Standards are replaced at least monthly. The probe is calibrated with pH 7 and 10 buffers in the drinking water laboratory the day of sampling. 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.