Buffers are replaced at least monthly. The instrument is zeroed with the sample or with lab millipore water depending on the procedure. Two standards are run, and bracket the sample value. New standards are prepared monthly. The amount of acid necessary to bring the sample pH down to 4.5 is proportional to the total alkalinity in the sample.
Ammonia is measured by the wastewater laboratory.
A small amount of dye is added to the sample, and buffer solution is added until the pH of the sample reaches 10. If calcium and magnesium are present in the sample, the sample turns red. The amount of EDTA required to turn the sample blue represents the hardness of the sample. Cadmium metal reduces nitrates present in the sample to nitrites. The nitrite ion reacts in an acidic medium with sulfanilic acid to form an intermediate diazonium salt which couples to chromotropic acid to form a pink-colored product.