Height of equivalent theoretical plate HETP

A column in which the ascending vapour is in contact with the refluxing liquid is used for this purpose. The reflux is generated by an overhead condenser. Due to the phase transfer in the column, a height equivalent of theoretical plate HETP can be defined where the two phases, liquid and vapour, are in thermodynamic equilibrium. The theoretical plate number is defined as... 

The main reason to preserve the structure of the monolith on different scales is to make the transfer of chromatographic methods very simple and straightforward. Keeping a constant structure, the resin efficiency, normally measured in terms of height equivalent of theoretical plate (HETP), is also kept constant. Therefore, method transfer time can be significantly shortened since fewer experiments are required. 

The separation efficiency of packed column is usually expressed in terms of height equivalent of theoretical plate (HETP). According to the Fenske equation, the slop of ln(ir ) versus Z plot is equal to where is the relative volatility of the... 

The width of the band eluting from the chromatographic system depends on the distance it has traveled. The proportionality factor between the two, termed height equivalent to theoretical plate (HETP), or plate height in short, is defined in the following way ... 

For a phenomenological description of chromatographic separation, the concept of theoretical plate is often used. Chromatographic column is considered to consist of a large number of theoretical plates, in each of which equilibrium relations between fluid and particle phases hold (Fig. 10.1). Height equivalent to theoretical plate (HETP) and number of theoretical plate (NTP) are then related to column length z as... 

GC = gas chromatography GLC = gas-liquid chromatography HETP = height equivalent of 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)... 

If the comparison between the two techniques were to be based on the criterion of HETP (height equivalent to theoretical plate) values, HPLC can easily be shown to be a more efficient technique than HPTLC. The conventionally packed HPLC columns used in most analytical laboratories are capable of providing approximately 10,000 theoretical plates. Special HPLC columns, such as capillary columns, are capable of even greater efficiency. However, HPTLC gains certain advantages, which are outlined below, because it is an open-bed system while HPLC is a closed-bed system. 

In the case of a plate column the performance of a real plate is related to the performance of a theoretical one by the plate efficiency. In the case of a packed column the height equivalent to a theoretical plate HETP) gives a measure of the contacting efficiency of the packing. 

Sometimes the height equivalent to a theoretical plate (HETP) is employed rather than and to characterize the performance of packed towers. The number of heights equivalent to one theoretical plate required for a specified absorption job is equal to the number of theoretical plates,... 

An alternative to determining packed height is through the use of an empirical term, height equivalent to a theoretical plate (HETP). This term can be measured in a fashion similar to that used for the overall plate efficiency of a column (eq. 44) ... 

Use of HETP Data for Absorber Design Distillation design methods (see Sec. 13) normally involve determination of the number of theoretical equihbrium stages or plates N. Thus, when packed towers are employed in distillation appRcations, it is common practice to rate the efficiency of tower packings in terms of the height of packing equivalent to one theoretical plate (HETP). 

Many operating variables, such as sample volume, flow rate, column length, and temperature, must be considered when performing any separation. The relative importance of these variables for Toyopearl HW-55F resin columns has been specifically evaluated. For example. Fig. 4.47 shows the relationship between column efficiency, or height equivalent of a theoretical plate (HETP),... 

Column efficiency (number of theoretical plates) As in batch chromatography, one needs to determine the efficiency of the column in order to evaluate the dispersion of the fronts due to hydrodynamics dispersion or kinetics limitations. The relationship of N proportional to L can be expressed in terms of the equation for height equivalent to a theoretical plate (HETP) as ... 

FP = flow parameter, dimensionless HETP = height equivalent of a theoretical plate, in. 

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. 

Before releasing a process column for chromatography, it is advisable to perform some test to measure efficiency, such as calculating height equivalent theoretical plates (HETP), both to forestall any problems in the column bed and to provide a benchmark by which to measure column reproducibility and predict degradation of the bed or material. Examples of compounds that are relatively innocuous for use in pharmaceutical applications are 1% NaCl (for gel filtration), concentrated buffer solutions (for ion exchange), and benzyl alcohol and parabens for reverse phase LC.10... 

Time-dominated processes inherently govern chromatography. The horizontal axis of a chromatogram is time (and not energy as in spectroscopy). To describe the quality of a chromatographic system the concepts of the height equivalent to a theoretical plate, HETP or H, and the number of theoretical plates N are used (Equation 4.1) ... 

The methods for estimating the heights of transfer units, HTU, given in Section 11.14.3 can be used for distillation. The relationship between transfer units and the height of an equivalent theoretical plate, HETP is given by ... 

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