What is the plate theory, what is the number of theoretical plates, and what does the number of plat

Martin and Synge were the first to propose the plate theory, which compared a column to a distillation column, and conceived of a continuous column consisting of many small segments. Within each segment, a portion of the space is occupied by the stationary phase and the other part is filled with the mobile phase. Once the components enter the column with the mobile phase, they are partitioned between the two phases.

It is assumed that within each segment the components can quickly reach partition equilibrium in the two phases, such a segment is called a theoretical plate, and the length of a theoretical plate is called the theoretical plate height h. After multiple distribution equilibriums, the components with small partition coefficients leave the distillation column first, and the components with large partition coefficients leave the distillation column later. Due to the large number of plates within the column, even small differences in component partition coefficients can still be achieved with good separations.

Plate theory is the basic theory of chromatography, the column is regarded as a fractionation column, the components to be separated move between the plates of the fractionation column, in each plate the component molecules form a balance between the stationary phase and the mobile phase, with the flow of the mobile phase, the component molecules continue to move from one plate to the next, and constantly form a new equilibrium. The greater the number of plates in a column, the better the separation.

That's the definition, and it couldn't be simpler.

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The plate theory was first proposed by Martin et al., which compared the column to a distillation column, followed the concept of the tray in the distillation column to describe the distribution behavior of components between the two phases, and introduced the number of plates as an index to measure the efficiency of the column.

The theory assumes:

i) Within a short length h of the column, the components can quickly equilibrate between the two phases. This small length of column is called the theoretical plate height h.

ii) In the case of gas chromatography, the entry of the carrier gas into the column is not continuous, but pulsating, with one plate volume (δVM) per inlet.

iii) All components are present at the beginning of plate 0 and the sample has negligible axial (longitudinal) diffusion.

iv) The partition coefficient is constant across all plates, independent of the amount of components on a particular plate.

For simplicity, the chromatogram is composed of 5 plates (n 5, n is the number of plates for the column), and the plate number is denoted by r, r = 1, 2....，n－l；The partition ratio of a component is k=1

Based on the above assumptions, the distribution of this component during chromatographic separation can be calculated as follows:

At the beginning, if there is a unit mass, i.e., m=1 (e.g., 1 mg or 1 g), the component is added to plate 0, and after the equilibrium is distributed, nm=ns= because k=1, i.e., ns=nm. When a plate volume (LδV) of carrier gas enters plate 0 in the form of pulsation, the carrier gas containing the NM component in the gas phase is pushed to the plate 1, and the NS component in the liquid phase (or solid phase) of plate 0 and the NM component in the gas phase of plate 1 will be redistributed between the two phases. Therefore, the total amount of components contained in plate 0 is 0 5, of which the gas-liquid (or gas-solid) phase is 0 25 each, and the total amount contained in plate 1 is also 0 5, and the gas-liquid (or gas-solid) phase is also 0 25.

This process is repeated each time a new plate-volume carrier gas pulsates into the column.

1. The number of theoretical plates.

n, column efficiency of chromatography.

One of the parameters, (referred to as column effect). n Depends on the type and nature of the stationary phase (particle size, particle size distribution, etc.), packing condition, column length such as rock, type and flow rate of the mobile phase, and the properties of the substances used to determine the column effect.

The plate theory cannot explain the experimental results of different column efficiencies under different carrier gas velocities, nor can it point out the factors that affect the column efficiency and the ways to improve the column efficiency.

The tray theory is based on the theory of thermodynamic approximation, and there are no isolated trays in the real column, nor can the premise of the tray theory be fully satisfied.

For example, the tray theory states that the material components can quickly establish equilibrium between the mobile phase and the stationary phase, and that the material components do not diffuse radially as they advance along the column, which is inconsistent with the actual situation of the column.

Therefore, although the plate theory can explain the peak shape and peak height of chromatographic peaks and objectively evaluate the column efficiency of chromatographic columns, it cannot explain some phenomena related to kinetic processes, such as the deformation of chromatographic peak shapes, the relationship between the number of theoretical plates and the flow rate of mobile phases.

The content tray theory is the basic theory of chromatography, the column is regarded as a fractionation column, the components to be separated move between the plates of the fractionation column, in each tray the component molecules form a balance between the stationary phase and the mobile phase, with the flow of the mobile phase, the component molecules continue to move from one plate to the next, and constantly form a new equilibrium. The greater the number of plates in a column, the better the separation.

The lower the theoretical plate height, the higher the number of plates per unit length of the column, and the better the separation. The factors that determine the height of the theoretical tray are: the material of the stationary phase, the uniformity of the column, the physicochemical properties of the mobile phase, and the flow rate of the mobile phase.

This theory cannot explain the different results of the same column under different carrier gas flow rates, nor can it affect the factors that affect the column efficiency and the ways to improve the column efficiency. Due to the rapid flow of the mobile phase and the presence of mass transfer resistance, the partition equilibrium of the two intermediate phases in the separation column cannot be established quickly. So,

There are many problems that the tray theory cannot explain! For example, the price problem...

The theoretical number of plates reflects the efficiency of the column.

Column efficiency is quantitatively expressed in terms of the number of theoretical plates: n=16*(t w)2. where t is the time from injection to the occurrence of the maximum elution peak, and w is the width of the elution peak at the baseline.

The ratio of the residence time of the different compounds to their elution peak widths is close to constant when the same elution conditions are used in a single column. As a result, columns with large theoretical plate counts are highly efficient.

Of course, the size of n is closely related to the length of the column: the theoretical plate height h = column length n, and h can be used to measure the efficiency of the column in the parafiber per unit length, and the smaller h is, the higher the column efficiency.

When n is constant, w varies proportionally to tr. On a multi-component chromatogram, if the components are comparable, the post-eluting peak is progressively wider and the peak height is progressively lower than the previous peak.

Calculating the theoretical plate number with half maximum width is more convenient and commonly used than calculating with peak width, because it is easier to accurately determine half maximum, especially for peaks with slightly tailing. n is directly proportional to the length of the column, and the longer the column, the larger n becomes. The column length should be indicated when the column efficiency is indicated by n, and if it is not indicated, the theoretical number of plates when the column length is 1 meter.

The combination of slabs and towers refers to the presence of some types of units in a buildingSlab floorsSome units have the characteristics of towers. Generally, the combination of slabs and towers is manifested as a building, with slab floors at both ends and towers in the middle.

There are two types of slab buildings: one is the long corridor type, where the residents are connected by a long corridor; The second is unit splicing, where several units are connected together to form a slab.

The house is fully completed, including: construction engineering, equipment installation engineering and internal and external decoration projects, and the completion acceptance.

To achieve "seven links and one level, that is, water access, sewerage, sewage access, power distribution pass, gas pass (gas, natural gas or liquefied gas), ** pass, road pass, site leveling.

The real estate management department refers to houses that have not obtained a house title certificate as off-plan housing.

That is to say, even if it has passed the completion acceptance, reached the "seven links and one level", and even obtained the license for the delivery and use of new residences, as long as the initial registration procedures for real estate have not been completed and the house ownership certificate has not been obtained, it is an off-plan house. The developer's ** off-plan house is called pre-sale, and the buyer must sign a pre-sale contract with the developer when buying the house.

The combination of slab and tower refers to the division of the main structure of the building into two parts in the design of high-rise buildings, one part is the "slab" structure, that is, the horizontal disc-shaped components that carry the floor load; The other part is the "tower" structure, i.e. the vertical member that is subjected to vertical forces and lateral wind loads. Through the combination of "plate" and "tower", Duan Minyin can achieve good structural stability and resistance, and can also improve the space utilization rate and visual effect of the building.

Specifically, for a high-rise building, due to its large height and wide area, it needs to bear large self-weight and external force loads, such as wind loads, ** loads, etc. If only the traditional frame structure is used, there may be problems such as insufficient strength and large deformation. The design scheme of combining plate and tower can be optimized by layering the structure, and a more suitable structure type can be used to take different loads, so as to achieve better structural stability and safety.

It is worth noting that the combination of slab and tower is not suitable for all high-rise building design, and whether to adopt this structural scheme should be comprehensively considered according to the specific situation of the building and the engineering needs.

Tower and Babel Theory is a linguistic theory used to explain why human beings are so rich in linguistic diversity. According to this theory, human languages originated from a common primitive language, and later led to linguistic differentiation and evolution due to factors such as isolation, migration, and cultural exchange, resulting in the formation of many languages in the world today.

The name of the tower theory comes from the biblical story of the Tower of Babel, in which the people who built the Tower of Babel used the same language, but due to mutual distrust and cultural differences, the language eventually diverged into different languages and dialects.

This theory is that if two groups of people are isolated for a long time, their language will gradually change to form a different language. Conversely, if two groups of people are in contact for a long time, their languages may communicate and merge, forming a new variant of the Yusan language.

In conclusion, the Tray Theory is a theory that explains linguistic diversity, arguing that human languages originated from a common primitive language, and later evolved and differentiated over a long period of time to form different languages and dialects.