Column performance, comparison

Table 9.7 summarizes the comparison of SEC column performance with regard to particle size of the packing material. The author tried to create this table using the test results of different manufacturers of styrene-divinyl-benzene columns. 

Alter the program to describe a cocurrent column. Compare the results with the countercurrent case for various extremes of liquid flow rate. Using the length found in Exercise 1, operate the column cocurrently to see whether the same degree of removal can be obtained. Show that the comparison depends on whether the column performance is reaction rate or transfer rate controlled. 

For comparison of similar columns, it is important that experimental conditions for the test chromatogram are faithfully reproduced and sufficient time is allowed for column equilibration before starting the test. The expected changes in column performance parameters that are due to changes in the experimental conditions are summarized in Table 15.13. 

Peter, A. et al.. Comparison of column performances in direct high performance hquid chromatographic enantioseparation of 1- or 3-methyl-substituted tetrahy-droisoquinohne analogs. Application of direct and indirect methods, Biomed. Chromatogr, 19, 459, 2005. 

Comparison of column performance among the different types of columns is not easy. Resolution and analysis time at a minimum temperature seem to be the best criteria for comparison. Golay (26) suggests the calculation of performance index (P.I.) for intercomparison of columns. 

Fig. 4.3. High performance liquid chromatography (HPLC) of the monosaccharides obtained from a partially purified preparation of microbubble glycopeptide surfactant from forest soil. Following hydrolysis (in 2 N HC1 for 6 hr at 100°C) and filtration, the carbohydrate mixture was charged on a Bio-Rad HPX-87 cation exchange column. For comparison, part A shows the chromatogram (using the same HPLC column) of a standard solution, which contained 4 pg of each of three different monosaccharides (i.e., the last three peaks shown are glucose, xylose and fiicose, in the order of increasing retention times). Part B shows the chromatogram obtained from hydrolysis of the partially purified (see text) microbubble surfactant (approximately 30 pg). All other experimental conditions were identical in the two cases, i.e., water eluent, 0.5 ml/min flow rate, 85°C, refractive index detector attenuation -2x. (Taken from ref. 322.)...

The most commonly used criterion for judging column performance is efficiency as measured by the number of theoretical plates or column plate count (N) exhibited by the column during the separation of a test mixture. The larger the number of theoretical plates, the more likely it is that the column will produce the desired separations. However, while popular, N is not a complete performance parameter for making comparisons. For example, N does not take into account particle size as does the reduced plate height, h. Another measurement, hmin, accounts for all of these factors as well as the mobile phase linear velocity and sample diffusion. However, N is the term most commonly recognized as being related to resolution (2), as shown in Equation 1 ... 

Figure 5. Comparison of capillary and packed column performances...

Column performance under different conditions or the comparison of different columns may be assessed by considering the height equivalent of a theoretical... 

Figure 9. Comparison of column performance at equivalent loading.

The quantities of W, and in equations (U) and (5) should have the same dimensions and consequently, the value of N is dimensionless. As the value of N is proportional to the column length, it is often expressed as the number of theoretical plate per 1 meter or 1 foot. Because the value of N for a SEC column varies with the sample type, the concentration and the injection volume of a test sample solution, column temperature, and the flow rate of the mobile phase, it is advisable to express the value of N with the experimental conditions of the N measurement. It is especially required for purposes of comparison of column performance, to measure N under the same experimental conditions. 

Figure 3.298 Performance comparison between DNAPac PA100 and PA200 using d (AC)io-ii 20-22-mers as an example. Column dimensions 250 mm x 4 mm i.d. column temperature 25 °C eluent (A) 20 mmol/L Tris (pH...

The performance comparison of classical DE algorithm and DE algorithm with switching scheme in crossover process is presented in Table 2 that composes 8 columns. Names of benchmark instances used in the experiment are in the first column. The results obtained from classical DE algorithm, objective function (total cost), number of vehicle used, and minimum distance are provided in columns 2, 3,... 

Thermodynamically and kinetically complex systems like azeotropic, extractive, and reactive systems pose additional bottlenecks in design and operation of batch columns. The following sections describe the methods for analyzing these complex systems. These methods also provide heuristics for synthesis of these columns especially in terms of the different cuts obtained in a single column or performance comparison of the complex columns. 

---