Determination of tungsten with pyrocatechol violet by first-derivative solid-phase spectrophotometry

Derivative spectrophotometry was applied to solid-phase spectrophotometry in order to enhance its sensitivity and remove the large background caused by the absorbance of the resin layer. Determination of micro-amounts of tungsten with pyrocatechol violet to form a 21 green complex in acid medium which is fixed on a dextran-type anion-exchange resin (Sephadex QAEA-25) is described as an example for the application of this technique. The absorbance of the resin packed in a 1-mm spectrophotometric cell, was measured directly. The characteristic peak amplitude of the signal at 674 nm in the first-derivative spectrum is useful for quantitative determination of tungsten (3–16 g 1^–1; RSD 5.8%) in natural and industrial water samples.     

Evaluation of Cu–Ethylenediamine Metal Ion Buffers as Calibrants for Ion‐Selective Electrode Measurement of Copper in Fresh Water Systems

An investigation was made into the accuracy of cupric ion selective electrode (ISE) measurement of Cu in solutions approximating acidic freshwaters with Cu‐ethylenediamine buffers used as the calibrants. This method overestimates the free Cu compared with calibration using Cu(NO₃)₂ standards, the standard addition method, and speciation modelling calculations. Statistical tests showed a small, but significant, difference between the intercepts of the linear Nernstian regressions of the calibration plots of Cu‐en buffer standardisation and direct calibration with Cu(NO₃)₂ standards in matrix that matches the samples. The difference in the intercepts, which corresponds with E_o values of the electrode, is not well understood, but is possibly caused by potentially interfering cations such as Fe²⁺. The results of this study showed that down to 10^?8 M Cu²⁺, where a linear Nernstian response is possible, the Cu ISE is probably better calibrated using Cu standards prepared in the same matrix as the sample solutions to avoid potential matrix effects.     

Determination of ammonium using a microplate-based fluorometric technique

The determination of ammonium (NH₄⁺) in concentrations ranging from nanomolar to micromolar in fresh and brackish waters often loaded in high suspended particulate matter and dissolved organic acids is presented. The newly described microplate-based fluorometric technique is allowing quick automated readings of different groups of samples with different background fluorescence and matrix effects. The lowest detectable concentration was estimated to 5 nM using the average detected blank ±3S.D. and the practical detection limit (LOD) determined with successive calibration curves was 50 nM with an excellent repeatability. High loading of suspended particular matter, coloured organic acids, and salinity changes were not interfering with the accurate determination of ammonium. To illustrate its robustness and efficiency, this technique has been applied to water samples taken from rivers, saltmarshes and estuaries, spanning a large range of ammonium levels and chemical properties. Measurements of ammonium on reddish turbid waters sampled in south shore of St. Lawrence Estuary showed ammonium concentrations between 0.05 ± 0.01 and 3.89 ± 0.03 μM, indicating a significant source of ammonium from terrestrial and saltmarsh ecosystems.     

Application of a novel chemometric approach to the determination of aqueous photolysis rates of organic compounds in natural waters

The utility of multivariate optimization methods in the determination of aqueous photolysis rates of organic compounds is examined in this study. A basic pursue was to designate the appropriate experimental design plan that extend the analytical utility of multivariate methods from qualitative data interpretation approaches, as applied thus far, to quantitative estimation methods. A three-level second-order central composite design with parameter concentrations (factor levels) beyond the environmental realistic concentrations was employed for that purpose enabling statistically significant effects to be determined. Method application is demonstrated in the first photodegradation study of two UV absorbing chemicals in natural waters. The results suggest that the proposed approach of enables a good approximation of the real behavior in terms of both qualitative and quantitative data interpretation with minimal loss of information.     

Polycyclic aromatic and aliphatic hydrocarbons in Mytella charruana, a bivalve mollusk from Mundaú Lagoon, Brazil

The levels of selected organic markers, such as 17 polycyclic aromatic hydrocarbons (PAHs), 16 of which are classified as priority pollutants by the US-EPA, perylene, aliphatic hydrocarbons (linear alkanes) and petroleum biomarkers (hopanes and steranes) were assessed in Mytella charruana, a common bivalve mollusk from the convergence of the Mundaú Lagoon, Maceió, Alagoas, Brazil. The organic markers were evaluated in three campaigns (Jul/2006, Oct/2007 and Feb/2008) aiming to identify pollution sources, understand their status of contamination and determine baseline data looking for future management strategies. Higher Σ16HPAs concentration was observed in organisms with 10-30 mm (80% of the total mass of organisms from Mundaú Lagoon) collected in Feb/2008, whereas in individuals with 30-40 mm, the PAH concentrations were higher during Jul/2006 and Oct/2007. The sugarcane burning in Maceió-AL occurs between October and March. The Flt/(Flt + Py) and BaA/(BaA + Chry) ratios in Feb/2008 indicated a combustion process source. The PAH concentrations in Mytella charruana are below of the limit value considered by the WHO (10 ng g⁻¹ for BaP). However, the results suggest that the sugarcane burning process lead to higher PAH concentrations in these organisms in Feb/2008. Many samples showed significant contamination by petroleum biomarkers, hopanes and steranes. Also, the aliphatic hydrocarbon chromatographic profiles were characteristic of petrogenic sources. The hydrocarbons measured in Mytella charruana from Mundaú Lagoon seems to be impacted by PAH in sugarcane burning periods. On the other hand, urban residues and fishing boats could be pointed as important petrogenic sources of aliphatic hydrocarbons in the same bivalve mollusk.     

Determination of Lead and Cadmium in Sea‐ and Freshwater by Anodic Stripping Voltammetry with a Vibrating Bismuth Electrode

A solid, bismuth (Bi), disk, electrode is used to determine lead (Pb) in natural waters including seawater. The diffusion layer thickness was lowered from 93 to 29 µm by stirring, and to 18 µm by using the vibrated version of the Bi electrode. The Bi electrode does not require removal of dissolved oxygen, which facilitates in situ detection. The electrode was tested for the determination of Pb in coastal seawater samples. The detection limit for Pb was 0.15 nM in acetate buffer and 0.5 nM in seawater using a 2 min deposition time. Cadmium can be determined together with Pb but the sensitivity is about 10×lower. The Bi electrode compares unfavourably to a mercury electrode in terms of sensitivity.     

An amperometric method for the detection of amitrole, glyphosate and its aminomethyl-phosphonic acid metabolite in environmental waters using passive samplers

The herbicides amitrole and glyphosate, and its metabolite aminomethyl-phosphonic acid (AMPA), in water samples have been directly analysed by high-performance liquid chromatography using an electrochemical (EC) detector. Limits of detection of 0.3 μg mL⁻¹ for glyphosate, 0.05 μg mL⁻¹ for AMPA and 0.03 μg mL⁻¹ for amitrole were comparable to those obtained by other authors using EC and also by liquid chromatography coupled to mass spectrometry, but the latter method requires derivatisation and pre-concentration of the sample whereas EC methods show similar sensitivity without the need of any derivatisation. The method was specifically designed to analyse extracts from passive samplers used for monitoring of polar herbicide residues in waters. To this purpose, three types of Empore^® disks were tested for their ability to adsorb and desorb these ionic, polar analytes. A procedure for their extraction from the membranes and reducing the interferences from other substances present in natural waters (i.e. humic acids) is described. The method is simple, does not require sophisticated equipment and is valid for the analysis and monitoring of herbicides residues using passive samplers.     

Determination of herbicides by solid phase extraction gas chromatography-mass spectrometry in drinking waters

A solid phase extraction (SPE) method has been optimized for the gas chromatography-mass spectrometry (GC-MS) simultaneous determination of herbicides belonging to the following different families: carbamate (molinate), atrazines (atrazine, propazine, simazine, ametryne, cyanazine, terbutylazine, deethylterbutylazine, deethylatrazine), dinitroaniline (trifluralin, pendimethalin), chloroacetamide (alachlor, metolachlor). Different solid substrates have been compared (C18, cyano, styrene-divinylbenzene, phenyl, graphitic carbon). The type of conditioning and elution solvent, its volume, and the sample flow rate have been considered as variables affecting the recovery yields of the herbicides.The optimized experimental conditions are C18 phase conditioned with 3 mL acetone, loaded with 1 L water sample at 5 mL min⁻¹, and eluted with 3 mL acetone. Good recoveries (included between 79% and 99%) and R.S.D. (included between 2% and 12%) have been obtained for all analytes, except for deethylatrazine whose recovery was 46 ± 7%. The recovery of deethylatrazine increases up to 94 ± 17% if a non-porous graphitic carbon is coupled to the C18 phase, keeping the other parameters constant as optimized. The optimized method has been successfully checked for the identification and quantitation of the selected herbicides in raw and drinking water samples, with quantitation limits as low as 0.01 μg L⁻¹, fully in agreement with the current legislation. The method is easily routinable. After development, the method is currently routinely applied for the analysis of herbicides in waters and, up today, more than one thousand samples have been analysed at the “Laboratorio della Società Metropolitana Acque di Torino” (Laboratory of the Municipal Waterworks of Turin) in charge of the control of drinking water quality in Torino.     

HPLC-UV and HPLC-MSn multiresidue determination of amidosulfuron, azimsulfuron, nicosulfuron, rimsulfuron, thifensulfuron methyl, tribenuron methyl and azoxystrobin in surface waters

The paper presents a new HPLC method, with UV and MSⁿ detection, for the determination of seven pesticides, including the sulfonylurea herbicides amidosulfuron, azimsulfuron, nicosulfuron, rimsulfuron, thifensulfuron methyl, tribenuron methyl, and the fungicide azoxystrobin characterised by a methoxyacrilate structure. The methodology consists of a preconcentration/SPE (solid phase extraction) step and HPLC-UV (240 nm detection wavelength)-MSⁿ analysis. Under the optimised conditions and after a 1000/1 preconcentration factor, the limits of detection were lower than 14.5 ng L⁻¹ for UV detection and lower than 8.1 ng L⁻¹ for MS detection. The limits of quantification were lower than 48.3 ng L⁻¹ in UV detection and than 26.9 ng L⁻¹ in MSⁿ detection. The analysis of two samples, spiked with a mixture of the pesticides at threshold level concentrations, gave more than 60% recovery.     

Detection of s-triazine pesticides in natural waters by modified large-volume direct injection HPLC

There is a need for simple and inexpensive methods to quantify potentially harmful persistent pesticides often found in our water-ways and water distribution systems. This paper presents a simple, relatively inexpensive method for the detection of a group of commonly used pesticides (atrazine, simazine and hexazinone) in natural waters using large-volume direct injection high performance liquid chromatography (HPLC) utilizing a monolithic column and a single wavelength ultraviolet-visible light (UV-vis) detector. The best results for this system were obtained with a mobile phase made up of acetonitrile and water in a 30:70 ratio, a flow rate of 2.0 mL min⁻¹, and a detector wavelength of 230 nm. Using this method, we achieved retention times of less than three minutes, and detection limits of 5.7 μg L⁻¹ for atrazine, 4.7 μg L⁻¹ for simazine and 4.0 μg L⁻¹ for hexazinone. The performance of this method was validated with an inter-laboratory trial against a National Association of Testing Authorities (NATA) accredited liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS) method commonly used in commercial laboratories.