Judith Gañán

Comparison of different mesoporous silicas for off-line solid phase extraction of 17β-estradiol from waters and its determination by HPLC-DAD.

Functionalized (SBA-C₁₈ and SM-C₁₈) and non-functionalized (SBA-15 and SM) mesoporous silicas were then examined as sorbents for solid-phase extraction of 17β-estradiol in aqueous media. Experiments were run in order to test critical factors affecting the procedure extraction efficiency, including the type of sorbent, the analyte concentration, the solvent and volume used for elution and the sample volume. Among the prepared materials, SBA-C₁₈ had the highest adsorption affinity towards 17β-estradiol and under optimized conditions (200mg of sorbent, 150 mL of water sample, elution with 3 × 2 mL of methanol) this sorbent proved good extraction capacity and elution efficiency for this hormone from aqueous media (recovery near 100%). To evaluate the analytical applicability of the proposed method, it was applied to the determination of 17β-estradiol in drinking water by high performance liquid chromatography with a photodiode array detector. Calibration curves were shown to be linear between 1.25 and 100 mg L(-1)with correlation coefficients ≥0.999 (n=5) for 17β-estradiol. The instrumental detection and quantitation limits calculated were 0.38 and 1.25 mg L(-1), respectively. The relative standard deviation obtained values were ≤3% and the mean recoveries obtained were of 82%. The results suggest that SBA-C18 is a promising material for the off-line solid phase extraction of 17β-estradiol from waters.

Novel supports in chiral stationary phase development for liquid chromatography. Preparation, characterization and application of ordered mesoporous silica particles.

Recent advances in the development of new materials are having a major impact on analytical chemistry. For example, the unique properties of ordered mesoporous silicas (OMSs) have been shown to enhance the analytical performance of many existing techniques or allow new, exciting ones to be developed. Likewise, the introduction of organo-functional groups makes OMSs highly versatile and enables them to perform specialized tasks, such as the separation of chiral compounds. This review provides an overview with the most relevant achievements in the preparation of OMS particles functionalized with chiral selectors. In addition, some examples from the last fifteen years regarding the analytical applications of functionalized OMS for chiral separations by high-performance liquid chromatography, ultra-high pressure high-performance liquid chromatography and capillary electrochromatography have been reviewed.

Evaluation of a molecularly imprinted polymer for determination of steroids in goat milk by matrix solid phase dispersion

A molecularly imprinted polymer-matrix solid-phase dispersion methodology for simultaneous determination of five steroids in goat milk samples was proposed. Factors affecting the extraction recovery such as sample/dispersant ratio and washing and elution solvents were investigated. The molecularly imprinted polymer used as dispersant in the matrix solid-phase dispersion procedure showed high affinity to steroids, and the obtained extracts were sufficiently cleaned to be directly analyzed. Analytical separation was performed by micellar electrokinetic chromatography using a capillary electrophoresis system equipped with a diode array detector. A background electrolyte composed of borate buffer (25mM, pH 9.3), sodium dodecyl sulfate (10mM) and acetonitrile (20%) was used. The developed MIP-MSPD methodology was applied for direct determination of testosterone (T), estrone (E1), 17β-estradiol (17β-E2), 17α-ethinylestradiol (EE2) and progesterone (P) in different goat milk samples. Mean recoveries obtained ranged from 81% to 110%, with relative standard deviations (RSD)≤12%. The molecularly imprinted polymer-matrix solid-phase dispersion method is fast, selective, cost-effective and environment-friendly compared with other pretreatment methods used for extraction of steroids in milk.

One-pot synthesized functionalized mesoporous silica as a reversed-phase sorbent for solid-phase extraction of endocrine disrupting compounds in milks.

A new procedure for the determination of 12 naturally occurring hormones and some related synthetic chemicals in milk, commonly used as growth promoters in cattle, is reported. The method is based on liquid-liquid extraction followed by solid-phase extraction (SPE) using a new one-pot synthesized ordered mesoporous silica (of the SBA-15 type) functionalized with octadecyl groups (denoted as SBA-15-C18-CO) as reversed-phase sorbent. The analytes were eluted with methanol and then submitted to HPLC with diode array detection. Under optimal conditions, the method quantification limit for the analytes ranged from 0.023 to 1.36μg/mL. The sorbent affored the extraction of estrone, 17β-estradiol, estriol, progesterone, hexestrol, diethylstilbestrol, 4-androstene-3,17-dione, ethinylestradiol, 17α-methyltestosterone, nandrolone, prednisolone and testosterone with mean recoveries ranging from 72% to 105% (except for diethylstilbestrol) with RSD<11%. These results were comparable and, in some cases, even better than those obtained with other extraction methods, therefore SBA-15-C18-CO mesoporous silica possess a high potential as a reversed-phase sorbent for SPE of the 12 mentioned endocrine disrupting compounds in milk samples.

On-line flow injection molecularly imprinted solid phase extraction for the preconcentration and determination of 1-hydroxypyrene in urine samples

New analytical strategies tend to automation of sample pre-treatment and flow analysis techniques provided a number of enhanced analytical methods allowing high throughput. Flow techniques are usually faster, more robust and more flexible than their batch equivalents. In addition, flow methods use less sample and reagent amounts and reduce analytical costs and waste. A flow injection solid-phase extraction pre-concentration system using a molecularly imprinted polymer (MIP) packed micro-column was developed for the determination of 1-hydroxypyrene in human urine with fluorescence detection. The pre-concentration of 1-hydroxypyrene on the MIP was carried out based on the specific retention of analyte by on-line introducing the sample into the micro-column system. Methanol and dichloromethane mixture was used to elute the retained analyte for fluorometric analysis. Important influencing factors were studied in detail, in batch and in flow (MISPE procedure optimisation, sample and eluent volumes, flow rate, dimensions of MIP micro-column and amounts of packing material, etc). To the best of our knowledge, this is the first on-line flow injection molecularly imprinted solid phase extraction for the pre-concentration and determination of hydroxylate PAH metabolite in urine samples. The optimised method was successfully applied to the determination of 1-Hydroxypyrene in spiked urine samples, with recoveries in the range of 74-85% and RSD<4.6%. Under optimum experimental conditions, the linearity concentration range used was 10-400μgL-1, R2>0.996. We obtained limit of detection and quantification of 3.1μgL-1 and 10.5μgL-1, respectively.

A novel hybrid mesostructured silica for the solid-phase extraction of estrogenic hormones from waters

Mesoporous silica functionalized with octadecyl groups (denoted as SBA-15-C18) was prepared and characterized. The adsorption capacity of the prepared SBA-15-C18 for a mixture of twelve endocrine disrupting compounds (synthetic and natural estrogenic hormones) in aqueous media was evaluated by off-line solid-phase extraction (SPE) and compared with a commercial phase for SPE (ExtraBond® C18). Analytes were determined by high performance liquid chromatography with UV-vis detection. Under optimized conditions (100 mg of SBA-15-C18 sorbent; conditioning: 2 mL methanol and 2 mL Milli-Q water; loading: 150 mL water sample; washing: 5 mL Milli-Q water; elution: 2 mL methanol; flow rate 0.5 mL min−1) the preconcentration factor achieved was 1000. The analytical characteristics of this methodology were evaluated, showing good precision, accuracy and linearity, with method quantification limits (MQLs) between 0.16 and 3.00 μg L−1. The SBA-15-C18 material enabled the extraction of the twelve estrogenic hormones in tap water (pH 6.6), mineral water (pH 5.0), groundwater (pH 7.3), river water (pH 5.0) and effluent wastewater (pH 5.0) with recoveries between 70 and 112% at the lower level studied (MQL).

Influence of Organic Modifier Additives to Separate Steroids by Micellar Electrokinetic Chromatography: Determination of Solute-Micelle Association Constants at Different Acetonitrile Concentrations

In this report, the determination of testosterone, progesterone, estrone, 17-β-estradiol, and ethynilestradiol by micellar electrokinetic chromatography (MEKC) is described. Several organic modifiers were investigated using sodium dodecyl sulfate as the surfactant agent in the background electrolyte. The effect of the acetonitrile concentration on the migration time of the steroids and on the selectivity was also studied by using different background electrolytes. Under the optimized conditions that included a sodium tetraborate (pH 9.3; 25 mM) buffer with 10 mM sodium dodecyl sulfate, 20% (v/v) of acetonitrile, 27 kV running voltage, and injection with a plug of background electrolyte (7 mbar × 1 s), the analytical performance of the method was evaluated. Good linearity (correlation coefficients, R 2 ≥ 0.99) and adequate precision were achieved, with limits of detection of 1.27, 2.17, 0.6, 1.13, and 1.7 µg/mL for testosterone, progesterone, estrone, 17-β-estradiol, and ethynilestradiol, respectively. To study the effect of the acetonitrile concentration on the solute-micelle interaction, the retention factor and association constants were determined. In all cases, the association constants decreased by increasing the acetonitrile concentration from 10% to 30%, suggesting that the presence of large amounts of organic modifier decreased the steroid-micelle interactions.