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        今日新聞   塔片理論

• 天然氣分析儀的塔片理論，為了研究色譜峰的形狀及評價柱效，建立了塔片理論。塔片理論是色譜的熱力學平衡理論，在色譜分離技術發(fā)展初期，人們把色譜柱看成了一個分餾塔，把樣品組分在柱中的分離視為在分餾塔中的分餾過程。因而直接引用了處理蒸餾過程的概念、理論和方法來處理色譜過程，即將連續(xù)的色譜過程看做許多小段平衡過程的重復。這樣，色譜柱可由許多假想的塔片組成（即色譜柱可分為許多小段），在每一小段內(nèi)，再達到分配平衡，經(jīng)過多次的分配平衡后，分配系數(shù)小的組分先出柱（先達到塔頂）。由于色譜柱的塔片相當多（HPLC-一般為10⁵   片/m）。因此分配系數(shù)的微小差別，即可獲得很好的分離效果。

• 塔片理論的基本假設可歸納為以下4點。

• 1、在柱內(nèi)一小段高度H內(nèi)，組分可很快達到分配平衡。H為理論塔片高度，用H表示，簡稱板高。

• 注：該假定是基于組分在兩相中分配，由于流動相移動較快，而固定相不動，樣品組分不可能在兩相間達到瞬時分配平衡。

• 2、流動相進入色譜柱（洗脫過程）不是連續(xù)的，而是間歇式的（脈動式的），且每次進入一個塔片體積。

• 3、樣品都加在第0號塔片上，且樣品沿色譜柱方向的擴散（縱向擴散）可以忽略。

• 4、分配系數(shù)在各塔片上是常數(shù)。塔片理論的假設，實際上是把組分在兩相間的連續(xù)轉(zhuǎn)移過程，分解為間歇的單個塔片中的分配平衡過程，也就是用分離過程的分解動作來說明色譜過程。可用逆流分配及二項式分布來說明。

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• News of the day     Tower piece of theory

• Column theory of gas chromatograph,In order to study the shape of chromatographic peaks and evaluate the column efficiency,the column plate theory was established.Column theory is the thermodynamic equilibrium theory of chromatography.In the early development of chromatographic separation technology,chromatographic column was regarded as a branch tower,ａnd the separation of sample components in the column was regarded an a branch process in the branch tower .Therefore,the concept,theory and method of dealing with steam chamber process are directly introduced to deal with chromatographic process,that is,the continuous chromatographic process is regarded an the repetition of many small equilibrium processes,chromatographic column can be made of many pieces of imaginary tower (that is,the chromatographic column can be divided into many small section),in each within a short period of sample components in relative to the flow of the phase fixed phase ,ａnd the balanced distribution and then be carried in phase transfer to another tower ,balanced allocation again,after a lot of balance,the distribution of the distribution coefficient of the components of the first column(first to reach the top of the tower).Due to the large number of column tablets (generally 10 tablets/m for HPLC),a small difference in the distribution coefficient can achieve a good separation effect.

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• The basic assumptions of tower plate theory can be summarized as the following four

• 1、Within a short interval of height H in the column,the components can quickly reach distrbutive equilibrium.H is the height of theoretical tower piece,denoted by H,referred to as plate height.

• Note:This assumption is based on the composition distrbution of components in the two phases,Since the phase moves faster while the stationary phase does not,it is impossible for the sample componts to achieve instantaneous distrbution equilibrium between the two phases.

• 2、The phase enters the column(elution process)not continuously,but intermittently (pulsating type),ａnd enters one column volume at a time.

• 3、All samples are added to column 0,ａnd the diffusion of samples along the column direction(longitudinal diffusion) can be ignored.

• 4、The distrbution coefficient is constant on each column.

• In fact,the hypothesis of column theory is to decompose the continuous transfer process of components in two phases into an inter mittent distribution equilibrium process in a single column,that is ,to illustrate the chromatographic process with the decomposition action of the separation process.It can be illustrated by countercurrent distribution and binomial distribution.