The application describes apparatus and methods using ultrasound transmitted through a chromatography column bed to determine the status of materials in the bed space, particularly during chromatography runs. Detected conditions include the profile of a band of eluting material—to see whether it is satisfactory—the arrival of a band of material at the column output, the fitness for use of the ed packing, the passage of different mobile phases, e.g. salt fronts, and other conditions. Aspects claimed include control processors and corresponding programmed products.