The function of the sample inlet is to introduce a representative portion of the sample as a narrow band onto the chromatographic column. Failure to achieve this objective will significantly reduce the separation capability of the GC column. The aims of this module is to outline the various injector categories for GC as well as describe the components and working principle of split and splitless injectors. We will look at problems associated with each of these injection types and explain how they are overcome practically and give examples of optimizing inlet parameters. The working principles, components, and optimization for a series of common GC inlets are explained, and choices for inlet consumables are also discussed.

At the end of this unit you will be able to describe the working principles and problems associated with split and splitless injection in GC, explain how these problems are overcome in a practical setting and demonstrate a working knowledge of which conditions to optimize, highlight various options for septa and liners used with split/splitless inlets, identify the major components and explain the working principles of various other inlet types for packed and capillary GC, and demonstrate a working knowledge of the important variables and optimization routines for these inlets. 

Topics include:

• GC inlet systems
• Split/splitless inlet
• Split injection
• Setting the split ratio
• Sample discrimination
• Injection volume
• Optimizing injection volume
• Split injection experiments
• Splitless injection
• Optimizing splitless injection - purging the inlet
• Optimizing splitless injection - analyte focusing
• Optimizing splitless injection - solvent choice
• Splitless injection experiments
• Choosing an inlet temperature
• Liners for split/splitless injection
• Septa for split/splitless injection
• Septa problems
• Cool-on-column (COC) inlet
• Optimizing COC injection
• Use of retention gaps for COC injection
• Programmed temperature vaporizing (PTV) inlet
• PTV sample flow rate
• PTV liner type and packing
• PTV flow and temperature
• PTV solvent elimination
• Direct (packed column) inlets