分子筛，一种多孔固体，通常是合成或天然沸石，用于分离分子尺寸的颗粒。沸石是水合金属铝硅酸盐化合物，具有明确的晶体结构。硅酸盐和铝酸盐群在空腔周围形成三维晶格，金属离子和水分子松散地固定在空腔中。通道贯穿整个晶体，将腔相互连接，并在晶体表面终止。加热后，沸石失去水分，其晶体结构几乎没有变化。脱水沸石可以可逆地吸收水或其他小到足以通过通道或孔隙的分子。金属离子也很容易被其他电荷和大小相似的离子单元所取代。
分子筛用于干燥气体和液体，并根据分子的大小和形状分离分子。当两个分子同样小并且可以进入孔隙时，分离是基于分子的极性（电荷分离），更极性的分子优先被吸附。比较凝胶色谱法。
Molecular sieve, a porous solid, usually a synthetic or a natural zeolite, that separates particles of molecular dimension. Zeolites are hydrated metal aluminosilicate compounds with well-defined crystalline structures. The silicate and aluminate groupings form three-dimensional crystal lattices surrounding cavities in which the metal ions and the water molecules are loosely held. Channels run through the entire crystal, interconnecting the cavities and terminating at the crystal surface. Upon heating, the zeolites lose their water content with little or no change in their crystal structure. The dehydrated zeolite can reversibly absorb water or other molecules that are small enough to pass through the channels or pores. The metal ions are also readily replaceable by other ionic units of similar charge and size.
Molecular sieves are used for drying gases and liquids and for separating molecules on the basis of their sizes and shapes. When two molecules are equally small and can enter the pores, separation is based on the polarity (charge separation) of the molecule, the more polar molecule being preferentially adsorbed. Compare gel chromatography.