[Chromatography Q & A] HPLC columns for nonionic surfactants analysis
"Solid-phase extraction-high performance liquid chromatography method" was added to the measurement method of nonionic surfactants in the Japanese water quality standard items (Notification No. 66 of the Japanese Ministry of Health, Labour and Welfare, 2012). The eluent used for the analysis is a basic condition with a pH 9.2 and the ODS columns of FUJIFILM Wako available under the basic conditions are Wakopak® Ultra C18 series. They are usable in the range of pH 1.5 to 10 and show a high durability. The products with particle sizes of 2 µm, 3 µm and 5 µm are available.
Here are the examples of measurement of nonionic surfactants (heptaoxyethylene dodecylether) using Wakopak® Ultra C18-5 and Wakopak® Ultra C18-2 for UHPLC.
For nonionic surfactants, the water quality standard of 0.02 mg/L is specified as a Japnese water quality standard item defined in the Ministerial Ordinance on Water Quality Standards (Ministerial Ordinance No. 101 of the Japanese Ministry of Health, Labour and Welfare, 2003). While the solid-phase extraction-spectrophotometry had been used as the test method, the ministerial ordinance was partially revised in April 2012* and the solid-phase extraction-high-performance liquid chromatography was added to the test method (*Notification No. 66 of the Japanese Ministry of Health, Labour and Welfare, 2012).
It is a method to form a complex between the nonionic surfactant in the testing water and Co(II), separate the sample colored with 4-(2-pyridylazo)resorcinol (PAR) by a HPLC column, and measure using an absorbance detector. Because sodium tetraborate solution of pH 9.2 is used as an eluent, it cannot be used in general silica gel ODS (C18) columns due to intense deterioration of the column.
Modification of the surface processing technology of silica gel packing agents made "Wakopak® Ultra C18" usable under a wide range of pH conditions. Even after continuous use for 1500 hours or longer under the below analytical conditions (using the eluent of pH 9.2), the retention rate was not less than 85% of the initial value demonstrating that it is possible to use the product stably.
Preparation of samples (notified method)
Standard sample: Heptaoxyethylene dodecylether was dissolved in toluene, complexed, and colored. It was prepared to 0.001 mg/L to 0.01 mg/L in an aqueous solution and analyzed.
Column: Wakopak® Ultra C18-5, 4.6 mm x 150 mm
Eluent: 0.01 mol/L Na2B4O7 (pH9.2)/CH3OH = 62/38 (v/v)
Flow Rate: 1.0 mL/min. at. 40℃
Detection: 510 nm
Figure 1. Example of analysis by the notified method
Column: Wakopak® Ultra C18-2, 2.1 mm x 50 mm
Eluent: 0.01 mol/L Na2B4O7 (pH9.2)/CH3OH = 62/38(v/v)
Flow Rate: 0.35mL/min. at. 40℃
Column Pressure: 6900 psi (47 MPa)
Detection : 510 nm
(Analysis is possible in about 1/3 of the analysis time.)
Figure 2. Example of rapid analysis using UHPLC column