Height equivalent per theoretical plate

The properties of a fractionating column which are important for isotope separation are (1) the throughput or boil-up rate which determines production (2) HETP (height equivalent per theoretical plate) which determines column length (3) the hold-up per plate which determines plant inventory and time to production (4) the pressure drop per plate which should be as small as possible. The choice of a particular column is invariably a compromise between these factors. The separation in a production column is of course less than it would be at total reflux (no product withdrawal). The concentration at any point in the enriching section can be calculated from the transport equation (see, e.g., London 1961)... 

Height equivalent per theoretical plate (H.E.T.P.), 95 n-Heptaldehyde, 251 n-Heptaldoxime, 348 n-Heptane, 238 1-Heptene, 240 n-Heptoic acid, 354, 356 n-Heptoic anhydride, 371, 374 n-Heptyl alcohol, 247, 251 n-Heptylamine, 413, 418 n-Heptyl chloride, 275 n-Heptyl iodide, 288 n-Hexacosane, 938, 941 Hexadecane-1 16-dicarboxylic acid, 938,940... 

HETP (Height equivalent per theoretical plate) Random Packings ... 

Now, the variance per unit length of a column is numerically equivalent to ratio of the column length to the column efficiency [2] [i.e., the height of the theoretical plate (//)] thus. 

Height equivalent to a theoretical plate (HETP) A measure of the efficiency of a column usually expressed in millimeters. HETP — LIN, where L is the length of a column and N is the number of theoretical plates. The reciprocal of HETP is also used to describe efficiency and is often expressed by the terms plates per meter. 

From this equation it can be seen that the efficiency per unit length is inversely proportional to the capillary diameter. Decreasing the diameter of the capillary will decrease the height equivalent to a theoretical plate. The efficiency per unit length increases. Therefore, smaller-diameter capillaries can be used at shorter lengths, which ultimately decreases the separation time. 

Efficiency (TV) may be expressed as the number of theoretical plates for the column under specific experimental conditions. Efficiency is also frequently defined as the number of plates per meter of chromatographic bed, or in terms of H, the height equivalent to a theoretical plate. 

Band broadening within the chromatographic column is described as a function of mobile phase linear velocity ( ) by the well known van Deemter equation [5] that relates the height equivalent to the theoretical plate (HETP) to u the lower the HETP, the higher the plate number per unit length of a column. It follows that the highest efficiency is obtained for the shortest HETP. The van Deemter equation is ... 

This is known as the plate time and has units of seconds. It is equivalent to the amount of time it takes to generate one theoretical plate. Its inverse would be plates per second, N/to. Plates per second may also be expressed more generally as N/t for elution times other than the void time [2,3]. These terms more effectively describe the criteria of resolution per unit time that are desired to be maximized (actually, N/t is proportional to resolution squared per time) unfortunately, they are not widely used in the literature, and for the sake of continuity will not be used in this discussion. The following sections will look at what influences plate height and velocity and how best to minimize H/u. 

With effects causing asymmetrical spreading assumed negligible, the plate height h (or HETP, height equivalent to a theoretical plate) for a gaussian distribution may be defined as variance per unit length of column ... 

Since coluriins are constructed in various lengths, it is convenient to have a measure of the efficiency per unit length. This is commonly known as the height equivalent to a theoretical plate (HETP) and is obtained by dividing the number of theoretical plates into the length. 

All separation processes are inherently accompanied by zone broadening, which is due to the dynamic spreading processes dispersing the concentration distribution achieved by the separation [1]. As long as the relative contributions of these dispersive processes decrease, the efficiency of the separation increases. A conventional empirical parameter describing, quantitatively, the efficiency of any separation system is the number of theoretical plates per separation unit, A, or the height equivalent to a theoretical plate (the theoretical plate height) H defined by... 

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