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     

Multivariate Statistical Assessment of Air Quality: A Case Study

The present paper deals with the application of several chemometrical methods (cluster and principal components analysis, source apportioning on absolute principal components scores) to an aerosol data collection from Unterloibach, Austria. It is shown that seven latent factors explaining almost 80% of the total variance are responsible for the data structure and are conditionally identified as secondary aerosol, mineral dust, oil burning, lead smelter, coal burning, salt and fertilizer emission sources. Furthermore, the contribution of each identified source to the formation of the particle total mass and chemical compounds total concentration is calculated. Thus, a reliable assessment of the air quality in the region is performed. The requirements of the sustainability concept for ecological indicators in this case is easily transformed into a multivariate statistical problem taking into account not separate indicators but the specific multivariate nature of aerosol pollution.     

Determination of total,and bound Se in sera by INAA

In this study we report on the comparison between the total selenium in serum (total Se) with that which is apparently bound to high molecular weight (>12,000 D) species, presumably proteins (bound Se). Nine hundred seventy seven (977) serum samples arising out of a population-based epidemiological study were prepared in duplicate for the determination of total Se by pipeting directly into irradiation vials; and separate duplicate aliquots were dialyzed against DI water for the determination of bound Se. All samples were analyzed by neutron activation analysis via^77mSe (17.4 s). A small dialyzable Se component (6%) (free Se), defined as the difference between the total Se minus the bound Se, was identified.     

Natural flavours of wine: correlation between instrumental analysis and sensory perception

Summary The aroma of wine consists of 600 to 800 aroma compounds from which especially those, typical for the variety, are already present in the grapes. The aroma extracts — received by extraction with trichlorofluoromethane — are separated by gas chromatography. There are significant varietal differences between the aromagrams (fingerprint pattern). Thus the amount of some flavour compounds (key substances) shows typical dependence on the variety. Especially monoterpene compounds play an important role in the differentiation of wine varieties.The German white wines can be differentiated into three groups only by quantitative determination of 12 monoterpenes (terpene profile). These groups are: Riesling type, Muscat type and Silvaner-Weißburgunder type. Such terpene profiles are also useful for the separation of real Riesling wines from others called Riesling (e.g. Welschriesling, Kap Riesling, Emerald Riesling) but not produced from grapes of the variety Riesling. Including further components and by means of statistical methods as for example linear discriminant analysis even the different varieties within the mentioned groups (for instance the Riesling-group: Riesling, Kerner, Ehrenfelser, Bacchus, Müller-Thurgau) can be separated from each other.To identify compounds causing off-flavours the sniffing technique is the method of choice. The off-flavour is pinpointed during gas chromatography separation of the complex aroma mixture by effluent sniffing. Once allocated, the chemical nature of the off-flavours is elucidated by spectroscopic methods. Substances contributing to the green pepper taint, the strawberry note, mousiness, corkiness etc. in wine could be found in this way.     

On the recognition of structural features: Some general problems illustrated by hamiltonian paths in polyhexes

Human and machine recognition skills are discussed, though not comprehensively reviewed, and some of the difficulties are illustrated by algorithms written to search for Hamiltonian paths in polyhexes. The most successful strategy for this is based upon the branching graph, a recently introduced graph-theoretical device which can aid the recognition of edges that arenot part of a Hamiltonian path. Another, more widely applicable approach that is interesting, although in this preliminary form only a little better than random methods, uses the metaphor of biological evolution, and tries to breed and grow paths subjected to natural selection.     

Interplay of Thermochemistry and Structural Chemistry,the Journal (Volume 13, 2002) and the Discipline

As practiced disciplines, structural chemistry and thermochemistry need not be related. In the current study they are: the contents of the journal Structural Chemistry (Vol. 13) for the year 2002 have been reviewed and then most articles that appeared therein were given a thermochemical commentary, spin or slant.     

Zur Literaturdokumentation in der Analytischen Chemie

Zusammenfassung Anhand von 298 Referaten aus Fresenius Z. Anal. Chem. werden systematisch geordnete Listen von Indexbegriffen für die Bereiche Methoden und Anwendungen erstellt und auf diese Referate angewendet. Diese vorläufige Systematik umfaßt 63 und 32 Hauptindexwörter. Den dokumentierten Referaten wurden 815 Schlüsselwörter (Hauptindexwörter) zugeordnet (116 Referate mit 2, 134 Referate mit 3 Hauptindexwörtern, Minimum: 1, Maximum: 5). Für zwei Indexabschnitte, Atomabsorptionsspektrometrie und Geologisches Material, wird die vorgeschlagene Indexierung vorgestellt und mit der bisherigen in Fresenius Z. Anal. Chem. verglichen. Die überschaubare Zahl von 95 Hauptindexwörtern, die erkennbare, einfache Systematik und die Wahlmöglichkeiten von zusätzlichen Nebenindexwörtern sollen zu einer benutzerfreundlichen Dokumentation beitragen, welche hiermit zur Diskussion gestellt wird.

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Literature documentation in analytical chemistryIV. Development of a systematic, easily usable index and documentation system

Summary By means of 298 abstracts from Fresenius Z. Anal. Chem. systematically arranged lists of index terms for the fields methods and applications were compiled and used for these abstracts. This preliminary system contains 63 and 32 first index terms. 815 Key words were allocated to the abstracts (= first index terms): 116 abstracts with 2, 134 abstracts with 3 first index terms, minimum: 1, maximum: 5. For two index sections, l.e. atomic absorption spectrometry and geological materials, the proposed indexing system is presented and compared with the system hitherto used in Fresenius Z. Anal. Chem.. The favourable number of 95 first index words, the obviously simple system and the possibility of selecting additional second index terms should contribute to an easily usable documentation, which is herewith presented for discussion.

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Teil III: Fresenius Z Anal Chem (1982) 312:448–454     

Meeting the need for reference measurements

Summary Reference materials do fulfil a very useful function in that they provide means to check, verify and calibrate measurement procedures and instrumentation. However, the material is often idealized compared to real life samples: it is either (very) pure or does not correspond in concentration level or matrix to the real life case. It is shown how this situation could be remedied if real life samples with carefully assessed reference values could be made available regularly as unknowns to measurement laboratories. Comparison of the latter's measurements with the reference values then would provide a picture of the real performance of the particular measurement community in general and of each participating laboratory in particular. The opinion is expressed that isotope-specific methods have now matured to the stage that, if they are correctly applied under rigorous control and based on highly skilled expertise, they can provide such reference values against which laboratories can then evaluate their routine performance in regular Interlaboratory Measurement Evaluation Programmes (IMEPs).

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Wie der Notwendigkeit von Referenzmessungen entsprochen werden kann

     

A Note on Distance Matrices Yielding Elementary Landscapes for the TSP

Symmetric and antisymmetric distance matrices in the single agent traveling salesman problem (TSP) are not the only distance matrices to generate elementary landscapes for swap and 2-opt neighborhoods.     

Electrochemical dissolution of magnetite in acid solutions

The present paper deals with the electrochemical behavior of magnetite microcrystals in an acid medium. A voltammetric method employing a carbon-paste electroactive electrode (CPEE) with an organic binder was used. It was found that the cathodic voltammograms, which were recorded at different scan rates, formed a set bounded in the space of i–E parameters by a generalizing voltammetric curve corresponding to the effective potential scan rate _eff. In other words, all curves are situated under one enveloping curve, just as the smaller dolls sit in the largest doll of a Russian doll. Reverse currents (a cathodic current in the anodic direction of the potential scan) were observed on the cyclic voltammogram. Forward and reverse currents obey the same laws and have one and the same generalizing curve, which could be taken as the magnetite characteristic.     

Understanding the properties of isospectral points and pairs in graphs: The concept of orthogonal relation

The mathematical property orthogonal relationship is used in proving the fact that isospectrality, isocodality and isocoefficiency of vertices within a graph are all equivalent. The same is true for isospectrality, strict isocodality and strict isocoefficiency of pairs (including edges) within a graph, whereas the weak versions of the latter properties are necessary but not sufficient for isospectrality of pairs. Similarly, necessary and sufficient conditions for isospectrality of vertices and pairs in different graphs are derived. In all these proofs, the concept of orthogonal relation plays a major role in that it allows the use of tools of elementary linear algebra.     

Beiträge zur Chemie der Pyrrolpigmente, 72. Mitt.

A strategy for the synthesis of bilatrienes-abc bridged between rings A and C has been developed and tested in case of a bibenzylethane bridging fragment. This strategy was then applied to the synthesis of a 2,3-dihydrobilatriene-abc bridged by a (S)-lysine moiety from ring A to ring C (positions 3 and 12) by means of peptide bonds between the two amino groups of lysine and the acetic and propionic acid side chains of the chromophoric unit. The two diastereomers resulting from the two chiral centers of the lysine residue and at position 3 of the chromophore were separated by chromatography.

     

Der o-Effekt in den Massenspektren aromatischer Verbindungen

Zusammenfassung Das Massenspektrum des O-Äthylsalicylsäureamides VII b ist von dem seiner m- und p-isomeren Verbindung völlig verschieden und zeigt einen typischen massenspektrometrischen o-Effekt.Die bisher aufgefundenen Verbindungen mit massenspektro-metrischem o-Effekt gehören einem relativ kleinen Kreis von Aromaten mit ganz bestimmten Strukturmerkmalen an. Die Bildung der für den o-Effekt charakteristischen Bruchstücke kann in allen diesen Fällen nach einem vonMcLafferty aufgestellten Mechanismus zwanglos erklärt werden. Verbindung VIIb hätte unter der Voraussetzung, daß eine Entstehung der für den o-Effekt typischen Fragmente nur nach diesem Mechanismus möglich ist, keinen o-Effekt zeigen dürfen.Das Auftreten des o-Effektes im Massenspektrum von VIIb läßt erkennen, daß die Bedingung zur Bildung der für den o-Effekt charakteristischen Bruchstücke lediglich in der Möglichkeit zur Ausbildung stabiler Spaltprodukte zu suchen ist, und daß daher weit mehr Verbindungen einen o-Effekt zeigen sollten als bisher anzunehmen war.Mit 1 Abbildung     

Von den unabhängigen Reaktionen

Zusammenfassung Es wird der Begriff derunabhängigen Reaktionen dargelegt, die chemische und mathematische Methode der Ermittlung dieser Reaktionen dargetan und auf ihre Bedeutung verwiesen.     

State-of-the-art in organic elemental micro and ultramicro analysis

Summary Nernst developed a quartz torsion microbalance in 1903. In consequence of this pioneering work, Emich in the Technical University of Graz, Austria, had systematized a series of chemical operations in microscale as well as a microchemical analysis. Further advances in technique and method of organic microanalysis had been accomplished by Pregl in Graz in 1912. His work had been strongly supported by a new microbalance which was known as Kuhlmann microbalance. Pregl's original methods of analysis were arranged and published in 1916 as Die quantitative organische Mikroanalyse. It is still noteable that the Nobel prize of 1933 had been presented to Dr. Pregl. In accordance with a combination of electronic microbalance and computer techniques, organic elemental microanalysis has grown to include advanced instrumentation and on-line computation. Successful adaptation of microchemical analysis has expanded today not only to pure organic compounds, but on industrial intermediates, polymers, food additives and many other compositions. The paper includes a discussion of the relative merits of traditional and modern analytical techniques together with the progression of microbalances. Recent developments in organic micro and ultramicro analysis in Japan are also described.     

Chemical algebra. II: Discriminating pairing products

The algebra of stereogenic pairing equlibria is presented in a very general context. Starting from the notions of fuzzy subgroup and conjugacy link, chemical pairing constants between molecular speciesu andv having a skeletal symmetry groupG are formulated as pairing products on aG-Hilbert space. Discriminating pairing productsK are defined by the conditions: K 1 and K = 1 the representative vectors of the paired species areG-equivalent. WhenG has only two elements, the pairing product is always discriminating. For several skeletal symmetries, if the vectors are enantiomorphic (v = u, ² =e, G), thenK is greater than 1 and reaches 1 only ifu is achiral: chirality indexes and general permutational indexes are then defined fromK(u u). The general model is illustrated by some examples.     

Computer-aided library search of combined LC-Retention and diode-array-UV-spectral data

An automated library search system for computer-aided identification of organic compounds using combined UV-spectral and LC-retention data, as acquired by HPLC with linear diodearray-UV-detection, is presented.The keystone of the system is a set of similarity indices which have been developed on the basis of mathematical-statistical models of the reproducibility of the spectral and retention data. The similarity indices have the form of a significance probability, a quantity originating from the general theory of hypothesis testing. The output of the LC-UV retrieval system is a compound identity or a list of identities (if any) for which the relevant similarity index has a value above a preset threshold. The data base used in this investigation contained 186 sets of UV-spectral and LC-retention data of 74 organophosphorus pesticides measured from standard solutions under various experimental conditions. A test set consisted of 186 alternative data sets of the same compounds as contained in the data base, however measured under different experimental conditions. The performance of the LC-UV reproducibility-based retrieval (LUVRR) system was evaluated using recall/reliability plots. The results appeared to be quite promising: for 95% of the unknowns, the target reference (correct positive) was on top of the hit list with a similarity index value being significantly higher than values found for false positives.The software is written in Pascal. The present (experimental) version of the system runs on a Data General Eclipse MV/4000 minicomputer.     

Is Chromatography a Science, a Process, a Method, or a Scientific Discipline?

In the controversy over an article entitled Chromatography as a Scientific Discipline by V.G. Berezkin, it was pointed out that the subdivision of chromatographic processes into sorption–sieve chromatography and field nonsorption chromatography is inadmissible. It was demonstrated that all chromatographic processes, including flow fractionation in a transverse force field, are in principle two-phase (or polyphase) processes. It was illustrated that a longitudinal field in a flow cannot introduce a chromatographic component into the system. An additional definition of chromatography as a phenomenon was proposed on the basis of key points revealed by Professor Berezkin.     

Nuclear repulsion effects in molecular bonding

Potential energy curves of a single electron moving in the joint Coulomb field of two fixed nuclei of equal arbitrary charge, Z, have been calculated exactly using a scaling relationship derived in an earlier paper. The resulting potential curves display some interesting features. For Z<1 the 2p antibonding orbital becomes bonding, while the 1s potential well becomes deeper. For larger Z, the 1s orbital eventually becomes antibonding but the potential curve passes through a number of distinct intermediate stages before a purely repulsive potential is reached.     

Determination of polychlorobiphenyls and polycyclic aromatic hydrocarbons in the atmospheric aerosol of the Venice Lagoon

An analytical method for simultaneous determination of particle-associated and gaseous-phase concentrations of polychlorinated biphenyls (PCB) and polycyclic aromatic hydrocarbons (PAH) in atmospheric aerosol samples obtained by high-volume samplers using polyurethane foam adsorbent (PUF) and quartz fibber filters (QFF) has been investigated. Quality control of the analytical procedure was carried out by blank control and by evaluating limits of detection, recoveries, accuracy, and repeatability. The proposed method was subsequently used to determine PAH and PCB in the gaseous and particulate phases of the aerosols that enter the Venice Lagoon atmosphere. The highest concentrations of PCB and PAH were predominantly in the gaseous phase. In both particulate and gaseous phases the penta-CB congeners dominated total PCB concentrations whereas phenanthrene, fluoranthene, and pyrene dominated the PAH concentrations. Total (gaseous plus particulate) PCB and PAH concentrations were higher at the site directly influenced by the industrial plants but the concentrations in marine aerosol samples were lower by a factor four only and must be taken into consideration when studying the chemical contamination of the Venice Lagoon.