離心技術是利用物體高速旋轉時產生強大的離心力，使置於旋轉體中的懸浮顆粒發生沉降或漂浮，從而使某些顆粒達到濃縮或與其他顆粒分離之目的。這裡的懸浮顆粒往往是指製成懸浮狀態的細胞、細胞器、病毒和生物大分子等。離心機轉子高速旋轉時，當懸浮顆粒密度大於周圍介質密度時，顆粒離開軸心方向移動，發生沉降；如果顆粒密度低於周圍介質的密度時，則顆粒朝向軸心方向移動而發生漂浮。常用的離心機有多種類型，一般低速離心機的最高轉速不超過6000rpm，高速離心機在25000rpm以下，超速離心機的最高速度達30000rpm以上。
Centrifugation techniques is to condense certain granule or to separate one granule from the other using a powerful centrifugal force which is generated by high speed revolving item. During the centrifugation process, granules in the rotating object either settles or floats. What worth mentioning is that the granule hereby refers to cell, organelle, virus and large biological molecule in suspension. While the centrifuge rotor is high speed revolving, the granule would depart the axis to settle if the granule density is higher than that of the ambient medium, and it would get closer to the axis to float if its density is lower than that of the ambient medium.
根據離心原理，可設計多種離心方法，常見下列三大類型：
Several centrifugation methods are designed based on the centrifugal principle, and following are the most commonly used three types.
1.差速離心法。通過逐步增加相對離心力，使一個非均相混合液內形狀不同的大小顆粒分步沉澱。
No.1 the differential centrifugation. It is to centrifugate different shape granules in uneven mixture step by step through gradually increase the centrifugation power.
2.密度梯度離心法。離心前，實驗室離心機的離心管內先裝入分離介質（如蔗糖、甘油等），使形成連續的或不連續的密度梯度介質，然後加入樣品進行離心，具體又可分為：
1）速度區帶離心法。離心前，離心管內先裝入蔗糖、甘油、CsCl、Percoll等密度梯度介質，待分離樣品鋪在梯度液的頂部，離心管底部或梯度層中間，同梯度液一起離心，利用各顆粒在梯度液中沉降速度或漂浮速度的不同，使具有不同沉降速度的顆粒處於不同密度的梯度層內，達到彼此分離的目的。本法可分離各種細胞、病毒、染色體、脂蛋白、DNA和RNA等生物樣品。
2）預製梯度等密度離心法。要求在離心前預先配製管底濃而管頂稀的密度梯度介質，常用介質有蔗糖、CsCl、Cs2SO4等，待分離樣品一般鋪在梯度液頂上，如需挾在梯度液中間或管底部，則需調節樣品液密度。離心后，不同密度的樣品顆粒到達與自身密度相等的梯度層，即達到等密度的位置而獲得分離。
No.2 the density gradient centrifugation. Before centrifuging, fill the tube with centrifugation medium such as sugar or glycerol so as to form continuous or un-continuous density gradient medium, and then put in the sample item to centrifugate. The density gradient centrifugation is then subdivided into speed zone centrifugation, preparative gradient even-density centrifugation and auto form gradient even-density centrifugation.
3）自成梯度等密度離心法。某些密度介質經過離心後會自成梯度，例Percoll，可迅速形成梯度，CsCl、Cs2SO4和三碘甲醯葡萄糖胺經長時間離心后也可產生穩定的梯度。需要離心分離的樣品可和梯度介質先均勻混合，離心開始后，梯度介質由於離心力的作用逐漸形成管底濃而管頂稀的密度梯度，與此同時，可以帶動原來混合的樣品顆粒也發生重新分佈，到達與其自身密度相等的梯度層里，即達到等密度的位置而獲得分離。
No. 3 the sedimentation equilibrium centrifugation. It is to centrifugate based on the sample granules' buoyant density difference. The medium primarily used shares the same density of that of the sample and the medium forms density gradient during centrifuging, granules either setting or floating to a proper position in the mixture.
3.沉降平衡離心法。根據被分離物質的浮力密度差別進行分離，所用的介質起始密度約等於被分離物質的密度，介質在離心過程中形成密度梯度，被分離物質沉降或上浮到達與之密度相等的介質區域中停留並形成區帶。
There are several different centrifuge types. Generally speaking, the max rev of low speed centrifuge won't pass 6000rpm, the max rev of high speed centrifuge won't pass 25000 rpm and the max rev of super speed centrifuge is over 30,000 rpm.
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