Validation of a multiresidue method for the determination of pesticides in honeybees by gas chromatography

The validation of a multiresidue method for the determination of organochlorine, organophosphorus, pyrethroid and dicarboximide pesticides in honeybees is described. The method involves the extraction of 25 pesticides using acetonitrile, liquid partitioning with n-hexane and a clean-up performed on a silica gel cartridge (1 g, 12 mL). Capillary gas chromatography with electron-capture and nitrogen–phosphorus detectors was used for analytes determination. Limit of quantification (LOQ), recovery and relative standard deviation (RSD) for each analyte were determined. The recovery data were obtained by spiking honeybee samples free of pesticides at three levels (LOQ, 4LOQ and 8LOQ) with organochlorine, organophosphorus, pyrethroid and dicarboximide pesticides. The recoveries were in the range between 90.0% and 101.5% for LOQ, between 90.3% and 104.8% for 4LOQ and between 88.1% and 101.6% for 8LOQ with RSD less than 20% for the three levels tested. The lowest LOQ value was 1 ng bee^?1 (corresponding to 10 ng g^?1) and the highest LOQ value was 10 ng bee^?1 (corresponding to 100 ng g^?1). These LOQ values are lower than the lethal doses LD₅₀ (acute contact toxicity and acute oral toxicity) of each pesticide for bees.     

LC-Fluorescence Detection of Abamectin, Ivermectin, Doramectin, and Eprinomectin in Rabbit Feces

A simple multi-residue method was developed for the simultaneous determination of abamectin, ivermectin, doramectin, and eprinomectin in rabbit feces. Samples were extracted with acetonitrile, cleaned up with a C18 solid-phase extraction cartridge, and analysed by LC with fluorescence detection after derivatization. Abamectin, ivermectin, doramectin, and eprinomectin were detected at levels of 2–500 ng g^?1; the average recoveries ranged from 73.2 to 99.6% with relative standard deviations of 2.5–11.3%. The limits of detection were 0.1–0.4 ng g^?1.     

Voltametric and Flow Injection Determination of Oxytetracycline Residues in Food Samples Using Carbon Fiber Microelectrodes

A voltammetric method for the determination of the antibiotic oxytetracycline (OTC) in food samples is reported. Carbon fiber microelectrodes (CFMEs), which allow voltammetric measurements to be performed in a small volume (1 mL) of the analyte extract from the samples, are employed. Repeatable electroanalytical responses were obtained with no need of applying cleaning treatments to the CFME. Under the optimized square‐wave conditions, a linear calibration plot for OTC was obtained in the 1.0×10^?6–1.0×10^?4 mol L^?1 range, with a detection limit of 2.9×10^?7 mol L^?1 (150 ng mL^?1) OTC. The determination of OTC by a flow‐injection method with amperometric detection using a homemade flow cell specially designed to work with CFMEs, was also evaluated using pure acetonitrile as the carrier. The SW voltammetric method was applied to the determination of OTC in spiked milk and eggs samples, at 100 ng mL^?1 and 200 ng g^?1 levels, respectively. The procedure involved the extraction of the analyte in ethyl acetate, evaporation of the solvent and reconstitution of the residue in acetonitrile ?5.0×10^?4 mol L^?1 tetrabutylammonium perchlorate medium. Recoveries of 96±8 and 91±8% were obtained for milk and eggs, respectively, by applying the standard additions method.     

Determination of Tetracyclines in Water Samples Using Liquid Chromatography with Fluorimetric Detection

A liquid chromatographic method with fluorimetric detection is proposed for the determination of trace levels of oxytetracycline, tetracycline, chlortetracycline and doxycycline in water samples. The analytes are preconcentrated by solid phase extraction using reversed phase polymeric cartridges and acetonitrile as eluent. Preconcentration factors up to 125 can be obtained. The chromatographic separation is performed on a polymeric column with a gradient elution program using mobile phases based on mixtures of acetonitrile and 0.01 mol L^?1 oxalic acid aqueous solution at a flow rate of 1.2 mL min^?1. Tetracyclines are post-column derivatized with a reagent solution consisting of 0.1 mol L^?1 Mg(II) at pH 9 at a flow rate of 0.6 mL min^?1. The highly fluorescent Mg(II) chelates are detected at λ _ex = 374 nm and λ _em = 499 nm. The detection limits of the whole process are in the low μg L^?1 level. The proposed method has been applied to the analysis of spiked natural water samples, and recovery rates higher than 80% have been obtained.     

Rapid extraction and sample clean-up for the fluorescence densitometric determination of aflatoxin M1 in milk and mil powder

The diluted sample is passed through a SepPak C18 cartridge and the toxin is eluted with acetonitrile/water (3:7, v/v). The extract is cleaned up on a SepPak silica cartridge. The antidiagonal spot application technique is used for two-dimensional thin-layer chromatography. Spots are quantified by fluorescence densitometry. Recoveries of aflatoxin M1 added in the range 0.03-0.1 ng g^?1 of milk are 86–97%. The detection limit is about 0.005 ng g^?1 for milk and 0.05 ng g^?1 for milk powder.     

Flow characteristics in a segmented closed-tube design for ion-mobility spectrometry

Closed-tube design with unidirectional flow of drift gas in ion-mobility spectrometry (i.m.s) was found to provide residence times for analyte from 10 s to 10 min based on drift gas flow rate. The volume of drift gas necessary to restore reactant ions completely to the original intensity, after addition of excess (>900 mg l^?1) of analyte to the ion source, was three times the inner volume of the tube, regardless of flow rate. Contamination of the i.m.s. tube from analyte in the external atmosphere occurred readily in the open-tube design and in the closed-tube design with or without a slight vacuum attached to the tube. Rates of migration of analyte from outside to inside the tube were similar in all designs and the present closed-tube design was largely non-resistant to external contamination. Product-ion intensities for aromatic and polynuclear aromatic hydrocarbons were independent of drift flow rate from 100 to 800 ml min^?1 in the closed-tube design with no formation of artifacts. Plots of ion intensity vs. concentration of o-xylene were linear int wo ranges, 0.05–0.08 μg l^?1 and 0.1–2 μg l^?1, with slopes of 1.2 × 10^?9 A l μg^?1 in the first range and 1.0 × 10^?11 A l μg^?1 in the second range. No changes in mobility of aromatic product-ion peaks were seen with increases in concentration when the analyte was added to the drift gas rather than near the reaction region in unidirectional flow.     

Determination of Palmatine in Rabbit Plasma by RP-HPLC with Solid-Phase Extraction

A rapid and specific reversed-phase high performance liquid chromatography (RP-HPLC) method for the determination of palmatine in rabbit plasma has been developed and validated. The chromatographic separation was performed on a C₁₈ column at 40 °C. The mobile phase, delivered at 1.0 mL min^?1, consisted of acetonitrile/phosphate buffer (pH 3.0) 40:60 (v/v). The detection wavelength was set at 345 nm. Palmatine and internal standard (IS) berberine were extracted from plasma by solid-phase extraction using C18 cartridges. Linearity was confirmed in the concentration range of 0.01 to 5 μg mL^?1, the inter-day and intra-day RSDs were within 10.0, the recoveries of palmatine ranged from 93.1 to 110.3, and the limit of detection (LOD, S/N > 3) was 0.002 μg mL^?1. The method is applicable to the determination of palmatine in rabbit plasma after intravenous administration of palmatine.     

Analysis of Dried Blood Spots for Polychlorinated Biphenyls and Organochlorine Pesticides by Gas Chromatography Coupled with Tandem Mass Spectrometry

Polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCs) are anthropogenic pollutants highly resistant to chemical degradation and readily absorbed by organic tissue. Their persistence in the environment and toxicological threat to mammals prompts swift, reliable methods of analysis. This study outlines a rapid, efficient and sensitive, validated methodology utilizing a simple liquid extraction technique, and subsequent analysis by gas chromatography coupled with tandem mass spectrometry (GC-MS/MS) for the determination of PCBs and OCs from dried blood spots. The PCBs and OCs were quantified in whole marine mammal blood spotted on Whatman Protein Saver cards (PSCs) by extracting the analytes into acetonitrile acidified with formic acid, followed by GC-MS/MS analysis. The samples were analyzed in positive electron impact (EI+) ionization mode with the electron energy set to 40?eV to preserve analyte integrity. Fortified blood with the analytes of interest was used for method validation and subsequent sample screening. The recoveries of targeted analytes ranged from 62.5% to 107.8%, with relative standard deviations ranging from 0.09% to 4.6% at a 100?ng·mL^?1 concentration level. The method detection limits were from 40.4?ng·g^?1 to 179.2?ng·g^?1 for the PCBs and 37.6?ng·g^?1 to 145.1?ng·g^?1 for the OCs. The use of dried blood spots provided for numerous advantages compared to whole blood samples while demonstrating reduced matrix effects and enhanced sample lifespan while retaining analyte sensitivity.     

Determination of organotin compounds (OTC) at low levels in seawater by solid-phase extraction (SPE) and gas chromatography-pulsed flame photometric detection (GC-PFPD)

In this work, a simple, sensitive and affordable analytical method for the simultaneous determination of nine organotin compounds (butyltins, phenyltins and methyltins) in seawater using solid-phase extraction (SPE) and gas chromatography-pulsed flame photometric detection was developed and validated. The performance of three different SPE cartridges (Envi C₁₈, Oasis HLB and Oasis MCX) and three elution solvents of different polarity (hexane, methanol and acetonitrile) was evaluated. The extraction parameters, such as solvent volume, presence of complexing and ion-pairing reagents, sample volume and pH and breakthrough volume, were also investigated. Tributyltin, as the organotin compound of special interest, was efficiently extracted using any of the cartridges and solvents tested. However, the simultaneous extraction of all nine organotin compounds was the most efficient using reversed-phase Envi C₁₈ cartridge and 0.1% (w/v) tropolone in methanol as eluent. The optimised method resulted in good recovery, precision and linearity for all compounds, particularly for tri- and disubstituted species. Method detection limits ranged from 0.22 to 1.27 ng(Sn) L^?1 for butyltins, 0.37 to 4.91 ng(Sn) L^?1 for phenyltins and 0.45 to 1.16 ng(Sn) L^?1 for methyltins. The accuracy of butyltins determination was further verified by the comparison with purchased derivatised standards. The developed method was successfully applied to the environmental samples.     

Validation of a highly sensitive method for the determination of neonicotinoid insecticides residues in honeybees by liquid chromatography with electrospray tandem mass spectrometry

The validation of a multi-residue method for the determination of five neonicotinoid insecticides (imidacloprid, clothianidin, acetamiprid, thiacloprid and thiamethoxam) in honeybees is described. The method involves the extraction of pesticides using acetonitrile and liquid partitioning with n-hexane. One clean-up is then performed on a florisil cartridge (1?g, 6?mL) and the extract is analysed by liquid chromatography-electrospray ionisation-tandem mass spectrometry (LC-ESI-MS/MS). The recovery data were obtained by spiking honeybees samples free of pesticides at two concentration levels of the various neonicotinoids. The recoveries were in the range between 93.3 and 104.0% with relative standard deviation (RSD) less than 20%. The limit of quantification (LOQ) was 0.5?ng?g^?1 (corresponding to 0.05?ng?bee^?1) for all pesticides except for acetamiprid which was 1?ng?g^?1 (corresponding to 0.1?ng?bee^?1).     

Preconcentration of Volatile Hydrocarbons as Air Pollutants by C-18 Bonded Silica used for Solid Phase Extraction

ABSTRACT

C₁₈-Silica used for Solid-Phase Extraction exhibits the same degree of adsorption of volatile hydrocarbons as compared to conventional Tenax adsorbent. The vapor pressure of the hydrocarbons and the velocity of the air sample through the sorbent are dominants of the preconcentration. Recovery of 80% for n-hexane and 98% for p-xylene at a concentration of 10 mg.m^?3 was obtained at 10 ml.g^?.min^? velocity.

C₁₈Bond Elut cartridges have been successfully used for quantitative determination of hydrocarbons as air pollutants by gas chromatography. The detection limit for p-xylene using preconcentration from 1 L air sample and a S/N ratio of 5 was 0.1 mg.m^?3. After regeneration of C₁₈Bond Elut cartridges by washing with acetonitrile and diethyl ether and drying at 85°C/15 min, their preconcentration potential remain acceptable upon reusing at least three times.     

Determination of sulfur,nickel and vanadium in fuel and residual oils by x-ray fluorescence spectrometry

The determination of sulfur, nickel and vanadium in fuel and residual oils by wavelength-dispersive x-ray fluorescence spectrometry is reported. Calibration is initially established with matrix-matched synthetic standards, and maintained free of instrumental drift by daily normalization to a reference standard. An epoxy-cast reference standard pellet offers mechanical rigidity and chemical stability for at least nine months. Matrix effects of sulfur and carbon are studied and corrected. Results for NBS SRM oils fall within the NBS certified values, with imprecision (% RSD) for S, Ni, and V of 1.1, 1.5 and 1.0%, respectively. Detection limits (3 s.d.) are 20 μg g^?1 for sulfur and 0.8 μg g^?1 for Ni and for V.     

A Fractional Factorial Design Applied to the Optimization of Microwave- and Ultrasound-Assisted Acid Leaching Methods for Heavy Metals Determination in Sludges by Flame Atomic Absorption Spectrometry

Abstract

The sampling performance of C₁₈ cartridges coated with DNPH has been studied for twenty four C₁-C₉ carbonyls in experiments involving sampling of parts per billion levels of carbonyls in urban air. indoor air and laboratory experiments. The cartridge background carbonyl content in thirty six batches of cartridges averaged 85, 137 and 155 nanogram/cartridge for formaldehyde, acetaldehyde and acetone, respectively, and was below analytical detection for all other carbonyls. Carbonyl-DNPH derivative recovery from the cartridge was complete in the first elution with 2 mL acetonitrile, and this for twenty four carbonyls at concentrations of 0.02–73 μg carbonyl/cartridge. Studies carried out using two cartridges in series showed no breakthrough, for the sixteen carbonyls tested, at concentrations of 0.10–49 μg carbonyl/cartridge and volumes of air sampled = 6–370 L. Average relative standard deviations (RSD) for replicate analyses were 0.20–13.2% for twenty one carbonyls. Average RSD for co-located samples were 0.9–16.2% for eighteen carbonyls. Comparison of RSD for replicates and RSD for co-located samples for thirteen carbonyls indicated that the overall method precision was limited by sampling precision rather than by analytical precision.     

Simultaneous Determination of Tranquilizers and Carazolol Residues in Swine Tissues by Liquid Chromatography-Tandem Mass Spectrometry

A sensitive and reliable liquid chromatography-tandem mass spectrometry (LC-MS-MS) method was developed for the simultaneous determination of the tranquilizers (chlorpromazine, promethazine, diazepam, azaperone, and its metabolite, azaperol) and a β-blocker (carazolol) in edible swine tissues. Sample was subjected to extract with acetonitrile, clean up by Oasis HLB solid phase extraction cartridge, and then analyzed by LC-MS-MS in multiple reaction monitoring positive ionization mode. The matrix-matched calibration curves were linear within the dynamic range of each analyte with a correlation coefficient higher than 0.99. The average recoveries of tranquilizers and carazolol spiked at three levels ranged from 74.2% to 91.8% with the relative standard deviation below 15%. The limits of detection were between 0.06 and 0.1 µg kg^?1 and the limits of quantification were between 0.2 and 0.4 µg kg^?1 for all analytes in swine muscle, liver, and kidney.     

The chromatographic interaction and separation of metal ions with 8-Quinolinol stationary phases in several aqueous eluents

Several 8-quinolinol silica gel (QSG) columns were used, with metal-uptake capacities of 10–156 μmol g^?1. Various transition and heavy metal ions were used as analytes in nitrate, sulfate, phosphate, citrate, tartrate, oxalate, phthalate, and maleate mobile phases. Metal-ion retention increased with column capacity and pH. Optimum capacity factors were obtained on columns of intermediate capacity (27 and 46 μmol g^?1). Retention times decreased with an increase in eluent buffer concentration, typically by half with a doubling of buffer. Evidence is presented for the occurence of mobile-phase complexation of analyte ions by eluent buffer species. Multiple or split peaks were often observed when the analyte solvent differed from the mobile phase. Chromatographic separation of up to six metals on the QSG columns is demonstrated in tartrate and maleate mobile phases.     

Entwicklung einer flieβinjectionsmethode zur bestimmung von chlorid im spurenbereich durch leitfähighkeitsdiffernzenA flow-injection method for the determination of trace amounts of chloride

The indirect determination of chloride in water is based on measurement of the difference in conductivity after the sample has passed through ion-exchange columns in the hydrogen form and silver form. The linear response range is about 0.5–10 μg g^?1 chloride (with 3 μg g^?1 nitrate and 5 μg g^?1 sulfate); the detection limit is about 50 ng g^?1 chloride but depends strongly on the concentrations of other anions.     

A portable lab‐on‐a‐chip instrument based on MCE with dual top–bottom capacitive coupled contactless conductivity detector in replaceable cell cartridge

A new design for a compact portable lab‐on‐a‐chip instrument based on MCE and dual capacitively coupled contactless conductivity detection (dC⁴D) is described. The instrument is battery powered with total dimension of 14 × 25 × 8 cm³ (w × l × h), and weighs 1.2 kg. The device consists of a front electrophoresis compartment which has the chip holder and the chip, the associated high‐voltage electrodes for electrophoresis injection and separation and the detector. The detection cell is integrated into the device housing with an exchangeable plug‐and‐play cartridge format. The design of the dC⁴D cell has been optimized for maximum performance. The cartridge includes the top–bottom excitation and pick up electrodes incorporated into the cell and connected to push‐pull self‐latching pins that are insulated with plastic. The metal frame of the cartridge is grounded completely to eliminate electronic interferences. The cartridge is designed to clamp a thin fluidic chip at the detection point. The cartridges are replaceable whereby different cartridges have different detection electrode configurations to employ according to the sensitivity or resolution needed in the specific analytical application. The second compartment consists of all the electronics, data acquisition card, high‐voltage modules of up to ±5 kV both polarity, and batteries for 10 h of operation. The improved detector performance is illustrated by the electrophoresis analysis of six cations (NH₄⁺, K⁺, Ca²⁺, Na⁺, Mg²⁺, Li⁺) with a detection limit of approximately 5 μM and the analysis of the anions (Br^?, Cl^?, NO₂^?, NO₃^?, SO₄^2?, F^?) with a detection limit of about 3 μM. Analytical capabilities of the instrument for food and medical applications were evaluated by simultaneous detection of organic and inorganic acids in fruit juice and inorganic cations and anions in rabbit blood samples and human urine samples are also demonstrated.     

Fast solid phase extraction of polychlorobiphenyls and chlorinated pesticide residues from mussels using sep-pak cartridges

Summary A rapid method for the determination of chlorinated pesticides and polychlorinated biphenyls in mussels (Mytilus sp.) is reported. The mussel sample is homogenized and extracted with acetonitrile. The organic solution is concentrated and successively diluted with distilled water solution (12 g L⁻¹ NaCl). The organic compounds from water solution are adsorbed onto a NH₂ Sep-Pak cartridge. The clean-up step, in which the polychlorobiphenyls and chiorinated pesticides are separated in different eluates, is achieved by passing 25 mL of a 40% methanol aqueous solution through the NH₂ Sep-Pak and the C₁₈ Sep-Pak cartridges connected in series. The polychloroblphenyls are desorbed from the NH₂ Sep-Pak cartridge whilst the chlorinated peslicides are recovered from the C₁₈ Sep-Pak cartridge. In the separation of polychlorobiphenyls from the chlorinated pesticides tested in this work, only aldrin, hepatachlor and 4,4′-DDD are partially adsorbed with the polychlorobiphenyls onto the NH₂ Sep-Pak cartridge. The average recovery is ≥95.0% with a relative standard deviation ≤5.0%. The limits of detection for different pesticides and polychlorobiphenyl congeners are 0.01 and 0.008 μg Kg⁻¹. The final determination is carried out by capillary gas chromatography with ECD.     

Atomic absorption spectrometric determination of selenium with carbon furnace atomization

A Varian Techtron model 63 carbon rod atomizer is used for the atomic absorption spectrometric determination of nanogram quantities of selenium. The pronounced interferences from the matrices in biological digests can be obviated by isolating selenium from sample matrices by precipitation with ascorbic acid. The precision of the determination is improved by incorporating 5000 μg Ni ml^?1 in the analytical solutions. Selenium at μg g^?1 and sub-μg g^?1 levels in a variety of biological samples can be determined. The detection limit is 25 ng Se g^?1.     

Determination of arsenic by hydride generation with a long absorption cell for atomic absorption spectrometry

A method is described for the determination of arsenic involving hydride generation and atomic absorption spectrometry with an improved long graphite-tube furnace capable of considerably higher temperatures than the conventional quartz-tube heaters. Arsine is generated with sodium tetrahydroborate, held in a nitrogen-cooled trap and then swept with helium into an alumina tube (19 cm long) placed within the graphite furnace. The optimum conditions for determination of arsenic are given. The detection limit is 0.2 ng ml^?1 with RSD of 2–3%. Results for various NBS Standard Reference Materials agreed well with expected values and were as follows: orchard leaves, 10 ± 1 μg g^?1; tomato leaves, 0.28 ± 0.03 μg g^?1; bovine liver, 0.046 ± 0.005 μg g^?1.