Determination of Mo and V in multiphase gasoline emulsions by electrothermal atomic absorption spectrometry

This paper proposes an alternative analytical method using electrothermal atomic absorption spectrometry to determine Mo and V in multiphase gasoline emulsions. Samples were prepared by mixing gasoline with a nitric acid solution (0.1% v/v) and two cationic surfactants. The mixture was sonicated, resulting in an emulsive system. Calibration was done by using the aforementioned solutions with added analyte. The detection limits (3σ) of Mo and V were 0.9 μg l^− 1 and 4.7 μg l^− 1, respectively. The accuracy and precision of the proposed method were evaluated by the analysis of samples spiked with metallo-organic standard and the relative standard deviation obtained ranged from 1.2% to 4.4% in samples spiked with 2 μg l^− 1 of each metal. The recovery rates varied from 91.2% to 101.6%. The proposed method was applied to determine Mo and V in samples of gasoline from different gas stations.     

Fully automated method based on on-line molecularly imprinted polymer solid-phase extraction for determination of lovastatin in dietary supplements containing red yeast rice

A fully automated method for the determination of lovastatin in dietary supplements containing red yeast rice has been developed. It uses a sequential injection analysis system combined with solid-phase extraction applying highly selective molecularly imprinted polymer sorbent. A miniaturized column for on-line extraction was prepared by packing 4.5 mg of the sorbent in a 5.0 × 2.5-mm-i.d. cartridge, which was used in the flow manifold. Sequential injection analysis manifold enabled all steps of lovastatin extraction and continuous spectrophotometric detection at 240 nm. A limit of detection of 60 μg g⁻¹, a limit of quantitation of 200 μg g⁻¹, and a linear calibration range of 200–2000 μg g⁻¹ were achieved. Intra-day and inter-day precision values (RSD) were ≤ 6.7% and ≤ 4.9%, respectively, and method recovery values of spiked red yeast rice extracts at 200, 1000, and 2000 μg g⁻¹ concentration levels were 82.9, 95.2, and 87.7%. Our method was used for determination of lovastatin lactone in four dietary supplements containing red yeast rice as a natural source of lovastatin, also known as monacolin K. The extracted samples were subsequently analyzed by the reference UHPLC-MS/MS method. Statistical comparison of results (F test, t test, α = 0.05) obtained by both methods did not reveal significant difference. A substantial advantage of the new automated approach is high sample throughput thanks to the analysis time of 7.5 min, miniaturization via down-scaling the extraction column, and smaller sample and solvent consumption, as well as reduced generation of waste.

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Synthesis of three haptens for the class-specific immunoassay of O,O-dimethyl organophosphorus pesticides and effect of hapten heterology on immunoassay sensitivity

A general and broad class-specific enzyme-linked immunosorbent assay was developed for the O,O-dimethyl organophosphorus pesticides, including malathion, dimethoate, phenthoate, phosmet, methidathion, fenitrothion, methyl parathion and fenthion. Three haptens with different spacer-arms were synthesized. The haptens were conjugated to bovine serum albumin (BSA) for immunogens and to ovalbumin (OVA) for coating antigens. Rabbits were immunized with the immunogens and six polyclonal antisera were produced and screened against each of the coating antigens using competitive indirect enzyme-linked immunosorbent assay for selecting the proper antiserum. The effect of hapten heterology on immunoassay sensitivity was also studied. The antibody-antigen combination with the most selectivity for malathion was further optimized and tested for tolerance to co-solvent, pH and ionic strength changes. The IC₅₀ values, under optimum conditions, were estimated to be 30.1 μg L⁻¹for malathion, 28.9 μg L⁻¹ for dimethoate, 88.3 μg L⁻¹ for phenthoate, 159.7 μg L⁻¹ for phosmet, 191.7 μg L⁻¹ for methidathion, 324.0 μg L⁻¹ for fenitrothion, 483.9 μg L⁻¹ for methyl parathion, and 788.9 μg L⁻¹ for fenthion. Recoveries of malathion, dimethoate, phenthoate, phosmet and methidathion from fortified Chinese cabbage samples ranged between 77.1% and 104.7%. This assay can be used in monitoring studies for the multi-residue determination of O,O-dimethyl organophosphorus pesticides.     

Surface functionalization of oxidized multi-walled carbon nanotubes: Candida rugosa lipase immobilization

This work examines two approaches for immobilization of lipase from Candida rugosa on oxidized multi-walled carbon nanotubes (o-MWCNTs). One method included the presence of activating agents to promote covalent bonding and the other the adsorption on o-MWCNTs to elucidate if non-specific bonding on the o-MWCNTs surface exists. The influence of the immobilization time and initial enzyme concentration on protein loading and the expressed lypolitic activity of the immobilized preparation were investigated. The results showed that the enzyme adsorbs on o-MWCNTs in a maximal amount of 37 μg mg⁻¹ CNTs, while the attached amount was more than 2-times higher under covalent promoting conditions (80 μg mg⁻¹ CNTs). Furthermore, similar trends were observed for the lypolitic activity, whereby preparations obtained under covalent promoting conditions had almost 3-times higher activity (560 IU g⁻¹ of immobilized enzyme). In addition, immobilization of the enzyme was confirmed by Fourier transformation infrared spectroscopy and thermogravimetric analysis.     

A methodology for the determination of reductive sulphur in optical and technical glass

This paper describes an analytical method for the determination of reductive sulphur (S(IV), S(-II)) in glass. The glass sample is dissolved in hydrofluoric/hydrochloric acid mixture and the sulphur is separated via distillation in an apparatus made of polyfluoralkoxyethylene (PFA). The distilled hydrogen sulphide is trapped in buffered boric acid-zinc acetate solution and subsequently determined after conversion to an ethylene blue dye. The range of the method lies within a range of 2-1200 μg g⁻¹ reductive sulphur. The quantification limit for reductive sulphur is 2 μg g⁻¹.Different analysed glass types show either no detectable reductive sulphur or up to 30% of the total sulphur content reductive sulphur. The inter-laboratory standard deviation shown by a round robin test performed is excellent (±4 μg g⁻¹; average 59 μg g⁻¹). Sources of error of the methodology are discussed.     

Modified QuEChERS method for phenolic compounds determination in mustard greens (Brassica juncea) using UHPLC-MS/MS

A modified QuEChERS method (Quick, Easy, Cheap, Effective, Rugged, and Safe) for the determination of fifteen phenolic compounds in mustard greens (Brassica juncea) using ultra-high-performance liquid chromatography coupled to tandem mass spectrometry (UHPLC-MS/MS) analysis was developed. The QuEChERS partitioning step and dispersive solid phase extraction (d-SPE) clean-up sorbents were investigated, aimed at phenolic compound extraction and pigment removal, respectively. QuEChERS acetate version combined with 25 mg of diatomaceous earth (DE) and 5.0 mg of graphitized carbon black (GCB) provided the best conditions for sample preparation of the target compounds. Under the optimized conditions, all phenolic compounds showed good linearity (r ≥ 0.99) over the concentration range of 0.1 to 8000 μg kg⁻¹, and the quantification limits were in the range of 0.06–230 μg kg⁻¹. The spectrophotometric analysis showed that the clean-up step promoted a significant removal of chlorophyll, which is the major pigment present in the sample. Furthermore, antioxidant activity analysis was also carried out after the clean-up step and, together with chromatographic data, showed that no significant retention of the phenolic compounds occurs in the clean-up step. Two mustard greens varieties – Southern Giant Curled (SGC) and Florida Broadleaf (FB) - were analyzed with the proposed method. Seven phenolic compounds (4-hydroxybenzoic, p-coumaric, ferulic and sinapic acids, naringenin, apigenin and kaempferol) were found in both varieties, the greatest abundance being for sinapic acid (1261.5 ± 23 μg kg⁻¹ in SGC and 1235.5 ± 26 μg kg⁻¹ in FB) and ferulic acid (2861 ± 24 μg kg⁻¹ in SGC and 3204.5 ± 45 μg kg⁻¹ in FB).     

Sulfonated poly(ether ether ketone)/manganese dioxide composite for the removal of low level radionuclide ions from aqueous solution

Various composite adsorbents based on sulfonated poly(ether ether ketone)/manganese dioxide were prepared for the removal of stable and radioactive ions from contaminated aqueous solution. Batch adsorption experiments revealed superior adsorption capacities of the composite using very low initial concentration of studied elements. Starting with 1000 µg L⁻¹ contaminated solution, the maximum equilibrium metal uptake capacity reached 2.0 mg g⁻¹ for Pb²⁺, 1.9 mg g⁻¹ for Cd²⁺, Cu²⁺ and Zn²⁺, and 3.7 mg g⁻¹ for Co²⁺. In addition, the distribution coefficient reached 11,600 mL g⁻¹ for ¹³⁷Cs and 70,000 mL g⁻¹ for ²¹⁰Pb.

     

Colorimetric technique for the detection of carbofuran and its application in various environmental samples

A large variety of pesticides have been used in the agriculture area to raise the quality, extend and yield storage life of crops. The nonstop uses of these pesticides have resulted in pollution of the environment and also caused risk to human health. For the rapid detection of selective CBFpesticide, we developed a simple and sensitive colorimetric detection method based on azo-coupling reaction. After a simple pre-treatment of carbofuran (2, 2-dimethyl-2, 3-dihydro-7-benzofuranyl N-methyl carbamate) (CBF) (1000 ​μg ​mL⁻¹) with a diazotized solution, the resulting is rapidly undergoing azo-coupling reaction with p-aminoantipyrine (1% alcoholic) with a dramatic color change only in few minutes. Finally, we successfully applied the concentrations of CBF pesticide on vegetable, fruit, soil, and water samples in the presence of natural interferences using UV–Vis spectrophotometer and FTIR with limits of detection at 0.004μgmL⁻¹. CBF had recoveries in the range of 93–98%, with relative standard deviation values less than 2% and good linearity was achieved with r ​≥ ​0.98. The inhibition rate was linear with CBF concentration in the range of 1μgmL⁻¹ to 10μgmL⁻¹. The proposed method applies to analyze CBF pesticide in real samples. FTIR technique was used to consider and gain structural information about the existing intermolecular interactions for vegetable samples.     

Development of a novel mixed hemimicelles dispersive micro solid phase extraction using 1-hexadecyl-3-methylimidazolium bromide coated magnetic graphene for the separation and preconcentration of fluoxetine in different matrices before its determination by fiber optic linear array spectrophotometry and mode-mismatched thermal lens spectroscopy

This study aims at developing a novel, sensitive, fast, simple and convenient method for separation and preconcentration of trace amounts of fluoxetine before its spectrophotometric determination. The method is based on combination of magnetic mixed hemimicelles solid phase extraction and dispersive micro solid phase extraction using 1-hexadecyl-3-methylimidazolium bromide coated magnetic graphene as a sorbent. The magnetic graphene was synthesized by a simple coprecipitation method and characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy and scanning electron microscopy (SEM). The retained analyte was eluted using a 100 μL mixture of methanol/acetic acid (9:1) and converted into fluoxetine-β-cyclodextrin inclusion complex. The analyte was then quantified by fiber optic linear array spectrophotometry as well as mode-mismatched thermal lens spectroscopy (TLS). The factors affecting the separation, preconcentration and determination of fluoxetine were investigated and optimized. With a 50 mL sample and under optimized conditions using the spectrophotometry technique, the method exhibited a linear dynamic range of 0.4–60.0 μg L⁻¹, a detection limit of 0.21 μg L⁻¹, an enrichment factor of 167, and a relative standard deviation of 2.1% and 3.8% (n = 6) at 60 μg L⁻¹ level of fluoxetine for intra- and inter-day analyses, respectively. However, with thermal lens spectrometry and a sample volume of 10 mL, the method exhibited a linear dynamic range of 0.05–300 μg L⁻¹, a detection limit of 0.016 μg L⁻¹ and a relative standard deviation of 3.8% and 5.6% (n = 6) at 60 μg L⁻¹ level of fluoxetine for intra- and inter-day analyses, respectively. The method was successfully applied to determine fluoxetine in pharmaceutical formulation, human urine and environmental water samples.     

Husk Cherry: Nutritional attributes,bioactive compounds and technological applications

Husk cherry (Physalis pruinosa; L) is a tropical fruit commonly grown in the Mediterranean region, and widely consumed fresh in most countries of the world. To enhance our knowledge about this promising fruit, the technological, therapeutic, and nutritional quality attributes of the raw fruits were investigated. The fruit had an orange yellowish color and a mild sweetness, with a pulp yield of 93.40 % (w/w) and a juice yield of 64.45 % (v/w). It contains high ratios of total sugar (41.65%), protein (14.56%), crude fibers (11.59 %), ascorbic acid (40.17 mg/100 g), ß-carotene (64.78 μg/g), total phenols (178.53 mg gallic acid 100 g⁻¹), anthocyanin (7.01 μg cyaniding-3-glucoside equivalents 100 g⁻¹), flavonoids (6.69 mg quercetin g⁻¹), and chlorophylls (19.03 μg g⁻¹). These fruit showed high antioxidant activities, which were found using DPPH and ABTS assays, and could be considered as a good source of antioxidants. The fruit contained several minerals, including potassium, phosphorus, sodium, and magnesium. The major amino acids in the fruit pulp were glutamic acid, aspartic acid, arginine, phenylalanine, proline, valine and alanine. The main polyphenols detected in the fruits were gallic acid, 4-hydroxybenzoic acid, benzoic acid, catechol, ellagic acid, chlorogenic acid, and epicatechin. Several flavonoids can be obtained in high concentrations, such as naringenin, luteolin, and rutin. Six functional food products (juice, jelly, jam, candied fruits, chocolate--coated dried fruits, and fruit leather) were manufactured using husk cherry fruits. The quality attributes of prepared products were determined. The highest crude fiber, ascorbic acid, β carotene, and total sugar compositions were found in chocolate-coated dry fruit products. All the manufactured products were well palatable amongst 25 trained panelists. The findings of this study confirmed the nutritional and technological potential of husk cherry fruits, which might be used effectively within the development of some functional products for food industries.     

Determination of zinc and copper in human hair by slurry sampling employing sequential multi-element flame atomic absorption spectrometry

The present work proposes a direct method based on slurry sampling for the determination of zinc and copper in human hair samples by multi-element sequential flame atomic absorption spectrometry. The slurries were prepared by cryogenic grinding and sonication of the samples. The optimization step was performed using univariate methodology and the factors studied were: nature and concentration of the acid solution, amount sample/slurry volume, sonication time, and particle size. The established experimental conditions are the use of a sample mass of 50 mg, 2 mol L^− 1 nitric acid solution, sonication time of 20 min and slurry volume of 10 mL. Adopting the optimized conditions, this method allows the determination of zinc and copper with detection limits of 88.3 and 53.3 ng g^− 1, respectively, and precision expressed as relative standard deviation (RSD) of 1.7% and 1.6% (both, n = 10) for contents of zinc and copper of 100.0 and 33.3 μg g^− 1, respectively. The accuracy was checked and confirmed by analysis of two certified reference materials of human hair. The procedure was applied for the determination of zinc and copper in two human hair samples. The zinc and copper contents varied from 100.0 to 175.6 and from 3.2 to 32.8 μg g^− 1, respectively. These samples were also analyzed after complete digestion in a closed system and determination by FAAS. The statistical comparison by t-test (95% confidence level) showed no significant difference between these results.     

Dissipation of chlortetracycline in the aquatic environment: Characterization in terms of a generalized multiphase pseudo–zero-order rate law

The kinetics of the dissipation of chlortetracycline in the aquatic environment was studied over a period of 90 days using microcosm experiments and distilled water controls. The distilled water control experiments, carried out under dark conditions as well as exposed to natural sunlight, exhibited biphasic linear rates of dissipation. The microcosm experiments exhibited triphasic linear rates of degradation both in the water phase (2.7 × 10⁻², 7 × 10⁻³, 1.3 × 10⁻³ μg g⁻¹ day^–1) and the sediment phase (3.4 × 10⁻², 6 × 10⁻³, 1 × 10⁻³ μg g⁻¹ day^–1). The initial slow rate of dissipation in the dark control (3 × 10⁻³ μg g⁻¹ day^–1) was attributed to a combination of evaporation and hydrolysis, whereas the subsequent fast rate (1.8 × 10⁻³ μg g⁻¹ day^–1) was attributed to a combination of evaporation, hydrolysis, and microbial degradation. For the sunlight-exposed control, the initial slow rate of dissipation (1.5 × 10⁻³ μg g⁻¹ day^–1) was attributed to a combination of evaporation, hydrolysis, and photolysis, whereas the subsequent fast rate was attributed to a combination of evaporation, hydrolysis, photolysis, and microbial degradation (5.1 × 10⁻³ μg g⁻¹ day^–1). The initial fast rate of dissipation in the water phase of the microcosm experiment is attributed to a combination of evaporation, hydrolysis, photolysis, and microbial degradation, whereas all subsequent slow rates in the water phase and all rates of degradation in the sediment phase are attributed to microbial degradation of the colloidal and sediment particle adsorbed antibiotic. A multiphase zero-order kinetic model is presented that takes into account (a) dissipation of the antibiotic via evaporation, hydrolysis, photolysis, microbial degradation, and adsorption by colloidal and sediment particles and (b) the dependence of the dissipation rate on the concentration of the antibiotic, type and count of microorganisms, and type and concentration of colloidal particles and sediment particle adsorption sites within a given aquatic environment.     

A novel silica supported chitosan/glutaraldehyde as an efficient sorbent in solid phase extraction coupling with HPLC for the determination of Penicillin G from water and wastewater samples

In this study, silica@chitosan-glutaraldehyde (Si@Cs-G) was synthesized as a novel adsorbent for extraction of Penicillin G (PG) from the synthetic and real samples followed by HPLC determination. The synthesized adsorbents were characterized by the scanning electron microscopy (SEM), X-ray diffraction (XRD), fourier transform infrared (FTIR), dynamic light scattering (DLS), transmission electron microscopy (TEM) and nitrogen adsorption–desorption techniques. The factors influencing the extraction efficiency including pH, sorbent dose, extraction time, extraction solvent type and its volume were investigated and optimized.Under the optimal conditions (sorbent dosage: 25 mg, desorption solvent (acetonitrile) with volume of 0.75 mL; pH: 6 and extraction time: 50 min), the Si@Cs-G demonstrated high efficiency and linearity (R² > 0.999) with the concentration of penicillin G ranging from 1 to 300 μg L⁻¹. Extraction recovery in synthetic samples was 98.977%, with LOD = 0.493 μg L⁻¹, LOQ = 1.638 μg L⁻¹ and RSD < 1.953%. The method was successfully applied for determination of PG in real water samples (tap, river, lake and well water) and wastewater samples (SH and SHB hospital effluent). The obtained relative recoveries were in the range of 91.31% -123.27% with RSD less than 6.34% for all the real samples. The dominant mechanism in the PG adsorption process was involved in the π-π interaction, hydrogen bonding, and electrostatic interaction.     

Square-wave adsorptive stripping voltammetric approaches at two in situ modified electrodes as first analytical methods for the quantitative determination of a new anticancer drug candidate

The two adsorptive stripping voltammetric approaches for detection and quantitative determination of diethyl (2E)-2-{(2E)-[1-(4-methylphenyl)imidazolidin-2-ylidene]hydrazinylidene}butanedioate (DIB)—a novel molecule of medical importance—using two sensitive sensors based on modified glassy carbon electrodes as reusable sensors, were developed for the first time. The proposed electrochemical methods are based on adsorptive/reductive behaviour of DIB at two modified carbonic electrodes: a bismuth film-modified glassy carbon electrode (BiF/GCE) and a lead film-modified glassy carbon electrode (PbF/GCE). The electron gain mechanism for the electrochemical reduction of DIB on both developed sensors was proposed for the first time. To achieve the highest sensitivity in adsorptive stripping determinations, various experimental variables (e.g. the composition and pH of the supporting electrolytes, deposition conditions of bismuth and lead films, concentrations of plating solutions, accumulation times and potentials of DIB, etc.) were extensively examined. The comparison of validation parameters obtained during the determination of DIB at two sensors was presented. The excellent linear correlation was found between the monitored adsorptive stripping voltammetric peak current and the DIB concentration in the range of 15–600 μg L⁻¹ at an accumulation time of 30 s (with LOD = 4.2 μg L⁻¹ and LOQ = 14.0 μg L⁻¹) using the BiF/GCE as a sensor. Furthermore, the excellent linear relationship was confirmed between the monitored adsorptive stripping voltammetric peak current and the DIB concentration in the range of 9–900 μg L⁻¹ at an accumulation time of 10 s (with better LOD = 1.5 μg L⁻¹ and LOQ = 5.0 μg L⁻¹), employing the PbF/GCE as a sensor. The two optimized adsorptive stripping voltammetric approaches—as facile, sensitive, reliable and inexpensive—were successfully used as first methods for the quantitative analysis of a novel anticancer agent (DIB) in its pure pharmaceutically acceptable form. However, the practical applicability of square-wave adsorptive stripping voltammetric determination of the electroactive DIB molecule at a PbF/GCE, as the modified electrode of higher sensitivity, was presented after its successful solid phase extraction from a real serum sample.

     

Rapid and simultaneous analysis of dichlorvos, malathion, carbaryl, and 2,4-dichlorophenoxy acetic acid in citrus fruit by flow-injection ion spray ionization tandem mass spectrometry

A simple method for the rapid and simultaneous analysis of dichlorvos (DDVP), malathion, carbaryl, and 2,4-dichlorophenoxy acetic acid (2,4-D) in citrus fruit, which uses flow-injection ion spray ionization tandem mass spectrometry, has been developed for the first time. The method involves the combined use of stable isotopically labeled internal standards (DDVP-d₆, malathion-d₁₀, carbaryl-d₇, and 2,4-D-d₅) and a multiple reaction monitoring technique. The average recoveries for the pesticides at the same concentrations as their tolerance levels (DDVP: 0.1-0.2 μg g⁻¹; malathion: 0.5-4.0 μg g⁻¹; carbaryl: 1.0 μg g⁻¹; 2,4-D: 1.0-2.0 μg g⁻¹) ranged from 90 to 119% with the relative standard deviation (R.S.D.) ranging from 1.0 to 13.1% (n = 5). Analysis time, including sample preparation and determination, was only 15 min. The present method is effective for screening DDVP, malathion, carbaryl, and 2,4-D in citrus fruit.     

A new and direct method for the trace element determination in cauliflower by differential pulse polarography

Using the DPP polarograms of wet digested cauliflower sample in acetate buffer at pH values of 2, 4 and 6, Fe, Zn, Mo, Se, Cr, Cd, Pb, Ti and Cu quantities were determined. The best separation and determination conditions for Zn, Se and Mo was pH 2; for Cr, Zn, Mo and As was pH 4; for Pb pH 6, for Ti, Cu and Fe was pH 6-7 EDTA, for Cd pH 2 EDTA and for lead pH 6, all in acetate buffer. The trace element ranges for cauliflowers from two different seasons were (first figure for winter, the second for summer) for Se 120-250 μg g⁻¹, Fe 70-85 μg g⁻¹, Cu 320-150 μg g⁻¹, Ti 90-120 μg g⁻¹, Cr 130-630 μg g⁻¹, Zn 90-550 μg g⁻¹, Mo 170-230 μg g⁻¹, Cd 20 μg g⁻¹ (in winter) and Pb 130-300 μg g⁻¹ in dry sample. Cd was under the detection limit in summer. The length of digestion time had no effect on the recovery of copper, iron, molybdenum and zinc between 15 and 3 h of digestion.     

Polyaniline immobilized on polycaprolactam nanofibers as a sorbent in electrochemically controlled solid-phase microextraction coupled with HPLC for the determination of angiotensin II receptor antagonists in human blood plasma

In this research, electrospun polycaprolactam nanofibers were collected on a fine stainless steel mesh sheet without a binder, and a layer of conductive polyaniline was chemically deposited on the nanofibers. The polyaniline immobilized on the polycaprolactam nanofibers provided high electrical conductivity, acceptable mechanical stability, and a large surface area. This assembly was then used as a working electrode in electrochemically controlled solid-phase microextraction (EC-SPME), a fast and environmentally friendly method. The polymer layers were characterized by SEM and FTIR techniques. Significant factors affecting the EC-SPME efficiency were investigated, including the desorption conditions, the sorbent used, the pH of the sample solution, the extraction voltage, the extraction time, and the ionic strength. Under the optimum conditions, the limits of detection and quantification for the target analytes were 0.9–1.8 μg L⁻¹ and 3.0–6.1 μg L⁻¹, respectively. The linear dynamic range was 5–2000 μg L⁻¹, with R² > 0.993. The method was coupled with HPLC analysis and applied to the determination of angiotensin ΙΙ receptor antagonists (ARA-ΙΙs) in human plasma, and relative recoveries of 91.1–104.3% with RSDs of ≤8.3% were obtained.

     

Chromogenic platform based on recombinant Drosophila melanogaster acetylcholinesterase for visible unidirectional assay of organophosphate and carbamate insecticide residues

In this study we propose a chromogenic platform for rapid analysis of organophosphate (OP) and carbamate (CM) insecticide residues, based on recombinant Drosophila melanogaster acetylcholinesterase (R-DmAChE) as enzyme and indoxyl acetate as substrate. The visible chromogenic strip had the advantages identical to those of commonly used lateral flow assays (LFAs) with utmost simplicity in sample loading and result observation. After optimization, depending on the color intensity (CI) values, the well-established assay has the capabilities of both qualitative measurement via naked eyes and quantitative analysis by colorimetric reader with the desirable IC₅₀ values against the tested six insecticides (0.06 μg mL⁻¹ of carbofuran, 0.28 μg mL⁻¹ of methomyl, 0.03 μg mL⁻¹ of dichlorvos, 31.6 μg mL⁻¹ of methamidophos, 2.0 μg mL⁻¹ of monocrotophos, 6.3 μg mL⁻¹ of omethoate). Acceptable matrix effects and satisfactory detection performance were confirmed by in-parallel LC–MS/MS analysis in different vegetable varieties at various spiked levels of 10⁻³ to 10¹ μg g⁻¹. Overall, the testified suitability and applicability of this novel platform meet the requirements for practical use in food safety management and environmental monitoring, especially in the developing world.     

Measurement of methyl mercury (I) and mercury (II) in fish tissues and sediments by HPLC-ICPMS and HPLC-HGAAS

A procedure for the extraction and determination of methyl mercury and mercury (II) in fish muscle tissues and sediment samples is presented. The procedure involves extraction with 5% (v/v) 2-mercaptoethanol, separation and determination of mercury species by HPLC-ICPMS using a Perkin-Elmer 3 μm C8 (33 mm × 3 mm) column and a mobile phase 3 containing 0.5% (v/v) 2-mercaptoethanol and 5% (v/v) CH₃OH (pH 5.5) at a flow rate 1.5 ml min⁻¹ and a temperature of 25 °C. Calibration curves for methyl mercury (I) and mercury (II) standards were linear in the range of 0-100 μg l⁻¹ (r² = 0.9990 and r² = 0.9995 respectively). The lowest measurable mercury was 0.4 μg l⁻¹ which corresponds to 0.01 μg g⁻¹ in fish tissues and sediments. Methyl mercury concentrations measured in biological certified reference materials, NRCC DORM - 2 Dogfish muscle (4.4 ± 0.8 μg g⁻¹), NRCC Dolt - 3 Dogfish liver (1.55 ± 0.09 μg g⁻¹), NIST RM 50 Albacore Tuna (0.89 ± 0.08 μg g⁻¹) and IRMM IMEP-20 Tuna fish (3.6 ± 0.6 μg g⁻¹) were in agreement with the certified value (4.47 ± 0.32 μg g⁻¹, 1.59 ± 0.12 μg g⁻¹, 0.87 ± 0.03 μg g⁻¹, 4.24 ± 0.27 μg g⁻¹ respectively). For the sediment reference material ERM CC 580, a methyl mercury concentration of 0.070 ± 0.002 μg g⁻¹ was measured which corresponds to an extraction efficiency of 92 ± 3% of certified values (0.076 ± 0.04 μg g⁻¹) but within the range of published values (0.040-0.084 μg g⁻¹; mean ± s.d.: 0.073 ± 0.05 μg g⁻¹, n = 40) for this material. The extraction procedure for the fish tissues was also compared against an enzymatic extraction using Protease type XIV that has been previously published and similar results were obtained. The use of HPLC-HGAAS with a Phenomenox 5 μm Luna C18 (250 mm × 4.6 mm) column and a mobile phase containing 0.06 mol l⁻¹ ammonium acetate (Merck Pty Limited, Australia) in 5% (v/v) methanol and 0.1% (w/v) l-cysteine at 25 °C was evaluated as a complementary alternative to HPLC-ICPMS for the measurement of mercury species in fish tissues. The lowest measurable mercury concentration was 2 μg l⁻¹ and this corresponds to 0.1 μg g⁻¹ in fish tissues. Analysis of enzymatic extracts analysed by HPLC-HGAAS and HPLC-ICPMS gave equivalent results.     

Study on the solid phase extraction and spectrophotometric determination of cobalt with 5-(2-benzothiazolylazo)-8-hydroxyquinolene

A highly sensitive, selective and rapid method for the determination of cobalt based on the rapid reaction of cobalt(II) with 5-(2-benzothiazolylazo)-8-hydroxyquinolene BTAHQ and the solid phase extraction of the Co(II)-BTAHQ complex with C18 membrane disks were developed. In the presence of pH = 6.4 buffer solution and cetylpyridenium chloride (CPC) medium, BTAHQ reacts with cobalt to form a deep violet complex with a molar ratio of 1:1 (cobalt to BTAHQ). This complex was enriched by the solid phase extraction with C18 membrane disks. An enrichment factor of 100 was obtained by elution of the complex from the disks with a minimal amount of isopentyl alcohol. In isopentyl alcohol medium, the molar absorptivity of the complex is 2.42 × 10⁵ L mol⁻¹ cm⁻¹ at 658 nm. Beer’s law is obeyed in the range of 0.01–0.38 μg mL⁻¹ in the measured solution. The relative standard deviation for 11 replicate samples of 0.20 μg mL⁻¹ level is 1.37%. The detection and quantification limits reach 3.1 and 9.7 ng mL⁻¹ in the original samples. This method was applied for the determination of cobalt in biological, water, soil and pharmaceutical preparation samples with good results.