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Boiler/Cooling Systems, Alkalinity/Chloride/Hardness/pH/Orthophosphate/Sulfite

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Analyte System Method/Chemistry Standard/Equivalance or Description Comparator Cell
Alkalinity, P/M & P/T Drop test Phenolphthalein/methyl orange/blended indicator 1 drop = 10 ppm P/M or P/T alkalinity as CaCO₃ NA 9198G
Chloride Drop test Argentometric 1 drop = 10 ppm Clˉ NA 9198O
Hardness, Total Drop test EDTA titration (includes inhibitors to prevent metal interference) 1 drop = 10 ppm total hardness as CaCO₃ NA 9198B
Orthophosphate Two-Standard comparator Stannous chloride 30 & 60 ppm PO₄³⁻ 9025 9021
pH Color Card Comparator Long range 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0, 11.0 5425 9017
Sulfite (Sodium) Drop test Iodometric 1 drop = 10 ppm Na₂SO₃ NA 9198W
Test Parameter Description
Alkalinity High halogen level may change indicator reaction from green/red to blue/yellow; to prevent, add thiosulfate prior to testing. Filming amines, quats, and biguanides may interfere and cause the endpoint to look purple; to prevent, add 10 drops of R-0884 prior to testing.
Chloride Orthophosphate at concentrations greater than 25 ppm will precipitate as silver phosphate to cause positive interference. This can be prevented by diluting orthophosphate concentrations below 25 ppm with DI water. Bromide, iodide, and cyanide at all levels titrate as equivalent chloride concentrations. Sulfide, thiosulfate, and sulfite interfere but can be removed by treatment with hydrogen peroxide. Quats may interfere; to prevent add 10 drops of R-0884.
Hardness Metal ions may cause interference; to prevent, add titrant containing EDTA to sample before buffer and indicator, then test as normal making sure to count drops of titrant added initially in total required to reach endpoint. If interference still occurs, dilute sample with DI water as necessary and retest. Quats may cause interference.
Orthophosphate Silica, ferrous iron, fluoride, and sulfide may cause interference; to prevent, test for suspected interfering agent, dilute sample with DI water as necessary, and retest.
pH Calcium salts may affect tolyl red indicator; to prevent, use acyl red indicator.
pH Iron > 10 ppm may cause negative interference.
pH Ortho- and polyphosphate may cause positive interference; to prevent, test for interfering agent, dilute sample with DI water as necessary, and retest.
Sulfite Erythorbic acid, sulfide and ferrous iron may cause positive interference; to prevent, test for suspected interfering agent, dilute sample with DI water as necessary, and retest. Copper and nitrite may cause negative interference; to prevent, test for suspected interfering agent, dilute sample with DI water as necessary, and retest. Delay between taking sample and testing may cause negative interference; to prevent, perform test immediately after sample is taken. Quats may cause interference by forming a precipitate and causing a yellow endpoint.


All reagents have a shelf life, whether they are liquids, powders, crystals, tablets, or test-strip pads. If kept dry, powders and crystals are very stable; acids are also long lived. Date of manufacture is not the controlling factor when it comes to shelf life—storage conditions are more important. As with all perishables, reagents are sensitive to environmental influences and will last longer under controlled conditions.

To this end, we recommend:

  • Storing reagents at a consistent temperature in the range if 36°–85°F (2°–29°C); extreme temperature fluctuation, say from a refrigerator to a hot car trunk, causes reagents to deteriorate.
  • Keeping them out of prolonged direct sunlight. (Note: their brown plastic bottles help protect very light-sensitive reagents.)
  • Segregating reagents from containers of treatment chemicals.
  • Replacing caps immediately and tightening them carefully so that exposure to air and humidity is limited.
  • Avoiding switching bottle caps, placing bottle caps on soiled surfaces, repouring reagents into contaminated containers, or touching test strip pads.

Taylor formulates its reagents to remain effective for at least one year, with only very few exceptions (molybdenum indicator in liquid form is one; after four months old it should be tested against a standard periodically). As a general precaution, replace all reagents more than one year old, or at the beginning of a new testing season.

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