Determination of anionic surfactants in detergents by microporous membrane liquid–liquid extraction and flow injection spectrophotometry

The applicability of microporous membrane liquid–liquid extraction (MMLLE) and flow injection spectrophotometry to the determination of anionic surfactants in detergents was studied. Optimization of variables of the flow injection manifold, groove length of the MMLLE unit, and pore size of the membrane was performed. Experiments showed that the long-term reproducibility of the system was limited when the peristaltic pump and the displacement bottle arrangement were used, but the system was still applicable in routine analysis if calibration was carried out every 20 min. The proposed method has a linear range of 0.2–2 mmol l−1 sodium dodecylbenzenesulfonate (DBS) and a detection limit (S/N=3) of 0.1 mmol l−1 DBS. The sampling rate was 50 h−1 and the relative standard deviation was 1.8% (n=11) at 1.0 mmol l−1 DBS level. Eleven washing powder samples were analyzed with the proposed procedure and the standard Epton method, and paired t-tests showed that there is no significant difference between these two methods.