Simultaneous Detection of Azodicarbonamide and the Metabolic Product Semicarbazide in Flour by Capillary Electrophoresis

In the present work, capillary electrophoresis (CE) was used for the first time for the simultaneous analysis of azodicarbonamide (ADA) and semicarbazide (SEM), and the capillary electrophoresis separation conditions, extraction agents, and derivatization conditions were investigated. In 20 mmol L^?1 sodium tetraborate, 30 mmol L^?1 β-cyclodextrin (β-CD), 17 % isopropanol (v/v), and 25 mmol L^?1 sodium dodecyl sulfate (SDS) running buffer, ADA and SEM previously derivatized with 9-fluorenylmethyl chloroformate (FMOC) were separated in less than 25 min with good sensitivity. The linear ranges were 8.3?×?10^?4～6.6?×?10^?2 mmol L^?1 and 1.9?×?10^?3～3.4?×?10^?2 mmol L^?1, and detection limits (S/N?=?10) were 0.5 and 0.15 mg kg^?1 for ADA and SEM, respectively. The proposed method was successfully applied for the simultaneous analysis of ADA and SEM in five flour samples with satisfactory recovery data from 88.0 to 93.0 % for ADA and 98.0 to 106.0 % for SEM, indicating the valuable potential application of this method for food analysis.     

Speciation Determination of Selenium in Seafood by High-Performance Ion-Exchange Chromatography-Hydride Generation-Atomic Fluorescence Spectrometry

A high-performance ion-exchange chromatography coupled with hydride generation-atomic fluorescence spectrometry (HPIEC-HG-AFS) method was developed for simultaneous speciation of selenium in seafood. Three selenium species including of selenocystine (Se-Cys), selenome-thionine (Se-Met), and selenite Se(IV) were separated on an anion-exchange column (PRP-X100) with eluent of 30 mM NH₄H₂PO₄ and methanol (39:1, v/v) in 10 min at the flow rate of 1.0 mL min^?1. Variables affecting the HG-AFS detection of selenium species were optimized. The optimum conditions found were the following: reducing agent, 2.0 % of KBH₄, and 5.0 % of HCl; lamp current, 90 mA; photomultiplier tube voltage, 280 V; flow rate of carrier gas, 300 mL min^?1; and shielding gas, 800 mL min^?1. Under the optimized conditions, the good linearity of calibration curves (R ²?>?0.999) between signal of fluorescence and concentration of selenium species was obtained in the range of detection limits (DLs), 80 μg L^?1, and the DLs of Se-Cys, Se-Met, Se(IV) were 1.66, 0.990, 1.10 μg L^?1, respectively. The repeatability of the method, expressed as relative standard deviation, was less than 5.0 % (n?=?10), and the average recoveries for spiked test were from 87.3 to 103 % for three analytes in real seafood samples. The developed HPIEC-HG-AFS method was successfully applied for the speciation of selenium in seafood samples.     

Determination of Major Sialic Acids in Dairy Products by Electrophoretic Stacking Technology with Contactless Conductivity Detection

Synergistic stacking technique by combining field-amplified sample injection with moving chemical reaction boundary was developed for the sensitive determination of two major sialic acids, N-acetylneuraminic acid (NANA) and N-glycolylneuraminic acid (NGNA) based on capillary electrophoresis with capacitively coupled contactless conductivity detection. A series of experimental parameters affecting electrophoretic separation, detection sensitivity, and hydrolysis efficiency of sialic acids were investigated. Under the optimum conditions, NANA and NGNA could be well separated from the common monosaccharides and disaccharides as well as other potential coexisting inorganic and organic anions in a running buffer of 30 mmol L^?1 NaOH–10 mmol L^?1 Na₂HPO₄/0.8 mmol L^?1 CTAB. This developed method has been applied to determine the target analytes in dairy products. In terms of its high sensitivity (LODs 1.7–2.2 ng mL^?1, namely, 5.5–7.2 nmol L^?1), good linearity (r > 0.999), acceptable recovery (93–107%), and reliability of acid hydrolysis step, this proposed method provides a simple, rapid, sensitive, and environmentally friendly alternative for the analyses of the main sialic acids in dairy products without derivatization.     

Automated Sequential Injection Method for Determination of Caffeine in Coffee Drinks

An automated sequential injection analysis spectrophotometric assay for the determination of purine alkaloids in coffee drinks was developed. The sample was treated with a carrez reagent for matrix suppression followed by filtration; subsequently, alkaloids were separated from organic acids using a short C18 monolithic column (10 × 4.6 mm). The flow rate of the separation step was 10 μL s^?1 with 10% v/v of methanol as the mobile phase. The sum of alkaloids evaluated as caffeine was detected at 274 nm. The influence of the main parameters affecting the quantification of purine alkaloids was optimized. One sample analysis lasted 15 min when aspirated in triplicate. The linear range was 1–15 mg L^?1, and the determination coefficient (r ²) was 0.9969. The limit of detection and limit of quantitation were 0.128 and 0.425 mg L^?1, respectively. The repeatability evaluated as the relative standard deviation (RSD) was 3.58% (n = 12, 10 mg L^?1). Under optimal conditions, the method was successfully applied to determine purine alkaloids in different real samples including soluble coffee, coffee from an espresso machine, and brewed coffee drinks.     

Tocopherols and Tocotrienols: an Adapted Methodology by UHPLC/MS Without Sample Pretreatment Steps

Ultra high-performance liquid chromatography-electrospray ionization-mass spectrometry (UHPLC/ESI/MS) methodology was adapted for identification and quantification of tocopherols and tocotrienols in vegetable oils with no derivatization or sample preparation steps. The UHPLC analysis was performed using a C18 column and mobile phase composed of methanol: water: ammonium hydroxide (99:1:0.1 v/v/v) and isopropanol. A single mass spectrometer with electrospray on negative mode was used as a detector for tocopherols and tocotrienols. The samples were diluted in isopropanol. The limit of quantification for tocopherols was 0.006 μg mL^?1, and the linear range was 0.006 to 0.01 μg mL^?1; for tocotrienols, the limit of quantification was 0.002 μg mL^?1, and the linear range of analysis was 0.002 to 0.003 μg mL^?1. The correlation coefficients were higher than 0.99, indicating that the method has suitable linearity. The methodology has proven to be precise, reproducible, and robust for the parameters studied.     

Hybrid Amine-Functionalized Titania/Silica Nanoparticles for Solid-Phase Extraction of Lead,Copper, and Zinc from Food and Water Samples: Kinetics and Equilibrium Studies

In the present study, hybrid amine-functionalized titania/silica nanoparticles were employed as a new and novel adsorbent for solid-phase extraction of Pb²⁺, Cu²⁺, and Zn²⁺ ions prior to their determination using flame atomic absorption spectrometry. Under the best conditions (including adsorbent, 0.4 g; eluent, 5.0 mL nitric acid (HNO₃), 3.0 mol L^?1, 1.0 mL min^?1; and sample, pH 5.0, 3.0 mL min^?1), detection limits, adsorption capacities, and preconcentration factors were 0.12–0.24 μg L^?1, 7.1–20.7 mg g^?1, and 200, respectively. To predict the adsorption isotherms, different isotherm models were studied and the obtained results showed that the Langmuir model is the most suitable one to explain the experimental data. The kinetics of the reaction followed pseudo-second-order kinetic model. Thermodynamic parameters like free energy (ΔG ⁰) and enthalpy (ΔH ⁰) confirmed the spontaneous and exothermic nature of the process. The method was successfully applied for determination of the analytes in different food and water samples.     

Antioxidant Activity and Determination of Phenolic Compounds from <Emphasis Type="Italic">Eugenia involucrata</Emphasis> DC. Fruits by UHPLC-MS/MS

Fruits have been the focus of several studies aimed at finding new antioxidant sources for protection against the damage caused by reactive species. In this study, the antioxidant activity and the presence of phenolic compounds in all parts (peel, pulp, and seeds) of Eugenia involucrata DC. fruits were evaluated. DPPH^·, ABTS^·+, and ORAC methods were used to determine the antioxidant activity, and an UHPLC-MS/MS method was developed for determining the phenolic compounds (gallic, chlorogenic, ferulic, p-coumaric and ellagic acids, quercetin, and myricetin). In the determination of both antioxidant activity and phenolic composition, the efficiency of solvents with different polarities—methanol/H₂O (80:20, v/v), ethanol/H₂O (80:20, v/v), methanol/acidified water with phosphoric acid pH 3.00 (80:20, v/v), and ethyl acetate—for the extraction of the phenolic compounds, was also evaluated. All parts of E. involucrata fruits showed antioxidant activity, in the range of 36.68 ± 1.44 to 873.87 ± 18.24 μmol TE g^?1, being the highest values found in the seeds and peel when more polar extraction solvents were used. Six, five, and three phenolic compounds were identified and quantified in the pulp, peel, and seeds, respectively, with the highest abundance as p-coumaric acid (14 ± 2 mg kg^?1) in the pulp, quercetin (47 ± 5 mg kg^?1) in the peel, and gallic acid (74 ± 4 mg kg^?1) in the seeds, also when more polar solvents were used. Although antioxidant activity methods suggested that the peel and seeds have more antioxidant potential, a wider variety of compounds were determined in the pulp.     

SWCNT-modified carbon paste electrode as an electrochemical sensor for histamine determination in alcoholic beverages

In this work, a simple and rapid electrochemical method is presented for the voltammetric determination of histamine based on carbon paste electrodes bulk-modified with single-walled carbon nanotubes. As monitored in cyclic voltammetry histamine undergoes an irreversible electrochemical oxidation with a peak potential of ca. +1.25 V (vs. Ag/AgCl, 3 mol L^?1 KCl) in phosphate buffer solution (PBS, 0.1 mol L^?1, pH 6.0). At optimized differential pulse voltammetric parameters, the current response of histamine was linearly proportional to its concentration in the range from 4.5 to 720 μmol L^?1. A low limit of detection of 1.26 μmol L^?1 and a limit of quantification of 3.78 μmol L^?1 of histamine, as well as good reproducibility (RSD?=?0.48–3.40 %) were obtained using the carbon paste electrode modified with single-walled carbon nanotubes. The proposed sensor was successfully applied to the determination of histamine in commercial beer and wine samples.     

Simultaneous Determination of Nitrate and Nitrite in Fish Products with Improved Sensitivity by Sample Stacking-Capillary Electrophoresis

A fast and reproducible method for the simultaneous determination of nitrate and nitrite ions in canned fish samples by capillary zone electrophoresis has been developed. The sensitivity of the method was increased by applying a sample stacking technique. Optimal separation conditions were selected as 30 mmol L^?1 formic acid and 30 mmol L^?1 sodium sulfate at a pH of 4.0. The separation of nitrate and nitrite ions was achieved within 2.5 min. The limits of detection obtained at a signal-to-noise ratio of 3 for nitrate and nitrite were 0.55 and 0.82 μmol L^?1, while the relative standard deviations of intra-day corrected peak areas were 0.99 and 2.74 %, respectively. Recovery values ranged between 88.7 and 104 % for both ions. The method was successfully applied to canned fish samples, namely tuna, mackerel and sardine.     

Development of CO<Subscript>2</Subscript>-Mediated Switchable Hydrophilicity Solvent-Based Microextraction Combined with HPLC-UV for the Determination of Bisphenols in Foods and Drinks

In traditional dispersive liquid-liquid microextraction procedures, both extraction and dispersive solvents are required, and thus, it increases the consumption of organic solvent. Herein, we reported a CO₂-mediated switchable hydrophilicity solvent-based microextraction (SHS-BME) for the determination of bisphenol compounds (BPCs) in complex milk and drink samples. N,N-Dimethylcyclohexylamine was used as a switchable hydrophilicity solvent; it can switch reversibly between one form that is miscible with water and another that forms a biphasic mixture with water, and thus allow extraction of the analytes in a homogeneous phase without dispersive solvent. Several important parameters were screened and optimized by single factor experiments and central composite design as follows: 782 μL of switchable solvent, 375 μL of NaOH solvent, and 1.1:1 switchable solvent/water (v/v). Under the optimized SHS-BME conditions, the limit of detections (LODs) for BPCs in milk, orange juice, and energy drink samples were in the range of 0.27–0.40 μg L^?1 for BPE, 0.17–0.30 μg L^?1 for BPA, and 0.50–0.67 μg L^?1 for BPB, respectively, and the extraction recoveries for BPCs were in the range of 79.5–103.4% in milk, of 84.5–97.5% in orange juice, and of 91.9–101.2% in energy drinks. The precision of the method, based on relative standard deviations (RSDs), ranged from 1.7 to 4.8% and from 2.1 to 5.7% for intra-day and inter-day comparisons, respectively. In total, this SHS-BME method possesses many advantages, such as high extraction recovery and high detection sensitivity (low LODs and RSDs), no requirement of dispersive solvent, simple operational procedure, reducing the pretreatment time and workload, and so on. Therefore, it has a great potential application value for detection of trace BPCs in routine food tests.     

Validation of a HS-SPME-GC Method for Determining Higher Fatty Esters and Oak Lactones in White Rums

Higher fatty esters and oak lactones are the main components of white rum aroma and furthermore, they have an important sensorial impact in these distilled alcoholic beverages. A method for analyzing these volatile compounds was validated. It involves a separation and concentration step using headspace solid-phase microextraction (HS-SPME) and determination by capillary gas chromatography using flame ionization detection. The method showed a good within-day (RSD?<?3 %) and between-day precision (RSD?<?5 %). The calibration curves were linear at the tested ranges (R?>?0.99) and the limits of detection and quantification were 0.001–0.018 and 0.003–0.054 mg L^?1 (12 %?v/v alcohol), respectively. Good recoveries were obtained (98.6–100.3 %). The method is suitable for the quality control of higher fatty esters and oak lactones in white rums.     

Determination of Eugenol in Aquatic Products by Dispersive Solid-Phase Extraction and Ultra-High-Performance Liquid Chromatography-Tandem Mass Spectrometry

A novel procedure, dispersive solid-phase extraction coupled with ultra-high-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS), was developed for the determination of eugenol in aquatic products (shrimp, crab, and carp). Aquatic products were extracted with acetonitrile and primarily purified by dispersive solid-phase extraction with graphitized carbon black as absorbent. The pretreated acetonitrile extract was detected by UHPLC-MS/MS. UHPLC was carried out on Dikma Endeavorsil C₁₈ (30 mm × 2.1 mm, 1.8 μm) column eluted by methanol and water (80:20 v/v) at a rate of 0.30 mL min^?1. Tandem mass spectrometry was performed by electrospray ionization in negative ion mode to identify and quantify eugenol during multiple reaction monitoring. Under optimized analytical conditions, the matrix-matched spiked calibration sample demonstrates good linearity between 5.0 and 500.0 μg kg^?1 with a linear regression coefficient of 0.9996. The average recovery of eugenol from aquatic products is 95.3–103.4% at spiked levels between 5 and 50 μg kg^?1 with a relative standard deviation (n = 6) less than 5.4%. The limits of detection and quantification for eugenol were calculated to be 1.47 and 4.91 μg kg^?1, respectively. In comparison with those reported, the proposed method has advantages in low detection limit, high recovery, and short analysis time, meeting the requirements for the determination of trace eugenol residue in aquatic products.     

Glucose Biosensor Based on a Glassy Carbon Electrode Modified with Multi-Walled Carbon Nanotubes-Chitosan for the Determination of Beef Freshness

In this study, the glucose biosensor was developed for the determination of the beef meat freshness based on a glassy carbon electrode (GCE) modified with multi-walled carbon nanotubes (MWCNTs) and chitosan (Chi). Glucose oxidase (GOx) was immobilized onto the MWCNTs-Chi/GCE surface by cross-linking the enzyme through glutaraldehyde with bovine serum albumin (BSA). Glutaraldehyde solution (0.25%, w/w) was also added to prevent enzyme release. The properties of the developed biosensor were characterized with cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS) using [Fe (CN)₆]^3?/4?as the supporting electrolyte. The influence of various parameters was investigated, and 0.1 mol L^?1 PBS with pH = 6.4 was chosen as the optimal supporting electrolyte for this experiment. The linear relationship between the current and the concentration of glucose was obtained from 0.2 to 1.2 mmol L^?1, with a detection limit of 0.05 mM at a signal-to-noise ratio of 3 and displayed good linearity (R ² = 0.9902), while the biosensor showed a rapid response to glucose. In addition, the developed glucose biosensor was applied in the determination of glucose in beef as an indicator of beef freshness compared to the total volatile basic nitrogen (TVB-N) method. The glucose level was decreased with increasing beef storage time.     

Determination of Trace Elements in Camellia Oil by Vortex-Assisted Extraction Followed by Inductively Coupled Plasma Mass Spectrometry

A simple vortex-assisted liquid–liquid extraction protocol followed by ICP-MS has been developed for the determination of nine elements (Cr, Mn, Fe, Ni, Cu, As, Zn, Cd, and Pb) in camellia oil samples. The key parameters affecting the extraction efficiency (extraction solvent characteristics, extraction time, and solvent/oil ratio) were carefully examined and optimized. Optimum results were obtained when 5 g of oil sample was used followed by vortex-assisted extraction for 20 min with 10 mL of 10 % HNO₃ (v/v). Detection limits ranging from 0.03 to 1 μg L^?1 and relative standard deviation lower than 6 % were obtained. The accuracy of the method was assessed by spiking experiments and comparison of the results from the extraction procedure with those obtained from microwave-assisted digestion of the samples. The recoveries were in the range of 84.3~102.3 %. No statistical differences, based on t test at a confidence level of 95 %, were detected. The proposed method was found to be simple, fast, and accurate when applied to camellia seed oil samples and has great potential in quantitatively detecting elements in various oils.     

HPLC Determination of Spectinomycin in Feed Premixes and Dosage Forms Using 1-Naphthyl Isocyanate Precolumn Derivatization with UV Detection

A new, simple, and sensitive HPLC method was developed for the determination of spectinomycin hydrochloride in dosage forms and feed premixes through derivatization with 1-naphthyl isocyanate. The separation was achieved on a C₁₈ column using a mobile phase consisting of acetonitrile/water (50:50 v/v, pH 3.2) in a flow rate of 1 mL/min with UV detection at 230 nm. The factors influencing the derivatization reaction yields were carefully studied and optimized. The method was linear over the concentration range of 10–100 μg/mL with a limit of detection 0.25 μg/mL and limit of quantitation 1.75 μg/mL. The developed method was successfully applied to the analysis the drug in the commercial dosage forms and spiked feed premix samples; the average recoveries were 99.79 and 99.56, respectively. The analytical performance of the method was fully validated and the results were satisfactory. A proposal of the reaction pathway was presented.     

Application of Ionic Liquid-Based Ultrasound-Assisted Extraction of Five Phenolic Compounds from Fig (<Emphasis Type="Italic">Ficus carica</Emphasis> L.) for HPLC-UV

Ionic liquid-based ultrasonic-assisted extraction (IL-UAE) was successfully developed to extract the known phenolics gallic acid, chlorogenic acid, rutin, psoralen, and bergapten present in the leaves, pulps, and peels of Ficus carica L. In this work, the proposed method was evaluated in comparison with regular ultrasonic-assisted extraction in which methanol was the extractant and exhibited higher efficiency. Moreover, ionic liquids with different cations were investigated and 1-butyl-3-methylimidazole hexafluorophosphate solution was selected as the optimal extractant at concentration of 1.0 mol L^?1. The corresponding extraction parameters including extraction solvent, the concentration of [BMIM][PF₆], solid–liquid ratio (g mL^?1), ultrasonic extraction time, and extraction temperature were optimized. The phenolics were then determined by high-performance liquid chromatography (HPLC). Under the optimized conditions, the content of gallic acid, chlorogenic acid, rutin, psoralen, and bergapten in leaves, pulps, and peels of F. carica L. was 12.67–37.16, 14.75–90.07, 107.91–222.37, 2.59–67.83, and 1.99–20.21 μg/0.1 g, respectively. This study suggests that IL-UAE is a rapid, simple, and green preparation technique.     

Cysteamine-CdTe Quantum Dots Electrochemically Synthesized as Fluorescence Probe for Resveratrol

This work proposes a fluorescent probe based on CdTe quantum dots (QDs) for the determination of resveratrol in wine samples. The synthesis of cysteamine (CA) capped CdTe QD was carried out in a one-pot eco-friendly process, resorting to the electrochemical reduction of metallic tellurium powder in a graphite macroelectrode (cavity cell). The reduced species of tellurium (Te^2? and Te₂^2?) migrated to an intermediate compartment of the electrochemical cell and in the presence of a cadmium salt and organic stabilizing agent (CA), forming the colloidal dispersion of CdTe in a single step. Under optimum synthesis conditions, the fluorescence intensity of the prepared nanoparticles varied linearly with the resveratrol concentration in the range from 3.25 to 75 μg L^?1 (R²?=?0.9984), with a detection limit of 0.97 μg L^?1 and RSD of 3.7% (5.0 μg L^?1 resveratrol, n?=?10). The method was successfully applied to the resveratrol determination in wines, with recoveries from 97.8 to 112.4%. Student’s t test was applied and no statistically significant difference was observed between the two methods (HPLC and proposed), with a confidence level of 95% (t_tabulated?=?2.45 and t_calculated?=?0.38). The resveratrol determination method, by using CdTe-CA QDs as fluorescence probe, was simple, rapid, inexpensive, and sensitive.     

Determination of Hormones Residues in Milk by Gas Chromatography-Mass Spectrometry

The article presents the use of gas chromatography-mass spectrometry (GC-MS) technique in a method for the determination of 18 anabolic hormones from synthetic stilbenes, steroids and resorcylic acid lactones (RALs) groups in raw milk and milk powder. Sample preparation consisted of liquid-liquid extraction with diethyl ether and purification by solid phase extraction (SPE). Prior to instrumental analysis, the reaction of derivatisation with the heptafluorobutyric anhydride or N-methyl-N-trimethylsilyltrifluoroacetamide was performed. Method validation was carried out according to the required performance criteria of the Commission Decision 2002/657/EC. The apparent recovery of all analytes at 1 μg L^?1 (kg^?1) level was ranged between 70.4 and 119.4 % with the coefficients of variation values less than 30 %. The decision limits (CCα) and the detection capabilities (CCβ) were in the range of from 0.11 to 0.44 μg L^?1 (kg^?1) and from 0.19 to 0.75 μg L^?1 (kg^?1), respectively. The procedure has been accredited and successfully applied as a screening method for the presence of hormone residues in the study of commercial samples of milk.     

Dynamic Reaction Cell-ICP-MS as a Powerful Tool for Quality Control of a Se-Enriched Dietary Supplement

The aim of this work was to evaluate different approaches employing a reaction cell to circumvent spectral interferences over ⁸⁰Se⁺ to increase the sensitivity in the determination of Se by inductively coupled plasma mass spectrometry (ICP-MS). Different gases (NH₃, CH₄, and O₂) were employed, and the operating conditions were optimized by a central composite design, evaluating the effect of the reaction gas flow rate and the rejection parameter q (Rpq) on the limit of detection (LOD) of the method. All reaction gases studied reduced the interference by ⁴⁰Ar₂ ⁺ over ⁸⁰Se⁺, reducing the LOD when compared to the LOD obtained with ICP-MS operating in the standard mode (LOD = 0.2 μg kg^?1). A better LOD (0.01 μg kg^?1) was obtained with CH₄, while 0.1 μg kg^?1 was the LOD with NH₃. The use of O₂ as a reaction gas enabled the determination of Se at m/z 96 (⁸⁰Se¹⁶O⁺) with adequate analytical performance (LOD = 0.03 μg kg^?1). The accuracy of the method was evaluated by analyzing the certified reference material (CRM) Selm-1, and the results obtained ranged from 99 to 104% of the certified value. In addition, Se dietary supplements of four different brands and commercial yeast were analyzed, and the major sources of uncertainty were studied. The dietary supplements followed the criteria adopted by Brazilian legislation, although the uncertainty study highlighted the great variation in the Se content of each brand. Clearly, the manufacturing process of dietary supplements needs more rigorous quality control, considering that this product can affect the health of consumers.     

The Use of Different MS Techniques to Determine Glutathione Levels in Marine Tissues

Several techniques were used, mainly mass spectrometry connected with gas chromatography, matrix-assisted laser desorption with ionization time-of-flight and mass spectrometry connected with liquid chromatography. A major problem was encountered in determining glutathione, which can be conditioned by the pH and selected reducing agents. The GSH form can be oxidized through derivatization, and a small glutathione amount in the biological samples may hinder the determination process. Another problem is the existence of a metal ion in the tested organism; therefore, often a reagent with a chelating function is added to the sample and the mobile phase in liquid chromatography is applied with appropriate polarity for GSH and GSSG. We determined the concentrations of total, reduced, and oxidized glutathione in the liver, hepatopancreas, muscle, and gonad tissues of brown shrimp (Crangon crangon) and fish (Psetta maxima and Clupea harengus membras). The highest concentrations of tGSH were recorded in the shrimp hepatopancreas (7.21?±?0.011 μmol g^?1 wet weight), in herring liver (2.85?±?0.025 μmol g^?1), and in turbot liver (1.86?±?0.063 μmol g^?1). In turn, the highest concentrations were reported for GSSG in the muscle of shrimp (0.140?±?0.000204 μmol g^?1), and in the testis of turbot (0.063?±?0.000170 μmol g^?1) and herring (0.009?±?0.000015 μmol g^?1). We also investigated seasonal changes in the concentrations of glutathione in the muscle of C. crangon shrimp in the annual cycle. The lowest values of total glutathione were recorded during spring and autumn, which could be correlated with the increase in lipid peroxidation and oxidative stress.