Why is Degassing of HPLC Mobile Phase Necessary ?

混合溶剂上的泡沫形成可导致许多问题HPLC.通过脱气的流动阶段可以防止分析。

Unstable and noisy baselines

Lower flow rate precision of pump due to cavitations in piston chamber or effect on check valve performance. Excessive pressure can develop which can lead to eventual pump failure.

通过探测器的气泡导致杂散的峰值

由于创建死亡体积，气泡可以通过HPLC柱进行流动阶段的流动转移。

在讨论脱气技术的特征之前，让我们了解问题的出现。溶剂与atomSpheric气体平衡到实验室环境中。在混合溶剂时，空气的溶解度小于其与纯溶剂的比例相同，并且过量的空气倾向于冒出泡出来。

Outgassing can occur on mixing or anywhere in the LC system where rough surfaces produce nucleation sites for bubble formation. Practically it is not necessary to remove the entire dissolved air but only a fraction can be removed to bring it below the supersaturation level in the mobile phase.

低压混合系统更容易发生泡沫形成。在低压混合中，溶剂在大气压下混合，并且除了流动路径的任何地方都可以发生除气。

另一方面，在通过泵之后，在高压混合溶剂中混合，并在混合室中的高压下进行混合。混合物可以是饱和的，但在升高的压力除气后，防止了。如果移动相离开柱并返回大气压，则可以进行气泡形成。

Degassing techniques

用于HPLC流动阶段的常用脱气实践是：

• 氦净化
• 真空脱气
• 超声处理

沸腾是完全摆脱溶解空气的最有效的技术，但由于挥发性组分丢失以及气体的损失以及将移动相平衡到所需的环境温度条件，因此从未建议过的技术。

氦净化消除多达80%的溶解空气。For organic – aqueous mobile phase an equal volume of helium for purging is adequate. The rate of supply of helium can be reduced after some time as excessive purging can lead to loss of more volatile mobile phase components.

真空脱气除去超过60％的溶解空气。一种选择是在过滤流动相通过0.45或0.22μm孔隙率膜过滤器期间施加真空。在线真空脱气可在大多数商业可用系统上获得。流动相通过置于HPLC内的真空室中的多孔聚合物管。管道的孔隙率允许通过壁排出气体，但液体保留在管道中

超声处理using ultrasonic baths is common in most laboratories but as a stand-alone technique it removes only up to 30% dissolved air so sonication in combination with any other technique is recommended..

For practical purposes it is advisable to degas mobile phase in both low and high pressure mixing systems and combination of different techniques can eliminate most of the problems associated with bubble formation.

As on-line vaccum degassing is offered on most commercially available systems sonication in combination with on-line degassing gives satisfactory results.

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