No abstract

An improved single-drop microextraction (SDME) method combined with high performance liquid chromatography has been developed for the detection of trace carbamate and organophosphorus pesticides in water samples. The most fascinating feature of the proposed method is the use of an oval-shaped polychloroprene rubber (PCR) tube to load the extraction solvent, which efficiently loads more solvent and improves the stability of extraction microdrop. Furthermore, this device provides a larger contact surface between the extraction solvent and the inner surface of the oval-shaped PCR tube than that between the extraction solvent and the tip of a microsyringe needle in the conventional SDME. It thereby avoids the problem of the drop floating upwards or dislodging from the tip of the microsyringe needle as observed in the traditional SDME. This method is significant for the great improvement it can offer in extraction efficiency. A series of extraction parameters were investigated systematically using carbamate and organophosphorus as the model analytes. Under the optimal conditions, the enrichment factors for analysis were between 117 and 177, and the limits of detection were ≦0.63 μg L(-1) (S/N = 3). The repeatability study was carried out by extracting the spiked water samples. Here the relative standard deviations varied between 4.0 and 5.8% (n = 5). Additionally, the proposed method was successfully applied to the determination of pesticides in real water samples, and good recoveries were obtained from 79% to 112%. The proposed method was demonstrated to hold advantages of low cost, simplicity of operation, and successful application to in real water samples.

A multifunctional cadmium–organic framework demonstrates impressive adsorption enthalpies for CO2 and H2, and possesses the second adsorption capacity for MO among the MOFs as well as displays strong guest-dependent luminescence.

In the proposed method, a free microdroplet of extraction solvent was placed on the top center of the aqueous sample while the solution was agitated with a stirring bar on the bottom of the sample vial. After extraction, the sample vial was cooled in an ice bath for 2 min. The solidified droplet was transferred into a conical vial and melted quickly at room temperature. Based on preliminary studies, 1-dodecanol was selected as the extraction solvent. Effective parameters such as the type and volume of organic solvent, stirring speed, extraction time, sample temperature and salt effect were optimized. Under the optimized conditions, the enrichment factors of fungicides varied between 103 and 175. Based on a signal-to-noise ratio of 3, the limits of detection in this method ranged between 1.01 and 1.49 µg L(-1). Linearity was obtained in the concentration range of 5-2000 μg L(-1) yielding correlation coefficients (r) >0.9985. Good reproducibility and recovery were also obtained.