Rapid analysis of organic microcontaminants in environmental water samples by trace enrichment and liquid chromatography on a single short column

Comparison of Multiwalled Carbon Nanotubes and a Conventional Absorbent on the Enrichment of Sulfonylurea Herbicides in Water Samples

Recently, multiwalled carbon nanotubes (MWCNTs) have been at the center of attention because of their applications in many fields. Efforts to investigate the possibility of MWCNTs as SPE absorbents for the enrichment of environmental pollutants yielded positive results. The goal of the present work was to compare the enrichment power of MWCNTs with that of regular adsorbents, such as C18 silica for SPE of five sulfonylurea herbicides. The results indicated that multiwalled carbon nanotubes were very suitable for the preconcentration of sulfonylurea herbicides in complex water samples, yielding better recoveries. C18 gave a lightly lower enrichment performance, and could not enrich nicosulfuron in complex samples. All of these experimental results indicated that multiwalled carbon nanotubes could be used as a valuable alternative adsorbent for the SPE of sulfonylurea herbicides in many real water samples.

Analysis of herbicides in water using temperature-responsive chromatography and an aqueous mobile phase

A simple and rapid method has been developed for herbicides in water using temperature-responsive liquid chromatography (LC) and a column packed with poly(N-isopropylacrylamide) (PNIPAAm), a polymer anchored on the stationary-phase surface of modified silica. PNIPAAm reversibly changes its hydrophilic/hydrophobic properties in water in response to temperature. The method was used to determine five sulfonylurea and three urea herbicides. Separation was achieved with a 10 mM ammonium acetate (pH 3.0) isocratic aqueous mobile phase, and by changing the column temperature. The analytes were extracted from water by off-line solid-phase extraction (SPE) with an N-vinyl-pyrrolidone polymer cartridge. The average recoveries of the eight herbicides from spiked pure water, tap water and river water were 70-130% with relative standard deviations (RSDs) of <10%. The limits of quantitation (LOQ) of the eight herbicides were between 1 and 4 microg l(-1).

Fast liquid chromatography-electrochemistry-mass spectrometry of ferrocenecarboxylic acid esters

Rapid liquid chromatographic separations of ferrocenecarboxylic esters of various alcohols and phenols have been achieved on reversed-phase columns of 20 mm length. After separation, the ferrocene derivatives are oxidized electrochemically under formation of the charged ferrocinium species, which are easily detected by mass spectrometry using an atmospheric pressure chemical ionization source operated in the heated nebulizer mode. While a series of nine phenol derivatives was separated within less than 1.5 min, six alcohol derivatives eluted within 1 min. Limits of detection using a single quadrupole mass analyzer ranged from 60 to 190 nmol/l. Additional work was directed on the use of a graphite in-line filter instead of a silica-based reversed-phase column to achieve the separation.

Trace-level determination of pesticides in water by means of liquid and gas chromatography

The trace-level determination of pesticides and their transformation products (TPs) in water by means of liquid and gas chromatography (LC and GC) is reviewed. Special attention is given to the use of (tandem) mass spectrometry for identification and confirmation purposes. The complementarity of LC- and GC-based techniques and the potential of comprehensive GCXGC are discussed, and also the impressive performance of time-of-flight mass spectrometry. It is also indicated that, in the near future, the TPs rather than the parent compounds should receive most attention--with a better understanding of matrix effects and eluent composition on the ionization efficiency of analytes being urgently required. Finally, the merits of using much shorter LC columns, or even no column at all (flow-injection analysis) in target analysis are shown, and a more cost-efficient and sophisticated strategy for monitoring programmes is briefly introduced.

Analysis of ethoxylated nonionic surfactants and their metabolites by liquid chromatography/atmospheric pressure ionization mass spectrometry

The widespread use and questionable environmental acceptability of nonionic surfactants make the alkylphenol ethoxylates (APEOs) and their neutral and acidic degradation products a focus of interest in environmental analytical chemistry. The characterization and especially quantification of polyethoxylate mixtures in environmental matrices is a challenge, because of the complexity of the mixtures. A review on trace analysis of APEOs using atmospheric pressure ionization mass spectrometry, including sample preparation and liquid chromatographic separation, is presented. In this Special Feature, the performances of two ionization methods, atmospheric pressure chemical ionization and electrospray ionization, is discussed in terms of selectivity and sensitivity toward oligomeric mixtures of APEOs. Capabilities and limitations associated with the liquid chromatographic/mass spectrometric detection of APEOs, their main degradation products and their halogenated metabolites, and also specific issues related to the sample preparation, formation of fragments, adducts and cluster ions, quantification of oligomeric mixtures and signal suppression effects in complex matrices, are discussed. Conclusions and future perspectives are outlined.

Preconcentration of contaminants in water analysis

Among the environmental areas, in this review attention will be focused on water matrices and both on organic (e.g., pesticides, herbicides, phenols, polycyclic aromatic hydrocarbons), inorganic species and anion pollutants, since these kinds of substances include a wide number of compounds with different physical and chemical properties and different effects on human health. Analytical methods for control of quality of waters are required to be highly specific and possibly highly sensitive for the determination of even low amounts of pollutants. The main problems encountered during the analysis are the separation of matrix components from the pollutants of interest and the achievement of low detection limits. Therefore an overview on different materials and techniques available for sample concentration and/or matrix removal will be provided and discussed according to the chemical characteristics of the pollutant that has to be enriched.

Solid-phase extraction for multiresidue analysis of organic contaminants in water

To overcome the limitations of the detection systems associated with gas or liquid chromatography, a sample pretreatment is required with the objective to provide a sample fraction enriched with all the target analytes and as free as possible from other matrix components. There is now no doubt that solid-phase extraction (SPE) has now become the method of choice for carrying out simultaneously the extraction and concentration of many compounds in aqueous samples. Many recent applications of SPE to multiresidue analysis are reviewed with an emphasis on the importance of the choice of the sorbent and of the sample volume. SPE is particularly well adapted to multiresidue analysis including compounds from a wide range of polarity or characterized by various physico-chemical properties. However, SPE is not completely free from practical problems inherent to the nature of the compounds or to the coupling to the chromatographic systems. Many examples are reported to illustrate these problems which can in most cases be circumvented. New developments in SPE are also reviewed.

Comparison of various liquid chromatographic methods involving UV and atmospheric pressure chemical ionization mass spectrometric detection for the efficient trace analysis of phenylurea herbicides in various types of water samples

The performance of mass spectrometric (MS) detection and UV detection in combination with reversed-phase liquid chromatography without and with the use of coupled column RPLC (LC-LC) has been compared for the trace analysis of phenylurea herbicides in environmental waters. The selected samples of this comparative study originated from an inter-laboratory study. For both detection modes, a 50 mm x 4.6 mm I.D. column and a 100 mm x 4.6 mm I.D. column packed with 3 microm C18 were used as the first (C-1) and second (C-2) column, respectively. Atmospheric pressure chemical ionization mass spectrometry was performed on a magnetic sector instrument. The LC-LC-MS analysis was carried out on-line by means of direct large volume (11.7 ml) injection (LVI). The performance of both on-line (LVI, 4 ml of sample) and off-line LC-LC-UV (244 nm) analysis was investigated. The latter procedure consisted of a solid-phase extraction (SPE) of 250 ml of water sample on a 500 mg C18 cartridge. The comparative study showed that LC-LC-MS is more selective then LC-LC-UV and, in most cases, more sensitive. The LVI-LC-LC-MS approach combines direct quantification and confirmation of most of the analytes down to a level of 0.01 microg/l in water samples in less then 30 min. As regards LC-LC-UV, the off-line method appeared to be a more viable approach in comparison with the on-line procedure. This method allows the screening of phenylurea's in various types of water samples down to a level of at least 0.05 microg/l. On-line analysis with LVI provided marginal sensitivity (limits of detection of about 0.1 microg/l) and selectivity was sometimes less in case of surface water samples. Both the on-line LVI-LC-LC-MS method and the LC-LC-UV method using off-line SPE were validated by analysing a series of real-life reference samples. These samples were part of an inter-laboratory test and contained residues of herbicides ranging from 0.02 to 0.8 microg/l. Beside good correlation between the methods the data agreed very well with the true values of the samples.

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.

On-line solid-phase extraction-short-column liquid chromatography combined with various tandem mass spectrometric scanning strategies for the rapid study of transformation of pesticides in surface water

The applicability of solid-phase extraction-short-column liquid chromatography using two short columns (i.e., 10 and 20 mm long) coupled on-line with tandem mass spectrometric detection is demonstrated for the rapid degradation study of pesticides and their transformation products in water at the low-microgram/l level. Photolysis was used as a means to transform the parent compounds into their degradation products and the experiments were carried out at environmentally relevant concentrations. The use of on-line sample enrichment/separation in photodegradation studies allows the rapid analysis of aqueous samples directly after irradiation without further transformation of the compounds of interest. The versatility of MS allows various selective screening strategies to be employed, i.e., full-scan mode, neutral loss, precursor-ion and product-ion scan modes. This allows the identification of possible degradation products and the calculation of the rates of disappearance of the parent compound and appearance of transformation products.

Rapid target analysis of microcontaminants in water by on-line single-short-column liquid chromatography combined with atmospheric pressure chemical ionization ion-trap mass spectrometry

The applicability of trace enrichment and separation of microcontaminants on a single 10 x 2 mm I.D. high-pressure-packed liquid chromatography (LC) column, combined on-line with an atmospheric pressure chemical ionization (APCI)-ion-trap tandem mass spectrometry (MS-MS) instrument was studied for the target analysis of herbicides in river water. The total analysis time was 15-20 min. With the on-line short-column LC-MS-MS method, detection limits of 0.1-1 microgram/l can be achieved using only 4 ml of river water. However, the results obtained for a mixture of six triazines were considerably better than those for a mixture of eight phenylureas. An attempt is made to explain this difference on the basis of various processes that occur within the ion trap and the measurement procedure itself.

Rapid target analysis of microcontaminants in water by on-line single-short-column liquid chromatography combined with atmospheric pressure chemical ionization tandem mass spectrometry

The applicability of trace enrichment and separation of microcontaminants on a 10 mm x 2 mm I.D. high-pressure packed (8 microns C18 bonded silica or 10-15 microns PLRP-S) column combined on-line with an atmospheric pressure chemical ionization MS-MS system is demonstrated for the target analysis of herbicides in river water. Tailor-made procedures are obtained for a limited number of analytes by tuning the chromatographic efficiency of the short LC column and the specificity of tandem MS, in order to minimize the analysis time. With the on-line short-column LC-MS-MS method, good linearity is obtained for the herbicides in the range of 0.1-10 micrograms/l. The relative standard deviations of peak areas are less than 5% and, with only 4-ml samples, detection limits of 0.01-0.1 microgram/l can be achieved. The total analysis time is 10-15 min. The 10 mm x 2 mm I.D. LC columns packed with 8 microns particles show good stability and can be used for at least 40 analyses. Target compound analyses of river water allowed the confirmation of the presence of herbicides such as diuron, simazine, atrazine and terbutylazine at sub-microgram/l levels.