Solid-phase microextraction: a powerful sample preparation tool prior to mass spectrometric analysis

Sample preparation is an essential step in analysis, greatly influencing the reliability and accuracy of resulted the time and cost of analysis. Solid-Phase Microextraction (SPME) is a very simple and efficient, solventless sample preparation method, invented by Pawliszyn in 1989. SPME has been widely used in different fields of analytical chemistry since its first applications to environmental and food analysis and is ideally suited for coupling with mass spectrometry (MS). All steps of the conventional liquid-liquid extraction (LLE) such as extraction, concentration, (derivatization) and transfer to the chromatograph are integrated into one step and one device, considerably simplifying the sample preparation procedure. It uses a fused-silica fibre that is coated on the outside with an appropriate stationary phase. The analytes in the sample are directly extracted to the fibre coating. The SPME technique can be routinely used in combination with gas chromatography, high-performance liquid chromatography and capillary electrophoresis and places no restriction on MS. SPME reduces the time necessary for sample preparation, decreases purchase and disposal costs of solvents and can improve detection limits. The SPME technique is ideally suited for MS applications, combining a simple and efficient sample preparation with versatile and sensitive detection. This review summarizes analytical characteristics and variants of the SPME technique and its applications in combination with MS.     

Critical comparison of automated purge and trap and solid-phase microextraction for routine determination of volatile organic compounds in drinking waters by GC-MS

The use of two automated sample preparation techniques, solid-phase microextraction (SPME) and purge and trap (P&T) systems are critically compared for the GC–MS determination of eight volatile organic compounds (VOCs), including trihalomethanes (THMs), in drinking water samples. Compounds chosen for the comparison are regulated by Spanish and European official guidelines for drinking waters. Experimental parameters investigated for the two sample preparation techniques included SPME type of fibers, SPME modality, P&T gas flow, extraction and desorption times and desorption temperatures. Thus, optimal experimental conditions have been worked out for the SPME and P&T techniques. Under such optimised conditions, detection limits, precision and accuracy were evaluated. Both methods fulfilled the values that the official guidelines establish. The P&T–GC–MS method offers LDs ranged from 0.004 to 0.2 ng mL⁻¹, repeatabilities below 6% and recoveries between 81 and 117%; while LDs ranging from 0.008 to 0.7 ng mL⁻¹, 1–12% R.S.D. and recoveries from 80 to 119% were achieved with the SPME–GC–MS method. Finally, we chose P&T–GC–MS method as the best for this determination and we validate this methodology by its application to the analysis of an Aquacheck Interlaboratory Exercise.     

Clean-up and analysis of carbazole and acridine type polycyclic aromatic nitrogen heterocyclics in complex sample matrices

A HPLC method for the analysis of polycyclic aromatic nitrogen heterocyclics (PANHs) in complex sample matrices is presented. It isolated and separated carbazole and acridine type PANHs with an absolute recovery of between 79–98%. Open column chromatography is used as an initial step to isolate a PANH fraction. By applying normal-phase liquid chromatography using a dimethylaminopropyl silica stationary phase and utilising back-flush technique it was possible to separate the PANH fraction into two fractions containing acridine type and carbazole type PANHs, respectively. The method applied on a sample of solvent refined coal heavy distillate (SRC II HD). A number of 3–5 ring acridines and carbazoles were identified with GC–electron impact MS and quantified with GC–nitrogen–phosphorous detection. Polycyclic aromatic hydrocarbons (PAHs) were determined in the SRC II HD sample by automated on-line clean-up and analysis of the obtained PAH fraction with coupled LC–GC–flame ionization detection. There was no overlap between the PANH and the PAH fractions with this method, and carbazoles and acridines were efficiently separated.     

Coupling solid-phase microextraction to liquid chromatography. A review

Solid-phase microextraction (SPME) is a technique for extraction of organic compounds from gaseous, aqueous, and solid matrices. SPME is rapid and simple, ideal for automation and for in situ measurements, and no harmful solvents are needed. The principle of SPME involves equilibration of the analytes between the sample matrix and an organic polymeric phase coated on a fused-silica fiber. SPME is traditionally combined with analysis by gas chromatography (GC) and this combination has proved sensitive, accurate, and precise for quantitative analysis of different classes of volatile compound. More recently SPME has been coupled with liquid chromatography to widen its range of application to non-volatile and thermally unstable compounds also. This article reviews the status of SPME coupled with liquid chromatography. It focuses on different applications of the technique, e.g. environmental samples, biological fluids, and food samples, to show that SPME-HPLC has great potential in the analysis of a wide range of compounds in different matrices.     

Evaluation of triclosan and biphenylol in marine sediments and urban wastewaters by pressurized liquid extraction and solid phase extraction followed by gas chromatography mass spectrometry and liquid chromatography mass spectrometry

Analytical methods, based on GC–MS and LC–MS, for the determination of traces of 2,4,4′-trichloro-2′-hydroxydiphenyl ether (triclosan) and biphenylol in urban wastewater and marine sediments were developed. These methods involve the use of diverse analytical techniques, such as solid phase extraction (SPE) and pressurized liquid extraction for sample preparation, and GC–negative chemical ionization MS and LC–electrospray ionization (ESI) MS–MS for identification and quantification. The recoveries of triclosan and biphenylol were 84 and 80% in wastewater and 100 and 73% in sediments, respectively. Detection limits obtained were in the range of ppb and ppt. To prove their applicability to real samples and as part of a more extensive monitoring program, the developed methods were applied to the analysis of wastewater samples, coming from an urban wastewater treatment plant (UWWTP), and of marine sediment samples collected at the outflow of two UWWTPs to the sea. Results obtained reveal the presence of triclosan in all the samples at concentrations that ranged from 0.8 to 37.8 μg/l in wastewater and from 0.27 to 130.7 μg/kg in sediments. These preliminary data reinforce the interest for further research on this topic.     

Practical approaches to fast gas chromatography-mass spectrometry

Fast gas chromatography–mass spectrometry (GC–MS) has the potential to be a powerful tool in routine analytical laboratories by increasing sample throughput and improving laboratory efficiency. However, this potential has rarely been met in practice because other laboratory operations and sample preparation typically limit sample throughput, not the GC–MS analysis. The intent of this article is to critically review current approaches to fast analysis using GC–MS and to discuss practical considerations in addressing their advantages and disadvantages to meet particular application needs. The practical ways to speed the analytical process in GC and MS individually and in combination are presented, and the trade-offs and compromises in terms of sensitivity and/or selectivity are discussed. Also, the five main current approaches to fast GC–MS are described, which involve the use of: (1) short, microbore capillary GC columns; (2) fast temperature programming; (3) low-pressure GC–MS; (4) supersonic molecular beam for MS at high GC carrier gas flow; and (5) pressure-tunable GC–GC. Aspects of the different fast GC–MS approaches can be combined in some cases, and different mass analyzers may be used depending on the analytical needs. Thus, the capabilities and costs of quadrupole, ion trap, time-of-flight, and magnetic sector instruments are discussed with emphasis placed on speed. Furthermore, applications of fast GC–MS that appear in the literature are compiled and reviewed. At this time, the future usefulness of fast GC–MS depends to some extent upon improvement of existing approaches and commercialization of interesting new techniques, but moreover, a greater emphasis is needed to streamline overall laboratory operations and sample preparation procedures if fast GC–MS is to become implemented in routine applications.     

Modern developments in gas chromatography-mass spectrometry-based environmental analysis

Gas chromatography coupled with mass spectrometry (GC–MS) continues to play an important role in the identification and quantification of organic contaminants in environmental samples. GC–MS is one of the most attractive and powerful techniques for routine analysis of some ubiquitous organic pollutants due to its good sensitivity and high selectivity and versatility. This paper presents an overview of recent developments and applications of the GC–MS technique in relation to the analysis in environmental samples of known persistent pollutants and some emerging contaminants. The use of different mass analysers such as linear quadrupole, quadrupole ion-trap, double-focusing sectors and time-of-flight analysers is examined. The advantages and limitations of GC–MS methods for selected applications in the field of environmental analysis are discussed. Recent developments in field-portable GC–MS are also examined.     

Surface and wastewater quality monitoring: combination of liquid chromatography with (geno)toxicity detection,diode array detection and tandem mass spectrometry for identification of pollutants

Identification of unknown water pollutants with liquid chromatography and tandem mass spectrometry (LC–MS–MS) is often more complex and time consuming than identification with gas chromatography and mass spectrometry (GC–MS). In order to focus the identification effort on relevant compounds, unknown peaks need to be selected carefully. Based on its frequency of occurrence in the LC–Diode Array Detection (LC–DAD) chromatograms of surface and infiltrated waters, an unknown peak was selected for identification with LC–MS–MS. This compound was identified as hexamethoxymethylmelamine (HMMM), a chemical often used in the coating industry. This is the first time the presence of this chemical in surface waters has been reported. In addition to HMMM, two other structurally related compounds were found to be present in the investigated surface water. A standard mixture of HMMM and its by-products did not exhibit (geno)toxicity under the test conditions applied in this study. In another example, a genotoxic fraction of an industrial wastewater was isolated and examined by LC–MS–MS using a modern quadrupole–orthogonal acceleration-time-of-flight mass spectrometer (Q-TOF). Four compounds were detected. The structures of two compounds present are proposed to be 9-amino-2-hydroxy-acridine and 9-hydroxy-acridine-N-oxide or its structural isomer dihydroxy-acridine. Confirmation with standards could not be carried out, as pure compounds are not available. The other two compounds (structural isomers) could not be identified based on the data available within this study.     

Automated sample preparation using in-tube solid-phase microextraction and its application -- a review

Sample preparation, such as extraction, concentration, and isolation of analytes, greatly influences their reliable and accurate analysis. In-tube solid-phase microextraction (SPME) is a new effective sample preparation technique using an open tubular fused-silica capillary column as an extraction device. Organic compounds in aqueous samples are directly extracted and concentrated into the stationary phase of capillary columns by repeated draw/eject cycles of sample solution, and they can be directly transferred to the liquid chromatographic column. In-tube SPME is an ideal sample preparation technique because it is fast to operate, easy to automate, solvent-free, and inexpensive. On-line in-tube SPME-performed continuous extraction, concentration, desorption, and injection using an autosampler, is usually used in combination with high performance liquid chromatography and liquid chromatography-mass spectrometry. This technique has successfully been applied to the determination of various compounds such as pesticides, drugs, environmental pollutants, and food contaminants. In this review, an overview of the development of in-tube SPME technique and its applications to environmental, clinical, forensic, and food analyses are described.     

Liquid chromatography-(tandem) mass spectrometry of selected emerging pollutants (steroid sex hormones,drugs and alkylphenolic surfactants) in the aquatic environment

Among the various compounds considered as emerging pollutants, alkylphenolic surfactants, steroid sex hormones, and pharmaceuticals are of particular concern, both because of the volume of these substances used and because of their activity as endocrine disruptors or as causative agents of bacterial resistance, as is the case of antibiotics. Today, the technique of choice for analysis of these groups of substances is liquid-chromatography coupled to mass spectrometry (LC–MS) and tandem mass spectrometry (LC–MS–MS). In the last decades, this technique has experienced an impressive progress that has made possible the analysis of many environmental pollutants in a faster, more convenient, and more sensitive way, and, in some cases, the analysis of compounds that could not be determined before. This article reviews the LC–MS and LC–MS–MS methods published so far for the determination of alkylphenolic surfactants, steroid sex hormones and drugs in the aquatic environment. Practical considerations with regards to the analysis of these groups of substances by using different mass spectrometers (single quadrupole, ion trap and triple quadrupole instruments, etc.), interfaces and ionization and monitoring modes, are presented. Sample preparation aspects, with special focus on the application of advanced techniques, such as immunosorbents, restricted access materials and molecular imprinted materials, for extraction/purification of aquatic environmental samples and extracts are also discussed.     

Solid-phase microextraction of polychlorinated biphenyls

The extraction and analysis of 21 polychlorinated biphenyls (PCBs) ranging from di- to decachlorobiphenyls in ocean, wetland and leachate water samples were achieved using solid-phase microextraction (SPME) with a 100-μm poly(dimethylsiloxane) (PDMS) fiber and gas chromatography–electron-capture detection (GC–ECD). Severe carryover between samples (e.g., 20%) occurs on both stir bars and the SPME fibers demonstrating that it is important to use a new stir bar for each sample, as well as to perform SPME–GC blanks between samples to avoid quantitative errors. The equilibrium partitioning coefficients of individual PCB congeners between PDMS and water were found to be surprisingly different compared to their octanol–water partitioning coefficient (K_ow), demonstrating that K_ow cannot be used to estimate the partitioning behavior of PCBs in the SPME process. Using a 15-min SPME extraction, SPME analysis with GC–ECD was linear (r²≥0.97) from 5 pg/ml to the solubility limit of each congener. Concentrations in water samples obtained by 15-min SPME extractions compared favorably with those obtained by toluene extractions, demonstrating that SPME combined with GC is a useful technique for the rapid determination of PCBs in water samples.     

Analysis of acrylamide in different foodstuffs using liquid chromatography–tandem mass spectrometry and gas chromatography–tandem mass spectrometry

Acrylamide levels over a wide range of different food products were analysed using both liquid chromatography–tandem mass spectrometry (HPLC–MS–MS) and gas chromatography–tandem mass spectrometry (GC–MS–MS). Two different sample preparation methods for HPLC–MS–MS analysis were developed and optimised with respect to a high sample throughput on the one hand, and a robust and reliable analysis of difficult matrices on the other hand. The first method is applicable to various foods like potato chips, French fries, cereals, bread, and roasted coffee, allowing the analysis of up to 60 samples per technician and day. The second preparation method is not as simple and fast but enables analysis of difficult matrices like cacao, soluble coffee, molasses, or malt. In addition, this method produces extracts which are also well suited for GC–MS–MS analysis. GC–MS–MS has proven to be a sensitive and selective method offering two transitions for acrylamide even at low levels up to 1 μg kg⁻¹. For the respective methods the repeatability (n=10), given as coefficient of variation, ranged from 3% (acrylamide content of 550 μg kg⁻¹) to 12% (acrylamide content of 8 μg kg⁻¹) depending on the food matrix. The repeatability (n=3) for different food samples spiked with acrylamide (5–1500 μg kg⁻¹) ranged from 1 to 20% depending on the spiking level and the food matrix. The limit of quantification (referred to a signal-to-noise ratio of 9:1) was 30 μg kg⁻¹ for HPLC–MS–MS and 5 μg kg⁻¹ for GC–MS–MS. It could be demonstrated that measurement uncertainties were not only a result of analytical variability but also of inhomogeneity and stability of the acrylamide in food.     

A novel sol-gel-based amino-functionalized fiber for headspace solid-phase microextraction of phenol and chlorophenols from environmental samples

A novel amino-functionalized polymer was synthesized using 3-(trimethoxysilyl) propyl amine (TMSPA) as precursor and hydroxy-terminated polydimethylsiloxane (OH-PDMS) by sol–gel technology and coated on fused-silica fiber. The synthesis was designed in a way to impart polar moiety into the coating network. The scanning electron microscopy (SEM) images of this new coating showed the homogeneity and the porous surface structure of the film. The efficiency of new coating was investigated for headspace solid-phase microextraction (SPME) of some environmentally important chlorophenols from aqueous samples followed by gas chromatography–mass spectrometry (GC–MS) analysis. Effect of different parameters influencing the extraction efficiency such as extraction temperature, extraction time, ionic strength and pH was investigated and optimized. In order to improve the separation efficiency of phenolic compounds on chromatography column all the analytes were derivatized prior to extraction using acetic anhydride at alkaline condition. The detection limits of the method under optimized conditions were in the range of 0.02–0.05 ng mL⁻¹. The relative standard deviations (R.S.D.) (n = 6) at a concentration level of 0.5 ng mL⁻¹ were obtained between 6.8 and 10%. The calibration curves of chlorophenols showed linearity in the range of 0.5–200 ng mL⁻¹. The proposed method was successfully applied to the extraction from spiked tap water samples and relative recoveries were higher than 90% for all the analytes.     

On-line coupled liquid chromatography-gas chromatography

On-line coupled liquid chromatography–gas chromatography (LC–GC) is a powerful technique that combines the best features of LC and GC and is ideal for the analysis of complex samples. This review describes the unique features of on-line coupled LC–GC. The different interfaces and evaporation techniques are presented, along with their advantages and disadvantages. Guidelines are given for selecting a suitable LC–GC technique and representative applications are noted.     

Determination of diethylhexyl phtalate in water by solid phase microextraction coupled to high performance liquid chromatography

Difficulties detected in the determination of the diethylhexylphthalate (DEHP) at trace levels by gas chromatography–mass spectrometry (GC–MS) using SPME, due to its ubiquitous distribution in the environment has been overcome and a new method for the determination of DEHP in drinking water has been proposed. The method is based on solid phase microextraction (SPME) coupled to high-performance liquid chromatography (HPLC). Detection was carried out spectrophotometrically. Calibration graph was linear in the range 10–110 μg/L with a regression coefficient of r² = 0.998 and a detection limit of 0.6 μg/L. The relative standard deviation was 5 and 2% (n = 4) for chromatographic areas and retention times, respectively. The usefulness of the SPME–HPLC technique was confirmed.     

Comparison between liquid chromatography-UV detection and liquid chromatography-mass spectrometry for the characterization of impurities and/or degradants present in trimethoprim tablets

The characterization of impurities and/or degradants present in pharmaceutical compounds is an important part of the drug development process. Although LC–UV is commonly employed for impurities and degradant compound determination, LC–MS techniques are proposed in this work to be a viable modern alternative for the characterization of these compounds. LC–UV and LC–MS were compared for the detection of impurities present in different brands of trimethoprim tablets by using an in-line LC–UV–MS system with atmospheric pressure chemical ionization source (APCI) coupled with a reversed-phase gradient HPLC system. It was shown that, although chemical noise was higher when using full-scan LC–MS compared to LC–UV, low level impurities were better detected by mass spectrometry (MS) when modern software algorithms are employed. These included the “Contour” chromatogram algorithm and/or the “component detection algorithm” (CODA). In addition, MS allowed for the simultaneous determination of the molecular masses and some structural information of the impurities and/or degradants. The results also showed a large difference in the purity of trimethoprim among different manufacturers. LC–MS and tandem MS techniques were employed to acquire fragmentation patterns for trimethoprim and its degradants to gain insight into their structures.     

Simple ion chromatographic method for the determination of chlormequat residues in pears

Current methods for quantitative determination of chlormequat residues in food crops are characterized by rather low recoveries and the need for derivatization (in case of gas chromatography, GC), or by high capital investment (in case of liquid chromatography–mass spectrometry, LC–MS). We propose a cation-exchange chromatography method for the analysis of chlormequat in pears. The method is based on extraction of the target compound with 40 mM HCl, followed by centrifugation and filtration. The filtrate is directly injected into an ion chromatograph equipped with a commercially available cation-exchange column and a suppressed conductivity detection system. While the limit of detection (LOD) (0.5 mg/kg) may not be small enough to allow dietary analysis, the method meets all validation requirements and is an alternative for the existing GC and LC–MS methods in quality control.     

Determination of theophylline and its metabolites in biological samples by liquid chromatography-mass spectrometry

Liquid chromatography–mass spectrometry (LC–MS) is a powerful tool for analysis of drugs and their metabolites. We used a column-switching system in combination with atmospheric pressure chemical ionization LC–MS (LC–APCI–MS) for the determination of theophylline and its metabolites in biological samples. The separation was carried out on a reversed-phase column using methanol–20 mM ammonium acetate as a mobile phase at a flow-rate of 1 ml/min in 30 min. In the mass spectrum, the molecular ions of these drugs and metabolites were clearly observed as base peaks. This method is sufficiently sensitive and accurate for the pharmacokinetic studies of these drugs.     

Determination of chemical warfare agents and related compounds in environmental samples by solid-phase microextraction with gas chromatography

Solid phase microextraction (SPME) is an increasingly common method of sample isolation and enhancement. SPME is a convenient and simple sample preparation technique for chromatographic analysis and a useful alternative to liquid-liquid extraction and solid phase extraction. SPME is speed and simply method, which has been widely used in environmental analysis because it is a rather safe method when dealing with highly toxic chemicals. A combination of SPME and gas chromatography (GC) permits both the qualitative and quantitative analysis of toxic industrial compounds, pesticides and chemical warfare agents (CWAs), including their degradation products, in air, water and soil samples. This work presents a combination of SPME and GC methods with various types of detectors in the analysis of CWAs and their degradation products in air, water, soil and other matrices. The combination of SPME and GC methods allows for low detection limits depending on the analyte, matrix and detection system. Commercially available fibers have been mainly used to extract CWAs in headspace analysis. However, attempts have been made to introduce new fiber coatings that are characterized by higher selectivities towards different analytes of interest. Environmental decomposition of CWAs leads to the formation of more hydrophilic products. These compounds may be isolated from samples using SPME and analyzed using GC however, they must often be derivatized first to produce good chromatography. In these cases, one must ensure that the SPME method also meets the same needs. Otherwise, it is helpful to use derivatization methods. SPME may also be used with fieldportable mass spectrometry (MS) and GC-MS instruments for chemical defense applications, including field sampling and analysis. SPME fibers can be taken into contaminated areas to directly sample air, headspaces above solutions, soils and water.     

Liquid chromatography-inductively coupled plasma mass spectrometry

It is known that while many elements are considered essential to human health, many others can be toxic. However, because the intake, accumulation, transport, storage and interaction of these different metals and metalloids in nature is strongly influenced by their specific elemental form, complete characterization of the element is essential when assessing its benefits and/or risk. Consequently, interest has grown rapidly in determining oxidation state, chemical ligand association, and complex forms of a many different elements. Elemental speciation, or the analyses that lead to determining the distribution of an element’s particular chemical species in a sample, typically involves the coupling of a separation technique and an element specific detector. A large number of methods have been developed which utilize a multitude of different separation mechanisms and detection instruments. Yet, because of its versatility, robustness, sensitivity and multi-elemental capabilities, the coupling of liquid chromatography to inductively coupled plasma mass spectrometry (LC–ICP–MS) has become one of the most popular techniques for elemental speciation studies. This review focuses on the basic principles of LC–ICP–MS, its historical development and the many ways in which this technique can be applied. Different liquid chromatography separations are discussed as well as the factors that must be considered when coupling each to ICP–MS. Recent applications of LC–ICP–MS to the speciation of environmental, biological and clinical samples are also presented.