Heinz Engelhardt – författare

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.

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.

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).

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).

Capillary electrophoresis (CE), also designated by the acronym HPCE for "High Per- formance Capillary Electrophoresis" is a rapidly growing analytical separation method. It unites the separation technique of classical electrophoresis on plates with the instrumental methods of chromatography with respect to direct detection of the solutes separated in the capillary and their ready identification and quantification. The initial problems of inadequate reproducibility in quantitative analysis, due to the necessity of handling extremely small volumes, have largely been solved in the sec- ond generation commercial instruments. Hence, a rapid and reliable separation sys- tem is available for ionic compounds from the smallest cation (the lithium ion) up to poly anions with molecular weights ranging in the millions (such as DNA molecules). The methods of gel electrophoresis and isoelectric focusing can be readily extended to separation techniques carried out in a capillary. For nonionic compounds an addi- tional separation method is available in the form of micellar electrokinetic chroma- tography (MEKC).This involves a true chromatographic separation process because the distribution of the analytes between the buffer and the micelles is superimposed on the electrophoretic migration, which contributes substantially to the selectivity.

Die Hochdruck-Flüssigkeits-Chromatographie entwickelt sich seit etwa 1969 mit großer Geschwindigkeit zu einer Standard-Trennmethode. Geprägt wurde die Entwicklung dadurch, daß ihre "Pioniere" fast ausschließlich Experten der Gas-Chromatographie gewesen sind. Sie glaubten, die Prin­ zipien und ~1ethoden der alten Methode auch im Bereich der schnellen Flüssigkeits-Chromatographie voll anwenden zu können. Es hat eine Weile gedauert, bis endgültig klar wurde, daß dies nicht so ist. Zwar ist es für die Theorie der Chromatographie gleich, ob der Eluent ein Gas oder eine Flüssigkeit ist, die quantitativen Unterschiede der Parameter (wie Viskosität, Diffusionskoeffizient) ändern das Bild aber wesent­ lich. Heute scheint allgemein akzeptiert zu werden, daß das Apparative der Hochdruck-Flüssigkeits-Chromatographie sogar einfacher als bei der Gas-Chromatographie ist. Weiterhin scheint man einig, daß optimale Analysen mit stationären Phasen mit Siebfraktion um 5 oder 10 ~m durch­ zuführen sind. Da die Entwicklung kommerzieller Geräte etwa zwei Jahre in An­ spruch nimmt, ist es selbstverständlich, daß es heute noch eine Lücke zwischen dem neuesten Stand der Technik und den kommerziell angebo­ tenen Geräten gibt. Es ist sehr viel getan, wenn es mit diesem Buch gelingt, dem Praktiker jene Fragen nahezubringen, die er sich stellen muß, bevor er ein hochdruck-flüssigkeits-chromatographisches Gerät anschafft, und wenn ihm das Auffinden des geeigneten Systems (statio­ näre Phase und Eluent) für sein spezifisches Trennproblem erleichtert wird. Das gelingt auch ohne detaillierte Diskussion der Theorie der Chromatographie.