A miniaturized monolith-MWCNTs-COOH multi-stir-rod microextractor device for trace parabens determination in cosmetic...

A portable and simple microextractor device was constructed by aligning six miniaturized multi-stir-rod microextractors. Each microextractor was prepared from rod-like multiwalled carbon nanotubes functionalized with a carboxylic group (MWCNTs-COOH) in composite monoliths that were bundled together and connected to a small DC motor. Using six of these microextractors, the device could extract six samples at the same time. A scanning electron microscope (SEM) showed the MWCNTs-COOH well distributed throughout the highly porous structure of the monolith-MWCNTs-COOH-stir-rod. This miniaturized multi-stir-rod microextractor device was used for the extraction of four parabens, methylparaben (MP), ethylparaben (EP), propylparaben (PP) and butylparaben (BP). Under optimized conditions, good linearities were obtained in the concentration range of 1.0 ng mL^-1 to 1.0 µg mL^-1 for MP and EP and 2.0 ng mL^-1 to 1.0 µg mL^-1 for PP and BP. The limits of detection were low, 636.2 ± 7.6 pg mL^-1 for MP, 675.5 ± 6.0 pg mL^-1 for EP, 676.6 ± 8.6 pg mL^-1 for PP and 803.4 ± 9.6 pg mL^-1 for BP. The developed microextractor could be used up to 15 times (%RSDs from 1.5 to 5.2) and also provided good preparation reproducibility (%RSD from 1.3 to 5.8, n = 6). The % RSDs of intra-day (n = 6) and inter-day (n = 6) precisions were obtained from 1.10-7.79 and 1.96-7.55, respectively. This developed device coupled with high performance liquid chromatography-diode array detector (HPLC-DAD) was applied for the extraction and preconcentration of four parabens in personal care products and cosmetics. The recoveries were studied by spiking the standard solution of parabens in real samples. Good recoveries were obtained in the range of 89.0 ± 2.7 to 102.7 ± 1.8% for MP, 88.09 ± 6.4 to 102.5 ± 1.0% for EP, 83.4 ± 6.4 to 102.9 ± 1.5% for PP and 83.5 ± 3.6 to 102.3 ± 2.0% for BP. This developed device might be easily applied for the extraction and preconcentration of other trace organic compounds in sample matrices.