The influence of sample preparation on the ion yield in s-SIMS for alkaline salts was investigated. Potassium chromate and permanganate, dissolved in water, have been spin-coated on silicon or gold substrate before being analyzed by ToF-SIMS under 15 keV Ga-69(+) primary ion bombardment. Analysis of powders pressed on In foil was also performed. The results were taken as reference to allow comparison. Spin coating on Si substrate did not lead to a significant modification as compared to the reference. In contrast, the cluster ion yield was increased by at least one order of magnitude when a gold substrate was used, especially in the negative detection mode. Moreover, large cluster ions were observed in the high mass range (up to m/z 1400) and anionized species were also detected. (C) 2002 Elsevier Science B.V. All rights reserved.