Studies on the flame ionization detector signal in the presence of organosilicon compounds : A method for the registration of the detector performance
Abstract
A method is described by means of which the response curves of a flame ionization detector may be recorded on the basis of a single chromatogram. The column effluent is divided into two equal streams which simultaneously enter a reference detector and the detector being examined. The relation between the two detector signals is recorded with the aid of an X-Y recorder. Providing that the performance of the reference detector is linear, and by determining its response factor, the abscissa of the X-Y diagram represents a scale of mass flow rates, and the diagram itself the response curve of the detector tested. The method was used for the investigation of the FID performance when detecting organosilicon compounds. Inversion of the gas chromatographic peaks takes place and the response curves display a maximum under certain operating conditions. The shape of the response curves, the height and situation of the maximum depend on the detector voltage, the electrode gap, the flow rate of gases and the carbon/silicon ratio of the compound detected. The estimation of the carbon/silicon ratio on the basis of the maximum ion current is suggested.
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1987, Journal of Chromatography AResponse enhancement by metal doping of a silicon-selective flame ionization detector for gas chromatography
1981, Journal of Chromatography AA detector selective for silicon-containing compounds eluting from a gas chromatograph was constructed by modifying a commercial flame ionization detector. This detector exhibited a sensitivity for silicon-containing compounds in the nanogram range and a selectivity for these compounds over normal hydrocarbons of approximately 2500. Both the sensitivity and the selectivity of this detector were increased by doping with a variety of metal compounds. When optimum amounts of vapors from organometallics were bled into the detector's hydrogen atmosphere, the minimum detectable amount of the detector to a silicon-containing standard was found to decrease to 50 pg. The sensitivity varied with the quantity of organometallic vapor introduced into the detector, and, at high doping concentrations, silicon-containing compounds were detected as decreases in background current. The potential for the utilization of internal doping sources (such as metal wires, ribbons, or pressed pellets placed on or around the tip of the detector's flame jet) was also investigated.
Gas chromatographic analysis of organosilicon compounds
1979, Journal of Chromatography AThe present review deals with some problems that may be of interest to chromatographers studying organosilicon compounds (OSC). It is shown that correlations between structure and retention values of OSC help to predict retention parameters of unexplored compounds and help to gain insight into the physico-chemical processes in the gas chromatography of OSC. The detectors used for OSC analysis are discussed. A combination of gas chromatography with other methods is shown to be useful in functional group analysis as well as in the identification of separated compounds. The conditions of 160 analytical methods are tabulated.
Thermal decomposition of cyclo-linear methylsiloxane polymers
1979, Journal of Organometallic ChemistryThe pyrolysis products from two cyclo-linear methylsiloxane polymers have been analysed, and formation of the important products interpreted in terms of a simple decomposition mechanism. This mechanism is very similar to that of the polydimethylsiloxane degradation; thus cyclic oligomers are formed from the linear segments, and polycyclic compounds from the cyclic segments of the cyclolinear methylsiloxane polymers.
Study of the kinetics and mechanisms of chemical transformations of polymers at elevated temperatures
1977, Journal of Chromatography LibraryThis chapter presents a study of the kinetics and mechanisms of chemical transformations of polymers at elevated temperatures. During the processing and use of polymeric materials at elevated temperatures, various chemical processes occur that are accompanied by the release of low-molecular-weight products and the formation of cross-linked structures. A change in the structure of the initial polymer leads, in most instances, to a deterioration in its properties. As a result of some particular properties of polymeric compounds, investigations into the kinetics of chemical transformations in polymer systems are more complicated than the studies of transformations of low-molecular-weight compounds. The role of impurities is also important. Even before the start of an experimental investigation into chemical reactions of polymers, it is essential that the initial compounds be characterized as fully as possible as different batches of the product and even different test samples may have different compositions. The low heat conductivity of polymer systems may give rise to temperature gradients in the polymer. Gas chromatography (GC) can be used for studying transformations not only of the polymer itself but also of the polymer-inhibitor system.
Thermal degradation of copolymers of styrene and methyl-vinyl-silane by pyrolysis gas chromatography
1974, European Polymer JournalPyrolysis gas chromatographic investigations have been carried out on copolymers of styrene with trimethyl-vinyl-silane and of styrene with dimethyl-phenyl-vinyl-silane, in order to study the mechansims of thermal degradation and the copolymer structures. We have identified the pyrolysis products and measured their relative amounts. The experiments show that the controlling factor in the mechanism of the degradation is the nature of the side-group attached to the carbon atom at which chain scission occurs. If this side-group is phenyl, the main degradation process is depropagation; if it is if it is trimethyl-silyl or dimethyl-phenyl-silyl, intramolecular hydrogen abstraction followed by β scission becomes more important than depropagation. From the point of view of degradation mechanism, the nature of the side-group attached to the carbon atom from which the hydrogen is abstracted is of minor importance.
We estimated the average copolymer block length from the amounts of products containing both comonomers as well as from the amounts of trimer composed of the same monomer.
Des études ont été effectuées en pyrolyse et chromatographie en phase gazeuse sur des copolymères de styrène et de triméthyl-vinyl-silane et de styrène et de diméthylphényl-vinyl-silane, dans le but d'étudier les mécanismes de dégradation thermique et les structures des copolymères. On a identifié les produits de pyrolyse et mesuré leurs quantités relatives. Les expériences ont montré que le facteur qui contróle le mécanisme de dégradation est la nature du groupe latéral attaché au carbone adjacent au site de rupture de la chaîne. Si le groupe latéral est un groupe phényle, le processus principal de dégradation est la dépropagation; si c'est un groupe triméthyl-silyle ou diméthyl-phényl-silyle, la réaction d'abstraction d'hydrogène intramoléculaire suivie d'une scission en β. devient plus importante que la dépropagation. La nature de groupe latéral attaché au carbone qui a perdu un hydrogène intervient peu dans le mécanisme de dégradation.
Nous avons estimé la longueur moyenne des séquences du copolymére à partir des quantités de produits contenant les deux co-monomères ainsi que les quantités de trimères constitués par le mème monomère.
Per studiare il meccanismo della degradazione termica e la struttura di copolimeri, si sono eseguite delle indagini cromatografiche su copolimeri di stirene con trimetil-vinil-silano e di stirene con dimetil-fenil-vinil-silano. Abbiamo identificato i prodotti di pirolisi e misurato le loro relative quantità. Gli esperimenti mostrano che il fattore determinante nel meccanismo della degradazione è la natura dei gruppi laterali attaccati all'atomo di carbonio in corrispondenza del quale avviene la scissione. Se tale gruppo laterali è il fenile, il processo principale di degradazione è depropagazione; se è il trimetil-silileoppure il dimetil-fenil-silile, la sottrazione di idrogeno intramolecolare seguito da scissione β diventa più importante della depropagazione. Dal punto di vista del meccanismo di degradazione, la natura del gruppo laterale attaccato all'atomo di carbonio da cui viooe sottratto l'idrogeno è di minor importanza.
Abbiamo calcolato la lunghezza media del blocco di copolimeri a partire dalla quantità di prodotti contenenti dia i comonomeri, come pure dalla quantità di trimero composto dello stesso monomero.
Untersuchungen mit der Pyrolysegaschromatographie an Copolymeren von Styrol mit Trimethylvinylsilan und von Styrol mit Dimethylphenylvinylsilan wurden vorgenommen, un den Mechanismus des thermischen Abbaus und die Struktur der Copolymeren zu untersuchen. Wir haben die Pyrolyseprodukte indentifiziert und ihre relativen Mengen gemessen. Diese Untersuchungen zeigen, daβ der kontrollierende Faktor für den Mechanismus des Abbaus in der Art der Seitengruppen liegt, die an das Kohlenstoffatom gebunden sind, an denen der Kettenbruch auftritt. Ist diese Seitengruppe ein Phenylring, dann ist der dominierende Prozess des Abbaus die Bildung von Monomeren; sind dies Trimethylsilyl- oder Dimethylphenylsilylgruppen, dann überwiegt intramolekulare Abspaltung von Wasserstoff mit anschlieβender β-Spaltung vor der Bildung der Monomeren. Vom Gesichtspunkt des Abbaumechanismus ist die Art der Seitengruppe, die an das Kohlenstoffatom gebunden ist, von dem ein Wasserstoffatom abstrahiert wird, von untergeordneter Bedeutung.
Wir schätzten die durchschnittliche Blocklänge im Copolymeren aus den Produktmengen, die sowohl beide Comonomeren enthielten wie auch aus den Mengen von Trimeren bestehend aus den gleichen Monomeren.