A sample analyzer for quantitating relatively small amounts of clinically significant compounds in a liquid sample together with a sample mixing device (sampler) is disclosed. The analyzer has a transparent cell for holding the liquid sample. A light source focuses a stable light beam onto the sample so that fluorescent particles in the sample cause fluorescent emissions, the intensity of which is a function of the intensity of the light beam and the concentration of fluorescent particles in the sample. A detector in optical communication with the cell receives and senses photons forming the fluorescent emissions of the particles when excited by the light beam. The sampler holds a multiplicity of vials in an upright position in a row, advances the vials in incremental steps to present them at an aspiration station and includes an aspirator having a downwardly open suction tube that is vertically inserted into and withdrawn from the vials. A vacuum source withdraws the liquid sample from the vials through the suction tube and flows it to the sample cell in the analyzer. A mixer surrounds the suction tube and is activated before the sample is withdrawn form a uniform suspension.