Why do we pre-rinse turbidity cuvettes exactly three times before measurement? On my rounds with a Hach 2100Q, I fill from the grab, rinse the vial three times, wipe with a lint-free cloth, fill, cap, tap to knock bubbles, wait 60 seconds, then log the NTU. I was taught it’s for temperature equilibration and surface conditioning, but is the “three” backed by a study or just lore?
a lint-free cloth, fill, cap, tap to knock bubbles, wait 60 seconds, then log the NTU. Agree on the 60 s with the 2100Q — ugh, the three-rinse thing feels like SOP inertia; when we tested it, NTU changed <0.1 after the second unless the prior grab was oily or high iron, so we standardized to two and only add a DI rinse between sites. Ever try logging 1 vs 2 vs 3 on the same grab to see if your matrix needs the third?
Short answer from my side: I’m seeing the same pattern — one concrete thing that helped was writing down the exact handoff and timebox it to 15–20 min. Does that match what you’re running into?
Have you tried logging rinse-to-rinse drift on the 2100Q to see if “three times” changes the read? I standardize on two when Δ<0.1 NTU and keep the “60 seconds” settle/tap the same, only sticking with three after an acid wash or when sample/air temps are far apart.
It’s mostly a carryover math thing: each rinse knocks down residual from the last sample, so “three” is the belt-and-suspenders habit, not a temperature study. Try this once: run a low-NTU blank after a muddy grab with two rinses, then do a third and see if it shaves another about 0.02–0.03 NTU; if not, two’s fine for your sites. @wevans68 I only stick with three when there’s obvious surfactant/oil that needs extra conditioning.