It's possible--especially in spice blends. However, there are companies you can buy from that are very upfront about their ingredients (and gluten) status. Penzeys is a good choice.

I strongly suspect that there are traces of gluten and even MSG in premixed spice blends, regardless of weather the ingredients state it or not. I've experienced phantom glutening and IBS symptoms after using premixed spice blends, those spices being the only thing from a "box" that I'd consume at the time. I made sure to choose only ones that have a good ingredients list eg salt, pepper, coriander, tumeric, cumin (nothing else) yet I still got sick from them. This was after trying a few different brands. I don't get sick when I blend the separate spices myself.

The only way to be sure is to buy whole spices and grind them up yourself :( yet another thing us ultra sensitive gut folks have to do from scratch just to be safe!

Some do, yes! My dear friend at work has celiac and I was so excited about something delicious I made and wanted to share it with her. Turns out she couldn't risk it because I used mustard powder and some mustard powder is cross-contaminated.

I react badly to spice mixtures. I think it's the MSG (not on the label, though!)

The problem with most commercially available spice blends is the handling of the spices before blending. Large companies store grains and spices in the same areas and process them on the same equipment.

Some may use wheat flour as a thickener or anticlumping agent, as an alternative to silicon dioxide.

I use all of my spices seperate.

There's some discussion of this over at celiac.com. There's another forum that uses home test kits for gluten over at Glutenzap. Celiac.com does not allow discussion of Glutenzap, due to concerns about spam.

So, check out the tips at celiac.com and if they do not work for you, you may be sensitive enough that you will need to consult glutenzap or purchase test kits.