Quantitative analysis of alkylamine ethoxylate by mass spectrometric method

Abstract

This research involves the method for determination of molecular weight distribution and quantitative analysis of alkylamine ethoxylate surfactant (AME), using matrix assisted laser desorption ionization mass spectrometry (MALDI-MS). The MALDIMS analysis was carried out by mixing the surfactant with various types of matrix such as dithranol, α-cyano-4-hydroxycinnamic acid (CCA), 2,5-dihydroxybenzoic acid. The surfactant-matrix mixture was applied to the target and bombarded with laser to generate ionic analyte. The following MALDI-MS conditions were found to provide the good MS spectrum of molecular weight distribution of the AME surfactant: sample preparation using dried droplet method, CCA as a matrix with ethanol and acetonitrile as solvent, the ratio of surfactant: matrix was 1:225 by volume, and the laser power was 260 uJ. These conditions were used for the analysis of AME surfactant in four commercial herbicides. The results showed that commercial-A, B, C and D consist of AME surfactant of the type C18H37N(CH2CH2O)8-20H2 and their molecular weight distributions are in the range of 800-900. Then, the amounts of this surfactant in commercial herbicides were found to be 5.77 ±0.12, 9.91 ± 0.08, 9.90 ± 0.09 and 1.57 ± 0.02 percent by weight, respectively. This method gave detection limit for quantitative analysis at 19.32 femtomole. Thus, the MALDI-MS technique was an excellent method for determination of the molecular weight distribution and quantitative analysis of alkylamine ethoxylate surfactant in the commercial herbicides.