Sequencing games without initial order

In this note we study uncertainty sequencing situations, i.e., one-machine sequencing situations in which no initial order is specified. We associate cooperative games with these sequencing situations, study their core, and provide links with the classic sequencing games introduced by Curiel et al. (Eur J Oper Res 40:344–351, 1989). Moreover, we propose and characterize two simple cost allocation rules for uncertainty sequencing situations with equal processing times.     

Chemistry of dithiocarbamate derivatives of amino acids. Part II. Complexes of nickel(II) with derivatives of branched and cyclic amino acids

Summary Barium salts of the dithiocarbamate derivates of the amino acids: DL-valine, L-valine, DL-leucine, DL-isoleucine and L-proline have been synthesized. The anions have been used to obtain the corresponding nickel(II) complexes in acid form. The complexes are diamagnetic, and coordination takes place in a near-square planar geometry around the nickel(II) ion through the sulphur atoms of the dithiocarbamate moiety, the structure being confirmed by i.r.,¹H n.m.r., u.v.-vis spectros copies and by chemical analysis.No significant difference has been found between the physicochemical properties (i.r. and 'H n.m.r. spectra and magnetic properties) of the complexes prepared from the dithiocarbamate derivatives of DL- and L-valine, but d-d bands in the u.v.-vis spectra show a slight different intensity.     

Coupling Cloud Point Extraction to Instrumental Detection Systems for Metal Analysis

The purpose of this article is to review and evaluate cloud point extraction of metals and its coupling to different contemporary instrumental methods of analysis. This review covers a selection of the literature published on this topic over the period mainly between 1997 and September 2005 (consisting of 50 publications). The current state of the art for CPE concerning metals and metal chelates is presented with special emphasis on the hyphenation of this interesting extraction/preconcentration approach mediated by surfactants to spectrophotometry, atomic spectroscopy and separation techniques. We present contemporary CPE developments concerning metal speciation and determination and their application to different environmental, clinical, geological and food samples. Strategies for method development as well as future perspectives are also covered.     

Automatic kinetic determination of Hg(II) by anodic stripping potentiometry with constant current oxidation

A new kinetic method for the determination of Hg(II) is proposed. It is based on the kinetic evolution of the anodic stripping potentiometric curves yielded by a gold electrode previously coated with mercury upon passage of constant electrical currents. The method features a linear determination range between 40 and 800 ppb of Hg(II) and a relative standard deviation of 5% (n = 9) for a mercury concentration of 200 ppb. The experiments were conducted on a customized automatic set-up, and instrumentation, data acquisition and processing were all governed by means of a QBASIC program (PSAKINEL) written by the authors.     

A multisyringe flow-through sequential extraction system for on-line monitoring of orthophosphate in soils and sediments

A fully automated flow-through microcolumn fractionation system with on-line post-extraction derivatization is proposed for monitoring of orthophosphate in solid samples of environmental relevance. The system integrates dynamic sequential extraction using 1.0 mol l⁻¹ NH₄Cl, 0.1 mol l⁻¹ NaOH and 0.5 mol l⁻¹ HCl as extractants according to the Hieltjes-Lijklema (HL) scheme for fractionation of phosphorus associated with different geological phases, and on-line processing of the extracts via the Molybdenum Blue (MB) reaction by exploiting multisyringe flow injection as the interface between the solid containing microcolumn and the flow-through detector. The proposed flow assembly, capitalizing on the features of the multicommutation concept, implies several advantages as compared to fractionation analysis in the batch mode in terms of saving of extractants and MB reagents, shortening of the operational times from days to hours, highly temporal resolution of the leaching process and the capability for immediate decision for stopping or proceeding with the ongoing extraction. Very importantly, accurate determination of the various orthophosphate pools is ensured by minimization of the hydrolysis of extracted organic phosphorus and condensed inorganic phosphates within the time frame of the assay. The potential of the novel system for accommodation of the harmonized protocol from the Standards, Measurement and Testing (SMT) Program of the Commission of the European Communities for inorganic phosphorus fractionation was also addressed. Under the optimized conditions, the lowest detectable concentration at the 3σ level was ≤0.02 mg P l⁻¹ for both the HL and SMT schemes regardless of the extracting media. The repeatability of the MB assay was better than 2.5% and the dynamic linear range extended up to 7.0 mg P l⁻¹ in NH₄Cl and NaOH media and 15 mg P l⁻¹ whenever HCl is utilized as extractant for both the HL and SMT protocols.     

Flow-through optical fiber sensor for automatic sulfide determination in waters by multisyringe flow injection analysis using solid-phase reflectometry

A software-controlled flow-through optical fiber diffuse reflectance sensor capitalized on the implementation of disk-based solid-phase pre-concentration schemes in a multisyringe flow injection analysis (MSFIA) set-up is proposed for the trace determination of sulfide in environmental waters and wastewaters. The fully automated flowing methodology is based on Fischer's coupling reaction of sulfide with N,N-dimethyl-p-phenylenediamine (DMPD) in the presence of Fe(iii) as oxidizing reagent in a 0.5 M HCl medium. The on-line generated methylene blue dye is subsequently delivered downstream to a dedicated optode cell furnished with an octadecyl-chemically modified (C(18)) disk, while continuously recording the diffuse reflectance spectrum of the pre-concentrated compound. A double regeneration protocol is finally executed to warrant minimum background noise and negligible baseline. Under the optimized chemical and hydrodynamic conditions, the optosensing MSFIA method features coefficients of variation better than 0.7%(n= 10) at 50 microg l(-1) concentration, a linear working range of 20-200 microg l(-1) sulfide, a 3sigma(blank) detection limit of 2.9 microg l(-1) sulfide and an injection throughput of 8 h(-1) for a pre-concentration sample volume of 2.9 ml. The interfacing of the robust and versatile multisyringe flow injection-based optode with a plug-in spectrophotometer furnished with a light emitting diode assures the miniaturization of the overall flow analyzer, which is, thus, readily adaptable to real-time monitoring schemes. The potential of the multisyringe flow method was assessed via the determination of sulfide traces in water samples of different complexity (namely, freshwater, seawater and wastewater).     

Synthesis of different chiral amino gamma-butyrolactones and amino gamma-butenolides

Different transformations of chiral epoxy esters 1 afford two different amino gamma-butyrolactones 2 and 6, and amino gamma-butenolides 8, by different nucleophilic opening-closing processes. [reaction: see text]     

Valgran, a program for potentiometric titrations with a versatile automatic modular system

A very flexible modular system for use with a portable IBM PC for potentiometric titrations is described. The appropriate software has been developed in order to obtain automatic end-points, and conventional, first-derivative, second-derivative and Gran curves, as well as a listing of the potentiometric points expressed in different ways. All these alternatives are selectable on menu presentations. The potentiometric system has been applied both the research and routine problems.     

Pyrrolodiazines. 2. Structure and Chemistry of Pyrrolo[1,2-a]pyrazine and 1,3-Dipolar Cycloaddition of Its Azomethine Ylides

A new synthesis of the pyrrolo[1,2-a]pyrazine system from pyrrole is described. In light of the ab initio calculations carried out on this heterocyclic system some of its basic chemistry was investigated and included electrophilic substitution, addition of organolithium reagents, metalation with lithium diisopropylamide and subsequent reaction with electrophiles, and formation of salts by quaternization of the nonbridgehead nitrogen. N-ylides obtained from these salts undergo 1,3-dipolar cycloaddition with suitable dipolarophiles to give dipyrrolo[1,2-a]pyrazines, pyrazolo[1,5-a]-pyrrolo[2,1-c]pyrazines, and heterobetaines. Examples of intramolecular 1,3-dipolar cycloadditions are also reported.     

Spectrophotometric determination of silicate with Rhodamine B by flow-injection analysis

A spectrophotometric flow-injection method for the determination of silicate based on the formation of an ion pair between molybdosilicic acid and Rhodamine B is proposed. It allows silicate to be determined over the concentration range 0.17–2.0 mg 1^?1 at a sampling rate of 40 h^?1, is reasonably precise and is highly tolerant to ions that commonly occur in waters. It has been applied with satisfactory results to the determination of silicate in various types of water.