Surfactant-based extraction methods

Optimization of ion-pair based hollow fiber liquid phase microextraction combined with HPLC-UV for the determination of methimazole in biological samples and animal feed

Ion-pair based hollow fiber liquid phase microextraction (IP-HFLPME) coupled with high performance liquid chromatography-ultraviolet detection was applied for the preconcentration and determination of methimazole in biological samples and animal feed. Optimization of the conditions for the high extraction efficiency was studied simultaneously using the experimental design. For the first step, the Plackett-Burman design was applied to screen the significant factors on the extraction efficiency. Central composite design (CCD) was then used for the optimization of important factors and the response surface equations were obtained. The optimum experimental conditions were donor phase pH, 12.2; extraction temperature, 45°C; extraction time, 50 min; sodium perchlorate concentration, 1.5 M; cetyltrimethylammonium bromide concentration, 0.65 mM, and without salt addition in donor phase. The limit of detection and the dynamic linear range were in the range of 0.1-0.7 μg L(-1) and 0.5-1000 μg L(-1), respectively. Preconcentration factors were obtained in the range of 93-155 in different matrices. Finally, the performance of the proposed method was tested for the determination of trace amounts of methimazole in plasma, urine, bovine milk, and animal feed samples, and satisfactory results were obtained (RSDs < 7.1%).

Effects of substituents in β-diketones and their tris-iron(III) complexes on partitioning between various micellar phases and the bulk aqueous phase

To determine the factors that affect the partitioning of solutes in micellar systems, we investigated the partitioning of several β-diketones and their tris-complexes with iron(III) between the bulk aqueous phase and micelles of various polyoxyethylene (POE)-type nonionic surfactants (C(12)POE(8), Brij 35, Brij 58, and Triton X-100). The trends of the partition constants in the micellar systems differed from those in typical liquid-liquid systems; these differences may have been due to the effects of the substituent groups on the extractants, and to the effects of the inner-sphere chemistry of the micelles. The bulkiness and the low wettability of the extractants and the complexes hindered their extraction into the micellar phase. The interaction between the polyoxyethylene moiety of the surfactants and water molecules dissolved in the micellar mantle may have hampered the penetration of such solutes with bulky or low-wettability substituents into the mantle. The locus of the solutes in the micelles seemed to play an important role in the partitioning behavior.

Investigation of analytical performance for rapidly synergistic cloud point extraction of trace amounts of copper combined with spectrophotometric determination

In this work, an improved preconcentration method named as rapidly synergistic cloud point extraction (RS-CPE) was established for copper preconcentration and determination. Non-ionic surfactant Triton X-100 (TX-100) was used as extractant. Octanol worked as cloud point revulsant and synergic reagent, which successfully decreased the cloud point temperature (CPT) of TX-100 to realize the room temperature (about 20°C) CPE without heating. The established RS-CPE pretreatment was simple, rapid and effective. Compared with traditional CPE (about 40 min for heating, incubation and cooling), the extraction time of the proposed method was very short (1 min). The improved extraction technique RS-CPE was combined with traditional spectrophotometer to improve the analytical performance and expand the application of spectrophotometric determination. The influence factors relevant to RS-CPE, such as concentrations of TX-100 and octanol, concentration of chelating agent, pH, conditions of phase separation, salt effect, environmental temperature and instrumental conditions, were studied in detail. Under the optimal conditions, the limit of detection (LOD) for copper was 0.4 μg L(-1), with sensitivity enhancement factor (EF) of 18. The proposed method was applied to the determination of trace copper in real samples and certified samples with satisfactory analytical results.