Bioanalytical applications of solid-phase microextraction

Recent Advances in Solid-Phase Extraction as a Platform for Sample Preparation in Biomarker Assay

Low levels of biomarkers and the complexity of bio sample make the analytical assay of several biomarkers a challenging issue. Suitable sample preparation run remain a vital part of the puzzle of diagnostic level. Enhancing the detection limit of bioanalytical methods start during the sample preparation procedure. A robust sample preparation method is needed to evaluate the number of biomarkers. As worldwide environmental issues attract expanding consideration, all the more harmless to the ecosystem investigations are liked. Solid-phase extraction (SPE) is an appealing strategy among the sample treatment methods due to the versatility of sorbent materials, less solvent consumption, and compatibility with analytical devices. Miniaturization of the SPE gives the chance to integrate the other analytical steps in a single run, known as an easy-to-use and effective method. SPE utilizes various SPE sorbent beds such as packed beads, porous polymer monoliths, molecularly imprinted polymers, membranes, or other magnetic form microstructures to achieve high surface-to-volume ratio and appropriate chemical properties effective extraction. Also, SPE is the methodology of interest to fulfill high recovery and efficiency demands. In this review, we intend to explain more recent methods for the rational design of SPE and miniaturized SPE to determine biomarkers from biological media. The headlines are subdivided into (1) packing materials in SPE, (2) setups for sample preparation by magnetic SPE, and (3) and future perspective for the application of SPE in sample preparation for analysis of biomarkers.

Comparison of liquid-liquid extraction, microextraction and ultrafiltration for measuring free concentrations of testosterone and phenytoin

Aim: The purpose of the study was to find methods suitable for measuring the free concentrations of testosterone and phenytoin. Materials & methods: Sample solutions of the compounds in buffer and human albumin were processed using liquid-liquid extraction, microextraction and ultrafiltration and analyzed by LC-MS/MS. Results: Liquid-liquid extraction with dibutyl phthalate provided complete extraction from buffer solutions and partial extraction from albumin samples. Spintip C18 devices provided exhaustive extraction from buffer and albumin samples. Spintip C8 devices offered complete extraction from buffer and approximately 50% recovery from albumin samples. Centrifree ultrafiltration devices showed high recovery of free concentrations from all the samples, while Amicon and Nanosep devices provided partial recovery. Conclusion: Spintip C8 and Centrifree devices proved useful for measuring free concentrations.

Optimizing a High-Throughput Solid-Phase Microextraction System to Determine the Plasma Protein Binding of Drugs in Human Plasma

Plasma protein binding refers to the binding of a drug to plasma proteins after entering the body. The measurement of plasma protein binding is essential during drug development and in clinical practice, as it provides a more detailed understanding of the available free concentration of a drug in the blood, which is in turn critical for pharmacokinetics and pharmacodynamics studies. In addition, the accurate determination of the free concentration of a drug in the blood is also highly important for therapeutic drug monitoring and in personalized medicine. The present study uses C₁₈-coated solid-phase microextraction 96-pin devices to determine the free concentrations of a set of drugs in plasma, as well as the plasma protein binding of drugs with a wide range of physicochemical properties. It should be noted that the extracted amounts used to calculate the binding constants and plasma protein bindings should be measured at respective equilibrium for plasma and phosphate buffer. Therefore, special attention is placed on properly determining the equilibration times required to correctly estimate the free concentrations of drugs in the investigated systems. The plasma protein binding values obtained with the 96-pin devices are consistent with those reported in the literature. The 96-pin device used in this research can be easily coupled with a Concept96 or other automated robotic systems to create an automated plasma protein binding determination protocol that is both more time and labor efficient compared to conventional equilibrium dialysis and ultrafiltration methods.

Solid-phase microextraction for assessment of plasma protein binding, a complement to rapid equilibrium dialysis

Aim: Determination of plasma protein binding (PPB) is considered vital for better understanding of pharmacokinetic and pharmacodynamic activities of drugs due to the role of free concentration in pharmacological response. Methodology & results: Solid-phase microextraction (SPME) was investigated for measurement of PPB from biological matrices and compared with a gold standard approach (rapid equilibrium dialysis [RED]). Discussion & conclusion: SPME-derived values of PPB correlated well with literature values, and those determined by RED. Respectively, average protein binding across three concentrations by RED and SPME was 33.1 and 31.7% for metoprolol, 89.0 and 86.6% for propranolol and 99.2 and 99.0% for diclofenac. This study generates some evidence for SPME as an alternative platform for the determination of PPB.

Method for Simultaneous Determination of Free Concentration, Total Concentration, and Plasma Binding Capacity in Clinical Samples

Most quantitative research methods are based on measuring either the total or the free concentration of an analyte in a sample. However, this is often insufficient for the study of complex biological systems. The main objective of this research was to develop new methods for providing more information from samples: the free concentration (C_f), the total concentration (C_t), and the plasma binding capacity (PBC). Samples were processed using microextraction and ultrafiltration. For each of these techniques, two quantification procedures were used: addition of isotopically labeled standard and repeated analysis of the same sample. The new methods were validated by analyzing clinical samples and samples with known concentrations. Methods based on addition of labeled compound were found to be the fastest, and most reproducible. For analysis of clinical samples, methods based on microextraction were more sensitive and more accurate than those based on ultrafiltration. For analysis of pooled plasma samples, the overall accuracy of all approaches to determine PBC, testosterone C_f, and testosterone C_t was between 94 and 109%, 87-113%, and 94-122% respectively. The new approach goes beyond a simple concentration measurement, giving more information from clinical samples, with great potential for personalizing drug dosage and therapy to the needs of individual patients.

Urinary volatilome analysis in a mouse model of anxiety and depression

Psychiatric disorders including depression and anxiety comprise a broad range of conditions with different symptoms. We have developed a mouse model of depression/anxiety in mice deficient in the St3gal4 gene. In this study, we performed a comparative analysis of urinary volatile organic compounds (VOCs) in St3gal4-deficient (St3gal4-KO) and wild-type mice using gas chromatography-mass spectrometry, and we screened 18 putative VOCs. Principal component analysis (PCA) based on these VOCs identified a major group of 11 VOCs, from which two groups were clarified by hierarchical clustering analysis. One group including six VOCs (pentanoic acid, 4-methyl-, ethyl ester; 3-heptanone, 6-methyl; benzaldehyde; 5,9-undecadien-2-ol, 6,10-dimethyl; and unknown compounds RI1291 and RI1237) was correlated with the startle response (r = 0.620), which is related to an unconscious defensive response. The other group including two VOCs (beta-farnesene and alpha-farnesene) comprised pheromones which increased in KO mice. Next, male mice underwent a social behavior test with female mice in the estrus stage, showing reduced access of KO male mice to female mice. Comparative analysis of urinary VOCs before and after encounters revealed that the six VOCs were not changed by these encounters. However, in WT mice, the two farnesenes increased after the encounters, reaching the level observed in KO mice, which was not altered following the encounter. Taken together, these results indicated that St3gal4 was involved in modulating urinary VOCs. Moreover, VOC clusters discovered by comparison of St3gal4-KO mice with WT mice were correlated with differential emotional behaviors.

A Novel Water-Swelling Sampling Probe for in Vivo Detection of Neonicotinoids in Plants

Ecotoxicological risks of neonicotinoid insecticides are raising significant concerns, including their potential role in bee population declines. Neonicotinoids are water-soluble, systemic insecticides, and exposure of nontarget organisms such as pollinators occurs mainly through residues in nectar and pollens of flowering plants. To better elucidate the underlying mechanisms for such nontarget exposure, it is highly valuable to develop analytical capabilities for in vivo monitoring of neonicotinoids in live plants. In this study, we developed a novel biomimetic water-swelling solid-phase microextraction (SPME) probe, with limits of detection for neonicotinoids as low as 0.03 ng mL^-1, and applied it for in vivo detection of seven neonicotinoids in plant sap. The preparation of this fiber was simple and free of stringent or complex physical-chemical reactions. Equilibrium in neonicotinoid accumulation on the fiber was reached in <10 min, allowing for near instantaneous sampling. The water-swelling fiber displayed much greater sampling capacity than the commercially available polydimethylsiloxane and polyacrylate fibers, good reproducibility (RSD of inter- and intrafiber <8.9% and 7.8%, respectively), and antibiofouling property (no loss in performance after 20 use cycles). After treating lettuce (Lactuca sativa L.) by foliar spray and soybean (Glycine max M.) by seed soaking, the in vivo assays provided a wealth of information, including changes in levels and distribution of neonicotinoids over time in the same plants. Kinetics and distribution patterns suggested that after treatment at the same level, neonicotinoids differed significantly in their levels in the sap. The in vivo sampling and monitoring of neonicotinoids in live plants may provide unique and much needed information in achieving breakthrough understanding of the connection between neonicotinoid use and pollinator exposure.

In vivo monitoring of rat brain endocannabinoids using solid-phase microextraction

Aim: Solid-phase microextraction is proposed to measure concentrations of anandamide and 2-arachidonoyl glycerol in live rat brains in response to stress. Materials & methods: Solid-phase microextraction fibers were prepared from steel with 1.5 mm extraction coating. 24 male rats were divided into groups based on brain region, stria terminalis or posterior hypothalamus and loud noise or control groups. The fibers were desorbed in acetonitrile-water (75:25) and analyzed by ultraperformance LC-MS/MS. The linear range of the method was 0.05-50 ng/ml and the in vivo concentrations were found to be between 0.3 and 40 ng/ml. Conclusion: The new approach was successfully used to determine the concentrations of anandamide and 2-arachidonoyl glycerol in vivo and could be used in the future to measure other endogenous compounds.

Implementing a central composite design for the optimization of solid phase microextraction to establish the urinary volatomic expression: a first approach for breast cancer

INTRODUCTION

Breast cancer (BC) is positioned as the second among all cancers remaining at the top of women´s diseases worldwide followed by colorectum, lung, cervix, and thyroid cancers. The main drawback of most the screening/diagnostic methods is their low sensitivity/specificity and in some cases the invasive procedure required to obtain the samples.

OBJECTIVES

On the present investigation, we report a statistical design was to evaluate by central composite design the influence towards the optimization of the most significant variables of solid-phase microextraction (SPME) procedure for the isolation of volatile organic metabolites (VOMs) from urine of BC patients (N = 31) and healthy individuals (CTL; N = 40). The establishment of the urinary volatomic composition, through gas chromatography-mass spectrometry (GC-MS) analysis, can boost the identification of volatile organic metabolites (VOMs) potential BC biomarkers useful to be used together or to complement the current BC diagnostics tools. Better early detection methods are needed to improve the outcomes of patients with BC.

METHODS

Several combinations of experiments were considered with a central composite design (CCD) of response surface methodology (RSM) for the urinary volatomic pattern. Three-level three-factor CCD was employed assessing the most important extraction-influencing variables-fiber coating, NaCl amount, extraction time and temperature. The optimal conditions were achieved using a carboxen/polydimethylsiloxane fiber with 15% (w/v) NaCl during 75 min at 50 °C.

RESULTS

A total of ten VOMs belonging to sulfur compounds, terpenoids and carbonyl compounds presented the highest contribution towards discrimination of BC patients from CTL (variable importance in projection (VIP) > 1, p < 0.05). The discrimination efficiency and accuracy of urinary metabolites was ascertained by receiver operating characteristic (ROC) curve analysis that allowed the identification of some metabolites with highest sensitivity and specificity to discriminate the groups.

CONCLUSIONS

The results obtained with this approach suggest the possibility to identify endogenous metabolites as a platform to discovery potential BC biomarkers and paves a way to explore the related metabolomic pathways in order to improve BC diagnostic tools.

Galvanic displacement-induced codeposition of reduced-graphene-oxide/silver on alloy fibers for non-destructive SPME@SERS analysis of antibiotics

This work describes the integration of solid-phase microextraction (SPME) and surface-enhanced Raman spectroscopy (SERS) by codeposition of a hybrid consisting of reduced graphene oxide and silver on silver-copper alloy fibers. The morphology and structure of the coating were characterized by a variety of microscopic and spectroscopic techniques that confirmed the hybrid structure of the material. A galvanic-displacement-induced process is assumed to be involved during the codeposition of the hybrid coating on the alloy. In this process, Ag(I) is reduced to Ag(0) by Cu(0), and the presence of conjugated domains in GO facilitates the long-range transfer of electrons from Cu to Ag+. Simultaneously, GO accepts electrons and is converted into RGO. The hybrid coating exhibits a high SERS enhancement factor and good spatial uniformity. The needle-like coated alloy fibers are shown to be a viable tool for non-destructive sampling and SERS-based determination of trace levels of the antibiotics sulfadiazine and sulfamethoxazole in a spiked tissue mimic. The SERS peaks at 1149 cm^-1 for sulfadiazine and 1144 cm^-1 for sulfamethoxazole are selected as the reference peaks in the quantitative analysis. The linear range is from 0.01 to 100 μg·cm^-3. The detection limits are 1.9 ng·cm^-3 for sulfadiazine and 4.4 ng·cm^-3 for sulfamethoxazole. Graphical abstract Schematic presentation of I: Galvanic-displacement-induced reduction of graphene oxide (brown films) and Ag⁺ (purple dots) on silver-copper alloy; II: Codeposition of reduced-graphene-oxide (grey films)/Ag (blue stars) on alloy fiber; III: Non-destructive SPME of antibiotics from spiked tissue mimic; IV: SERS detection using Raman spectroscope.

PLGA-based nanofibers with a biomimetic polynoradrenaline sheath for rapid in vivo sampling of tetrodotoxin and sulfonamides in pufferfish

PLGA nanofibers with PNA sheath modification achieve enhanced extraction performance and antibiofouling capacity for in vivo sampling in pufferfish.

Review of geometries and coating materials in solid phase microextraction: Opportunities, limitations, and future perspectives

The development of new support and geometries of solid phase microextraction (SPME), including metal fiber assemblies, coated-tip, and thin film microextraction (TFME) (i.e. self-supported, fabric and blade supported), as well as their effects on diffusion and extraction rate of analytes were discussed in the current review. Application of main techniques widely used for preparation of a variety of coating materials of SPME, including sol-gel technique, electrochemical and electrospinning methods as well as the available commercial coatings, were presented. Advantages and limitations of each technique from several aspects, such as range of application, biocompatibility, availability in different geometrical configurations, method of preparation, incorporation of various materials to tune the coating properties, and thermal and physical stability, were also investigated. Future perspectives of each technique to improve the efficiency and stability of the coatings were also summarized. Some interesting materials including ionic liquids (ILs), metal organic frameworks (MOFs) and particle loaded coatings were briefly presented.

Solid-phase microextraction set-up for the analysis of liver volatolome to detect livestock exposure to micropollutants

Starting from a critical analysis of a first "proof of concept" study on the utility of the liver volatolome for detecting livestock exposure to environmental micropollutants (Berge et al., 2011), the primary aim of this paper is to improve extraction conditions so as to obtain more representative extracts by using an extraction temperature closer to livestock physiological conditions while minimizing analytical variability and maximizing Volatile Organic Compound (VOC) abundancies. Levers related to extraction conditions and sample preparation were assessed in the light of both abundance and coefficient of variation of 22 candidate VOC markers identified in earlier volatolomic studies. Starting with a CAR/PDMS fiber and a 30min extraction, the reduction of SPME temperature to 40°C resulted in a significant decrease in the area of 14 candidate VOC markers (p<0.05), mainly carbonyls and alcohols but also a reduction in the coefficient of variation for 17 of them. In order to restore VOC abundances and to minimize variability, two approaches dealing with sample preparation were investigated. By increasing sample defrosting time at 4°C from 0 to 24h yielded higher abundances and lower variabilities for 15 and 13 compounds, respectively. Lastly, by using additives favouring the release of VOCs (1.2g of NaCl) the sensitivity of the analysis was improved with a significant increase in VOC abundances of more than 50% for 13 out of the 22 candidate markers. The modified SPME parameters significantly enhanced the abundances while decreasing the analytical variability for most candidate VOC markers. The second step was to validate the ability of the revised SPME protocol to discriminate intentionally contaminated broiler chickens from controls, under case/control animal testing conditions. After verification of the contamination levels of the animals by national reference laboratories, data analysis by a multivariate chemometric method (Common Components and Specific Weights Analysis - ComDim) showed that the liver volatolome could reveal dietary exposure of broilers to a group of environmental pollutants (PCBs), a veterinary treatment (monensin), and a pesticide (deltamethrin), thus confirming the usefulness of this analytical set-up.

Separation/Preconcentration Techniques for Rare Earth Elements Analysis

The main aim of this chapter exactly characterizes the contribution. The analytical chemistry of the rare earth elements (REEs) very often is highly complicated and the determination of a specific element is impossible without a sample pre-concentration. Sample preparation can be carried out either by separation of the REEs from the matrix or by concentrating the REEs. The separation of REEs from each other is mainly made by chromatography.

At the beginning of REE analysis, the method of precipitation/coprecipitation was applied for the treatment of REE mixtures. The method is not applicable for the separation of trace amounts of REEs. The majority of the methods used are based on the distribution of REEs in a two-phase system, a liquid–liquid or a liquid–solid system. Various techniques have been developed for the liquid–liquid extraction (LLE), in particular the liquid phase micro-extraction. The extraction is always combined with a pre-concentration of the REEs in a single drop of extractant or in a hollow fiber filled with the extractant. Further modified techniques for special applications and for difficult REE separation have been developed. Compared to the LLE, the solid phase micro-extraction is preferred. The method is robust and easy to handle, in which the solid phase loaded with the REEs can be used directly for subsequent determination methods. At present, very new solid materials, like nanotubes, are developed and tested for solid phase extraction.

Self-assembled benzyl mercaptan monolayer as a coating in electromembrane surrounded solid-phase microextraction of antihistamines in urine and plasma samples

Electromembrane extraction based on a monolayer of benzyl mercaptan on a copper wire was applied to extract naphazoline and antazoline from biological samples.

In vivo and ex vivo SPME: a low invasive sampling and sample preparation tool in clinical bioanalysis

Solid phase microextraction (SPME) is well-established technology in bioanalysis. Current review discusses the features of SPME, which determine the non- or low-invasiveness of the method in biomedical analysis. In the first section we analyze the factors, which have significant influence on the SPME sampling device performance in the view of sampling safety and efficiency. In the later sections applicability of various SPME approaches for analysis of easily accessible samples routinely used for analysis (e.g., urine, blood) as well as limited availability samples (tissues) is discussed. Moreover, the examples of sampling alternative matrices such as hair, saliva, sweat or breath are presented. The advantages and limitation of the technology in the view of future development of SPME are also reviewed.

Biological sample preparation: attempts on productivity increasing in bioanalysis

Sample preparation is an important step of any biomedical analysis. Development and validation of fast, reproducible and reliable sample preparation methods would be very helpful in increasing productivity. Except for a few direct injection methods, almost all biological samples should at least be diluted before any analysis. Sometimes dilution is not possible because of the low concentration of the target analyte in the sample, and alternative pretreatments, such as filtration, precipitation and sample clean up using different extraction methods, are needed. This review focuses on the recent achievements in the pretreatment of biological samples and investigates them in six categories (i.e., dilution, filtration/dialysis, precipitation, extraction [solid-phase extraction, liquid–liquid extraction], novel techniques [turbulent flow chromatography, immunoaffinity method, electromembrane extraction] and combined methods). Each category will be discussed according to its productivity rate and suitability for routine analysis, and the discussed methods will be compared according to the mentioned indices.

Distinctive characteristics of Madeira wine regarding its traditional winemaking and modern analytical methodologies

Madeira wine, a fortified wine produced in Madeira Island, is a special wine among all types of wine due its specific winemaking process. The aim of this chapter is to describe important aspects of Madeira winemaking and some scientific research currently carried out in these particular kinds of wines. The first part of the chapter concerns the most important aspects of winemaking technology used in Madeira wine production. The second part, the more extensive, deals with the different groups of compounds and how these are modified during the various steps of the production process, namely the aging period.

Headspace solid-phase microextraction combined with mass spectrometry as a powerful analytical tool for profiling the terpenoid metabolomic pattern of hop-essential oil derived from Saaz variety

Hop (Humulus lupulus L., Cannabaceae family) is prized for its essential oil contents, used in beer production and, more recently, in biological and pharmacological applications. In this work, a method involving headspace solid-phase microextraction and gas chromatography-mass spectrometry was developed and optimized to establish the terpenoid (monoterpenes and sesquiterpenes) metabolomic pattern of hop-essential oil derived from Saaz variety as a mean to explore this matrix as a powerful biological source for newer, more selective, biodegradable and naturally produced antimicrobial and antioxidant compounds. Different parameters affecting terpenoid metabolites extraction by headspace solid-phase microextraction were considered and optimized: type of fiber coatings, extraction temperature, extraction time, ionic strength, and sample agitation. In the optimized method, analytes were extracted for 30 min at 40°C in the sample headspace with a 50/30 μm divinylbenzene/carboxen/polydimethylsiloxane coating fiber. The methodology allowed the identification of a total of 27 terpenoid metabolites, representing 92.5% of the total Saaz hop-essential oil volatile terpenoid composition. The headspace composition was dominated by monoterpenes (56.1%, 13 compounds), sesquiterpenes (34.9%, 10), oxygenated monoterpenes (1.41%, 3), and hemiterpenes (0.04%, 1) some of which can probably contribute to the hop of Saaz variety aroma. Mass spectrometry analysis revealed that the main metabolites are the monoterpene β-myrcene (53.0 ± 1.1% of the total volatile fraction), and the cyclic sesquiterpenes, α-humulene (16.6 ± 0.8%), and β-caryophyllene (14.7 ± 0.4%), which together represent about 80% of the total volatile fraction from the hop-essential oil. These findings suggest that this matrix can be explored as a powerful biosource of terpenoid metabolites.

Exploring the human urine metabolomic potentialities by comprehensive two-dimensional gas chromatography coupled to time of flight mass spectrometry

Metabolomics represents an emerging issue that can aid in the diagnosis and/or prognosis of different diseases. Metabolomic study of urine is particularly interesting as it can be on the base of the developing of new faster and non-invasive methodologies. In response to this actual trend, comprehensive two-dimensional gas chromatography-time of flight mass spectrometry (GC×GC-ToFMS) combined with headspace solid phase microextraction (HS-SPME) is applied, for the first time to our knowledge, to the untargeted and comprehensive study of the volatile composition of human urine. From a total of ca. 700 compounds detected per sample, 294 were tentatively identified and distributed over the chemical families of hydrocarbons, amines, amides, esters, ketones, aldehydes, alcohols, carboxylic acids, ethers, nitriles, halides, sulfides, thiols, terpenoids, and heterocyclic compounds. To our knowledge, this is the most complete information available so far about whole human urine volatile composition, which represents a valuable data for future advanced studies in the clinical field based on urine fingerprinting. Relevant SPME and GC×GC parameters were considered. Complex sample characterization of human urine is significantly simplified due to the structured GC×GC chromatogram that produces distinct spaces for metabolite chemical families. Furthermore, the potential of this methodology in health related applications was explored by comparing the urinary volatile profiles between smoker (high-risk population for lung cancer) vs. non-smoker adults, focusing on metabolites related to oxidative stress (aliphatic alkanes and aldehydes). In spite of the small sample numbers considered, the results suggest that the urinary volatile profiles may be useful for differentiating subjects with different physiological conditions, thus making it worth to further explore its diagnostic potential.

Investigation of urinary volatile organic metabolites as potential cancer biomarkers by solid-phase microextraction in combination with gas chromatography-mass spectrometry

BACKGROUND

Non-invasive diagnostic strategies aimed at identifying biomarkers of cancer are of great interest for early cancer detection. Urine is potentially a rich source of volatile organic metabolites (VOMs) that can be used as potential cancer biomarkers. Our aim was to develop a generally reliable, rapid, sensitive, and robust analytical method for screening large numbers of urine samples, resulting in a broad spectrum of native VOMs, as a tool to evaluate the potential of these metabolites in the early diagnosis of cancer.

METHODS

To investigate urinary volatile metabolites as potential cancer biomarkers, urine samples from 33 cancer patients (oncological group: 14 leukaemia, 12 colorectal and 7 lymphoma) and 21 healthy (control group, cancer-free) individuals were qualitatively and quantitatively analysed. Dynamic solid-phase microextraction in headspace mode (dHS-SPME) using a carboxen-polydimethylsiloxane (CAR/PDMS) sorbent in combination with GC-qMS-based metabolomics was applied to isolate and identify the volatile metabolites. This method provides a potential non-invasive method for early cancer diagnosis as a first approach. To fulfil this objective, three important dHS-SPME experimental parameters that influence extraction efficiency (fibre coating, extraction time and temperature of sampling) were optimised using a univariate optimisation design. The highest extraction efficiency was obtained when sampling was performed at 50°C for 60 min using samples with high ionic strengths (17% sodium chloride, w v(-1)) and under agitation.

RESULTS

A total of 82 volatile metabolites belonging to distinct chemical classes were identified in the control and oncological groups. Benzene derivatives, terpenoids and phenols were the most common classes for the oncological group, whereas ketones and sulphur compounds were the main classes that were isolated from the urine headspace of healthy subjects. The results demonstrate that compound concentrations were dramatically different between cancer patients and healthy volunteers. The positive rates of 16 patients among the 82 identified were found to be statistically different (P<0.05). A significant increase in the peak area of 2-methyl-3-phenyl-2-propenal, p-cymene, anisole, 4-methyl-phenol and 1,2-dihydro-1,1,6-trimethyl-naphthalene in cancer patients was observed. On average, statistically significant lower abundances of dimethyl disulphide were found in cancer patients.

CONCLUSIONS

Gas chromatographic peak areas were submitted to multivariate analysis (principal component analysis and supervised linear discriminant analysis) to visualise clusters within cases and to detect the volatile metabolites that are able to differentiate cancer patients from healthy individuals. Very good discrimination within cancer groups and between cancer and control groups was achieved.