Acetonitrile injections don’t damage Rxi-5Sil MS GC columns. But urban legends persist, so analysts sometimes do unnecessary and laborious solvent exchanges for QuEChERS extracts.
A real problem that might warrant solvent exchange is mismatch between the polar solvent acetonitrile and non-polar pesticide GC columns (e.g. DB-5ms, Rxi-5Sil MS). Upon injection, lack of wetting leads to split GC peaks, especially severe for early eluters. Adjusting GC oven start temperatures rarely eliminates the problem.
A simple method for avoiding split GC peaks for acetonitrile extracts is to add toluene to the extract. At 50% toluene, peak splitting is gone, and sensitivity is only reduced by 2 (not even that, considering height reduction of split peaks). Even 25% toluene can eradicate peak splitting. Adding internal standard in toluene to a QuEChERS extract prior to injection is an elegant way to kill two European Starlings with one Accrington brick. And, no solvent exchange!