Instrument incorporating electrochemiluminescent technology

An apparatus as provided for use in carrying out electrochemiluminescence test measurements. The apparatus includes a fluid container having an inlet for introducing an electrochemiluminescence sample fluid and a fluid outlet. The fluid container is composed of a durable, transparent, chemically inert, and electrically nonconductive material. A working electrode is disposed to one side of a fluid flow path of the container which has a light transmissive wall opposite the working electrode. A counter electrode is secured to the light transmissive wall. A first portion of the counter electrode is disposed upstream of the working electrode, while a second portion of the counter electrode is disposed downstream of the working electrode.