Analytical device for the automated determination of analytes in fluids

An apparatus for measuring reflectance from a porous matrix containing a reagent that reacts with an analyte suspected of being present in a liquid sample applied to a surface in said porous matrix, where said sample can migrate through said porous matrix and react with said reagent if said analyte is present in said sample, which comprises:

• a housing;
• an internal chamber in said housing;
• means for accessing said internal chamber, whereby said porous matrix can be inserted in or removed from said internal chamber through said means for accessing;
• means for excluding external light from entering said internal chamber through said means for accessing;
• means for retaining said porous matrix in said internal chamber, wherein said porous matrix is retained with a first surface accessable for applying said liquid sample through said means for accessing;
• means for illuminating a second surface of said porous matrix when said porous matrix is retained in said internal chamber, wherein said second surface is different from said first surface;
• means for detecting intensity of light reflected from said second surface of said porous matrix when said porous matrix is retained in said internal chamber and illuminated by said means for illuminating, wherein said means for detecting produces an output related to said intensity, said means for detecting intensity being adapted to provide a series of outputs;
• control means for processing said outputs, said control means including means for comparing outputs in said series and determining whether said outputs decrease by a predetermined difference sufficient to indicate that said sample of body fluid has reached said second surface, wherein said predetermined decrease in outputs causes said control means to initiate a timing period which results in a measurement reading being taken from said surface at a predetermined time after said second timing period is initiated without having determined the time at which said sample of body fluid was initially applied to said porous matrix;
• and
• means for reporting said measurement reading.