Ultrasonic Assisted Salting-Out Micro-Liquid–Liquid Extraction Followed by Gas Chromatography for Determination of Ethanolamines in Sweetening Natural Gas Solutions

The high solubility of ethanolamines in the aqueous solutions is a big challenge for extracting these compounds. To overcome this problem, in this research, an easy sample preparation method based on salting-out micro-liquid–liquid extraction has been introduced to extract ethanolamines from aqueous samples, and determination has been done by gas chromatography-flame ionization detector (GC-FID). The solvent 1-propanol demonstrated significantly greater extraction efficiency than other solvents, including tetrahydrofuran, acetonitrile, and diethyl carbonate. Different variables affecting the extraction and derivatization of the target compounds were also investigated and optimized. The highest response was achieved with NaCl at a concentration of 35%, using 1000 µL of 1-propanol, a sonication power of 30 W for 20 s, a derivatization agent volume of 25 µL, and a derivatization time of 5 min. The analytical performances of the method were evaluated in optimal conditions. The linear ranges varied from 2 to 4000 mg/L, depending on the compound. The method demonstrated good repeatability, with relative standard deviations ranging from 2.4 to 10.3%. Limit of detections (LODs) were in the range of 0.5–2.3 mg/L. The method was finally used to determine ethanolamines in the commercial sweetening solutions. The relative recoveries (RR%) were achieved between 89 and 111%.