From a glimpse into the key aspects of calibration and correlation to their practical considerations in chemical analysis.

In this tutorial review, we provide a guiding reference on the good practice in building calibration and correlation experiments, and we explain how the results should be evaluated and interpreted. The review centers on calibration experiments where the relationship between response and concentration is expected to be linear, although certain of the described principles of good practice can be applied to non-linear systems, as well. Furthermore, it gives prominence to the meaning and correct interpretation of some of the statistical terms commonly associated with calibration and regression. To reach a mutual understanding in this significant field, we present, through a practical example, a step-by-step procedure, which deals with typical challenges related to linearity and outlier assessment, calculation of the associated error of the predicted concentration, and limits of detection. The utilization of regression lines to compare analytical methods is also elaborated. The results of regression and correlation data are acquired by implementing the Excel spreadsheet of Microsoft, being perhaps one of the most widely used user-friendly software in education and research.

Benzophenones in the Environment: Occurrence, Fate and Sample Preparation in the Analysis.

The ubiquitous presence of emerging contaminants in the environment is an issue of great concern. Notably, for some of them, no established regulation exists. Benzophenones are listed as emerging contaminants, which have been identified in the environment as well as in human fluids, such as urine, placenta, and breast milk. Their accumulation and stability in the environment, combined with the revealed adverse effects on ecosystems including endocrine, reproductive, and other disorders, have triggered significant interest for research. Benzophenones should be extracted from environmental samples and determined for environmental-monitoring purposes to assess their presence and possible dangers. Numerous sample preparation methods for benzophenones in environmental matrices and industrial effluents have been proposed and their detection in more complex matrices, such as fish and sludges, has also been reported. These methods range from classical to more state-of-the-art methods, such as solid-phase extraction, dispersive SPE, LLE, SBSE, etc., and the analysis is mostly completed with liquid chromatography, using several detection modes. This review critically outlines sample preparation methods that have been proposed to date, for the extraction of benzophenones from simple and complex environmental matrices and for cleaning up sample extracts to eliminate potential interfering components that coexist therein. Moreover, it provides a brief overview of their occurrence, fate, and toxicity.

Untargeted metabolomics of human keratinocytes reveals the impact of exposure to 2,6-dichloro-1,4-benzoquinone and 2,6-dichloro-3-hydroxy-1,4-benzoquinone as emerging disinfection by-products.

INTRODUCTION: The 2,6-dichloro-1,4-benzoquinone (DCBQ) and its derivative 2,6-dichloro-3-hydroxy-1,4-benzoquinone (DCBQ-OH) are disinfection by-products (DBPs) and emerging pollutants in the environment. They are considered to be of particular importance as they have a high potential of toxicity and they are likely to be carcinogenic. OBJECTIVES: In this study, human epidermal keratinocyte cells (HaCaT) were exposed to the DCBQ and its derivative DCBQ-OH, at concentrations equivalent to their IC20 and IC50, and a study of the metabolic phenotype of cells was performed. METHODS: The perturbations induced in cellular metabolites and their relative content were screened and evaluated through a metabolomic study, using 1H-NMR and MS spectroscopy. RESULTS: Changes in the metabolic pathways of HaCaT at concentrations corresponding to IC20 and IC50 of DCBQ-OH involved the activation of cell membrane α-linolenic acid, biotin, and glutathione and deactivation of glycolysis/gluconeogenesis at IC50. The changes in metabolic pathways at IC20 and IC50 of DCBQ were associated with the activation of inositol phosphate, pertaining to the transfer of messages from the receptors of the membrane to the interior as well as with riboflavin. Deactivation of biotin metabolism was recorded, among others. The cells exposed to DCBQ exhibited a concentration-dependent decrease in saccharide concentrations. The concentration of steroids increased when cells were exposed to IC20 and decreased at IC50. Although both chemical factors stressed the cells, DCBQ led to the activation of transporting messages through phosphorylated derivatives of inositol. CONCLUSION: Our findings provided insights into the impact of the two DBPs on human keratinocytes. Both chemical factors induced energy production perturbations, oxidative stress, and membrane damage.

Layered Double Hydroxide/Graphene Quantum Dots as a New Sorbent for the Dispersive Solid-Phase Microextraction of Selected Benzophenones, Phenols, and Parabens.

In this study, the synthesis of a layered double hydroxide (LDH) composite with graphene quantum dots (GQDs) and its utilization for the development of a dispersive solid-phase extraction procedure are described. To this end, a carbonate-free Mg-Al LDH was synthesized. The development of the composite material made feasible the use of GQDs in a sample preparation procedure, while the incorporation of the GQDs in the LDH structure resulted in an 80% increase in extraction efficiency, compared to the bare LDH. As a proof of concept, the composite material was used for the development of an analytical method for the extraction, and preconcentration, of benzophenones, phenols, and parabens in lake water using high-performance liquid chromatography, coupled to a diode array detector. The analytical method exhibits low limits of quantification (0.10-1.33 µg L-1), good recoveries (92-100%), and satisfactory enrichment factors (169-186). Due to the abovementioned merits, the easy synthesis and simple extraction, the developed method can be used for the routine analysis of the target compounds.

In the Swim of Cannabis: Developmental Toxicity and Metabolomic Pathway Alterations of Zebrafish Larvae Exposed to THC for the Assessment of Its Potential Environmental and Human Health Impact.

As the pharmacological properties and therapeutic applications of Cannabis sativa L. pace with the upsurge of interest of the scientific community in harnessing its constituent phytocannabinoids, illicit use may raise serious health issues. Tetrahydrocannabinol (THC) is one of the most well-known phytoactive constituents of cannabis and continues to garner scientific and public attention not only because of its pharmacological value but also because over-the-counter products of THC and prescription medications are becoming increasingly available from pharmacies, dispensaries, Internet, local retail stores, or by illicit means. Hence, a multidimensional approach was employed to examine the impact of THC on zebrafish larvae. The acute toxicity, expressed as LC50, was 1.54 mg/L. Adverse effects were observed on the phenotype, such as tail bending, pericardial edema, etc., even at concentrations lower than LC50, and fundamental functions of larvae (e.g., heart rate and cardiac contractility, and rhythm) were significantly affected. Behavioral changes were noticed, which were reflected in locomotor activity and sensitivity to light/dark changes. Finally, an untargeted metabolomic study was carried out to shed light on the metabolic alterations that occurred, providing substantiating evidence of the observed phenotype alterations. Overall, the potentially detrimental effects of THC on a vertebrate model are depicted.

The Unexplored Wound Healing Activity of Urtica dioica L. Extract: An In Vitro and In Vivo Study.

Wound healing is a great challenge in many health conditions, especially in non-healing conditions. The search for new wound healing agents continues unabated, as the use of growth factors is accompanied by several limitations. Medicinal plants have been used for a long time in would healing, despite the lack of scientific evidence veryfying their efficacy. Up to now, the number of reports about medicinal plants with wound healing properties is limited. Urtica dioica L. is a well-known plant, widely used in many applications. Reports regarding its wound healing potential are scant and sparse. In this study, the effect of an Urtica dioica L. extract (containing fewer antioxidant compounds compared to methanolic or hydroalcoholic extracts) on cell proliferation, the cell cycle, and migration were examined. Additionally, antioxidant and anti-inflammatory properties were examined. Finally, in vivo experiments were carried out on full-thickness wounds on Wistar rats. It was found that the extract increases the proliferation rate of HEK-293 and HaCaT cells up to 39% and 30% after 24 h, respectively, compared to control cells. The extract was found to increase the population of cells in the G2/M phase by almost 10%. Additionally, the extract caused a two-fold increase in the cell migration rate of both cell lines compared to control cells. Moreover, the extract was found to have anti-inflammatory properties and moderate antioxidant properties that augment its overall wound healing potential. Results from the in vivo experiments showed that wounds treated with an ointment of the extract healed in 9 days, while wounds not treated with the extract healed in 13 days. Histopathological examination of the wound tissue revealed, among other findings, that inflammation was significantly reduced compared to the control. Urtica dioica L. extract application results in faster wound healing, making the extract ideal for wound healing applications and a novel drug candidate for wound healing.

Sponges and Sponge-Like Materials in Sample Preparation: A Journey from Past to Present and into the Future.

Even though instrumental advancements are constantly being made in analytical chemistry, sample preparation is still considered the bottleneck of analytical methods. To this end, researchers are developing new sorbent materials to improve and replace existing ones, with the ultimate goal to improve current methods and make them more efficient and effective. A few years ago, an alternative trend was started toward sample preparation: the use of sponge or sponge-like materials. These materials possess favorable characteristics, such as negligible weight, open-hole structure, high surface area, and variable surface chemistry. Although their use seemed promising, this trend soon reversed, due to either the increasing use of nanomaterials in sample preparation or the limited scope of the first materials. Currently, with the development of new materials, such as melamine sponges, along with the advancement in nanotechnology, this topic was revived, and various functionalizations were carried out on such materials. The new materials are used as sorbents in sample preparation in analytical chemistry. This review explores the development of such materials, from the past to the present and into the future, as well as their use in analytical chemistry.

Melamine Sponge Functionalized with Urea-Formaldehyde Co-Oligomers as a Sorbent for the Solid-Phase Extraction of Hydrophobic Analytes.

A new procedure for the functionalization of melamine sponge (MeS) with urea-formaldehyde (UF) co-oligomers is put forward. The procedure differs from the typical synthesis of the UF co-polymer, as it employs a base-catalyzed condensation step at certain concentrations of urea and formaldehyde. The produced melamine-urea-formaldehyde (MUF) sponge cubes are hydrophobic, despite the presence of hydrophilic groups in the oligomers. The MUF sponge developed herein is used as a sorbent for the solid-phase extraction of 10 analytes, from 6 different classes (i.e., non-steroidal anti-inflammatory drugs, benzophenones, parabens, phenols, pesticides and musks) and an analytical method is developed for their liquid chromatographic separation and detection. Low limits of quantification (0.03 and 1.0 µg L-1), wide linear ranges and excellent recoveries (92⁻100%) are some of the benefits of the proposed procedure. The study of the synthesis conditions of MUF cubes reveals that by altering them the hydrophilic/lipophilic balance of the MUF cubes can be tuned, hinting towards a strong potential for many other applications.

Qualitative Alterations of Bacterial Metabolome after Exposure to Metal Nanoparticles with Bactericidal Properties: A Comprehensive Workflow Based on (1)H NMR, UHPLC-HRMS, and Metabolic Databases.

Metal nanoparticles (NPs) have proven to be more toxic than bulk analogues of the same chemical composition due to their unique physical properties. The NPs, lately, have drawn the attention of researchers because of their antibacterial and biocidal properties. In an effort to shed light on the mechanism through which the bacteria elimination is achieved and the metabolic changes they undergo, an untargeted metabolomic fingerprint study was carried out on Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria species. The (1)H NMR spectroscopy, in conjunction with high resolution mass-spectrometry (HRMS) and an unsophisticated data processing workflow were implemented. The combined NMR/HRMS data, supported by an open-access metabolomic database, proved to be efficacious in the process of assigning a putative annotation to a wide range of metabolite signals and is a useful tool to appraise the metabolome alterations, as a consequence of bacterial response to NPs. Interestingly, not all the NPs diminished the intracellular metabolites; bacteria treated with iron NPs produced metabolites not present in the nonexposed bacteria sample, implying the activation of previously inactive metabolic pathways. In contrast, copper and iron-copper NPs reduced the annotated metabolites, alluding to the conclusion that the metabolic pathways (mainly alanine, aspartate, and glutamate metabolism, beta-alanine metabolism, glutathione metabolism, and arginine and proline metabolism) were hindered by the interactions of NPs with the intracellular metabolites.

Magnetic octadecyl-based matrix solid-phase dispersion coupled with gas chromatography with mass spectrometry in a proof-of-concept determination of multi-class pesticide residues in carrots.

A novel procedure is put forward based on the combination of the well-established matrix solid-phase dispersion and the magnetic and sorption properties of magnetic octadecyl in the presence of n-octanol and was employed in a proof-of-concept sample preparation and determination of several classes of pesticide residues in carrots. The procedure does not require the transfer of blend to cartridge and subsequent packing, nor any co-sorbent for extract clean up. The hydrophobic magnetic nanoparticles utilized as a sorbent, can be retrieved by n-octanol under the application of a magnetic field due to hydrophobic interactions. Elution of pesticide residues is then carried out with an organic solvent. A total of 26 pesticides were included in this procedure and the target compounds were analyzed using gas chromatography with mass spectrometry in the selective ion monitoring mode. The average extraction recoveries obtained from carrot samples fortified at three different concentrations (20, 50, and 500 µg/kg) were 77-107%. The estimated limits of quantitation for most target analytes were in the low µg/kg level. The study demonstrates that the proposed extraction procedure is simple and effective, avoiding a clean-up step for the sample preparation of vegetable.

Graphene-coated cotton fibers as a sorbent for the extraction of multiclass pesticide residues from water and their determination by gas chromatography with mass spectrometry.

A straightforward functionalization procedure is proposed for synthesizing a cotton-supported graphene as an extraction material, which is effectively employed for the extraction of multiclass pesticides from environmental waters prior to their determination by gas chromatography with mass spectrometry. Different experimental parameters that affect the extraction efficiency, including pH of the extraction, stirring rate, extraction time, ionic strength, presence of humic acid, sample volume, amount of sorbent, and elution conditions, were investigated and properly established. The advantages of the present extraction method are the simplicity of implementation, rapidity, and low consumption of sorbent per extraction. Moreover, the pesticides on the adsorbent are stable, under certain storage conditions, rendering the cotton-supported graphene suitable for environmental field studies. The applicability of the cotton-graphene-based procedure for routine analysis was demonstrated by the determination of pesticides in a lake water sample. The recoveries ranged from 83 to 107%, the limits of quantitation were in the range of 0.02-0.09 µg/L, and the calculated relative standard deviations varied from 3 to 8% (data obtained with the same batch of sorbent). Because of the acceptable analytical characteristics, the developed method shows great prospects in determining certain classes of pesticides in water.

Octyl-modified magnetic graphene as a sorbent for the extraction and simultaneous determination of fragrance allergens, musks, and phthalates in aqueous samples by gas chromatography with mass spectrometry.

An effective, simple, and low-cost sample preparation method based on dispersive SPE followed by GC with MS is developed for the multianalyte determination of fragrance allergens, musks, and phthalates, at sub-ppb levels. The extraction procedure is based on a novel magnetic graphene sorbent, which is functionalized with octylamine, taking advantage of the functionalization's hydrophobic properties and π-π interactions with the analytes. Two alkyl amines, the octylamine and octadecylamine are studied to introduce alkyl chains in the basal plane of graphene. Magnetic graphene- octadecylamine is proved to be highly hydrophobic to such a degree that is hard to disperse in the bulk aqueous matrixes. Because of this behavior, its extraction efficiency for the target analytes is low. The synthesis and applicability of the magnetic graphene-octylamine as more favored sorbent are optimized in terms of the most determining experimental conditions. The detection and quantification limits, which are calculated based on S/N ratio of 3 and 10, respectively, ranged from 0.29 to 3.2 ng L(-1) and from 0.89 to 9.6, respectively. The dispersive SPE is successfully applied to routine analysis for the determination of the target analytes in samples from municipal treatment plant of Ioannina (Greece), from Pamvotis Lake and baby bathwater. The reproducibility of the spiked biological treatment plant water sample is evaluated and the relative standard deviation values range between 2.1 and 9.4%.

Metabolomic Fingerprint Assay in Zebrafish Embryos.

In order for new drugs to enter the market, extensive studies are needed to examine toxic effects. Among others, teratogenicity studies are of paramount importance. Of even higher importance is to gain knowledge on the biological responses that take place upon drug exposure, so as to have a better understanding of the molecular mechanisms that govern developmental changes. Metabolomics is the research field that studies the changes in the chemical composition of metabolites contained within cells. Conducting metabolomics studies results in valuable information. Zebrafish is a vertebrate model organism that bridges in vivo assays and in vivo studies. In this chapter, we propose a metabolomic fingerprint assay for the study of metabolic changes in zebrafish embryos upon exposure to various drugs. The metabolome of zebrafish is extracted, and the 1H-NMR spectrum is recorded. Using open-access metabolomic databases, a list of tentative metabolites is retrieved. The presence of the tentative metabolites is further confirmed by UHPLC-HRMS. Ultimately, after a metabolic pathway analysis, the metabolic network is revealed and useful conclusions can be drawn.

Two-Birds-with-One-Stone Synthesis of Hydrophilic and Hydrophobic Fluorescent Carbon Nanodots from Dunaliella salina Biomass as 4-Nitrophenol Nanoprobes Based on Inner Filter Effect and First Derivative Redshift of Emission Band.

4-Nitrophenol (4-NP) has been listed as a priority pollutant and has also been reported as a human urinary metabolite used as a marker to evaluate exposure to certain pesticides. In the work herein, a solvothermal approach is applied to the one-pot synthesis of both hydrophilic and hydrophobic fluorescent carbon nanodots (CNDs), utilizing the halophilic microalgae Dunaliella salina as a biomass precursor. Both kinds of the produced CNDs showed appreciable optical properties and quantum yields, good photostability and they were capable of probing 4-NP by quenching their fluorescence through the inner filter effect. Interestingly, a prominent 4-NP concentration-dependent redshift of the corresponding emission band of the hydrophilic CNDs was noticed, which was further exploited, for the first time, as an analytical platform. Capitalizing on these properties, analytical methods were developed and applied to a variety of matrixes, such as tap water, treated municipal wastewater and human urine. The method based on the hydrophilic CNDs (λex/λem: 330/420 nm) was linear in the range of 0.80-45.0 µM and showed acceptable recoveries (from 102.2 to 113.7%) with relative standard deviations of 2.1% (intra-day) and 2.8% (inter-day) for the quenching-based detection mode and 2.9% (intra-day) and 3.5% (inter-day) for the redshift one. The method based on the hydrophobic CNDs (λex/λem: 380/465 nm) was linear in the range of 1.4-23.0 µM, with recoveries laying within the range of 98.2-104.5% and relative standard deviations of 3.3% and 4.0% for intra-day and inter-day assays, respectively.

Detection of microcystins in Pamvotis lake water and assessment of cyanobacterial bloom toxicity.

Lake Pamvotis is a shallow, eutrophic Mediterranean lake with ecological significance. This paper deals with the evaluation of cyanobacterial toxicity in Lake Pamvotis. ELISA and HPLC revealed the presence of significant amounts of MCYST-LR. Danio rerio bioassay confirmed the toxic nature of the bloom. Cyanobacterial extracts had adverse toxic effects on development of D. rerio. Also, it was shown that cyanobacterial extracts containing environmentally detected concentrations of MCYST can cause reduced survival rate of fish species. The results clearly indicate that cyanobacterial blooms in Lake Pamvotis may be regarded as human and fish health hazard. Continuous monitoring of the lake is suggested, in order to prevent future possible intoxications.

Melamine sponge functionalized with carbon nanodots for the extraction of polyaromatic hydrocarbons and musks from environmental samples prior to their determination by gas chromatography-mass spectrometry.

In this study, the functionalization of melamine sponge (MeS) with graphene quantum dots (GQDs) and its use as a sorbent for the extraction of polycyclic aromatic hydrocarbons (PAHs) and musks from environmental samples are presented. The MeS@GQDs is prepared by modification of the MeS with GQDs in a one-pot, single-step, in situ synthesis, using citric acid as carbon source. The produced MeS@GQDs was used to develop and optimize an analytical method based on solid-phase extraction mode, for the subsequent analysis of soil samples and treated effluents exploiting the extraction properties of the synthesized MeS@GQDs. The developed method not only presented satisfactory repeatability (RSD<8.7%) and inter-day repeatability (RSD<9.6%), but also its limits of quantification were found to be low (15-80 ng L-1). Moreover, the proposed method was linear in a wide range of concentrations (0.015-11.8 µg L-1) and the recoveries from difficult matrixes, such as treated effluents and soil, were satisfactory. Overall, the use of the sorbent for the development of a new analytical method was found to be advantageous as compared with other reported methods.

Metabolomic Profiling Unveils the Impact of Non-Doped and Heteroatom-Doped Carbon Nanodots on Zebrafish (Danio rerio) Embryos.

Recently, concern has been raised over the transport, transformation, and fate of carbon nanodots (CNDs) after their release into the environment. Their toxicity towards organisms and humans has recently been addressed as an important issue. In this study, a metabolomic approach was employed to obtain an insight into the effect of CNDs (either pristine or doped with nitrogen and nitrogen/sulfur) on zebrafish. Embryos were exposed to concentrations corresponding to lethal concentration (LC) LC50 (550, 400, and 150 µg mL-1), LC50/2 (275, 200, and 75 µg mL-1), and LC50/4 (138, 100, and 38 µg mL-1) of the three CNDs (non-doped, N-doped, and N,S-codoped, respectively) to scrutinize the interactions of the CNDs with the larvae. Numerous differences in the metabolic pathways were recorded in all cases. Seven metabolic pathways were detected in the control larvae. When the larvae were exposed to concentrations equal to LC50, LC50/2, and LC50/4 of non-doped CNDs, 12, 12, and 3 metabolic pathways were detected, respectively. In the case of N-doped CNDs, 4, 7, and 4 pathways were detected, while in the case of N,S-codoped CNDs, 8, 5, and 5 pathways were detected when exposed to concentrations of LC50, LC50/2, and LC50/4, respectively. In all cases, certain metabolic pathways were altered while others were either down-regulated or up-regulated. Some of these changes include the activation of alanine, aspartate, and glutamate metabolism, aminoacyl-tRNA biosynthesis, butanoate metabolism, D-glutamine, and D-glutamate metabolism, glutathione metabolism, selenoamino acid metabolism, valine, leucine, and isoleucine degradation pathways. Moreover, the deactivation of starch and sucrose metabolism, the glycine, serine, and threonine metabolism, among others, were recorded. Our findings underline the importance to further study the impact of CNDs on marine organisms. As zebrafish has been shown to share many similarities with humans in bioprocesses and genome, it can be assumed that CNDs may also pose a threat to human health.

Induced toxicity in early-life stage zebrafish (Danio rerio) and its behavioral analysis after exposure to non-doped, nitrogen-doped and nitrogen, sulfur-co doped carbon quantum dots.

In this study, the effects of doping of CQDs with alternative functional groups (dopants) were evaluated through embryonic development of zebrafish (Danio rerio). The CQDs were synthesized using simple and low-cost sources: Non-doped (citric acid was used as the carbon source), nitrogen-doped (N-doped) and nitrogen, sulfur-co-doped (N,S-doped). The CQDs induced significant toxicity to zebrafish (>150 µg/mL) and the toxic effects were dose-dependent. The N,S-doped CQDs were the most toxic (LD50 = 149.92 µg/mL), followed by the N-doped CQDs (LD50 = 399.95 µg/mL) while the non-doped CQDs were the least toxic (LD50 = 548.48 µg/mL) of the three. The growth rate (GR) was affected following the toxicity pattern (GRNS-doped

Cannabinol in the spotlight: Toxicometabolomic study and behavioral analysis of zebrafish embryos exposed to the unknown cannabinoid.

Cannabinol (CBN) is a degradation product of the cannabis metabolite Δ9-tetrahydrocannabinol. The CBN concentration in cannabis leaves ranges between 0.1 and 1.6% (w/w of dry weight); it increases as the plant ages and its formation is affected by the storage conditions. As CBN has not been extensively studied so far, the need to examine its impact in vivo is imperative due to the increasing use of cannabis globally. In the study herein, the CBN toxicity, effects on heart physiology, morphological malformations, behavioral changes and alterations in metabolic pathways of zebrafish larvae upon CBN exposure to sublethal concentrations were examined. The LD50 value was estimated at 1.12 mg/l. At the same time, malformations in zebrafish larvae increased significantly in a dose-dependent manner and exposure to CBN concentrations greater than 0.75 mg/l provoked abnormalities like pericardial edema, yolk sac anomalies and tail bending. Concentrations above this threshold resulted in elongated and shorter in width hearts and in separation of ventricle from atrium. The total movement distance and velocity were increased in dark and decreased in light conditions, in a concentration-dependent manner. Our results showed that CBN acts both as a stimulant and a sedative, with larvae to exhibit altered velocity and bradycardia, respectively. The metabolomic analysis revealed alterations mainly to amino acids, which are related to acute toxicity and hint towards systemic metabolic and neuropathophysiological changes. Taken together, our data indicate increased toxic effects as CBN exposure concentration increases, which should be taken into consideration when studying the impact of cannabis on organisms.

Developments on chemometric approaches to optimize and evaluate microextraction.

Chemometric experimental design in microextraction plays a crucial role in sustaining the highest quality of analytical data. Making use of the main significant points of chemometric experimental design and microextraction in analytical chemistry we formed the core of this review article. A step-by-step chemometric approach is provided to optimize and validate microextraction-based analytical processes. Significant applications are reported with developments related to microextraction combined with chemometric optimization processes. As it appears from the numerous examples provided in this review, a great number of researchers give credit to the combination of microextraction and chemometrics recognizing that it significantly streamlines sample processing. Moreover, the combination of microextraction with chemometrics addresses problems relating to improvement in detectability and method validation. A worked example on the microextraction of polychlorinated biphenyls is incorporated into the relevant sections of this article and comprehensively provides in a rational and integrated way guidance to people dealing with this subject.