Maitane Olivares

Classification and identification of organic binding media in artworks by means of Fourier transform infrared spectroscopy and principal component analysis

AbstractFourier transform infrared spectroscopy is a powerful analytical technique to study organic materials. However, in Cultural Heritage, since the sample under analysis is always a complicated matrix of several materials, data analysis performed through peak-by-peak comparisons of sample spectra with those of standard compounds is a tedious method that does not always provide good results. To overcome this problem, a chemometric model based on principal component analysis was developed to classify and identify organic binding media in artworks. The model allows the differentiation of five families of binders: drying oils, waxes, proteins, gums, and resins, taking into account the absorption bands in two characteristic spectral windows: C–H stretching and carbonyl band. This new methodology was applied in the characterization of binders in three kinds of artworks: papers of historical, archeological, and artistic value, easel paintings, and polychromed stone-based sculptures. FigureAnalysis of the binder in a wallpaper of the 19th century by means of FTIR spectroscopy and chemometrics

Retention-time locked methods in gas chromatography.

Retention time is one of the most important chromatographic features for analytical chemists since it is the key parameter to separate, identify and quantify compounds of interest from complex mixtures. Although detectors with higher-dimensional signals ease the identification of many components, there are demanding requirements on the retention time, particularly when high-throughput methods are considered. In addition to this, gas chromatographic elution shows significant run-to-run variations due to fluctuations in temperature and pressure, column degradation or matrix effects. In this sense, different approaches have been developed to minimise those variations: the introduction of electronic pneumatic control (EPC) systems, which allow a very efficient control of the flow of the carrier gas, the use of peak alignment algorithms to treat the chromatograms, or the use of retention-time locking (RTL). The RTL is a feature of the Agilent ChemStation software available for those GC instruments equipped with EPC systems. Originally it was developed to assure method translation but it has extended to fix the retention time and to implement peak deconvolution algorithms and database building and searching facilities. In this manuscript, the RTL basis and practical aspects are summarised together with a brief description of some applications.

Optimisation and characterisation of marihuana extracts obtained by supercritical fluid extraction and focused ultrasound extraction and retention time locking GC-MS.

The optimisation of focused ultrasound extraction and supercritical fluid extraction of volatile oils and cannabinoids from marihuana has been accomplished by experimental design approach. On the one hand, the focused ultrasound extraction method of volatile compounds and cannabinoids was studied based on the optimisation of cyclohexane and isopropanol solvent mixtures, and the instrumental variables. The optimal working conditions were finally fixed at isopropanol/cyclohexane 1:1 mixture, cycles (3 s(-1)), amplitude (80%) and sonication time (5 min). On the other hand, the supercritical fluid extraction method was optimised in order to obtain a deterpenation of the plant and a subsequent cannabinoid extraction. For this purpose, pressure, temperature, flow and co-solvent percentage were optimised and the optimal working conditions were set at 100 bar, 35°C, 1 mL/min, no co-solvent for the terpenes and 20% of ethanol for the cannabinoids. Based on the retention time locking GC-MS analysis of the supercritical fluid extracts the classification of the samples according to the type of plant, the growing area and season was attained. Finally, three monoterpenes and three cannabinoids were quantified in the ranges of 0.006-6.2 μg/g and 0.96-324 mg/g, respectively.

Microencapsulation and storage stability of polyphenols from Vitis vinifera grape wastes

Wine production wastes are an interesting source of natural polyphenols. In this work, wine wastes extracts were encapsulated through vibration nozzle microencapsulation using sodium alginate as polymer and calcium chloride as hardening reagent. An experimental design approach was used to obtain calcium-alginate microbeads with high polyphenol content and good morphological features. In this way, the effect of pressure, frequency, voltage and the distance to the gelling bath were optimized for two nozzles of 150 and 300 μm. Long-term stability of the microbeads was studied for 6 months taking into account different storage conditions: temperatures (4 °C and room temperature), in darkness and in presence of light, and the addition of chitosan to the gelling bath. Encapsulated polyphenols were found to be much more stable compared to free polyphenols regardless the encapsulation procedure and storage conditions. Moreover, slightly lower degradation rates were obtained when chitosan was added to the gelling bath.

Matrix effect during the membrane-assisted solvent extraction coupled to liquid chromatography tandem mass spectrometry for the determination of a variety of endocrine disrupting compounds in wastewater

Membrane-assisted solvent extraction (MASE) coupled to liquid chromatography-triple quadrupole mass spectrometry (LC-MS/MS) was studied for the determination of a variety of emerging and priority compounds in wastewater. Among the target analytes studied certain hormones (estrone (E1), 17β-estradiol (E2), androsterone (ADT), 17α-ethynyl estradiol (EE2), diethylstilbestrol (DES), equilin (EQ), testosterone (TT), mestranol (MeEE2), 19-norethisterone (NT), progesterone (PG) and equilenin (EQN)), alkylphenols (APs) (4-tert-octylphenol (4tOP), nonylphenol technical mixture (NPs) and 4n-octylphenol (4nOP)) and BPA were included. The work was primarily focused in the LC-MS/MS detection step, both in terms of variable optimization and with respect to the matrix effect study. Both, electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) were assessed both in the negative and positive mode, including the optimization of MS/MS operating conditions. The best results were obtained, in most of the cases, for ESI using 0.05% ammonium hydroxide as buffer solution in the mobile phase, composed with methanol and water. Under optimum detection conditions, matrix effect during the detection step was thoroughly studied. Dilution, correction with deuterated analogues and clean-up of the extracts were evaluated for matrix effect correction. Clean-up with Florisil together with correction with deuterated analogues provided the most satisfactory results, with apparent recoveries in the 57-136% range and method detection limits in the low ngL(-1) level for most of the analytes. For further validation of the method, two separated extraction procedures, the above mentioned MASE, and conventional solid phase extraction (SPE) were compared during the analysis of real samples and comparable results were successfully obtained for E1, E2, EE2, DES, NT, TT, EQ, PG, BPA, ADT, 4nOP, 4tOP, NPs and EQN.

Membrane assisted solvent extraction coupled to large volume injection-gas chromatography–mass spectrometry for trace analysis of synthetic musks in environmental water samples

This work describes the optimisation, validation and application of membrane assisted solvent extraction (MASE) together with a large volume injection (LVI) in a programmable temperature vaporisation (PTV) injector coupled to gas chromatography-mass spectrometry (GC-MS) for the quantification of ten synthetic musk fragrances (musks) in surface and wastewater samples. Regarding the MASE, musks were extracted from 150 mL of aqueous samples to 200 μL of n-hexane hold in home-made low density polyethylene (LDPE) bags. The extraction took 240 min and the performance of the method made possible the direct analysis of the extracts by LVI-PTV-GC-MS without needing any further treatment and avoiding losses of analytes. During the optimisation of LVI-PTV set-up, the response surfaces of every analyte signal against the cryo-focussing temperature, injection speed and vent time were built. Finally, the figures of merit of the whole procedure allowed the analysis of most of the musks owing to the low method detection limits (between 4 and 25 ng L⁻¹) and good precisions (<20%). In fact, this method was successfully applied to the analysis of musks in surface and wastewater samples. Galaxolide and tonalide are the main two synthetic musks observed in most of the analysed environmental water samples.

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.

Resolution of co-eluting compounds of Cannabis Sativa in comprehensive two-dimensional gas chromatography/mass spectrometry detection with Multivariate Curve Resolution-Alternating Least Squares

Comprehensive Two Dimensional Gas Chromatography - Mass Spectrometry (GC × GC/qMS) analysis of Cannabis sativa extracts shows a high complexity due to the large variety of terpenes and cannabinoids and to the fact that the complete resolution of the peaks is not straightforwardly achieved. In order to support the resolution of the co-eluted peaks in the sesquiterpene and the cannabinoid chromatographic region the combination of Multivariate Curve Resolution and Alternating Least Squares algorithms was satisfactorily applied. As a result, four co-eluting areas were totally resolved in the sesquiterpene region and one in the cannabinoid region in different samples of Cannabis sativa. The comparison of the mass spectral profiles obtained for each resolved peak with theoretical mass spectra allowed the identification of some of the co-eluted peaks. Finally, the classification of the studied samples was achieved based on the relative concentrations of the resolved peaks.

Optimization of large volume injection-programmable temperature vaporization-gas chromatography-mass spectrometry analysis for the determination of estrogenic compounds in environmental samples.

Large volume injection-programmable temperature vaporization-gas chromatography-mass spectrometry (LVI-PTV-GC-MS) was optimized for the determination of estrone (E1), 17β-estradiol (E2), 17α-ethynyl estradiol (EE2), mestranol (MeEE2) and estriol (E3) for their determination in environmental samples (estuarine water, wastewater, fish bile and fish homogenate) after derivatization with 25 μL (BSTFA+1% TMCS) and 125 μL of pyridine. Experimental designs such as Plackett-Burman (PBD) and central composite designs (CCDs) were used to optimize the LVI-PTV variables (cryo-focusing temperature, vent time, vent flow, vent pressure, injection volume, purge flow to split vent, splitless time and injection speed). Optimized conditions were as follows: 45 μL of n-hexane extract are injected at 60°C and 6 μL/s with a vent flow and a vent pressure of 50 mL/min and 7.7 psi, respectively, during 5 min; then the split valve is closed for 1.5 min and afterwards the injector is cleaned at 100 mL/min before the next injection. The method was applied to the determination of estrogenic compounds in environmental samples such as estuarine water, wastewater, and fish homogenate and bile. Limits of detection (0.04-0.15 ng/L for water samples, 0.04-0.67 ng/g for fish bile and 0.1-7.5 ng for fish homogenate) obtained were approx. ten times lower than those obtained by means of a common split/splitless inlet.

Non-destructive spectrometry methods to study the distribution of archaeological and geological chert samples

The study of lithic raw materials recovered from archaeological sites offers relevant data on source catchment areas. Additionally, it can provide first hand information on artefact displacement, interchange networks and it can reflect the way in which the artefacts were employed. In order to characterize geological and archaeological chert samples and with the aim of finding an analytical fingerprint infrared and Raman spectroscopies were used for molecular analysis and X-ray Fluorescence spectrometry for elemental analysis. In this work, different chert samples coming from several localities with geological and archaeological importance from the Basque Country have been collected and analysed. As a consequence, Raman spectroscopy allowed to distinguish between alpha-quartz and moganite in chert samples without organic matter and it is suggested that the ratio of those two components is related to the source of the chert. In addition, the impurities that appear in the samples (CaCO(3), iron oxides and organic matter) can open new features to distinguish the samples and in this way, it would be possible to discuss the use and transport of the lithic artifacts from the sources to the final settlements.