The column inside the Mini GC and Mini GC Plus is a Restek MXT-1 stainless steel capillary column with dimethyl polysiloxane. Injecting anything through the column that is not on the approved list of compounds (see the accompanying booklet or online) can cause damage to the column and shorten its life. Therefore, no real guarantees of lifetime can be made.
However, if only approved compounds have been injected, you can expect several years of good use. Dimethyl polysiloxane will slowly oxidize when room air is used as the carrier gas at higher temperatures. However, testing has shown that three years of use, running 8 hr/day, resulted in less than a 3% shift in retention times. Typical educational use, being far less demanding, should see the column last for a long time.
If you suspect your column is ready to be replaced, please email chemistry@vernier.com to make arrangements.