New methods for the direct determination of dissolved inorganic, organic and total carbon in natural waters by Reagent-Free Ion Chromatography and inductively coupled plasma atomic emission spectrometry

New methods have been developed and applied successfully for the determination of dissolved inorganic, organic and total carbon in water samples. The new methods utilize two instrumental setups, Reagent-Free™ Ion Chromatography (RF™-IC) and inductively coupled plasma atomic emission spectrometry (ICP-AES). Dissolved inorganic carbon (DIC) was measured in untreated samples along with Cl⁻, F⁻ and SO₄²⁻ using RF™-IC and by in-line mixing with 0.1 M HNO₃ to enhance CO₂ removal in the nebulizer, followed by ICP-AES analysis. Total dissolved carbon (TDC) was measured by in-line mixing with 0.1 M NaOH following ICP-AES analysis. Dissolved organic carbon (DOC) was obtained as the difference between DIC and TDC. Only non-volatile organic carbon could be detected by the present method. The workable limits of detection obtained in the present study were 0.5 mM (RF™-IC) and 0.1 mM (ICP-AES) for dissolved inorganic and organic carbon, respectively. The power of the new methods lies in routine analysis of DIC and DOC in samples of natural waters of variable composition and salinity using analytical techniques and facilities available in most laboratories doing water sample analysis. The techniques are sensitive and precise, can be automated using gas-tight sample vials and auto-samplers, and are independent of most elemental interferences with the exception of chloride overload by saline samples when using RF™-IC. The new methods were successfully applied for analysis of DIC and DOC in selected samples of natural and synthetic waters.     

Hexakis(urea‐κO)zinc(II) dinitrate at 110 and 250 K: uniaxial negative thermal expansion

The crystal structure of the title compound, [Zn{CO(NH₂)₂}₆](NO₃)₂, has been determined at 110 and 250 K. The structure is stabilized by 12 individual hydrogen bonds, both intra‐ and intermolecular. Analysis of the thermal expansion tensor, based on unit cells determined over a temperature range of 180 K, shows uniaxial compression in the direction of the b axis during warming. The hydrogen bonds form layers perpendicular to this axis and these layers are connected by coordinative bonds parallel to the axis. As expected, the intermolecular hydrogen bonds expand during warming. Surprisingly, the coordinative bonds contract, accompanied by changes in the O—Zn—O angles. Overall, this behaviour can be described as an accordion‐like effect.     

Comparison of sample preparation methods based on proteolytic enzymatic processes for Se-speciation of edible mushroom (Agaricus bisporus) samples

A sequential sample preparation process was developed for the speciation analysis for Se-enriched edible mushroom, Agaricus bisporus containing 110.2 mug of total Se/g sample. Five different sample extraction methods were compared and the most efficient method (a three-step process involving the use of water extraction and two proteolytic enzymes - pepsin and trypsin) proved to be the most suitable for extracting selenium, with an extraction efficiency of 75%. As the analogues of these enzymes play an important role in human digestion the bioavailability of the selenium present in the sample was estimated. Selenocystine (SeCys(2)) and Se(IV) were detected in considerable amounts (27.7 mug Se/g sample and 46.4 mug Se/g sample, respectively). For the quality control of peak identification a spiking procedure was developed, using a low selenium mushroom containing 4.3 mug of total Se/g sample. During the analysis with HPLC-HHPN (Hydraulic High Pressure Nebuliser)-AFS complicated background effects and matrix problems were observed: stable and reproducible signals generated by the low selenium mushroom and the compounds used in sample preparation were detected. The three-step sample preparation method connected with the HPLC-HHPN-AFS system proved to be applicable for the speciation analysis of the Se-enriched Agaricus bisporus.     

Strong equilibria in claim games corresponding to convex games

This paper deals with a specific aspect of the problem of coalition formation in a situation described by a TU-game. First, we define a very simple normal form game which models the process of coalition formation. To define the payoff functions of the players we use an allocation rule for TU-games. The main objective of this paper is ascertain what conditions of the allocation rule lead to the grand coalition being a strong equilibrium of the normal form game, when the original TU-game is convex. Received January 1996/Revised version December 1996/Final version May 1997     

Drop out monotonic rules for sequencing situations

This note introduces a new monotonicity property for sequencing situations. A sequencing rule is called drop out monotonic if no player will be worse off whenever one of the players decides to drop out of the queue before processing starts. This intuitively appealing property turns out to be very strong: we show that there is at most one rule satisfying both stability and drop out monotonicity. For the standard model of linear cost functions, the existence of this rule is established.     

Various characterizations of convex fuzzy games

This note enlarges the literature on convex fuzzy games with new characterizing properties of such games besides the increasing average marginal return property, namely: the monotonicity of the first partial derivatives, the directional convexity and forC ²-functions the non-negativity of the second order partial derivatives.     

The core and related solution concepts for infinite assignment games

Assignment problems where both sets of agents that have to be matched are countably infinite, the so-called infinite assignment problems, are studied as well as the related cooperative assignment games. Further, several solution concepts for these assignment games are studied. The first one is the utopia payoff for games with an infinite value. In this solution each player receives the maximal amount he can think of with respect to the underlying assignment problem. This solution is contained in the core of the game. Second, we study two solutions for assignment games with a finite value. Our main result is the existence of core-elements of these games, although they are hard to calculate. Therefore another solution, the f-strong ε-core is studied. This particular solution takes into account that due to organisational limitations it seems reasonable that only finite groups of agents will eventually protest against unfair proposals of profit distributions. The f-strong ε-core is shown to be nonempty. These authors’ research is partially supported by the Generalitat Valenciana (Grant number GV-CTIDIA-2002-32) and by the Government of Spain (through a joint research grant Universidad Miguel Hernández — Università degli Studi di Genova HI2002-0032).