proved the coincidence of linear and nonlinear conditional stability parameters for Taylor numbers less or equal than 80π4, Prandtl and Schmidt numbers greater or equal than l. Die nichtlineare Stabilitat des rotierenden Benard-Problems fur eine binare Mischung wird mit der direkten Ljapunov-Methode untersucht. Es wird gezeigt, das die erhaltenen Stabilitatsbedingungen fur ein homogenes Fluid fur nichtlineare Stabilitat im Falle einer Mischung hinreichend sind. Es wird ebenfalls die Ubereinstimmung der linearen und nichtlinearen Stabilitatsparameter-Bedingungen fur Taylor-Zahlen kleiner oder gleich 80π4, der Prandtl- und Schmidt-Zahlen groser oder gleich I bewiesen.

Previous computer models for the estimation of urinary saturation of the salts which form renal stones1,2 are not always reliable because of the use of activity coefficients (at ionic strength higher than 0.1 mol ⋅ dm-3) and of the difficulty of finding in the literature values of stability constants determined at 37°C. In this paper we present an improved model in which conditional stability constants, determined at 37°C and at the actual ionic strengths of the urine, are used.

Various methods have been developed which intend to investigate organic metal speciation by extraction of the inorganic metal fraction or of the combined organic fraction. Extraction techniques, using either liquid/liquid or liquid/solid separating techniques, never obtain 100% recovery of the isolated material, and comparison of such methods can give rather contradictory results. For instance, both Hirose et al. (1982) and Kremling et al. (1981)make use of XAD-2 resin to adsorb the dissolved organic fraction. Kremling et al. (1981) studied the effect of pH on the adsorption efficiency and found that at pH 2 more organic material was collected than at neutral pH. Also the collected organic copper fraction was found to be greater at low pH (3%) than at neutral pH (7%) even though one might expect a considerable degree of complex dissociation at low pH. Hirose et al. (1982) on the other hand found a much greater organic copper fraction at the natural pH, of around 98%. It is evidently advisable to determine metal speciation in situ, i.e. without any preceding concentration procedures.

Carminic acid forms red fluorescent complexes with molybdenum(VI) and tungsten(VI) which provide spectrofluorimetric methods for the determination of these metals in the range 0.1–0.9 ppm and 0.4–0.36 ppm at pH 5.2 and 4.6 respectively. The optimum conditions for the analytical procedures have been established, and the effects of a wide range of cations and anions have been investigated. The reagent forms 1:1 complexes with both molybdenum and tungsten, and the conditional stability constants have been evaluated.

Arsenazo III is proposed as metallochromic indicator for calcium in slightly alkaline medium. The visual titration with EDTA was performed at pH 8 and 40 μg—12 mg of calcium were determined. The interference of some ions was considered and it was found that phosphate does not interfere appreciably. Spectrophotometric detection of the end-point was used for titration of calcium in the presence of magnesium at pH 9. For the estimation of the titration error, the conditional stability constants of the calcium—arsenazo III complex were found.

A potentiometric determination of the stability constants of lead(II)-dithiocarbaminoacetic acid complexes has been made. Potentiometric data have been used for estimating the maximum number of co-ordinated ligands. After graphical solution of the Fronaeus integral, the relationship between the concentration variables has been found, and the curve-fitting method, in which both variables are normalised, has been used for determining the stability constants. The values found are log beta(1) = 7.32 +/- 0.12 and log beta(2) = 13.03 +/- 0.20 (mu = 0.1; 25 degrees ). From these data, the relationship between the conditional stability constant logbeta(2)' and pH has been calculated, thus furnishing a full description of TCA as a masking agent for lead ions.

System theory methods are developed and applied within the two-port modeling approach to the problem of thermo-acoustic instability in a combustion appliance. An analogy between thermo-acoustics of combustion and small-signal operation of microwave amplifier is utilized. Notions of unconditional and conditional stabilities of an (active) two-port, representing a burner with flame, are introduced and analyzed. Unconditional stability of two-port means the absence of autonomous oscillation at any embedding of the given two-port by any passive network at the system’s upstream (source) and downstream (load) sides. It has been shown that for velocity-sensitive compact burner in the limit of zero Mach number the condition of unconditional stability cannot be fulfilled. The analysis is performed in the spirit of a known criterion in microwave network theory, the so-called Edwards-Sinsky’s criterion. Therefore, two methods have been applied to originate the necessary and sufficient conditions of a linear active two-port system to be conditionally stable. The first method is a new algebraic technique to prove and derive the conditional and unconditional stability criteria, and the second method is based on certain properties of Mobius (bilinear) transformations for combinations of reflection coefficients and scattering matrix of (active) two-ports. The developed framework allows formulating design requirements for the stabilization of operation of a combustion appliance via purposeful modifications of either the burner properties or/and of its acoustic embeddings.

The dependence of the colour intensity of the iron(III)-thiocyanate complex formed at two different ratios of thiocyanate to iron on the nature and concentration of the acid anion was studied. Four different acids were tested over the concentration range 0.05–1.0 N: perchloric acid, nitric acid, hydrochloric acid and sulphuric acid. Fading of the iron(III)-thiocyanate colour was ascribed to a specific effect of the anion caused by progressive masking of iron(III) ions of the highly dissociated iron(III)-thiocyanate by the more strongly complexing anion ligand. The results were interpreted in the light of the calculated values of side-reaction coefficients between iron(III) and the added ligand, as well as on the magnitude of conditional stability constants of iron(III)-thiocyanate in the various media. That the order of effectiveness of the added anions towards complexing iron(III) ions is SO42– > Cl– > NO3– ClO4– was further substantiated.

A method based on potentiometric stripping analysis (PSA) for the study of the complexation of lead by casein is described. The procedure allows the determination of the conditional stability constant of the complex, the complexation capacity and the number of binding sites of the protein. The advantage of using a flow PSA system equipped with a carbon fibre electrode is also demonstrated.

The fluorescence reactions of magnesium with three quadridentate azomethine ligands have been compared in semi- and non-aqueous media. The reactions of one of these ligands, NN′-bis-salicylidene-2,3-diaminobenzofuran, with other metal ions have been related to its stereochemistry. The dependence of the fluorescence intensity of the metal chelate on the ionic radius of the metal has been discussed and the structure and conditional stability constant of the magnesium complex of this ligand have been determined.

In this paper, we consider the problem for identifying the unknown source in the Poisson equation in a half unbounded domain. A conditional stability result is given and a quasi-boundary value regularization method is presented to deal with this problem. For the regularization solution, the Holder type stability estimate between the regularization solution and the exact solution is given. Numerical results are presented to illustrate the accuracy and efficiency of this method. MSC:35R25, 47A52, 35R30.