Efficiency of chromatographic column

For the analysis of semivolatile organics, a column performance test for base/neutral and acid fractions must be performed to test the efficiency of chromatographic column for separation of the analytes. For the base/neutral fraction, inject 100 ng of benzidine and determine the benzidine tailing factor which must be less than three. Similarly, for acid fraction, inject 50 ng of pentachlorophenol and calculate its tailing factor which must be less than five. 

From the usual definition of equilibrium-staged separations, the plate height is calculated as // = L/N. The efficiency of chromatographic columns increases as the number of plates increases and as the plate height decreases. Both of these values are used widely in the literature as measures of column performance. 

The efficiency of chromatographic columns is usually measured under conditions of linear adsorption equilibria from pulse tests. The Height Equivalent to a Theoretical Plate (HETP) is calculated from the first moment /ij and the variance of a chromatographic peak obtained in a column of length I by ... 

Diffusion and dissolution of substances chromatographed on stationary phases are determined by the mass transfer resistance, which affects the efficiencies of chromatographic columns. Efficiencies of columns with LCSPs are generally lower than those of columns with conventional stationary phases. Therefore, mixtures of LCSPs with conventional stationary phases can be advantageous. The mixture of a liquid crystal with a conventional stationary phase increases the efficiency of a column by improving the homogeneity of the stationary phase film on the wall of a capillary column. The mixture of two hquid crystals can also prove advantageous. The properties of combined stationary phases are described elsewhere. ... 

With highly efficient capillary chromatographic columns, very small amounts of complex mixtures can be separated in the gas phase. Generally, the separated components cannot be positively identified by GC alone. 

The high degree of sensitivity, selectivity, and efficiency of gas chromatography allows the elucidation of a complete profile of the volatile components of distilled spirits. The wide selection of chromatographic columns and techniques, such as gc-ms, gc-ftir, and gc-ms-ftir, has allowed the chemist to routinely identify and quantify individual constituents on a parts-per-biUion level. The two most critical variables in the analysis of volatile components of distilled spirits by gas chromatography are the selection of a suitable chromatographic column and of the most appropriate detector. 

Plate number The number of theoretical plates in a chromatographic column. This is a measure of the efficiency of the column. 

Injection systems of a capillary gas chromatography should fulfil two essential requirements (i) the injected amount should not overload the column (ii) the width of the injected sample plug should be small compared with band broadening due to the chromatographic separation. Good injection techniques are those which achieve optimum separation efficiency of the column, allow accurate... 

One advantage of small bore columns is that they are operated at much lower mobile phase flow rates than the 4.6 mm columns, so there is a large reduction in solvent consumption and hence operating costs of the chromatograph. The efficiency of hplc columns does not depend on their diameter but it does depend on the velocity of the mobile phase in the column, so microbore columns are operated at velocities corresponding to the flow rates used with larger columns. If / (cm3 min-1) is the flow rate in a column with diameter d cm, and the mobile phase velocity is v cm min-1, / and v are related by ... 

The peak width relates to retention time of the peak and the efficiency of a chromatographic column. The efficiency of a column is directly related to the total number of theoretical plates (N) offered by it. 

In general, the resolution (Rs) between two peaks in chromatographic and related separation techniques is determined by the efficiency of the column and the selectivity of the separation [10] ... 

Recent chromatographic data indicate that the interactions between the hydrophobic surface of a molded poly(styrene-co-divinylbenzene) monolith and solutes such as alkylbenzenes do not differ from those observed with beads under similar chromatographic conditions [67]. The average retention increase, which reflects the contribution of one methylene group to the overall retention of a particular solute, has a value of 1.42. This value is close to that published in the literature for typical polystyrene-based beads [115]. However, the efficiency of the monolithic polymer column is only about 13,000 plates/m for the isocratic separation of three alkylbenzenes. This value is much lower than the efficiencies of typical columns packed with small beads. 

As readily observed in most chromatograms, peaks tend to be Gaussian in shape and broaden with time, where W, becomes larger with longer This is caused by band-broadening effects inside the column, and is fundamental to all chromatographic processes.The term, plate number (N), is a quantitative measure of the efficiency of the column, and is related to the ratio of the retention time and the standard deviation of... 

The broader a chromatographic peak is relative to its retention time the less efficient the column it is eluting from. Figure 10.2 shows a chromatographic peak emerging at time t, after injection the efficiency of the column is most readily assessed from the width of the peak at half its height and its retention time using Equation 1 ... 

Efficiency of the chromatographic system can be determined from the number of theoretical plates per meter. Although this term primarily describes the property and resolution efficiency of a column, other extra column variables, such as the... 

The efficiency of a column, N, is a number that describes peak broadening as a function of retention and is dependent on the entire chromatographic system. The most common method for calculating N is the tangent method. 

The column is the heart of the chromatograph, providing the means for separating a mixture into components. The selectivity, capacity, and efficiency of the column are all affected by the nature of the packing material or the materials of construction.7 Figure 3.16 indicates how the components of the column contribute to chromatographic performance. 

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