Module 7.3 — Titrations and manual test methods still essential for parameters that don't automate well, revisited from Module 1.4's grab sample introduction.
Click the burette or the endpoint to see its role. The volume of titrant used to reach the endpoint directly calculates the unknown concentration.
Module 1.4 noted that grab samples exist partly "for parameters that are harder to automate reliably." This module explains what that manual analysis actually involves, since wet chemistry technique — despite decades of advancing online instrumentation — remains essential for a meaningful set of parameters throughout this course, from hardness (Module 1.3) to certain chloride and alkalinity determinations relevant across several tracks.
Titration measures an unknown concentration by adding a reagent of precisely known concentration (the titrant) to a sample until a reaction between them is judged complete — the endpoint — typically signaled by a color change from an indicator chemical or a shift detected by an electrode. The volume of titrant required to reach the endpoint, combined with its known concentration, allows direct calculation of how much of the target substance was present in the original sample. This is the method behind manual hardness testing (EDTA titration, directly relevant to Module 1.3's makeup water hardness discussion), chloride determination (relevant to Module 5.2's cycles of concentration tracer ion), and total alkalinity measurements used in several treatment program contexts throughout Track 2.
| Method Type | How It Works | Common Application |
|---|---|---|
| Colorimetric titration | Indicator chemical changes color at endpoint | Hardness (EDTA), some alkalinity tests |
| Potentiometric titration | Electrode detects a sharp signal change at endpoint, no visible color change needed | Chloride, some pH-based endpoints |
| Colorimetric (non-titration) | Reagent produces a color proportional to concentration, read by eye or spectrophotometer | Silica, phosphate, iron — concentration read directly, no titrant volume involved |
Unlike an online instrument, a manual titration's accuracy depends heavily on the technician's technique: consistent drop size when approaching the endpoint, correct sample volume measurement, proper reagent storage and expiration tracking, and correctly judging exactly when the endpoint color change or electrode signal has occurred (not too early, not too late). This is why lab technique training and periodic proficiency verification — sometimes through blind reference samples with a known concentration — matters as a distinct discipline from the instrument calibration covered in Module 7.2, even though both serve the same underlying goal of trustworthy data.