The below link is to an article about a recent Canadian study on spices. 63 out of 268 pure spices tested positive for gluten. The range of detected gluten was 5 ppm - 20,000 ppm gluten, however the majority of spices with higher contamination were not domestically processed. And the one with the highest test result is considered to probably have had wheat illegally added.
All spices that tested positive were ground, and the positive tests were on: clove, coriander, cumin, fenugreek, mace, sage, thyme, and white pepper.