An overview of sample preparation approaches prior to liquid chromatography methods for the determination of parabens in biological matrices

Nonlinear responses of biofilm bacteria to alkyl-chain length of parabens by DFT calculation

Parabens can particularly raise significant concerns regarding the disruption of microbial ecology due to their antimicrobial properties. However, the responses of biofilm bacteria to diverse parabens with different alkyl-chain length remains unclear. Here, theoretical calculations and bioinformatic analysis were performed to decipher the influence of parabens varying alkyl-chain lengths on the biofilm bacteria. Our results showed that the disturbances in bacterial community did not linearly response to the alkyl-chain length of parabens, and propylparaben (PrP), with median chain length, had more severe impact on bacterial community. Despite the fact that paraben lethality linearly increased with chain length, the PrP had a higher chemical reactions potential than parabens with shorter or longer alkyl-chain. The chemical reactions potential was critical in the nonlinear responses of bacterial community to alkyl-chain length of parabens. PrP could impose selective pressure to disturb the bacterial community, because it had a more profound contribution to deterministic assembly process. Furthermore, N-acyl-homoserine lactones was also significantly promoted under PrP exposure, confirming that PrP could affect the bacterial community by influencing the quorum-sensing system. Overall, our study reveals the nonlinear responses of bacterial communities to the alkyl-chain lengths of parabens and provides insightful perspectives for the better regulation of parabens. ENVIRONMENTAL IMPLICATION: Parabens are recognized as emerging organic pollutants, which specially raise great concerns due to their antimicrobial properties disturbing microbial ecology. However, few study have addressed the relationship between bacterial community responses and the molecular structural features of parabens with different alkyl-chain length. This investigation revealed nonlinear responses of the bacterial community to the alkyl-chain length of parabens through DFT calculation and bioinformatic analysis and identified the critical roles of chemical reactions potential in nonlinear responses of bacterial community. Our results benefit the precise evaluation of ecological hazards posed by parabens and provide useful insights for better regulation of parabens.

Presence of parabens in children's faeces. Optimization and validation of a new analytical method based on the use of ultrasound-assisted extraction and liquid chromatography-tandem mass spectrometry

Due to their antimicrobial properties, parabens are a family of synthetic chemical compounds widely used as preservative additives in food and cosmetics. For this reason, humans are highly exposed to them. These substances are capable of altering the proper functioning of the endocrine system and are classified as endocrine disrupting chemicals (EDCs). Traditionally, urine has been the typical matrix studied as an excretion route. However, faeces contain valuable information. In the present study, the presence of methyl-, ethyl-, isopropyl-, propyl-, isobutyl-, butyl- and phenylparaben in stool samples from children has been evaluated. A new analytical method has been optimised and validated. The method is based on the use of ultrasound-assisted extraction followed by clean-up of the extracts by dispersive solid phase extraction dSPE). Parabens were analysed by ultrahigh performance liquid chromatography coupled to tandem mass spectrometry (UHPLC-MS/MS). The matrix effect was evaluated and a significant effect was observed for all analytes. Therefore, calibration and validation were performed by addition of different concentrations of analytes to faecal blanks. The coefficient of determination (%R²) for calibration curves was higher than 98.9% in all cases. The limits of detection and quantification were between 0.2 and 0.4 and 0.6-1.0 ng g^-1 respectively. The recovery for accuracy assessment had values between 89.0% and 112.7% with an RSD of less than 15% in all cases. The method was successfully applied to 14 samples from children volunteers, 100% of which showed contamination by at least one of the analysed compounds.

Polyvinyl alcohol-based hydrogel sorbent for extraction of parabens in human milk samples by in-tube SPME–LC–UV

In this work, we developed an in-tube solid-phase microextraction (SPME) device consisting of a fused silica capillary modified with a polyvinyl alcohol (PVOH) hydrogel. Methylparaben, ethylparaben, propylparaben, and butylparaben were determined in human milk samples by using the in-tube SPME device coupled with liquid chromatography with spectrophotometric detection in the ultraviolet region (LC-UV). The inner surface of the fused silica capillary was silanized to allow covalent modification with the PVOH-hydrogel, using glutaraldehyde as cross-linking agent. The developed device was used up to 250 times with no reduction in the analytes' peak areas or carryover effect, besides having a low production cost. The human milk samples showed a significant matrix effect for parabens with higher logKo/w. Low limits of quantification (LLOQ) between 10.0 and 15.0 ng mL-1 were obtained with RSD values in the range of 1.18 to 18.3%. For the intra- and inter-day assays, RSD values from 5.6 to 16.5% and accuracy from 74.5 to 128.8% were achieved. The PVOH-based hydrogel sorbent allowed the use of water as desorption solvent, eliminating the use of organic solvents, which follows the principles of green chemistry. The results showed a great application potential of the PVOH-based hydrogel sorbent for the extraction of organic compounds from high-complexity samples.

Determination of methomyl in grain using deep eutectic solvent-based extraction combined with fluorescence-based enzyme inhibition assays

A deep eutectic solvent (DES)-based extraction method is established to facilitate the determination of methomyl in grain via enzyme inhibition fluorescence. The environmentally-friendly DES was synthesized from proline and ethylene glycol and used as a green replacement for traditional extraction solvents that are generally toxic. The DES was added to grain samples and vortex extraction of methomyl, the supernatant was then collected for fluorescence detection. Biomass carbon quantum dots (CQDs) synthesized from millet were used as fluorescent probes. Acetylcholinesterase catalyzes the hydrolysis of acetylthiocholine iodide to thiocholine. The positively-charged thiocholine interacts electrostatically with the negatively-charged quantum dots resulting in the quenching of their fluorescent emission. The pesticide extract solution blocks the enzyme activity and thus recovers the fluorescent from the quantum dots. The fluorescence response was correlated with the amount of methomyl residue in the grain over the range 0.01 to 5 mg kg^-1. The limit of detection was found to be 0.003 mg kg^-1, and the limit of quantification 0.01 mg kg^-1. Recoveries of 86.5% to 107.8% were obtained using real samples, including millet, rice, wheat, and barley, with a relative standard deviation of less than 3.8%. The method is efficient and convenient and has good application prospects for extracting and detecting pesticides in grain samples.

Recent advances in analysis of bisphenols and their derivatives in biological matrices

Biomonitoring is a very useful tool to evaluate human exposure to endocrine-disrupting compounds (EDCs), like bisphenols (BPs), which are widely used in the manufacture of plastics. The development of reliable analytical methods is key in the field of public health surveillance to obtain biomonitoring data to determine what BPs are reaching people's bodies. This review discusses recent methods for the quantitative measurement of bisphenols and their derivatives in biological samples like urine, blood, breast milk, saliva, and hair, among others. We also discuss the different procedures commonly used for sample treatment, which includes extraction and clean-up, and instrumental techniques currently used to determine these compounds. Sample preparation techniques continue to play an important role in the analysis of complex matrices, for liquid matrices the most commonly employed is solid-phase extraction, although microextraction techniques are gaining importance in this field, and for solid samples ultrasound-assisted extraction. The main instrumental techniques used are liquid and gas chromatography coupled with mass spectrometry. Finally, we present data on the main parameters obtained in the validation of the revised methods. This review focuses on various methods developed and applied for trace analysis of bisphenols, their conjugates, halogenated derivatives, and diglycidyl ethers in biological samples to enable the required selectivity and sensitivity. For this purpose, a review is carried out of the most recent relevant publications from 2016 up to present.

Tailored amino/hydroxyl bifunctional microporous organic network for efficient stir bar sorptive extraction of parabens and flavors from cosmetic and food samples

As an effective sample pretreatment approach, stir bar sorptive extraction (SBSE) has shown great prospects in static microextraction and selective enrichment. In this work, bifunctional microporous organic network (B-MON) with the coexistence of amino and hydroxyl groups was firstly designed and synthesized as a novel coating for efficient SBSE of parabens and flavors in combination with high-performance liquid chromatography coupled with photodiode array detection (HPLC-PDA). Linked by covalent bonds to form an extension of the aromatic ring skeleton, B-MON was a tailored adsorbent featured by porous structure and abundant hydrogen bonding sites for analytes with benzene/naphthalene rings and OH/COOH groups. The extraction and desorption parameters were evaluated in detail. Under the optimized conditions, the proposed B-MON-SBSE-HPLC-PDA method offered good linearity (0.10-100 μg L^-1) with correlation coefficients R² ≥ 0.995, low limits of detection (0.010-0.035 μg L^-1) and limits of quantification (0.035-0.115 μg L^-1), and favorable enrichment factors (40-49). Furthermore, the developed method has been applied to the analysis of parabens and flavors in cosmetic and food samples with recoveries ranging from 80.4 to 109.6%. This method was also feasible to extract the analytes with benzene/naphthalene rings and OH/COOH groups, such as the plant growth regulators and non-steroidal anti-inflammatory drugs. The present study provided a new way to synthesize bifunctional MONs for SBSE of trace analytes in complex samples.

Magnet integrated fabric phase sorptive extraction of selected endocrine disrupting chemicals from human urine followed by high-performance liquid chromatography - photodiode array analysis

In current paper, a new advanced modification of fabric phase sorptive extraction is introduced for the first time. This advantageous configuration that integrates the stirring and extraction mechanism into a single sample preparation device was originated by equally considering the beneficial role of the increase of extraction kinetics and more specifically of diffusion on the extraction efficiency of the equilibrium based microextraction techniques and the need for integrating and unite processes for better promotion and implementation of the principles of Green Analytical Chemistry. The resulted magnet integrated fabric phase sorptive extraction (MI-FPSE) device was the spearhead to develop a new analytical methodology for the determination of selected very common endocrine disrupting chemicals as model analytes in human urine by high-performance liquid chromatography-photodiode array analysis. More specifically, the sol-gel Carbowax 20 M coated on hydrophilic cellulose fabric substrate, MI-FPSE device was efficiently employed for the establishment of a new extraction protocol before the chromatographic determination. The sample preparation workflow was methodically optimized in terms of the elution solvent mixture, the volume of the sample, the extraction and the elution time, the stirring speed during the extraction, the ionic strength, and the pH of the sample matrix. The chromatographic separation was performed on a Spherisorb C18 column and a gradient elution program within 14 minutes. Mobile phase consisted of 0.05 ammonium acetate aqueous solution and acetonitrile. The method was validated towards linearity, sensitivity, selectivity, precision, accuracy, and stability. LOD and LOQ ranged between 1.05-1.80 and 3.5-6.0 ng/mL, while %RSD values were found lower than 9.0% in all cases. The method was efficiently applied to the bioanalysis of real samples. All the chosen EDCs were measured at high detection levels. The new MI-FPSE device has demonstrated its performance superiority as a magnet integrated stand-alone extraction device and could be considered as a significant improvement in the field of analytical/bioanalytical sample preparation.