Columns performance characteristics

SIMDIS analyses (54-57), since most commercial high-resolution columns can surpass the recommended column performance characteristics. 

This matrix will contain information regarding loading characteristics such as flooding hmits, exchanger areas, pump curves, reactor volumes, and the like. While this matrix may be adjusted during the course of model development, it is a boundary on any possible interpretation of the measurements. For example, distillation-column performance markedly deteriorates as flood is approached. Flooding represents a boundary. These boundaries and nonlinearities in equipment performance must be accounted for. 

Occasionally, samples are run that adsorb onto the packing material. Generally, if one of the performance characteristics of the column changes by 10% or more, it is prudent to clean the column. These performance characteristics are (1) asymmetry factor, retention time, resolution, and theoretical plates. 

Relative Performance Characteristics of Tower Packing and Column Trays ... 

We first note the very large differences in column performance for the two methods. Effective plates per second represents the speed characteristics of a column (e.g., the number of plates that can be generated in a given time interval) (13). As can be seen, HPLC is 100 to 1000 times faster than classTcal LC. (We shall discuss the differences between PLB and PB in the next section.) This improved performance arises mainly from the use of significantly smaller particle sizes in HPLC. Moreover, in classical LC, the mobile phase is delivered to the column by gravity feed, hence, the very low mobile phase velocities. In HPLC, it is desireable to improve performance... 

Unger, K.K. (editor)(1979). Silica columns packing procedure and performance characteristics. Porous Silica Journal of Chromatography Library, Volume 16. Elsevier, Amsterdam. pp.169 186. 

Cryofocusing traps are often used to interface purge and trap concentrators to gas chromatographs with capillary columns. The enhanced performance characteristics of the design provide a significant improvement over previous systems. The use of a sophisticated cyrotrap with a thermal gradient ensures that the sample will be trapped and injected with high efficiency. 

Residue chemists would be most interested in comparable confidence bands or confidence bandwidths. These values become a performance characteristic for any detection system. The values indicate the precision of not only the prepared standards but also the precision of the overall operating detection system. It is ultimately envisioned that a given system of a separation column in a chromatograph with a certain type of detector should give bands of standardized values. If a chemist finds he has not met... 

Since its creation around 1973, modern high-pressure liquid chromatography (HPLC) has played a dominant role in the analysis of pharmaceuticals. It is used in many different applications for example, in content uniformity assays and stability-indicating methods, for the purity profiles of drug substances, or in the analysis of drug metabolism in animals and humans. The heart of all of these assays is the HPLC column. In this chapter, we will describe the fundamental properties of HPLC columns as well as how these properties influence column performance and separation characteristics in pharmaceutical assays. 

Because column performance decreases with age, it is important to keep good records of its performance. Entries useful to keep track of are chromatogram number, sample identification number, amount injected, volume injected, solvents used (A and B components), column characteristics (ID number, packing, size), back pressure, flow rate, detector setting (UV, absorbance units full scale at given wavelength), gradient conditions, results (retention time of desired product), remarks (baseline shifts, unusual wash profile, etc.), and date. 

Samples are injected onto the turbulent-flow column similar to single-column methods. The analytes of interest are retained in the turbulent-flow column while the large macromolecules are eluted to waste. Once the analytes are separated from the matrix, the samples are then eluted into the analytical column. The characteristics of the analytical column determine the peak shape and separation seen at the MS detector. Flow rates which are compatible with the mass spectrometer can then be used and the chromatograms are based on conventional HPLC parameters. The key to dual-column methods is that the retentive properties of the analytical column must be sufficiently stronger than that of the turbulent-flow column the dual-column approach is performed in such a manner so that the mobile-phase composition needed to elute the analyte from the turbulent-flow column does not elute the analyte from the analytical column. The sample is then focused at the head of the analytical column until the mobile-phase conditions are changed to elute the analyte. The choice of columns is critical to the success of dual-column methods. Table 10.2 lists some of the applications of dual-column methods found in the literature. 

Our main focus for this review is to briefly and critically describe some of the defluoridation techniques as a means of getting a basis to support the adsorption technique, to evaluate the defluoridation adsorbents now being utilized and those novel defluoridation adsorbents reported in literature over the last two decades, with special reference to drinking water. Emphasis is laid toward the adsorbents availability, fluoride sorption capacity and where applicable their kinetic adsorption characteristics and column performances are reported. Detailed characteristics of fluoride adsorption onto surface-tailored zeolite are provided. In addition, various adsorber configurations are reexamined and challenges to and prospects for their application to less developed countries (LDCs) are discussed. 

Sulzer Bros. Ltd., Performance Characteristics, Suiter Column Packing Mellapak, Winterthur. Switzerland. 1985. 

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