Microextraction by packed sorbent coupled with gas chromatography–mass spectrometry: A comparison between “draw-eject” and “extract-discard” methods under equilibrium conditions for the determination of polycyclic aromatic hydrocarbons in water (original) (raw)
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Journal of Chromatography A, 2012
In this work, partition equilibriums and extraction rates of different polycyclic aromatic hydrocarbons (PAHs) have been calculated by multivariate nonlinear regression from data obtained after microextraction by packed sorbent (MEPS) of 16 PAHs from water samples. The MEPS gas chromatography-mass spectrometry (MEPS-GC-MS) method has been optimized investigating the partitioning parameters for a priori prediction of solute sorption equilibrium, recoveries, pre-concentration effects in aqueous and solvent systems. Finally, real samples from sea, agricultural irrigation wells, streams and tap water were analyzed. Detection (S/N ≥ 3) and quantification (S/N ≥ 10) limits were strictly dependent on the volume of water and methanol used during the extraction process. Under the experimental conditions used, these values range from 0.5 to 2 ng L −1 and from 1.6 to 6.2 ng L −1 , respectively. The reasonably good correlation between the logarithm of the partition MEPS-water constants (log K meps/water) and the logarithm of the octanol-water partition coefficients (log K ow) (R 2 = 0.807) allows a rough estimation of K ow from the measure of K meps/water .
Journal of Chromatography A, 2012
This study proposes a new optimization approach for the simultaneous determination of polycyclic aromatic hydrocarbons (PAHs) and benzene, toluene, ethylbenzene and xylene isomers (BTEX) from water samples using the solid-phase microextraction technique followed by gas chromatography-mass spectrometry (GC-MS) separation and detection. The objective of the study was to achieve compromise extraction conditions, suitable for all semi-volatile and volatile compounds, under which the amount extracted is maximized for all analytes. This was achieved by careful optimization of the fiber coating, salting-out effect, extraction time and temperature and extraction mode (headspace or direct immersion). With the optimized fiber coating -PDMS/DVB 65 m -the other selected factors were optimized using a response surface methodology through central composite designs. As expected, the optimized results for each class of analytes varied significantly, probably due to the differences in their volatility and the equilibrium constants for the analyte/fiber coating. In order to overcome this issue, a new optimization approach was proposed based on a combination of extraction modes and extraction temperatures in a single extraction procedure. The final optimized procedure was: 48 min of extraction in direct immersion mode with the sample maintained at 80 • C followed by a further 32 min of headspace extraction with the sample temperature kept at 10 • C. The proposed procedure was compared with conventional methods based on the use of a single extraction mode and temperature (80 min of headspace extraction at 60 • C or 80 min of direct immersion extraction at 50 • C). The newly proposed method was shown to be more attractive as it extracted higher amounts of both semi-volatile and volatile compounds in a single extraction procedure compared to the conventional approaches. The optimized method was validated and excellent results were obtained.
Analytica Chimica Acta, 2020
The use of a thick sorbent coating in headspace sorptive extraction (HSSE) increases the amount of analytes extracted at equilibrium as well as the time needed to reach it. In this work we propose HSSE sampling under vacuum conditions to reduce equilibration times. A theoretical model is presented that describes the pressure dependence of the so-called vacuum-assisted HSSE (Vac-HSSE) method, and predicts the reduction in equilibration times when lowering the sampling pressure. We take advantage of the theoretical formulation to reach some general conclusions for HSSE on the relationship between the physical characteristics of the stir bar, uptake rates and equilibration times. The theoretical predictions were experimentally verified using water solutions spiked with naphthalene, acenaphthene and fluo-ranthene as model compounds. The effects of sampling temperature and extraction time under vacuum and regular pressure conditions were thoroughly investigated. The positive combined effect of heating the sample under low sampling pressure pointed that high humidity did not affect the performance of the extraction phase; an effect commonly recorded in headspace solid-phase microextraction. The extraction time profiles built at 25 and 55 C visualized the substantial improvement in extraction ki-netics with Vac-HSSE compared to the regular HSSE method. The results on naphthalene (assumed to evaporate relatively fast from the water sample) provided evidence that at 1 atm gas-sided resistance limited analyte uptake by the stir-bar and that this limitation could be effectively reduced by adopting the vacuum sampling approach. The accelerations of acenaphthene and fluoranthene suggested that gas-phase constraints limited both the evaporation and analyte uptake processes. Independent method optimization of HSSE under each pressure condition yielded a shorter sampling time for Vac-HSSE compared to the regular HSSE procedure (30 min vs. 60 min respectively). The analytical performances of the two optimized methods were evaluated and it was concluded that Vac-HSSE was performing Analytica Chimica Acta 1096 (2020) 100e107 similar (naphthalene and acenaphthene) or better (fluoranthene) than regular HSSE in half the sampling time needed.
Environmental Science and Technology
The chromatographic determination of 15 Polycyclic Aromatic Hydrocarbons (PAHs) in cookies has been improved in order to obtain a fast method with a low limit of detection through the combination of Microwave Assisted Extraction (MAE), oil saponification and solid phase extraction clean-up prior to the injection of purified extracts in a C18 201TP52 (5 µm, 250 mm x 2.1 mm) column. Using acetonitrile:water as mobile phase, with a 50 % to 95% w/w acetonitrile gradient for a fixed flow of 0.250 ml min-1 , 15 PAHs were separated in 45 min. The column temperature was maintained at 15ºC and fluorimetric detection was made at a fixed excitation wavelength of 264 nm and emission measurements at the best wavelength for each analyte, from 352 nm for 11H-benzo[b]fluorene to 500 nm for Indeno[1,2,3cd]pyrene. Recoveries for all 15 PAHs varied between 96 ± 4 and 105 ± 4 %, and the limits of detection ranged from 0.015 ng g-1 for chrysene to 0.7 ng g-1 for phenantrene. Results were compared with those obtained by conventional Soxhlet extraction during 8 hours refluxing with toluene, demonstrating that the methodology proposed is appropriate to quantify PAHs in cookies. Furthermore, the microwave assisted method was faster and used less solvent than the conventional and ultrasound assisted methods. The extraction time has been reduced to 9 min compared to the 8 hours required for Soxhlet extraction and 60 min required for ultrasound assisted treatment, and the solvent consumption has been reduced to 25 ml compared to the 155 ml and 90 ml required using Soxhlet and ultrasound respectively.
Journal of Chromatography A, 2000
A solid-phase microextraction (SPME) procedure has been developed for the determination of 16 US Environmental Protection Agency promulgated polycyclic aromatic hydrocarbons (PAHs). Five kinds of SPME fibers were used and compared in this study. The extracted sample was analyzed by gas chromatography with flame ionization detection or mass spectrometry. Parameters affecting the sorption of analyte into the fibers, including sampling time, thickness of the fiber coating, and the effect of temperature, have been examined. Moreover, the feasibility of headspace SPME with different working temperatures was evaluated. The method was also applied to real samples. The 85-mm polyacrylate (PA) and 100-mm poly(dimethylsiloxane) (PDMS) fibers were shown to have the highest affinities for the selected PAHs. The PA fiber was more suitable than the PDMS fiber for the determination of low-ring PAHs while high sensitivity of high-ring PAHs was observed when a 100-mm PDMS fiber was used. The method showed good linearity between 0.1 and 100 ng / ml with regression coefficients ranging from 0.94 to 0.999. The reproducibility of the measurements between fibers was found to be very good. The precisions of PA and PDMS fibers were from 3 to 24% and from 3 to 14%, respectively. Headspace SPME is a valid alternative for the determination of two-to five-ring PAHs. A working temperature of 608C provides significant 26 enhancement in sensitivity of two-to five-ring PAHs having low vapor pressures (.10 mmHg at 258C) (1 mmHg5133.3 5 Pa) and low Henry's constants (.10 atm ml / mol) (1 atm51.01?10 Pa).
Liquid-phase microextraction of polycyclic aromatic hydrocarbons: A review
Reviews in Analytical Chemistry, 2020
Polycyclic aromatic hydrocarbons (PAHs) are a large group of organic compounds comprised of two or more fused benzene rings, which arise from the incomplete combustion of organic materials. These compounds have been of concern as carcinogens and mutagens for the past 50-60 years. Lately, they are also receiving attention as endocrine-disrupting chemicals. Therefore, proper analytical methods are required for sampling and analyzing these compounds. In response to problems associated with the conventional methods like solid-phase extraction (SPE) and liquid-liquid extraction (LLE), many studies have focused on the miniaturization of different sample preparation techniques. In this regard, the use of different types of liquid phase microextraction (LPME) techniques has increased significantly during the recent few decades. LPME techniques are advantageous because they use single-step sample preparation and have shown a greater sensitivity, selectivity, and efficiency than the conventio...
Chromatographia, 2006
Benzene, toluene, ethylbenzene and o-, m-, and p-xylenes (BTEX), were extracted from aqueous samples by capillary extraction (CEx), a manual form of in-tube microextraction inherently compatible with capillary GC, and analyzed by HRGC analysis in order to quantify the post-extraction losses of these volatile organic compounds. Accuracy of the VOC determination by CEx-HRGC is dependent on these losses. The used active extraction devices were fused silica open-tubular capillaries of 0.25 mm i.d., with lengths in the range of 3-15 cm, coated with a 0.25 lm film of PTE-5 (5% phenyl methylpolysiloxane) stationary phase. The losses decreased remarkably when the extractor lengths were increased. In particular, the losses were modest or negligible for capillary extractors of usual length, though the losses increased with rising solute volatility and 'lag time' (the length of time required to connect in-line the laden capillary extractors with the HRGC column). BTEX losses between 2% (benzene) and 0.5% (o-xylene) resulted from CEx conducted under very usual conditions, independently from sample concentration. The short-term precision of the CE-HRGC experiments, expressed as relative standard deviation, was 0.8-4.9% (n = 5).
Microchemical Journal, 2020
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