Capillary Direct Inlet

What is a Capillary Direct Inlet?

Of the nine sample introduction methods, the capillary direct inlet is the only inlet where the injected volume is routed directly to the ion source. A minimal amount of hardware is needed to get a capillary column in close proximity with the ion source. A capillary direct interface, in simple terms, is the capillary column itself. This allows a sample to be introduced into the vacuum system of the Mass Spectrometer from the atmosphere.

In a capillary system, all the flow of the column enters the Mass Spectrometer. This implies the ion source and vacuum system can handle the amount of flow. The optimal rate of total column flow is typically about 1 ml/min.

The capillary direct inlet consists of a piece of tubing which supports the capillary column as it leaves the GC oven and enters the Mass Spectrometer's ion source. For chromatographicperformance, the interface is heated.

Capillary Direct Advantages

  • simple
  • all sample goes to the Mass Spectrometer
  • best GC sensitivity

Capillary Direct Disadvantages

  • cross-linked columns only
  • retention time may be off due to vacuum effects
  • MS dependent
  • everything injected enters the ion source

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