Abstract: A method was developed for the determination the effective contents of “small cation”, 2,3-epoxypropyltrimethylammonium chloride (EPTMAC) and 3-chloro-2-hydroxypropyl-trimethylammonium chloride (CHPTMAC), in drilling fluid additives using ion-pair reversed-phase liquid chromatography with evaporative light scattering detection. The separation was performed on an Atlantis column (150 mm×4.6 mm, 5 μm) with the mobile phase of methanol-5 mmol/L heptafluorobutyric acid (10:90, v/v)at a flow rate of 1 mL/min. The drift tube temperature of the evaporative light scattering detector was set at 50 ℃ and the gas pressure was set at 206.7 kPa (30 psi). The sample was diluted by extra pure water and filtrated for analysis. The EPTMAC and CHPTMAC were completely separated and determined within 10 min. The calibration curves of them were fitted by quadratic equations. The correlation coefficients for both of them were 0.9995. The limits of detection were 13 mg/L and 18 mg/L, and the limits of quantifications were 45 mg/L and 61 mg/L for EPTMAC and CHPTMAC, respectively. Their average recoveries were 91.2%~98.6% and 93.2%~102.3% with the relative standard deviations (n=5) of 1.7%~2.5% and 1.2%~1.8%. These results demonstrate that the proposed method is simple and fast for the quality control of “small cation” in drilling fluid additives in oilfield.

Key words: 2,3-epoxypropyltrimethylammonium chloride, 3-chloro-2-hydroxypropyltrimethylammonium chloride, additives, drilling fluid, evaporative light scattering detection, quaternary ammonium, ion-pair reversed-phase liquid chromatography