Ana María Casas Ferreira

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.

Stir bar sorptive extraction of parabens, triclosan and methyl triclosan from soil, sediment and sludge with in situ derivatization and determination by gas chromatography–mass spectrometry

The aim of this research work was the evaluation of stir-bar sorptive extraction (SBSE) in combination with an in situ derivatization to determine parabens (methylparaben, isopropylparaben, n-propylparaben, butylparaben and benzylparaben), triclosan and methyltriclosan in soil samples. This is the first time that this approach has been applied to the determination of these compounds in soil samples, providing important advantages over conventional extraction techniques, such as minimization of sampling handling, complete elimination of the use of organic solvents and simplification of the analytical procedure with reduced time consumption. The enriched target analytes were desorbed thermally using a thermodesorption system coupled to a gas chromatograph and a mass spectrometer. The optimized derivatization and SBSE extraction conditions, as well as the analytical characteristics of the method were obtained using spiked soil samples. The proposed methodology proved to be easy to use and sensitive, with limits of detection between 80 ng/kg and 1.06 μg/kg, and reproducibility values below 13%. The accuracy of the method was evaluated at two concentration levels, obtaining apparent recoveries between 91% and 110%. The matrix composition significantly influenced the extraction procedure, and a need to adopt a standard additions protocol is apparent. The analytes assayed were determined successfully in different environmental soil samples.

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.

Headspace generation coupled to gas chromatography–mass spectrometry for the automated determination and quantification of endogenous compounds in urine. Aldehydes as possible markers of oxidative stress

A methodology for the determination of five aldehydes in urine has been developed based on the coupling of a headspace generation sampler with a gas chromatography-mass spectrometry system equipped with a programmed temperature vaporizer. This instrumental configuration minimizes sample manipulation and allows the determination of these compounds without the need for a derivatization step so that the methodology is largely shortened and simplified. An experimental design was carried out in order to optimize the headspace sampling. Sample matrix effect was eliminated by means of dilution of urine samples. The calibration models displayed good linearity (0.1-10 μg/L) and their validity was checked using ANOVA, and it was observed that they did not exhibit any lack of fit. The LODs obtained ranged between 0.04 and 0.08 μg/L and the LOQs between 0.12 and 0.24 μg/L. The accuracy of the method was evaluated in terms of apparent recoveries which were between 86 and 120%. The method developed was applied to the analysis of 17 samples of urine from different subjects in order to quantify these endogenous compounds.

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.

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.

Use of microextraction by packed sorbents and gas chromatography-mass spectrometry for the determination of polyamines and related compounds in urine

A novel methodology for the determination of ornithine, putrescine, cadaverine, spermidine and gamma-amino butyric acid in urine samples has been developed. The method uses in situ aqueous derivatization followed by automated microextraction by packed sorbent coupled to a gas chromatography-mass spectrometry system equipped with a programmed temperature vaporizer. This instrumental configuration minimizes sample manipulation due to from the mixing of the reagents, the process is completely automated. The analytes were derivatized using ethyl chloroformate as derivatization reagent. The reaction occurred in aqueous medium and was carried out in 1min in the vial of an autosampler used to perform microextraction by packed sorbent. The parameters affecting derivatization, extraction and separation were optimized in order to obtain maximum sensitivity. Calibration curves were obtained for five calibration levels in three different matrices. All the calibration models displayed good linearity, with R(2) values higher than 0.95. The validity of the models was checked using ANOVA, and it was observed that they did not exhibit any lack of fit. Repeatability and reproducibility was evaluated, with values below 15% in both cases. LOD and LOQ values were found to be in the low μg/L level. Influence of the matrix was confirmed, thus quantification was performed using the standard additions method and normalization to IS. The method developed was applied to the analysis of these compounds in urine samples from healthy individuals and cancer diagnosed patients (Internal Medicine Unit of the Virgen de la Vega Hospital, Salamanca, Spain). Significant differences (Mann-Whitney U test) were observed for putrescine and ornithine concentrations.

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).