The ASTM has released a new method for Acid Number (AN) determination in crude oil and petroleum products by thermometric titration.
Compared with potentiometric titration (ASTM D664), this method is more robust, faster, and simpler. Above all, this method will save you money, as you will need less solvent per analysis.
Why go with thermometric titration?
- Robust: Oil matrix does not interfere with the measurement.
- Fast: Analysis in one third of the time (compared with potentiometric titration).
- Simple: Sensor requires no maintenance or conditioning.
- Inexpensive: Less solvent and reagent per analysis.
It's all in the numbers: potentiometric vs. thermometric titration
| D664 using potentiometric titration | D8045 using thermometric titration | |
|---|---|---|
| Volume of solvent required for analysis | 125 mL | 30-35 mL |
| Electrode conditioning | 3-5 min | Not necessary |
| Electrode storage | LiCL in ethanol | Dry |
| Titration duration (averaged) | 132-268 s | 45-73 s |
| Method repeatability when measuring 1.0 mg KOH/g in crude oil |
Not established | 0.07 mg KOH/g |
| Method reproducibility when measuring 1.0 mg KOH/g in crude oil | Not established | 0.31 mg KOH/g |
How does thermometric titration work?
Thermometric titration measures the temperature change in the titration solution (resulting from the reaction enthalpy) rather than the potential change. This technique can therefore be applied for difficult samples or matrices where potentiometric titration is difficult or not feasible.
As thermometric titration uses a temperature sensor and not an electrode, the sample matrix does not interfere with the measurement and sensor handling is as easy as it gets.