R.A. Lorenzo

Determination of acidic drugs in sewage water by gas chromatography–mass spectrometry as tert.-butyldimethylsilyl derivatives

A procedure is described for the determination of five acidic non-steroidal anti-inflammatory pharmaceuticals (ibuprofen, naproxen, ketoprofen, tolfenamic acid and diclofenac) in sewage water. The analytical method involves the concentration of water samples using a solid-phase extraction polymeric sorbent, functionalized with N-vinylpyrrolidone. Analytes were eluted with ethyl acetate. derivatized using N-methyl-N-(tert.-butyldimethylsilyl)trifluoroacetamide (MTBSTFA) and analyzed by GC-MS. Influence of time, temperature and volume of MTBSTFA in the yield of the derivatization step were studied in detail using a factorial central composite design. Quantification limits of the analytical procedure for 500 ml of sewage water ranged from 20 to 50 ng/l. Recoveries from 90 to 115% were found for sewage water samples spiked with the studied compounds at the low ng/ml level. Results obtained for real samples show the presence of ibuprofen and naproxen in both influent and effluent of a sewage water treatment plant.

Methylmercury determination in biological samples by derivatization, solid-phase microextraction and gas chromatography with microwave-induced plasma atomic emission spectrometry.

A method for the extraction and gas chromatographic determination of methylmercury in biological matrices is presented. By combining the advantages of two extraction techniques-microwave-assisted extraction (MAE) and solid-phase microextraction (SPME)--the separation of methylmercury from biological samples is possible. Specifically, the procedure involves microwave extraction with 3 M hydrochloric acid, followed by aqueous-phase derivatization with sodium tetraphenylborate and headspace SPME with a silica fibre coated with polydimethylsiloxane (PDMS). For optimization of the derivatization-SPME procedure, a central composite experimental design with alpha = 1.682 and two central points was used to model gas-chromatographic peak areas as functions of pH, extraction temperature and sorption time. A desirability function was then used for the simultaneous optimization for methylmercury and Hg(II). The optimal derivatization-SPME conditions identified were close to pH 5, temperature 100 degrees C, and sorption time 15 min. The identification and quantification of the extracted methylmercury is carried out by gas chromatography with microwave-induced plasma atomic emission spectrometry detection. The validity of the new procedure is shown by the results of analyses of certified reference materials.

Evaluation of supercritical fluid extraction, microwave-assisted extraction and sonication in the determination of some phenolic compounds from various soil matrices

Abstract Extraction methods using supercritical fluid extraction (SFE) and microwave-assisted process (MAP) techniques, with or without a one-step in situ derivatisation, were evaluated for the extraction of phenol, o-cresol, m-cresol and p-cresol from soils. Five artificially spiked soil matrices were prepared; three of them were prepared by adding various amounts of activated charcoal in order to increase the degree of analyte–matrix interaction. We also applied the methods to a real phenol contaminated soil with a high carbon content (18%). To provide a basis for comparison, all the soils were extracted using an US Environmental Protection Agency-approved sonication protocol. The extracts obtained were analyzed on a GC–MS system without any preliminary clean-up or concentration steps. The results showed that SFE and MAP are more efficient than sonication with at least twice the recovery in all the soils tested. MAP and MAP-derivatisation showed the best recoveries (>80%) for the five spiked matrices studied with the exception of o-cresol in soils with activated charcoal content higher than 5%. In these specific soils, SFE showed very low recoveries for the four phenols. However, recoveries were significantly improved when a derivatisation step was combined to SFE. In the real soil tested, the recoveries using derivatisation–extraction process were lower than the recoveries using extraction process. In general, derivatisation–extractions perform better and do not require extreme extraction conditions.

To remove or not to remove? The challenge of extracting the template to make the cavities available in Molecularly Imprinted Polymers (MIPs).

Template removal is a critical step in the preparation of most molecularly imprinted polymers (MIPs). The polymer network itself and the affinity of the imprinted cavities for the template make its removal hard. If there are remaining template molecules in the MIPs, less cavities will be available for rebinding, which decreases efficiency. Furthermore, if template bleeding occurs during analytical applications, errors will arise. Despite the relevance to the MIPs performance, template removal has received scarce attention and is currently the least cost-effective step of the MIP development. Attempts to reach complete template removal may involve the use of too drastic conditions in conventional extraction techniques, resulting in the damage or the collapse of the imprinted cavities. Advances in the extraction techniques in the last decade may provide optimized tools. The aim of this review is to analyze the available data on the efficiency of diverse extraction techniques for template removal, paying attention not only to the removal yield but also to MIPs performance. Such an analysis is expected to be useful for opening a way to rational approaches for template removal (minimizing the costs of solvents and time) instead of the current trial-and-error methods.

A rapid ultrasound-assisted dispersive liquid–liquid microextraction followed by ultra-performance liquid chromatography for the simultaneous determination of seven benzodiazepines in human plasma samples ☆

A simple and efficient ultrasound-assisted dispersive liquid-liquid microextraction (UA-DLLME) method has been developed for the determination of seven benzodiazepines (alprazolam, bromazepam, clonazepam, diazepam, lorazepam, lormetazepam and tetrazepam) in human plasma samples. Chloroform and methanol were used as extractant and disperser solvents, respectively. The influence of several variables (e.g., type and volume of dispersant and extraction solvents, pH, ultrasonic time and ionic strength) was carefully evaluated and optimized, using an asymmetric screening design 3(2)4(2)//16. Analysis of extracts was performed by ultra-performance liquid chromatography coupled with photodiode array detection (UPLC-PDA). Under the optimum conditions, two reversed-phases, Shield RP18 and C18 columns were successfully tested, obtaining good linearity in a range of 0.01-5μgmL(-1), with correlation coefficients r>0.996. Quantification limits ranged between 4.3-13.2ngmL(-1) and 4.0-14.8ngmL(-1), were obtained for C18 and Shield RP18 columns, respectively. The optimized method exhibited a good precision level, with relative standard deviation values lower than 8%. The recoveries studied at two spiked levels, ranged from 71 to 102% for all considered compounds. The proposed method was successfully applied to the analysis of seven benzodiazepines in real human plasma samples.

Optimization of a microwave-assisted extraction method for phenol and methylphenol isomers in soil samples using a central composite design

A simple and rapid microwave-assisted extraction (MAE) procedure was developed and optimized for phenol, o-cresol, m-cresol and p-cresol in soil samples. The spiked soil used was prepared 25 d before treatment to simulate weathering processes and to allow for the formation of analyte-matrix interactions. The samples, immersed in hexane–acetone, were irradiated with microwaves in a closed-vessel system. Optimization of the method was achieved by using a factorial design approach on parameters such as the volume of solvent, the percentage of acetone and the extraction temperature. The MAE procedure yielded extracts that could be analyzed directly using a GC–flame ionization detection system without any preliminary clean-up or concentration steps.

Optimization of a rapid microwave-assisted extraction method for the simultaneous determination of opiates, cocaine and their metabolites in human hair

A rapid and cleanup-free microwave-assisted extraction (MAE) method is proposed for the simultaneous extraction of six illegal drugs of abuse - cocaine, benzoylecgonine (BZE), cocaethylene (CCE), morphine, 6-monoacethylmorphine (6AM) and codeine - from human hair samples. The analytes were determined using high performance liquid chromatography (HPLC) with photodiode array UV detection. The influence of several variables on the efficiency of the MAE procedure was investigated in detail by a multi-objective optimization approach based on a hybrid experimental design (17 experiments) and desirability functions. Six drugs were successfully extracted from human hair with recoveries close to 100% and good reproducibility (<3.6% RSD) under the optimal MAE conditions: 11 mL dichloromethane (DCM) extraction solvent, 60 degrees C extraction temperature, 9 min extraction time and 0.5 mL of methanol (MeOH) added to 50mg of the hair sample in the extraction vessels. Limits of quantification of 0.2 ng mg(-1) were found for the studied compounds. A comparison of sample preparation procedures, including MAE, enzymatic digestion and digestion by aqueous acids, was also conducted. The results indicated that the global behaviour of sample procedures provided similar satisfactory recoveries ranging from 86 to 100%. Indeed, the MAE procedure resulted in a reduction of extraction time by 100-fold and the elimination of cleanup steps. Slightly higher recoveries of morphine, 6AM, BZE and CCE, at 1 ng mg(-1) concentration level and cocaine at 40 ng mg(-1) concentration level, were achieved using MAE. Lastly, the proposed MAE method was applied to several human hair samples from multidrug abusers.

Speciation of mercury compounds by gas chromatography with atomic emission detection. Simultaneous optimization of a headspace solid-phase microextraction and derivatization procedure by use of chemometric techniques

SummaryA method is proposed for the extraction and determination of organomercury compounds and Hg(II) in seawater samples by headspace solid-phase microextraction (HS-SPME) combined with capillary gas chromatography-microwave-induced plasma atomic emission spectrometry. The mercury species were derivatized with sodium tetraphenylborate, sorbed on a polydimethylsiloxane-coated fused-silica fibre, and desorbed in the injection port of the GC, in splitless mode.Experimental design methodology was used to evaluate the effect of six HS-SPME-derivatization vairables: sample, volume, NaBPh4 volume, pH, sorption time, extraction-derivatization temperature, and rate of stirring. Use of a multicriterion decision-making approach, with the desirability function, enabled determination of the optimum working conditions of the procedure for simultaneous analysis of three mercury species.

Experimental design of a microwave-assisted extraction-derivatization method for the analysis of methylmercury.

A simultaneous microwave-assisted extraction-derivatization procedure was developed and optimized for methylmercury analysis from biological samples. The analyte was derivatized with sodium tetraphenylborate forming a more hydrophobic compound, methylphenylmercury, which was extractable in toluene. The microwave extraction-derivatization procedure was optimized using experimental design, 2(5-1) fractional factorial. This chemometrical approach considers main effects as well as interactions of the influential parameters, indicating that temperature and its interaction with NaBPh4 and acetic acid volumes were the variables that significantly affected methylmercury recoveries.

Methylmercury extraction from aquatic sediments: A comparison between manual, supercritical fluid and microwave-assisted techniques

Abstract During recent decades the speciation of organomercurials has been a challenge to analytical laboratories dealing with environmental studies. Although easily detectable levels of organomercurials, and especially of methylmercury, are found in marine predators and biota, sediments are of fundamental interest as they provide a tool for assessing the impact of anthropogenic emissions on the environment. However, as in many other analytical problems, the sample-preparation stage has received less attention than the determination stage itself, although it is universally recognised that it determines the reliability of the analytical results. Recent developments in sample preparation have now been applied to the methylmercury problem. In this article a direct comparison is made between manual extraction, supercritical fluid extraction and microwave-assisted extraction. Each technique was used to extract methylmercury from polluted sediments. The efficiencies, merits and disadvantages of each technique are discussed.