New trends in sample preparation for clinical and pharmaceutical analysis

Single-drop microextraction in bioanalysis

Bioanalysis usually requires a preparation procedure for sample cleanup or preconcentration. Conventional sample preparation techniques are often time consuming and labor intensive. Among recent progress in sample preparation, single drop microextraction (SDME) is one of the most efficient techniques providing both sample cleanup and preconcentration capabilities. In SDME, analytes are extracted from a sample solution into an acceptor drop and the drop is introduced to subsequent analysis. Since the volume of the acceptor drop is 1–10 µl or less, the consumption of solvents can be minimized and the preconcentration effect is enhanced. In this review, the basic principles of two-phase and three-phase SDME are described briefly and then recently developed modes of SDME, coupling with analytical instruments, and methods to enhance the drop stability are discussed. Recent applications of SDME to biological samples, including urine, blood and saliva, for the analysis of drugs, metal ions and biomarkers are reviewed.

Advanced CE for chiral analysis of drugs, metabolites, and biomarkers in biological samples

An analysis of recent trends indicates that CE can show real advantages over chromatographic methods in ultratrace enantioselective determination of biologically active compounds in complex biological matrices. It is due to high separation efficiency and many applicable in-capillary electromigration effects in CE (countercurrent migration, stacking effects) enhancing significantly (enantio)separability and enabling effective sample preparation (preconcentration, purification, analyte derivatization). Other possible on-line combinations of CE, such as column coupled CE-CE techniques and implementation of nonelectrophoretic techniques (extraction, membrane filtration, flow injection) into CE, offer additional approaches for highly effective sample preparation and separation. CE matured to a highly flexible and compatible technique enabling its hyphenation with powerful detection systems allowing extremely sensitive detection (e.g. LIF) and/or structural characterization of analytes (e.g. MS). Within the last decade, more as well as less conventional analytical on-line approaches have been effectively utilized in this field and their practical potentialities are demonstrated on many new application examples in this article. Here, three basic areas of (enantioselective) drug bioanalysis are highlighted and supported by a brief theoretical description of each individual approach in a compact review structure (to create integrated view on the topic), including (i) progressive enantioseparation approaches and new enantioselective agents, (ii) in-capillary sample preparation (preconcentration, purification, derivatization), and (iii) detection possibilities related to enhanced sensitivity and structural characterization.

Liquid-phase microextraction combined with high-performance liquid chromatography for the enantioselective analysis of mefloquine in plasma samples

A simple and rapid method, which involves liquid-phase microextraction (LPME) followed by HPLC analysis using Chiralpak AD column and UV detection, was developed for the enantioselective determination of mefloquine in plasma samples. Several factors that influence the efficiency of three-phase LPME were investigated and optimized. Under the optimal extraction conditions, the mean recoveries were 33.2 and 35.0% for (-)-(SR-)-mefloquine and (+)-(RS)-mefloquine, respectively. The method was linear over 50-1500 ng/ml range. Within-day and between-day assay precision and accuracy were below 15% for both enantiomers at concentrations of 150, 600 and 1200 ng/ml. Furthermore, no racemization or degradation were seen with the method described.

In vivo sampling with solid phase microextraction

This review discusses the most recent developments and future challenges in the application of solid phase microextraction (SPME) for sampling of live biological samples. The emphasis is placed on applications of fiber SPME for analysis of volatile emissions and drugs in biological fluids. The method development section highlights the main parameters that need to be considered in the case of in vivo experiments: extraction techniques, selection of extraction phases, calibration procedures, determination of free concentrations, and automation.

Analysis of abietic acid and dehydroabietic acid in food samples by in-tube solid-phase microextraction coupled with liquid chromatography-mass spectrometry

A simple and sensitive method for the determination of abietic acid and dehydroabietic acid in food samples was developed using a fully automated method consisting of in-tube solid-phase microextraction (SPME) coupled with liquid chromatography-mass spectrometry (LC/MS). These compounds were separated within 5min by HPLC using an ODS-3 column and 5mM ammonium formate/acetonitrile (10/90, v/v). Electrospray ionization conditions in the negative ion mode were optimized for MS detection of abietic acid and dehydroabietic acid. The optimum in-tube SPME conditions were 20draw/eject cycles of 40microL of sample using a Supel Q PLOT capillary column as an extraction device. The extracted compounds were easily desorbed from the capillary by passage of the mobile phase, and no carryover was observed. Using the in-tube SPME LC/MS method, good linearity of the calibration curve (r>0.9998) was obtained in the concentration range from 0 to 50ng/mL, and the detection limits (S/N=3) of abietic acid and dehydroabietic acid were 2.9 and 2.1pg/mL, respectively. The in-tube SPME method showed above 75-fold greater sensitivity than the direct injection method (5microL injection). This method was applied successfully to analysis of food samples without interference peaks. The recoveries of abietic acid and dehydroabietic acid spiked into liquid samples were above 79%, and the relative standard deviations were below 6.6%. These compounds were detected at ng/mL or ng/g levels in various liquid or solid food samples contacted with paper.

Pseudo-homogeneous micelle extraction of ion-associates formed between tetrabutylammonium ion and some aromatic sulfonate ions into nonionic surfactant micelle studied through the mobility measurements in capillary zone electrophoresis

Ion-association extraction of some aromatic sulfonate ions including alkylbenzene sulfonates with tetrabutylammonium ion (TBA+) into nonionic surfactant micelle has been investigated through the changes in the electrophoretic mobility. Nonionic surfactants of Brij 35 and Brij 58 were used as micelle substrates to which the ion-associates formed could distribute. The electrophoretic mobility of the aromatic sulfonate ions was measured by capillary zone electrophoresis in the presence of TBA+ and/or the nonionic surfactant to determine ion-association constants (K(ass)), binding constants of the anions to the nonionic surfactant micelle (K(B)), and binding constants of the ion-associates to the nonionic surfactant micelle (K(B,IA)). Nonlinear phenomena induced with the alkyl chain moiety were observed on K(ass) and K(B) by its linear structure and the mixed micelle formation, respectively. Larger K(B) values were obtained with Brij 58 as micelle matrix than with Brij 35, while the differences in K(B,IA) were small between Brij 58 and Brij 35.

Ion-association extraction of nitrophenolate ions with tetrabutylammonium ion into nonionic surfactant micelle

Ion-association extraction of some nitrophenolate ions with tetrabutylammonium ion (TBA(+)) into nonionic surfactant micelle has been investigated through the changes in the electrophoretic mobility. Nonionic surfactants of Brij 35 and Brij 58 were used as micelle substrates to which the ion-associates formed could distribute. The electrophoretic mobility of the phenolate ions was measured by capillary zone electrophoresis in the presence of TBA(+) and/or the nonionic surfactant. The electrophoretic mobility of the analyte anions decreased with increasing concentrations of the interacting reagent. Ion association constants (K(ass)) between TBA(+) and the phenolate ions, as well as binding constants of the anions to the nonionic surfactant micelle (K(B)), were determined through the mobility change by applying it to a non-linear least-squares analysis. Binding of the ion-associates was also observed from the aqueous phase to the micelle phase, when both TBA(+) and the nonionic surfactant are present. Binding constants of the ion-associates to the nonionic surfactant micelle (K(B,IA)), as well as micelle extraction constants of the ion-associates (K(ex,m)), were also determined by using the mobility change. The K(ex,m) values obtained were compared with the ion association-solvent extraction constants (K(ex,S)) between water and chloroform.

Centrifuge Microextraction Coupled with On-Line Back-Extraction Field-Amplified Sample Injection Method for the Determination of Trace Ephedrine Derivatives in the Urine and Serum

Although sample stacking has enjoyed some degree of success in electrophoretic separation techniques, there is still a major problem with complex matrix sample as it suffers tremendously from sample matrix effects. A novel method that combines two concentration techniques, centrifuge microextraction (CME) and on-line back-extraction field-amplified sample injection (OLBE-FASI), is used to determine trace ephedrine derivatives in urine and serum by capillary zone electrophoresis. The CME, integrating the sample cleanup and preconcentration into a single step, is a promising sample preparation method for biological samples. The CME technique provided 9-14-fold enrichment within 10 min. The OLBE-FASI eliminated the need to perform solvent exchange and provided a further concentration of the analytes. Using CME coupled with OLBE-FASI, over a 3800-fold increase in sensitivity could be obtained as compared with the normal hydrodynamic injection without sample stacking. For a 1-mL urine sample, the linear range was 5/10-200 ng/mL with the square of the correlation coefficients (r(2)) ranging from 0.9988 to 0.9994. Detection limits were from 0.15 to 0.25 ng/mL using a photodiode array UV detection at wavelength 192 nm. The possibility of this method to determine ephedrine derivatives in 20-muL serum samples was also demonstrated.

Fast and sensitive environmental analysis utilizing microextraction in packed syringe online with gas chromatography–mass spectrometry

A new sensitive, selective, fast and accurate technique for online sample preparation was developed. Microextraction in a packed syringe (MEPS) is a new miniaturised, solid-phase extraction (SPE) technique that can be connected online to GC or LC without any modifications. In MEPS approximately 1mg of the solid packing material is inserted into a syringe (100-250 ml) as a plug. Sample preparation takes place on the packed bed. The bed can be coated to provide selective and suitable sampling conditions. The new method is very promising. It is very easy to use, fully automated, of low cost and rapid in comparison with previously used methods. The determination of polycyclic hydrocarbons (PAHs) in water was performed using MEPS as sample preparation method online with gas chromatography and mass spectrometry (MEPS-GC-MS). The results from MEPS as sample preparation were compared with other techniques such as stir bar sorptive extraction (SBSE) and solid-phase microextraction (SPME). The method was validated and the standard curves were evaluated by the means of quadratic regression and weighted by inverse of the concentration: 1/x for the calibration range 5-1,000 ng/L. The MEPS applied polymer (silica-C8) could be used more than 400 times before the syringe was discarded. The extraction recovery was about 70%. The results showed close correlation coefficients (R>0.998) for all analytes in the calibration range studied. The accuracy of MEPS-GC-MS was between 90 and 113% and the inter-day precision (n=3 days), expressed as the relative standard deviation (RSD%), was 8-16%. MEPS reduced the handling time by 30 and 100 times compared to SPME and SBSE, respectively.

Automated microcolumn-switching system for drug analysis by direct injection of human plasma

This study presents the application of a system that joins the known advantages of capillary liquid chromatography (e.g., higher concentration of the analytes and lower consumption of mobile phase) with those of column-switching using restricted access material (RAM) (sample clean up and extraction) to the analysis of fluoxetine in plasma samples. Automatically, the system loads the biological sample, while a RAM-BSA-C18 column (50 mm x 520 microm) excludes the macromolecules and focuses the analytes; afterwards, a second mobile phase elutes the analytes, in backflush mode, and provides the separation in a C18 analytical column (100 mm x 520 microm). We optimized the procedure for a total analysis time of 25 min. Using this approach the calibration curve shows r=0.998 with a linearity range from 20 to 500 ng ml(-1). Precision, calculated as relative standard deviation (RSD), was<20%. The developed miniaturized system showed to be adequate and attractive, demonstrating a large potential for sample preparation.

Sensitive chiral analysis by capillary electrophoresis

In this review, an updated view of the different strategies used up to now to enhance the sensitivity of detection in chiral analysis by CE will be provided to the readers. With this aim, it will include a brief description of the fundamentals and most of the recent applications performed in sensitive chiral analysis by CE using offline and online sample treatment techniques (SPE, liquid-liquid extraction, microdialysis, etc.), on-column preconcentration techniques based on electrophoretic principles (ITP, stacking, and sweeping), and alternative detection systems (spectroscopic, spectrometric, and electrochemical) to the widely used UV-Vis absorption detection.

Application of sequential injection analysis to pharmaceutical analysis

Sequential injection analysis is a well established tool for automation of pharmaceutical analysis. A short historical background of this technique is given as well as a brief discussion on the basic principles and potentials. The current applications of SIA in the pharmaceutical analysis are also described and discussed. The manifolds developed offer good analytical characteristics and are suitable for analysis of drug formulations, process analysis, drug-dissolution, drug-release testing and functional assays for screening potential drugs. The results obtained are in good agreement with those furnished by the application of the reference methods presented in the pharmacopoeias.

Fully automated analysis of estrogens in environmental waters by in-tube solid-phase microextraction coupled with liquid chromatography–tandem mass spectrometry

A simple, rapid and sensitive method for the determination of five estrogens, estrone, 17beta-estradiol, estriol, ethynyl estradiol, and diethylstilbestrol, was developed using a fully automated method consisting of in-tube solid-phase microextraction (SPME) coupled with liquid chromatography-tandem mass spectrometry (LC/MS/MS). These estrogens were separated within 8 min by HPLC using an XDB-C8 column and 0.01% ammonia/acetonitrile (60/40, v/v) at a flow rate of 0.2 mL/min. Electrospray ionization conditions in the negative ion mode were optimized for MS/MS detection of the estrogens. The optimum in-tube SPME conditions were 20 draw/eject cycles of 40 microL of sample using a Supel-Q PLOT capillary column as an extraction device. The extracted compounds were easily desorbed from the capillary by passage of the mobile phase, and no carryover was observed. Using the in-tube SPME LC/MS/MS method, good linearity of the calibration curve (r > or = 0.9996) was obtained in the concentration range from 10 to 200 pg/mL for all compounds examined. The limits of detection (S/N= 3) of the five estrogens examined ranged from 2.7 to 11.7 pg/mL. The in-tube SPME method showed 34-90-fold higher sensitivity than the direct injection method (5 microL injection). This method was applied successfully to the analysis of environmental water samples without any other pretreatment and interference peaks. Several surface water and wastewater samples were collected from the area around Asahi River, and estriol was detected at 35.7 pg/mL in the effluent of a sewage treatment plant. The recoveries of estrogens spiked into river waters were above 86%, except for estriol, and the relative standard deviations were below 0.9-8.8%.

Molecularly-imprinted polypyrrole-modified stainless steel frits for selective solid phase preconcentration of ochratoxin A

A molecularly-imprinted polymer (MIP) was prepared by electropolymerization of pyrrole (Py) onto a stainless steel frit, using ochratoxin A (OTA) as the template, in order to make a micro solid phase preconcentration (microSPP) device. The OTA template was removed with 1% triethylamine (TEA) in methanol. Compared to non-imprinted polypyrrole (PPy), the molecularly-imprinted polypyrrole (MIPPy) enhanced the selective binding of OTA. The percentage recovery improved from 0 to 40% when the OTA sample solution was acidified with 1 M HCl (1% by volume). At a flow rate of 0.2 mL/min, maximum OTA binding was reached in 6 min after a total loading of 3.2 ng OTA. Final elution of the OTA was analyzed by high performance liquid chromatography (HPLC) with fluorescence detection, using 20:80 v/v acetonitrile-ammonia buffer (NH4Cl/NH3, 20 mM, pH 9.2) as the mobile phase. The MIPPy-microSPP-HPLC results clearly demonstrated that the MIPPy-microSPP device afforded selective preconcentration of OTA from red wine samples, at OTA concentration levels as low as 0.05 ppb, prior to HPLC analysis.

Development of a High-Throughput Format for Solid-Phase Extraction of Enantiomers Using an Immunosorbent in 384-Well Plates

An antibody-based solid-phase extraction method for filtered 384-well plates was developed for a medical drug candidate having two enantiomeric forms in order to demonstrate the potential of the use of recombinant antibody fragments as specific and efficient immunosorbents. An immobilization method using a six-histidine tag of the antibody fragment and mild oxidation was applied in order to immobilize antibody fragments in an oriented and kinetically stable way that ensured high capacity of the antibody support. Phosphate buffer or plasma spiked with enantiomers were used as samples. Selective solid-phase extraction was followed by liquid chromatography-mass spectrometry analysis. Average recoveries for buffer and plasma samples ranged from 79 to 122% and 80 to 108%, respectively. Good linearity was observed in the concentration range of 30-3000 ng/mL of the enantiomer.

Development of headspace solid-phase microextraction–gas chromatography method for the determination of solvent residues in edible oils and pharmaceuticals

The application of headspace solid-phase microextraction for isolation and enrichment of solvent residues from oils and pharmaceuticals is discussed. The optimal parameters for isolation and preconcentration of common process solvents (hexane, benzene, toluene and selected chloroderivatives of hydrocarbons) were established. Four fiber types (100 microm polydimethylsiloxane (PDMS), 75 microm Carboxen-PDMS, 65 microm PDMS-divinylbenzene and 85 microm polyacrylate) were evaluated to choose the most efficient coating, able to absorb the greatest amount of analytes. GC-flame ionization detection (FID) and GC-electron-capture detection systems were used for quantitative and qualitative analysis, adequately to the appropriate group of the analytes. For all compounds the limit of detection (LOD), linearity, dynamic range, repeatability and intermediate precision were estimated.