Microwave-assisted extraction of OCPs, PCBs and PAHs concentrated by semi-permeable membrane devices (SPMDs)

Microwave-assisted extraction (MAE) has been evaluated as an alternative to dialysis for extraction of some water-borne hydrophobic contaminants sampled by semi-permeable membrane devices (SPMDs). Seven organochlorine pesticides (OCPs), 11 polychlorinated biphenyls (PCBs) and 13 polycyclic aromatic hydrocarbons (PAHs) were accumulated in SPMDs at nanogram levels and extracted with three 3-min irradiation cycles with 33 mL of a solvent mixture hexane–water (10:1,v/v) in each cycle. The developed MAE method gave for all analytes investigated statistically comparable extraction yields with those found by dialysis carried out with a total volume of 250 mL hexane for 48 h at room temperature. The recoveries of all the targeted contaminants were in the range of 65–105% with variation coefficients not exceeding 19%. The applicability of the MAE extraction was tested in field SPMDs samples deployed for 15 days in a sewage-treatment process. Our results show that MAE provides a remarkable reduction of time and solvent volume when used as an extraction method in the analysis of SPMDs.     

New perspectives in the use of semipermeable membrane devices as passive samplers

This review shows the state of the art, from 2000 to nowadays, of the use of semipermeable membrane devices (SPMDs) for monitoring persistent organic pollutants in both, air and aquatic environments. Since their first use in 1990, SPMDs have been employed for many environmental purposes, like air and water pollution monitoring. We have focussed the study in three subjects: (i) novel compounds accumulated by SPMDs, (ii) modifications of SPMDs to improve their specific uptake properties and (iii) alternatives in sample pre-treatment for the determination of pollutants accumulated in SPMDs.     

Determination of volatile organic compounds in contaminated air using semipermeable membrane devices

Semipermeable membrane devices (SPMDs) were evaluated as passive samplers for the determination of 26 volatile organic compounds (VOCs) in contaminated air of occupational environments. A direct methodology based on the use of head-space-gas chromatography-mass spectrometry (HS-GC-MS) was developed for VOCs determinations in SPMDs, without any sample pre-treatment and avoiding the use of solvents. A desorption temperature of 150 °C for 10 min was sufficient for a sensitive VOCs determination providing limits of detection in the range of 15 ng SPMD⁻¹ for 21 of 26 studied compounds. Linear and equilibrium uptake models were established for each VOC from compound isotherms. Highly volatile compounds were slightly absorbed and moderately volatile compounds were strongly absorbed by SPMDs. This study is the first precedent of the use of SPMDs for the simultaneous sampling of a wide number of VOCs. The use of SPMDs is a simple and low cost alternative to ordinary sampling devices such as Radiello^® diffusive samplers or badge-type solid-phase supports.     

Microwave-assisted extraction of pyrethroid insecticides from semi permeable membrane devices (SPMDs) used to indoor air monitoring

A rapid and environmentally friendly methodology was developed for the extraction of pyrethroid insecticides from semi permeable membrane devices (SPMDs), in which they were preconcentrated in gas phase. The method was based on gas chromatography mass–mass spectrometry determination after a microwave-assisted extraction, in front of the widely employed dialysis method. SPMDs were extracted twice with 30 mL hexane:acetone, irradiated with 250 W power output, until 90 °C in 10 min, this temperature being held for another 10 min. Clean-up of the extracts was performed by acetonitrile–hexane partitioning and solid-phase extraction (SPE) with a combined cartridge of 2 g basic-alumina, deactivated with 5% water, and 500 mg C₁₈.

Pyrethroids investigated were Allethrin, Prallethrin, Tetramethrin, Bifenthrin, Phenothrin, λ-Cyhalothrin, Permethrin, Cyfluthrin, Cypermethrin, Flucythrinate, Esfenvalerate, Fluvalinate and Deltamethrin. The main pyrethroid synergist compound, Pyperonyl Butoxide, was also studied. Limit of detection values ranging from 0.3 to 0.9 ng/SPMD and repeatability data, as relative standard deviation, from 2.9 to 9.4%, were achieved. Pyrethroid recoveries, for spiked SPMDs, with 100 ng of each one of the pyrethroids evaluated, were from 61 ± 8 to 103 ± 7% for microwave-assisted extraction, versus 54 ± 4 to 104 ± 3% for dialysis reference method. Substantial reduction of solvent consumed (from 400 to 60 mL) and analysis time (from 48 to 1 h) was achieved by using the developed procedure.

High concentration levels of pyrethroid compounds, from 0.14 to 7.3 μg/SPMD, were found in indoor air after 2 h of a standard application.     

Microwave-assisted extraction of polybrominated diphenyl ethers and polychlorinated naphthalenes concentrated on semipermeable membrane devices

Microwave-assisted extraction (MAE) has been evaluated as an alternative to dialysis for the extraction of polybrominated diphenyl ethers (PBDEs) and polychlorinated naphthalenes (PCNs) sampled by semipermeable membrane devices (SPMDs), using gas chromatography coupled to tandem mass spectrometry (GC-MS-MS).For MAE optimization a two level full factorial design 2³, plus a centre point, which involves 11 randomized runs was used. The results showed that the temperature had a significant influence on the extraction of the nine PBDEs and four PCNs tested. Also, the solvent volume had a positive influence on the extraction of PBDEs and PCNs, but only in latter compounds, it achieves statistical significance. The time had only statistical significance for the most volatile specie studied, PCN-54. The selected MAE conditions (60 mL of hexane-acetone, 1:1 (v/v), 85 °C, 1 min, two cycles) lead to recoveries between 72 and 91% for PBDEs and between 96 and 103% for PCNs. The applicability of the MAE extraction was tested in field SPMDs deployed for 20 days in a sewage treatment plant.The MAE method developed is about 300 times faster than the conventional dialysis and remarkably reduces the solvent consumption.     

Evaluation of working air quality by using semipermeable membrane devices. Analysis of organophosphorus pesticides

It has been evaluated the use of semipermeable membrane devices (SPMDs) as passive samplers of organophosphorus pesticides from air, in order to determine the contamination of working environments. Additionally, the use of SPMDs as portable samplers has been also considered. The analytical methodology for the determination of diazinon, chlorpyrifos-methyl, pirimiphos-methyl, chlorpyrifos and fenthion in SPMDs exposed to contaminated air was based on microwave-assisted extraction and gas chromatography with mass spectrometry determination. Limit of detection (LOD) values from 2 to 4 ng SPMD⁻¹ and repeatability from 2 to 7% were obtained by using the aforementioned methodology. Theoretical calculated sampling rates were employed for the estimation of the pesticide concentration in air, by using the pesticide mass retained in the deployed SPMD. The obtained LOD values, for a sampling time of 7 days, were from 1 to 2 ng m⁻³. The evaluation of the air quality of a pesticide laboratory with an intensive use of diazinon and chlorpyrifos has been made in order to check the operation safety conditions.     

A coaxially heated membrane introduction mass spectrometry interface for the rapid and sensitive on-line measurement of volatile and semi-volatile organic contaminants in air and water at parts-per-trillion levels

A coaxially heated membrane introduction mass spectrometry (MIMS) sampling interface is presented that demonstrates improved on-line performance for the direct measurement of semi-volatile organic compounds (SVOCs) in air and water samples at parts-per-trillion levels. The device is based on a polydimethylsiloxane (PDMS) capillary hollow fibre membrane (HFM) in a pneumatically assisted "flow-over" configuration that is resistively heated on the membrane interior via a coaxial nichrome wire, establishing a thermal gradient counter to the analyte concentration gradient. This arrangement allows for continuous and/or pulsed heating modes, affording excellent sensitivity for the on-line measurement of SVOCs while retaining sensitivity for volatile organic compounds (VOCs). In addition, the signal response time for SVOCs is reduced substantially over conventional "flow-over" MIMS interfaces. Separation and quantitation of analytes are achieved using quadrupole ion trap tandem mass spectrometry.     

Headspace-solid-phase microextraction preconcentration of phenols, indoles and on-fibre derivatised volatile fatty acids in liquid and gas samples from cow slurries

Odorous organic compounds from liquid and gas samples of animal wastes were studied by headspace (HS)-solid-phase microextraction (SPME)-GC-MS. 1-Pirenyldiazomethane (PDAM) was adsorbed/absorbed on the SPME fibre in order to obtain the corresponding ester derivatives during the preconcentration step. The SPME fibre was immersed into a PDAM solution. Then, the SPME fibre was withdrawn and exposed to the HS of the liquid cow slurry. This way derivatisation of VFAs took place in the SPME fibre together with the preconcentration of the rest of the analytes of interest. The analytes were desorbed in the hot injection port (300 degrees C) of a GC-MS for 3 min. Four different fibre types and different immersion periods of the fibre in the PDAM solution were studied in order to obtain the best sensitivity with the selected fibre. Accuracy, precision and the LODs were calculated using spiked liquid and gas samples. The possibility of storing liquid samples after sampling by preconcentration on the fibre was also considered. Storage time and temperature were studied. The optimised method was applied to the determination of the analytes in liquid and gas samples from cow slurries from an intensive production farm.     

Development of an adapted version of polar organic chemical integrative samplers (POCIS-Nylon)

POCIS (polar organic chemical integrative samplers) are increasingly used for sampling polar compounds. Although very efficient for a wide range of pollutants, the classic configuration of the device has a number of limitations, in particular for the sampling of highly polar analytes and hydrophobic compounds. This study presents a new version of the POCIS passive sampler which uses a highly porous Nylon membrane of 30 μm pore size, enabling the sampling of hydrophobic pollutants and improving the accumulation rate of other pollutants. This newly designed tool and the classic POCIS were both tested during a laboratory experiment to evaluate the accumulation kinetics of a selection of pesticides and pharmaceuticals. The observed results show unexpected accumulation kinetics for the new version of POCIS. To explain the data, the use of an intraparticulate diffusion model was required, which also enabled us to propose another explanation of the burst effect observed with the classic POCIS, primarily related to the potential wetting of the device as the first step in the accumulation of compounds.

Considerations involved with the use of semipermeable membrane devices for monitoring environmental contaminants

Semipermeable membrane devices (SPMDs) are used with increasing frequency, and throughout the world as samplers of organic contaminants. The devices can be used to detect a variety of lipophilic chemicals in water, sediment/soil, and air. SPMDs are designed to sample nonpolar, hydrophobic chemicals. The maximum concentration factor achievable for a particular chemical is proportional to its octanol-water partition coefficient. Techniques used for cleanup of SPMD extracts for targeted analytes and for general screening by full-scan mass spectrometry do not differ greatly from techniques used for extracts of other matrices. However, SPMD extracts contain potential interferences that are specific to the membrane-lipid matrix. Procedures have been developed or modified to alleviate these potential interferences. The SPMD approach has been demonstrated to be applicable to sequestering and analyzing a wide array of environmental contaminants including organochlorine pesticides, polychlorinated biphenyls, polycyclic aromatic hydrocarbons, polychlorinated dioxins and dibenzofurans, selected organophosphate pesticides and pyrethroid insecticides, and other nonpolar organic chemicals. We present herein an overview of effective procedural steps for analyzing exposed SPMDs for trace to ultra-trace levels of contaminants sequestered from environmental matrices.     

Time-weighted average sampling of volatile and semi-volatile airborne organic compounds by the solid-phase microextraction device

The ultimate goal of the chemist is to perform sample preparation, and analysis, if possible at the place where a sample is located rather than moving the sample to laboratory, as is common practice in many cases at the present time. This approach eliminates errors and time associated with sample transport and storage and therefore it would result in more accurate, precise and faster analytical data. In addition to portability, two other important features of ideal field sample preparation technique are elimination of solvent use and integration with a sampling step. A method is developed which addresses these requirements for the determination of time-weighted average concentration of gas phase compounds using a solid-phase microextraction device. Quantification of target analytes in air using this method can be carried out without external calibration. The volatile and semi-volatile organic compounds in air diffuse into the fiber coating which is retracted a known distance into its needle housing during the sampling period. The coatings used are poly(dimethylsiloxane) and poly(dimethylsiloxane)-divinylbenzene. The sampling rate at which gas phase analytes load onto the fiber is determined for a wide range of hydrocarbons. There is a good agreement between the theoretical and experimental sampling rates. Sampling time ranges from 1 min to 24 h depending on the coating used and its retraction distance. Effect of the flow-rate on the uptake rate by the fiber is studied. The method is tested in the field and compared with National Institute of Occupational Health and Safety Method 1550. Good agreement between the results is obtained.     

Ultrasound-assisted extraction and silylation prior to gas chromatography-mass spectrometry for the characterization of the triterpenic fraction in olive leaves

One of the most important fractions of bioactive compounds isolated from plants is that formed by triterpenic compounds, which have proved to be anti-bacterial, antifungal, anti-inflammatory, cytotoxic and anti-tumour. A method for leaching and determination of the main triterpenic compounds (oleanolic acid, ursolic acid, uvaol, erythrodiol) in olive leaves is here presented. Quantitative leaching was obtained with ethanol as leachant and ultrasonic assistance for 20 min, a very short time as compared to conventional procedures by maceration, which usually requires at least 5 h. After isolation, an aliquot of the ethanolic leachate was silylated to derivatize the analytes prior to gas chromatography-mass spectrometry analysis. Silylation reaction was also assisted with ultrasound in order to accelerate the derivatization step, which only required 5 min--a dramatic shortening in comparison to conventional silylation of terpenic compounds with derivatization times ranging from 30 min to 3 h. The proposed method has demonstrated to be useful for isolation and characterization of the triterpenic fraction in plants; the capability of ultrasound to assist sample preparation (acceleration of leaching and derivatization) has also been proved.     

A chemical potential driven micro-membrane sampler and its application for the determination of trace carbonyl compounds in air

A chemical potential driven micro-membrane sampler for enrichment of trace gaseous carbonyl compounds has been developed. The sampler is composed of exposed parts with membrane and analysis parts with polypropylene tube. The membrane acts as a barrier, through which the analytes dynamically diffuse and transfer from absorbents present outside to extract solvent inside through the difference of chemical potential. Formaldehyde and acetic acid were selected as verification samples. Quantification is achieved through high performance liquid chromatography (HPLC) analysis. The mass of analytes determined shows a linear correlation with concentration of the gaseous analytes. The limits of detection of formaldehyde and acetic acid after 8 h sampling were 3.32 and 0.76 μg m⁻³.     

Rapid and sensitive determination of pyrethroids indoors using active sampling followed by ultrasound-assisted solvent extraction and gas chromatography

A fast and simple method to analyze pyrethroids as well as other components of frequently used domestic insecticide preparations in indoor air is presented. The proposed method, based on sampling with an adsorbent followed by ultrasound-assisted solvent extraction, was developed with the aim to simplify the traditional extraction methodologies applied up to date to determine pesticides in air. The analytes were retained on a very small amount of adsorbent, which allowed using solely 1 mL of solvent for desorption. The quantification was performed by gas chromatography with microelectron-capture detection (GC-muECD) and gas chromatography coupled to mass spectrometry (GC-MS). The influence of main factors involved in the ultrasound-assisted solvent extraction step (type of adsorbent and type of solvent, solvent volume and extraction time) was studied using an experimental design approach to account for possible factor interactions. The sampling step was studied for two adsorbents (Tenax TA and Florisil), finding that 1 m(3) air could be sampled without losses of analytes. In this way, the analysis of pyrethroids in air by the proposed method could be carried out within a total time shorter than an hour, including sampling. Linearity was demonstrated in a wide concentration range. Efficiency of the total sampling-extraction process was studied at several concentration levels (2, 10, 100 and 1000 ng/m(3)), obtaining quantitative recoveries for all compounds, with good precision (RSD < 10%). Method detection limits were below 1 ng/m(3) in air when GC-muECD was employed, and about one order of magnitude higher for GC-MS. In addition, the proposed method was applied to real samples collected in contaminated closed rooms, in which some of the target compounds were determined.     

Determination of aromatic compounds in eluates of pyrolysis solid residues using HS-GC-MS and DLLME-GC-MS

A method for the determination of 15 aromatic hydrocarbons in eluates from solid residues produced during the co-pyrolysis of plastics and pine biomass was developed. In a first step, several sampling techniques (headspace solid phase microextraction (HS-SPME), static headspace sampling (HS), and dispersive liquid-liquid microextraction (DLLME) were compared in order to evaluate their sensitivity towards these analytes. HS-SPME and HS sampling had the better performance, but DLLME was itself as a technique able to extract volatiles with a significant enrichment factor.HS sampling coupled with GC-MS was chosen for method validation for the analytes tested. Calibration curves were constructed for each analyte with correlation coefficients higher than 0.999. The limits of detection were in the range of 0.66-37.85 ng/L. The precision of the HS method was evaluated and good repeatability was achieved with relative standard deviations of 4.8-13.2%. The recoveries of the analytes were evaluated by analysing fortified real eluate samples and were in the range of 60.6-113.9%.The validated method was applied in real eluate samples. Benzene, toluene, ethylbenzene and xylenes (BTEX) were the compounds in higher concentrations.The DLLME technique coupled with GC-MS was used to investigate the presence of less volatile contaminants in eluate samples. This analysis revealed the presence of significant amounts of alkyl phenols and other aromatic compounds with appreciable water solubility.     

Separation and preconcentration phenomena in internally heated poly(dimethylsilicone) capillaries: preliminary modelling and demonstration studies

The concept of achieving low-resolution separations in internally heated capillary membranes is discussed in terms of controlling the diffusion coefficients of volatile organic compounds in poly(dimethylsilicone) membranes in space and time. The behaviour of 1,1,1-trichloroethane in polydimethylsilicone was used in conjunction with a mixed-physics finite element model, incorporating second order partial differential equations, to describe time and spatial variations of mass-flux, membrane temperature and diffusion coefficients. The model, coded with Femlab, predicted highly non-linear diffusion coefficient profiles resulting from temperature programming a 500 [micro sign]m thick membrane, with an increase in the diffusion coefficient of approximately 30% in the last 30% of the membrane thickness. Simulations of sampling hypothetical analytes, with disparate temperature dependent diffusion coefficient relationships, predicted distinct thermal desorption profiles with selectivities that reflected the extent of diffusion through the membrane. The predicted desorption profiles of these analytes also indicated that low resolution separations were possible. An internally heated poly(dimethylsilicone) capillary membrane was constructed from a 10 cm long, 1.5 mm od capillary with 0.5 mm thick walls. Thirteen aqueous standards of volatile organic compounds of environmental significance were studied, and low-resolution separations were indicated, with temperature programming of the membrane enabling desorption profiles to be differentiated. Further, analytically useful relationships in the [micro sign]g cm(-3) concentration range were demonstrated with correlation coefficients >0.96 observed for linear regressions of desorption profile intensities to analyte concentrations.     

Determination of aflatoxin M1 using a dialysis-based immunoaffinity sample pretreatment system coupled on-line to liquid chromatography. Reusable immunoaffinity columns.

A liquid chromatographic column-switching system containing a dialysis unit and an anti-aflatoxin immunoaffinity precolumn (immuno precolumn) is described for the automated determination of aflatoxin M1 in milk samples. Both a flat membrane dialysis unit working according to the flowing donor-flowing acceptor principle and a laboratory made hollow-fibre dialysis unit working according to the stagnant donor-flowing acceptor principle were evaluated. The hollow-fibre unit is superior with respect to repeatability (3% relative standard deviation) and detection limit (10 ng/l for aflatoxin M1 in milk), in spite of the fact that the overall recovery is only 6%. Interfering compounds, which would destroy the activity of the immuno precolumn, are efficiently removed from the system by the dialysis step; a single immuno precolumn can then be used for over 70 milk analyses. No decrease in the performance of either the immuno precolumn or the hollow-fibre dialysis unit is observed.     

Vacuum-assisted headspace solid phase microextraction of polycyclic aromatic hydrocarbons in solid samples

For the first time, Vacuum Assisted Headspace Solid Phase Microextraction (Vac-HSSPME) is used for the recovery of polycyclic aromatic hydrocarbons (PAHs) from solid matrices. The procedure was investigated both theoretically and experimentally. According to the theory, reducing the total pressure increases the vapor flux of chemicals at the soil surface, and hence improves HSSPME extraction kinetics. Vac-HSSPME sampling could be further enhanced by adding water as a modifier and creating a slurry mixture. For these soil-water mixtures, reduced pressure conditions may increase the volatilization rates of compounds with a low K_H present in the aqueous phase of the slurry mixture and result in a faster HSSPME extraction process. Nevertheless, analyte desorption from soil to water may become a rate-limiting step when significant depletion of the aqueous analyte concentration takes place during Vac-HSSPME. Sand samples spiked with PAHs were used as simple solid matrices and the effect of different experimental parameters was investigated (extraction temperature, modifiers and extraction time). Vac-HSSPME sampling of dry spiked sand samples provided the first experimental evidence of the positive combined effect of reduced pressure and temperature on HSSPME. Although adding 2 mL of water as a modifier improved Vac-HSSPME, humidity decreased the amount of naphthalene extracted at equilibrium as well as impaired extraction of all analytes at elevated sampling temperatures. Within short HSSPME sampling times and under mild sampling temperatures, Vac-HSSPME yielded linear calibration curves in the range of 1–400 ng g⁻¹ and, with the exception of fluorene, regression coefficients were found higher than 0.99. The limits of detection for spiked sand samples ranged from 0.003 to 0.233 ng g⁻¹ and repeatability from 4.3 to 10 %. Finally, the amount of PAHs extracted from spiked soil samples was smaller compared to spiked sand samples, confirming that soil could bind target analytes more strongly and thus decrease the readily available fraction of target analytes.     

Investigation of membrane dryers and evaluation of a new ozone scrubbing material for the sampling of organosulphur compounds in air.

The applicability of two different types of Nafion membrane dryers (based on counter-current flow and desiccant drying) and of a new ozone scrubbing material, polyphenylene sulphide wool (noXon-S), to adsorptive sampling of selected volatile sulphur compounds (methanethiol, dimethyl sulphide, isopropanethiol and isobutanethiol) is investigated at the low ppb (v/v) level (1-5 ppb). No analyte losses occur with either type of dryer at relative humidities (RH) of < or = 50%, while at higher RH values particularly the thiols tend to be lost (between 6 and 32%) even after conditioning. The actual losses depend more on the state of the individual permeation membrane rather than on the type of dryer. NoXon-S is a highly suitable ozone scrubber material for sulphur compounds since it efficiently removes ozone without retainment of the analytes and without the formation of blanks or artefacts from the scrubber material. The combined use of a Nafion membrane dryer and a noXon-S ozone scrubber is thus recommended for artifact-free sampling of sulphur compounds.     

Diffusion and calibration properties of microdialysis sampling membranes in biological media

The diffusion and calibration properties for three commercially available microdialysis membranes (polycarbonate-polyether (PC), polyacrylonitrile (PAN), and cuprophan (CUP)) were evaluated. The analytes studied had molecular weights between 94 (phenol) and 1355 (vitamin B12). For each analyte-membrane pair, an effective membrane diffusion coefficient was calculated. Effective membrane diffusion coefficients varied considerably between the microdialysis membranes. For Vitamin B12, CUP and PAN membranes gave relative recovery values of greater than 20% at 0.5 microl min(-1), while the PC membrane had a 1% recovery. When backpressure was applied. PC and PAN membranes exhibited more ultrafiltration than CUP membranes. Ultrafiltration did not affect analyte relative recovery through either PC or PAN membranes. Effective membrane diffusion coefficients were not significantly altered for some membrane-analyte combinations when exposed to 4% bovine serum albumin or 0.3% fibrinogen. These data suggest that reductions in relative recovery during long-term microdialysis sampling experiments may be due to other physiologically relevant proteins or to tissue reactions near the dialysis membrane.