Background: Cationic surfactants (CSs) such as quaternary ammonium compounds are
used as fabric softeners, anti-bacterial agents, and human hair cosmetics. Accurate determination of
CSs in environmental water samples is very difficult because of their very low concentration and
strong adsorptivity to not only glassware but also to plasticware due to strong hydrophobic and electrostatic
attractions. Linear alkylbenzene sulfonates (LASs), anionic surfactants, are produced in the
largest quantity as the main components of laundry detergents, dishwashing liquids, and other cleaning
formulations. In this study, a liquid chromatography/mass spectrometry (LC/MS) method was
developed for simultaneous determination of CSs, cetyltrimethylammonium ion (CTMA) and
trimethylstearylammonium ion (TMSA), and LASs in environmental water samples.
Materials and Methods: This method involves a solid-phase extraction of CSs and LASs from the
water samples using a solid-phase extraction cartridge, InertSep Slim-J PLS-3. A hydrophilic
polymer column, Shodex MSpak GF-310 4D was used for the separation of CSs and LASs with a
mobile phase gradient from 36 to 44 % (v/v) acetonitrile-water containing 0.8 mM di-nbutylammonium
acetate and 0.2 M acetic acid. Di-n-butylammonium ion acts as the ion-pair reagent
for retention of LASs on the column, while it makes the retention of CSs moderate. Positive
and negative electrospray ionization modes were used for the MS detection for CSs and LASs, respectively.
Results and Discussion: Instrument detection limits of the developed method based on selected
ion monitoring technique for the mixed standard solutions of CSs and LASs were 3 and 6 ng L-1
for CTMA and TMSA, respectively and 13 – 47 ng L-1 for the C10-C14 LASs. The total concentration
of the CSs was determined to be 6.6 μg L-1 for river water (Ebi river, Japan) and 0.028 μg L-1
for seawater (Tokyo Bay, Japan) samples. The concentration of total LAS was determined to be
1122 μg L-1 for the river and 10.8 μg L-1 for the seawater samples.
Conclusion: These results demonstrate that the solid-phase extraction and the LC/MS method developed
in this study are useful for the simultaneous determination of trace amounts of CSs and
LASs in environmental water samples.