Alejandra Delgado

Microextraction with polyethersulfone for bisphenol-A, alkylphenols and hormones determination in water samples by means of gas chromatography–mass spectrometry and liquid chromatography–tandem mass spectrometry analysis

In the present work, the suitability of polyethersulfone (PES) tube was assessed for the simultaneous sorptive microextraction of commonly found endocrine disrupting compounds in natural waters such as bisphenol-A (BPA), nonylphenol technical mixture (NP mix), 4-tert-octylphenol (4tOP), 4-n-octylphenol (4-nOP), 17β-estradiol (E2) and 17α-ethynilestradiol (EE2). After the concentration of target compounds in the PES polymer, the analytes were recovered soaking the polymer with a suitable solvent (ethyl acetate or methanol), derivatized using N,O-bis(trimethylsilyl)trifluoroacetamide with 1% of trimethylchlorosilane (BSTFA+1% TMCS) and determined by gas chromatography-mass spectrometry (GC-MS). The analysis was also performed without derivatization step by means of liquid chromatography-tandem mass spectrometry (LC-MS/MS). Extraction parameters (addition of MeOH, ionic strength, extraction speed and time and desorption time) were evaluated and the optimum conditions were fixed as follows: 150 mL water samples containing a 10% (w/v) of sodium chloride and using 5 tubular PES sorbent fibers (1.5 cm length×0.7 mm o.d.). Equilibrium conditions were achieved after 9 h, with absolute extraction efficiencies ranging from 27 to 56%. On the whole, good apparent recoveries were achieved (68-103% and 81-122% for GC-MS and LC-MS/MS, respectively) using deuterated analogues as surrogates. Achieved quantification limits (LOQs) varied between 2-154 ng/L and 2-63 ng/L for all the compounds using GC-MS and LC-MS/MS, respectively. The effect of organic matter was evaluated previous to apply the final method to the analysis of estuarine and wastewater real samples. The comparison of both methods showed that overall, PES-LC-MS/MS provided shorter sample preparation time and better LODs, but PES-silylation-GC-MS allowed the simultaneous determination of all the studied compounds with adequate repeatability and accuracy.

Multiscreening determination of organic pollutants in molluscs using matrix solid phase dispersion

This work describes the optimisation, validation and application of matrix solid-phase dispersion (MSPD) coupled to gas chromatography mass spectrometry, both single quadrupole (GC-MS) and tandem (GC-MS/MS), for the quantification in molluscs of up to 40 different analytes belonging to several families of priority and emerging organic contaminants, including polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), organochlorine pesticides (OCPs), organophosphorus pesticides (OPPs) and musk fragrances. The MSPD procedure was fully optimised with a special focus on the clean-up strategy. The best recoveries were obtained using glass syringes, 0.30 g of freeze-dried sample, 0.30 g of Florisil as solid support, 4.00 g of activated silica and 25 mL of dichloromethane as elution solvent. Using GC-MS/MS the method afforded good linearities (r(2), between 0.980 and 0.9996), adequate repeatability and reproducibility (RSD<17% and 33%, respectively) and low instrumental limits of detection (between 0.010 and 2.74 ng mL(-1)). The accuracy of the method was evaluated using different approaches, i.e. assessment of spiked fish hatchery samples, laboratory reference material and standard reference material (SRM 2977). Satisfactory apparent recoveries were obtained for all the target analytes after correction with the corresponding labelled surrogate, except for PAHs in the case of SRM 2977, which required the use of the standard addition method. Finally, MSPD was applied to mollusc species collected in Colombia and Nicaragua, where PAHs, PCBs, musks and pesticides were detected at low ng g(-1) levels.

Optimisation of the headspace-solid phase microextraction for organomercury and organotin compound determination in sediment and biota.

Headspace solid-phase microextraction was optimised for the simultaneous preconcentration of methylmercury (MeHg+), monobutyltin, dibutyltin, tributyltin, monophenyltin (MPhT), diphenyltin (DPhT), and triphenyltin (TPhT) from sediments and biota. Extraction time (3-24 min), extraction temperature (20-90 degrees C), desorption time (1-10.4 min), desorption temperature (152-260 degrees C), and sample volume (5-22 mL) were simultaneously optimised, while variables such as fibre type (30 microm polydimethylsiloxane, PDMS), pH (acetic acid/sodium acetate, HOAc/NaOAc, 2 mol/L, pH approximately 4.8), the concentration of the derivatisation agent (sodium tetraethylborate, NaBEt4, 0.1% m/v), and the ionic strength (fixed by the buffer solution) were kept constant. The variables were optimised according to the experiments proposed by the MultiSimplex program and the responses were considered in order to establish the optimum conditions. The repeatability (relative standard deviation, RSD, 5-20.6%) and limits of detection (LODs, 0.05-0.97 ng/g) of the overall method were also estimated. The lowest precisions were obtained for DPhT and TPhT. The optimised preconcentration method was applied to the determination of MeHg+), butyl- and phenyltins in certified reference materials (IAEA-405 MeHg+) in estuarine sediment, BCR-646 butyl- and phenyltins in marine sediment, BCR-463 MeHg+ in tuna fish, DOLT-2 MeHg+ in dogfish liver, and BCR-477 butyltins in mussel tissue) by GC with microwave-induced plasma/atomic-emission detection.

Silicone rod extraction followed by liquid desorption-large volume injection-programmable temperature vaporiser-gas chromatography-mass spectrometry for trace analysis of priority organic pollutants in environmental water samples

In this study a priority organic pollutants usually found in environmental water samples were considered to accomplish two extraction and analysis approaches. Among those compounds organochlorine compounds, pesticides, phthalates, phenols and residues of pharmaceutical and personal care products were included. The extraction and analysis steps were based on silicone rod extraction (SR) followed by liquid desorption in combination with large volume injection-programmable temperature vaporiser (LVI-PTV) and gas chromatography-mass spectrometry (GC-MS). Variables affecting the analytical response as a function of the programmable temperature vaporiser (PTV) parameters were firstly optimised following an experimental design approach. The SR extraction and desorption conditions were assessed afterwards, including matrix modification, time extraction, and stripping solvent composition. Subsequently, the possibility of performing membrane enclosed sorptive coating extraction (MESCO) as a modified extraction approach was also evaluated. The optimised method showed low method detection limits (3-35 ng L(-1)), acceptable accuracy (78-114%) and precision values (<13%) for most of the studied analytes regardless of the aqueous matrix. Finally, the developed approach was successfully applied to the determination of target analytes in aqueous environmental matrices including estuarine and wastewater samples.

Applicability of polydimethylsiloxane (PDMS) and polyethersulfone (PES) as passive samplers of more hydrophobic organic compounds in intertidal estuarine environments

The uptake calibration of three passive samplers, stir-bars, MESCO/stir-bars and polyethersulfone tubes (PESt), was assessed in seawater at different salinities for 17 organic compounds including organochlorine compounds, pesticides, phthalates, musk fragrances and triclosan. The calibration procedure was accomplished by exposing the samplers to a continuous flow of fortified seawater for up to 14days under laboratory conditions. Prior to the exposure, stir-bars and MESCO/stir-bars were loaded with a known amount of deuterated PAH mixture as performance reference compounds (PRC). For most of the studied compounds, the sampling rates (Rs, mL·day-1) were determined for each sampler at two salinities (15 and 30‰) and two nominal concentrations (25 and 50ng·L-1). Among the tested devices, though PES can be an outstanding cheap alternative to other passive samplers, naked or free stir-bars provided the best results in terms of uptake rates (i.e., the Rs values ranged from 30 to 350mL·day-1). Regarding the variation of the salinity, the Rs values obtained with naked stir-bars were statistically comparable in the full range of salinities (0-30‰) but the values obtained with MESCO/stir-bars and PESt were salinity dependent. Consequently, only stir-bars assured the required robustness to be used as passive samplers in intertidal estuarine environments. Finally, the stir-bars were applied to estimate the time-weighted average concentration of some of those contaminants in the feeding seawater of the experimental aquaria at the Plentzia Marine Station (Basque Country) and low levels of musks fragrances (0.1-0.2ng·L-1) were estimated.