centrION Overview

The centrION, within the isoprime precisION IRMS, is the gas control inlet system. The mass spectrometer requires a controllable  gas supply for normal operation, and this can be split into different, specific functions:

  1. Carrier gas
  2. Inlet sample transfer
  3. Inlet sample conditioning
  4. Dilution
  5. System control
  6. Source Inlet Valve (SIV)

Carrier Gas

The carrier gas used on the isoprime precisION and the majority of inlets is helium. For Continuous Flow “CF” systems, the centrION supplies this to the isoprime precisION at a flow rate of 3-5ml/min, via the monitoring gas capillaries which are connected to the source. This helium flow creates an optimal environment for  ionization and source operation.

Inlet Sample Transfer

The inlet sample is introduced to the centrION via ports on either the EA inlet port, the inlet gas selector or directly to the GC inlet capillary. This is then transferred to the Source Inlet Valve (SIV) which allows for both a GC and another inlet (e.g. EA, iso FLOW etc.) to be connected directly to the source. The introduction of the SIV enables faster switching between inlet options.

The EA port allows for optional dilution, dependent on sample type and size.

The inlet gas selector allows for multiple inlets to be connected, and thus chosen.

The GC inlet capillary essentially bypasses most of the centrION, except for the Nafion dryer phase, before reaching the GC side of the SIV.

Inlet Sample Conditioning

The GC has a dedicated Nafion dryer, whereas the EA and optional inlets share a single Nafion dryer. This Nafion dryer helps remove water from the pathways. The sample is passed along a selectively permeable membrane, which sits within an opposing helium flow. The membrane allows for water molecules to pass through the membrane into the flushing helium flow.

Dilution

The dilution process simply adds an extra amount of helium to the sample. This effectively reduces the percentage of sample within the ion source of the isoprime precisION. This method is required for large samples, or samples which contain an unbalanced proportion of one or more isotopes.

System Control

Within the isoprime precisION, centrION and associated inlets, there are many valves which need to be operated to control the system as a whole. The pneumatic valve gas supply is controlled by centrION, as is the control signal for several electrical solenoid valves.

Electrical Connections and Control

The centrION is controlled directly from a dedicated USB port on the PC. It should be connected via the provided USB repeater extender cable as well as the USB to Mini-USB cable.

The 24V power is supplied internally from the isoprime precisION IRMS MPSU.

The centrION PCB controls the monitoring gas MFCs, monitoring gas selection valve and the SIV (Source Inlet Valve).