Effect of chromatographic parameters and detector settings on the response of HILIC-evaporative light-scattering detection system using experimental design approach and multicriteria optimization methodology

Four polar compounds, i.e. pantothenic acid, inositol, taurine and caffeine were used as probe solutes in conjunction with chemometric methods to find out meaningful implications of chromatographic conditions and detector settings on the system performance. Putting a premium on the conditions of hydrophilic interaction liquid chromatography (HILIC) and settings of evaporative light-scattering detection (ELSD), we scrutinize the importance of certain factors on signal-to-noise ratio and its variability. The application of a central composite design reveals that caffeine, which sublimes, differentiates from the relatively thermosensitive pantothenic acid as well as from inositol and taurine, which are thermostable, do not sublime and have high melting points. It seems that prior knowledge of solute characteristics is critical to estimate the chromatographic response as a function of chromatographic conditions and detection settings. Reducing the responses to just one by combining them “ad hoc”, results in an overall desirability function, which brings out the global optimal chromatographic conditions and detector settings.     

Comprehensive Analysis of LC/MS Data Using Pseudocolor Plots

We have developed new applications of the pseudocolor plot for the analysis of LC/MS data. These applications include spectral averaging, analysis of variance, differential comparison of spectra, and qualitative filtering by compound class. These applications have been motivated by the need to better understand LC/MS data generated from analysis of human biofluids. The examples presented use data generated to profile steroid hormones in urine extracts from a Cushing’s disease patient relative to a healthy control, but are general to any discovery-based scanning mass spectrometry technique. In addition to new visualization techniques, we introduce a new metric of variance: the relative maximum difference from the mean. We also introduce the concept of substructure-dependent analysis of steroid hormones using precursor ion scans. These new analytical techniques provide an alternative approach to traditional untargeted metabolomics workflow. We present an approach to discovery using MS that essentially eliminates alignment or preprocessing of spectra. Moreover, we demonstrate the concept that untargeted metabolomics can be achieved using low mass resolution instrumentation.      

Sensitive determination of pesticides residues in wine samples with the aid of single-drop microextraction and response surface methodology

The multi-residue trace-level determination of six pesticides (diazinon, dimethoate, chlorpyrifos, vinclozolin, fenthion and quinalphos) in wine samples, after their single-drop microextraction (SDME) is presented herein. The extraction procedure was optimized using the multivariate optimization approach following a two-stage process. The first screening experimental design brought out the significant parameters and was followed by a central composite design (CCD) experiment, which revealed the simultaneous effect of the significant factors affecting the SDME process. High level of linearity for all target analytes was recorded with r² ranging between 0.9978 and 0.9999 while repeatability (intra-day) and reproducibility (inter-day) varied from 5.6% to 7.4% and 4.9% to 12.5%, respectively. Limits of detection (LODs) and limits of quantification (LOQs) were found to range in the low μg L⁻¹ level. In general, the developed methodology presented simplicity and enhanced sensitivity, rendering it appropriate for routine wine screening purposes.     

Bare Clusters Derived from Protein Templates: Au25+, Au38+ and Au102+

A discrete sequence of bare gold clusters of well‐defined nuclearity, namely Au₂₅⁺, Au₃₈⁺ and Au₁₀₂⁺, formed in a process that starts from gold‐bound adducts of the protein lysozyme, were detected in the gas phase. It is proposed that subsequent to laser desorption ionization, gold clusters form in the gas phase, with the protein serving as a confining growth environment that provides an effective reservoir for dissipation of the cluster aggregation and stabilization energy. First‐principles calculations reveal that the growing gold clusters can be electronically stabilized in the protein environment, achieving electronic closed‐shell structures as a result of bonding interactions with the protein. Calculations for a cluster with 38 gold atoms reveal that gold interaction with the protein results in breaking of the disulfide bonds of the cystine units, and that the binding of the cysteine residues to the cluster depletes the number of delocalized electrons in the cluster, resulting in opening of a super‐atom electronic gap. This shell‐closure stabilization mechanism confers enhanced stability to the gold clusters. Once formed as stable magic number aggregates in the protein growth medium, the gold clusters become detached from the protein template and are observed as bare Au_n⁺ (n=25, 38, and 102) clusters.     

Improved method for the in vitro assessment of antioxidant activity of plant extracts by headspace solid-phase microextraction and gas chromatography-electron capture detection

The simultaneous monitoring of malondialdehyde, pentanal and hexanal, final products of lipid peroxidation is reported, using a headspace solid-phase microextraction (HS-SPME) technique with on-fibre derivatisation. The aldehydes are extracted and subjected to on-sorbent derivatisation into stable hydrazones with 2,4,6-trichlorophenylhydrazine (TCPH) and analyzed. The degree of inhibition of oxidation is performed by monitoring the chlorinated hydrazones after thermal desorption, by gas chromatography-electron capture detection. The procedure was employed to evaluate in vitro the antioxidant activity of Hypericum perforatum L. extracts and of the well-known antioxidant vitamin E following induction of oxidation of sunflower oil, as a model lipid system. Prior to the measurement of antioxidant activity, the optimal process conditions, i.e. headspace volume, temperature, agitation, extraction/derivatisation time and desorption time and temperature were properly established. Aqueous extracts of H. perforatum L. exhibited the highest antioxidative effect. The method is shown to be promising for screening purposes for antioxidant substances and natural extracts.     

Respiratory deficiency enhances the sensitivity of the pathogenic fungus Candida to photodynamic treatment

Mucosal infections caused by the pathogenic fungus Candida are a significant infectious disease problem and are often difficult to eradicate because of the high frequency of resistance to conventional antifungal agents. Photodynamic treatment (PDT) offers an attractive therapeutic alternative. Previous studies demonstrated that filamentous forms and biofilms of Candida albicans were sensitive to PDT using Photofrin as a photosensitizer. However, early stationary phase yeast forms of C. albicans and Candida glabrata were not adversely affected by treatment. We report that the cationic porphyrin photosensitizer meso-tetra (N-methyl-4-pyridyl) porphine tetra tosylate (TMP-1363) is effective in PDT against yeast forms of C. albicans and C. glabrata. Respiratory-deficient (RD) strains of C. albicans and C. glabrata display a pleiotropic resistance pattern, including resistance to members of the azole family of antifungals, the salivary antimicrobial peptides histatins and other types of toxic stresses. In contrast to this pattern, RD mutants of both C. albicans and C. glabrata were significantly more sensitive to PDT compared to parental strains. These data suggest that intact mitochondrial function may provide a basal level of anti-oxidant defense against PDT-induced phototoxicity in Candida, and reveals pathways of resistance to oxidative stress that can potentially be targeted to increase the efficacy of PDT against this pathogenic fungus.     

BV solutions for hyperbolic systems of balance laws with relaxation

For hyperbolic systems of balance laws with source manifesting relaxation, it is shown that the Kawashima condition, which yields global classical solutions with smooth initial values near equilibrium, is also instrumental in inducing the existence of global admissible BV solutions, accommodating shocks.     

Examining Optimal Criterion Weights in Mixed Integer Programming Approaches to the Multiple-group Classification Problem

Several mixed integer programming approaches to the multiple-group statistical classification problem are examined. Many papers have investigated conditions under which a degenerate solution occurs in linear programming approaches to the two-group discriminant problem. Very little research has been conducted in the multiple-group case. We investigate conditions under which a degenerate solution can occur in mixed integer programming approaches to the multiple-group classification problem. A multiple-group ‘minimize the sum of deviations’ model is presented. This model is similar in structure to the general single function classification model. Also, a two-goal approach to the multiple-group classification problem is discussed.