An online colorimetric analyzer that generates an indication of a material in a sample is provided. The analyzer includes a peristaltic pump configured to convey. A photometric cell is operably coupled to the peristaltic pump to receive the sample. An illumination source is disposed to direct illumination through the sample in the photometric cell along an angle of incidence. A photodetector disposed to receive illumination passing through the photometric cell along the angle of incidence and provide a signal indicative of a color of the sample. A controller is coupled to the illumination source, the photodetector and the peristaltic pump. The photometric cell is tilted relative to vertical such that a surface of liquid present when the photometric cell is partially filled substantially reflects the illumination away from the angle of incidence.