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The restrictions imposed by instrumentation and some methodological constraints make that only volatile organic compounds have been analyzed by in situ instruments in planetary exploration. It has been argued that polycarboxilic acids like the hexacarboxylic acid (mellitic acid) can be produced and accumulated in the martian regolith from the oxidation of meteoritic organic matter. However, these compounds are non-volatile and instruments designed for the analysis of volatile compounds would not detect them. Herein we report the production of an antibody to mellitic acid and the development of a fluorescent inhibition microarray immunoassay (IMI) to detect this substance to a limit of 5 ppb (ng mL(-1)). We used the anti-mellitic antibody to detect mellitic acid in drill core samples obtained from different depths in the Atacama desert (Chile), a highly relevant terrestrial analogue for Mars. The presence of mellitic acid was corroborated by organic extraction and GC/MS analysis. Our results showed a smooth gradient of mellitic acid concentration, being higher at the surface and near the surface (1.17-1.57 ppm) and diminishing with depth to be undetectable at a depth of 4 m. Our immunoassay can be easily implemented in instruments for in situ analysis. (c) 2012 Elsevier Inc. All rights reserved.