Retention of the N-nitrosodiethanolamine by hydrophilic interaction liquid chromatography on different polar columns: mechanism study and optimization

To investigate the retention mechanism of N-nitrosodiethanolamine (NDELA) in liquid chromatography, the mobile phase composition was changed on five stationary phases including silica, diol, cyano, amino, and zwitterionic. Afterward, temperature, pH, and buffer concentration effects are studied. Results demonstrate a dual hydrophilic interaction liquid chromatography (HILIC)-reversed phase (RP) mechanism for the retention of NDELA. The transition between the HILIC and RP behavior on a different column, “U-turn” points, was observed between 43 and 68% of water in acetonitrile. The depiction of the natural logarithm of retention factor vs. inverse of the absolute temperature was linear for cyano, amino, and zwitterionic columns. In contrast, it was curvature for silica and diol columns. In each column, the positive slopes indicate a negative retention enthalpy, signifying an exothermic process of transferring analytes from the mobile phase to the stationary phases being examined. In the case of buffer pH and concentration, an ammonium acetate solution with a pH of 5.7 and a concentration of 10 mM was selected for further investigation. Finally, the selectivity of this method in optimal conditions for the analysis of NDELA in shampoo has been investigated. According to the well-obtained selectivity of NDELA in shampoo and the advantages of the HILIC method, this method seems to be a suitable alternative to RP methods.