A miniaturized stir bar sorptive dispersive microextraction method for the determination of bisphenols in follicular fluid using a magnetic covalent organic framework.

BACKGROUND: Bisphenols, particularly bisphenol A (BPA), are the primary monomers used as additives in the manufacturing of many consumer products. The exposure to these compounds is related to endocrine-disrupting and reproductive effects, among others. For this reason, the development of analytical methods for their determination in biological matrixes is needed to monitor the population exposure to these compounds. Their quantification at ovarian level (i.e., follicular fluid) is interesting for the assessment of the bisphenol content to draw conclusions about infertility problems. However, the background does not meet all requirements by focusing mainly on BPA. RESULTS: In this work, a miniaturized stir bar sorptive dispersive microextraction (mSBSDME) approach has been developed for the determination of BPA and eight analogues in follicular fluid. In the proposed method, the sample is previously cleaned-up using a zirconia-based solid-phase extraction cartridge, removing proteins and phospholipids, and then subjected to the mSBSDME for the preconcentration of the analytes. For this purpose, a magnetic covalent organic framework was used as sorbent. A Plackett-Burman design was applied to select the significant variables affecting the mSBSDME. Afterwards, the only significant variable (i.e., sorbent amount) was optimized. Under the optimized conditions, the proposed method was properly validated, and satisfactory analytical parameters in terms of linearity (up to 50 ng mL-1), enrichment factors (8.5-14.3), limits of detection in the low ng mL-1 range, and precision (relative standard deviations below 11.5 %) were obtained. Finally, the method was successfully applied to five samples, detecting BPA and other two analogues. SIGNIFICANCE: This method expands the potential applicability of the mSBSDME to other low-availability complex matrixes, which would otherwise be difficult to analyze. Moreover, it offers a valuable tool for monitoring the female population's exposure to bisphenols with the final aim of evaluating if infertility problems of women might be associated to the exposure to these highly endocrine disrupting compounds.

Solid-phase immunoextraction followed by liquid chromatography-tandem mass spectrometry for the selective determination of thyroxine in human serum.

In this work, an analytical method based on solid-phase extraction (SPE) followed by liquid chromatography-tandem mass spectrometry analysis (LC-MS/MS) has been developed for the selective determination of thyroxine (T4) in human serum. For this purpose, two immunosorbents (ISs) specific to T4 were synthesized by grafting two different T4-specific monoclonal antibodies on a cyanogen bromide (CNBr)-activated-Sepharose® 4B solid support. The grafting yields obtained from the immobilization of each antibody on the CNBr-activated-Sepharose® 4B were over 90%, demonstrating that most of the antibodies were covalently bound to the solid support. The SPE procedure was optimized by studying the retention capability and selectivity of the two ISs in pure media fortified with T4. Under the optimized conditions, high elution efficiencies were achieved in the elution fraction for both specific ISs (i.e., 85%), whereas low ones were obtained in the control ISs (ca. 2%), showing the selectivity of the specific ISs. The ISs were also characterized by studying extraction and synthesis repeatability (RSD <8%), and capacity (104 ng of T4 per 35 mg of ISs, i.e., 3 µg g-1). Finally, the methodology was applied to a pooled human serum sample in order to study its analytical utility and accuracy. Relative recovery (RR) values between 81 and 107% were obtained, showing no matrix effects during the global methodology. Furthermore, the need to perform the immunoextraction was evidenced by comparing the LC-MS scan chromatograms and RR values with and without applying the immunoextraction procedure on a serum sample submitted to protein precipitation. This works exploits, for the first time, the use of an IS on the selective determination of T4 in human serum samples.

Stir bar sorptive-dispersive microextraction by a poly(methacrylic acid-co-ethylene glycol dimethacrylate)-based magnetic sorbent for the determination of tricyclic antidepressants and their main active metabolites in human urine.

A poly(methacrylic acid-co-ethylene glycol dimethacrylate)-based magnetic sorbent was used for the rapid and sensitive determination of tricyclic antidepressants and their main active metabolites in human urine. This material was characterized by magnetism measurements, zeta potential, scanning electron microscopy, nitrogen adsorption-desorption isotherms, and thermogravimetric analysis. The proposed analytical method is based on stir bar sorptive-dispersive microextraction (SBSDME) followed by liquid chromatography-tandem mass spectrometry. The main parameters involved in the extraction step were optimized by using the response surface methodology as a multivariate optimization method, whereas a univariate approach was employed to study the desorption parameters. Under the optimized conditions, the proposed method was properly validated showing good linearity (at least up to 50 ng mL-1) and enrichment factors (13-22), limits of detection and quantification in the low ng L-1 range (1.4-7.0 ng L-1), and good intra- and inter-day repeatability (relative standard deviations below 15%). Matrix effects were observed for the direct analysis of urine samples, but they were negligible when a 1:1 v/v dilution with deionized water was performed. Finally, the method was successfully applied to human urine samples from three volunteers, one of them consuming a prescribed drug for depression that tested positive for clomipramine and its main active metabolite. Quantitative relative recoveries (80-113%) were obtained by external calibration. The present work expands the applicability of the SBSDME to new analytes and new types of magnetic sorbents.

Green determination of eight water-soluble B vitamins in cosmetic products by liquid chromatography with ultraviolet detection.

B vitamins are a group of compounds with beneficious properties for dermatologic care, and therefore they are included in the cosmetic formulations as high added-value ingredients. In this paper, an analytical method for the simultaneous determination of eight water-soluble B vitamins in cosmetic products is reported for the first time. This method is based on liquid chromatography with ultraviolet detection (LC-UV) analysis after simple water leaching of the analytes from the cosmetic matrix. No organic solvents are required, beyond the ethanol used in the chromatographic mobile phase. The proposed method has been successfully validated showing good linearity, limits of detection in the low µg mL-1 range (from 0.14 to 0.43 µg mL-1) and good repeatability (relative standard deviation below 11 %). The accuracy of the method has been proven by the analysis of laboratory-made samples (i.e., a cream and a gel) with known concentrations of the analytes, providing low relative errors (below 12 %). Finally, the method has been successfully applied to four commercial cosmetic samples of different formulations without significant matrix effects. The results obtained and the environmentally friendly features of the method showed its usefulness for carrying out both pre- and in-market quality control of final cosmetic products.

Fundamentals and applications of stir bar sorptive dispersive microextraction: A tutorial review.

Current trends in sample preparation focus on the miniaturization of the process resulting in what is known as microextraction techniques. Among them stir bar sorptive dispersive microextraction (SBSDME) is one of the most recent techniques. It was presented a few years ago as a hybrid microextraction technique that combines the principles of stir bar sorptive extraction (SBSE) and dispersive solid phase extraction (DSPE). This novel technique introduces, into the sample solution, a bar-shaped magnet coated with a magnetic (nano)material, which is maintained on the surface by magnetism. Once stirring starts, the competitive action between magnetism and rotational force is exploited. At low rotational speed the (nano)material is retained on the magnet reminding SBSE, whereas at high sufficiently rotational speed the rotational force surpasses magnetism so that the magnetic (nano)material is dispersed into the sample solution as in DSPE. Upon halting rotation, the magnetic field prevails again and attracts the magnetic (nano)material containing the analytes back on the surface of the stirring bar. Finally, the extracted analytes are chemically or thermally desorbed before their measurement with the appropriate analytical instrument. When compared separately to SBSE and DSPE procedures, SBSDME affords, in a single approach, advantages such as lower extraction times than SBSE and easier extraction and post-extraction treatment than DSPE. The main purpose of this tutorial review is to describe the fundamentals and the experimental variables involved in this technique, as well as to compile and critically discuss the published papers concerning analytical methods based on the use of the SBSDME approach, analyzing its evolution and future prospects.

Reduced graphene oxide-based magnetic composite for trace determination of polycyclic aromatic hydrocarbons in cosmetics by stir bar sorptive dispersive microextraction.

This work describes a sensitive and rapid analytical method for trace determination of polycyclic aromatic hydrocarbons (PAHs) in cosmetic samples. The proposed method is based on stir bar sorptive-dispersive microextraction (SBSDME). A magnetic composite made of CoFe2O4 magnetic nanoparticles embedded into reduced graphene oxide sheets is used as sorbent phase. After the extraction, the target analytes are desorbed in toluene and then analyzed by gas chromatography-mass spectrometry (GC-MS). The main parameters involved in the extraction procedure (i.e., composite amount, extraction time and desorption time) were evaluated and optimized to provide the best extraction efficiency. The method was successfully validated under the selected conditions, showing a linear range of at least up to 125 ng mL-1, instrumental and method limits of detection from 0.02 to 2.50 ng mL-1 and from 0.15 to 24.22 ng g-1, respectively, and relative standard deviations (RSD) below 10 % for all the target analytes. Standard addition combined with internal standard calibration was employed for quantification. The proposed method was successfully applied to the analysis of ten PAHs in four cosmetic products of different matrix. Several analytes between 14 and 464 ng g-1 were found, some of them prohibited in cosmetic products. This work expands the analytical potential of SBSDME technique to other analytes and to the use of new sorbent phases, showing the great versatility of this approach depending on the characteristics of the analytes.