Conjugate of Enkephalin and Temporin Peptides as a Novel Therapeutic Agent for Sepsis.

Antimicrobial peptides (AMPs) exhibit a wide spectrum of actions, ranging from a direct bactericidal effect to multifunctional activities as immune effector molecules. The aim of this study was to examine the anti-inflammatory properties of a DAL-PEG-DK5 conjugate composed of a lysine-rich derivative of amphibian temporin-1CEb (DK5) and dalargin (DAL), the synthetic Leu-enkephalin analogue. Detailed study of the endotoxin-neutralizing activity of the peptide revealed that DAL-PEG-DK5 interacts with LPS and the LPS binding protein (LBP). Moreover, DAL-PEG-DK5 prevented dimerization of TLR4 at the macrophage surface upon LPS stimulation. This inhibited activation of the NF-κB signaling pathway and markedly reduced pro-inflammatory cytokine production. Finally, we showed that aggregation of DAL-PEG-DK5 into amyloid-like structures induced by LPS neutralized the endotoxin proinflammatory activity. Consequently, DAL-PEG-DK5 reduced morbidity and mortality in vivo, in a mouse model of endotoxin-induced septic shock. Collectively, the data suggest that DAL-PEG-DK5 is a promising therapeutic compound for sepsis.

Successful therapy of Clostridium difficile infection with fecal microbiota transplantation.

Clostridium difficile infection (CDI) is the most common cause of infectious diarrhea and represents an important burden for healthcare worldwide. Symptoms of severe CDI include watery, foul-smelling diarrhea, peripheral leucocytosis, increased C-reactive protein (CRP), acute renal failure, hypotension and pseudomembranous colitis. Recent studies indicate that the main cause of CDI is dysbiosis, an imbalance in the normal gut microbiota. The restoration of a healthy gut microbiota composition via fecal microbiota transplantation (FMT) recently became more popular. The aim of the present study was to assess the effect of FMT on the healing of CDI and to analyze the changes in the level of pro-inflammatory markers (C-reactive protein, fecal calprotectin) and pro-inflammatory cytokines. Eighteen patients with CDI were included in our study (6 males and 12 females) with recurrent and/or severe CDI. The FMT was performed in 17 patients using colonoscopy, including 16 patients receiving a one-time FMT and 1 patient who needed 2 additional FMTs. One patient was treated with a single round of FMT using push-and-pull enteroscopy. In all CDI patients, before and 3 weeks after FMT, the following parameters were analyzed: C-reactive protein, fecal calprotectin, and plasma interleukin (IL)-6, IL-8 and IL-12, and tumor necrosis factor-alpha (TNF-α). In addition, the plasma level of LL-37, a cathelicidine peptide was assessed by fluorescence-activated cell sorting (FACS) before and 3 months after FMT. Finally, in 7 patients a microbiome analysis was performed by sequencing of 16SrRNA in stool probes obtained before and 3 weeks after FMT. The healing rate of CDI was 94%. In all successfully treated patients no recurrent CDI was observed during follow-up (16 months). The serum level of pro-inflammatory cytokines (TNF-α, IL-1ß, IL-6, IL-8 and IL-12) significantly decreased after FMT. Similarly, CRP and fecal calprotectin normalized after FMT. 3 months after FMT a significant increase of LL-37 in the plasma of successfully treated patients was monitored. The sequencing analysis demonstrated an elevated abundance of beneficial bacterial species such as Lactobacillaceae, Ruminococcaceae, Desulfovibrionaceae, Sutterellaceae and Porphyromonodacea after FMT. No serious side effects were observed. We concluded that FMT represented a very effective and safe treatment of recurrent and/or severe CDI and led to favorable shifts in the composition of gut microbiome.

Emerging role of fecal microbiota therapy in the treatment of gastrointestinal and extra-gastrointestinal diseases.

In the recent decade our understanding of the role of the human gut microbiome has been revolutionized by advances in development of molecular methods. Approximately, up to 100 trillion (10(14)) microorganisms per human body colonize the intestinal tract making an additional acquired organ that provides many vital functions to the host. A healthy gut microbiome can be defined by the presence of the various classes of microbes that enhance metabolism, resistance to infection and inflammation, prevention against cancer and autoimmunity and that positively influence so called braingut axis. Diet represents one of the most important driving forces that besides environmental and genetic factors, can define and influence the microbial composition of the gut. Aging process due to different changes in gut physiology (i.e. gastric hypochlorhydria, motility disorders, use of drugs, degenerative changes in enteric nervous system) has a profound effect on the composition, diversity and functional features of gut microbiota. A perturbed aged gut microbiome has been associated with the increasing number of gastrointestinal (e.g. Clostridium difficile infection - CDI) and non-gastrointestinal diseases (metabolic syndrome, diabetes mellitus, fatty liver disease, atherosclerosis etc.). Fecal microbiota transplantation (FMT) is a highly effective method in the treatment of refractory CDI. FMT is the term used when stool is taken from a healthy individual and instilled during endoscopy (colonoscopy or enteroscopy) into a gut of the sick person to cure certain disease. FMT represents an effective therapy in patient with recurrent CDI and the effectiveness of FMT in the prevention of CDI recurrence had reached approx. 90%. There is also an increasing evidence that the manipulation of gut microbiota by FMT represents a promising therapeutic method in patients with inflammatory bowel disease and irritable bowel syndrome. There is also an increased interest in the role of FMT for the treatment of metabolic syndrome and obesity which collectively present the greatest health challenge in the developed world nowadays. Targeting of gut microbiota by FMT represents an exciting new frontier in the prevention and management of gastrointestinal and non-gastrointestinal diseases that awaits further studies in preclinical and clinical settings.

A pathogenic trace of Tannerella forsythia - shedding of soluble fully active tumor necrosis factor α from the macrophage surface by karilysin.

Tannerella forsythia is implicated as a pathogen causing chronic and aggressive periodontitis. However, its virulence factors, including numerous putative proteases, are mostly uncharacterized. Karilysin is a newly described matrix metalloprotease-like enzyme of T. forsythia. Since pathogen-derived proteases may affect the host defense system via modulation of the cytokine network, the aim of this study was to determine the influence of karilysin on tumor necrosis factor-α (TNF-α). The results showed that karilysin cleaved the membrane form of TNF-α on the surface of macrophages, and that this led to an increased concentration of soluble TNF-α in the conditioned medium. Importantly, despite partial degradation of soluble TNF-α by karilysin, the released cytokine retained its biological activity, inducing apoptosis and stimulating autocrine pathway of pro-inflammatory gene expression. Notably, the observed effect required proteolytic activity by karilysin, since a catalytically inactive mutant of the enzyme did not affect TNF-α secretion. The shedding was independent of the activity of ADAM17, a major endogenous TNF-α converting enzyme. Karilysin-dependent TNF-α release from the cell surface is likely to occur in vivo because human plasma, the main constituent of gingival crevicular fluid, only slightly affected the sheddase activity of karilysin. Taken together, these results indicate that karilysin modulates the host immune response through regulation of TNF-α secretion, and should therefore be considered as a new virulence factor of T. forsythia.

Peptidylarginine deiminase from Porphyromonas gingivalis contributes to infection of gingival fibroblasts and induction of prostaglandin E2 -signaling pathway.

Porphyromonas gingivalis (P. gingivalis) expres-ses the enzyme peptidylarginine deiminase (PPAD), which has a strong preference for C-terminal arginines. Due to the combined activity of PPAD and Arg-specific gingipains, P. gingivalis on the cell surface is highly citrullinated. To investigate the contribution of PPAD to the interaction of P. gingivalis with primary human gingival fibroblasts (PHGF) and P. gingivalis-induced synthesis of prostaglandin E2 (PGE2 ), PHGF were infected with wild-type P. gingivalis ATCC 33277, an isogenic PPAD-knockout strain (∆ppad) or a mutated strain (C351A) expressing an inactive enzyme in which the catalytic cysteine has been mutated to alanine (PPAD(C351A) ). Cells were infected in medium containing the mutants alone or in medium supplemented with purified, active PPAD. PHGF infection was assessed by colony-forming assay, microscopic analysis and flow cytometry. Expression of cyclo-oxygenase 2 (COX-2) and microsomal PGE synthase-1 (mPGES-1), key factors in the prostaglandin synthesis pathway, was examined by quantitative reverse transcription polymerase chain reaction (qRT-PCR), while PGE2 synthesis was evaluated by enzyme immunoassay. PHGF were infected more efficiently by wild-type P. gingivalis than by the ∆ppad strain, which correlated with strong induction of COX-2 and mPGES-1 expression by wild-type P. gingivalis, but not by the PPAD activity-null mutant strains (Δppad and C351A). The impaired ability of the Δppad strain to adhere to and/or invade PHGF and both Δppad and C351A to stimulate the PGE2 -synthesis pathway was fully restored by the addition of purified PPAD. The latter effect was strongly inhibited by aspirin. Collectively, our results implicate PPAD activity, but not PPAD itself, as an important factor for gingival fibroblast infection and activation of PGE2 synthesis, the latter of which may strongly contribute to bone resorption and eventual tooth loss.

Differential regulation by Toll-like receptor agonists reveals that MCPIP1 is the potent regulator of innate immunity in bacterial and viral infections.

Toll-like receptors (TLRs) are key molecules in innate immunity that recognize a variety of pathogen-associated molecular patterns. Activation of TLRs by their agonists initiates several signaling cascades, which eventually result in the expression of immune modifiers. Despite the fact that MCPIP1 is reported as an important immune regulator involved in macrophage activation, modulation of its expression by all known TLR agonists has never been documented. In this study, we present for the first time that in human monocyte-derived macrophages all TLR agonists, except CpG, markedly induced the expression of MCPIP1. The level of the induced transcript, as well as the protein and time of their appearance varied depending on the agonist. Furthermore, we confirmed the strong and differential upregulation of MCPIP1 during bacteria, virus and fungus infection. MCPIP1 belongs to a group of early-response genes; however, in the present study, we show for the first time the sustained high level of MCPIP1 expression during long-term Staphylococcus aureus infection. Taken together, our results implicate MCPIP1 as a potent regulator of innate immunity, which can be strongly engaged in the pathogenesis of acute and chronic infective diseases.

Gastric ulcer healing and stress-lesion preventive properties of pioglitazone are attenuated in diabetic rats.

Diabetes mellitus increases susceptibility to acute gastric injury and impairs ulcer healing. Pioglitazone as an agonist of peroxisome proliferator-activated receptor gamma (PPARgamma) is used as anti-diabetic drug and has additionally gastroprotective activities. However, the effect of pioglitazone on the protection and healing of gastric mucosa under diabetic conditions is poorly understood. The aim of the present study was: 1) to compare the effects of treatment with PPARg ligand (pioglitazone) on healing of acetic acid-induced gastric ulcers and prevention of acute water immersion and restraint stress (WRS)-induced gastric lesions in normal rats and those with streptozotocin (STZ)-induced diabetes mellitus; 2) to assess the effects of pioglitazone on the mRNA expression of cyclooxygenase-2 (COX-2), c-NOS, interleukin-1beta and hypoxia inducible factor-1 alpha (HIF-1alpha) in the gastric mucosa of rats with or without STZ-induced diabetes mellitus; 3) to investigate the involvement of endogenous NO and proinflammatory cytokines (IL-1beta, TNF-alpha) in healing of chronic gastric ulcers and in prevention of acute stress lesions by pioglitazone in rats with or without STZ-induced diabetes mellitus. Diabetes was induced in rats by single injection of STZ (70 mg/kg i.p.) four weeks prior to production of gastric ulcers by acetic acid method or induction of stress lesions by 3.5 hours of WRS. Non-diabetic rats were used as controls. Two major animal groups (A and B) were tested; A) diabetic and non-diabetic rats with chronic gastric ulcers treated with 1) pioglitazone (40 mg/kg-d i.g.), 2) pioglitazone in combination of blocker of NO synthase (L-NNA 20 mg/kg-d i.p.), and 3) saline (vehicle-control); and B) diabetic and non-diabetic rats exposed to 3.5 hours of WRS and pretreated with 1) pioglitazone (40 mg/kg i.g.), 2) pioglitazone in combination of blocker of NO synthase (L-NNA 20 mg/kg i.p.), and 3) saline (vehicle-control). The gastric mucosal blood flow was assessed by H(2)-gas clearance method. The area of chronic acetic acid ulcers and number of acute WRS-induced gastric lesions were assessed by planimetry or by counting of number of lesions, respectively. In rats with chronic ulcers, the mRNA expression of HIF-1alpha, IL-1beta and COX-2 was assessed by RT-PCR and protein expression of platelet endothelial cell adhesion molecule-1 (PECAM-1), COX-2 and cNOS was examined by Western blot. In rats with stress lesions, the protein expression of COX-2, cNOS, catalase, PPAR and heat shock protein 70 (HSP70) was examined by Western blot. In diabetic rats, a marked delay in ulcer healing and increased susceptibility to WRS lesions were observed and these effects were accompanied by a significant decrease in GBF. Pioglitazone significantly increased healing of chronic gastric ulcers and exerted a strong protective effect against WRS-induced lesions, but these effects were attenuated by NO-inhibition with L-NNA. Interestingly, the ulcer healing and gastroprotective effects of pioglitazone were weak under diabetic conditions, and this effect on ulcer healing was accompanied by impaired angiogenesis due to decreased PECAM-1 expression, attenuated expression of COX-2 and the increased expression of proinflammatory cytokines compared to those in diabetic rats treated with vehicle. We conclude that: 1) experimental diabetes in rats impairs healing of chronic ulcers and enhances acute stress lesions due to an increase in the expression and release of proinflammatory cytokines such as TNF-alpha and IL-1beta; 2) the ulcer healing effect of pioglitazone, which is, at least in part, mediated by endogenous NO, is significantly attenuated by L-NNA in diabetic rats despite increased COX-2 expression at the ulcer edge; 3) the formation of acute gastric lesions induced by WRS is also attenuated by pretreatment with pioglitazone due to increased GBF probably mediated by NO, as the administration of L-NNA reversed, in part, the preventive action induced by this PPARgamma ligand, and 4) pioglitazone is effective both in healing of chronic ulcers and protection against WRS lesions though its action under diabetic conditions seems to be attenuated, possibly due to reduction in NOS-NO system, angiogenesis and increased expression and release of proinflammatory cytokines.

Probiotic bacteria Escherichia coli strain Nissle 1917 attenuates acute gastric lesions induced by stress.

Probiotic bacteria Escherichia coli Nissle (EcN) was shown to prevent or heal acute murine colitis, but gastroprotective effects of EcN against mucosal injury have been little studied. In this study, the effects of EcN on formation of stress-induced gastric erosions were assessed in rats. Rats were divided in following treatment groups: 1) vehicle (control); 2) EcN 10(1) CFU/ml; 3) EcN 10(4) CFU/ml and 4) EcN 10(8) CFU/ml. One hour after treatment, the rats were exposed to 3.5 h of water immersion and restraint stress (WRS) and then sacrificed. Involvement of prostaglandins was tested using indomethacin given one hour before EcN, whereas that of sensory nerves was assessed using neurotoxic dose of capsaicin in rats pretreated with EcN or vehicle. The expression of proinflammatory cytokine (IL-1beta), ghrelin, peroxisome proliferator receptor gamma (PPARgamma) and heat-shock protein (HSP70) was assessed by RT-PCR and Western blot. Exposure to WRS in vehicle-pretreated rats induced acute erosions. Pretreatment with EcN significantly reduced WRS lesions and increased gastric blood flow. This protective effect was completely abolished by indomethacin and significantly attenuated by capsaicin-denervation. The exposure to WRS was accompanied by an increase in gastric mucosal expression of IL-1beta, ghrelin, PPARgamma, HSP70 and COX-2. In rats pretreated with EcN, a significant downregulation of mRNA and protein expression for IL-1beta, COX-2 and PPARgamma and increased expression of HSP70 without major change in activation of NFkappaB were observed. We conclude that EcN protects gastric mucosa against WRS erosions due to antiinflammatory and vasodilatory actions involving HSP70, prostaglandins and sensory afferent neurons.

Anti-inflammatory effects of extracts from some traditional Mediterranean diet plants.

It is believed that bioactive compounds from plant foods may have health beneficial effects and reduce the risk of chronic inflammatory diseases. In this study extracts of 121 plants typical for the traditional Mediterranean diet have been screened for their potential anti-inflammatory activities. The ability of the extracts to inhibit cytokine-stimulated, iNOS-dependent synthesis of nitric oxide in murine endothelial cells, without affecting cell viability, was the primary indicator of their anti-inflammatory properties. Based on these experiments we selected eight plant extracts for further analysis: Chrysanthemum coronarium L., Scandix pecten-veneris L., Urospermum picroides (L.) Scop. Ex F. W. Smith, Amaranthus cf. graecizans L., Onopordum macracanthum Schousboe, Eryngium campestre L., Artemisia alba Turra and Merendera pyrenaica (Pourret) Fourn. Only the effects of Onopordum macracanthum could be non-specific since the extract strongly inhibited total protein synthesis. All remaining 7 extracts decreased nitric oxide and TNFalpha synthesis in the cells of monocyte origin activated with LPS, and 4 of them significantly reduced surface expression of VCAM1 on TNFalpha-stimulated endothelial cells. All seven plant extracts decreased cytokine or LPS-stimulated iNOS mRNA levels in both cell types. Further research to identify bioactive compounds influencing intracellular signaling pathways activated by cytokines and LPS will consequently be needed in order to better understand these in vitro effects.

Sampling and Raman confocal microspectroscopic analysis of airborne particulate matter using poly(dimethylsiloxane) solid-phase microextraction fibers.

Commercial poly(dimethylsiloxane) (PDMS) 7-microm solid-phase microextraction (SPME) fibers were used for sampling and Raman spectroscopic analysis of a tailpipe diesel exhaust, candle smoke, cigarette smoke, and asbestos dust. Samples were collected via direct exposure of the SPME fiber to contaminated air. The mass loading for SPME fibers was varied by changing the sampling time. Results indicate that PDMS-coated fibers provide a simple, fast, reusable, and cost-effective air sampling tool for airborne particulates. The PDMS coating was stable; Raman bands of the PDMS coating were observed exactly at the same wavenumber positions before and after air sampling. Raman spectroscopic analysis resulted in identification of several characteristic bands allowing chemical speciation of particulates. The advantage of the SPME fiber is the open bed geometry allowing for application of various spectroscopic methods of particulate analysis. This paper describes the first-ever combined application of SPME technology with Raman confocal microspectroscopy for sampling and analysis of airborne particulates. Advantages of the combination of solid-phase microextraction and Raman microspectroscopy for airborne particulate analysis are discussed. Challenges associated with combined SPME sampling and Raman analysis of single particles are also described.

Field sampling and determination of formaldehyde in indoor air with solid-phase microextraction and on-fiber derivatization.

A new sampling and analysis method for formaldehyde in indoor air was tested in several indoor air surveys. The method was based on the use of solid-phase microextraction (SPME) poly(dimethylsiloxane)/divinylbenzene,65-microm fiber and gas chromatography. Indoor air surveys included grab and time-weighted average (TWA) sampling and were completed at six locations using (a) the SPME method employing on-fiber formaldehyde derivatization with o-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine hydrochloride and (b)the conventional National Institute for Occupational Safety and Health (NIOSH) 2451 method. Sampling time for SPME fiber ranged from 10 min for grab sampling to 8 h for TWA sampling. Sampling locations included a residential house, a rental apartment, an office building, and industrial workplaces. The air concentrations measured by SPME ranged from 10 to 380 ppbv and correlated well with those estimated by the NIOSH method. Results also indicated thatin some cases the formaldehyde concentrations measured in residential air could be much higher than those allowed in occupational settings. The SPME method proved to be accurate, fast, sensitive, and cost-efficient in field sampling applications. This research should be of interest to research, industrial, and regulatory agencies as well as to the general public concerned with indoor air quality.

Air sampling and analysis of volatile organic compounds with solid phase microextraction.

Solid phase microextraction (SPME) presents many advantages over conventional analytical methods by combining sampling, preconcentration, and direct transfer of the analytes into a standard gas chromatograph (GC). Since its commercial introduction in the early 1990s, SPME has been successfully applied to the sampling and analysis of environmental samples. This paper presents an overview of the current methods for air sampling and analysis with SPME using both grab and time-weighted average (TWA) modes. Methods include total volatile organic compounds (TVOCs), formaldehyde, and several target volatile organic compounds (VOCs). Field sampling data obtained with these methods in indoor air were validated with conventional methods based on sorbent tubes. The advantages and challenges associated with SPME for air sampling are also discussed. SPME is accurate, fast, sensitive, versatile, and cost-efficient, and could serve as a powerful alternative to conventional methods used by the research, industrial, regulatory, and academic communities.

Diffusion-based calibration for SPME analysis of aqueous samples.

When an SPME fiber is exposed for a short period of time to a flowing fluid sample, the amount of extracted analyte depends on its diffusion coefficient in the matrix medium, and it can be correlated to its concentration using a simple mathematical model. This work discusses the extension of this approach, already validated for gaseous samples and SPME fibers coated with strong adsorbent coatings, to the diffusion-based quantification of analytes present in aqueous samples. Dilute aqueous solutions of aromatic hydrocarbons were used as model samples and vials were modified to use conventional magnetic agitation with controlled tangential flow of the test solution around the fiber. It was demonstrated that, with proper selection of the stirring speed and sampling time, the same diffusion-based quantitative model used for gas samples could be employed. Under optimal conditions, the concentrations of the evaluated aromatic hydrocarbons were estimated with relative standard deviations between 0.8 and 3.6% and without deviation from the expected values within this precision range. Considering the extraction times involved, between 30 and 60 s, the approach here presented is the fastest possible technique for direct extraction of analytes from liquid samples.

Sampling and analysis of airborne particulate matter and aerosols using in-needle trap and SPME fiber devices.

A needle trap device (NTD) and commercial poly(dimethylsiloxane) (PDMS) 7-microm film thickness solid-phase microextraction (SPME) fibers were used for the sampling and analysis of aerosols and airborne particulate matter (PM) from an inhaler-administered drug, spray insect repellant, and tailpipe diesel exhaust. The NTD consisted of a 0.53-mm o.d. stainless steel needle having 5 mm of quartz wool packing section near the needle tip. Samples were collected by drawing air across the NTD with a Luertip syringe or via direct exposure of the SPME fiber. The mass loading of PM was varied by adjusting the volume of air pulled through the NTD or by varying the sampling time for the SPME fiber. The air volumes ranged from 0.1 to 50 mL, and sampling times varied from 10 s to 16 min. Particulates were either trapped on the needle packing or sorbed onto the SPME fiber. The devices were introduced to a chromatograph/mass spectrometer (GC/MS) injector for 5 min desorption. In the case of the NTD, 10 microL of clean air was delivered by a gas-tight syringe to aid the introduction of desorbed analytes. The compounds sorbed onto particles extracted by the SPME fiber or trapped in the needle device were desorbed in the injector and no carry-over was observed. Both devices performed well in extracting airborne polycyclic aromatic hydrocarbons (PAHs) in diesel exhaust, triamcinolone acetonide in a dose of asthma drug and DEET in a dose of insect repellant spray. Results suggest that the NTDs and PDMS 7-microm fibers can be used for airborne particulate sampling and analysis, providing a simple, fast, reusable, and cost-effective screening tool. The advantage of the SPME fiber is the open-bed geometry allowing spectroscopic investigations of particulates; for example, with Raman microspectroscopy.

Design and validation of portable SPME devices for rapid field air sampling and diffusion-based calibration.

The use of SPME fibers coated with porous polymer solid phases for quantitative purposes is limited due to effects such as interanalyte displacement and competitive adsorption. For air analysis, these problems can be averted by employing short exposure times to air samples flowing around the fiber. In these conditions, a simple mathematical model allows quantification without the need of calibration curves. This work describes two portable dynamic air sampling (PDAS) devices designed for application of this approach to nonequilibrium SPME sampling and determination of airborne volatile organic compounds (VOCs). The use of a PDAS device resulted in greater adsorbed VOC mass compared to the conventional SPME extraction in static air for qualitative screening of live plant aromas and contaminants in indoor air. For all studied air samples, an increase in the number of detected compounds and sensitivity was also observed. Quantification of aromatic VOCs in indoor air was also carried out using this approach and the PDAS/SPME device. Measured VOC concentrations were in low parts-per-billion by volume range using only 30-s SPME fiber exposure and were comparable to those obtained with a standard NIOSH method 1501. The use of PDAS/SPME devices reduced the total air sampling and analysis time by several orders of magnitude compared to the NIOSH 1501 method.

Air sampling with porous solid-phase microextraction fibers

A new, rapid air sampling/sample preparation methodology was investigated using adsorptive solid-phase microextraction (SPME) fiber coatings and nonequilibrium conditions for volatile organic compounds (VOCs). This method is the fastest extraction technique for air sampling at typical airborne VOC concentrations. A theoretical model for the extraction was formulated based on the diffusion through the interface between the sampled (bulk) air and the SPME coating. Parameters that affect the extraction process including sampling time, air velocity, air temperature, and relative humidity were investigated with the porous (solid) PDMS/DVB and Carboxen/PDMS coatings. Very short sampling times from 5 s to 1 min were used to minimize the effects of competitive adsorption and to calibrate the extraction process in the initial linear extraction region. The predicted amounts of extracted mass compared well with the measured amounts of target VOCs. Findings presented in this study extend the existing fundamental knowledge related to sampling/sample preparation with SPME, thereby enabling the development of new sampling devices for the rapid sampling of air, headspace, water, and soil.

Kinetics of solid-phase extraction and solid-phase microextraction in thin adsorbent layer with saturation sorption isotherm.

The effects of sorbent saturation in thin adsorbent layers have been much overlooked in earlier research and should be taken into account in both the theory and practice of solid-phase extraction (SPE) and solid-phase microextraction (SPME). The adsorption kinetics of a single analyte into a thin adsorptive layer was modeled for several cases of agitation conditions in the analyzed volume. The extraction process in the adsorbent layer was modeled using a Langmuir isotherm approximated by the linear isotherm at low concentrations and by a saturation plateau at concentrations exceeding the critical saturation concentration. Laplace transformations were used to estimate the equilibration time and adsorbed analyte concentration profile for no agitation, practical and perfect agitation in the analyzed volume. The equilibration time may be significantly reduced at high degrees of oversaturation and/or agitation in the analyzed volume. The resulting models indicated that the adsorbent layer becomes saturated at some critical value of the oversaturation degree parameter. The critical value of the oversaturation parameter is affected by both the concentration of the analyte in the analyzed volume and the sorbent characteristics. It was also shown that the adsorption process is carried out via the propagation of the saturation adsorption boundary toward the inner boundary of the adsorbent layer. These new adsorption models should serve as "stepping stones" for the development of competitive adsorption kinetic models for both SPE and SPME, particularly in cases where fast sampling is used.