and optical detectors alternatively a saw device is used in the form of a mass sensor a layer of the saw substrate is coated with biologics such as receptors or antibodies reactive to ecf compounds or metabolites and the presence of the compound is detected by changes in the saw generated e g a shift in the resonance frequency a phase shift of the acoustic wave or a shift in the amplitude of an acoustic wave since the preferred embodiments utilize a saw device to extract ecf it is advantageous to incorporate a portion of the substrate within a region capable of providing detection in this embodiment another pair of idts can be incorporated onto the saw substrate in combination with a detection portion of the fluid transport coupling medium this portion of the fluid transport medium is coated with biologics providing specificity to the metabolites of interests a separate set of electronic controls provides excitation of the second set of idts as well as detection of the frequency phase or amplitude shifts due to the presence of the analytes the extraction and detection functions can operate at the same frequency or at combinations of frequencies the spacing arrangements of the detection idts with respect to the operating surface provides optimal extraction and detection means when appropriate electronics are included the saw device can detect the presence of increase or decrease in.