15 Inletsï€
Operation Manual 211
About the Multimode Inlet
The Agilent Multimode (MMI) Inlet System has seven operating modes:
• The split mode is generally used for major component analyses.
• The pulsed split mode is like the split mode, but with a pressure pulse applied to the inlet
during sample introduction to speed the transfer of material to the column.
• The splitless mode is used for trace analyses.
• The pulsed splitless mode allows for a pressure pulse during sample introduction.
• The solvent vent mode is used for large volume injection. Either single or multiple injections
can be made for each run.
• The direct mode allows for a direct forward pressure of carrier gas through the column.
The split vent valve is closed.
• Sleep mode is used for creating sleep methods, or if all gas needs to flow onto the column.
The MMI can be used with both manual and automatic injection.
Automatic multiple injections (large volume injections) is not available under GC control alone.
MMI split mode minimum operating pressures
The minimum recommended inlet total flow is 20 mL/minute. When the inlet is operated in a
Split mode, there will be a minimum pressure at which the inlet can operate. Typically, low inlet
pressures may be required for shorter, wide bore columns. The minimum pressure is a
function of carrier gas type, total inlet flow, liner design, and possible contamination of the split
vent tube or trap.
A wide bore column requires a much lower inlet pressure than a typical capillary column to
maintain a given flow. Setting the split ratio (total flow) too high when using a wide bore
column can create an unstable control relationship between the pressure and flow control
loops.
These numbers are based on the resistance to flow of new, clean inlet systems. Sample
condensation in the split vent tube or a dirty filter can make these values non-attainable.
Table 28 Approximate minimum viable inlet pressures for MMI in split mode, in psi (kPa)
Split vent flow (mL/min)
50–100 100–200 200–400 400–600
Helium and hydrogen carrier gases
Split liners - 5183-4647, 19251-60540 2.5 (17.2) 3.5 (24.1 4.5 (31) 6.0 (41.4)
Splitless liners - 5062-3587, 5181-8818 4.0 (27.6) 5.5 (37.9) 8.0 (55.2) 11.0 (75.4)
Nitrogen carrier gas
Split liners - 19251-60540, 5183-4647 3.0 (20.7) 4.0(27.6) — —
Splitless liners - 5062-3587, 5181-8818 4.0 (27.6) 6.0 (41.4) — —
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