The challenge of optimizing expensive black boxes: a scatter search/rough set theory approach

There is renewed interest in the development of effective and efficient methods for optimizing models of which the optimizer has no structural knowledge. This is what in the literature is referred to as optimization of black boxes. In particular, we address the challenge of optimizing expensive black boxes, that is, those that require a significant computational effort to be evaluated. We describe the use of rough set theory within a scatter search framework, with the goal of identifying high-quality solutions with a limited number of objective function evaluations. The rough set strategies that we developed take advantage of the information provided by the best and diverse solutions found during the search, in order to define areas of the solution space that are promising for search intensification. We test our procedure on a set of 92 nonlinear multimodal functions of varied complexity and size and compare the results with a state-of-the-art procedure based on particle swarm optimization.     

Evaluation of two sample treatment methodologies for large-scale pesticide residue analysis in olive oil by fast liquid chromatography–electrospray mass spectrometry

In this study, a comprehensive evaluation of two simple sample treatment methodologies has been carried out for the development of large-scale multi-residue methods for pesticide testing in olive oil. The proposed methodologies are based on (a) liquid–liquid partitioning with acetonitrile followed by dispersive solid-phase extraction clean-up using graphitized carbon black, primary-secondary amine and C₁₈ sorbents; (b) liquid partitioning with acetonitrile saturated with petroleum ether followed by matrix solid-phase dispersion (MSPD) using aminopropyl as sorbent material and a Florisil cartridge for final clean-up in the elution step. To evaluate the proposed sample treatment methodologies, 105 representative multi-class pesticides were studied using fast liquid chromatography–electrospray time-of-flight mass spectrometry (LC–TOFMS). For validation purposes, recoveries studies were carried out at 10 and 100 μg kg⁻¹ levels, yielding recovery rates in the range 70–130% for 72% of analytes using liquid–liquid procedure and for 57% analytes using MSPD procedure. The LC–MS method provided good linearity, precision and accuracy. The limits of detection obtained were lower than 10 μg kg⁻¹ for more than 85% analytes using both sample treatment methodologies. In addition, minor matrix effects (i.e. signal suppression or enhancement ≤20%) were observed in ca. 70% of the studied compounds. Data obtained shows that both sample treatment methodologies proposed can be successfully applied for large-scale pesticide testing in olive oil samples, showing the ability to quickly detect trace amount of over one hundred target species with different physicochemical properties, without requiring expensive instrumentation for sample treatment step and involving relatively low amounts of solvent consumption and waste generation.     

A novel method for the determination of total 1,3-octanediols in apple juice via 1,3-dioxanes by solid-phase microextraction and high-speed gas chromatography

In this work, a novel, simple and fast method based on solid-phase microextraction (SPME) followed by high-speed gas chromatography (HSGC) was developed for the analysis of total 1,3-octanediols in apple juices by means of derivatization reaction to volatile 1,3-dioxanes. The derivatization reaction, SPME conditions, glycosidically bound fraction and 1,3-nonanediol as a surrogate standard were studied. The formation of 1,3-dioxanes from 1,3-diols was confirmed by GC–MS. The method was validated obtaining a regression coefficient (r²) of 0.9996, precisions between 0.3 and 9.8%, extraction recoveries in the range 94.7–112.2% and LOD of 2.9 μg l⁻¹. Experimental design has been employed in the optimization of extraction factors and robustness assessment. The method was applied to the analysis of 21 Asturian apple varieties finding a double reciprocal relationship between the concentrations of saturated and unsaturated 1,3-octanediol.     

Synthesis,characterization and olefin hydroformylation reactions of <Emphasis Type="Italic">mer</Emphasis>-[Mo(CO)<Subscript>3</Subscript>(p-C<Subscript>5</Subscript>H<Subscript>4</Subscript>N-CN)<Subscript>3</Subscript>]

Mer-[Mo(CO)₃(p-C₅H₄N-CN)₃] was prepared by UV-irradiation of a THF solution of Mo(CO)₆ and para-cyanopyridine under heating. The complex was characterized by FT-IR, MS, ¹H and ¹³C NMR and showed catalytic activity for olefin hydroformylation (1-hexene, cyclohexene and 2,3-dimethyl-2-butene as model olefins; 600 psi synthesis gas (pCO/pH₂ = 1); 100 °C; 24 h; toluene). An examination of the complex catalyzed hydroformylation of a real naphtha cut (El Palito refinery, Venezuela), under the same conditions, also showed activity in the conversion to oxygenated products.     

Thermal Analysis,Quantum Chemical Calculations,and Structural Characterization by Single Crystal Synchrotron Radiation of a Monoclinic Polymorph of Citraconic acid

Abstract  

The crystal structure of a monoclinic polymorph of methyl maleic acid (citraconic acid, polymorph II) was determined using single crystal synchrotron data from a small fragment extracted from the reagent bottle. The material crystallizes in space group P2₁/c with unit cell parameters a = 8.109(2), b = 7.090(2), c = 10.709(3) ?, β = 114.148(16)°, V = 561.8(3) ?³, Z = 4, d _c = 1.538 g cm⁻³. In this polymorph, the carboxylic group with the α-methyl group participates in cyclic hydrogen bonds with graph set symbol R₂² (8) R_{2}^{2} (8) , while the other carboxylic group participates in a hydrogen bonding pattern represented by the C(4) graph set symbol. In contrast, in a previously reported polymorph (polymorph I) obtained by slow evaporation from ethyl acetate, both carboxylic groups participate in cyclic hydrogen bonding motifs. Thermal analysis suggests that the transformation of polymorph II into polymorph I is monotropic.     

Absolute Configuration of Two Eudesmane Derivatives from <Emphasis Type="Italic">Verbesina turbacensis</Emphasis> H.B.K.

Abstract  

Two compounds isolated from the aerial parts of Verbesina turbacensis H.B.K, are reported in this work. Both compounds crystallize in the orthorhombic system, space group P2₁2₁2₁. Compound (1), 6β-[cinnamoyloxy]-3β,4α-dihydroxyeudesmane, formula C₂₄H₃₄O_4, has unit cell parameters a = 9.6234(2), b = 12.3137(3) and c = 18.6277(5) Å, V = 2207.38(9) Å³, Z = 4. On the other hand, 6β-[cinnamoyloxy]-eudesman-15-oic acid (2), formula C₂₄H₃₂O_4, has cell parameters a = 8.7035(3), b = 14.2020(4), c = 17.1590(5) Å, V = 2120.97(11) Å³, Z = 4.     

Evaluation of different sample extraction strategies for selenium determination in selenium-enriched plants (Alliumsativum and Brassicajuncea) and Se speciation by HPLC-ICP-MS

Several sample extraction techniques have been evaluated in order to obtain highest selenium (Se) extraction efficiency in two types of selenium-enriched plants (Allium sativum and Brassica juncea). Three extracting solutions have been studied for this purpose: 0.1 M HCl, 25 mM ammonium acetate buffer (pH 5.6) and protease in aqueous solution. In each case, the effect of the ultrasonic probe during extraction was also evaluated. Selenium extraction yields were calculated based on the ICP-MS determination of the total selenium content in the corresponding extracts and in the plant tissue after its microwave digestion. The action of ultrasounds allowed the reduction on the extraction time while maintaining good Se recoveries (which ranged from 75 to 120% of the total Se in the plant). The accuracy of total Se determination was controlled by analyzing a reference material (aquatic plant, BCR-670). On the other hand, speciation studies of the extracts were carried out by using ion-pairing reversed phase and size exclusion/ion exchange (Shodex Asshipak) liquid chromatographic columns. The two separation mechanisms were suitable to isolate the main extractable Se species which were identified as Se-methyl selenocysteine and Se-methionine in both systems. The extracts of both plants (A. Sativum and B. juncea) exhibited also the presence of several unknown Se-species.     

Enzymatic rotating biosensor for ciprofloxacin determination

The high sensitivity that can be attained using an enzymatic system and mediated by catechol has been verified by on-line interfacing of a rotating biosensor and continuous flow/stopped-flow/continuous-flow processing. Horseradish peroxidase, HRP [EC 1.11.1.7], immobilized on a rotating disk, in the presence of hydrogen peroxide, catalyzed the oxidation of catechol, whose back electrochemical reduction was detected on a glassy carbon electrode surface at −200 mV. Thus, when ciprofloxacin (CF) was added to the solution, this piperazine-containing compound participate in Michael addition reactions with catechol to form the corresponding piperazine-quinone derivatives, decreasing the peak current obtained, in proportion with the increase of its concentration. The highest response for CF was obtained around pH 7. This method could be used to determine CF concentration in the range of 0.02-65 μM (r = 0.999). The determination of CF concentration was possible with a detection limit of 0.4 nM, in the processing of as many as 25 samples per hour. Application of this analysis to different pharmaceutical samples containing CF supports the utility of the HRP-rotating biosensor.     

The potential of combining solid-phase optosensing and multicommutation principles for routine analyses of pharmaceuticals

In this work, we have explored the analytical potential of combining solid-phase optosensing and multicommutation principles, applied to the field of routine analyses of pharmaceuticals. This marriage benefits from the advantaging features of both concepts: the ability of multicommutation to provide increased repeatability, easier sample handling, reduced sample and reagent consumption as well as minor waste generation, combined with the enhancement of both sensitivity and selectivity obtained when a solid support is used to carry out the spectroscopic measurements directly on it. This approach has been evaluated by developing a method for the simultaneous analysis of two active principles (piroxicam and pyridoxine) in pharmaceutical formulations, using a non-polar sorbent as a solid support to attain the separation and subsequent preconcentration/detection of the targeted analytes. A multicommutated flow-through multisensor based on the direct intrinsic solid-phase UV absorbance measurements of the analytes on a packed C₁₈ silica gel bed was then thoroughly developed. The usefulness of this approach was assessed when it was applied to the determination of piroxicam and pyridoxine in different pharmaceutical formulations obtaining remarkable results.