Liquid Chromatographic-Electro-Chemical Technique for Determination of Ethylenethiourea Residues

Abstract

A high performance liquid chromatographic-electrochemical (HPLC-EC) technique was developed to selectively determine ethylenethiourea (ETU) at residue levels without derivatization. ETU was eluted from a C-8 column with water, a phosphoric acid electrolyte solution was added to the column eluate, and then ETU was detected with an electrochemical detector containing a Au/Hg working electrode. The HPLC-EC system produced a sharp chromatographic peak for ETU that was detected by the Au/Hg electrode at an applied potential of +0.36 V. With detector sensitivity adjusted so that 10 ng ETU produced a 50% full scale deflection peak (1% baseline noise), the detector's response was linear from 2 to 400 ng ETU. No peaks were observed in potato and spinach controls, and only small apparent ETU peaks of 7 and 3 ppb, respectively, were found in apple and grape controls. Detector response was equivalent to 90% of actual ETU added (0.1 ppm) to purified spinach extracts. Crop coextractives from apples, grapes and potatoes did not affect detector response to ETU at the 0.1 ppm fortification level.     

A high performance liquid chromatographic method for the determination of ethylenethiourea in urine and on filters

Urine samples are evaporated and pretreated with silica gel and alumina. Filters undergo ultrasonic treatment in water. Ethylenethiourea (ETU) is then determined by reversed-phase high-performance liquid chromatography with detection at 230 nm. The detection limit for ETU is 0.1 ng per injection and linear response is found for the range 0.3–110 ng; 0.2 μg 1^?1 ETU can be detected in urine. Recoveries from spiked filters (7 μg ETU/filter) varied from 79 to 94%. The methods are sensitive enough for application in occupational hygiene work.     

A new chemiluminescence system: MnO(-)(4)-Na(2)CO(3)-KOH and its application in the determination of manganese

A new, fast and simple inorganic chemiluminescence method for the determination of trace amounts of manganese is described. When MnO(-)(4) is injected into 0.40M Na(2)CO(3)-0.70M KOH mixed solution in a reaction cell, the strong chemiluminescence occurs and is recorded. The detection limit is 0.1 ppb Mn and the linear range extends from 0.1 to 10 ppb Mn. A 5-ppb Mn concentration can be determined with a relative standard deviation of 5.6% (15 replicates). The commonly encountered cations do not interfere with the determinations. This method has been successfully applied to the direct determination of manganese in bauxite. The reaction mechanism is also briefly discussed.     

Off-Line and On-Line Preconcentration Techniques for the Determination of Phenylureas in Freshwaters

Abstract

Phenylurea herbicides are analysed by reversed-phase liquid chromatography using UV detection at 244 nm after a concentration step in order to determine ppb or sub-ppb levels in drinking and river waters. With an average UV detection limit of 5 ng, a 500 ml sample volume is necessary to reach the 10 ppt level for spiked LC grade water samples and enables easy determination of concentrations below the ppb level for river water samples. Off-line and on-line methods are compared for the concentration step. Off-line concentration consists in a liquid sorption on n-octadecyl silica (C18) and elution by a suitable organic solvent. Polar phenylureas have low retention volumes on C18 silica and consequently the length of the concentration column has to be 10 cm to concentrate them at the ppb level from 100 ml of water and longer for lower levels of detection. Nevertheless, we show that increasing the size of the concentration column does not improve the limits of detection because of the numerous interferences also concentrated when percolating high volumes of water. On-line technology can be used only with short precolumns and requires a sorbent with a great retention for phenylureas. The copolymer-based PRP-1 is found to be an excellent sorbent and it is then possible to apply on-line precolumn technology with preconcentration through two precolumns (10 × 21 mm ID) in series, the first one being packed with C18 silica and the other with the PRP-1 polymer. Interfering compounds are then trapped onto the first precolumn acting as a filter and common phenylurea-breakthrough volumes on the PRP-1 precolumn are higher than 500 ml. Knowing the amounts preconcentrated on both precolumns and using UV and electrochemical detection help the identification of phenylureas in river water.     

Enhancing concentration and mass sensitivities for liquid chromatography trace analysis of clopyralid in drinking water

A theoretical treatment was developed and validated that relates analyte concentration and mass sensitivities to injection volume, retention factor, particle diameter, column length, column inner diameter and detection wavelength in liquid chromatography, and sample volume and extracted volume in solid‐phase extraction (SPE). The principles were applied to improve sensitivity for trace analysis of clopyralid in drinking water. It was demonstrated that a concentration limit of detection of 0.02 ppb (μg/L) for clopyralid could be achieved with the use of simple UV detection and 100 mL of a spiked drinking water sample. This enabled reliable quantitation of clopyralid at the targeted 0.1 ppb level. Using a buffered solution as the elution solvent (potassium acetate buffer, pH 4.5, containing 10% of methanol) in the SPE procedures was found superior to using 100% methanol, as it provided better extraction recovery (70–90%) and precision (5% for a concentration at 0.1 ppb level). In addition, the eluted sample was in a weaker solvent than the mobile phase, permitting the direct injection of the extracted sample, which enabled a faster cycle time of the overall analysis. Excluding the preparation of calibration standards, the analysis of a single sample, including acidification, extraction, elution and LC run, could be completed in 1 h. The method was used successfully for the determination of clopyralid in over 200 clopyralid monoethanolamine‐fortified drinking water samples, which were treated with various water treatment resins.     

In-line coupling capillary electrochromatography with amperometric detection for analysis of explosive compounds

Amperometric detection at a bare gold electrode has been in-line coupled with capillary electrochromatography (CEC) for analysis of nitroaromatic and nitroamine explosives in contaminated soils and ground water. The CEC column packed with 3 microm C18 particles performed best using a mobile phase containing 70-80% methanol, 30 or 20% water, 5 mM sodium dodecyl sulfate (SDS) and 10mM 2-(N-morpholino)ethanesulfonic acid (MES). In contrast, the separation column packed with 1.5 km C18 particles exhibited the best separation when only 30% methanol was added to a mobile phase containing 70% water, 7 mM SDS, and 10 mM MES. The detection, based on electrochemical reduction of the explosives (-0.7 or -1 V vs. Ag/AgCl, depending upon the level of methanol in the mobile phase), was compatible with such mobile phases. The detection limits for 13 explosives ranged from 100 to 200 ppb, i.e., about twofold better than those obtained with electrokinetic chromatography (EKC)/amperometric detection. From an operational viewpoint, exhaustive column conditioning was a prerequisite and care should be taken to prevent bubble formation and current breakdown during the course of separation. The CEC column equipped with amperometric detection successfully measured explosives in ground water and extracts prepared from contaminated soils and the results obtained agreed well with those of the U.S. Environmental protection Agency (EPA) method.     

An original approach to determining traces of tetracycline antibiotics in milk and eggs by solid-phase extraction and liquid chromatography/mass spectrometry

An original and highly specific method able to identify and quantify traces of five tetracycline antibiotics (TCAs) in milk and eggs is presented. This method uses a single solid-phase extraction (SPE) cartridge for simultaneous extraction and purification of TCAs in the above matrices. After diluting 5 mL of intact whole milk or 2 g egg samples with Na(2)EDTA-containing water, samples are passed through a 0.5-g Carbograph 4 extraction cartridge. After analyte elution from the SPE cartridge, an aliquot of the final extract is injected into a liquid chromatography/mass spectrometry (LC/MS) instrument equipped with an electrospray ion source and a single quadrupole. MS data acquisition is performed in the positive-ion mode and by a time-scheduled multiple-ion selected ion-monitoring program. With methanol as organic modifier, the in-source collision-induced dissociation (CID) process generated fragment ions able to pick up one methanol molecule. In several cases, these methanol-adduct fragment ions have m/z values higher than those of the protonated molecules. This event is rarely encountered in MS, thus making the analysis of TCAs by this method extremely specific. Compared with a conventional published method, the present protocol extracted larger amounts of TCAs from both milk and egg and decreased the analysis time by a factor of 3. Recovery of TCAs in milk at the 25-ppb level ranged between 81 and 96% with relative standard deviation (RSD) no larger than 9%. Recovery of TCAs in egg at the 50-ppb level ranged between 72 and 92% with RSD no larger than 7%. Estimated limits of quantification(S/N = 10) of the method were 2-9 ppb TCAs in whole milk and 2-19 ppb TCAs in eggs.     

Effect of Surfactant Loading on the Extraction Properties of C-18 Bonded Silica used for Solid-Phase Extraction of Phenols

ABSTRACT

A solid phase extraction (SPE) system has been modified with cationic surfactants and evaluated for extraction and preconcentration of trace phenolic compounds contaminants in water at low ppb concentrations. Cationic surfactants such as cetyl trimethyl ammonium bromide (CTAB) has been steadily adsorbed on the surface of C-18 bonded silica, and the ionized functional group of the surfactant can then act as an ion–exchange site to attract the ionized phenolic compounds from water samples. The method includes enrichment of the phenolic compounds by the surfactant-loaded solid phase extraction system, followed by elution of the analyte with methylene chloride and derivatization of the phenolic compounds with acetic anhydride. Thirty-two phenolic analytes were identified and quantitatively determined by this method; identification and quantification of the compounds is performed with GC/FID using 2-bromophenol as internal standard. SPME analysis with this method was linear over 3-6 orders of magnitude, with linear correlation coefficient (R²) greater than 0.96. Experimentally determined FID detection limits ranged from ～30 ppt for methyl-substituted phenols to ～0.1ppb for phenol and chloro-substituted phenols. We tested the influence of sample pH, the loading amount of surfactant on the solid phase, and the volume and matrixes of the sample were studied. Absolute recoveries from pure water spiked with 0.2 ppb phenolic compounds were 96 – 103%. The method has been applied to analysis of various natural waters, including ground water, lake water, seawater, and wastewater. Recoveries from ground water, lake water, seawater, and wastewater were 92 – 106%, 75 – 93%, 87 – 103%, 86 – 99%, respectively. Therefore, the new technique proved to be an excellent tool for trace enrichments of phenolic compounds at low ppb concentration of these analytes, from different natural water samples.     

Liquid chromatographic determination of ethylenethiourea using pulsed amperometric detection.

A liquid chromatographic method was developed using pulsed amperometric detection at a gold working electrode to measure residue levels of ethylenethiourea (ETU) in crops and groundwater. Use of the sequential pulsing program eliminates electrode fouling while preserving the sensitive and selective detection of ETU. Minimum detection limits in crops were 5-10 ppb (1.25-2.5 ng on-column) and 5 ppb (0.5 ng) in groundwater. The commercial availability of the pulsed electrochemical detector and its gold working electrode that remains functional with a minimum of conditioning is an improvement in method simplicity.     

Reduction of uranium concentration in well water by Chlorella (Chlorella pyrendoidosa) a fresh water algae immobilized in calcium alginate

A great deal of research has been directed towards the problem of reduction of uranium concentration from few hundreds of ppb to less than 20 ppb, a limit of uranium in drinking water from ground water resources fixed in Dec, 2001 by US, Environmental Protection Agency. Laboratory simulated experiments were carried out for the reduction of U(VI) concentration in well water from few thousands of ppb to less than 20 ppb. Well water samples were spiked with U(IV) ranging from 1000 to 2000 ppb. The contaminated solutions were passed through a glass column containing of chlorella impregnated beads of calcium alginate. Chlorella(Chlorella pyrendoidosa), a fresh water algae, was immobilized in sodium alginate in the form of beads by using 0.2M calcium chloride solution. The solution was passed again through a charcoal solution to remove any trace of impurities. The concentration of uranium after treatment ranged from 10 to 20 ppb. The concentration of other major cations and anions in the solution were also monitored. This low cost kit was proposed for on-line removal of uranium from ground water used for drinking purposes. For taking care of waste disposal, 99-100% of the adsorbed uranium on beads was recovered by 0.1M HNO₃. The desorption results suggest that the uptake of uranium by Chlorella is a physico-chemical adsorption on the cell surface, not a biological activity. The uranium in the algal cells is coupled to the ligand, which can be easily substituted with NO₃ ^-. This revised version was published online in July 2006 with corrections to the Cover Date.     

Cooperative Study of Precision and Accuracy on the Determinations of Around-Ppb Levels of Copper and Lead in Environmental Waters

The results of a series of inter-laboratory cross-check on the determinations of ppb and sub-ppb levels of copper and lead in environmental samples are described. Thirteen laboratories participated during a five-stage comparison. Seven analytical methods and two pre-concentration procedures were performed on certified and real samples. For controlled and blind standards at higher concentration levels (10 ppb or above) the data reported by different participants show good agreement for both elements regardless of the method chosen. However, for samples having lower concentrations (1-10 ppb level), the relative standard deviation (R.S.D.) and bias increased. A high degree of scattering on data were demonstrated for a deep ocean water at less than 1 ppb level. The results of the present study give direct comparison between different analytical methods, and also reflect the average aptitude of analytical laboratories in Taiwan on the measurements of copper and lead in environmental samples.     

Construction and Evaluation of a Gold Tubular Electrode for Flow Analysis: Application to Speciation of Antimony in Water Samples

A tubular gold electrode (TGE) is described for the first time by summarizing the important aspects of its construction and evaluation. Applicability of the TGE is evaluated in the speciation of Sb(III) and Sb(V) using anodic stripping voltammetry in a single flow manifold. Studies with surface active interferences and metallic cations were performed. The proposed conditions for antimony determination showed good tolerance towards cationic, anionic and nonionic surface active substances. A linear response for antimony was obtained for solutions containing significant amounts of several metallic cations. Linear calibration curves for Sb(III) were obtained in the range 1–10 ppb with a detection limit of 0.19 ppb (CV=2.91%, n=5, [Sb(III)]=5 ppb). For Sb(V), linear calibration curves were in the range 1–15 ppb with a detection limit of 0.32 ppb (CV=1.41%, n=5, [Sb(V)]=5 ppb). The figures of merit achieved sustain for the good applicability of the proposed method as it allows the determination of antimony at levels below maximum values permitted in consuming waters. Results of antimony concentration determined in water samples were validated against the ICP‐MS reference procedure or compared with reference water samples.     

Determination of benzoylureas in ground water samples by fully automated on-line pre-concentration and liquid chromatography-fluorescence detection

An on-line pre-concentration method for the analysis of five benzoylureas (diflubenzuron, triflumuron, hexaflumuron, lufenuron and flufenoxuron) in ground water samples was evaluated using two C(18) columns, and fluorescence detection after photochemical induced fluorescence (PIF) post-column derivatization. The trace enrichment was carried out with 35 mL of ground water modified with 15 mL of MeOH on a 50 mm x 4.6 mm I.D. first enrichment column (C-1) packed with 5 microm Hypersil Elite C(18). Retention properties of pesticides and humic acids usually contained in ground water were studied on C-1 at concentration levels ranging between 0.04 and 14.00 microg/L in water samples. The results obtained in this study show that the pesticides are pre-concentrated in the first short column while the humic acids contained in the ground water samples are eluted to waste. Pesticides recoveries ranged between 92.3 and 109.5%. The methodology proposed was used to determine benzoylureas in ground water samples at levels lower than 0.1 microg/L (maximum levels established by the European Union).     

Development of a multi-component chemically reactive detection conjugate for the determination of Hg(II) in water samples

Mercury ions (Hg(II)) are considered highly toxic and hazardous element even at low levels. The contamination of Hg(II) is a global problem. To develop selective and sensitive technique for the detection of Hg(II) has attracted considerable attention. In this study, a multi-component chemically reactive detection conjugate for determination of Hg(II) has been synthesized and a competitive format assay was proposed. In the technique, the chemically reactive capture conjugate was coated on the plate. The reactive detection conjugate was then captured by the capture conjugate. TMB solution was added and catalyzed by HRP molecules immobilized on AuNPs. Finally, the developed enzymatic signal was measured at 450 nm. The linear range of the assay was 0.35–350 ppb with a detection limit of 0.1 ppb. The average recoveries of Hg(II) from mineral water, tap water and lake water were 100.03%, 103.13% and 102.03%, respectively. All coefficients of variation (CVs) were less than 10%. The results are closely correlated with those from inductively coupled plasma mass spectrometry (ICP-MS), which indicated that the developed technique is a reliable method for and sensitive detection of Hg(II) in water samples.     

Determination of Ethylenethiourea (ETU) at Trace Levels in Water Samples by Cathodic Stripping Voltammetry

A stripping voltammetric method for the determination of ethylenethiourea in water samples is described based on its adsorptive deposition at the hanging mercury drop electrode (HMDE). In a borate buffer (pH 9.0) as supporting electrolyte, ETU is deposited at +100 mV (vs. Ag/AgCl) and stripped during the cathodic scan. The linear range for the measurements was from 2.0 to 100 μg L^?1, with a detection limit calculated as 1.4 μg L^?1 after a deposition time of 300 s and a RSD of 1.9% (n=5) for 50 μg L^?1 of ETU measured. The interferences of some organic compounds and metallic ions were tested. Recoveries between 93 and 110% were obtained using the standard addition method for spiked samples of natural and drinking waters. The method is rapid and applicable in the monitoring of ETU residues in water samples.     

Stereoselective analysis of acid herbicides in natural waters by capillary electrophoresis.

A capillary electrophoretic method for the stereoselective analysis of aryloxypropionic and aryloxyphenoxypropionic acidic herbicides in ground water and river water was performed. Vancomycin and gamma-cyclodextrin were added to the background electrolyte (BGE) as chiral selectors. Water sample preconcentration was accomplished by solid-phase extraction on styrene-divinylbenzene packed cartridges (2 L of ground water and 1 L of river water). The analytical method allowed for the resolution of mecoprop, fenoprop, fluazifop and haloxyfop racemic mixtures in natural water samples spiked with enantiomer concentration levels in the range 0.1-0.13 ppb for ground water and 0.4-0.54 ppb for river water.     

An improved thermal desorption GC/MS method for the determination of low ppb concentrations of chloromethane in ambient air

An improved thermal desorption method for the qualitative and quantitative determination of low ppb concentrations of chloromethane in ambient air was developed. The method utilizes traps containing petroleum-based carbon, and a simple desorbing device for injecting the concentrated sample into a GC/MS system. Experiments show that chloromethane can be confidently and reproducibly determined at the 10-ppb level and probably can be determined at a concentration <1 ppb.     

The impact of nitrogen fertilizers on degradation and leaching of chlorotoluron in soil

Abstract

This study presents the developed and applied methods for the determination of carbendazim in environmental samples originating from several field studies.

For water samples sample pretreatment consisted of a solid phase extraction (SPE) on cartridges packed with 200 mg SDB-1. In case of solid samples the performance of microwave assisted solvent extraction (MASE) and classical ultrasonic extraction with acetone-ethyl acetate were studied. The latter technique was selected because of the reduced time of manual operations. Instrumental analysis of extracts of water samples was performed on-line with coupled column reversed phase liquid chromatography (LC/LC) and UV detection (280 nm) allowing to assay carbendazim to a level of at least 0.1 μg/l. Improved column life time was obtained by performing the favorable LC separation of carbendazim at high pH on newly developed 5 μm Extend-pH bidentate C18 material.

The combination of a short column packed with 5 μm Inertsil ODS-5 and a mobile phase at low pH material was most adequate as the regards the robust and fast processing of extracts of solid samples and allowed in most cases the screening of carbendazim in soils and sediments to a level of 10μg/kg.

The developed procedures yield overall recoveries for carbendazim of 101, 80 and 71 % in water (levels, 0.1—1.2 μg/l: n=12), soil (levels, 10 and 100 μg/kg; n=22) and sediments (levels, 10 and 100 μg/kg; n=11), respectively, with a repeatability and reproducibility below 7 % for all method/matrix combinations. Soil samples with aged residues (level, 100 μg/kg; n=10) provided an overall recovery of 71% and no significant decrease of carbendazim was observed during nine weeks of storage in the refrigerator.     

Pressurized Liquid Extraction Coupled with LC–ESI–MS–MS for the Determination of Herbicides Chlormequat and Mepiquat in Flours

This paper describes a new method for the rapid extraction and unequivocal confirmation of herbicides chlormequat and mepiquat in wheat flours and various flours utilized in infant foods. The highly automated extraction procedure is based on accelerated solvent extraction, followed by liquid chromatography-tandem mass spectrometry as a confirmatory analysis. Typical recoveries from flours and baby food samples ranged from 83 to 99% at a fortification level of 10 ppb, corresponding to the maximum residue limits established by the European Union; while relative standard deviations (RSD) were less than 10% for all samples. The limit of detection (signal-to-noise ratio = 3) of the method for the considered phenols in baby food samples are less than 0.1 μg g^?1. Traces of the selected herbicides have been detected in about 50% of baby foods, bought from different Roman supermarkets and butcher shops, applying the described methodology.     

Analysis of ethylenethiourea as a biomarker in human urine using liquid chromatography/triple quadrupole mass spectrometry

Ethylenebisdithiocarbamates (EBDCs) are widely used fungicides. Ethylenethiourea (ETU), the main metabolite and also a contaminant in the commercially available products, is of major toxicological concern. In this study, a method using liquid chromatography/triple quadrupole mass spectrometry (LC/MS/MS) is described for the analysis of ETU in human urine after a single-step extractive derivatization using pentafluorobenzyl bromide (PFBBr). Analysis was carried out using selected reaction monitoring (SRM) in the positive ion mode. Quantification of ETU was performed using [(2)H(4)]-labeled ETU as internal standard (IS). The limit of detection (LOD) was determined to 0.05 ng/mL. The method was linear in the range 0.1-54 ng/mL urine and had a within-run precision of 3-5%. The between-run precision was determined at an average urine level of 2 and 10 ng/mL urine and found to be 9%. The inter-batch precision was 6%. To validate ETU as a biomarker of exposure, the method was applied in a human experimental oral exposure to the commercial fungicide Ridomil Gold, containing 64% mancozeb and 4.5% ETU. Two healthy volunteers received 8.9 microg/kg body weight (b.w.) Ridomil Gold in a single oral dose followed by urine sampling for 104 h post-exposure. The elimination half-life of ETU was estimated to 17-23 h.