Papers by Elefteria Psillakis
Analytical and Bioanalytical Chemistry, 2020
The effect of vacuum is an emerging experimental parameter to consider during optimization of a v... more The effect of vacuum is an emerging experimental parameter to consider during optimization of a variety of headspace microextraction methodologies. The positive effect of vacuum was initially demonstrated for headspace solid-phase microextraction and was recently expanded to single-drop microextraction and higher capacity sorbents i.e. stir bar sorptive extraction. In all cases, sampling under vacuum greatly accelerated the extraction kinetics of analytes exhibiting long equilibra-tion times under atmospheric pressure. At the same time, the extraction of analytes that reached equilibrium fast was not affected. In all optimized methods, extraction times were greatly reduced and/or sampling temperatures were lower to those reported with the standard methodology under atmospheric pressure. This work succinctly overviews the effect of vacuum on the different headspace microextraction technologies reported so far. The fundamental concepts describing the pressure dependence of each methodology are pulled together and presented in a simplified manner. The latest findings on the combined effects of vacuum and several selected experimental parameters typically examined during method optimization are then presented and the practical aspects of past outcomes are highlighted. The discussion also includes the air-evacuation step and the analysis of complex matrices. This article is intended for readers who are either new to the field of vacuum headspace microextraction sampling or its use and want to exploit this powerful approach.
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Analytica Chimica Acta, 2019
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Science of the Total Environment, 2020
• Total metal concentrations in heated tobacco sticks are lower than that in unused cigarettes. •... more • Total metal concentrations in heated tobacco sticks are lower than that in unused cigarettes. • The ash produced from conventional cigarettes retains a substantial amount of metals. • Leaching of almost all metals from all types of tobacco products occurs. • Tobacco is the major source of metal contamination. • Varying the solution characteristics at environmentally relevant values did not affect metal leaching. The leaching behavior of Al, Cr, Ni, Cu, Zn, As, Se, Cd, Ba, Hg and Pb in water from two types of heat-not-burn tobacco sticks is presented here, and compared to that from conventional cigarettes. The total concentration of each metal in solid tobacco products was initially determined. Concentrations in used and unused tobacco sticks were similar and generally, lower than those in unused conventional cigarettes. Studies on the contribution of paper, filter and tobacco revealed that tobacco was the major source of metal contamination. Smoking conventional cigarettes reduced the total metal concentrations since a substantial amount of metals was retained in the ash; a post-consumption waste that is difficult to collect. Batch leaching tests were performed to determine dissolved concentrations as a function of time. With the exceptions of As and (in most cases) Hg that were not detected, metals were released at varying rates. At 24 h of soaking the percentage of metals leached ranged from 0.2-43%. The contribution of paper, filter and tobacco to the dissolved concentrations at 24 h of leaching was investigated and in almost all cases tobacco was the major source of metal contamination. The dissolved concentrations from ash were low as metals were strongly bound. Varying the pH, ionic strength and humic acids content at environmentally relevant values did not affect leaching of metals at 24 h of soaking. The use of river water, rain water and seawater as leachants was also not found to alter dissolved concentrations at 24 h compared to ultrapure water. The results presented here suggest that the consequences of improper disposal of tobacco products in the environment are two-sided and that next to the generation of plastic litter, discarded tobacco products can also act as point sources of metal contamination. Public education campaigns focusing on the environmental impact and best disposal practices are urgently needed.
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Analytica Chimica Acta, 2020
The use of a thick sorbent coating in headspace sorptive extraction (HSSE) increases the amount o... more 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.
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Analytica Chimica Acta, 2020
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Journal of Chromatography A, 2019
Headspace solid-phase microextraction (HSSPME) is a widespread technique used to extract trace am... more Headspace solid-phase microextraction (HSSPME) is a widespread technique used to extract trace amounts of haloanisoles from wine samples. A major challenge to overcome is the high ethanol content in wines that affects the solubilities of haloanisoles and reduces their headspace abundance. To overcome this obstacle and meet sensitivity requirements, reported HSSPME procedures typically suggest heating the wine samples and/or sampling for extended times. The present work proposes the use of vacuum-assisted HSSPME (Vac-HSSPME) to accelerate the extraction kinetics whilst sampling at room temperature. Although ethanol affected the physico-chemical properties of the target analytes, these changes were not sufficient to prevent the positive effect of vacuum on HSSPME sampling. To demonstrate the benefits of adopting the vacuum approach, Vac-HSSPME and regular HSSPME methods were independently optimized and the results were compared at all times. The effect of ethanol under each pressure condition was also discussed. Under the optimum conditions found, Vac-HSSPME sampling for 30 min at room temperature at 25 • C yielded lower detection limits (0.13 to 0.19 ng L −1) than those obtained with regular HSSPME sampling for 30 min at 55 • C (0.26 to 0.76 ng L −1). The proposed Vac-HSSPME method was successfully applied to quantify haloanisoles in bottled red wines and a discussion on the effect of wine volatiles was included. The standard addition method was used to minimize matrix effects. The increase in total pressure due to the presence of ethanol and other volatile wine components did not reduce the positive effect of vacuum on HSSPME. Nonetheless, in accordance to past HSSPME methods, the limits of detection and quantification were affected due to the noise level increase and analyte interaction with matrix. The proposed Vac-HSSPME procedure was applied to twelve bottled red wines and one sample was found positive on 2,4,6-trichloronanisole.
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Environmental Research, 2019
In this work, we investigate the photolysis behavior of 2,3-dibromo-5,6-dimethyl-1,4-benzoquinone... more In this work, we investigate the photolysis behavior of 2,3-dibromo-5,6-dimethyl-1,4-benzoquinone (DDBQ), the only dibrominated benzoquinone detected in treated water so far. DDBQ solutions prepared in ultra-pure water were exposed to UV radiation centered at 254 nm (UV 254), and the photolysis of the parent compound was monitored together with by-product formation. The DDBQ pseudo-first order photolysis rate constants decreased when increasing the initial DDBQ concentration, and this behavior was caused by saturation of absorption. The photodegradation kinetics was found not to depend on pH and 1-butanol addition, but was affected by humic acids and components that occur in both natural waters and treated wastewater. For the first time with this class of compounds, photolysis studies were also performed using natural and treated wastewater matrices, where photodegradation was always found to proceed significantly slower than in ultra-pure water. The implications for the radiation dose that is required to reach a given treatment target are discussed, and a numerical approach by which to foresee the extent of degradation inhibition is provided that should be taken into account when planning the UV 254 treatment of DDBQ. The phototransformation of DDBQ yielded hydroxyderivatives, most likely via a debromination-hydroxylation pathway. In-silico toxicity screening suggested that the transformation of DDBQ into the detected hydroxyderivatives would not eliminate toxicity. Although the monohydroxylated derivative underwent relatively fast transformation, the dihydroxylated compound was found to accumulate during irradiation. As a compromise, the irradiation conditions that produce over 90% degradation of DDBQ in the studied samples, and at the same time keep by-product formation low are discussed.
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Trends in Analytical Chemistry, 2019
In 2010, we proposed vortex-assisted liquid-liquid microextraction (VALLME) that used vortex agit... more In 2010, we proposed vortex-assisted liquid-liquid microextraction (VALLME) that used vortex agitation to disperse microliters of a water-immiscible solvent into an aqueous sample. After extraction, the two phases were separated by centrifugation and the extracting solvent was collected and used for analysis. The seemingly easy steps of VALLME involve complex and poorly understood processes that require consideration of solvent drop breakup and coalescence plus the problem of interphase analyte mass transfer. The overall aim of this review is to transfer knowledge from other disciplines and improve current understanding of VALLME. Initially, the fundamental hydrodynamic and interfacial science concepts of emulsion formation and phase separation applying to VALLME are presented. Building on this knowledge, the effects of several experimental parameters on VALLME are discussed. Advancing the current (and limited) knowledge on the fundamentals behind VALLME is critical to allow cognitive control and full exploitation of the method.
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Marine Pollution Bulletin, 2018
Plastic pollution in the marine environment is one of the foremost environmental problems of our ... more Plastic pollution in the marine environment is one of the foremost environmental problems of our time, as it affects wildlife and human health both directly and indirectly through the effects of contaminants carried by microplastics. This study investigates the temporal and spatial distribution of plastic pellets and fragments in sandy beaches along the coastline of Northern Crete, during 2013. Their densities varied throughout the year in each beach, with highest densities during the summer and towards the upper parts of the beaches. The concentrations
of 16 polycyclic aromatic hydrocarbons (PAHs) sorbed on microplastics sampled from nine sandy beaches of Northern Crete was quantified using Gas chromatography – Ion Trap Mass Spectrometry (GC-ITMS).
PAHs concentrations ranged from non-detectable levels to 1592 ng/g and fluctuated between sampling periods. Based on the observed patterns of meso- and microplastics distribution, practical guidelines are proposed to minimize the entrance of microplastics into the seawater wherefrom they are exceptionally difficult to collect, if mitigation actions are to be applied.
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This article appeared in a journal published by Elsevier. The attached copy is furnished to the a... more This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/copyright a b s t r a c t Nonequilibrium headspace solid-phase microextraction (HSSPME) sampling under vacuum conditions may dramatically improve extraction kinetics compared to regular HSSPME at room temperature. This paper investigates the effects of organic analyte properties and sampling parameters (headspace volume and sample agitation) on vacuum-assisted HSSPME (Vac-HSSPME). It was found that at room temperature , acceleration effects on extraction rates induced by reducing the total pressure of the sample container are important for those compounds where the Henry's law constant, K H , is close or below the reported threshold values for low K H solutes. For these compounds evaporation rate is controlled by mass transfer resistance in the thin gas-film adjacent to the gas/sample interface and reducing the total pressure will increase evaporation rates and result in a faster overall extraction process. Conversely, for analytes with an intermediate K H value, Vac-HSSPME is not expected to improve extraction rates compared to regular HSSPME given that mass transfer resistance in the liquid-film becomes important. In accordance with the theory, at equilibrium, the amount of analyte extracted by the SPME fiber is not affected by the pressure conditions inside the sample container. Furthermore, Vac-HSSPME extraction kinetics for low K H analytes were marginally affected by the tested change in headspace volume as evaporation rates dramatically increase under reduced pressure conditions and the sample responds much faster to the concentration drops in the headspace when compared to regular HSSPME. At equilibrium however, increasing the headspace volume may result in a loss of sensitivity for Vac-HSSPME similar to that observed for regular HSSPME. As expected, stirring the liquid sample was found to improve Vac-HSSPME. Finally, the method yielded a linearity of 0.998 and detection limits in the ppt level. The precision varied between 1.8% and 8.4%.
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Recently, we proposed a new headspace solid-phase microextraction (HSSPME) procedure, termed vacu... more Recently, we proposed a new headspace solid-phase microextraction (HSSPME) procedure, termed vacuum-assisted HSSPME (Vac-HSSPME), where headspace sampling of 10 mL aqueous sample volumes took place in 500 or 1000 mL sample containers under vacuum conditions. In the present study, we down-sized the extraction device to a 22 mL modified sample vial and concluded that changes in the final total pressure of the pre-evacuated vial following sample introduction were sufficiently low to allow efficient Vac-HSSPME sampling. The downsized extraction device was used to extract five low molecular weight polycyclic aromatic hydrocarbons and several experimental parameters were controlled and optimized. For those compounds whose mass transfer resistance in the thin gas-film adjacent to the gas/sample interface controls evaporation rates, reducing the total pressure during HSSPME sampling dramatically enhanced extraction kinetics in the 22 mL modified vial. Humidity was found to affect the amount of naphthalene (intermediate K H compound) extracted by the fiber at equilibrium as well as impair extraction of all analytes at elevated sampling temperatures. All the same, the high extraction efficiency and very good sensitivity achieved at room temperature and within short sampling times comprised the most important features of Vac-HSSPME in this downsized extraction device. Analytically, the developed method was found to yield linear calibration curves with limits of detection in the low ng L −1 level and relative standard deviations ranging between 1.3 and 5.8%. Matrix was found not to affect extraction.
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Analytica Chimica Acta, 2012
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This article appeared in a journal published by Elsevier. The attached copy is furnished to the a... more This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/authorsrights
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The sonochemical degradation of 5 μg l-1triclosan, a priority micro-pollutant, in various environ... more The sonochemical degradation of 5 μg l-1triclosan, a priority micro-pollutant, in various environmental samples (seawater, urbanrunoff and influent domestic wastewater) as well as in model solutions (pure and saline water) was investigated. Experiments were con-ducted with a horn-type sonicator operating at 80 kHz frequency and a nominal applied power of 135 W, while solid-phase microextrac-tion coupled with gas chromatography–electron capture detector (SPME/GC–ECD) was employed to monitor triclosan degradation.The latter followed pseudo-first order kinetics with the rate constant being (min-1): 0.2284 for seawater > 0.1051 for 3.5% NaCl in deion-ised water > 0.0597 for centrifuged urban runoff 0.0523 for untreated urban runoff > 0.0272 for deionised water > 0.0063 for wastewa-ter influent. SPME/GC–ECD and SPME coupled with gas chromatography–mass spectrometry (SPME/GC–MS) were also used tocheck for the formation of chlorinated and other toxic by-products; at the conditions in question, the presence of such compounds was not confirmed
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The continuous quest for novel sample preparation procedures has led to the development of new me... more The continuous quest for novel sample preparation procedures has led to the development of new methods, whose main advantages are their speed and negligible volume of solvents used. The most recent trends include solvent microextraction, a miniaturisation of the traditional liquid^liquid extraction method, where the solvent to aqueous ratio is greatly reduced. Single-drop microextrac-tion is a methodology that evolved from this approach. It is a simple, inexpensive, fast, effective and virtually solvent-free sample pretreatment technique. This article provides a detailed and updated discussion of the developments, modes and applications of single-drop microextraction, followed by a brief description of the theoretical background of the method. Finally, the most important parameters as well as some practical considerations for method optimisation and development are summarised.
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A new and fast equilibrium-based solvent microextraction technique termed vortex-assisted liquid–... more A new and fast equilibrium-based solvent microextraction technique termed vortex-assisted liquid–liquid microextraction (VALLME) has been developed and used for the trace analysis of octylphe-nol, nonylphenol and bisphenol-A in water and wastewater samples. According to VALLME, dispersion of microvolumes of a low density extractant organic solvent into the aqueous sample is achieved by using for the first time vortex mixing, a mild emulsification procedure. The fine droplets formed could extract target analytes towards equilibrium faster because of the shorter diffusion distance and larger specific surface area. Upon centrifugation the floating extractant acceptor phase restored its initial single micro-drop shape and was used for high-performance liquid chromatographic analysis. Different experimental parameters were controlled and the optimum conditions found were: 50 l of octanol as the extractant phase; 20 ml aqueous donor samples; a 2 min vortex extraction time with the vortex agitator set at a 2500 rpm rotational speed; centrifugation for 2 min at 3500 rpm; no ionic strength or pH adjustment. The calculated calibration curves gave high levels of linearity yielding correlation coefficients (r 2) greater than 0.9935. The repeatability and reproducibility of the proposed method were found to be good and the limits of the detection were calculated in the low g l −1 level ranging between 0.01 and 0.07 g l −1. Matrix effects were determined by applying the proposed method to spiked tap, river water and treated municipal wastewater samples. The proposed method was finally applied to the determination of target pollutants in real wastewater effluent samples using the standard addition method.
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Papers by Elefteria Psillakis
of 16 polycyclic aromatic hydrocarbons (PAHs) sorbed on microplastics sampled from nine sandy beaches of Northern Crete was quantified using Gas chromatography – Ion Trap Mass Spectrometry (GC-ITMS).
PAHs concentrations ranged from non-detectable levels to 1592 ng/g and fluctuated between sampling periods. Based on the observed patterns of meso- and microplastics distribution, practical guidelines are proposed to minimize the entrance of microplastics into the seawater wherefrom they are exceptionally difficult to collect, if mitigation actions are to be applied.
of 16 polycyclic aromatic hydrocarbons (PAHs) sorbed on microplastics sampled from nine sandy beaches of Northern Crete was quantified using Gas chromatography – Ion Trap Mass Spectrometry (GC-ITMS).
PAHs concentrations ranged from non-detectable levels to 1592 ng/g and fluctuated between sampling periods. Based on the observed patterns of meso- and microplastics distribution, practical guidelines are proposed to minimize the entrance of microplastics into the seawater wherefrom they are exceptionally difficult to collect, if mitigation actions are to be applied.