Chloride determination in crude oil by potentiometric titration after reversed-phase dispersive liquid-liquid...

Sustainable practices in analytical chemistry are essential for reducing environmental impact. In this work, a simple, accurate, and environmentally friendly method based on reversed-phase dispersive liquid-liquid microextraction (RP-DLLME) with a very high sample mass (10 g) was developed for the subsequent determination of chloride in crude oil by potentiometric titration avoiding the use of high volume of reagents.

The proposed method was optimized for medium crude oil (API 22.6 to 30.2) just using 1000 μL of chemical demulsifier, 20 min of heating at 75 °C, 350 μL of 1.0 mol L^-1 HNO₃, and 650 μL of isopropyl alcohol (totaling 1000 μL), followed by 10 min of centrifugation. The procedure suggested by ASTM D6470-99(2020) was used to establish reference values. Despite using a relatively poor-sensitive technique for chloride determination, low and suitable limits of detection and quantification (0.30 and 1.0 μg g^-1, respectively) were reached. Precision, expressed as relative standard deviation, was below 5% and agreement better than 95% was obtained with the reference method. The RGBfast metric was applied to evaluate the impact of RP-DLLME and ASTM D6470-99(2020) on analytical, environmental, and practical criteria. The scores achieved were 65.0 and 40.0 respectively, showing the good performance of the proposed method.

The proposed RP-DLLME allowed chlorine pre-concentration in just a few microliters of an aqueous solution, very low consumption of reagents, reduced waste generation, capability to process up to 90 replicates in 24 h, and ease of operation. The RP-DLLME contributes to the advancement of sustainable analytical protocols, making it a practical and efficient method for routine applications.