A colorimetric analyzer includes a reaction chamber configured to receive a sample and at least one reagent. A measurement cell is operably coupled to the reaction chamber. The colorimetric analyzer has an illumination source configured to emit illumination at a first wavelength during a first absorbance measurement and at a second wavelength during a second absorbance measurement. The colorimetric analyzer also includes an illumination detector spaced from the illumination source such that illumination from the illumination source passes through the measurement cell to the illumination detector. A controller is coupled to the illumination source and the illumination detector. The controller is configured to detect an obstruction of light between the illumination source and the illumination detector based on the first and the second absorbance measurements.