Co-injections to avoid peak distortion due to partial solvent trapping in capillary gas chromatography (GC)

Summary

Co-injection techniques (introducing additional pure solvent with the sample) were tested to eliminate peak distortion due to partial solvent trapping. Co-injections of solvent identical with the sample solvent were not successful, because first only partial solvent trapping of the strong type could be eliminated and second, there was no practicable method of placing a band of pure solvent ahead of the sample in the column inlet. Successful co-injections have to accept mixing of the sample with the pure solvent. Either the solvent trapping is improved by co-injection of a solvent which enhances solution of the critical solutes in the sample layer, or it creates a phase soaking effect in the stationary phase and reconcentrates broadened bands beyond the flooded inlet. The added solvent must have the appropriate polarity and some of it must remain in the column inlet at least until the sample solvent has completely evaporated.