A typical analysis program in the Model CA-6 Ammonia Analyzer would have the following structure: Rinse the colorimetric reaction cell with the sample solution and take a sample, add one or more reagents (buffer or masking agent), and then make the first measurement, which would be the reference measurement. The reference measurement eliminates interfering factors such as sample color and turbidity, miscellaneous color from the reagents, and refractive index variations.
After the reference reading, the color producing reagent(s) are added. The sample is mixed and allowed time to complete the color forming reactions before taking the second measurement, the reading measurement. The reference and reading values are used to calculate the concentration using the calibration factor. The reaction cell is drained and rinsed several times before starting the next measurement.