The stability of selected herbicides preconcentrated from estuarine river waters on solid-phase extraction disks

Stability of organochlorine pesticides during storage in water and loaded SPE disks containing sediment

With regard to the Water Framework Directive (WFD) and the required investigation of the whole water sample including suspended particulate matter (SPM), a storage stability study was conducted to determine the suitable storage time and conditions of 21 organochlorine pesticides (OCPs) spiked in water samples and pre-concentrated on solid-phase extraction disks (SPE disks). Furthermore, this work demonstrates the behaviour of three different certified sediment reference materials (CRMs) contaminated with OCPs in water samples as well as loaded on SPE disks under different temperature conditions and storage time periods. Extracts collected on SPE disks were stored for 3, 14 and 30 days at both 4 °C and -18 °C in darkness covered in (a) freezer bags and (b) aluminum foil. With few exceptions the results of these tests demonstrate stability of OCPs up to 30 days at -18 °C. The recoveries for most substances range between 84% and 133%. Furthermore, the stability of OCPs in water samples additionally spiked with CRM up to 500 mg and stored at a temperature of 4 °C in darkness up to 56 days was investigated. The addition of sodium azide enhanced the stability of some substances during storage, especially the endosulfans (I, II) but most substances were stable regardless of sodium azide addition over the entire storage period. An important conclusion of this study is that the storage of loaded SPE disks is an appropriate alternative to storing water samples.

Feasibility study of a reference material for water chemistry: long term stability of triazine and phenylurea residues stored in vials or on polymeric sorbents

Matrix Reference Materials (MRM) are essential tools for the validation of analytical protocols. Nowadays, there are no such materials for the determination of herbicides in water. So, a feasibility study of a MRM for the analysis of triazines and phenylureas in water was carried out. Different kinds of candidates MRM were prepared: solutions of pesticides diluted in acetonitrile and stored in sealed vials or stored at the dry state after the evaporation of the solvent to dryness, pesticides stored on two different types of polymeric solid-phase extraction (SPE) sorbents after the percolation of drinking or river waters spiked with pesticides. The stability of these candidates MRM stored at various temperatures (room temperature, 0.5 degrees C or -18 degrees C) was studied over a period of approximately 1 year. Two different levels of concentration were studied for each kind of material. During the storage, some samples of each different MRM candidate were monthly analyzed by liquid chromatography. Results showed that, among the candidate materials, some of them presented satisfactory enough stability to consider a further certification. They were either pesticides in solution in sealed vials or pesticides stored on cartridges after the percolation of spiked water samples. However, it was shown that these different MRM candidates had to be stored at a temperature lower than 0.5 degrees C.

Sample preparation for GC analysis of selected pesticides in surface water

A new isolation procedure for the determination of nitrogen/phosphorous containing pesticides and organochlorine pesticides in water was tested, and statistical evaluation of the recoveries was performed. The procedure, designed specifically for the analysis of semi-volatile compounds in water containing Suspended Particulate Matter (SPM), utilizes a specially designed filtration vessel coupled directly to an SPE cartridge. The studies were based on surface water samples (from the Vistula River) spiked with pesticides. SPM separation and analyte isolation/concentration were carried out in a special filtration vessel. Pesticides were sorbed both on the SPE cartridge and on the suspended matter. The cartridge and the filter with the suspended matter were extracted separately with a solvent, which enabled the determination of analyte distribution between the two. For organochlorine pesticides, between 3 and 60% of the initial amount was found on the filter, while the recoveries in the filtrate ranged from 30 to 98%. Total recoveries of organochlorine pesticides from surface water samples spiked with pesticides using the method described were high, ranging from 90 to 101%. The amounts of nitrogen/phosphorus containing pesticides recovered from the filter were lower than 2%, while those from the filtrate ranged from 69 to 92%. Total recoveries of nitrogen/phosphorus containing pesticides from surface water samples were high, ranging from 71 to 92%.

Solid-phase extraction: method development, sorbents, and coupling with liquid chromatography

The objective of this review is to provide updated information about the most important features of the new solid-phase extraction (SPE) materials, their interaction mode and their potential for modern SPE. First, the recent developments are given in formats, phases, automation, high throughput purpose and set-up of new types of procedures. Emphasis is then placed on the large choice of sorbents for trapping analytes over a wide range of polarities, such as highly cross-linked copolymers, functionalized copolymers, graphitized carbons or some specific n-alkylsilicas. The method development is given which is based on prediction from liquid chromatographic retention data or solvation parameters in order to determine the main parameters of any sequence (type and amount of sorbent, sample volume which can be applied without loss of recovery, composition and volume of the clean-up solution, composition and volume of the desorption solution). Obtaining extracts free from matrix interferences in a few steps--one step when possible--is now included in the development of SPE procedure. New selective phases such as mixed-mode and restricted access matrix sorbents or emerging phases such as immunosorbents or molecularly imprinted polymers are reviewed. Selectivity obtained by combining two sorbents is described with the use of ion-exchange or ion-pair sorbents. Special attention is given to complete automation of the SPE sequence with its on-line coupling with liquid chromatography followed by various detection modes. This represents a fast, modern and reliable approach to trace analysis. Many examples illustrate the various features of modern SPE which are discussed in this review. They have been selected in both biological and environmental areas.

Photodegradation and stability of chlorothalonil in water studied by solid-phase disk extraction, followed by gas chromatographic techniques

Photodegradation of chlorothalonil was studied in deionized and ground water with sunlight and Suntest apparatus, with and without FeCl3/H2O2 and TiO2/H2O2. After irradiation of the water samples spiked at 28-100 micrograms/l of chlorothalonil, the water solutions were preconcentrated using solid-phase disk extraction with C18 and analyzed by gas chromatography-electron capture and gas chromatography-mass spectrometric detection. The degradation products identified by GC-MS were: trichloro-1,3-dicyanobenzene, dichloro-1,3-dicyanobenzene and chloro-1,3-dicyanobenzene. The degradation kinetics followed a first order reaction and the R.S.D. of rate constants, for n = 3, varied from 2 to 14%. Halflives varied between 0.7 and 101 h. The stability of chlorothalonil on C18 Empore disks was also investigated at 20 degrees C, 4 degrees C and -20 degrees C for periods of up to 3 months. Chlorothalonil was not degraded on C18 Empore disks.

Application of C18 disks followed by gas chromatography techniques to degradation kinetics, stability and monitoring of endosulfan in water

A comparative degradation study of endosulfan spiked at 35 micrograms/l in water using photocatalysis with (FeCl3/H2O2)/(TiO2/H2O2) and photolysis using either a xenon arc lamp and/or sunlight was performed. After irradiation the water samples were preconcentrated using C18 solid-phase disk extraction and analysis by gas chromatography-electron capture and mass spectrometric detection. Endosulfan sulphate was found in the photodegradation studies. Endosulfan showed high stability in water when it was exposed to sunlight and xenon are lamp, but by means of photocatalysis with FeCl3/H2O2, TiO2/H2O2, the degradation was very fast with half lives varying from 59-98 min. The degradation kinetics followed a first order reaction and the R.S.D. of rate constants, for n = 3, varied from 4-17%. The stability of endosulfan on C18 Empore disks has been determined at 20 degrees C, 4 degrees C and -20 degrees C for periods up to 3 months. Endosulfan was not degraded on C18 Empore disks. Ground water samples from south of Spain (Almeria) were monitored during 1 year. The compounds alpha-, beta- and endosulfan sulphate were detected at concentration values varying from 0.5-540 ng/l.

Stability of pesticides stored on polymeric solid-phase extraction cartridges

The stability of four pesticides (desethylatrazine, fenamiphos, fenitrothion and fonofos) was examined under different storage conditions after preconcentration in disposable solid-phase extraction (SPE) cartridges containing new polymer sorbent materials (Hysphere-1, IST EnviroLut and LiChrolut). Complete recovery for all the compounds was observed in precolumns kept at -20 degrees C for 1 month when preconcentrating 26 ml of ground water sample spiked at 10 micrograms/l. Degradation of fenamiphos and fenitrothion occurred in precolumns stored at 4 degrees C and at room temperature after 1 month. Fonofos was stable when compared to their storage in C18 precolumns. Problems in the quantification of the analytes after storage at 4 degrees C and at room temperature were encountered due to the presence of many interfering peaks in the chromatograms. Analysis of blanks with C18 precolumns was carried out, to determine the interferences. The stability of the pesticides was also examined in acidifed and non-acidified ground water in order to compare it to the stability of pesticides stored on SPE cartridges. Significant losses of fenamiphos and fenitrothion were achieved and were related to the pH of the water sample and their chemical structure. Finally, the new polymeric sorbent Hysphere-I was evaluated in terms of breakthroughs and compared with those of C18, obtaining higher recoveries for desethylatrazine.