From Potentiometric Titration to Electrometric Conductivity: A Critical Review and Metrological Comparison of ASTM D6470 and ASTM D3230 toward Method Replacement in Salt in Crude Analysis.

Chloride-salt determination in crude oil is essential to prevent corrosion, emulsions, and fouling. ASTM D6470, based on potentiometric titration, requires approximately 90 min and large solvent volumes, limiting responsiveness and increasing health, safety, and environmental concerns. ASTM D3230, based on electrometric conductivity, provides a turnaround in approximately 20 min with less handling. However, evidence of metrological comparability for Brazilian crudes remains limited. This study evaluated 49 pre- and post-salt Brazilian crude oils spanning 23.9-32.4 °API and 0.02-0.30% BSW. Standard-addition, mineral-oil dilution, and self-dilution tests indicated negligible matrix interference after 1:10 dilution and ±3 °C temperature control. For ASTM D3230, detection and quantification limits were 1.2 and 3.9 mg kg⁻¹ NaCl, respectively; repeatability was ≤5% and intermediate precision ≤16% across 25-225 mg kg⁻¹. A paired t-test identified significant bias relative to ASTM D6470. Regression-based correction removed this bias, yielding statistically comparable results within the validated range. The correction enables traceable conversion while retaining ASTM D6470 as the reference procedure for final confirmatory or compliance-related decisions. ASTM D3230 is therefore a practical alternative for the evaluated crude oils when the correction is applied. Generalization beyond the investigated concentration, dilution, temperature, °API, and BSW ranges requires independent and interlaboratory validation.