Determination of organophosphorus insecticides in natural waters using SPE-disks and SPME followed by GC/FTD and GC/MS

Two methods for the analysis of ten organophosphorus insecticides in natural waters using solid phase extraction disks containing C₁₈ and SDB and solid phase microextraction fibers containing polyacrylate (PA) are developed. Bromophos ethyl, bromophos methyl, dichlofenthion, ethion, fenamiphos, fenitrothion, fenthion, malathion, parathion ethyl and parathion methyl were determined by GC/MS and GC/FTD. The SPE-disks require only 1000 mL of sample and provide a method limit of detection in the range of 0.01–0.07 μg/L and recovery rates from 60.7 to 104.1%. The solid phase microextraction (SPME) technique requires 2–5 mL of water sample and provides a method limit of detection in the range of 0.01 to 0.05 μg/L for all detectors and the recoveries compared to distilled water ranged from 86.2 to 119.7%. The proposed methods were applied to the trace level screening determination of insecticides in river water samples originating from different Greek regions.     

Determination of organophosphorus insecticides in natural waters using SPE-disks and SPME followed by GC/FTD and GC/MS

Two methods for the analysis of ten organophosphorus insecticides in natural waters using solid phase extraction disks containing C18 and SDB and solid phase microextraction fibers containing polyacrylate (PA) are developed. Bromophos ethyl, bromophos methyl, dichlofenthion, ethion, fenamiphos, fenitrothion, fenthion, malathion, parathion ethyl and parathion methyl were determined by GC/MS and GC/FTD. The SPE-disks require only 1000 mL of sample and provide a method limit of detection in the range of 0.01-0.07 microgram/L and recovery rates from 60.7 to 104.1%. The solid phase microextraction (SPME) technique requires 2-5 mL of water sample and provides a method limit of detection in the range of 0.01 to 0.05 microgram/L for all detectors and the recoveries compared to distilled water ranged from 86.2 to 119.7%. The proposed methods were applied to the trace level screening determination of insecticides in river water samples originating from different Greek regions.     

Degradation study of selected organophosphorus insecticides in natural waters

The degradation of 15 organophosphorus insecticides was studied in drinking, ground, and surface waters under different laboratory-controlled and environmental conditions. Surface waters originated from rivers Savinja (near the city of Celje) and Kamniska Bistrica (at the spring), which both belong to the Danube river basin. Groundwater was collected from wells (70?m deep) in Ljubljana, which are the direct source of drinking water for the capital. These matrices were selected on the basis of their different chemical composition and microbial activity. Major factors influencing the degradation were determined, such as temperature, oxygen, sunlight, pH, and type of water. The degradation of atrazine, present in many water sources in Slovenija, was followed simultaneously as a reference under the same conditions. The degradation kinetics was followed by gas chromatography with mass-selective detection, which also allowed the identification of some degradation by-products, such as oxon analogues paraoxon, dyfoxon, malaoxon, phenyl-methyl sulfoxide, fenthion sulfone, phorate sulfoxide, and phorate sulfone. The results show that the half-lives of the selected organophosphorus insecticides varied from 4 to 192 days or more, depending on the water source and experimental conditions. As a result, kinetically constants and half-lives were calculated for every tested insecticide, and major degradation products were determined.     

Optimization of headspace solid-phase microextraction conditions for the determination of organophosphorus insecticides in natural waters

Headspace solid-phase microextraction (HS-SPME) has been developed for the analysis of seven organophosphorus insecticides, i.e. diazinon, fenitrothion, fenthion, ethyl parathion, methyl bromophos, ethyl bromophos and ethion in natural waters. Their determination was carried out using gas chromatography with flame thermionic and mass spectrometric detection. To perform the HS-SPME, two types of fibre have been assayed and compared: polyacrylate (PA 85 microm), and polydimethylsiloxane (PDMS 100 microm). The main parameters affecting the HS-SPME process such as temperature, salt additives, memory effect, stirring rate and adsorption-time profile were studied. The method was developed using spiked natural waters such as ground, sea, river and lake water in a concentration range of 0.05-1 microg/l. The HS-SPME conditions were optimized in order to obtain the maximum sensitivity. Detection limits varied from 0.01 to 0.04 microg/l and relative standard deviations (RSD <17%) were obtained showing that the precision of the method is reliable. The method showed also good linearity for the tested concentration range with regression coefficients ranging between 0.985 and 0.999. Recoveries were in relatively high levels for all the analytes and ranged from 80 to 120%. Water samples collected from different stations along the flow of Kalamas river (NW Greece) were analyzed using the optimized conditions in order to evaluate the potential of the proposed method to the trace-level screening determination of organophosphorus insecticides. The analysis with HS-SPME has less background interference and the advantage of its non-destructive nature reveal the possibility of the repetitive use of the SPME fibre.     

Analysis of organic volatile flavor compounds in fermented stinky tofu using SPME with different fiber coatings

The organic volatile flavor compounds in fermented stinky tofu (FST) were studied using SPME-GC/MS. A total of 39 volatile compounds were identified, including nine esters, seven alcohols, five alkenes, four sulfides, three heterocycles, three carboxylic acids, three ketones, two aldehydes, one phenol, one amine and one ether. These compounds were determined by MS, and conformed by comparison of the retention times of the separated constituents with those of authentic samples and by comparison of retention indexes (RIs) of separated constituents with the RIs reported in the literature. The predominant volatile compound in FST was indole, followed by dimethyl trisulfide, phenol, dimethyl disulfide and dimethyl tetrasulfide. In order to find a better extraction time, the extraction times was optimized for each type of SPME fiber; the results show that the best extraction time for Carboxen/PDMS is 60 min, for PDMS/DVB 30 min, for DVB/CAR/PDMS 60 min and for PDMS 75 min. Of the four fibers used in this work, Carboxen/PDMS is found to be the most suitable to extract the organic volatile flavor compounds in fermented stinky tofu.     

A method for the determination of some organophosphorus insecticides in human serum

Summary A simple and rapid method for the determination of organophosphorus insecticides in serum of poisoned patients is described. The compounds are extracted with benzene and the extraction residue is gas chromatographed on a glass capillary column with alkali flame ionisation detection. Concentrations from 2 ng cm⁻³ can be determined. As an example, results of the analysis of serum samples of three patients, poisoned with parathion and methylparation, are given.     

Low-temperature clean-up method for the determination of organophosphorus insecticides in olive oil

A simple, extremely low-cost method using low-temperature lipid precipitation has been developed for the rapid analysis of virgin olive oil for organophosphorus insecticides and triazine herbicides commonly used in olive groves. The method gives good clean-up for GC analysis with nitrogen-phosphorus detection and recoveries between 77 and 104%, with RSD values of 7-16%. Matrix enhancement was observed for some pesticides and metabolites.     

Supported liquid membrane enrichment using an organophosphorus extractant for analytical trace metal determinations in river waters

Metal ions were preconcentrated from water samples using supported liquid membranes containing 40% w/w di-2-ethylhexyl phosphoric acid (DEHPA) dissolved in kerosene as the membrane liquid. The driving force for the mass transport of analytes in this system is the pH gradient across the membrane. The effect of the carrier concentration on the extraction efficiency was studied. The mechanism for the mass transport in the system was investigated by measuring changes in pH and analyte ion concentration as well as changes in the concentration of other interfering metal ions present in large excess during the enrichment. The extraction efficiency was found to be unchanged as long as the pH difference across the membrane was more than 2 pH units. The long-term stability of the system was investigated at different pHs in the donor solution. Under optimal conditions, the membrane was stable for at least 200 h with reagent water samples and at least 80 h for river water samples. Enrichment factors of approximately 15 times could be obtained. The corresponding extraction efficiencies were over 80% for some of the investigated metal ions. The detection limits of blank samples for Cu²⁺, Cd²⁺ and Pb²⁺ using 120 min processing time were 0.19, 0.024 and 0.09 ng/mL, respectively. Received: 29 October 1996 / Revised: 17 February 1997 / Accepted: 23 February 1997     

Practical method validation: Validation sufficient for an analysis method

Validation of an analysis method depends on the purpose of the method, the chosen technique and the procedure in question. Methods are used for different research, product development, process control and quality control purposes. The human and economical importance of results vary. Each of the techniques used, such as chromatography-(HPLC, HRGC, TLC), capillary electrophoresis-(CE), spectrophotometry-(UV/VIS, IR, fluorescence, AAS, ICP) or spectrometric techniques (NMR, MS) as well as the hyphenated methods, have their own special features and deficiencies which must be considered. The method can include a simple pretreatment or it may include many demanding steps, it can use automation and data processing in various ways, it can have an official status, it can be a thoroughly verified or less studied one. How should these differences be accounted for during the validation? What would be a sufficient certainty that the method does what is expected, that the method fits for the purpose it was intended? The client (or authority) decides the required timetable, cost and quality level. This is why within a laboratory different quality levels and associated levels of validation exist. This paper tries to outline a practical test frame for validation efforts to assist the analyst when planning validation of a method.     

Headspace solid-phase microextraction for the gas chromatographic analysis of organophosphorus insecticides in vegetables

Residues of organophosphorus insecticides (diazinon, methyl parathion, fenitrothion, malathion, and parathion) were determined in 13 different vegetable matrixes by headspace solid-phase microextraction performed with a polydimethyl-siloxane fiber (100 microm). Determination was carried out by gas chromatography with a nitrogen-phosphorus detector. Limits of detection and quantification were < 0.005 and 0.017 mg/kg, respectively; thus, the limits of maximum residue levels (MRLs) required by European regulations can be verified without difficulty. Pesticide residues were found in 38% of the 125 fresh commercial samples (imported and domestic) that were analyzed. Residues of methyl parathion and parathion, which were withdrawn in Greece in 2003, were detected in 36.8 and 4% of all samples, respectively. The MRLs were exceeded overall by 1%.     

Analysis of the chloroacetanilide herbicides in water using SPME with CAR/PDMS and GC/ECD

The solid-phase microextraction (SPME) technique using a 75 mm film of carboxen/polydimethylsiloxane was applied to the analysis of chloroacetanilide herbicides (acetochlor, alachlor, butachlor, metolachlor, and propachlor) residues. The feasibility of SPME with gas chromatography electron capture detection analysis has been evaluated. The effects of experimental parameters such as magnetic stirring, salt addition, humic acid addition, pH value, and extraction time, as well as desorption temperature and time, were investigated. Analytical parameters such as linearity, repeatability and limit of detection were also evaluated. The inhibition of humic acid to the extraction of chloroacetanilide herbicides was observed. A standard addition method for calibration was recommended to reduce deviations caused by matrix interferences. The proposed method provided a simple and rapid analytical procedure for chloroacetanilide herbicides in water with limits of detection 0.002-0.065 microg/L for deionized water, and 0.005-0.22 microg/L for farm water. The relative standard deviations (n = 5) for analyses of farm water were 7-20% for 5 [corrected] microg/L chloroacetanilide herbicides. This application was illustrated by the analysis of sample collected from farm water in the Chung-hwa area, Taiwan.     

Continuous solid-phase extraction and gas chromatographic determination of organophosphorus pesticides in natural and drinking waters

A simple, rapid continuous-flow solid-phase extraction method with gas chromatographic detection for the determination of organophosphorus pesticides is proposed. The continuous system consists of an adsorbent column where pesticides are preconcentrated and subsequently eluted with ethyl acetate. Various sorbent materials were assayed of which RP-C18 was found to provide the best results, with a sorption efficiency close to 100%. A comparative study of the determination of pesticides in aqueous samples was conducted using gas chromatography with nitrogen-phosphorus (NPD) and flame ionization (FID) detection. The detection limits of the method for 10 ml of sample were between 50-130 ng/l and 4.5-1 1.7 microg/l with NPD and FID detection, respectively. The method was used to determine organophosphorus pesticides in river, pond, well and tap waters, all with good precision (2.9-4.3%) and recoveries ranging from 93.8 to 104.5%.     

Cellulose fiber biodegradation in natural waters: river water,brackish water,and seawater

Cellulose, the main component of plant cell walls, is degradable in nature. However, to the best of our knowledge, this is the first report that compares the biodegradability of cellulose fibers with different structures in natural waters. River water, brackish water, and seawater were collected from the Kamo River and Osaka Bay, Japan. Biodegradation of cellulose fibers with different structures and crystallinities, ramie, mercerized ramie, and regenerated cellulose fibers in the collected natural water was investigated in the dark at 20 °C for 30 days. The primary and aerobic ultimate biodegradability were evaluated by weight loss and biochemical oxygen demand (BOD) tests, respectively. In the weight-loss test, cellulose fibers were found to be degraded by more than 50% in any natural water within 30 days. However, in the BOD test, biodegradation was diminished, with values of 40%, 20–30%, and 2–10% in river water, brackish water, and seawater, respectively. These results indicate that cellulose fibers are easily degraded into fine fragments, but it is difficult to cause their ultimate decomposition into water and carbon dioxide. Existence of such a tendency in the degree of biodegradation among the cellulose fibers remains unclear. The molecular weight of cellulose fibers in natural water was also measured during their degradation. The degradation behavior in river water and seawater was observed to be different from that in brackish water. The results thus obtained indicate that the microorganisms and enzymes that degrade cellulose fibers differ depending on the natural water, which influences the degree and mechanism of biodegradation.

     

Fluorimetric method for the determination of uranium in natural waters

A method is described for the fluorimetric determination of uranium in natural waters. The limit of detection is 0.3 ppM. Ion-exchange is used to preconcentrate the uranium by a factor of 22 and separate it from quenching ions in the sample. The fluorescence is measured in a medium that is 1.35M in both sulphuric and phosphoric acids. The uranyl ions are excited by radiation of wavelength 280 nm and bandwidth 40 nm. The emitted signal is scanned from 470 to 510 nm. After spiking of the sample solution with a small volume of standard uranium solution, the fluorescence signal is scanned again and the uranium content of the sample calculated from the two readings. The coefficient of variation is 8.5% for determinations of U in a synthetic water sample having a uranium content of 1.9 ppM. Destruction of organic matter in the eluates gives 0.1 ppM detection limit.     

Field method for the estimation of uranium in natural waters

Summary A method, applicable in the field, for the quantitative determination of uranium at the 1-ppm level in natural water has been developed. Equipment and reagents have been assembled and listed for convenience. While 1-ppm solutions have been analyzed lower concentrations can probably be evaluated in the same way.

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Zusammenfassung Eine Feldmethode zur Bestimmung von etwa 1 ppm Uran in natürlichen Wässern wurde entwickelt. Die dazu nötigen Geräte und Reagenzien wurden angegeben. Wahrscheinlich können auch noch geringere Konzentrationen in gleicher Weise bestimmt werden.

     

Ultrasound-assisted emulsification microextraction using low density solvent for analysis of toxic nitrophenols in natural waters

An ultrasound-assisted emulsification microextraction (USAEME) based on low-density solvents was successfully applied for the extraction and pre-concentration of four toxic nitrophenols in water samples. The extracted analytes were analyzed by high-performance liquid chromatography-UV detection. The important parameters influencing the extraction efficiency were studied and optimized utilizing two different optimization methods: one variable at a time (OVAT) and central composite design (CCD). The results showed that the emulsification process can be completed in a few seconds using low-density solvents, but almost 10–20?min is necessary for high-density solvents. Under the optimum conditions (extraction solvent, 1-octanol; extraction solvent volume, 40?µL; sample pH, 3.0; salt concentration, 20% (w/v) NaCl; extraction temperature, 40 (±3)°C), limits of detection of the method were in the range of 0.25 to 1?µg?L^?1 and the repeatability and reproducibility of the proposed method, expressed as relative deviation, varied in the range of 2.2–4.2% and 4.7–6.9%, respectively. Linearity was found to be in the range of 1 to 200?µg?L^?1 and the preconcentration factors (PFs) were between 77 and 175. The relative recoveries of the four nitrophenols from water samples at spiking level of 10.0?µg?L^?1 were in the range of 92.0 to 115.0%.