R. Rodríguez-Gómez

Stir bar sorptive extraction: Recent applications, limitations and future trends

Stir bar sorptive extraction (SBSE) has generated growing interest due to its high effectiveness for the extraction of non-polar and medium-polarity compounds from liquid samples or liquid extracts. In particular, in recent years, a large amount of new analytical applications of SBSE has been proposed for the extraction of natural compounds, pollutants and other organic compounds in foods, biological samples, environmental matrices and pharmaceutical products. The present review summarizes and discusses the theory behind SBSE and the most recent developments concerning its effectiveness. In addition, the main results of recent analytical approaches and their applications, published in the last three years, are described. The advantages, limitations and disadvantages of SBSE are described and an overview of future trends and novel extraction sorbents and supports is given.

Determination of benzophenones in human placental tissue samples by liquid chromatography-tandem mass spectrometry.

Benzophenones (BPs) are a family of compounds widely used to protect the skin and hair from UV irradiation. Despite human exposure to BPs through dermal application of products containing sunscreen agents and the increasing evidence that BPs are able to interfere with endocrine systems, few studies have examined the occurrence of BPs in humans. In this work, we propose a new liquid chromatography-tandem mass spectrometry (LC-MS/MS) method to determine six BPs, namely, benzophenone-1 (BP-1), benzophenone-2 (BP-2), benzophenone-3 (BP-3), benzophenone-6 (BP-6), benzophenone-8 (BP-8) and 4-hydroxybenzophenone (4-OH-BP) in human placental tissue samples. The method involves an extraction step of the analytes from the samples using ethyl acetate, followed by a clean-up step using centrifugation prior to their quantification by LC-MS/MS using an atmospheric pressure chemical ionization (APCI) interface in the positive mode. Benzophenone-d(10) (BP-d(10)) was used as surrogate. Found detection limits (LOD) ranged from 0.07 to 0.3 ng g(-1) and quantification limits (LOQ) from 0.3 to 1.0 ng g(-1), while inter- and intra-day variability was under 5%. The method was validated using standard addition calibration and a recovery assay. Recovery rates for spiked samples ranged from 98 to 104%. This method was satisfactorily applied for the determination of BPs in 16 placental tissue samples collected from women who live in Granada (Spain).

Analytical methods for the assessment of endocrine disrupting chemical exposure during human fetal and lactation stages: a review.

In the present work, a review of the analytical methods developed in the last 15 years for the determination of endocrine disrupting chemicals (EDCs) in human samples related with children, including placenta, cord blood, amniotic fluid, maternal blood, maternal urine and breast milk, is proposed. Children are highly vulnerable to toxic chemicals in the environment. Among these environmental contaminants to which children are at risk of exposure are EDCs -substances able to alter the normal hormone function of wildlife and humans-. The work focuses mainly on sample preparation and instrumental techniques used for the detection and quantification of the analytes. The sample preparation techniques include, not only liquid-liquid extraction (LLE) and solid-phase extraction (SPE), but also modern microextraction techniques such as extraction with molecular imprinted polymers (MIPs), stir-bar sorptive extraction (SBSE), hollow-fiber liquid-phase microextraction (HF-LPME), dispersive liquid-liquid microextraction (DLLME), matrix solid phase dispersion (MSPD) or ultrasound-assisted extraction (UAE), which are becoming alternatives in the analysis of human samples. Most studies focus on minimizing the number of steps and using the lowest solvent amounts in the sample treatment. The usual instrumental techniques employed include liquid chromatography (LC), gas chromatography (GC) mainly coupled to tandem mass spectrometry. Multiresidue methods are being developed for the determination of several families of EDCs with one extraction step and limited sample preparation.

Gas chromatography and ultra high performance liquid chromatography tandem mass spectrometry methods for the determination of selected endocrine disrupting chemicals in human breast milk after stir-bar sorptive extraction

In the present work, two specific, accurate and sensitive methods for the determination of endocrine disrupting chemicals (EDCs) in human breast milk are developed and validated. Bisphenol A and its main chlorinated derivatives, five benzophenone-UV filters and four parabens were selected as target analytes. The method involves a stir-bar sorptive extraction (SBSE) procedure followed by a solvent desorption prior to GC-MS/MS or UHPLC-MS/MS analysis. A derivatization step is also necessary when GC analysis is performed. The GC column used was a capillary HP-5MS with a run time of 26min. For UHPLC analysis, the stationary phase was a non-polar Acquity UPLC(®) BEH C18 column and the run time was 10min. In both cases, the analytes were detected and quantified using a triple quadrupole mass spectrometer (QqQ). Quality parameters such as linearity, accuracy (trueness and precision), sensitivity and selectivity were examined and yielded good results. The limits of quantification (LOQs) ranged from 0.3 to 5.0ngmL(-1) for GC and from 0.2 to 1.0ngmL(-1) for LC. The relative standard deviation (RSD) was lower than 15% and the recoveries ranged from 92 to 114% in all cases, being slightly unfavorable the results obtained with LC. The methods were satisfactorily applied for the determination of target compounds in human milk samples from 10 randomly selected women.

A multiclass method for endocrine disrupting chemical residue analysis in human placental tissue samples by UHPLC–MS/MS

The group of compounds commonly called endocrine-disrupting chemicals covers a wide range of synthetic and natural substances able to alter the normal hormone function of wildlife and humans, consequently causing adverse health effects. Bisphenol A (BPA) and its chlorinated derivatives, benzophenones (BPs) and parabens (PBs), belong to this group of compounds. In this work, we propose a multiclass ultra-high-performance liquid chromatography-tandem mass spectrometry (UHPLC–MS/MS) method to determine BPA, its four chlorinated derivatives (monochloro-, dichloro-, trichloro- and tetrachloro-bisphenol A), six BPs (benzophenone-1, benzophenone-2, benzophenone-3, benzophenone-6, benzophenone-8 and 4-hidroxybenzophenone) and four PBs (methylparaben, ethylparaben, propylparaben and butylparaben) in human placental tissue samples. The method involves an extraction step of the analytes from the samples using ethyl acetate, followed by a clean-up step by centrifugation prior to their quantification by UHPLC–MS/MS using an atmospheric pressure chemical ionization (APCI) interface in the negative mode. Deuterated bisphenol A (BPA-d16) was used as surrogate. The limits of detection (LOD) found ranged from 0.03 to 0.6 ng g−1, the limits of quantification (LOQ) from 0.1 to 1.4 ng g−1, while inter- and intra-day variability was under 8%. The method was validated using matrix-matched calibration standard and a spike recovery assay. Recovery rates for spiked samples ranged from 95% to 106%. This method was satisfactorily applied to the determination of these compounds in 50 placental tissue samples collected from women who live in the province of Granada (Spain).

A multiresidue method for the determination of selected endocrine disrupting chemicals in human breast milk based on a simple extraction procedure

In recent decades, in parallel to industrial development, a large amount of new chemicals have emerged that are able to produce disorders in human endocrine system. These groups of substances, so-called endocrine disrupting chemicals (EDCs), include many families of compounds, such as parabens, benzophenone-UV filters and bisphenols. Given the demonstrated biological activity of those compounds, it is necessary to develop new analytical procedures to evaluate the exposure with the final objective of establishing, in an accurate way, relationships between EDCs concentrations and the harmful health effects observed in population. In the present work, a method based on a simplified sample treatment involving steps of precipitation, evaporation and clean-up of the extracts with C18 followed by ultrahigh performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) analysis for the determination of bisphenol A and its chlorinated derivatives (monochloro-, dichloro-, trichloro- and tetrachlorobisphenol A), parabens (methyl-, ethyl-, propyl- and butylparaben) and benzophenone-UV filters (benzophenone -1,-2, -3, -6, -8 and 4-hydroxybenzophenone) in human breast milk samples is proposed and validated. The limits of detections found ranged from 0.02 to 0.05 ng mL(-1). The method was validated using matrix-matched standard calibration followed by a recovery assay with spiked samples. Recovery rates ranged from 91% to 110% and the precision (evaluated as relative standard deviation) was lower than 15% for all compounds, being within the acceptable limits for the selected bioanalytical method validation guide. The method was satisfactorily applied for the determination of these compounds in human breast milk samples collected from 10 randomly selected women.

Stir-membrane solid-liquid-liquid microextraction for the determination of parabens in human breast milk samples by ultra high performance liquid chromatography-tandem mass spectrometry.

In this article, stir-membrane solid-liquid-liquid microextraction (SM-SLLME) is tailored for the analysis of solid matrices and it has been evaluated for the determination of parabens in l breast milk samples. A three-phase microextraction mode was used for the extraction of the target compounds taking advantage of their acid-base properties. The unit allows the simultaneous extraction of the target compounds from the solid sample to an organic media and the subsequent transference of the analytes to an aqueous acceptor phase. The method includes the identification and quantification of the analytes by ultra high performance liquid chromatography coupled to tandem mass spectrometry (UHPLC-MS/MS). All the variables involved in the extraction procedure have been accurately studied and optimized. The analytes were detected and quantified using a triple quadrupole mass spectrometer (QqQ). The selection of two specific fragmentation transitions for each compound allowed simultaneous quantification and identification. The method has been analytically characterized on the basis of its linearity, sensitivity and precision. Limits of detection ranged from 0.1 to 0.2ngmL(-1) with precision better than 8%, (expressed as relative standard deviation). Relative recoveries were in the range from 91 to 106% which demonstrated the applicability of the stir-membrane solid-liquid-liquid microextraction for the proposed analytical problem. Moreover, the method has been satisfactorily applied for the determination of parabens in lyophilized breast milk samples from 10 randomly selected individuals.

Determination of benzophenone-UV filters in human milk samples using ultrasound-assisted extraction and clean-up with dispersive sorbents followed by UHPLC-MS/MS analysis

A new sample preparation method for the determination of five benzophenone UV-filters in human breast milk has been developed. The procedure involves the lyophilization of the sample, and its subsequent extraction by ultrasound sonication using acetonitrile. In order to reduce matrix effects produced by milk components that are coextracted, mainly proteins, sugars and lipids, a further clean-up step with a mixture of dispersive-SPE sorbents, C18 and PSA, was applied. Extraction parameters were optimized using experimental design, and the compounds were detected and quantified by ultrahigh performance liquid-chromatography tandem mass spectrometry (UHPLC-MS/MS) in positive ESI mode. Analytes were separated in 10 min. BP-d10 was used as internal standard. The limits of detection (LODs) were between 0.1 and 0.2 ng mL(-1), and the limits of quantification (LOQs) were between 0.3 and 0.6 ng mL(-1) for the target analytes. The inter- and intra-day variability was <12%. The method was validated using matrix-matched calibration and recovery assays with spiked samples. Recovery rates were between 90.9 and 109.5%. The method was successfully applied for the determination of these compounds in human milk samples collected from volunteers lactating mothers with no known occupational exposure to these compounds who live in the province of Granada (Spain). The analytical method developed here may be useful for the development of more in-depth studies on the prenatal exposure and biomonitoring of these commonly used UV-filters.

Disposable biosensor based on cathodic electrochemiluminescence of tris(2,2-bipyridine)ruthenium(II) for uric acid determination.

A new method for uric acid (UA) determination based on the quenching of the cathodic ECL of the tris(2,2-bipyridine)ruthenium(II)-uricase system is described. The biosensor is based on a double-layer design containing first tris(2,2-bipyridine)ruthenium(II) (Ru(bpy)3(2+)) electrochemically immobilized on graphite screen-printed cells and uricase in chitosan as a second layer. The uric acid biosensing is based on the ECL quenching produced by uric acid over the cathodic ECL caused by immobilized Ru(bpy)3(2+) in the presence of uricase. The use of a -1.1 V pulse for 1s with a dwelling time of 10s makes it possible to estimate the initial enzymatic rate, which is used as the analytical signal. The Stern-Volmer type calibration function shows a dynamic range from 1.0×10(-5) to 1.0×10(-3)M with a limit of detection of 3.1×10(-6)M and an accuracy of 13.6% (1.0×10(-4)M, n=5) as relative standard deviation. Satisfactory results were obtained for urine samples, creating an affordable alternative for uric acid determination.

New method for the determination of parabens and bisphenol A in human milk samples using ultrasound-assisted extraction and clean-up with dispersive sorbents prior to UHPLC-MS/MS analysis.

A sensitive and accurate analytical method for the determination of methyl-, ethyl-, propyl- and butylparaben and bisphenol A in human milk samples has been developed and validated. The combination of ultrasound-assisted extraction (UAE) and a simplified and rapid clean-up technique that uses sorbent materials has been successfully applied for the preparation of samples prior to ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) analysis. The analytes were extracted from freeze-dried human milk samples using acetonitrile and ultrasonic radiation (three 15-min cycles at 70% amplitude), and further cleaned-up with C18 sorbents. The most influential parameters affecting the UAE method and the clean-up steps were optimized using design of experiments. Negative electrospray ionization (ESI) in the selected reaction monitoring (SRM) mode was used for MS detection. The use of two reactions for each compound allowed simultaneous quantification and identification in one run. The analytes were separated in less than 10min. Deuterium-labeled ethylparaben-d5 (EPB-d5) and deuterium-labeled bisphenol A-d16 (BPA-d16) were used as surrogates. The limits of quantification ranged from 0.4 to 0.7ngmL(-1), while inter- and intra-day variability was under 11.1% in all cases. In the absence of certified reference materials, recovery assays with spiked samples using matrix-matched calibration were used to validate the method. Recovery rates ranged from 93.8% to 112.2%. The proposed method was satisfactorily applied for the determination of four selected parabens and bisphenol A in human milk samples obtained from nursing mothers living in the province of Granada (Spain).