When to use it

In-scope / Out-of-scope

Minimum you must report (checklist)

• Solution 1: product/device medium without surfactants (include pH, tonicity, and other relevant inactives).
• Solution 2: surfactant system identity and ratio(s) (if multiple surfactants) plus starting concentration.
• Solution 3: dilution series concentrations (explicit list) and preparation scheme (volumes/dilution factor) with lot IDs where applicable.
• Measurement conditions: temperature setpoint and actual temperature (per point or per run), plus any required inputs (e.g., density if needed for your method).
• Instrument/method: tensiometer type/geometry (e.g., pendant drop) and key acquisition settings (including any dwell/equilibration time).
• Data quality rules: fit/acceptance criteria and any re-run rules (e.g., unstable drop, poor fit, out-of-spec temperature).
• Results table: γ at each concentration with replicates and summary statistic (e.g., mean ± SD) and the number of replicates.
• Analysis outputs: γ vs log(C) plot, regression approach/ranges used, and the estimated CMC (breakpoint concentration) with units (and uncertainty if required by SOP).

How to interpret results (guardrails)

• Pre‑CMC vs post‑CMC behavior: expect a decreasing γ region (adsorption) followed by a plateau; the CMC is the regression breakpoint between these regions.
• Only compare like-with-like: CMC shifts with temperature and medium composition—do not compare runs unless pH/tonicity/inactives and temperature are controlled and recorded.
• Set internal margins and limits: use the CMC estimate to define product-specific targets (e.g., “surfactant concentration ≥ X× CMC in product medium”) based on your performance/QC evidence.
• Reject bad points, not just bad curves: rerun concentration points that fail fit/QC gates or input limits, and ensure regression ranges reflect true linear/plateau regions rather than noise.