Chromatographic reviews最新文献

The free zone electrophoresis method described in this monograph can be used for the fractionation of small molecules, large molecules, and particles. Its versatility is illustrated in runs with inorganic ions, organic ions, nucleic acid bases, nucleosides, nucleotides, proteins, nucleic acids, subcellular particles, viruses, and erythrocytes. The principles of the construction of the electrophoresis equipment are described in detail. The separation chamber is a horizontal tube which slowly rotates round its long axis. The rotation eliminates the need for a supporting medium. A mathematical treatment of this rotational stabilization is given. The equipment is fitted with a unique U.V.-scanning system and is automated so that it requires no attention after the introduction of the sample. Because the “boundary anomaly” effects cause the concentration of any ion inside a migrating zone to be different from that outside, the scanning system can also be used to detect substances which have no U.V.-absorption if the buffer contains appropriate U.V.-absorbing ions. Free zone electrophoresis is intended primarily for analytical purposes but can also be used for preparative experiments on a small scale. The amount of material required is about the same as in paper electrophoresis. The mobility values obtained by free zone electrophoresis agree well with those determined by the classical Tiselius moving boundary method. Free zone electrophoresis also permits determinations of electroendosmotic mobilities, and thereby ζ-potentials of the surface of the revolving electrophoresis chamber. The empirical relationship between recorder deflection and zone concentration fits the theoretically derived curve closely. Using these calibration curves an accuracy of about 4% was obtained in quantitative determinations. Some sections also apply to electrophoresis methods other than free zone electrophoresis, e.g. the sections dealing with the electrophoretic migration velocity profile, the elimination of the electroendosmotic disturbances, and the detection of substances which have no U.V.-absorption.

We have attempted to stress the major areas of chromatographic techniques for carbamate analyses and also to illustrate the influence of carbamate moiety substituents on chromatographic behavior.

The remarkable versatility of chromatographic techniques, as demonstrated by their many applications to complex analyses, is apparent from the foregoing review. It has also been shown how powerful a tool chromatography is for research as well as for routine analytical work.

Thin-layer chromatography, introduced by Sthal in 1956²¹⁶, has largely replaced paper chromatography in many applications. In the past three years it has been increasingly applied to pharmaceutical and pesticidal analysis because of its simplicity of operation, rapidity and the high degree of resolution achieved. Under specified conditions, TLC lends itself to quantitation interpretation and is being used for analytical control and toxicological investigation.

Although gas chromatography was introduced only in 1952, it has seen extensive utility in many areas. However, it has not, until recent years, been widely used for either pesticidal or pharmaceutical analysis. This has been due not entirely to the expense of the equipment or the degree of operational sophistication required. A major difficulty has been the thermal instability of many of the carbamates and the necessary high operating temperatures required for compound volatilization. Derivatives of carbamates, such as trimethylsilyl¹³⁵ and acetyl²¹⁷ (successfully utilized in pesticidal gas chromatographic analysis because of the thermally stable nature of the respective compounds formed) suggest a similar feasibility for pharmaceutical carbamate analysis.

The desirability of a satisfactory selective detection system for nitrogen (alluded to in the work of Coulson¹³⁴ should greatly enhance the utility of gas chromatography to pharmaceutical and pesticidal carbamate analysis.

Chromatographic and electrophoretic techniques for the separation of denaturation and degradation products of collagen and other fibrous proteins are reviewed. Further progress in these techniques is to be expected, especially for myosin and keratin breakdown products, where the molecular interpretation of results is still missing. No such difficulties exist in the case of collagen, where the relation between fractions and spots which appear during chromatographic separations and their place in the collagen molecule has already been elucidated.

It can be seen from this review that gas chromatography is a method highly suitable for trace analysis. Its advantage over the other chemical and physical analytical methods is that it is a separation method which mostly yields a qualitative and quantitative result.

The high-sensitivity ionisation detectors fulfil most of the requirements of trace analysis with respect to sensitivity and often also with respect to selectivity. Particularly promising in this respect are the sodium thermionic detectors and the electron-capture detectors. The possibility of connecting specific detectors in parallel with those which yield signals for all substances, e.g. coupling of a flame-ionisation detector with one or more other detectors is also promising. The sodium thermionic detector with two burners, which is a parallel combination of two systems, and makes it possible to record with special sensitivity both substances containing phosphorus and halogens and to record the other components, deserves special attention.

Although gas chromatography is at present sufficiently equipped for highly sensitive detection of trace components, the work in this direction has not yet been completed. It is frequently the case that one is so impressed by the sensitivity of the ionisation reactions and by the modern instrumentation of detectors and apparatus, that the possibilities offered by the other analytical principles, especially the colorimetric ones, tend to be disregarded.

The sensitivity of the chromatographic method can be relatively simply increased by using some concentration process. In this respect, the most valuable methods are those which use temperature programming and the sorption-type methods of concentration of the trace components. The technique of temperature programming substantially shortens the time of analysis, brings about a narrowing of the chromatographic bands, and sometimes allows continuous operation. The sorption method for enrichment using phase equilibrium in the sorption system is specially significant for the analysis of air and gases. It eliminates one of the major problems of trace analysis, i.e. the interference from common components such as water vapour. Inverse chromatography (vacancy chromatography) appears to be advantageous for trace analysis under industrial conditions.

Trace analysis by means of gas chromatography is of fundamental importance for the solution of problems relating to air pollution and industrial hygiene; for the production and processing of pure volatile substances, especially monomers, and for modern agricultural chemistry and the foodstuff industry. There is no doubt that it will play an important role in the further investigation and control of effects that modern industrial civilisation has on living Nature. Some of the most serious problems which can be clarified by GC trace analysis are, e.g., the composition of air pollutants, residue analyses of a