Are You Testing for the Right Chemical Form?

I brought a sample of cooling water to my chemist one day and asked him to check the chloride levels. He told me the sample had 3300 parts per million (ppm) chloride. According to my test results, it was only 2000 ppm. I asked him to retest it, and when he did, the result was the same as before. Confused, I asked him if he had performed a chloride test. It turns out his test was for sodium chloride. Aha! Our results were correct for the type of test we were running, but he was testing for and recording his results as ppm sodium chloride (NaCl), whereas I was testing for and recording my results as ppm chloride (Cl‒).

Which raises an important question: “Are you using the right test method and recording your results in the correct chemical form?” The difference could be important.

Chloride, sulfite, and nitrite are just three of the analytes which often can be reported in different forms: chloride, as chloride or sodium chloride; sulfite, as sulfite or sodium sulfite; nitrite, as nitrite or sodium nitrite. Careful attention should be paid to how the results for these analytes are measured, especially if there is a specification range they need to meet. Simple conversion factors can be applied to change from one form to the other. It’s not rocket science, but it does take a degree of awareness.

Take a second look at your test method and your spec range — be sure they are the same, for the sake of your systems!