Determination of metoprolol enantiomers in human plasma and saliva samples utilizing microextraction by packed sorbent and liquid chromatography-tandem mass spectrometry.

A sensitive, accurate and reliable bioanalytical method for the enantioselective determination of metoprolol in plasma and saliva samples utilizing liquid chromatography-electrospray ionization tandem mass spectrometry was developed and validated. Human plasma and saliva samples were pretreated by microextraction by packed sorbent (MEPS) prior to analysis. A new MEPS syringe form with two inputs was used. Metoprolol enantiomers and internal standard pentycaine (IS) were eluted from MEPS sorbent using isopropanol after removal of matrix interferences using aliquots of 5% methanol in water. Complete separation of metoprolol enantiomers was achieved on a Cellulose-SB column (150 × 4.6 mm, 5 µm) using isocratic elution with mobile phase 0.1% ammonium hydroxide in hexane-isopropanol (80:20, v/v) with a flow rate of 0.8 mL/min. A post-column solvent-assisted ionization was applied to enhance metoprolol ionization signal in positive mode monitoring (+ES) using 0.5% formic acid in isopropanol at a flow rate of 0.2 mL/min. The total chromatographic run time was 10 min for each injection. The detection of metoprolol in plasma and saliva samples was performed using triple quadrupole tandem mass spectrometer in +ES under the following mass transitions: m/z 268.08 → 72.09 for metoprolol and m/z 303.3 → 154.3 for IS. The linearity range was 2.5-500 ng/mL for both R- and S-metoprolol in plasma and saliva. The limits of detection and quantitation for both enantiomers were 0.5 and 2.5 ng/mL respectively, in both matrices (plasma and saliva). The intra- and inter-day precisions were presented in terms of RSD values for replicate analysis of quality control samples and were <5%; the accuracy of determinations varied from 96 to 99%. The method was able to determine the therapeutic levels of metoprolol enantiomers in both human plasma and saliva samples successfully, which can aid in therapeutic drug monitoring in clinical laboratories. Copyright © 2016 John Wiley & Sons, Ltd.

Application of graphitic sorbent for online microextraction of drugs in human plasma samples.

In the present work a new sorbent based on graphitized carbon (CarbonX(®) COA) was evaluated in microextraction by packed sorbent (MEPS) for extraction of lidocaine and ropivacaine from human plasma samples. The new graphitic sorbent showed high recoveries of lidocaine and ropivacaine compared to C18 sorbent. In the present study the G-MEPS (syringe packed with graphitic sorbent) was connect online with liquid chromatography tandem mass spectrometry (LC-MS/MS). In order to obtain a fast and reliable method different factors affecting MEPS performance were investigated. The extraction efficiency of the graphitic sorbent was compared with silica-based sorbents used in MEPS. The G-MEPS was also evaluated for reuse (50-100 times). The recoveries of lidocaine and ropivacaine from plasma samples were 79% and 82%; respectively. The method was validated according to FDA (Food and Drug Administration) guideline for bioanalytical method validation. Linearity was assessed in the range 5-2000nmol/L, with coefficient of determination r(2)>0,995 (n=3) for lidocaine and r(2)>0.997 (n=3) for ropivacaine. The lower limit of quantification (LLOQ) was 5nmol/L and the limit of detection (LOD) was 1nmol/L for studied analytes in plasma samples. For both analytes considered in this study the accuracy values in plasma samples were ranged from 86% to 113%. The Inter-day precisions, expressed as relative standard deviation (%RSD), at three different concentrations (QC-samples) ranged from 8% to 9% for lidocaine, and from 4% to 11% for ropivacaine.

A needle extraction utilizing a molecularly imprinted-sol-gel xerogel for on-line microextraction of the lung cancer biomarker bilirubin from plasma and urine samples.

In the present work, a needle trap utilizing a molecularly imprinted sol-gel xerogel was prepared for the on-line microextraction of bilirubin from plasma and urine samples. Each prepared needle could be used for approximately one hundred extractions before it was discarded. Imprinted and non-imprinted sol-gel xerogel were applied for the extraction of bilirubin from plasma and urine samples. The produced molecularly imprinted sol-gel xerogel polymer showed high binding capacity and fast adsorption/desorption kinetics for bilirubin in plasma and urine samples. The adsorption capacity of molecularly imprinted sol-gel xerogel polymer was approximately 60% higher than that of non-imprinted polymer. The effect of the conditioning, washing and elution solvents, pH, extraction time, adsorption capacity and imprinting factor were investigated. The limit of detection and the lower limit of quantification were set to 1.6 and 5nmolL(-1), respectively using plasma or urine samples. The standard calibration curves were obtained within the concentration range of 5-1000nmolL(-1) in both plasma and urine samples. The coefficients of determination values (R(2)) were ≥0.998 for all runs. The extraction recovery was approximately 80% for BR in the human plasma and urine samples.

Microextraction by packed sorbent: an emerging, selective and high-throughput extraction technique in bioanalysis.

Sample preparation is an important analytical step regarding the isolation and concentration of desired components from complex matrices and greatly influences their reliable and accurate analysis and data quality. It is the most labor-intensive and error-prone process in analytical methodology and, therefore, may influence the analytical performance of the target analytes quantification. Many conventional sample preparation methods are relatively complicated, involving time-consuming procedures and requiring large volumes of organic solvents. Recent trends in sample preparation include miniaturization, automation, high-throughput performance, on-line coupling with analytical instruments and low-cost operation through extremely low volume or no solvent consumption. Micro-extraction techniques, such as micro-extraction by packed sorbent (MEPS), have these advantages over the traditional techniques. This paper gives an overview of MEPS technique, including the role of sample preparation in bioanalysis, the MEPS description namely MEPS formats (on- and off-line), sorbents, experimental and protocols, factors that affect the MEPS performance, and the major advantages and limitations of MEPS compared with other sample preparation techniques. We also summarize MEPS recent applications in bioanalysis.

Molecularly imprinted polymer in microextraction by packed sorbent for the simultaneous determination of local anesthetics: lidocaine, ropivacaine, mepivacaine and bupivacaine in plasma and urine samples.

This study presents the use of molecularly imprinted polymer (MIP) as packing material for microextraction by packed syringe (MEPS) to achieve higher extraction selectivity. Pentycaine was used as template for MIP. Development and validation of the determination of lidocaine, ropivacaine, mepivacaine and bupivacaine in human plasma and urine samples utilizing MIP-MEPS and liquid chromatography-tandem mass spectrometry (LC-MS/MS) were carried out. The MEPS MIP-cartridge could be used for 100 extractions before it was discarded. The extraction recovery ranged from 60 to 80%. The correlation coefficients values were >0.999 for all assays using lidocaine, ropivacaine, mepivacaine and bupivacaine in the calibration range 5-2000 nmol/L. The accuracy of the studied compounds, given as a percentage variation from the nominal concentration values, ranged from -4.9 to 8.4% using plasma and urine samples. The between-batch precision, given as the relative standard deviation, at three different concentrations (quality control samples) was ranged from -4.7 to 14.0% and from 1.8 to 12.7% in plasma and urine, respectively. The lower limit of quantification and limit of detection of the studied substances were 5.0 and 1.0 nm, respectively.

Extraction of explosives from soil followed by gas chromatography-mass spectrometry analysis with negative chemical ionization.

A new, simple and accurate method for extraction of explosives from soil was developed and validated. The method includes one hour gentle extraction of compounds from soil in acetonitrile:dichloromethane 50:50 at 30°C. Further analysis was made with GC-MS using cool on-column injection and negative chemical ionization. The method increased the recovery of the more volatile products, generated higher accuracy and was extensively time-saving compared to the conventional EPA (US Environmental Protection Agency) 8330 method. Applications are demonstrated on commercial reference materials.

Comparing columns for gas chromatography with the two-parameter model for retention prediction.

The retention times of selected compounds in temperature programmed gas chromatography were predicted using a two-parameter model, on the basis of thermodynamic data obtained from isothermal runs on seven capillary columns, primarily substituted with 5% diphenylsiloxane. The scope for using thermodynamic data obtained from isothermal runs on one column to optimize separation on a different column or a different instrument setup was investigated. Additionally, the predictive utility of thermodynamic data obtained using a DB-5 column that had been in use for three years was compared to that of a new column of the same model. It was found that satisfactory separation could be achieved on one capillary column or instrument setup on the basis of thermodynamic data obtained using a different column or instrument set-up.

An automated multidimensional preparative gas chromatographic system for isolation and enrichment of trace amounts of xenon from ambient air.

The monitoring of radioactive xenon isotopes is one of the principal methods for the detection of nuclear explosions in order to identify clandestine nuclear testing. In this work, a miniaturized, multiple-oven, six-column, preparative gas chromatograph was constructed in order to isolate trace quantities of radioactive xenon isotopes from ambient air, utilizing nitrogen as the carrier gas. The multidimensional chromatograph comprised preparative stainless steel columns packed with molecular sieves, activated carbon, and synthetic carbon adsorbents (e.g., Anasorb®-747 and Carbosphere®). A combination of purification techniques--ambient adsorption, thermal desorption, back-flushing, thermal focusing, and heart cutting--was selectively optimized to produce a well-defined xenon peak that facilitated reproducible heart cutting and accurate quantification. The chromatographic purification of a sample requires approximately 4 h and provides complete separation of xenon from potentially interfering components (such as water vapor, methane, carbon dioxide, and radon) with recovery and accuracy close to 100%. The preparative enrichment process isolates and concentrates a highly purified xenon gas fraction that is suitable for subsequent ultra-low-level γ-, ß/γ-spectroscopic or high-resolution mass spectrometric measurement (e.g., to monitor the gaseous fission products of nuclear explosions at remote locations). The Xenon Processing Unit is a free-standing, relatively lightweight, and transportable system that can be interfaced to a variety of sampling and detection systems. It has a relatively inexpensive, rugged, and compact modular (19-inch rack) design that provides easy access to all parts for maintenance and has a low power requirement.

Study of the gas chromatographic behavior of selected alcohols and amines.

The gas chromatographic behavior of selected linear and non-linear alcohols and amines was investigated using four capillary columns containing phenyl substitution levels of 0%, 5%, and 50% and 50% cyanopropyl substitution. In a previous study, the positions of specific compounds inside the capillary column were iteratively modeled using only two thermodynamic parameters (ΔH and ΔS). The present study addresses the validation of the two-parameter model for retention time prediction for selected alcohols and amines using thermodynamic data obtained from as few as two data points. The difference between predicted and observed retention times under different temperature conditions was generally less than 1% of the experimental value and the predicted order of elution was correct in the used model.

Dynamic non-equilibrium SPME combined with GC, PICI, and ion trap MS for determination of organophosphate esters in air.

Methodology for time-weighted average (TWA) air measurements of semivolatile organophosphate triesters, widely used flame-retardants and plasticizers, and common indoor pollutants is presented. Dynamic non-equilibrium solid-phase microextraction (SPME) for air sampling, in combination with GC/PICI and ion trap tandem MS, yields a fast, almost solvent-free method with low detection limits. Methanol was used as reagent gas for PICI, yielding stable protonated molecules and few fragments. A field sampler, in which a pumped airflow over three polydimethylsiloxane (PDMS) 100-mum fibers in series was applied, was constructed, evaluated, and used for the measurements. The method LODs were in the range 2-26 ng m(-3) for a sampling period of 2 h. The uptake on the SPME fibers was shown to be about five times faster for triphenyl phosphate compared to the other investigated organophosphate esters, most likely due to more lipophilic properties of the aromatic compound. The boundary layer for triphenyl phosphate when using a 100-microm PDMS sorbent was determined to 0.08 mm at a linear air velocity of 34 cm s(-1). Five different organophosphate triesters were detected in air from a laboratory and a lecture hall, at concentrations ranging from 7 ng m(-3) up to 2.8 microg m(-3).

Study of mass transfer in a dynamic hollow-fibre liquid phase microextraction system.

The extraction characteristics of a dynamic hollow-fibre liquid phase microextraction system were investigated by studying the mass transfer and diffusion rates of dinitrophenols from plasma samples over the liquid membrane (dihexylether). The measured diffusion coefficients were compared with theoretical values calculated from Stokes diameters. The diffusion mechanism was simulated by computer and the most polar compounds, 2,4-dinitrophenol and 4,6-o-dinitrocresol, had associated diffusion coefficients that were close to the calculated theoretical values. 2-sec-Butyl-4,6 dinitrophenol and 2-tert-butyl-4,6-dinitrophenol, the compounds with the highest log P values, were retained by the polypropylene membrane, which reduced the experimentally observed diffusion rates to about half of the theoretical values. The retention was most likely due to dispersive forces interacting with the pore inner walls. Extraction was linearly correlated with time for all compounds and the repeatability was high (RSDs 7-11%), even for the shortest extraction times. Method LOD as the amount injected ranged between 0.3 and 3.1 ng for an extraction cycle of 213 s.

Prediction of retention times and peak widths in temperature-programmed gas chromatography using the finite element method.

Optimization of separations in gas chromatography is often a time-consuming task. However, computer simulations of chromatographic experiments may greatly reduce the time required. In this study, the finite element method was used to predict the retention times and peak widths of three analytes eluting from each of four columns during chromatographic separations with two temperature programs. The data acquired were displayed in predicted chromatograms that were then compared to experimentally acquired chromatograms. The differences between the predicted and measured retention times were typically less than 0.1%, although the experimental peak widths were typically 10% larger than expected from the idealized calculations. Input data for the retention and peak dispersion calculations were obtained from isothermal experiments, and converted to thermodynamic parameters.

Retention time prediction of compounds in Grob standard mixture for apolar capillary columns in temperature-programmed gas chromatography.

This paper presents an extension of a previous investigation in which the behavior of nonpolar compounds in temperature-programmed gas chromatographic runs was predicted using thermodynamic (entropy and enthalpy) parameters derived from isothermal runs. In a similar manner, entropy and enthalpy parameters were determined for a Grob standard mixture of compounds with widely varying chemical characteristics. These parameters were used to predict the retention times and chromatographic behaviors of the compounds on four gas chromatography capillary columns: three that had phenyl-based stationary phases (with degrees of substitution of 0%, 5% and 50%) and one with (50%) cyanopropyl substitution. The predictions matched data empirically obtained from temperature-programmed chromatographic runs for all of the compounds extremely well, despite the wide variations in polarity of both the compounds and stationary phases. Thus, the results indicate that such simulations could greatly reduce the time and material costs of chromatographic optimizations.

Prediction of retention times of polycyclic aromatic hydrocarbons and n-alkanes in temperature-programmed gas chromatography.

We have developed an iterative procedure for predicting the retention times of polycyclic aromatic hydrocarbons (PAHs) and n-alkanes during separations by temperature-programmed gas chromatography. The procedure is based on estimates of two thermodynamic properties for each analyte (the differences in enthalpy and entropy associated with movements between the stationary and mobile phases) derived from data acquired experimentally in separations under isothermal conditions at temperatures spanning the range covered by the temperature programs in ten-degree increments. The columns used for this purpose were capillary columns containing polydimethylsiloxane-based stationary phases with three degrees of phenyl substitution (0%, 5%, and 50%). Predicted values were mostly within 1% of experimentally determined values, implying that the method is stable and precise.

Investigation of a cylindrical chemosorptive denuder for sampling and phase separation of toluene diisocyanate aerosols.

A cylindrical chemosorptive denuder in series with a glass fibre filter has been evaluated for sampling toluene diisocyanate (TDI) aerosols. The sampler is designed for measuring personal exposure to diisocyanates. Several denuder coatings and derivatising reagents were investigated. Dimethylpolysiloxane (SE-30) and 5% phenyl dimethylpolysiloxane (SE-54) with either dibutylamine (DBA) or dipentylamine (DPeA) as derivatising reagents yielded the lowest vapour breakthrough (the amount (%) of the vapour that passes through the denuder), close to values predicted by theory. Immobilisation of the SE-30 denuder coating by in-situ cross-linking yielded comparable results. With an SE-30/DBA-coated denuder operating within an airflow range of 100-500 mL min(-1), the phase separation was shown to be consistent with theoretical predictions derived by use of the Gormley-Kennedy equation. This provides a means of calculating the vapour breakthrough and correcting experimentally obtained values with regard to vapour-particulate phase distribution, suggesting that the denuder can provide accurate phase-distribution measurements. The SE-30/DBA denuder can be used over a concentration range spanning nearly six orders of magnitude. Its capacity is sufficient to perform 15-min exposure measurements of a TDI aerosol with air concentrations as high as 1,700 microg m(-3), 40 times higher than the Swedish occupational exposure limit (OEL). At the other end of the range, the estimated limit of detection (LOD) was less than 2 ng m(-3) for both the vapour and the aerosol phases when LC-ESI-MS-MS was used for chemical analysis.

A chemosorptive cylindrical denuder designed for personal exposure measurements of isocyanates-evaluation on generated aerosols of 4,4'-methylenediphenyl diisocyanate.

A denuder/filter system constructed for solvent-free personal exposure measurements was evaluated for separation of vapour and particulate 4,4'-methylenediphenyl diisocyanate (4,4'-MDI) generated from heated PUR-foam. The two different phases were collected in the denuder and on the filter, respectively, by chemosorption on a polydimethylsiloxane (SE-30)-dibutylamine (DBA) stationary phase. Both repeatability and the total mass concentration of 4,4'-MDI were similar to that obtained from the reference method, in this case an impinger/filter system. The penetration of particles through the denuder at 300 ml min(-1) was nearly 100% in the particle size range 25 to 700 nm, which fits well with the Gormley-Kennedy equation. Denuder/filter sampling of the 4,4'-MDI aerosol at 500 ml min(-1) yielded a phase distribution that was in accordance with the results from the reference method. The method limit of detection was 6 ng m(-3) and 4 ng m(-3) for the denuder and filter, respectively, when using an air sampling flow rate of 300 ml min(-1) and a sampling period of 15 min. This is well below the Swedish occupational exposure limit (OEL) of 50 and 100 microg m(-3) for an 8-hour working day and a 5-min period, respectively.

Evaluation of solid-phase microextraction with PDMS for air sampling of gaseous organophosphate flame-retardants and plasticizers.

As an inexpensive, simple, and low-solvent consuming extraction technique, the suitability of solid-phase microextraction (SPME) with polydimethylsiloxane (PDMS) sorbent was investigated as a quantitative method for sampling gaseous organophosphate triesters in air. These compounds have become ubiquitous in indoor air, because of their widespread use as additive flame retardants/plasticizers in various indoor materials. Results obtained by sampling these compounds at controlled air concentrations using SPME and active sampling on glass fibre filters were compared to evaluate the method. A constant linear airflow of 10 cm s(-1) over the fibres was applied to increase the extraction rate. For extraction of triethyl phosphate with a 100-microm PDMS fibre, equilibrium was achieved after 8 h. The limit of detection was determined to be less than 10 pg m(-3). The PDMS-air partition coefficients, Kfs, for the individual organophosphate triesters were determined to be in the range 5-60 x 10(6) at room temperature (22-23 degrees C). Air measurements were performed utilising the determined coefficients for quantification. In samples taken from a lecture room four different airborne organophosphate esters were identified, the most abundant of which was tris(chloropropyl) phosphate, at the comparatively high level of 1.1 microg m(-3). The results from SPME and active sampling had comparable repeatability (RSD less than 17%), and the determined concentrations were also similar. The results suggest that the investigated compounds were almost entirely associated with the gaseous phase at the time and place sampled.

Air sampling of organophosphate triesters using SPME under non-equilibrium conditions.

Solid phase micro-extraction (SPME) was used to collect air samples of semi-volatile organophosphate triesters, a group of compounds that are commonly used as flame retardants/plasticisers and have therefore become ubiquitous indoor air pollutants. SPME is a simple sampling technique with several major advantages, including time-efficiency and low solvent consumption. Analyte losses also tend to be relatively low. In quantitative SPME, measurements are normally taken after the analyte has reached partitioning equilibrium between the fibre and the sample matrix. However, equilibrium sampling of semi-volatile compounds in air with SPME often takes several hours. Clearly, time-weighted average (TWA) sampling using SPME under non-equilibrium conditions could be considerably faster. So, in this study, the possibility of sampling organophosphate triesters under non-equilibrium conditions was tested. The most important variables proved to be the fibre coating and the air velocity during sampling. The highest uptake rate was obtained with polydimethylsiloxane (PDMS, 100 microm). The rate for this fibre was 150-fold higher than obtained with PDMS/DVB and Carbowax/DVB, both 65 microm. Contrary to theoretical expectations, the uptake rate appeared to be constant for all tested air velocities over the fibre surface >7 cm/s. These findings suggest that the uptake rate for non-equilibrium SPME sampling is independent of the sampling flow above this flow rate, which would considerably enhance the robustness and flexibility of the method. Applying this method for TWA sampling, with sampling periods of 1 h, detection limits lower than 2 ng/m(3) for individual organophosphate esters were obtained.

Enhanced detection of nitroaromatic explosive vapors combining solid-phase extraction-air sampling, supercritical fluid extraction, and large-volume injection-GC.

A complete method for sampling and analyzing of energetic compounds in the atmosphere is described. The method consists of the hyphenation of several techniques: active air sampling using a solid-phase extraction cartridge to collect the analytes, extraction of the sorbed analytes by toluene/methyl tert-butyl ether modified supercritical fluid extraction (SFE), and analysis of the extract by large-volume injection GC-nitrogen/phosphorus detection. The GC system is equipped with a loop-type injection interface with an early solvent vapor exit, a utilizing concurrent solvent evaporation technique. Chemometric approaches, based on a Plackett-Burman screening design and a central composite design for response surface modeling, were used to determine the optimum SFE conditions. The relative standard deviations of the optimized method were determined to be 4.3 to 7.7%, giving raise to method detection limits ranging from 0.06 to 0.36 ng in the sampling cartridge, equivalent to 6.2-36.4 pg/L in the atmosphere, standard sampling volume 10 L. The analytical method was applied to characterize headspace composition above military grade trinitrotoluene (TNT). Results confirm that 2,4-dinitrotoluene (DNT) and 1,3-dinitrobenzene (DNB) constitute the largest vapor flux, but TNT, 2,6-DNT, and trinitrobenzene TNB were also consistently detected in all the samples.

Determination of organophosphate esters in air samples by dynamic sonication-assisted solvent extraction coupled on-line with large-volume injection gas chromatography utilizing a programmed-temperature vaporizer.

An on-line method for the determination of airborne organophosphate esters based on dynamic sonication-assisted solvent extraction and large-volume injection (LVI) gas chromatography with nitrogen-phosphorous detection is introduced. The LVI is performed with a programmed-temperature vaporizer. The entire extracted fraction of 800 microl (hexane-methyl-tert.-butyl ether, 7:3, v/v) is introduced directly into the GC system without any clean-up step following extraction. The extraction and analysis step were completed in less than 15 min. The limit of detection of the investigated organophosphate esters was established to be in the range of 5-32 pg/filter. The correlation coefficients (r2) were investigated in the linear range study of the entire system and established to be approximately 0.9900 for all the investigated organophosphates esters. Applications of the method was demonstrated with the extraction of air samples collected onto glass fiber filters from different indoor environments. Six organophosphate esters were found at the levels 0.4-138 ng/m3.