Simultaneous determination of fluorophores with overlapped spectra by sequential injection analysis coupled to variable angle scanning fluorescence spectrometry and multivariate linear regression algorithms

An automated and versatile sequential injection spectrofluorimetric procedure for the simultaneous determination of multicomponent mixtures in micellar medium without prior separation processes is reported. The methodology is based upon the segmentation of a sample slug between two different buffer zones in order to attain both an improvement of sensitivity and residual minimization for the whole species. Resolution of overlapping fluorescence profiles is achieved using a variable angle scanning technique coupled to multivariate least-squares regression (MLR) algorithms at both sample edges.The potentialities of the described methodology are illustrated with the spectrofluorimetric determination of four widespread pesticides with different acid-base properties; viz. carbaryl (CBL) (1-naphthyl-N-methylcarbamate), fuberidazole (FBZ) (2-(2′-furyl)benzimidazole), thiabendazole (TBZ) (2-(4′-thiazolyl)benzimidazole) and warfarin (W) (3-α-acetonylbenzyl)-4-hydroxycoumarin). Detection limits at the 3σ level were 3.9, 0.02, 0.03 and 10 μg l⁻¹ for CBL, FBZ, TBZ and W, respectively at the maximum sensitivity pH. Dynamic ranges of 13-720 μg l⁻¹ CBL, 0.10-14 μg l⁻¹ FBZ, 0.19-60 μg l⁻¹ TBZ and 0.05-5 mg l⁻¹ W were achieved. Relative standard deviations (n=10) were 0.2% for 100 μg l⁻¹ CBL and 2.4 μg l⁻¹ FBZ, 0.7% for 8 μg l⁻¹ TBZ and 1.0% for 1 mg l⁻¹ W. The proposed automated methodology, which handles 17 samples/h, was validated and applied to spiked real water samples with very satisfactory results.     

Preconcentration and speciation of chromium in drinking water samples by coupling of on-line sorption on activated carbon to ETAAS determination

An on-line flow injection (FI) preconcentration-electrothermal atomic absorption spectrometry (ETAAS) method is developed for trace determination of chromium in drinking water samples by sorption on a conical minicolumn packed with activated carbon (AC) at pH 5.0. The chromium was removed from the minicolumn with 1.0% (v/v) nitric acid. An enrichment factor (EF) of 35-fold for a sample volume of 10 ml was obtained. The detection limit (DL) value for the preconcentration method proposed was 3.0 ng l⁻¹. The precision for 10 replicate determinations at the 0.5 μg l⁻¹ Cr level was 4.0% relative standard deviation (R.S.D.), calculate with the peak heights obtained. The calibration graph using the preconcentration system for chromium was linear with a correlation coefficient of 0.9992 at levels near the detection limits up to at least 50 μg l⁻¹. The method was successfully applied to the determination of Cr(III) and Cr(VI) in drinking water samples.     

Electrochemical studies and square wave stripping voltammetry of five common pesticides on poly 3,4-ethylenedioxythiophene modified wall-jet electrode

The cyclic voltammetric behavior of five common pesticides such as dicofol (DCF), cypermethrin (CYP), monocrotophos (MCP), chlorpyrifos (CPF) and phosalone (PAS) was investigated at a poly 3,4-ethylenedioxythiophene modified glassy carbon electrode (PEDOT/GCE). A method was developed for the detection and determination of these pesticides in trace level flowing stream, based on their redox behavior. The square wave stripping voltammetric principle was used to analyze the selected pesticides on PEDOT/GCE. Varying the accumulation potential and accumulation time, the best accumulation conditions were found out. Effects of initial scan potential, square wave pulse amplitude, step potential and frequency were examined for the optimization of stripping conditions. The peak current responses of analyte under optimum conditions were correlated over flow rate by using wall-jet PEDOT/GCE assembly. The calibration plots were linear over the pesticide's concentration range 0.10-72.60 μg l⁻¹ for DCF, 0.41-198.24 μg l⁻¹ for CYP, 0.22-220.95 μg l⁻¹ for MCP, 0.35-259.69 μg l⁻¹ for CPF and 1.07-141.46 μg l⁻¹ for PAS. The limit of detection was obtained between <0.09 and <1.0 μg l⁻¹ for five pesticides. It is low enough for trace pesticide determination in real samples. This method is applied for the determination of the five pesticides in soil samples. The recovery values obtained in spiked soil samples are 95.4 ± 5.4% for DCF, 93.7 ± 4.2% for CYP, 85.3 ± 8.4% for MCP, 94.6 ± 6.6% for CPF and 93.5 ± 4.9% for PAS.     

Synthesis and application of a functionalized resin for flow injection/F AAS copper determination in waters

This paper reports the development of a new strategy for low-level determination of copper in water samples by using a flow-injection system coupled to solid-phase extraction (SPE) using flame atomic absorption spectrometry (F AAS) as detector. In order to preconcentrate copper from samples, a minicolumn packed with a styrene-divinylbenzene resin functionalized with (S)-2-[hydroxy-bis-(4-vinyl-phenyl)-methyl]-pyrrolidine-1-carboxylic acid ethyl ester was used and the synthesis procedure is described. System operation is based on the on-line retention of Cu(II) ions at pH 9.0 ± 0.2 in a such minicolumn with posterior analyte elution with 2 mol l⁻¹ HCl directly to the F AAS nebulizer. The influence of several chemical (sample pH, buffer concentration, HCl eluent concentration and effect of the ionic strength) and flow (sample and eluent flow rates and preconcentration time) variables that could affect the performance of this system were investigated as well as the possible interferents. At optimized conditions, for 2 min of preconcentration time (13.2 ml of sample volume), the system achieved a detection limit of 1.1 μg l⁻¹, a R.S.D. 1% at 20 μg g l⁻¹ and an analytical throughput of 25 h⁻¹, whereas for 4 min of preconcentration time (26.4 ml of sample volume), a detection limit of 0.93 μg l⁻¹, a R.S.D. 5.3% at 5 μg l⁻¹ and a sampling frequency of 13 h⁻¹ were reported.     

A new functionalized resin and its application in preconcentration system with multivariate optimization for nickel determination in food samples

In this work, Amberlite XAD-2 resin functionalized with 4,5-dihydroxy-1,3-benzenedisulfonic acid was synthesized, characterized and applied as a new packing material for an on-line system to nickel preconcentration. The method is based on the sorption of Ni(II) ions in a minicolumn containing the synthesized resin, posterior desorption using an acid solution and measurement of the nickel by spectrophotometry (PAR method). The optimization of the system was performed using factorial design and Doehlert matrix considering five variables: eluent concentration, PAR solution pH, sample flow rate, PAR solution concentration and sample pH. Signals were measured as peak height by using an instrument software. Using the experimental conditions defined in the optimization, the method allowed nickel determination with achieved sampling rate of 25 samples per hour, detection limit (3 s) of 2 μg l⁻¹ and precision (assessed as the relative standard deviation) of 8.2-2.6%, for nickel solutions of 10.0-200.0 μg l⁻¹ concentration, respectively. The experimental enrichment factor of the proposed system was 46, for 120 s preconcentration time. The proposed procedure was applied for nickel determination in food samples. Recoveries of spike additions (5 or 10 μg g⁻¹) to food samples were quantitative (94-110%).     

Use of Nb(2)O(5)-SiO(2) in an automated on-line preconcentration system for determination of copper and cadmium by FAAS

A procedure for the determination of trace level of copper(II) and cadmium(II) by FAAS using an on-line preconcentration system has been proposed. In this system, copper and cadmium ions were adsorbed onto a minicolumn packed with silica gel modified with niobium(V) oxide (Nb₂O₅-SiO₂), followed by nitric acid elution in reverse mode and determination on-line by flame atomic absorption spectrometry (AAS) without interference of the matrix. Chemical and flow variables as well as concomitant ions were studied in the developed procedure. The enrichment factor for copper(II) and cadmium(II) was 34.2 and 33.0, respectively, using a preconcentration time of 2 min. The limit of detection for copper(II) and cadmium(II) was 0.4, and 0.1 μg l⁻¹, respectively. The precision of the method, evaluated as the relative standard deviation in solutions containing 15 μg l⁻¹ of copper and 10 μg l⁻¹ of cadmium, by analyzing a series of seven replicates, was 1.8 and 1.6%, respectively. The accuracy was assessed through recovery experiments of certified material and water samples.     

An automated system for liquid-liquid extraction based on a new micro-batch extraction chamber with on-line detection: Preconcentration and determination of copper(II)

An automated system to perform liquid-liquid extraction is proposed, in which the effective mixture (the intimate contact) between the aqueous phase and the organic phase, as well as the separation of the phases, are carried out in a micro-batch glass extraction chamber. Sample, reagents and organic solvent are introduced into the glass extraction chamber by a peristaltic pump using air as carrier. The detection of the extracted species from the aqueous phase is made in a small volume (120-150 μl) of isobutyl methyl ketone (MIBK). The system allows enrichment factors of 2-10-fold. The proposed automatic system was evaluated for Cu(II) extraction based on complex formation between copper(II) and 1-(2′-pyridylazo)naphthol (PAN) in MIBK. When a volumetric ration of 2:1 (aqueous:organic) was implemented, copper was detected in the concentration range of 100-1600 μg l⁻¹ (r = 0.9995) with a relative standard deviation of 2% (200 μg l⁻¹, n = 5) and a detection limit of 20 μg l⁻¹. The analytical curve was linear over the concentration range 25-500 μg l⁻¹ (r = 0.9994) when a volumetric ratio of 10:1 was employed. With this ratio, the detection limit was 5.0 μg l⁻¹ and the relative standard deviation was 6% (50 μg l⁻¹, n = 5).     

On-line preconcentration system using a minicolumn of polyurethane foam loaded with Me-BTABr for zinc determination by Flame Atomic Absorption Spectrometry

In the present paper, an on-line system for preconcentration and determination of zinc by Flame Atomic Absorption Spectrometry (FAAS) is proposed. It is based in the sorption of zinc(II) ions on a minicolumn packed with polyurethane foam loaded with 2-[2′-(6-methyl-benzothiazolylazo)]-4-bromophenol (Me-BTABr) reagent. Chemical and flow variables as pH effect, sample flow rate and eluent concentration were optimized using univariate methodology. The results demonstrated that zinc can determinate using the sample pH in the range of 6.5-9.2, sample flow rate of 6.0 ml min⁻¹, and the elution step using 0.10 mol l⁻¹ hydrochloric acid solution at flow rate of 5.5 ml min⁻¹. In these conditions, an enrichment factor of 23 and a sampling rate of 48 samples per hour were achieved. The detection limit (DL, 3σ) as IUPAC recommendation was 0.37 μg l⁻¹ and the precision (assessed as the relative standard deviation, R.S.D.) reached values of 5.9-1.8% in zinc solutions of 1.0-10.0 μg l⁻¹ concentration, respectively. The method was successfully applied to the determination of trace amounts of zinc in natural water samples from Salvador (Brazil).     

Flow system with in-line separation/preconcentration coupled to graphite furnace atomic absorption spectrometry with W-Rh permanent modifier for copper determination in seawater

A flow system was coupled to a graphite furnace with a platform coated with tungsten-rhodium permanent chemical modifier for in-line separation and preconcentration of copper by employing a minicolumn loaded with 1-(2-tiazolylazo)-2-naphthol (TAN) immobilized on C₁₈-bonded silica fixed in the tip of the autosampler arm. Elution was made by sampling 35 μl of 0.50 mol l⁻¹ HCl with further delivering into a coated platform. Remarkable improvements in both selectivity and sensitivity were observed. Copper(II) was effectively separated from solutions containing up to 20 g l⁻¹ Na⁺; 10 g l⁻¹ K⁺, Ca²⁺ and Mg²⁺; 1.0 g l⁻¹ Fe³⁺ and Zn²⁺. For a sample flowing at 3.0 ml min⁻¹ and a loading of 60 s, the detection limit was estimated as 5 ng l⁻¹ Cu(II) at the 99.7% confidence level, and an enrichment factor of 33 was calculated. Coefficient of variation was estimated as 4% for a 0.30 μg l⁻¹ copper solution (n=20). The W-Rh permanent chemical modifier was used to improve system stability, analytical performance and atomizer lifetime. More than 1500 firings were carried out with the same atomizer without significant variations in sensitivity and precision. On account of the reagent immobilization, its consumption was lower than 0.2 μg per determination. In addition, TAN purification was unnecessary.     

Chelating resin from functionalization of chitosan with complexing agent 8-hydroxyquinoline: application for metal ions on line preconcentration system

This study describes the functionalization of biopolymer chitosan, using the complexing agent 8-hydroxyquinoline (oxine) by reaction of diazotization. The chelating resin was characterized by degree of deacetylation, infrared, Raman spectroscopy. The efficiency of the chelating resin and accuracy of the proposed method was evaluated by the metal ion recovery technique in the analysis of potable water, lake water, seawater and a certified sample of oyster tissue. The metal ions Cd(II) and Cu(II) in the samples were previously enriched in a minicolumn and flow injection flame atomic absorption spectrometry (FI-FAAS) determined the concentrations of the analytes. The chelating resin exhibited high selectivity for Cd(II) at pH 7 and for Cu(II) at pH 10. The eluent concentration was tested by the use of HNO₃ in concentrations of 0.1-3 mol l⁻¹ maximum response was obtained at 0.5 mol l⁻¹ for Cd(II) and Cu(II), with R.S.D. values of 0.4%. The analytes gave relative standard deviations (R.S.D.) of 1.5 and 0.7% for solutions of Cd(II) and Cu(II), respectively (n = 7) containing 20 μg l⁻¹ of the metal ions, defining a high reproducibility. The limits of detection (LOD) were 0.1 μg l⁻¹ for Cd(II) and 0.4 μg l⁻¹ for Cu(II). The analytical properties of merit were obtained using the parameters previously optimized with preconcentration time of 90 s. The chelating resin showed chemical stability within a wide range of pH and the efficiency was not altered for the preconcentration of the metal ions during all the experiments.     

Determination of atrazine using square wave voltammetry with the Hanging Mercury Drop Electrode (HMDE)

This paper presents the optimization of instrumental and solution parameters for determination of atrazine in river waters and formulation by square wave voltammetry (SWV) using a hanging mercury drop electrode. The best sensitivity (35.2±0.4 μA ml μg⁻¹) was achieved using a frequency of 400 Hz and a medium composed of 40 mmol l⁻¹ Britton-Robinson (BR) buffer at pH 1.9. The detection limit was 2 μg l⁻¹ with a linear dynamic range between 10 and 250 μg l⁻¹. Application of the method to real samples of river waters fortified with 10 μg l⁻¹ of atrazine resulted recoveries between 92 and 116%. Additionally, good agreement was observed between results obtained by the proposed method and by HPLC for river water samples spiked with 25 μg l⁻¹ of atrazine. The determination was not affected by the presence of humic acid at concentration of 5 mg l⁻¹, indicating that interactions of the herbicide with this class of compounds are fully labile. The stability of the voltammetric signal for samples spiked with 250 μg l⁻¹ atrazine was evaluated over a period of 14 days in four samples. For two samples, no systematic variation was observed, while for the other two, a decrease of peak current between 3 and 15% occurred, suggesting that the stability is dependent on the sample nature. HPLC analyses suggest formation of deethylatrazine during the second week of storage in the samples for which the SWV peak current had the more intense decrease.     

Part-per-trillion determination of chlorobenzenes in water using dispersive liquid-liquid microextraction combined gas chromatography-electron capture detection

In this study, a simple, rapid and efficient method, dispersive liquid-liquid microextraction (DLLME) combined gas chromatography-electron capture detection (GC-ECD), for the determination of chlorobenzenes (CBs) in water samples, has been described. This method involves the use of an appropriate mixture of extraction solvent (9.5 μl chlorobenzene) and disperser solvent (0.50 ml acetone) for the formation of cloudy solution in 5.00 ml aqueous sample containing analytes. After extraction, phase separation was performed by centrifugation and the enriched analytes in sedimented phase were determined by gas chromatography-electron capture detection (GC-ECD). Our simple conditions were conducted at room temperature with no stiring and no salt addition in order to minimize sample preparation steps. Parameters such as the kind and volume of extraction solvent, the kind and volume of disperser solvent, extraction time and salt effect, were studied and optimized. The method exhibited enrichment factors and recoveries ranging from 711 to 813 and 71.1 to 81.3%, respectively, within very short extraction time. The linearity of the method ranged from 0.05 to 100 μg l⁻¹ for dichlorobenzene isomers (DCB), 0.002-20 μg l⁻¹ for trichlorobenzene (TCB) and tetrachlorobenzene (TeCB) isomers and from 0.001 to 4 μg l⁻¹ for pentachlorobenzene (PeCB) and hexachlorobenzene (HCB). The limit of detection was in the low μg l⁻¹ level, ranging between 0.0005 and 0.05 μg l⁻¹. The relative standard deviations (R.S.D.s) for the concentration of DCB isomers, 5.00 μg l⁻¹, TCB and TeCB isomers, 0.500 μg l⁻¹, PeCB and HCB 0.100 μg l⁻¹ in water by using the internal standard were in the range of 0.52-2.8% (n = 5) and without the internal standard were in the range of 4.6-6.0% (n = 5). The relative recoveries of spiked CBs at different levels of chlorobenzene isomers in tap, well and river water samples were 109-121%, 105-113% and 87-120%, respectively. It is concluded that this method can be successfully applied for the determination of CBs in tap, river and well water samples.     

Analysis of phenylurea and propanil herbicides by solid-phase microextraction and liquid chromatography combined with post-column photochemically induced fluorimetry derivatization and fluorescence detection

This study examines the application of solid-phase microextraction coupled with high performance liquid chromatography combined with post-column photochemically induced fluorimetry derivatization and fluorescence detection (SPME-HPLC-PIF-FD) for the determination of four phenylurea herbicides (monolinuron, diuron, linuron and neburon) and propanil in groundwater. Direct immersion (DI) SPME was applied using a 60 μm polydimethylsiloxane/divinylbenzene (PDMS/DVB) fiber for the extraction of the pesticides from groundwater samples. An AQUASIL C₁₈ column (150 mm × 4.6 mm i.d., 5 μm) was used for separation and determination in HPLC. The method was evaluated with respect to the limits of detection (LODs) and the limits of quantification (LOQs) according to IUPAC. The limits of detection varied between 0.019 μg L⁻¹ and 0.034 μg L⁻¹. Limits of quantification ranged between 0.051 μg L⁻¹ and 0.088 μg L⁻¹. These values meet the recommended limits for individual pesticides in groundwater (0.1 μg L⁻¹) established by the EU. Recoveries ranged between 86% and 105% and relative standard deviation values between 2% and 8%.     

Determination of ethylphenol compounds in wine by headspace solid-phase microextraction in conjunction with gas chromatography and flame ionization detection

Headspace solid phase microextraction (HS-SPME) was investigated as a solvent-free alternative method for the extraction and determination of 4-ethylphenol (EP) and 4-ethylguaiacol (EG) in red wine by capillary gas chromatography with flame ionization detection (FID) and compared to liquid-liquid extraction.For HS-SPME, better results were obtained with saturated sodium chloride samples, at 55 °C, using a 85 μm polyacrylate fiber. An absorption time of 40 min was needed to reach the absorption equilibrium for EG. This 40-min duration corresponds to the beginning of EP equilibrium and was selected for the experiments. In these conditions, the calibration graphs were linear in the range 5-5000 μg l⁻¹ and the sensitivity was nearly the same for the two compounds. The detection limits were in the low μg l⁻¹ range. In model wine solutions, result obtained with the liquid-liquid extraction method exhibit a linear calibration between 25 and 10,000 μg l⁻¹ with a detection limit of 1 μg l⁻¹, but, the relative standard deviations of the EP and EG result in the low concentration range (<50 μg l⁻¹) are higher than those obtained by HS-SPME (15% compared to 2% for EP and 12% compared to 5% for EG). Taking into account the numerous volatile compounds in wine, HS-SPME is a rapid and valid alternative technique for use in the determination of ethylphenols at trace levels.     

Detection capability of tetracyclines analysed by a fluorescence technique: comparison between bilinear and trilinear partial least squares models

According to the committee decision of 12 August 2002 (2002/657/EC) the capability of detection, CCβ, must be set in all analytical methods not only at concentration levels close to zero but also at the maximum permitted limit (PL). In this work we describe a methodology which evaluates the capability of detection of a fluorescence technique with soft calibration models (bilinear and trilinear PLS) to determine tetracyclines (group B1 substances from annex 1 of Directive 96/23/EC). Its estimation is based on the generalisation of the procedure described in International Union of Pure and Applied Chemistry and in the ISO standard 11843 for univariate signals which evaluates the probabilities of false positive (α) and false negative (β). The capability of detection, CCβ, estimated from the second-order signal and the trilinear PLS model is 9.93 μg l⁻¹ of tetracycline, 17.75 μg l⁻¹ of oxytetracycline and 26.31 μg l⁻¹ of chlortetracycline, setting α and β at 0.05. The capability of detection, CCβ, determined around the PL (100 μg kg⁻¹ in milk and muscle) with the second-order signal is 109.4 μg l⁻¹ of tetracycline, 117.0 μg l⁻¹ of oxytetracycline and 124.9 μg l⁻¹ of chlortetracycline, setting α and β at 0.05. The results were compared with those obtained with zero and first-order signals. The effect of the interferences on the capability of detection was also analysed as well as the number of standards used to build the models and their calibration range.When a tetracycline is quantified in presence of uncalibrated ones by means of the trilinear PLS model the errors oscillate between 14.70% for TC and 9.57% for OTC.     

Spectrophotometric catalytic determination of Fe(III) in estuarine waters using a flow-batch system

A flow-batch system was developed for the determination of Fe(III) in estuarine waters with high variability in salinity. The method is based on the catalytic effect of iron(III) on the oxidation rate of N,N-dimethyl-p-phenylenediammonium dichloride (DmPD) by hydrogen peroxide and the formed product is spectrophotometrically monitored at 554 nm. A controlled addition of sodium chloride to every assayed sample is accomplished for in-line individual salinity matching.The proposed system processes about 30 samples h⁻¹ and yields reproducible results. Relative standard deviations were estimated as <1.5% after 10 injections of typical samples (10.0-50.0 μg l⁻¹ Fe; ca. 0.5 mol l⁻¹ Cl). Synthetic samples (15.0 μg l⁻¹ Fe; 0.25-1.0 mol l⁻¹ NaCl) were efficiently processed, and no significant differences in results were found at a probability level of 99.7%. The method works for the full range of salinities. Only 120 μg DmPD are consumed per determination. The analytical curve is linear up to about 60 μg l⁻¹ Fe (r>0.999; n=5) and the detection limit is 5 μg l⁻¹ Fe. Results are in agreement with graphite furnace atomic absorption spectrometry.     

Ochratoxin A in wines-assessing global uncertainty associated with the results

Ochratoxin A (OTA) is a mycotoxin (potentially carcinogenic secondary metabolite derived from fungal contamination), produced by some Aspergillus and Penicillium strains. Although present and legislated in different food sources in the human diet, the regulation for wine intake is still under discussion. The Office International de la Vigne et du Vin (OIV) recommended maximum levels in wine of 2 μg l⁻¹. Some reports refer to OTA contamination in wines up to 15 μg l⁻¹ and a special incidence in red wines from the southern regions of Europe and the north of Africa, but the majority of the data available are below 1 μg l⁻¹. When working at such low concentrations, the problem of the uncertainty of the results becomes decisive towards the implementation of legal limits. In order to assess the global uncertainty associated with OTA determination in wines and widen the data set and knowledge of the situation in Portugal, 340 wines were analysed (189 Port Wine, 85 Vinho Verde and 66 wines from other regions in the country) by a high performance liquid chromatography (HPLC)-fluorescence detection (FD) method using immunoaffinity columns for clean up. OTA was detected in 69 wines by the method used, but in concentrations below 0.5 μg l⁻¹, except for two which showed levels up to a maximum of 2.1 μg l⁻¹. However, the global uncertainty for OTA is close to 37% for concentrations above 0.5 μg l⁻¹, and therefore, such value can be below or exceed the OIV limit. In the vicinity of the limit of detection, 0.084 μg l⁻¹, the global uncertainty rises exponentially to a maximum of about 70%. This can be an obstacle when discussing safety intake limits. Ethanol and glucose content did not interfere in the clean up of OTA by immunoaffinity columns.     

Speciation and preconcentration of inorganic antimony in waters by Duolite GT-73 microcolumn and determination by segmented flow injection-hydride generation atomic absorption spectrometry (SFI-HGAAS)

A selective matrix removal/separation/enrichment method, utilizing a microcolumn of a chelating resin with SH functional groups (Duolite GT-73), was proposed for the determination of Sb(III) in waters by segmented flow injection-hydride generation atomic absorption spectrometry (SFI-HGAAS). The resin was selective to Sb(III) at almost all pH and acidity values employed, whereas Sb(V) was not retained at all and could be determined after a pre-reduction step with l-cysteine. Spike recoveries were tested at various concentration levels in different water types and were found to vary between 85 and 118%. Accuracy of the proposed methodology was checked by analyzing a standard reference material and a good correlation was found between the determined (13.3 ± 1.1 μg l⁻¹) and the certified value (13.79 ± 0.42 μg l⁻¹). The method was applied to several bottled drinking water samples for antimony determination with and without preconcentration and none of the samples were found to contain antimony above the permissible level (5 μg l⁻¹). The characteristic concentration (the concentration of the analyte corresponding to an absorbance of 0.0044) was 0.55 μg l⁻¹ and the 3 s limit of detection (LOD) based on five times preconcentration was 0.06 μg l⁻¹. The applicability of the microcolumn separation/preconcentration/matrix removal method for flow injection systems was also demonstrated.     

Time-based multisyringe flow injection system for the spectrofluorimetric determination of aluminium

A time-based multisyringe flow injection procedure with spectrofluorimetric detection is proposed in this paper for the determination of aluminium in drinking water. The flow methodology is based on the simultaneous or sequential injection of sample and chelating reagent (viz. 8-hydroxyquinoline-5-sulphonic acid) plugs using a multicommutation approach so that three successive injections may be performed with a sole displacement of the piston driver bar of the burette. Thus, an injection throughput as high as 154 h⁻¹ is achieved by sampling a 182 μl sample zone. In order to enhance the luminescence, the reaction is carried out in micellar medium using hexadecyltrimethylammonium chloride as surfactant. The influence of geometric and hydrodynamic variables as well as several parameters such as multicommutation timing, ligand and surfactant concentration and reagent pH was assessed.Under the selected working conditions, a linear dynamic range from 10 to 500 μg l⁻¹ Al(III), a 3σ detection limit of 0.5 μg l⁻¹ and a coefficient of variation of 0.6% at the 30 μg l⁻¹ level were obtained. The analytical features were compared with those reported in previous flow injection and sequential injection methods. The multisyringe technique was successfully applied to the determination of aluminium in drinking water at low mineralisation levels, validating the results by inductively coupled plasma atomic emission spectrometry.     

FI automatic method for the determination of copper(II) based on coproporphyrin I-Cu(II)/TCPO/H(2)O(2) chemiluminescence reaction for the screening of waters

In this paper, an automatic method for the screening of water samples containing Cu(II) was proposed, based on peryoxalate chemiluminescence reaction using coproporphyrin I as fluorophor compound to provide selectivity and a simple flow injection (FI) chemiluminescence detector (CLD). FI system conditions were chosen in order to distinguish samples over or under legislation limit established (50 μg l⁻¹) with high reliability. The detection limit found was 9 μg l⁻¹ and the linear dynamic range was 15-125 μg l⁻¹ of Cu(II). Repeatibility and reproducibility studies gave good precision and accuracy with recovery near 100%. Under these conditions, the method resulted selective and only Fe(II), Fe(III) and Pb(II) could interfere, but at a concentration level higher than their normal concentration in waters. The proposed method was found to be highly reliable for screening purposes and it was successfully applied to the screening of a variety of real water samples.