[Chromatography Q & A] What are the differences between Wakopak® Wakosil AS-Aqua for anionic surfactant analysis and ODS columns?
Wakopak® Wakosil AS-Aqua is a column developed as a HPLC column suitable for the analysis of anionic surfactants (alkylbenzenesulfonates, ABSs hereinafter) in an aqueous solution.
Anionic surfactants are one of the Japanese water quality standard items (50 items), derive from contaminations such as industrial wastewater and domestic sewage, become a cause of foaming if present in water, and are said to be an important indicator of pollution. Since the enforcement of the revised Japanese Waterworks Act on April 1, 2004, an analytical method to measure ABSs, the active ingredient of synthetic detergents, by the solid-phase extraction-HPLC method has been adopted as the measurement method for anionic surfactants.
In this method, an ABS with a branched alkyl chain of a carbon number of 10 to 14 derived from synthetic detergents is the target of analysis and the reference value is 0.2 mg/L as the total ABSs. When these ABSs are analyzed with an ODS column, the branched alkyl chain tends to split (Figure 1).
Wakopak® Wakosil AS-Aqua was developed for improvement in detection sensitivity and simplification of quantitative calculation as well as shortening of the analysis time by separates ABSs as a single peak by each carbon number. The examples of analysis of ABS standard solutions and detergent by the HPLC-fluorimetric detection are shown in Figure 2. In addition, a linear chain ABS not contained as an active ingredient of synthetic detergents is separated from the branched alkyl chain type and can be distinguished. There is no significant difference from the measured values using an ODS column*1 and more accurate measurement is possible even in the low concentration range.
The solid-phase extraction column Presep® C C18 (ODS) is less affected by water quality and gives an excellent recovery rate of ABSs. Please use this as well.
*1: Tochimoto, H. et al.: Annual Research Report, Tokyo Metropolitan Institute of Public Health, 58 (2007).
Figure 1. Wakopak®Navi C18-5, 4.6 x 250 mm (Flow rate: 1.0 mL/min.)
Figure 2. Wakopak®WS AS-Aqua, 4.6 x 250 mm (Flow rate: 0.7 mL/min.)
Figure 3. ABSs mixture standard solution containing linear type
Eluent: CH3CN/H2O = 65/35 (v/v), NaClO4 12.3 g/1000 mL added.
Detection: Ex. 221 nm, Em. 284 nm
Injection: 10 mg/L (CH3OH), 10 μL
Sample: Mixture standard solution for anionic surfactant analysis (ABSs: C10, C11, C12, C13, C14)