Theoretical plate effective

The efficiency of an open tubular column can be measured in several ways the most widely used methods are the number of theoretical plates (n), the nu3aber of effective theoretical plates (N), the height equivalent to a theoretical plate (HETP) or effective plate, the coating efficiency and the separation number (SM). No single method is ideal, standardization is lacking and... 

Effective theoretical plate number (Aeff), 4, 100 Eluent, 89 Enthalpy, 117, 128 Entropy, 128... 

M mass of solute to be separated N number of effective theoretical plates P pressure Q flow rate R resolution S peak capacity Sm specific heat of mobile phase Ss specific heat of adsorbent Sg specific heat of detector cell walls V volume in conventional units Vo system dead volume Vr retention volume V r corrected retention volume Vm volume of mobile phase in the column Vs volume of stationary phase in the column Ve extra column volume... 

Effective theoretical plate number. N eff " number relating to column performance when resolution is taken into account. 

Open-tubular columns utilized In gas chromatography have, with few exceptions, been of 0.2 mm diameter or larger and have therefore provided at most only a few thousand effective theoretical plates per meter length. Nevertheless, the theoretical background for design of column efficiencies of 10 or more effective plates per meter was presented as early as 1958. Laub et (19) have explored the practical limits of the early theoretical work and in particular, the fabrication and properties of capillary columns of Inner diameter ranging from 0.3 to 0.035 mm. The latter exhibits on the order of 2 x 10 N j /m for k of 17. Much higher efficiencies could be realized with the mass spectrometrlc detector. 

While extremely large numbers of theoretical plates are possible with larger diameter columns (22, 23), calculations from chromatographic theory of the Internal diameters and column lengths necessary to achieve relatively high efficiencies in reasonable analysis times Indicate that column diameters of 50 to 100 ym l.d. are necessary for high-resolution SFC (23). For example, more than 10 effective theoretical plates are possible In less than two hours on 30-m long columns of 50 ym l.d. 

Presented in Table I are the dimensions and properties of the several columns prepared in this work. The internal diameter was varied as shown from 0.278 mm to 0.0345 mm, while the stationary-phase film thickness was held constant for all but the last of the columns. Thus, the phase ratio (V] /Vc) decreases on passing from column 1 to 6 over the range 231.5 to 54.25. The solute capacity factors increase accordingly from 6.83 to 29.47. The number of theoretical plates per meter leng N/m for all columns except the first is therefore very nearly equal to the number of effective theoretical plates per meter, since the capacity factors are close to or exceed 10. 

Effective theoretical plates N ff, the effective or true number of separation steps in a column, takes into account the column dead time in the calculation of column efficiency (see column efficiency). 

Number of theoretical plates N, refers to the number of separation steps in a column, is used to describe the efficiency of a column for a given separation and is calculated using observed retention times see column efficiency and effective theoretical plates. 

A eff Number of effective theoretical plates, effective column efficiency... 

A somewhat more realistic measure of the separation efficiency of a column is the effective theoretical plate number N pp ... 

An efficiency of 60,000-70,000 effective theoretical plates for methyl oleate was regularly attained and satisfactory separation of the four methyl octade-canoates (9-trans, 6-c/s, 9-c/s) was achieved (Fig. 6-19 [72]). 

An improved method, utilizing a capillary Pasteur pipet for introducing the sample onto the chromatographic column approximately doubles the effectiveness (theoretical plates) of the column. Dry-column flash chromatography has been adapted for use in the instructional laboratory. The "column" consists of a dry bed of silica gel in a sintered glass funnel placed in a standard vacuum filtration flask the solvent is eluted by suction. Small (16 X 150-mm) test tubes inserted into the flask below the stem of the funnel are used to collect the fractions. This technique has been used successfully to separate mixtures ranging from 150 to 1000 mg. 

Theoretical plate number N and effective theoretical plate number may then be calculated for both the discrete- and continuous-flow models. A number of chromatographic systems from the literature were examined by Fritz and Scott. In all cases they demonshated the applicability of the actual data to their system. 

FIGURE 4,14 Example of isothermal gas chromatogram simulation. The Analysis tab (shown) displays the elution conditions plus the retention times, peak widths, effective theoretical plate numbers, and resolution for the two peaks flanking the cursor. Program GC-SOS V 5.1 (ChemSW, Inc., North Fairfield, CA). 

Figure 3.2. Plot of height of an effective theoretical plate (HETP) against carrier gas velocity (Van Deemter curve) for hydrogen, nitrogen and helium, obtained on a 25 m WCOT column (0.25 mm i.d.).

The number of effective theoretical plates in a column, taking the dead volume into consideration also HETP). 

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