María Esther Fernández Laespada

Simplified QuEChERS approach for the extraction of chlorinated compounds from soil samples.

A simplified version of the QuEChERS method for the extraction of chlorinated pollutant compounds from soil samples is proposed. The procedure involves simple liquid extraction of the soil sample with ethyl acetate, followed by the addition of anhydrous MgSO(4). Gas chromatography/electron capture detection (ECD) is then used to analyse the extracts without any other sample pretreatment. This new QuEChERS version includes, therefore, fewer treatment stages of the sample, which makes the final procedure simpler, faster, and cheaper and minimizes the creation of errors associated with this step. Three chlorinated compounds (chloroform, 1,2-dichlorobenzene, and hexachlorobenzene) of different volatility and polarity have been selected as target compounds and two different solvents (acetonitrile and ethyl acetate) have been evaluated in order to prove the suitability of the proposed approach for the extraction of these compounds from different soil samples. The suitability of the acetonitrile and ethyl acetate for PTV-GC analysis has also been evaluated. Recoveries between 62 and 93% and reproducibilities between 3.5 and 7.6% have been achieved.

Microextraction by packed sorbent for the analysis of pharmaceutical residues in environmental water samples by in situ derivatization-programmed temperature vaporizer–gas chromatography–mass spectrometry

The present work describes the development and validation of a method for the determination of five non-steroidal anti-inflammatory drugs (NSAIDs: clofibric acid, ibuprofen, naproxen, diclofenac and ketoprofen) in water samples. The fully automated method includes in situ aqueous derivatization followed by analyte enrichment by microextraction by packed sorbent (MEPS) coupled directly to programmed temperature vaporizer-gas chromatography-mass spectrometry (PTV-GC-MS). The MEPS variables, such as sample volume, elution solvent, elution volume, fill and injection speed and washing steps were optimized. It was possible to use the MEPS polymer (silica-C18) 250 times. Ibuprofen-d3 was used as internal standard. The reproducibility of the method, calculated as the relative standard deviation (RSD), was below 10% for all compounds. Detection limits in ultrapure water were between 3.0 and 110 ngL(-1) for ibuprofen and ketoprofen, respectively. External calibration was used in the determination of NSAIDs in several types of water samples, including tap, river, sea and influent and effluent wastewater. The results obtained revealed the presence of ibuprofen and naproxen in the influent wastewater sample and of naproxen in the effluent wastewater sample.

In situ aqueous derivatization as sample preparation technique for gas chromatographic determinations

The use of derivatization reactions is a common practice in analytical laboratories. Although in many cases it is tedious and time-consuming, it does offer a good alternative for the determination of analytes not compatible to gas chromatography. Many of the reactions reported in the literature occur in organic medium. However, in situ aqueous derivatization reactions, which can be performed directly in aqueous medium, offer important advantages over those mentioned above, such as no need of a previous extraction step and easy automation. Here we review the most recent developments and applications of in situ aqueous derivatization. The discussion focuses on the derivatization reactions used for the determination of alcohols and phenols, carboxylic acids, aldehydes and ketones, nitrogen-containing compounds and thiols in different aqueous matrices, such as environmental, biological and food samples. Several reactions are described for each functional group (acylation, alkylation, esterification, among others) and, in some cases, the same reagents can be used for several functional groups, such that there is an unavoidable overlap between sections. Finally, attention is also focused on the techniques used for the introduction of the derivatives formed in the aqueous medium into the chromatographic system. The implementation of in situ aqueous derivatization coupled to preconcentration techniques has permitted the enhancement of recoveries and improvements in the separation, selectivity and sensitivity of the analytical methods.

Use of a programmed temperature vaporizer and an in situ derivatization reaction to improve sensitivity in headspace-gas chromatography. Application to the analysis of chlorophenols in water.

In the present work we propose the combined use of a derivatization reaction within the vial of a headspace sampler with a programmed temperature vaporizer (PTV) inlet in the solvent vent mode as a new methodology for obtaining an increase in sensitivity in headspace-gas chromatography (HS-GC) for the analysis of sparingly volatile compounds. As test analytes the following chlorophenols were used: 2-chlorophenol (2CP), 2,4-dichlorophenol (24DCP), 4-chloro-3-methylphenol (4C3MP) and 2,4,6-trichlorophenol (246TCP). The derivatization reaction was carried out with acetic anhydride because it can be carried out in situ in aqueous medium. In the programmed temperature vaporizer inlet, three different liners, one of them empty and the others with materials of different trapping strengths (glass wool and Tenax-TA), were compared. The best results were obtained when an empty liner was used, with better repeatability and S/N ratios. In the case of the liner filled with Tenax-TA, a considerable lack of repeatability was observed, this being attributed to interactions between the derivatized compounds and the adsorbent. The proposed methodology affords very low limits of detection, in the range of a few ng/L for all the compounds, with good precision and accuracy values.

In situ derivatization reaction and determination of ibuprofen in water samples using headspace generation-programmed temperature vaporization-gas chromatography-mass spectrometry.

The aim of the present work is to propose a method for the determination of ibuprofen, as a typical representative of pharmaceutical compounds, in aqueous samples. To do so, an in situ derivatization reaction in aqueous medium was employed in the vial of a headspace sampler (HS), after which instrumental measurements were made with gas chromatography-mass spectrometry (GC-MS). As the injection system we propose a programmed temperature vaporizer (PTV) where, in solvent vent mode, better results can be obtained than with the conventional split and splitless injection modes. Since the derivatization reaction takes place in the HS vial, after the mixing of reagents and the sealing of the vial, the whole process takes place on-line, with no need for intermediate steps. The simplicity and speed of the method--analysis throughput: 10.5 min--together with the limit of detection obtained (0.23 microg/L), bearing in mind that no preconcentration step or later clean-up step are required, make this a good method for the analysis of ibuprofen in aqueous samples of urban waste water.

Determination of aromatic and polycyclic aromatic hydrocarbons in gasoline using programmed temperature vaporization-gas chromatography–mass spectrometry

A sensitive method is presented for the fast analysis of three aromatic and six polycyclic aromatic hydrocarbons (biphenyl, 3-methylbiphenyl, 4-methylbiphenyl, fluorene, phenanthrene, fluoranthene, pyrene, 1,2-benz(a)anthracene and chrysene) in gasoline samples. The applicability of a GC device equipped with a programmable temperature vaporizer (PTV) and an MS detector is explored. Additionally, a modular accelerated column heater (MACH) was used to control the temperature of the capillary gas chromatography column. This module can be heated and cooled very rapidly, making total analysis cycle times very short. The proposed method does not require any previous analyte extraction and preconcentration step, as in most methods described to date. Sample preparation is reduced to simply diluting the gasoline samples in methanol. This reduces the experimental errors associated with this step of the analytical process. By using sampling injection in the solvent vent mode, and through choice of a suitable temperature, the lightest major components of the gasoline were removed. Moreover, use of a liner packed with Tenax-TA allowed the compounds of interest to be retained during the process. This working strategy could be extended to other groups of compounds through the choice of different venting temperatures. In this way, a large part of the gasoline components are eliminated, the life of the liner is prolonged, and it is possible to inject sample volumes that will not saturate the chromatographic column. The limits of detection ranged from 0.61 microg/L (pyrene) to 6.1 microg/L (biphenyl), and precision (measured as the relative standard deviation) was equal to or lower than 7.3%. The method was applied to the determination of analytes in gasoline samples and the results obtained can be considered highly satisfactory.

Headspace sampling with in situ carbodiimide-mediated derivatization for the determination of ibuprofen in water samples.

A method using headspace generation and in situ derivatization with water soluble EDC (1-[3-(dimethylamino)propyl]-3-ethylcarbodiimide) and TFEA (2,2,2-trifluoroethylamine) has been optimized for the determination of ibuprofen (2-(p-isobutylphenyl)propionic acid), one of the most common non-steroid anti-inflammatory drug (NSAIDs) residues in surface and wastewater samples. Derivatization was carried out in the vial of the headspace sampler (HS) in only 15 min, after which instrumental measurements were made with gas chromatography-mass spectrometry (GC-MS). As the injection system, a programmed temperature vaporizer (PTV) in the solvent-vent injection mode is proposed in order to increase the sensitivity of the measurements. The effects of the variables affecting HS generation, the derivatization reaction, and the instrumental PTV conditions were studied. A limit of quantification as low as 32 ng/L was achieved, and repeatability values were below 10%. Accuracy of the method was evaluated using spiked ultrapure water at three concentration levels, obtaining apparent recoveries between 96% and 104%. The proposed method was applied to the quantification of ibuprofen in sea water and urban wastewater samples.

Comparative study of silicone and microporous membranes for the separation of some phenols prior to high performance liquid chromatography analysis

A membrane separation module has been coupled on-line to a high-resolution liquid chromatographic system. A microcomputer controls the set of operations required in the overall automatic process. Two types of membranes, homogeneous (silicone) and microporous with air-filled pores, have been investigated and the results obtained for five chlorophenols, of different polarities and volatilities, have been compared. The most important variables affecting the process are the composition of the donor and acceptor phases and the enrichment time. The method using the silicone membrane, was applied to the determination of the analytes in real water samples.

Development of an environmentally friendly methodological approach to determine chlorinated hydrocarbons and chlorobenzenes in soils

A modified version of the quick, easy, cheap, efficient, rugged, and safe method is proposed for the determination of chlorinated pollutants in soil samples. Measurements were collected using a programmed temperature vaporizer coupled to a gas chromatograph and a µ-electron capture detector. The optimization and validation of this extraction technique for these compounds in soils have been performed in order to provide an alternative tool for determining these kinds of pollutants in soils. Advantages over conventional extraction techniques include the applicability to compounds of very different volatilities and polarities, the low cost of the reagents employed, and the possibility of being used by nonspecialist operators, with standard analytical tools. This method can be considered more environmentally friendly, due to the reduction of solvent and energy consumption and to the elimination of harmful organic solvents, reducing the negative impact of chemical analyses on the environment (principles of gre...A modified version of the quick, easy, cheap, efficient, rugged, and safe method is proposed for the determination of chlorinated pollutants in soil samples. Measurements were collected using a programmed temperature vaporizer coupled to a gas chromatograph and a µ-electron capture detector. The optimization and validation of this extraction technique for these compounds in soils have been performed in order to provide an alternative tool for determining these kinds of pollutants in soils. Advantages over conventional extraction techniques include the applicability to compounds of very different volatilities and polarities, the low cost of the reagents employed, and the possibility of being used by nonspecialist operators, with standard analytical tools. This method can be considered more environmentally friendly, due to the reduction of solvent and energy consumption and to the elimination of harmful organic solvents, reducing the negative impact of chemical analyses on the environment (principles of green analytical chemistry).