According to this principle-the integrating sphere collects the scattered light

The good news is that this problem can be solved. Optical absorption, used to assess the concentration of dissolved matter, could be measured through a standard spectrometer arrangement using an input light source and a detector behind the sample. According to this principle-the integrating sphere collects the scattered light and keeps it within the measurement system; the light bounces around the cavity and will eventually contribute to the detected signal-researchers find a method to solve the difficulty. Researchers at North West Water (Warrington, England) have developed a method that overcomes both problems. In the technique, the water flows in an unconstrained stream through an integrating sphere. Within the integrating sphere, optical absorption is measured independent of scattering and this combination of scattering-independent and window-free absorption measurement offers a highly reliable industrial instrument.

Another difficulty arises is the sample also contains particles and bubbles. The only practical restriction is that the input beam makes at least one reflection off the surface of the sphere before reaching the detector; if not, the directly transmitted light would dominate the detected power. It is possible to avoid this interference by making the measurement in an integrating sphere. Scattering from these contribute to the reduction in the light reaching the detector. The light loss through scattering out of the beam path is indistinguishable from absorption in a simple system.

The integrating sphere is an optical instrument. You can find this measurement is so good for anything, like it doesn’t have any weakness. But in a drinking-water treatment plant, it is important to measure both dissolved materials and particles to ensure that the water meets quality standards. Many dissolved materials can be detected by their optical absorption; however, absorption measurement is made difficult by interference from scattering caused by particles. In addition, the cuvette windows of a standard measurement system are often fouled, which reduces instrument reliability.