A non-ionic surfactant contains a hydrophilic group which does not ionize when dissolved in water and has chemical properties making it unaffected by water hardness or electrolytes. A non-ionic surfactant can be used together with virtually any other type of surfactant. The use of non-ionic surfactants has increased dramatically in recent years due to the wide range of properties they offer such as ease of use, high detergency, excellent emulsification/dispersibility and low stimulation.
Water quality standards established in 2004 specify that the concentration of non-ionic surfactants must be less than 0.02 mg/L.
The established routine analysis method employs Solid-phase Extraction with Absorption Spectrophotometry where the absorbance is measured of complex formed by the reaction of the non-ionic surfactant-Co(II) with a coloring reagent 4-(2-pyridylazo) resorcinol (PAR). In 2012, a new method based on SPE-HPLC was added to the water quality standard for the measurement of non-ionic surfactants. The water quality standard stipulates that measurement of a non-ionic surfactant should be sensitive to at least one-tenth of the acceptable concentration limits and the coefficient of variation required is better than 20%.
In this application note a non-ionic surfactant was analyzed using the newly defined SPE-HPLC method and the results are reported as below.
|Column:||YMC-Triart C18 (4.6 mmI.D. x 150 mmL, 5 µm)|
|Eluent:||10 mM Sodium tetraborate/ Methanol (62/38)|
|Flow Rate:||1.0 mL/min|
|Column Temp.:||40 ºC|
|Wave Length:||510 nm|
|Injection Volume:||20 µL|
|Standard Sample:||Heptaoxyethylene dodecyl ether|
SPE-HPLC, Non-ionic surfactant, Heptaoxyethylene dodecyl ether, 5 µm, C18 column
Fig. 2 shows the chromatogram of sample with added non-ionic surfactant and table 1 shows the peak area. This result satisfies the criteria of measurement quality where the coefficient of variation of measured values is less than 20% when measuring a sample at one-tenth the acceptable concentration defined in the water quality standard.
Fig. 2. Chromatogram of Sample Added with Non-ionic Surfactant* (n=6) 1: Heptaoxyethylene dodecyl ether (0.002 mg/L) *Sample preparation is described on Fig. 1.
Fig. 3 linearity of sample with added non-ionic surfactant. Four standard samples were measured with concentrations ranging from 0.002 to 0.01 mg/L as specified in the official analytical method, linearity was R2=0.985.
Fig. 3. Linearity of Sample with added Non-ionic Surfactant (0.002 ~ 0.01 mg/L)