Use of data-processing in modern rapid methods of elemental analysis

Automated methods for the rapid determination of carbon, hydrogen, nitrogen, and oxygen have been developed for use in conjunction with modern data processing equipment. Details as to the methods, apparatus, programming of procedures, and evaluation of the results are presented.     

Decomposition methods in elemental trace analysis

Frequently, systematic errors in the decomposition step of a trace analytical multistage procedure lead to erroneous results in spite of the fact that expensive and powerful apparatus has been used for the determination. Of the numerous decomposition methods that have been published only a few meet the requirements of modern trace analysis.     

Physicochemical measuring methods for end-point determination in organic elemental microanalysis

In the last 10 years a series of physicochemical methods of measuring have been developed which could replace the classic weighing of combustion products in microelemental analysis. Microelemental analysis can be automated using these methods. The measuring principle and the commercial apparatuses for determining carbon, hydrogen, nitrogen, and oxygen are discussed extensively.     

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.     

Limitations of reaction frontal gas chromatography in organic elemental analysis

Summary The basic phenomena affecting the precision and accuracy of reaction frontal GC in organic elemental microanalysis are discussed with special reference to determination of C, H, N, O and S. Attention is paid to the concentration changes occurring during the frontal GC separation, and it is shown that their effect is generally negligible if proper standards and conditions are used.

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Grenzen der Reaktions-Gaschromatographie in der organischen Elementaranalyse

Zusammenfassung Die grundlegenden Vorgänge der frontalen Reaktions-Gaschromatographie und ihr Einfluß auf die Genauigkeit organischer Elementaranalysen, besonders der Bestimmung von C, H, N, O und S wurden erörtert. Besondere Aufmerksamkeit wurde dabei den Konzentrationsveränderungen geschenkt, die während der Trennungsvorgänge auftreten, wobei gezeigt werden konnte, daß deren Wirkung im allgemeinen vernachlässigt werden kann, wenn geeignete Standardproben und Versuchsbedingungen angewendet werden.

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Presented at the 8th International Microchemical Symposium, Graz, August 25–30, 1980.     

A new method for handling liquid samples in organic elemental analysis

Summary A method for handling liquid samples in automatic CHN analysis is described. It involves the use of an aluminum pan in which the sample is hermatically sealed by means of a sealing press. Satisfactory results have been obtained with liquids boiling between 35° and 290°.

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Zusammenfassung Zur Einwaage flüssiger Proben für die automatische CHN-Analyse werden Aluminiumschälehen verwendet, die sich mit einer Presse hermetisch verschließen lassen. Zwischen 35 und 290° siedende Flüssigkeiten lassen sich so mit gutem Erfolg analysieren.

     

Uncertainty estimation in organic elemental analysis using information from proficiency tests

We evaluate the uncertainty in organic elemental analysis of C, H, N, and S. We use data from six proficiency tests (PTs), in which some 35 Spanish laboratories participated. The uncertainty of the technique is estimated from the relative within-laboratory and between-laboratory variances for pure substances and samples with complex matrices (soil, powdered milk, oil, ash, and petroleum coke). We also calculate the relative standard uncertainties for individual laboratories when analysing pure substances using historical data from the participation of each laboratory in different editions of PTs. The uncertainty values obtained for the individual laboratories are comparable with the uncertainty of the technique and correlate with the combined z-scores. The evolution over time of those laboratories participating in common editions of PTs is also evaluated.     

Nuclear methods of elemental analysis of ocean bottom sediments

Results of development of nuclear-physical research installations and methods of ocean bottom sediments analysis using radionuclide sources of neutron, gamma and X-ray radiations are presented. Practical applications of the above developments in expeditionary conditions aboard research vessels are summarized.     

Determination of arsenic in organic compounds rapid micro and semimicro methods

Rapid micro and semimicro methods for determination of arsenic in organic compounds have been developed using 28% chloric acid as the digesting agent for the organic arsenical. This wet acid digestion procedure does not lead to loss of arsenic even in the presence of 4 M chloride.The semimicro method completes the assay by reduction of the pentavalent arsenic with iodide, destruction of the iodine liberated with thiosulfate and re-oxidation to pentavalent arsenic with iodine in a buffered solution. The micro method completes the assay by development of a heteropoly molybdenum blue using a single solution reagent at room temperature. The color is reproducible so that only a single calibration curve for the instrument used is necessary.     

Automated determination of sulphur in organic compounds

The paper reviews methods of sulphur determination over the last 120 years. Classical methods are presented in a historical view, and the present state of automatic procedures of sulphur estimation is discussed. 104 key references concerning sulphur analysis are cited. On the basis of the present level of the development of elemental analysis, a prognosis of directions of the development of sulphur microanalysis is attempted.     

Sub-micro methods for the analysis of organic compounds

Summary A new technique is described which enables organic compounds to be analysed for elements and functional groups using sample weights of 30–50 micrograms (0.03 to 0.05 mg). These amounts are only just visible to the naked eye. The accuracy is similar to that of the microscale, and the technique is fairly simple.It is expected that these methods will be of value in biochemistry and associated fields where amounts of sample are often limited. The new technique is not intended to replace micro-methods. Investigations are still proceeding to develop further methods for the determination of functional groups and to refine earlier procedures.     

Selective activation of organic molecules by elemental fluorine

Reactions on tertiary hydrogen atoms, attached to unactivated saturated carbons, are very rare and usually inefficient. The electron density however, of a carbon-tertiary hydrogen bond is relatively high and therefore there is a chance it will react with a strong electrophile. One of the strongest electrophiles existing is, of course, the electrophilic fluorine. Two main sources for such an unusual species exist. One source is the various fluoroxy compounds like CF₃OF or CF₃COOF ant the other is the elemental fluorine itself.Indeed, when fluorine is allowed to react, at low temperatures, with various alkylcyclohexanol esters, a highly regio- and an absolutely stereospecific electrophilic substitution on the tertiary unactivated hydrogen takes place as for example:

The radical pathway possibility of these reactions is excluded and it is believed that they are of ionic nature. By dehydrofluorination, a double bond is introduced in sites that no other reagent is known to do, thus activating the molecule towards further chemical transformations. The influence of the electron-withdrawing group on the reaction center will also be discussed.The described reaction is not restricted only to cyclic compounds as aliphatic chains also react as expected, i.e.

The scope of these unusual reactions in both alicyclic and aliphatic fields will be evaluated.     

Microcomputers in electrochemical trace elemental analysis

The advantages of incorporating digital computers in devices for electrochemical trace elemental analysis are discussed on the basis of examples from the literature. Apart from easing data interpretation, the digital computer may control and monitor electrode processes at a high interaction frequency. For elements undergoing reversible electrode reactions, the resolution and sensitivity of electrochemical techniques can be improved by such rapid real-time interaction. Moreover, for quasi-reversible systems, the application of computerized broad-band potential excitation and simultaneous monitoring of broad band relaxation signals, permits rapid extraction of analytical information from data which represent the electrode process more accurately than do traditional single-frequency a.c. polarographic data.     

Determination of organic substances by kinetic-catalytic methods of analysis

A review on the determination of organic substances by kinetic-catalytic methods of analysis is given.Methods based on homogeneous catalyzed solution reactions as well as those based on heterogeneous catalyzed electrode reactions are discussed.     

Automated analysis of proton NMR spectra from combinatorial rapid parallel synthesis using self-organizing maps

It is now quite routine to acquire proton NMR spectra of compounds in 96-well plates prepared in a rapid parallel synthesis fashion using a flow-NMR automation setup. However, the analysis of 96 NMR spectra obtained in this manner is often laborious and painstakingly slow. We have developed a new, automated method for rapidly analyzing 96 NMR spectra of compounds synthesized in an 8 x 12 matrix using self-organizing maps (SOM). This unsupervised neural network is capable of clustering together NMR spectra containing a common pattern of -R groups and identifying outliers from within such clusters. Analysis of these outlier spectra can quickly help indicate the presence of undesired products, impurities, starting materials, and other unexpected errors in a 96-well plate synthesis by focusing the chemists' attention on the aberrant NMR spectra. Thus, SOM can be a valuable tool in performing efficient quality control on combinatorial libraries.     

Synthesis of vicinal bromo-fluoro organic compounds using elemental fluorine

The direct action of fluorine on bromine at ?78° produces BrF which, without any isolation or purification, adds readily across various double bonds providing there is some hydrogen donor in the reaction mixture. Only trans addition of the elements of BrF was observed. When the reaction was applied to enons an easy elimination of HF can take place thus producing α-bromo enons.In our previous work we described the reaction of some olefins with IF, a reagent which was prepared $\text{in}$$\text{situ}$ by the action of F₂ on I₂[1]. The literature deals with several other fluorohalogens, among them the three known bromo-fluoro compounds, BrF, BrF₃ and BrF₅, although only the last two are well characterized[2]. However, because of the instability and the high reactivity of these compounds, they have hardly been employed in organic chemistry[3].We wish to describe here for the first time, an efficient and convenient method of synthesizing vicinal bromo-fluoro compounds using the primary source of the fluorine atoms, namely elemental fluorine itself[4].When a mixture of F₂/N₂ is bubbled through a cold (?78°C), dilute solution of Br₂ (20 mmolar) in CFCl₃ (Freon) the bromine disappears and mainly BrF is produced. However, despite previous efforts, it seems that this compound cannot be isolated since it disproportionates easily to the very reactive BrF₃ and halogen on the aromatic ring can not be ascertained. The third product proved to be the corresponding bromo-ethoxy compound XV (15% yield). Prolonged chromatography or traces of HF from the reaction mixture results in the elimination of HF thus producing, quantitatively, 6-bromocumarin XVI[8]. 2-Bromo-3-fluoro cyclopentanone XVII (oil) if formed in 90% yield and isolated in almost pure form. As in the case of cumarin, XVII readily loses HF producing the 2-bromoclopentenone (XVIII)[9] in quantitative yield.     

Computerized technique in organic microelemental analysis: Part IV: Automated determination of chlorine,bromine, and iodine in organic compounds

The automatic and computerized rapid microanalytical determination of chlorine, bromine, and iodine in organic and organometallic compounds is described. The method consists of combustion of the compound in a large diameter empty tube connected to a titration vessel. The combustion products are transferred from the end of the combustion tube to the titration vessel by means of an automatic reductive SO₂-containing wash. Automatic potentiometric titration with AgClO₄ to the preset endpoint potential, using a combination silver microelectrode, serves as the endpoint detection of the titration of halides. The entire analysis, including automatic preparation of the equipment for the next determination, is programmed in a 6-min cycle. The method is blank-free; the results are accurate. Standard deviations amount to: 0.05, 0.14, and 0.18% absolute for Cl, Br, and I, respectively.The analyzer is interfaced to a real-time, time-sharing computer along with electronic microbalances and other analyzers, as part of the microanalytical laboratory computer service. The results of the analyses are reported on CR-terminals and are stored on magnetic disk for further processing.     

Traceability system for elemental analysis

A complete metrological traceability system for measurement results of chemical analysis was set up. Core components are pure substances (national standards) characterised at the highest metrological level, primary solutions prepared from these pure substances and secondary solutions deduced from the primary solutions and intended for sale. The relative uncertainty of the element mass fraction of the primary substances and solutions is < 0.01 and < 0.05%, respectively. For the certification of transfer solutions and for stability testing, a precision measurement method for element contents has been developed by means of optical emission spectrometry (ICP OES) by which uncertainties between 0.1 and 0.05% can be achieved. The dissemination to field laboratories is effected with the aid of a calibration laboratory of the German Calibration Service (DKD) which certifies the element content of the secondary solutions with an uncertainty ≤ 0.3%. Calibration with these solutions enables the user to establish traceability of his measurement results to the International System of Units (SI). Currently, the system comprises Cu, Fe, Bi, Ga, Si, Na, K, Sn, W, and Pb.