Identification of novel illicit amphetamines from vapor-phase FTIR spectra - a chemometrical solution

A computer-aided procedure automating the identification of illicit amphetamine analogs eluting from a gas chromatograph coupled to a Fourier transform infrared spectrometer is presented. The expert system discriminates novel amphetamines from other classes of drugs of abuse normally screened in illicit tablets or powders. The main analytical advantages of the system over the automated procedures dedicated to general unknown analysis are the objectivity and the accuracy in predicting the class identity of the compound (i.e. stimulant, hallucinogen) when the reference spectrum is not present in the spectral library. The expert system uses quantitative thresholds defining the similarity of the unknown to the classes of illicit amphetamines and checks the presence of the molecular skeletons associated with different psychotropic effects of amphetamines. The challenge in building the system was the fuzziness of vapor-phase Fourier transform infrared spectrometer spectra of low-weight molecules such as amphetamines. This paper emphasizes the chemometrical techniques found most appropriate for modeling such spectral behavior. An exploratory (principal component) analysis indicated the sample preparation and the feature weight function yielding the best input for the knowledge base. The class identity of a compound was assigned using Soft Independent Modeling of Class Analogy. A rule-based decision system was implemented to enhance the accuracy in identity assignment. The flow diagram optimizing the knowledge base content of each model is presented. Finally, up to 81.13% (out of 159 tested compounds) were classified with a 5% confidence level. The total correct classification rate was 93.93%, for a yield of 96.30% true positive amphetamines.     

Techniques in chemometrical modeling for micro-pollutants assessment

Summary Chemometrics have been described as effective tools for exploring chemical data, and many software packages are now available on micro-computers. This work evaluate their suitability for environmental analytical chemistry. Guidelines for multivariate method selection are proposed. They are based on the type of variables and the goal of the study. Two examples are proposed to illustrate these methods and their efficiency. Firstly it is shown that a global assessment of Rhine basin mercuric pollution in the Alsace region is possible with Multiple Correspondence Factor Analysis. Several goals are simultaneously reached: a mapping of pollution, a detection of pollution changes during the study period and an evaluation of bio-accumulation as a function of fish species. Secondly the modeling of industrial soil pollution by heavy metals is studied by Multiple Linear Regression. It demonstrates that chemometrics provide us with necessary tools for environmental analytical chemistry but also for toxicological studies or ecosystem modeling.     

Analytical investigations and chemometrical characterization of polluted soils

Summary Soil samples were taken in the surroundings of an industrial plant with heavy metal emission. A convenient digestion method for the determination of the mobile anthropogenic part of the heavy metal contents of soils was selected. This heavy metal contents were determined by atomic absorption spectrometry. The application of different multivariate statistical methods such as cluster analysis, multi-dimensional variance and discriminant analysis and factor analysis enables the objective characterization of polluted areas and of the degree of pollution as well as the identification of emission sources.     

Heavy metals in river sediments — A chemometrical evaluation

First results are presented to support decisions within projects of recultivation in the Merseburg region. From two places of the river Luppe eight sediment samples were taken at four different days. The total concentrations of Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn were determined by ICP-AES after digestion with aqua regia both in the gross samples and in four particle size fractions obtained by wet sieving. Subsequently each fraction was split into six classes by a sequential extraction to characterise the pattern of heavy metal binding form. Questions about the difference of the regions, the importance of the particle size fractions, the mobility of the metals, and the influence of the seasonal factor were tried to answer by the help of chemometrical methods. It was possible to show that the two sampling places situated only about 7 km from each other have different total metal concentrations as well as different binding form patterns. The trend of the heavy metal enrichment in the smallest particle size fraction can easily be seen in two-dimensional diagrams, but could in general not be confirmed statistically for all metals. The consideration of all four factors together (region, particle size fraction, mobilisation class, and time) shows the significant influence caused by all factors and all interactions. Multivariate covariance analysis is used to include also the influence of sampling conditions.Dedicated on the occasion of his 70th birthday to Professor Dr. Klaus Doerffel, who has spent much of his life in teaching and introducing statistical and other chemometrical techniques in Analytical Chemistry     

Philosophical aspects of chemometrical strategy in Analytical Chemistry

Summary This paper discusses the philosophical aspects of the three main chemometrical strategies in analytical chemistry: statistical data treatment, optimization and modelling, pattern recognition. It is possible by a more general consideration of these approaches to find a proper place of different philosophical categories such as form and content, induction and deduction, concrete and general in analytical chemistry. The philosophical aspect of the considerations allows a deeper penetration into the theoretical basis of chemical analysis.

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Philosophische Betrachtungen zu chemometrischen Strategien in der Analytischen Chemie

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Presented at the First International Symposium on History and Philosophy in Analytical Chemistry, Vienna, November 22–23, 1985     

Endocrine disruption profile analysis of 11,416 chemicals from chemometrical tools

A number of chemicals released into the environment have the potential to disturb the normal functioning of the endocrine system. These chemicals termed endocrine disruptors (EDs) act by mimicking or antagonizing the normal functions of natural hormones and may pose serious threats to the reproductive capability and development of living species. Batteries of laboratory bioassays exist for detecting these chemicals. However, due to time and cost limitations, they cannot be used for all the chemicals which can be found in the ecosystems. SAR and QSAR models are particularly suited to overcome this problem but they only deal with specific targets/endpoints. The interest to account for profiles of endocrine activities instead of unique endpoints to better gauge the complexity of endocrine disruption is discussed through a SAR study performed on 11,416 chemicals retrieved from the US-NCI database and for which 13 different PASS (Prediction of Activity Spectra for Substances) endocrine activities were available. Various multivariate analyses and graphical displays were used for deriving structure-activity relationships based on specific structural features.     

Gravimetric estimation of uranium as oxinate using complexone as a masking agent

Summary The scope of complexone (disodium salt of ethylenediamine tetraacetic acid) as masking agent has been further extended. Uranium is estimated as oxinate in presence of Th, R. E. and Zr. Uranium is also estimated in presence of 100 mg. of Th, and 30 mg. of R. E. respectively in presence of 100 mg. of P₂O₅. Uranium has been separated from V₂O₅ by reducing the latter in mild acid solution with complexone itself.     

Uncertainty estimation to evaluate mass balances on a combustion system

Mass balances of ash and potassium for a fluidized bed combustor were performed incorporating measurement uncertainties. The total output mass of ash or a chemical element should be equal to the mass in the input fuel; however, this is not often achieved. A realistic estimation of recovery uncertainty can support the reliability of a mass balance. Estimation of uncertainty helps to establish a reliable evaluation of the recovery ratio of ash mass and elemental mass. This may clarify whether any apparent lack in closing the mass balance can be attributed to uncertainties. The evaluation of measurement uncertainty for different matrices, namely coal, biomass, sand and ashes from different streams was based on internal quality control data and external quality control data, namely analysis of samples from proficiency tests or use of a certified reference material. The evaluation of intermediate precision and trueness allowed the estimation of measurement uncertainty. Due to the different physic and chemical characteristics of the studied matrices, the uncertainty of precision was evaluated using R-charts of data obtained from the analysis of duplicates for the majority of samples. This allowed evaluating sample heterogeneity effects. The instrumental acceptance criterion was also considered and included in the combined uncertainty. The trueness was evaluated using data from several proficiency tests and from analysis of a certified reference material or sample spiking. Statistically significant bias was included.     

Volumetric estimation of persulphate using arsenite as a primary standard

The method of estimating the persulphate by direct titration using arsenious acid or sodium arsenite as a primary standard has been described.This method consists in taking a mixture of arsenious acid or sodium arsenite and an excess of potassium iodide in the titration mixture. The mixture is heated to 80°C and solid sodium bicarbonate is added. Persulphate solution is run in from a burette and the liberated iodine is instantaneously consumed by trivalent arsenic. At the end-point an excess drop of persulphate gives a yellow colour due to the liberated iodine remaining unreacted. The results are satisfactory and the error lies within permissible limits.     

Tiron as a spectrophotometric reagent for the estimation of osmium

A method for the spectrophotometric determination of osmium with tiron as a reagent has been described. The reagent forms a soluble and stable coloured complex on heating with osmium in the presence of sodium acetate. The regions of maximum and minimum absorptions are at 470 mμ and 410 mμ, respectively, and the system obeys Beer's law from 2 to 32 p.p.m. of osmium. But the optimum range, with the relative analysis error of 2.878% per 1% absolute photometric error, is from 8 to 24 p.p.m. of osmium. The sensitivity of the reaction is 0.033 μg/cm² (SANDELL) and the molar extinction coefficient is 5706. In solution, the complex is formed when the osmium and the reagent are in a ratio of l : 1 ; it has an instability constant equal to approximately 5.57? 10^-5.     

Microemulsion liquid chromatographic method for characterisation of fosinopril sodium and fosinoprilat separation with chemometrical support

The properties of the eluent are the essential factors governing the efficiency in the high-performance liquid chromatography (HPLC) method. A novel approach in retention modelling in the liquid chromatographic separation of fosinopril sodium and its degradation product, fosinoprilat, applying a microemulsion as the mobile phase, was used. The modifications of the mobile phase included the changes to the type of the lipophilic phase, the type and concentration of co-surfactant and surfactant, as well as the pH of the mobile phase. In this study, a full factorial 2³ design, as the optimal method for screening of the experiment, was applied for selecting factors which had an influence on separation. Optimisation was done by a central composite design. An appropriate resolution with reasonable retention times was obtained with a microemulsion containing 0.9% w/w of cyclohexane, 2.2% w/w of sodium dodecyl sulphate (SDS), 8.0% w/w of n-butanol and 88.9% of aqueous 25 mM disodium phosphate, the pH of which was adjusted to 2.8 with 85% orthophosphoric acid. Separations were performed on an X-Terra 50-mm×4.6-mm, 3.5-μm particle size column at 30°C. UV detection was performed at 220 nm and with a flow rate of 0.3 mL min⁻¹. The established method was validated and applied for analysis of appropriate tablets. The proposed chromatographic procedure for the separation of fosinopril sodium and its degradation product is less expensive compared with the conventional reversed-phase HPLC method, as well as being simple and rapid. The optimised and validated method can be used for separation, identification and simultaneous determination of fosinopril sodium and fosinoprilat in bulk drug and in pharmaceutical dose forms.     

Potentiometric estimation of thorium as oxalate

Summary The potentiometric determination of thorium as oxalate yields values with a constant error and therefore can be employed for analysis with a suitable correction.

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Zusammenfassung Die potentiometrische Thoriumbestimmung als Oxalat liefert Werte mit konstantem Fehler und kann daher mit entsprechender Korrektur zur Analyse verwendet werden.

     

Comparative toxicity and hazards of pesticides to Apis and non-Apis bees. A chemometrical study

The adverse effects of 158 pesticides to the Honey bee (Apis mellifera), the alfalfa leafcutting bee (Megachile rotundata) and the alkali bee (Nomia melanderi) were compared by means of various linear and non-linear multivariate analyses. A comparison exercise including the bumble bee (Bombus spp.) was also performed from a more restricted set of 32 pesticides. While no difference of sensitivity was found between A. mellifera and Bombus spp., M. rotundata appeared the most susceptible to pesticides followed by N. melanderi.     

State estimation in discrete titrations with kalman filtering and fixed-interval smoothing

The suitability of a state space model for processing titration curves and their derivatives is described. The Kalman filter gives a systematic deviation in the evaluated inflection points, which is removed completely by subsequent fixed-interval smoothing. The estimation procedures can be used for on-line control in order to obtain equidistant measurements with variable volume increments. The precision is shown to depend on the minimal delivery of the buret and on the noise variance of the detector. The algorithms are illustrated with a simulated example and applied successfully in practice.     

Simultaneous analysis of six cardiovascular drugs by capillary electrophoresis coupled with electrochemical and electrochemiluminescence detection,using a chemometrical optimization approach

CE coupled with dual electrochemical (EC) and electrochemiluminescence (ECL) detection was optimized for simultaneous analysis of six cardiovascular drugs (alprenolol, propafenone, acebutolol, verapamil, atenolol and metoprolol) via central composite design. Following this study, three critical electrophoretic factors governing the CE separation were investigated: Tris‐H₃PO₄ buffer concentration, buffer pH value and separation voltage. A modified chromatographic response was adopted for evaluating CE separation quality. Optimum conditions were achieved using Tris‐H₃PO₄ buffer 35.6 mM (pH 2.3) separated at 13.9 kV, which was employed experimentally and led to the successful simultaneous separation of the above six drugs. The good agreement of the chromatographic response was observed between predicted data and actual experimental results using these optimized conditions (RSD=3.75%). The proposed method was validated for linearity, repeatability and sensitivity, and subsequently successfully applied to determine six basic drugs in urine samples.     

A mediator-type biosensor as a new approach to biochemical oxygen demand estimation

A novel biosensor for the determination of biochemical oxygen demand (BOD) was developed using potassium hexacyanoferrate(III) [HCF(III)] as a mediator. The sensor element consists of a three-electrode system, with both working and counter electrodes compactly integrated as a disposable using etching and electroplating processes. Pseudomonas fluorescens biovar V (isolated from a wastewater treatment plant) was immobilized on the surface of the working electrode using poly(vinyl alcohol)-quaternized stilbazol (PVA-SbQ) photopolymer gel. Synthetic wastewater described by the Organization for Economic Cooperation and Development (OECD) was used as a standard solution instead of glucose-glutamic acid synthetic wastewater. The conditions of amperometric measurement were optimized at +600 mV (vs. Ag/AgCl) operating potential, namely 40 mM HCF(III) in a 0.1 M phosphate buffer (pH 7.0) at 20 degrees C. The sensor response was linear from 15 up to 200 mg O l-1 BOD. The response time was 15 min at 200 mg O l-1 BOD. To demonstrate the wide metabolic range of activity of the sensor, the sensor response to 14 substances in four categories of organic compounds was investigated. Further, it was shown that the response of this BOD sensor was not influenced in samples with low concentrations of dissolved oxygen under the measuring conditions used. For real wastewaters, the BOD values were determined using the sensor and compared favorably with those determined by the conventional BOD5 method.     

The Twin-Excited State as a Probe for the Transition State in Concerted Unimolecular Reactions: The Semibullvalene Rearrangement

A twin of the transition state , which can be investigated spectroscopically and can thus supply information about the structure of the transition state, has now been characterized for the Cope rearrangement of semibullvalene (shown below). It involves an excited state with B₂ symmetry and results from a linear combination of the ground-state wave functions of (mirror-image) reactant and product.     

Hyphenation of column liquid chromatography and Raman spectroscopy via a liquid-core waveguide: chemometrical elimination of spectral eluent background

In column liquid chromatography (LC) coupled to conventional Raman spectroscopy (RS) removal of the spectral background of the eluent is often demanding, because of the strong signals of the organic modifier. A new chemometrical method is proposed, called the eluent background subtraction (EBS) method, which can correct for small shape and intensity differences of the eluent spectra. The variations in the eluent spectra are modelled using principal component analysis (PCA). The PCA loading vectors are subsequently used for eluent background correction of the elution spectra of the analyte. The loading vectors are fitted under these spectra by an asymmetric least-squares method. This method was successfully applied under various experimental conditions and performed much better than conventional background correction methods. Analyte detectability was improved by (weighted) averaging of all elution spectra and smoothing via a p-spline function.     

Gravimetric estimation of bismuth as bismuthyl dichromate

Summary Conditions are described for the quantitative precipitation of bismuthyl dichromate, (BiO)₂Cr₂O₇, and the suitability of this reaction for the gravimetric estimation of bismuth is shown. The use of arsenious oxide as a primary standard for the iodometric titration of excess chromate is emphasised.Sincere thanks of the authors are due to Prof. S. S. Joshi for research facilities and to Dr. G. S. Deshmukh for keen interest in the work.     

High-Resolution Transmission Electron Microscopy Re-examined as a Tool in Solid State Chemistry

Transmission electron microscopy (TEM) can be used with crystalline solids to obtain direct images of small structural groups comprising a few coordination polyhedra with resolution nearly down to atomic scale (“lattice imaging”). More exact knowledge of the conditions required for direct imaging, as well as improvements in the instruments themselves, have now made it possible to examine very small defect regions (microdomains), faults in the stacking sequence of structural groups or atom layers (planar or Wadsley defects), and isolated defects in narrowly delimited areas that may actually be below the dimensions of the unit cell. The structural principle of the very smallest ordered regions can even be determined when X-ray structure analysis proves unable to do this. “Block structures” are particularly suitable as models for the testing and further development of the high-resolution method; the detection of three-dimensional, two-dimensional, and one-dimensional defects has been studied on such structures.