Optimizing Splitless Injections: Introduction

Split and splitless are the two most common modes of injection for GC.  Each has its own set of pros and cons, with the required method sensitivity vs the sample concentration ultimately dictating which one to use.  For trace level analyses, a splitless injection is often the best choice, as the goal is to recover close to 100% of everything that is injected into the instrument.  Unfortunately, splitless injections can be tricky to optimize. There are a number of parameters that must be carefully adjusted to ensure the best chromatography possible.

During a splitless injection, the split vent is closed, directing all flow to the column (with the exception of the septum purge).  Because of this, total inlet flows are relatively slow, leading to slower transfer of the analytes to the column compared to split injection.  This can lead to diffusional band broadening (wider peaks), as well as increased time for adverse interactions to occur within the inlet.

The first critical decision one must make when performing splitless injections is selection of an appropriate inlet liner.  I have discussed liner selection in detail in a previous blog series, so I will refer you to the following blogs for detailed information pertaining to splitless liner selection:

Splitless Liner Selection (Geometry): https://blog.restek.com/gc-inlet-liner-selection-part-i-splitless-liner-selection/

Liner Inertness: https://blog.restek.com/gc-inlet-liner-selection-part-iii-inertness/

Liner Volume: https://blog.restek.com/gc-inlet-liner-selection-part-iv-liner-volume-and-diameter/

Beyond the liner there are several instrument settings that must be optimized to ensure successful splitless injections.  These include inlet temperature, splitless hold time, and initial oven temperature.  In the upcoming blog series, I will discuss the importance of each of these parameters, what can go wrong if they are not properly optimized, and some tips for optimizing them for your analysis.

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