The injector rapidly introduces the sample into the system with minimal disruption of the solvent flow. HPLC systems currently use variable loop, fixed loop, and syringe-type injectors. These are activated manually, pneumatically, or electrically.
Mechanical problems involving the injector (e.g., leaks, plugged capillary tubing, worn seals) are easy to spot and correct. Use a precolumn filter to prevent plugging of the column frit due to physical degradation of the injector seal. Other problems, such as irreproducible injections, are more difficult to solve.
Variable peak heights, split peaks, and broad peaks can be caused by incompletely filled sample loops, incompatibility of the injection solvent with the mobile phase, or poor sample solubility. Whenever possible, dissolve and inject samples in mobile phase. Otherwise, be sure the injection solvent is of lower eluting strength than the mobile phase (Table 3). Be aware that some autosamplers use separate syringe washing solutions. Make sure that the wash solution is compatible with and weaker than the mobile phase. This is especially important when switching between reversed and normal phase analyses.