In this study, the suitability of solid-phase extraction (SPE) coupled in-line to CE with UV-Vis detection was evaluated for the preconcentration and separation of diluted solutions of five pharmaceuticals compounds: benzafibrate, piroxicam, diclofenac sodium, naproxen and clofibric acid. An SPE analyte concentrator containing Oasis(®) HLB sorbent was constructed without frits and placed near the inlet end of the separation capillary. Different parameters such as sample pH, composition and volume of the elution plug and sample loading time were studied in order to obtain the maximum preconcentration factors. The LODs reached for standard samples were in the range 0.06-0.5 ng/mL with good reproducibility, and the developed strategy provides sensitivity enhancement factors around 14,000-fold in peak area and 5900-fold in peak height compared with the normal hydrodynamic injection. Finally, river water samples fortified with the pharmaceutical compounds were analyzed by the developed in-line SPE-CE-UV method in order to show the potential of the methodology for the analysis of environmental aquatic samples. For these samples, high values of relative recoveries, between 73-107% and 79-103% for two concentration levels, 5 and 25 ng/mL, respectively, were obtained and LODs ranged between 0.19 and 1 ng/mL.

The use of SPE coupled in-line to CE using electrospray MS detection (in-line SPE-CE-ESI-MS) was investigated for the preconcentration and separation of four UV filters: benzophenone-3, 2,2-dihydroxy-4-methoxybenzophenone, 2,4-dihydroxybenzophenone and 2-phenylbenzimidazole-5-sulphonic acid. First, a CE-ESI-MS method was developed and validated using standard samples, obtaining LODs between 0.06 μg/mL and 0.40 μg/mL. For the in-line SPE-CE-ESI-MS method, three different sorbents were evaluated and compared: Oasis HLB, Oasis MCX, and Oasis MAX. For each sorbent, the main parameters affecting the preconcentration performance, such as sample pH, volume, and composition of the elution plug, and sample injection time were studied. The Oasis MCX sorbent showed the best performance and was used to validate the in-line SPE-CE-ESI-MS methodology. The LODs reached for standard samples were in the range between 0.01 and 0.05 ng/mL with good reproducibility and the developed strategy provided sensitivity enhancement factors between 3400-fold and 34 000-fold. The applicability of the developed methodology was demonstrated by the analysis of UV filters in river water samples.

Several strategies, namely, large volume sample stacking (LVSS), field-amplified sample injection (FASI), sweeping, and in-line SPE-CE, were investigated for the simultaneous separation and preconcentration of a group of parabens. A BGE consisting of 20 mM sodium dihydrogenphosphate (pH 2.28) and 150 mM SDS with 15% ACN was used for the separation and preconcentration of the compounds by sweeping, and a BGE consisting of 30 mM sodium borate (pH 9.5) was used for the separation and preconcentration of the compounds by LVSS, FASI, and in-line SPE-CE. Several factors affecting the preconcentration process were investigated in order to obtain the maximum enhancement of sensitivity. The LODs obtained for parabens were in the range of 18-27, 3-4, 2, and 0.01-0.02 ng/mL, and the sensitivity evaluated in terms of LODs was improved up to 29-, 77-, 120-, and 18,400-fold for sweeping, LVSS, FASI, and in-line SPE-CE, respectively. These preconcentration techniques showed potential as good strategies for focusing parabens. The four methods were validated with standard samples to show the potential of these techniques for future applications in real samples, such as biological and environmental samples.

A high-sensitivity on-column preconcentration method, anion selective exhaustive injection (ASEI)-sweeping in micellar electrokinetic capillary chromatography (MEKC) has been developed for the analysis of non-steroidal anti-inflammatory drugs (NSAIDs): diclofenac sodium, ibuprofen, fenoprofen, naproxen, and ketoprofen in water samples. To achieve the best results of the ASEIsweeping-MEKC method, conditions which affected preconcentration were examined, including the sodium dodecyl sulfate concentration, composition of the sample matrix, composition and injection length of the water plug, the concentration and the injection length of the high-conductivity buffer, and finally the sample injection time. Under the optimum stacking conditions the method was validated for the determination of the studied NSAIDs in river water samples with limits of detection ranging between 29 and 58 ng mL -1 , and without any previous sample pretreatment.

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