Height equivalent to theoretical plates

HETP height equivalent to theoretical plate, m HTU height equivalent to a transfer unit, m... 

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. 

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 ... 

Figure 12.7 Van Deempter plots for three GC carrier gases N2, He, H2 H (height equivalent to theoretical plate) vs. u (linear flow velocity, cm/s).

The efficiency contribution to the resolution, i.e., the column plate number, N, is directly proportional to the column length, L, and increases with decreasing particle size of the column packing and—to a lesser extent—with decreasing flow rate of the mobile phase. The dispersion of a solute band as it migrates along the column is characterized by the height equivalent to theoretical plate, H = UN, and depends on experimental conditions, such as the velocity of the mobile phase, u, described to a first approximation by the well-known van Deemter equation ... 

MPa, as is usual in conventional LC, and at the optimum flow velocity, u, corresponding to the minimum height equivalent to theoretical plate, H, on the van Deemter H-u curve (Eq. 5). An example of the kinetic plots for... 

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... 

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