This technique acts like a fast assembly line for chemical testing. A pump keeps a main liquid flowing through narrow plastic tubes. This main liquid is called the carrier stream.
The machine adds a precise tiny squirt of the sample into this moving stream. As the sample travels down the tube, it mixes with the carrier liquid. We often add color-changing chemicals into the stream at specific points.
The sample and chemicals react together as they flow toward the detector. The most important rule of this method is strict timing. The liquid never stops moving, so the chemical reaction never finishes completely.
It never reaches a state of full chemical equilibrium. Instead, we rely on the fact that every single drop takes the exact same time to travel. Because the timing is perfectly constant, the partial chemical reaction is perfectly reproducible.
A detector at the end measures the color or electrical change as the liquid zooms past. The machine compares this reading against known standard samples tested the exact same way. This method is incredibly fast and uses very small amounts of expensive chemicals. It is widely used in industrial plants to test hundreds of samples every hour.