Chromatographic systems sample preparation

The radius of an analytical column is determined, among other factors, by the extra column dispersion of the chromatographic system. For preparative columns, however, the radius is determined by the sample load that is required to be placed on the column to obtain the necessary throughput. 

Every chromatographic investigation begins with the preparation of the sample and the chromatographic system. This is followed by the crux of the separation process (development of the chromatogram) which is in turn followed by the visualization of the separated substances and the preservation of the chromatogram and finally by the analysis of the results. 

The optimization of preparative and even micropreparative chromatography depends on the choice of an appropriate chromatographic system (adsorbent and eluent), sample application and development mode to ensure high purity, and yield of desirable compounds isolated from the layer. For the so-called difficult separations, it is necessary to perform rechromatography by using a system with a different selectivity. But it should be taken into account that achievement of satisfactory results frequently depends on a compromise between yield and the purity of the mixture component that is being isolated. 

Gas chromatographic analysis starts with introduction of the sample on the column, with or without sample preparation steps. The choice of inlet system will be dictated primarily by the characteristics of the sample after any preparation steps outside the inlet. Clearly, sample preparation has a profound influence on the choice of injection technique. For example, analysts may skip the solvent evaporation step after extraction by eliminating solvent in the inlet with splitless transfer into the column. Sample introduction techniques are essentially of two types conventional and programmed temperature sample introduction. Vogt et al. [89] first described the latter in 1979. Injection of samples, which... 

Principles and Characteristics Because of the limited selectivity of extraction, a chromatographic analysis is almost always needed. Recently, a fair amount of progress has been made regarding the front end of the total analysis procedure, namely the integration of sample preparation (this being the analytical bottleneck) and separation. The idea behind such systems is to perform sample extraction, cleanup and concentration as an integral part of the analysis in a closed system. Scheme 7.2 shows the main procedures related to sample preparation for chromatographic analysis. 

Cycle time consists of several individual components. One is the separation time of a sample. Another component is instrument overhead time that may be subdivided into conditioning, sample preparation, and post-separation phases. The final component is system overhead time that covers delays caused outside the LC modules (Figure 3.9). These times do not necessarily have to follow the fixed order shown in the figure. In particular, the position of the instrument conditioning may vary and the tasks do not have to be arranged linearly. Cycle times in early chromatographic systems... 

Since the HPLC-MS cycle time (the chromatographic run time plus the autosampler injection time) is usually governed by the chromatographic system, focus has been given to sample preparation and chromatographic techniques. 

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