Testing Techniques Review for Industrial Water Treaters
Technique is one of the keys to accurate, repeatable, and reliable test readings. Follow these guidelines for your best results.
Familiarize yourself with the instructions before beginning a test—especially when it's new to you—and follow them exactly. Note any special considerations such as required wait times, safety warnings, and conversion factors for test results. Make sure you have the necessary reagents and labware at hand, and verify all components are in good condition. Replace cracked or stained sample tubes/cells and color comparators. After testing, flush out the sample tube/cell and test cell cap with fresh sample or demineralized water to avoid contaminating the next test, and wipe equipment down with a clean, dry cloth.
For meaningful test results, take a water sample representative of conditions in the whole system. Always use a sample of the proper volume: The sample's meniscus (lowest point in curvature) should rest on the test cell’s calibration mark. Test immediately after sampling, since some parameters can change within minutes. Boiler water samples that should be at room temperature before testing can be cooled in a cold-water bath. When gathering a sample for off-site analysis, fill the container to overflowing and cap it so no air is present. (Some highly reactive substances, the oxygen scavenger sulfite for example, should always be tested on-site.) Store water to be tested off-site for iron or copper in a dedicated sample container, and acidify it so the metal doesn't come out of solution.
Like medications, all reagent bottles need to be clearly and accurately labeled. If you repour from bulk quantities, be extra cautious about labeling and rinse reagent bottles, tips, and caps with distilled or deionized water and let air dry BEFORE adding new reagent. To prevent contamination of reagents, don't exchange bottle caps and always replace them securely. Don't cap a sample container with your finger either—the oils in your skin can affect the test result. Never interchange one manufacturer's reagents with another's because they may not be equivalent strength. To keep reagents fresh, store them out of direct sunlight at 36°F–85°F (2°C–29°C) away from other treatment chemicals, and avoid extreme temperature fluctuations. For best results, replace reagents more than one year old. Hold dropper bottles straight up and down when dispensing reagent to guarantee the proper drop size. Swirl after adding each drop to thoroughly incorporate the reagent. A static charge can build up at a dropper bottle's tip causing a visible, progressive decrease in drop size. Consequently, the drop equivalence will be shortchanged. Periodically wiping the dropper tip with a clean, damp cloth or paper towel will eliminate this problem.
When matching colors outdoors, hold the comparator at eye level with the sun off to your side or behind you (i.e., not shining directly through the comparator nor directly onto the faceplate). Don't wear sunglasses when taking the reading. When testing indoors, use a special lamp that simulates natural daylight—not incandescent or fluorescent lighting. Taylor offers the Daylight Comparator Lamp (#9199) for use with Midget™ comparators. The Daylight Comparator Lamp can be placed on a lightbox stand (#9200) to accommodate our longer Slide™ comparators. Performing drop-count or buret titrations over a white background makes the endpoint readily apparent. Remember, the white cap that comes with our #9188 and #9198 sample tubes is not for capping the opening. It's meant for the bottom to give the high contrast needed for easy detection of a titration's endpoint. Review test instructions and field manuals carefully for information on potential test interferences and how to avoid or mitigate them. For example, glycol antifreeze can interfere with non-CAN nitrite tests. The Product Info section of this website contains information on potential test interferences.