The present invention relates to methods and materials for the detection of ketone and aldehyde analytes in fluid samples by means of reacting analyte containing samples with a matrix comprising a hydrazine compound coupled to an H<+> ion exchange resin to produce a hydrazone reaction product with a characteristic color. Methods are also provided for ascertaining the fat catabolism effects of a weight loss dietary regimen comprising determining the breath acetone concentration of the subject by means of contacting said breath with a device comprising an H<+> ion exchange resin to which a hydrazine compound has been coupled and correlating the breath acetone concentration to a standard reflecting the effect on breath acetone of fixed rates of fat metabolism.
