Biomedical subjects

Janusz Pawliszyn

Publications and source records attributed to Janusz Pawliszyn.

At least 19 recordsLinked to original sources

PubMed2003

Sample preparation: quo vadis?

The sample preparation step in an analytical process typically consists of an extraction procedure that results in the isolation and enrichment of components of interest from a sample matrix. Extraction can vary in degree of selectivity, speed, and convenience and depends not only on the approach and conditions used but on the geometric configurations of the extraction phase. Increased interest in sample preparation research has been generated by the introduction of nontraditional extraction technologies. These technologies address the need for reduction of solvent use, automation, and miniaturization and ultimately lead to on-site in situ and in vivo implementation. These extraction approaches are frequently easier to operate but provide optimization challenges. More fundamental knowledge is required by an analytical chemist not only about equilibrium conditions but, more importantly, about the kinetics of mass transfer in the extraction systems. Optimization of this extraction process enhances overall analysis. Proper design of the extraction devices and procedures facilitates convenient on-site implementation, integration with sampling, and separation/quantification, automation, or both. The key to rational choice, optimization, and design is an understanding of the fundamental principles governing mass transfer of analytes in multiphase systems. The objective of this perspective is to summarize the fundamental aspects of sample preparation and anticipate future developments and research needs.

Journal Article↗

PubMed2003

On-site calibration method based on stepwise solid-phase microextraction.

A stepwise solid-phase microextraction (SPME) method was developed for on-site calibration of SPME for volatile organic compounds analysis. In this approach, a 75-microm Carboxen-polydimethylsiloxane coated fibre was loaded with a prior to exposure to samples of interest Extraction time for the target analytes can be controlled independently from that of the standard, and the response factors for the target analytes can be adjusted accordingly. A good reproducibility of the response factors for BTEXs (benzene, toluene, ethylbenzene and xylenes) was obtained with stepwise SPME. Satisfactory results were obtained by using this method for quantitative analysis of BTEXs in the air of a gas station when tetrachloroethylene was used as a standard. The introduction of standard via the stepwise SPME procedure makes SPME more useful in field applications. It can be used to detect leaks, contaminations and losses from loading of a standard onto a fibre to introduction of the fibre to an analytical instrument. However, this method cannot be used for compensation of sample matrix effects.

Benzene↗

PubMed2003

Time-weighted average passive sampling with a solid-phase microextraction device.

A modified Solid-Phase Microextraction (SPME) device has been used as a passive sampler to determine the time-weighted average (TWA) concentration of volatile organic compounds (VOCs) in air. Unlike conventional sampling with SPME, in which the fiber is extended outside its needle housing, during TWA passive sampling, the fiber is retracted a known distance into its needle housing. The SPME passive sampler collects the VOCs by the mechanism of molecular diffusion and sorption on to a coated fiber as collection medium. This process has been shown to be described by Fick's first law of diffusion, whereby determination of the amounts of analytes accumulated over time enable measurement of the TWA concentration to which the sampler was exposed. A series of fibers, 100-microm poly(dimethylsiloxane), 65-microm poly(dimethylsiloxane)/divinylbenzene, and 75-microm Carboxen/poly(dimethylsiloxane), were tested for their "zero sink", face velocity, and response time behavior. Of the fibers tested, that coated with 75-microm Carboxen/poly(dimethylsiloxane) was found to be an excellent passive sampler for VOCs. TWA passive sampling with a SPME device was shown to be almost independent of face velocity and to be more tolerant of high and low analyte concentrations and long and short sampling times, because of the ease with which the diffusion path length could be changed. It was found that environmental conditions, e.g., temperature, pressure, relative humidity, and ozone, have little or no effect on sampling. The 75-microm Carboxen/poly(dimethylsiloxane) fiber can retain VOCs for up to two weeks without significant loss. When the SPME device was tested in the field and the results were compared with those from National Institute of Occupational Health and Safety method 1501, good agreement was obtained.

Air Pollutants, Occupational↗

PubMed2003

Solid-phase microextraction of volatile compounds from the chopped leaves of three species of Eucalyptus.

Headspace solid-phase microextraction (HS-SPME) coupled with gas chromatography and ion-trap mass spectrometry has been used to identify biogenic volatile organic compounds present in the headspace of chopped leaves of Eucalyptus (E.) dunnii, E. citriodora, and E. saligna. A simple HS-SPME method entailing 30 min of extraction at 30 degrees C was developed for this purpose. Thirty compounds were identified in the headspace of 60 juvenile chopped Eucalyptus leaves, and another 30 were tentatively identified. The presence of compounds such as (E)-4,8-dimethyl-1,3,7-nonatriene (DMNT), (E,E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene (TMNT), (E,E)-alpha-farnesene, (E,E,E)-3,7,11,15-tetramethyl-1,3,6,10,14-hexadecapentaene (TMHP), beta-caryophyllene, alpha-humulene, germacrene D, and beta-cubebene in the headspace of the leaves but not in the essential oils from the same Eucalyptus trees and information about the infochemical roles of some of these compounds in other living plant systems suggest they might play a bioactive role in Eucalyptus leaves.

Eucalyptus↗

PubMed2003

Thin-film microextraction.

The properties of a thin sheet of poly(dimethylsiloxane) (PDMS) membrane as an extraction phase were examined and compared to solid-phase microextraction (SPME) PDMS-coated fiber for application to semivolatile analytes in direct and headspace modes. This new PDMS extraction approach showed much higher extraction rates because of the larger surface area to extraction-phase volume ratio of the thin film. Unlike the coated rod formats of SPME using thick coatings, the high extraction rate of the membrane SPME technique allows larger amounts of analytes to be extracted within a short period of time. Therefore, higher extraction efficiency and sensitivity can be achieved without sacrificing analysis time. In direct membrane SPME extraction, a linear relationship was found between the initial rate of extraction and the surface area of the extraction phase. However, for headspace extraction, the rates were somewhat lower because of the resistance to analyte transport at the sample matrix/headspace barrier. It was found that the effect of this barrier could be reduced by increasing either agitation, temperature, or surface area of the sample matrix/headspace interface. A method for the determination of PAHs in spiked lake water samples was developed based on the membrane PDMS extraction coupled with GC/MS. A linearity of 0.9960 and detection limits in the low-ppt level were found. The reproducibility was found to vary from 2.8% to 10.7%.

Chromatography, Gas↗

PubMed2002

SPME applied to the study of volatile organic compounds emitted by three species of Eucalyptus in situ. Solid-phase micro extraction.

Headspace solid-phase microextraction coupled to gas chromatography/ion trap mass spectrometry-65 microm polydimethylsiloxane/divinylbenzene (PDMS/DVB) was used to identify and monitor the emission patterns of biogenic volatile organic compounds from leaves of Eucalyptus dunnii, Eucalyptus saligna, and Eucalyptus citriodora in situ. Short extractions (1 min) were performed every 30 min for periods of 8-10 h during 24 days taking advantage of the high capacity of this porous polymer coating. Forty-two compounds were detected and 20 identified in the headspace of E. saligna leaves, and 19 of 27 compounds were identified in the headspace of E. dunnii leaves. The emission pattern of (E)-beta-ocimene and rose oxide suggests that they may play a bioactive role in Eucalyptus.

Acyclic Monoterpenes↗

PubMed2002

Analysis of polar pesticides in water and wine samples by automated in-tube solid-phase microextraction coupled with high-performance liquid chromatography-mass spectrometry.

A simple and sensitive method for the determination of polar pesticides in water and wine samples was developed by coupling automated in-tube solid-phase microextraction (SPME) to high-performance liquid chromatography-electrospray ionization mass spectrometry (HPLC-ESI-MS). To achieve optimum performance, the conditions for both the in-tube SPME and the ESI-MS detection were investigated. In-tube SPME conditions were optimized by selecting the appropriate extraction parameters, especially the stationary phases used for SPME. For the compounds studied, a custom-made polypyrrole (PPY)-coated capillary showed superior extraction efficiency as compared to several commercial capillaries tested, and therefore, it was selected for in-tube SPME. The influence of the ethanol content on the performance of in-tube SPME was also investigated. It was found that the amount of pesticides extracted decreased with the increase of ethanol content in the solutions. The ESI-MS detection conditions were optimized as follows: nebulizer gas, N2 (30 p.s.i.; 1 p.s.i.=6894.76 Pa); drying gas, N2 (10 l/min, 350 degrees C); capillary voltage, 4500 V; ionization mode, positive; mass scan range, 50-350 amu; fragmentor voltage, variable depending on the ions selected. Due to the high extraction efficiency of the PPY coating and the high sensitive mass detection, the detection limits (S/N = 3) of this method for the compounds studied are in the range of 0.01 to 1.2 ng/ml, which are more than one order of magnitude lower than those of the previous in-tube SPME-HPLC-UV method. A linear relationship was obtained for each analyte in the concentration range of 0.5 to 200 ng/ml with MS detection. This method was applied to the analysis of phenylurea and carbamate pesticides in spiked water and wine samples.

Automation↗

PubMed2002

Breath analysis and monitoring by membrane extraction with sorbent interface.

An analytical system consisting of a sampling chamber, membrane extraction module, sorbent trap and gas chromatograph with flame ionization or ion mobility detector was used for on-line monitoring of the composition of the last 250 mL portion of human expired breath. The sampling chamber consisted of a tube fitted with check valves on both ends to allow the air to pass through during expiration, but not to return or allow mixing with ambient air. The last portion of breath was held in the chamber at the end of breath expiration. The organic components in the trapped breath were transferred to the carrier gas by permeation through the membrane in the extraction module and were concentrated in the sorbent trap before introduction as a sharp plug on the front of chromatographic column. Moisture in the breath did not penetrate the membrane to a substantial degree. This system was used to investigate presence of acetone as a biologically important marker of human health as well as exposure to volatile compounds.

Acetone↗

PubMed2002

Sampling and monitoring of biogenic emissions by eucalyptus leaves using membrane extraction with sorbent interface (MESI).

Membrane extraction with sorbent interface (MESI) has been applied to monitor plant fragrance volatiles emitted into indoor air. The main components of the MESI system are a membrane module and a trap, which can be connected directly to a GC or GC-MS for simultaneous multicomponent extraction and monitoring. A polydimethylsiloxane (PDMS) membrane and two different traps, PDMS and Tenax, as well as a DC current supply for trap desorption have been applied in this research. After the membrane module is placed in contact with the plant, the MESI/GC-MS provides semicontinuous characterization of volatile compounds emitted. The MESI device has been applied to monitor the biogenic volatile organic compounds released during the first 8 h after a branch was cut from a Eucalyptus dunnii tree. The study demonstrates that the MESI system is a simple and useful tool for monitoring changes in emission processes as a function of time.

Chemistry Techniques, Analytical↗

PubMed2002

Electrochemically controlled solid-phase microextraction based on conductive polypyrrole films.

Solid-phase microextraction (SPME) fiber coatings based on conductive polypyrrole films were prepared for the electrochemical extraction and desorption of ionic analytes. Simple preparation of each of the PPY extraction coatings on a platinum wire was possible with a constant potential method, but more importantly, cycling of the film between oxidation and reduction potentials facilitated the extraction and desorption of ionic analytes. The analytes were desorbed into a sample aliquot of water and were determined by flow injection analysis using a mass spectrometer. The fiber coatings and the developed electrochemical SPME method were found to be stable and reproducible (RSD < 5%; N = 5) and could be extended to several cations and anions, confirming the versatility of the approach. Preconcentration of the analyte on the fiber was also possible by repeating the processes to increase the amount of analyte extracted.

Letter↗

PubMed2002

Analysis of anatoxin-a in aqueous samples by solid-phase microextraction coupled to high-performance liquid chromatography with fluorescence detection and on-fiber derivatization.

A simple method for analysis of anatoxin-a in aqueous samples was developed using solid-phase microextraction (SPME) and high-performance liquid chromatography (HPLC) with fluorescence detection. Anatoxin-a was derivatized to a fluorogenic agent on the surface of the SPME fiber. In the method an SPME fiber was immersed for 30 min in the aqueous sample. The fluorogenic derivatizing reagent (4-fluoro-7-nitro-2,1,3-benzoxadiazole, 1.0 mg/ml in methanol) was dropped or sprayed onto the fiber containing extracted analytes. The fiber was then heated for 10 min in an empty vial at 70 degrees C in a waterbath to promote derivatization. The derivatives formed on the fiber were desorbed in a SPME-HPLC interface. The interface was filled with methanol-1 mM hydrochloric acid (7:3, v/v) before inserting of the fiber into the interface. For desorption, the fiber was inserted in the interface for 5 min. For anatoxin-a in an aqueous sample, the calibration curve showed linearity in the range of 50-1500 ng/ml and the limit of detection of anatoxin-a was 20 ng/ml. No interferences were found, and the time for analysis was 55 min for one sample.

Bacterial Toxins↗

PubMed2002

Microwave-assisted generation of standard gas mixtures.

Microwave heating was employed for preparation of the standard gas of volatile organic compounds (VOCs) and semivolatile organic compounds (semi-VOCs) by using a 1000 W commercial domestic microwave oven and 1 L gas-sampling bulbs. The VOCs investigated were benzene, chloroform, 1,3-dichlorobenzene, tetrachloroethylene, toluene, and 1,1,2-trichloroethane, and the semi-VOCs used were the polychlorinated biphenyls (PCBs) PCB 1016 and PCB 1248. Since these weakly or nonpolar molecules are very poor absorbers of microwave energy, an appropriate amount of water was introduced to accept microwave radiation and act as the thermal source to accelerate their evaporation. The glass bulb may also contribute thermal energy to the VOCs/semi-VOCs by accepting microwave energy to a small degree. For 0.5 microL of liquid VOCs on 10 mg of glass wool, it was shown that 15 microL of H2O and 60 s of microwave heating yielded a very efficient evaporation [97.2-106.4%, compared with a classic method (Muller, L; Gorecki, T.; Pawliszyn, J. Fresenius' J. Anal. Chem. 1999, 364, 610-616)]. For 1 microL of PCB solution (1000 microg/mL in hexane), 15 microL of H2O and 90 s of microwave heating also provided a complete evaporation. The addition of water was particularly significant for microwave-assisted evaporation of PCBs because semi-VOCs are much more difficult to evaporate than VOCs. This developed microwave technique proved to be quite simple, powerful, rapid, accurate, and safe for the preparation of VOC/semi-VOC standard gas. Solid- phase microextraction combined with gas chromatography was used for the gas analysis.

Air Pollution↗

PubMed2002

Automated in-tube solid-phase microextraction coupled with HPLC for the determination of N-nitrosamines in cell cultures.

An automated in-tube solid-phase microextraction (SPME) HPLC analysis method for 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and several metabolites has been developed. NNK is one of the tobacco-specific N-nitrosamines (TSNA), which has been linked to cancers associated with the use of or exposure to tobacco products. In-tube SPME is an on-line extraction technique in which analytes are extracted and concentrated from the sample directly into a coated capillary by repeated draw/eject steps. In this study, a tailor-made polypyrrole (PPY)-coated capillary and several commercially available capillaries (capillary GC columns) were used to evaluate their extraction efficiencies for NNK and several metabolites in cell cultures. Compared with commercial capillaries that were currently used for in-tube SPME, the PPY-coated capillary showed better extraction efficiency for all of the compounds studied. After optimization of the extraction conditions, NNK and five metabolite compounds were analyzed in spiked cell cultures, confirming the applicability of the developed method. Excellent linearity was observed for all compounds (av R2 = 0.9942) and detection limits that ranged from 20 to 250 ng/mL. The average within-day and between day variations (% RSD) were 2.9 and 3.6%, respectively. This automated extraction and analysis method simplified the determination of the TSNA, requiring a total sample analysis time of only approximately 30 min.

Animals↗

PubMed2002

Direct determination of benzodiazepines in biological fluids by restricted-access solid-phase microextraction.

A biocompatible solid-phase microextraction (SPME) fiber was prepared using an alkyl-diol-silica (ADS) restricted-access material as the SPME coating. The ADS-SPME fiber was able to simultaneously fractionate the protein component from a biological sample, while directly extracting several benzodiazepines, overcoming the present disadvantages of direct sampling in biological matrixes by SPME. The fiber was interfaced with an HPLC-UV system, and an isocratic mobile phase was used to desorb, separate, and quantify the extracted compounds. The calculated clonazepam, oxazepam, temazepam, nordazepam, and diazepam detection limits were 600, 750, 333, 100, and 46 ng/mL in urine, respectively. The method was confirmed to be linear over the range of 500-50000 ng/mL with an average linear coefficient (R2) value of 0.9918. The injection repeatability and intraassay precision of the method were evaluated over 10 injections, resulting in a RSD of approximately 6%. The ADS-SPME fiber was robust and simple to use, providing many direct extractions and subsequent determination of benzodiazepines in biological fluids.

Anti-Anxiety Agents↗

PubMed2002

Whole-column imaging capillary electrophoresis of proteins with a short capillary.

Whole-column imaging capillary electrophoresis with a short capillary is discussed. A short capillary (3-6 cm) coated with either fluorocarbon or polyacrylamide was used as a separation capillary. The whole capillary was illuminated with 280 nm light, and the transmitted light was monitored by a linear charge-coupled device (CCD). For the short capillary, hydrodynamic flow caused by a subtle height difference between the anodic and cathodic reservoirs affected the sample migration in the capillary greatly. Several sample injection methods, including use of a cross connection, sealing of the capillary ends with a gel, and use of a gel-filled capillary, have been discussed. The experimental results showed that the peak height decreased and peak width increased with the electromigration distance. Therefore, higher sensitivity was obtained in a short capillary rather than a long capillary. The whole-column imaging CE with the short capillary has been applied for the study of conjugation reactions of protein cytochrome c with sodium dodecyl sulfate (SDS) and the dye Congo Red. The method has also been used for in situ monitoring of the electrophoretic protein desorption process. Our technique is a unique tool for the study of protein binding reactions and the interaction between analyte and inner wall of the capillary.

Adsorption↗

PubMed2002

Microfabrication of a tapered channel for isoelectric focusing with thermally generated pH gradient.

A simple microfabrication technique for the preparation of a tapered microchannel for thermally generated pH gradient isoelectric focusing (IEF) has been demonstrated. The tapered channel was cut into a plastic sheet (thickness was 120 microm), and the channel was closed by sandwiching the plastic sheet between two glass microscope slides. The length of the microchannel was 5 cm. The width of the separation channel was 0.4 mm at the narrow end and 4 mm at the wide end. The channel was coated with polyacrylamide to prevent electroosmotic flow (EOF) during focusing. Two electrolyte vials were mounted on top of each end of the channel with the wide end of the channel connected to the cathodic vial and the narrow to the anodic vial. The feasibility of the thermally generated pH gradient in a tapered channel was demonstrated. Important parameters that determined the feasibility of using a thermally generated pH gradient in a tapered channel were analyzed. Parameters to be optimized were control of EOF and hydrodynamic flow, selection of power supply mode and prevention of local overheating and air bubble formation. Tris-HCl buffer, which has a high pK(a) dependence with temperature, was used both to dissolve proteins and as the electrolyte. The thermally generated pH gradient separation of proteins was tested by focusing dog, cat and human hemoglobins with a whole column detection capillary IEF (CIEF) system.

Hemoglobin A↗

PubMed2002

A laboratory technique for investigation of diffusion and transformation of volatile organic compounds in low permeability media.

A laboratory diffusion cell technique that permits spatial and temporal estimates of porewater concentrations over short intervals suitable for estimation of effective diffusion coefficients (De) and degradation rate constants (k) of volatile organic compounds (VOCs) in saturated low permeability media is presented. The diffusion cell is a sealed cylinder containing vapour reservoirs for sampling, including a vapour reservoir source and an array of vapour-filled "mini-boreholes", which are maintained water- and sediment-free by slightly negative porewater pressures. The vapour reservoirs were sampled by Solid Phase Micro-Extraction (SPME), resulting in minimal disturbance to the experimental system. Porewater concentrations are estimated from the measured vapour concentrations. Experiments were conducted using a non-reactive medium and five VOCs with a range in partitioning properties. Calibration experiments showed that equilibrium partition coefficients could be used for calculating concentrations in the vapour reservoir source from concentrations in the SPME coating after a 1-min microextraction and that the reservoir concentration was insignificantly affected by sampling. However, equilibrium was not reached during the one-min extraction of the boreholes; the microextraction reduced the borehole vapour concentrations, leading to diffusion of VOCs from porewater into the vapour-filled borehole. Thus, empirical partitioning coefficients were required for the determination of porewater VOC concentrations. The experimental data and numerical modelling indicate masses extracted by SPME extraction are relatively small, with minimal perturbation on processes studied in diffusion experiments. This technique shows promise for laboratory investigation of diffusion and transformation processes in low permeability media.

Carbon Disulfide↗

PubMed2002

Membrane extraction with sorbent interface-gas chromatography as an effective and fast means for continuous monitoring of thermal degradation products of polyacrylonitrile.

A novel sample preparation technique, membrane extraction with a sorbent interface (MESI) has been optimized and used for continuous monitoring thermal degradation products in polyacrylonitrile (PAN) polymer headspace at different temperatures, followed by gas chromatography-mass spectrometry (GC-MS). MESI with a flat sheet poly(dimethyl siloxane)-polycarbonate (PDMS-PC) membrane and Tenax trap was used. The system is very simple, fast and reliable and allowed us to extract, enrich and continuously monitor major volatile compounds released from the polymer at different temperatures. The volatile and semi-volatile gaseous degradation products were identified. Sensitivity of the method depends on the length of time for trapping.

Journal Article↗