Determination Of Different Classes Research Articles

Development of Nano Poly(3-methyl thiophene)/Multiwalled Carbon Nanotubes Sensor for the Efficient Detection of Some Pesticides

A modified electrode fabricated by coating multiwalled carbon nanotubes (MWCNTs)/poly(3-methyl thiophene, P3MT) film on a glassy carbon electrode (GCE) and was used for the adsorptive stripping voltammetric determination of different classes of pesticides. These include herbicide (isoproturon), insecticides (voltage, cypermethrin, deltamethrin, fenvalerate) and an acaricide (dicofol). Electrochemical behaviour of all the selected pesticides was investigated on P3MT/MWCNT/GCE nano composite surface at selected pHs 1, 4, 7, 9.2 and 13. In cyclic voltammetry, isoproturon (ISO) and voltage (VOL) exhibited one well-defined oxidation peak at pH 1, while remaining pesticides gave one reduction peak at pH 13. Adsorptive stripping voltammetric determination of above-said pesticides was developed on the same modified system and lowest detection limits were achieved. The proposed analytical procedure was applied to natural water samples spiked with the selected pesticides to validate the developed stripping procedure.

Validation of method for determination of different classes of pesticides in aqueous samples by dispersive liquid–liquid microextraction with liquid chromatography–tandem mass spectrometric detection

In this study, a simple, rapid and efficient method has been developed for the extraction and preconcentration of different classes of pesticides, carbofuran (insecticide), clomazone (herbicide) and tebuconazole (fungicide) in aqueous samples by dispersive liquid–liquid microextraction (DLLME) coupled with liquid chromatography–tandem mass spectrometric detection. Some experimental parameters that influence the extraction efficiency, such as the type and volume of the disperser solvents and extraction solvents, extraction time, speed of centrifugation, pH and addition of salt were examined and optimized. Under the optimum conditions, the recoveries of pesticides in water at spiking levels between 0.02 and 2.0 μg L −1 ranged from 62.7% to 120.0%. The relative standard deviations varied between 1.9% and 9.1% ( n = 3). The limits of quantification of the method considering a 50-fold preconcentration step were 0.02 μg L −1. The linearity of the method ranged from 1.0 to 1000 μg L −1 for all compounds, with correlation coefficients varying from 0.9982 to 0.9992. Results show that the method we propose can meet the requirements for the determination of pesticides in water samples. The comparison of this method with solid-phase extraction indicates that DLLME is a simple, fast, and low-cost method for the determination of pesticides in natural waters.

Experimental designs dedicated to the evaluation of a membrane extraction method: membrane-assisted solvent extraction for compounds having different polarities by means of gas chromatography–mass detection

Membrane-assisted solvent extraction was applied for the determination of different classes of compounds in water, having K(o/w) (octanol-water partition coefficient) values between 10(1) (aniline) and 10(8) (methyl stearate), by means of experimental designs. Four solvents were investigated--propan-2-ol, ethyl acetate, diisopropyl ether and cyclohexane--as well as extraction time, temperature, salt impact, pH and methanol addition. The best choice was diisopropyl ether, 50 degrees C, 30 min and an addition of 3 g of sodium chloride at pH 2 for polar compounds. The relative standard deviation (n = 3) was found in the range from 5 to 17%. Recoveries ranged between 34 and 100%. Membrane-assisted solvent extraction was successfully applied to a fast screening method dedicated to an unknown wastewater sample.

Simultaneous determination of different classes of antibiotics in fish and livestock by CE‐MS

A specific CE-MS method was developed for the simultaneous determination of 12 antibacterial residues (four sulfonamides: sulfamethazine, sulfathiazole, sulfadiazine, and sulfachlorpyridazine; four beta-lactams: amoxicillin, ampicillin, oxacillin, and penicillin V, and four quinolones: danofloxacin, enrofloxacin, ofloxacin, and flumequine) in fish and livestock. Separation conditions, sheath liquid composition and electrospray parameters were optimized to obtain adequate CE separation and a high sensitivity. CE employed a 75 cm long fused-silica capillary (50 cm thermostated plus 25 cm at room temperature) 75 microm id and a 60 mM ammonium acetate separation buffer at pH 8 with 10% of methanol. The minimum number of identification points, according to the 2002/657/EC European Decision, was achieved using an IT in multiple reaction monitoring (MRM) mode. For quantification in meat and fish samples, a two-step procedure was developed using ACN to extract the antibacterials and to precipitate the proteins and dispersive SPE, with C18 to clean up the extract. External matrix matched calibration curves were used to achieve accurate quantitative results. The LODs and LOQs (below 18 and 50 ng/kg, respectively) were in all cases lower than the maximum residue limits for these compounds in meat and fish. The recoveries ranged from 78 to 97% and the precision with RSDs lower than 18% indicate the potential of CE-MS for the analysis of multiclass antibacterial residues in food. The method was applied to meat and fish samples taken from markets, slaughterhouses, and fish farms.

Simplified multiresidue method for determination of pesticide residues in lettuce by gas chromatography with nitrogen-phosphorus detection.

A rapid and simple method has been developed for simultaneous determination of different classes of pesticide in different varieties of lettuce (Lactuca sativum). Lettuce samples were extracted by homogenization with acetone and partitioned into ethyl acetate-cyclohexane. Subsequent sample clean-up was not needed. Pesticide residues were determined by capillary gas chromatography with nitrogen-phosphorus detection (NPD). Confirmatory analysis of the pesticides was performed by capillary gas chromatography coupled with mass spectrometry in selected-ion-monitoring (SIM) mode. Recovery at two levels of fortification (ca. 0.05 and 0.20 mg kg(-1)) ranged from 63.9 to 118.6%, and relative standard deviations were below 9.5%. The proposed method was used to determine pesticide levels in different types of lettuce grown in soil from experimental fields.

Determination of different classes of amines with capillary zone electrophoresis and contactless conductivity detection

The use of contactless conductivity detection for the determination of different organic amines in CE was successfully demonstrated. Aliphatic non UV-absorbing species could be determined along absorbing compounds by measuring the conductivity of their protonated forms. The species tested included short-chained aliphatic primary, secondary and tertiary amines, branched aliphatic amines, diamines, hydroxyl-substituted amines as well as species incorporating aromatic and non-aromatic cyclic moieties. Highest sensitivity was obtained with BGE solutions containing solely acetic acid. A concentration of 0.5 M at a pH value of 2.5 was used. Detection limits were in the order of 1 microM. Complete separation of cis- and trans-1,2-diaminocyclohexane could be achieved by adding 18-crown-6 as modifier to the electrolyte solution.

Fully automated multianalyte determination of different classes of pesticides, at picogram per litre levels in water, by on-line solid-phase extraction–liquid chromatography–electrospray–tandem mass spectrometry

This paper reports the development of a fully automated method for the multianalyte determination of twenty pesticides belonging to different classes (triazines, phenylureas, organophosphates, anilines, acidic, propanil, and molinate) in natural and treated waters. The method, based on on-line solid-phase extraction-liquid chromatography-electrospray-tandem mass spectrometry, is highly sensitive (limits of detection between 0.004 and 2.8 ng L(-1)), precise (relative standard deviations between 2.0 and 12.1%), reliable (two selected reaction-monitoring transitions are monitored per compound), rapid (45 min per sample), and simple. The application of this method to the monitoring of the target compounds in a waterworks revealed the presence of the pesticides investigated at concentrations up to 516 and 82 ng L(-1) (total pesticide concentration) in river water and ground water, respectively, used as sources, and their gradual removal through the purification process.

Analysis and fate of surfactants in sludge and sludge-amended soils

Surfactants are among the most prevalent organic pollutants of anthropogenic origin with the potential to enter the environment through the discharge of wastewater and sewage sludge. We give an overview of analytical methods currently in use for the determination of different classes of surfactants in sewage sludge and soil. The main focus is on the application of liquid chromatography-mass spectrometry (LC-MS) and gas chromatography-mass spectrometry (GC-MS), discussing various aspects of these two techniques, including sample preparation. We give an overview of data on the occurrence of sludge and sludge-amended soils, and we draw conclusions about the fate of surfactants and their metabolites in sludge-amended soils. Finally, we briefly discuss the current European legislation relating to the use of sludge in agriculture.

Multianalyte determination of different classes of pesticides (acidic, triazines, phenyl ureas, anilines, organophosphates, molinate and propanil) by liquid chromatography-electrospray-tandem mass spectrometry

This work describes the optimization of a liquid chromatography-electrospray-tandem mass spectrometry (LC-ESI-MS-MS) method for the multianalyte determination of twenty pesticides, selected based on current regulations and extent of use. Chromatographic separation was carried out on a Purospher STAR RP-18e column using gradient acetonitrile-water as mobile phase. Triazines, phenylureas, organophosphates, anilines, and molinate were determined in the positive ionization mode, and acidic pesticides and propanil in the negative ion mode. Two different precursor ion-product ion transitions were selected for each analyte and monitored under time scheduled multiple reaction monitoring (MRM) conditions. The optimized method was shown to be linear in the range 1 to 1000 ng/mL with correlation coefficients higher than 0.99 for all but one (diazinon) of the analytes, very sensitive (with limits of detection between 0.010 and 4.528 ng/mL), and repeatable (with relative standard deviations, calculated from the replicate analysis of standard mixtures, lower than 14%). The present work was also devoted to the elucidation of the structures of the principal fragment ions obtained after collision-induced dissociation of the pesticides investigated, an aspect often overlooked in the literature.

Simultaneous Determination of Different Classes of Lipid Hydroperoxides by High-Performance Liquid Chromatography with Post Column Detection by a Ferrous/Xylenol Orange Reagent.

A novel high-performance liquid chromatographic (HPLC) method with post-column detection was developed to simultaneously analyze the lipid hydroperoxides of polar and nonpolar lipids. The HPLC method uses a reversed-phase column (octyl-bonded silica) and a mobile phase of water/acetonitrile/methanol. Hydroperoxides were detected at 592 nm by using a ferrous (II)/xylenol orange (FeXO) reagent. This method enabled the separation of fatty acid hydroperoxides, phosphatidylcholine hydroperoxides, and hydroperoxides of neutral lipids, including triacylglycerol hydroperoxides and cholesterol ester hydroperoxides, by chromatography. These hydroperoxides could be quantified in a range between 40 pmol and 2 nmol. This new method was applied to estimate the lipid hydroperoxides formed during the photosensitized oxidation of rat plasma.

Capillary Electrophoretic Determination of Different Classes of Organic Ions by Potentiometric Detection with Coated-Wire Ion-Selective Electrodes

Singly charged amines and sulfonic acids as cationic and anionic aliphatic model substances, respectively, were detected in capillary electrophoresis with all-solid-state ion-selective electrodes. The sensitivity for these compounds is a function of their lipophilicity. The signal detected is generally greater for molecules with a larger organic part. The utility of the method is further demonstrated by the detection of a group of aromatic compounds in the form of the anionic analgesics (S)-(+)-2-(4-isobutylphenyl)propionic acid, 2-[(2,6-dichlorophenyl)amino]benzeneacetic acid, and o-acetylsalicylic acid. Further determined were the artificial sweeteners cyclamate, acesulfame-K, and saccharin. Detection limits for the different substances were between 2.5 × 10(-)(6) and 1 × 10(-)(5) M.

Multiresidue Analysis of Pesticides in Water from Rice Cultures by On-line Solid Phase Extraction Followed by LC-DAD

An automated on-line solid phase extraction procedure followed by liquid chromatography with diode array detection was investigated for the determination of different classes of pesticides in water samples containing varied amount of humic substances. The different pesticides used were: carbendazin, carbofuran, atrazine, diuron, propanil, molinate, alachlor, parathion-ethyl, diazinon, trifluralin and the degradation products deisopropylatrazine and deethylatrazine. Humic substances extracted from a Brazilian sediment were used from 5 to 80 mg/l and their influence on recoveries was evaluated in neutral and acidic media. Recoveries higher than 70% were obtained for all the pesticides, from the preconcentration of 75 ml of aqueous sample fortified at 2 ng/ml using precolumns packed with PLRP-S. Good recoveries were obtained at neutral pH for most of the analytes up to 40 mg/l of humic acid. Only at 80 mg/l the recoveries were significantly affected, both at acidic and neutral pH. The method was applied to the determination of pesticides in river water spiked at 0.1 to 1 ng/ml. Detection limits obtained for water containing 10 mg/l of humic acid were between 0.05 and 0.3 ng/ml.

New approach to the characterization of pyrolysis coal products by gas chromatography-mass spectrometry

A method for the characterization of coal thermal behaviour, based on gas chromatographic-mass spectrometric analysis of the pyrolysate, is presented. Twelve different coal samples, representative of the entire coal rank, were selected for this study. The pyrolysis products, obtained at 800°C, were first collected and then analysed in two GC-MS systems. The sampling apparatus consisted of three different traps in order to separate the products into three fractions on the basis of their volatility. The GC-MS analysis was also arranged according to this criterion. A packed column, coupled to a double-focusing magnetic mass spectrometer, was used for the volatile fractions of the pyrolysate and a capillary column, coupled to a quadrupole analyser, was employed for the analysis of the condensed fraction. Sampling and analysis procedures were carried out separately, thus allowing careful optimization of the strategy for the characterization of the pyrolysate. The condensate was analysed in the selected-ion monitoring mode for the determination of different classes of compounds. Some evaluations and comparisons, extrapolated from the results obtained, are presented.

Occurrence and determination of organic pollutants in tap and surface waters of the Gdańsk district

The results of the determination of different classes of organic pollutants (trihalomethanes, polycyclic aromatic hydrocarbons (PAHs), pesticides, volatile hydrocarbons and phenols) in ground water and drinking water sampled at different sites in the Gdańsk District are presented. Different methods were used to determine organic compounds in water: direct aqueous injection or sorption on solid sorbent (XAD-4) and extraction with pentane followed by a gas chromatography-electron capture detection (GC-ECD) for determination of volatile organohalogen compounds; purge and trap with a gas chromatography-flame ionization detection for determination of volatile hydrocarbons; sorption on solid sorbent XAD-4 or C 18, elution with organic solvent and GC-ECD for determination of pesticides; sorption on solid sorbent C 18, elution with organic solvent and a gas chromatography-mass spectrometry for determination of PAHs and sorption on solid sorbent C 18, elution with organic solvent and high performance liquid chromatography-ultraviolet determination of phenols. The proposed methods have been used successfully for the determination of organic compounds in samples of tap, swimming pool, river and sea waters. The content of analysed organic compounds in the water delivered to the water supply system for Gdańsk from the surface water intake in Straszyn and from other selected intakes satisfies Polish, EC and WHO standards. The surface water bodies, i.e., rivers, sea and lakes in the Gdańsk District are not very polluted by anthropogenic compounds originating from municipal and industrial sewages and from agriculture.

Chemical and Microbiological Assessments of Mackerel (Scomber scombrus) Stored in Ice

The storage time of mackerel stored in ice was determined by sensory, chemical, and bacterial analyses. Ice: fish ratios of 1:2, 1:3, and 1:4 were used. Sensory analysis revealed that the storage time was directly related to ice: fish ratio and was 9, 8, and 6 d, respectively,At time of rejection, the levels of total volatile bases, trimethylamine and histamine were 23, 5, and 2 mg/100 g, respectively. At this time, a bacterial load limit of 1 × 106 CFU/g was reached for all the flora studied (total mesophilic aerobic, psychrotrophic, moderately halophilic) except the sulfide-producing flora.The data presented show the efficiency of adequate icing and allow for the recommendation of chemical standards for the evaluation of mackerel deterioration and/or for determination of different classes of freshness.

Properties and efficient algorithmic determination of different classes of rings in finite and infinite polyhedral networks

Different definitions of rings in polyhedral networks are considered and some of their properties are discussed. An efficient algorithm is presented for the automatic determination of rings in finite as well as in infinite networks. A sketch is given of the proof that there is always an upper limit to the length of rings in any crystal.

New chiral solvating agents: 1,5-Benzothiazepines

For the first time it is reported that 1,5-benzothiazepines (1a–e) (Figure I) behave as effective chiral solvating agents (CSA) for NMR enantiomeric excess (ee) determination of different classes of compounds such as α-arylalkanoic acids, α-hydroxy acids, alkanesulfonic acids, alcohols and 1,5-benzothiazepines. The molecular association between CSA and substrate is explained in terms of NH and/or OH hydrogen bonding.

Determination of surfactant activity and anionic detergents in seawater and sea surface microlayer in the Mediterranean

The study of the physico-chemical properties and the determination of different classes of organic substances in the sea are of substantial interest and importance for understanding biogeochemical processes in the sea. The preferable method should be sensitive enough for direct measurement without pretreatment procedures in order to avoid changes in the composition of organic substances initially present in the sample. Surfactant activity data are presented here as measured by electrochemical methods during 1979, 1980 and 1981 in samples from open waters of the Western Mediterranean, and in a few characteristic coastal areas of the Adriatic Sea with different biological activity and different influence of man's activities. Data on sea surface microlayer samples collected during 1977, 1978 and 1981 at different locations and seasons in the Rijeka Bay, which is an integral part of the Adriatic Sea, are presented and discussed in more detail. It was found that the type and concentration of natural surface active material vary within different Mediterranean regions and along the depth profile of the water column. Petroleum hydrocarbons and detergents were found to be prevalent pollutants responsible for high surfactant activity values. Pollution effects are most pronounced in the sea surface microlayer. Electrochemical methods are proposed for research and monitoring of surface-active substances in the sea.

Chromatopolarography of N-nitrosamines including determination of N-nitrosodiethanolamine in cosmetic products

A simple and sensitive method for trace level determination of different classes of N-nitrosamines is described. The method is based on a combination of high-performance liquid chromatography and differential pulse polarography. The separation of N-nitrosamines from their composite mixtures or interfering species is carried out on a reverse phase column followed by continuous detection with the polarographic detector. Analysis at nanogram levels is demonstrated. In addition, procedures are presented for the recovery and determination of N-nitrosodiethanolamine in various cosmetic products.

GROUP DETERMINATIONS OF URINARY ADRENAL STEROIDS BY GAS CHROMATOGRAPHY

Routine clinical methods for the determination of urinary metabolites of adrenal steroids, which depend on the development of a colour have tended to be unspecific. The determination of different classes (i.e. 17-hydroxysteroids, 1I-oxysteroids, 11-deoxysteroids, etc.) has usually meant the use of differential extraction procedures or chromatographic separations. We wish to describe a gas chromatographic method which separates the main classes and is useful in the evaluation of adrenocortical function.