Erasmus Cudjoe

Solid-phase microextraction in bioanalysis: New devices and directions

The primary objective of this review is to discuss recent technological developments in the field of solid-phase microextraction that have enhanced the utility of this sample preparation technique in the field of bioanalysis. These developments include introduction of various new biocompatible coating phases suitable for bioanalysis, such as commercial prototype in vivo SPME devices, as well as the development of sampling interfaces that extend the use of this methodology to small animals such as mice. These new devices permit application of in vivo SPME to a variety of analyses, including pharmacokinetics, bioaccumulation and metabolomics studies, with good temporal and spatial resolution. New calibration approaches have also been introduced to facilitate in vivo studies and provide fast and quantitative results without the need to achieve equilibrium. In combination with the drastic improvement in the analytical sensitivity of modern liquid chromatography-tandem mass spectrometry instrumentation, full potential of in vivo SPME as a sample preparation tool in life sciences can finally be explored. From the instrumentation perspective, SPME was successfully automated in 96-well format for the first time. This opens up new opportunities for high-throughput applications (>1000 samples/day) such as for the determination of unbound and total drug concentrations in complex matrices such as whole blood with no need for sample pretreatment, studies of distribution of drugs in various compartments and/or determination of plasma protein binding and other ligand-receptor binding studies, and this review will summarize the progress in this research area to date.

SPME – Quo vadis?

Solid phase microextraction (SPME) has experienced rapid development and growth in number of application areas since its inception over 20 years ago. It has had a major impact on sampling and sample preparation practices in chemical analysis, bioanalysis, food and environmental sciences. A significant impact is expected in clinical analysis as well as pharmaceutical and medical sciences in the near future. In this review, recent developments of SPME and related technologies are discussed including an in-vial standard gas system for calibration of SPME in high throughput mode; a thin film geometry with high extraction efficiency SPME for gas chromatography (GC) and liquid chromatography (LC) analyses; and couplings of SPME with portable instruments permitting on-site measurements. Also, the latest advances in the preparation of sorbents applicable for direct extraction from complex biological matrices as well as applications of these extraction phases in food analysis and biomedical studies such as therapeutic drug monitoring and pharmacokinetics are described. Finally, recent trends in metabolomics analysis and examples of clinical monitoring of biomarkers with SPME are reviewed.

Automation of solid-phase microextraction in high-throughput format and applications to drug analysis.

The automation of solid-phase microextraction (SPME) coupled to liquid chromatography-tandem mass spectrometry (LC-MS/MS) was accomplished using a 96 multiwell plate format, a SPME multifiber device, two orbital shakers, and a three-arm robotic system. Extensive optimization of the proposed setup was performed including coating selection, optimization of the fiber coating procedure, confirmation of uniform agitation in all wells, and the selection of the optimal calibration method. The system allows the use of pre-equilibrium extraction times with no deterioration in method precision due to reproducible timing of extraction and desorption steps and reproducible positioning of all fibers within the wells. The applicability of the system for the extraction of several common drugs is demonstrated. The optimized multifiber SPME-LC-MS/MS was subsequently fully validated for the high-throughput analysis of diazepam, lorazepam, nordiazepam, and oxazepam in human whole blood. The proposed method allowed the automated sample preparation of 96 samples in 100 min, which represents the highest throughput of any SPME technique to date, while achieving excellent accuracy (87-113%), precision (<or=20% RSD), and sensitivity (limit of quantitation 4 ng/mL). Automated SPME provides unique advantages over automated solid-phase extraction (SPE) including lower cost, the ability to quantitatively determine free and total drug concentrations in a single biofluid sample, and the ability to directly process whole blood samples with absolutely no sample pretreatment required.

Automated solid-phase microextraction and thin-film microextraction for high-throughput analysis of biological fluids and ligand-receptor binding studies.

This protocol describes how to perform automated solid-phase microextraction (SPME) and thin-film microextraction (TFME) in a 96-well plate format for high-throughput analysis of drugs, metabolites and any other analytes of interest in biological fluids using liquid chromatography–electrospray tandem mass spectrometry. Sample preparation time required is typically 1 min per sample; hence, the throughput achievable with automated SPME/TFME is comparable with automated 96-well liquid–liquid extraction and solid-phase extraction methods, but greater than most online solid-phase extraction methods. The technique is applicable to complex samples such as whole blood without additional pretreatment. The amount of analyte extracted by SPME/TFME is proportional to the free (unbound) concentration of the analyte; hence, SPME/TFME can be used to determine both total and free concentrations of analytes from a single biofluid sample and to perform automated ligand–receptor binding studies in order to determine binding affinity and/or overall extent of ligand binding to a complex biofluid.

Investigation of the Effect of the Extraction Phase Geometry on the Performance of Automated Solid-Phase Microextraction

A new configuration of C(18) thin film extraction phase designed for high sample throughput has been developed and applied to the analysis of benzodiazepines in spiked urine samples using high performance liquid chromatography coupled with tandem mass spectrometry. The high throughput analysis was achieved with the use of a robotic autosampler which enabled parallel analyte extraction in a 96-well plate format. Factors affecting data reproducibility, extraction kinetics, sample throughput, and reliability of the system were investigated and optimized. The intrawell reproducibility was 4.5-7.3%, while interwell reproducibility was 7.0-11% in urine and PBS samples. The limits of detection and quantitation were 0.05-0.15 ng/mL and 0.2-2.0 ng/mL for all analytes, respectively. By comparison with optimized automated multifiber SPME relying on rod geometry, the C(18) thin films showed higher extraction rates (approximate 2-fold increase) and hence higher sample throughput because of the improved configuration and more effective agitation/mass transfer. In addition, this new configuration provided an extraction phase with greater surface area to volume ratio and greater extraction phase volume, which resulted in approximately 2-fold increase in the extraction capacity for diazepam compared with the extractions with automated multifiber SPME rod geometry. The results of this investigation demonstrated the advantages of using thin films to improve extraction kinetics and sensitivity of automated SPME methods for high performance liquid chromatography.

Solid-Phase Microextraction: A Complementary In Vivo Sampling Method to Microdialysis†

Given the intricate organization of the brain, tissue sampling for chemical profiling studies have always been a challenging task. It is often exceptionally difficult to obtain homogeneous samples for in vitro/ex vivo experiments without altering or losing valuable information. The obvious approach has been to develop in vivo analytical methods that may cause minimal perturbation to this complex chemical network so as to improve overall reliability of acquired information. Methods such as biosensors and microdialysis (MD) are among sampling methods applied to in vivo brain chemical profiling studies despite their unique challenges. MD is a well-established in vivo analytical sampling method used over the years for monitoring often low-molecular-weight hydrophilic compounds from the interstitial space. The successful application of the method to neuroscience, especially monitoring of neurotransmitters, led to its expansion to a wider range of analytes, including drugs, metabolites, and peptides. A major challenge, however, associated with MD is its difficulty in sampling hydrophobic compounds. Hydrophobic compounds are often highly protein-bound and bind to the MD probe and tubing, thereby affecting relative recovery. The addition of modifiers, such as bovine serum albumin, glycerol in water, or cyclodextrin, is among the approaches that have been used to prevent hydrophobic interactions and to improve relative recoveries. But these techniques often may complicate the pharmacology of the neurological analytes, as the additives are known to interact with the tissue surrounding the probe. Thus, in typical global metabolomics studies, for example, the composition of a measured metabolome can be significantly affected by the analytical procedure, leaving the analysts with results which likely do not adequately reflect accurate composition of the metabolome during sampling. In effect, it will compromise the already challenging efforts in diagnosis, prognostics, and searching for potential biomarkers for therapeutic purposes. Herein, we demonstrate a novel application of solid-phase microextraction (SPME) for in vivo sampling for brain study. For the first time an application of in vivo SPME as a complementary method to MD for braintissue bioanalysis has been presented. Our technique was first validated against MD in targeted analysis of selected neurotransmitters. Their complementary nature was subsequently shown in global profiling of the brain metabolome. From the profiling study, SPME detected groups of lipids such as gangliosides, fatty acids, and lysophospholipids, which are of particular interest in relation to neurodegenerative diseases. SPME derives its selectivity from the extracting sorbent type. Thus, SPME provides the needed flexibility to analysts to tailor investigations to specific biologically hydrophilic/ hydrophobic compounds. For a global study of the metabolome, however, the sorbent choice is one of low selectivity; that is, the sorbent chemical property must enhance simultaneous extraction of hydrophilic and hydrophobic biochemical species. A unique advantage of the new biocompatible in vivo SPME probe is, it prevents extraction of proteins and other bio-interferences owing to the small pore size of the coating and the adhesive biocompatibility, and thus minimizes matrix effect significantly. Furthermore, the in vivo characteristics guarantees enriched chemical information for tissue bioanalysis over other methods when coupled to analytical techniques. Herein, we introduce in vivo SPME and MD coupled to liquid chromatography mass spectrometry (LC-MS) to study the chemical components of the brain extracellular fluid in freely moving rat. Briefly, the approach involved surgically implanting the two probes (SPME and MD), respectively, into the left and right hemispheres of the striata of freely moving rats for continuous chemical monitoring over a period of time. The SPME probe is a simple device placed in a commercial MD guide cannula without extended tubes to an external pumping system contrary to what is typical for the MD probe. Samples collected for both MD and SPME were subjected to a reversed reverse-phase chromatographic separation on a pentafluorophenyl stationary phase in a positive-mode mass spectrometry analysis. Knowing that SPME sorbent can extract relatively wider range of analytes, including hydrophobic biomolecules contrary to MD, initial investigations focused on the effectiveness of the sampling technique for monitoring small polar endogenous compounds in a targeted metabolomics study. Subsequently, we simultaneously monitored the effect of single dose (10 mgkg ) fluoxetine on multiple neurotransmitters: dopamine (DA), serotonin (5-HT), gamma aminobutyric acid (GABA), and glutamic acid (GA) using both SPME and MD. The purpose was to evaluate the ability of SPME to monitor at each time point changes in multiple neurochemicals with a single probe similar to MD. The [*] E. Cudjoe, Dr. B. Bojko, Prof. J. Pawliszyn Department of Chemistry, University of Waterloo 200 University Avenue, Waterloo, N2L 3G1 (Canada) E-mail: janusz@uwaterloo.ca Homepage: http://spme.uwaterloo.ca

Direct monitoring of ochratoxin A in cheese with solid-phase microextraction coupled to liquid chromatography-tandem mass spectrometry.

An in situ application of solid-phase microextraction (SPME) as a sampling and sample preparation method coupled to HPLC-MS/MS for direct monitoring of ochratoxin A (OTA) distribution at different locations in a single cheese piece is proposed. To be suited to the acidic analyte, the extraction phase (carbon-tape SPME fiber) was acidified with aqueous solution of HCl at pH 2, instead of the traditional sample pre-treatment with acids before SPME sampling. For calibration, kinetic on-fiber-standardization was used, which allowed the use of short sampling time (20 min) and accurate quantification of the OTA in the semi-solid cheese sample. In addition, the traditional kinetic calibration that used deuterated compounds as standards was extended to use a non-deuterated analogue ochratoxin B (OTB) as the standard of the analyte OTA, which was supported by both theoretical discussion and experimental verification. Finally, the miniaturized SPME fiber was adopted so that the concentration distribution of OTA in a small-sized cheese piece could be directly probed. The detection limit of the resulting SPME method in semi-solid gel was 1.5 ng/mL and the linear range was 3.5-500 ng/mL. The SPME-LC-MS/MS method showed good precision (RSD: approximately 10%) and accuracy (relative recovery: 93%) in the gel model. The direct cheese analysis showed comparable accuracy and precision to the established liquid extraction. As a result, the developed in situ SPME-LC-MS/MS method was sensitive, simple, accurate and applicable for the analysis of complicated lipid-rich samples such as cheese.

Determination of tranexamic acid concentration by solid phase microextraction and liquid chromatography–tandem mass spectrometry: First step to in vivo analysis

A solid phase microextraction (SPME) method followed by LC-MS/MS analysis was developed to determine the concentration of tranexamic acid (TA) in plasma. The use of a new biocompatible C18 coating allowed the direct extraction from complex biological samples without prior sample preparation; no matrix effect was observed. The results revealed that SPME was suitable for the analysis of polar drugs such as TA; such an application was previously inaccessible because of the limited availability of SPME coatings that can extract polar molecules. The proposed method was validated according to the bioanalytical method validation guidelines. LOD and LLOQ were 0.5 and 1.5 μg/ml, respectively. The recovery for the method was 0.19%, and the accuracy and precision of the method were <9 and <11%, respectively, with the exception of LLOQ, where the values were <16 and <13%, respectively. The performance of the proposed method was also compared against that of the standard techniques of protein precipitation and ultrafiltration. A statistical analysis indicated a clinically significant agreement among all assays. Another advantage of SPME over conventional techniques was the easy automation and feasibility of in vivo analysis; this advantage makes it possible to use the proposed method for an on-site analysis in clinical practice.

A new approach to the application of solid phase extraction disks with LC-MS/MS for the analysis of drugs on a 96-well plate format.

A new 96-well disk solid phase extraction sample preparation technique which does not involve vacuum pumps integrated with liquid chromatographic tandem mass spectrometric (LC-MS/MS) was developed for high throughput determination of benzodiazepines (nordiazepam, diazepam, lorazepam and oxazepam). In addition, the method completely allows the re-use of the SPE disk membranes for subsequent analyses after re-conditioning. The method utilizes a robotic autosampler for parallel extractions in a 96-well plate format. Results have been presented for independent extractions from three matrices; phosphate buffer solution, urine, and plasma. Factors affecting data reproducibility, extraction kinetics, sample throughput, and reliability of the system were investigated and optimized. A total time required per sample was 0.94 min using 96-well format. Method reproducibility was < or =9% relative standard deviation for all three matrices. Limits of detection and quantitation recorded were respectively in the range 0.02-0.15 and 0.2-2.0 ng/mL with linearity ranging from 0.2 to 500 ng/mL for all matrices.

Solid phase microextraction fills the gap in tissue sampling protocols.

Metabolomics and biomarkers discovery are an integral part of bioanalysis. However, untargeted tissue analysis remains as the bottleneck of such studies due to the invasiveness of sample collection, as well as the laborious and time-consuming sample preparation protocols. In the current study, technology integrating in vivo sampling, sample preparation and global extraction of metabolites--solid phase microextraction was presented and evaluated during liver and lung transplantation in pig model. Sampling approaches, including selection of the probe, transportation, storage conditions and analyte coverage were discussed. The applicability of the method for metabolomics studies was demonstrated during lung transplantation experiments.