Sanja Risticevic

Recent developments in solid-phase microextraction

AbstractThe main objective of this review is to describe the recent developments in solid-phase microextraction technology in food, environmental and bioanalytical chemistry applications. We briefly introduce the historical perspective on the very early work associated with the development of theoretical principles of SPME, but particular emphasis is placed on the more recent developments in the area of automation, high-throughput analysis, SPME method optimization approaches and construction of new SPME devices and their applications. The area of SPME automation for both GC and LC applications is particularly addressed in this review, as the most recent developments in this field have allowed the use of this technology for high-throughput applications. The development of new autosamplers with SPME compatibility and new-generation metal fibre assemblies has enhanced sample throughput for SPME-GC applications, the latter being attributed to the possibility of using the same fibre for several hundred extraction/injection cycles. For LC applications, high-throughput analysis (>1,000 samples per day) can be achieved for the first time with a multi-SPME autosampler which uses multi-well plate technology and allows SPME sample preparation of up to 96 samples in parallel. The development and evolution of new SPME devices such as needle trap, thin-film microextraction and cold-fibre headspace SPME have offered significant improvements in performance characteristics compared with the conventional fibre-SPME arrangement. FigurePhoto of a high-throughput multi-fibre SPME PAS autosampler

Protocol for solid-phase microextraction method development.

Solid-phase microextraction (SPME) is a sample preparation method developed to solve some of the analytical challenges of sample preparation as well as sample introduction and integration of different analytical steps into one system. Since its development, the utilization of SPME has addressed the need to facilitate rapid sample preparation and integrate sampling, extraction, concentration and sample introduction to an analytical instrument into one solvent-free step. This achievement resulted in fast adoption of the technique in many fields of analytical chemistry and successful hyphenation to continuously developing sophisticated separation and detection systems. However, the facilitation of high-quality analytical methods in combination with SPME requires optimization of the parameters that affect the extraction efficiency of this sample preparation method. Therefore, the objective of the current protocol is to provide a detailed sequence of SPME optimization steps that can be applied toward development of SPME methods for a wide range of analytical applications.

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.

Headspace solid-phase microextraction-gas chromatographic-time-of-flight mass spectrometric methodology for geographical origin verification of coffee

Increasing consumer awareness of food safety issues requires the development of highly sophisticated techniques for the authentication of food commodities. The food products targeted for falsification are either products of high commercial value or those produced in large quantities. For this reason, the present investigation is directed towards the characterization of coffee samples according to the geographical origin. The conducted research involves the development of a rapid headspace solid-phase microextraction (HS-SPME)-gas chromatography-time-of-flight mass spectrometry (GC-TOFMS) method that is utilized for the verification of geographical origin traceability of coffee samples. As opposed to the utilization of traditional univariate optimization methods, the current study employs the application of multivariate experimental designs to the optimization of extraction-influencing parameters. Hence, the two-level full factorial first-order design aided in the identification of two influential variables: extraction time and sample temperature. The optimum set of conditions for the two variables was 12 min and 55 degrees C, respectively, as directed by utilization of Doehlert matrix and response surface methodology. The high-throughput automated SPME procedure was completed by implementing a single divinylbenzene/carboxen/polydimethylsiloxane (DVB/CAR/PDMS) 50/30 microm metal fiber with excellent durability properties ensuring the completion of overall sequence of coffee samples. The utilization of high-speed TOFMS instrument ensured the completion of one GC-MS run of a complex coffee sample in 7.9 min and the complete list of benefits provided by ChromaTOF software including fully automated background subtraction, baseline correction, peak find and mass spectral deconvolution algorithms was exploited during the data evaluation procedure. The combination of the retention index (RI) system using C(8)-C(40) alkanes and the mass spectral library search was utilized for the confirmation of analyte identity in the reference authentic Brazilian coffee sample. The semi-quantitative results were then submitted to statistical evaluation, namely principal component analysis (PCA) for the establishment of geographical origin discriminations.

In vivo solid-phase microextraction in metabolomics: opportunities for the direct investigation of biological systems.

Sample preparation has a strong impact on the quality of metabolomics studies. The use of solid-phase microextraction (SPME), particularly its in vivo format, enables the capture of a more representative metabolome and presents opportunities to detect low-abundance, short-lived, and/or unstable species not easily captured by traditional methods. The technique is ideally suited for temporal, spatial, and longitudinal studies of the same living system, as well as multicompartmental studies of the same organism. SPME is useful for the investigation of biological systems ranging in complexity from cells to mammalian tissues. Selected examples are highlighted in this Minireview in order to place the technique within the context of conventional methods of sample preparation for metabolomics.

Solid phase microextraction coupled with comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry for high-resolution metabolite profiling in apples: implementation of structured separations for optimization of sample preparation procedure in complex samples.

Metabolomics currently represents one of the fastest growing high-throughput molecular analysis platforms that refer to the simultaneous and unbiased analysis of metabolite pools constituting a particular biological system under investigation. In response to the ever increasing interest in development of reliable methods competent with obtaining a complete and accurate metabolomic snapshot for subsequent identification, quantification and profiling studies, the purpose of the current investigation is to test the feasibility of solid phase microextraction for advanced fingerprinting of volatile and semivolatile metabolites in complex samples. In particular, the current study is focussed on the development and optimization of solid phase microextraction (SPME) - comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry (GC × GC-ToFMS) methodology for metabolite profiling of apples (Malus × domestica Borkh.). For the first time, GC × GC attributes in terms of molecular structure-retention relationships and utilization of two-dimensional separation space on orthogonal GC × GC setup were exploited in the field of SPME method optimization for complex sample analysis. Analytical performance data were assessed in terms of method precision when commercial coatings are employed in spiked metabolite aqueous sample analysis. The optimized method consisted of the implementation of direct immersion SPME (DI-SPME) extraction mode and its application to metabolite profiling of apples, and resulted in a tentative identification of 399 metabolites and the composition of a metabolite database far more comprehensive than those obtainable with classical one-dimensional GC approaches. Considering that specific metabolome constituents were for the first time reported in the current study, a valuable approach for future advanced fingerprinting studies in the field of fruit biology is proposed. The current study also intensifies the understanding of SPME-GC×GC-ToFMS hyphenation and outlines the benefits of facilitating GC×GC for SPME method optimization. The obtained results clearly illustrate that acquisition of a more complete metabolome snapshot is only attainable under optimized conditions for both techniques.

Protocol for the development of automated high-throughput SPME-GC methods for the analysis of volatile and semivolatile constituents in wine samples.

Ever since the invention of gas chromatography (GC), numerous efforts within the chromatographic community have been directed toward the development of fast GC methods. However, the developments in high-speed GC technologies have simultaneously created demand for the availability of compatible detection and sample preparation methods, so that the speed of the overall analytical process is increased. Solid phase micro extraction (SPME) is a sample preparation technique developed to address the need for rapid sample preparation. Therefore, the objective of this protocol is to outline recent developments in SPME technology that can be applied toward high-throughput automated qualitative and quantitative analyses of volatile and semivolatile compounds in wine samples. The use of this protocol facilitates routine high-throughput determinations of 200–500 analytes of different physicochemical properties with SPME step requiring only 10–15 min per sample.

Detection of extraction artifacts in the analysis of honey volatiles using comprehensive two-dimensional gas chromatography

Extraction using headspace solid phase microextraction (HS-SPME) coupled to comprehensive two-dimensional gas chromatography with flame ionisation detection (GC×GC-FID) was employed to evaluate the effect of SPME fractionation conditions (heating time and temperature) on the generation of artifacts. The occurrence of artifacts was more pronounced at higher fractionation temperatures and times which caused significant changes in the chromatographic profiles. The identification of the volatile fraction of the honey blend was performed through a two-dimensional gas chromatograph coupled to a mass spectrometer with time of flight analyser (GC×GC-ToFMS) by comparing the first dimension linear temperature programmed retention index ((1)D-LTPRI) with the peaks identities provided by the mass spectral similarity search. Several artifacts were found and identified - such as hydroxymethylfurfural, methyl-furone and furfural - and some of them were not previously detected as such in honey samples. These compounds were either the result of hydrolysis or thermal decomposition of components already present in the honey samples. This occurrence was attributed to the increased detectability provided by GC×GC compared to conventional GC. The possible emergence of previously unknown extraction artifacts as a general tendency related use of GC×GC instead of conventional GC is discussed as a result of these observations.

Simultaneous sampling and analysis of indoor air infested with Cimex lectularius L. (Hemiptera: Cimicidae) by solid phase microextraction, thin film microextraction and needle trap device.

Air in a room infested by Cimex lectularius L. (Hemiptera: Cimicidae) was sampled simultaneously by three different sampling devices including solid phase microextraction (SPME) fiber coatings, thin film microextraction (TFME) devices, and needle trap devices (NTDs) and then analyzed by gas chromatography-mass spectrometry (GC-MS). The main focus of this study was to fully characterize indoor air by identifying compounds extracted by three different microextraction formats and, therefore, perform both the device comparison and more complete characterization of C. lectularius pheromone. The NTD technique was capable of extracting both (E)-2-hexenal and (E)-2-octenal, which were previously identified as alarm pheromones of bedbugs, and superior NTD recoveries for these two components allowed reliable identification based on mass spectral library searching and linear temperature programmed retention index (LTPRI) technique. While the use of DVB/CAR/PDMS SPME fiber coatings provided complementary sample fingerprinting and profiling results, TFME sampling devices provided discriminative extraction coverage toward highly volatile analytes. In addition to two alarm pheromones, relative abundances of all other analytes were recorded for all three devices and aligned across all examined samples, namely, highly infested area, less infested area, and control samples which were characterized by different bedbug populations. The results presented in the current study illustrate comprehensive characterization of infested indoor air samples through the use of three different non-invasive SPME formats and identification of novel components comprising C. lectularius pheromone, therefore, promising future alternatives for use of potential synthetic pheromones for detection of infestations.

Evaluation of a completely automated cold fiber device using compounds with varying volatility and polarity

A fully automated cold fiber solid phase microextraction device has been developed by coupling to a GERSTEL multipurpose (MPS 2) autosampler and applied to the analysis of volatiles and semi-volatiles in aqueous and solid matrices. The proposed device was thoroughly evaluated for its extraction performance, robustness, reproducibility and reliability by gas chromatograph/mass spectrometer (GC/MS). With the use of a septumless head injector, the entire automated setup was capable of analyzing over 200 samples without any GC injector leakages. Evaluation of the automated cold fiber device was carried out using a group of compounds characterized by different volatilities and polarities. Extraction efficiency as well as analytical figures of merit was compared to commercial solid phase microextraction fibers. The automated cold fiber device showed significantly improved extraction efficiency compared to the commercial polydimethylsiloxane (PDMS) and cold fiber without cooling for the analysis of aqueous standard samples due to the low temperature of the coating. Comparing results obtained from cold fiber and commercial divinylbenzene/carboxen/polydimethylsiloxane (DVB/CAR/PDMS) fiber temperature profile demonstrated that the temperature gap between the sample matrix and the coating improved the distribution coefficient and therefore the extraction amount. The linear dynamic range of the cold fiber device was 0.5 ng mL(-1) to 100 ng mL(-1) with a linear regression coefficient ≥0.9963 for all compounds. The limit of detection for all analytes ranged from 1.0 ng mL(-1) to 9.4 ng mL(-1). The newly automated cold fiber device presents a platform for headspace analysis of volatiles and semi-volatiles for large number of samples with improved throughput and sensitivity.