Chemical Laboratory Practice – serie

Modern liquid column chromatography (LC) has developed rapidly since 1969 to become a standard method of separation. If the statisticians are to be believed, the recent growth of LC has been the most specta­ cular development in analytical chemistry and has not yet abated be­ cause its vast potential for application remains to be fully exploit­ ed. Significant factors contributing to this continued rise are the simplicity and low cost of the required basic equipment and the rela­ tive ease of acquiring and interpreting the data. Unfortunately, in LC, as so often in the field of analytical chemistry, the available commercial instruments are frequently far more complicated - and consequently far more expensive - than is nec­ essary for routine application. Therein also lies the risk of propa­ gating a "black box" philosophy that would be particularly detrimen­ tal to chromatography. Moreover, it appears to have been forgotten, as was done previously with gas chromatography, that inadequate sep­ aration by a column can be remedied only with great difficulty, if at all, by electronic means. Also, whether the capillary columns recent­ ly advocated with great enthusiasm for LC will fulfill the expecta­ tions of their proponents is highly questionable unless someone comes up with some new and revolutionary ideas.

The first section introduces the electrochemical nomenclature necessary for under­ standing the literature on ion-selective electrodes and discusses the general principles behind all electrodes. The second section is concerned with the problems which arise in any accurate elec­ trode potential measurement in practice. Here the most important reference electrodes are discussed with special reference to their use in conjunction with ion-selective elec­ trodes. From experience, almost 75% of all problems which arise when working with ion-selective electrodes are on account of the reference electrode. After the reader is aquainted with the basic problems involved, the third section deals with individual ion-selective electrodes; their properties, handling and methods of pre­ paration. Here the discussion of these electrodes is not arranged according to the spe­ cies detected, but rather according to the kind of construction, since from this view­ point characteristic properties are much the same and handling procedures need only be described once for an entire series of similar electrodes. The fourth section discusses amplifiers. Here the problems of high-ohmic EMF meas­ urements such as noise level, insulation, static charging and ground loops are discussed. The fifth section is devoted to the various evaluation methods. Here a few schemes and examples are provided to indicate optimum practical procedures and the accura­ cies attainable with the various methods are discussed. The last section describes special set-ups such as clinical flow-thru cells, microelec­ trodes for measuring intracellular ionic activities, industrial on-line techniques and continuous environmental protection monitors.

During its short 20 year history High Performance Liquid Chro­ matography (HPLC) has won itself a firm place amongst the instrumental methods of analysis. HPLC has caused a revolution in biological and pharmaceutical chemistry. Approximately two thirds of the publications on HPLC are concerned with problems from this area of life science. Biotechnology, where it is necessary to isolate substances from complicated mixtures, is likely to give further impetus to the dissemination of modern liquid chromatog­ raphy in columns, particularly on the preparative scale. This book presents, by means of examples, the application of HPLC to various fields, as well as fundamental discussions of chromatographic methods. The quality of the analytical result is decisively dependent on the qualities of the equipment employed (by Colin, Guiochon, and Martin). Especially the demands are discussed that are placed on the components of the instrument including those for data acquisition and processing. The section on "quantitative analy­ sis" (by ABhauer, Ullner) covers besides the principles also the problems of ensuring the quality of the data in detail. The basic problems arising by enlarging the sample size to preparative di­ mensions and the requirements put on the aparatus are discussed in the section on "preparative applications" (by Wehrli).