Optimization of experimental parameters in single-drop microextraction-gas chromatography-mass spectrometry for the determination of periodate by the Malaprade reaction, and its application to ethylene glycol

The aim of present work was to optimize the experimental parameters in single drop microextraction under solution immersion (SDME) and headspace (HS-SDME) extraction modes for the determination of periodate using guaifenesine [3-(2′-methoxyphenoxy)-1,2-propane diol] and norephedrine (phenylpropanolamine) as new and alternative reagents for the Malaprade reaction. The reactions were complete within 5 min resulting in the formation of 2-(2′-methoxyphenoxy)-acetaldehyde and benzaldehyde, respectively. SDME/HS-SDME of oxidation products with 2 μl of anisole or 1 μl of toluene, respectively, has permitted the determination of periodate at μg l⁻¹ concentration levels. The results indicated that HS-SDME (range 0.01-10 mg l⁻¹, r² = 0.9990; limit of detection 1.55 μg l⁻¹) was more sensitive than SDME (range 0.05-50 mg l⁻¹, r² = 0.9984; limit of detection 3.42 μg l⁻¹), and was inexpensive, rapid and convenient. Tolerance of excess of iodate has permitted the application of this method in the determination of ethylene glycol in motor oil; the average recovery on spiked sample was 98.6% with R.S.D. of 4.2%.     

Sequential injection lab-on-valve simultaneous spectrophotometric determination of trace amounts of copper and iron

A sequential injection (SI) method in a lab-on-valve (LOV) format for simultaneous spectrophotometric determination of copper and iron has been devised. The detection chemistry is based on the complex formation of 2-(5-bromo-2-pyridylazo)-5-[N-n-propyl-N-(3-sulfopropyl)amino]aniline (5-Br-PSAA) with copper(II) and/or iron(II) at pH 4.6. Copper(II) reacts with 5-Br-PSAA to form the complex which has an absorption maximum at 580 nm but iron(III) does not react. In the presence of a reducing agent only iron(II)-5-Br-PSAA complex is formed and detected at 558 nm. Under the optimum experimental conditions, the determinable ranges are 0.1-2 mg l⁻¹ for copper and 0.1-5 mg l⁻¹ for iron, respectively, with a sampling rate of 18 h⁻¹. The limits of detection are 50 μg l⁻¹ for copper and 25 μg l⁻¹ for iron. The relative standard deviations (n = 15) are 2% for 0.5 mg l⁻¹ copper and 1.8% for 0.5 mg l⁻¹ iron when determined in standard solutions. The recoveries range between 96 and 105% when determining 0.25-2 mg l⁻¹ of copper and 0.2-5 mg l⁻¹ of iron in artificial mixtures at copper/iron ratios of 1:10 to 5:1. The proposed SI-LOV method is successfully applied to the simultaneous determination of copper and iron in multi-element standard solution and in industrial wastewater 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).     

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.     

Liquid-phase microextraction and GC for the determination of primary, secondary and tertiary aromatic amines as their iodo-derivatives

Presence of iodine in aromatic amines, introduced by their reaction with iodine, and other electron withdrawing substituents such as chlorine and nitro, has been found to afford excellent liquid-phase microextraction (LPME) in toluene and separation by gas chromatography in the determination of primary, secondary and tertiary aromatic amines. The effect is due to decreased basic nature of amines when electronegative substituents are present. Single drop microextraction (SDME) of the amines in 2 μl of toluene and injection of the whole extract into GC, or LPME into 50 μl of toluene and injection of 2 μl of extract, were used. LPME has been found more robust and to give better extraction in shorter period than SDME. In SDME-GC-FID, the average correlation coefficient was 0.9939 and average limit of detection 25 μg l⁻¹ (range 12-61 μg l⁻¹) whereas the corresponding values in LPME-GC-MS were, respectively, 0.9953 and 33 ng l⁻¹ (range 18-60 ng l⁻¹). The method has been applied to determine aromatic amines in river water, dye factory effluents and food dye stuffs. The LPME was found as robust, rugged and simple extraction method.     

Flow injection analysis of ultratrace orthophosphate in seawater with solid-phase enrichment and luminol chemiluminescence detection

Solid-phase extraction technique had been applied to extract molybdophosphoric heteropoly acid (MoP) paired with cetyltrimethylammonium bromide (CTAB) from seawater matrix using C18 sorbent. Chemiluminescence emission could be generated via MoP reaction with alkaline luminol. Based on these, a novel on-line solid-phase extraction method coupled with flow injection (FI) analysis and luminol chemiluminescence detection had been established to determine ultratrace orthophosphate in seawater. The MoP-CTAB compound could be efficiently extracted on an in-line Sep-Pak C18 cartridge, and rapidly eluted by 0.3 mol l⁻¹ sulphuric acid-ethanol solution. Then the compound was reduced by luminol to produce chemiluminescence light, which could be detected using a luminescence analyzer. Experimental parameters were optimized using a univariate experimental design. Using artificial seawater with salinity of 35 as a matrix, the standard curve with a linear range between 0.005 and 0.194 μmol l⁻¹ had been obtained, and the recovery and the detection limit of the proposed method were found to be 92.5% and 0.002 μmol l⁻¹, respectively. The relative standard deviation (R.S.D.), which was determined over eight hour, was 4.66% (n = 7) for the artificial seawater at a concentration of 0.097 μmol l⁻¹ orthophosphate. Si of 200 μmol l⁻¹ would not interfere with the detection of 0.012 μmol l⁻¹ orthophosphate compound. Three typical seawater samples were analyzed using both the proposed method and the magnesium hydroxide-induced coprecipitation (MAGIC) method, and the results of the two methods showed no significant difference using the t test. Compared to the MAGIC method, the proposed method was more sensitive, time saving and easy for on-line analysis.     

Development of xylitol oxidase-based flow injection analysis for monitoring of xylitol concentrations

A flow injection method for monitoring xylitol was developed using xylitol oxidase (XYO) immobilized on a VA-Epoxy Biosynth E3-support. The immobilized XYO cartridge had a good operational lifetime (up to 24 h) and storage stability (up to 1 month). The XYO-FIA system with an oxygen electrode was investigated systematically regarding the factors that can affect enzyme activity, such as pH, reaction temperature, carrier solution and sample matrix. In order to attain high activity of the immobilized XYO, potassium phosphate solution (1 M) with 0.5 g l⁻¹ Triton X-100 adjusted to pH 8.5 was used as the carrier solution. Sample matrix effects on the immobilized XYO were also investigated. High concentrations of some components (arabinose, 20 g l⁻¹; xylose, 30 g l⁻¹; NaCl, 30 g l⁻¹) in the sample had significant inhibitory effects on the response of the XYO-FIA system. The performance of the XYO-FIA system was tested by using different sample injection volumes (75-250 μl) and carrier flow rates (0.7-2.0 ml min⁻¹).     

An environmentally friendly multicommutated alternative to the reference method for anionic surfactant determination in water

It has been developed a fully mechanized procedure for the spectrophotometric determination of anionic surfactants in water expressed in terms of SDS concentration. The reference method, based on the reaction of SDS with methylene blue (MB) followed by extraction in chloroform, was mechanized in order to reduce the consumption of organic solvents. The system was based on the multicommutation approach and provided a 35 times reduction of the waste production without sacrificing the figures of merit of the method in terms of sensitivity and repeatability, for a dynamic linear range from 0.2 to 1.7 mg l⁻¹. Results obtained for washing water samples were comparable with those obtained using the reference method and no significant differences, at 95% confidence level, were observed. Other useful characteristics are a solvent consumption of 0.7 ml per determination, a sampling throughput of 40 determinations per hour, a relative standard deviation of 5.9% (n = 10) for a sample containing 2 × 10⁻⁶ mol l⁻¹ (576 μg l⁻¹) surfactant and a limit of detection of 6.1 × 10⁻⁹ mol l⁻¹ (1.7 μg l⁻¹).     

Use of 2-mercaptopyridine for the determination of alkylating agents in complex matrices: application to dimethyl sulfate

A rapid and sensitive method for the determination of alkylating agents in complex reaction mixtures was developed and characterized. Analyses are based on the alkylation of 2-mercaptopyridine by the analyte; the derivative is separated by RP-HPLC and measured by fluorescence detection. When applied to the determination of dimethyl sulfate, the method is linear over four orders of magnitude: 0.01-10 μg mL⁻¹. By using recrystallized 2-mercaptopyridine, quantitation limits of 10 ng mL⁻¹ can be achieved. Precision of the assay is 2% R.S.D. in the 1-10 μg mL⁻¹ range and about 15% R.S.D. at 10 ng mL⁻¹. Studies on the pH dependence of the derivatization reaction were key to minimizing interference from the dimethyl sulfate degradation product, monomethyl sulfate, in quenched reaction samples.     

Analysis of isoproturon at trace level by solid phase competitive fluoroimmunosensing after enrichment in a sol-gel immunosorbent

Isoproturon was extracted selectively from environmental materials (water samples) using an immunosorbent column containing anti-isoproturon antibodies encapsulated in a silica matrix by a sol-gel process. A phosphate buffered saline (PBS) conditioned immunosorbent column was used to on-line preconcentrate 5 ml well and tap water containing 0.05 μg l⁻¹ of isoproturon, which were desorbed with 75 μl of citric acid and determined with a solid phase competitive fluoroimmunoassay. The solid phase of the immunosensor, consisting of a sol-gel glass doped with anti-isoproturon monoclonal antibody, was placed on the flow-cell of the spectrofluorometer. Free isoproturon in solution competed with a fluorescent conjugated isoproturon and reduced the support bonded fluorescence in a concentration-dependent manner. The on-line method has a detection limit of 9.7 ng l⁻¹, relative standard deviation of 4 and 3% for 0.05 and 0.5 μg l⁻¹, respectively, and recoveries higher than 90% for tap and well water. For comparison the off-line extraction and clean up using a C18 cartridge is also reported.     

Determination of formaldehyde in shiitake mushroom by ionic liquid-based liquid-phase microextraction coupled with liquid chromatography

Using ionic liquid as extraction solvent and 2,4-dinitrophenylhydrazine (DNPH) as derivative agent, formaldehyde in shiitake mushroom was determined by liquid-phase microextraction coupled with high-performance liquid chromatography (HPLC). Shiitake mushroom was leached with water and filtrated, then the formaldehyde in filtrate was derivatized with DNPH and extracted simultaneously into a 10 μl drop of ionic liquid suspended on the tip of the microsyringe, and finally injected into the HPLC system for determination. The proposed procedure has a detection limit of 5 μg l⁻¹ formaldehyde in extraction solution, thus the mushroom sample filtrate could be diluted with a large ratio to eliminate the influence of sample matrix. The method has a relative standard deviation of 3.5% between days for 53.5 μg l⁻¹ formaldehyde standards. High contents of formaldehyde (119-494 μg g⁻¹ wet weight), which is harmful for human beings, were detected in shiitake mushroom. Therefore, strategies must be taken to prevent the accumulation and strictly control the content of formaldehyde in shiitake mushroom.     

Direct and simultaneous determination of arsenic, manganese, cobalt and nickel in urine with a multielement graphite furnace atomic absorption spectrometer

A simple method was developed for the direct and simultaneous determination of arsenic (As), manganese (Mn), cobalt (Co), and nickel (Ni) in urine by a multi-element graphite furnace atomic absorption spectrometer (Perkin-Elmer SIMAA 6000) equipped with the transversely heated graphite atomizer and longitudinal Zeeman-effect background correction. Pd was used as the chemical modifier along with either the internal furnace gas or a internal furnace gas containing hydrogen and a double stage pyrolysis process. A standard reference material (SRM) of Seronorm™ Trace Elements in urine was used to confirm the accuracy of the method. The optimum conditions for the analysis of urine samples are pyrolysis at 1350 °C (using 5% H₂ v/v in Ar as the inter furnace gas during the first pyrolysis stage and pure Ar during the second pyrolysis stage) and atomization at 2100 °C. The use of Ar and matrix-free standards resulted in concentrations for all the analytes within 85% (As) to 110% (Ni) of the certified values. The recovery for As was improved when mixture of 5% H₂ and 95% Ar (v/v) internal furnace gas was applied during the first step of a two-stage pyrolysis at 1350 °C, and the found values of the analytes were within 91-110% of the certified value. The recoveries for real urine samples were in the range 88-95% for these four elements. The detection limits were 0.78 μg l⁻¹ for As, 0.054 μg l⁻¹ for Mn, 0.22 μg l⁻¹ for Co, and 0.35 μg l⁻¹ for Ni. The upper limits of the linear calibration curve are 60 μg l⁻¹ (As); 12 μg l⁻¹ (Mn); 12 μg l⁻¹ (Co) and 25 μg l⁻¹ (Ni), respectively. The relative standard deviations (R.S.D.s) for the analysis of SRM were 2% or less. The R.S.D.s of a real urine sample are 1.6% (As), 6.3% (Mn), 7.0% (Ni) and 8.0% (Co), respectively.     

Thermal modified Kaolinite as useful material for separation and preconcentration of trace amounts of manganese ions

This work assesses for the first time the potential of natural Kaolinite as adsorptive material for preconcentration of metal traces. Manganese is quantitatively retained by 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) on thermal modified Kaolinite by column method in pH range of 8.5-10.0 at flow rate of 2 ml min⁻¹. Manganese was removed from column with 5.0 ml of H₂SO₄ 4 mol l⁻¹ and determined by flame atomic absorption spectrometric at 279.5 nm. In this case, 0.l μg of manganese can be concentrated from 800 ml of aqueous sample (where concentration is as low as 0.125 μg l⁻¹). Detection limit is 4.3 μg l⁻¹ (3 δ_bl m⁻¹) and analytical curve is linear in the 0.02-10 mg l⁻¹ in final solution with correlation coefficient 0.9997 and relative standard deviation for eight replicate determination of 5 μg of manganese in final solution is 0.71%. The interference of a large number of anions and cations has been studied in detail to optimize the conditions and method was successfully applied for determination of manganese in complex materials.     

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.     

Flow injection direct spectrophotometric assay for the speciation of trace chromium(III) and chromium(VI) using chromotropic acid as chromogenic reagent

A new rapid and sensitive FI assay is reported for the simultaneous direct spectrophotometric determination of trace Cr(VI) and Cr(III) in real samples. The method is based upon the reaction of Cr(VI) with chromotropic acid (CA) in highly acidic medium to form a water-soluble complex (λ_max = 370 nm). Cr(III) reacts with CA only after its on-line oxidation to Cr(VI) by alkaline KIO₄. The determination of each chromium species in the sample was achieved by absorbance differences. The calibration curves were linear over the range 3-4000 μg l⁻¹ and 30-1200 μg l⁻¹ for Cr(VI) and Cr(III), respectively, while the precision close to the quantitation limit was satisfactory in both cases (s_r = 3.0% for Cr(VI) and 4.0% for Cr(III) (n = 10) at 10 and 50 μg l⁻¹ level, respectively). The method developed proved to be adequately selective and sensitive (c_L = 1 and 10 μg l⁻¹ for Cr(VI) and Cr(III), respectively). The application of the method to the analysis of water samples (tap and mineral water) gave accurate results based on recovery studies (93-106%). Analytical results of real sample analysis were in good agreement with certified values.     

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.     

Catalytic adsorptive stripping voltammetry versus electrothermal atomic absorption spectrometry in the determination of trace cobalt and chromium in human urine

Two methods of the determination of cobalt and chromium in human urine of non-occupationally exposed populations—highly sensitive catalytic adsorptive stripping voltammetry (CAdSV) and electrothermal atomic absorption spectrometry (ET-AAS)—are evaluated and compared. The CAdSV methods are based on adsorptive accumulation of a cobalt-nioxime (1,2-cyclohexanedione dioxime) or a chromium-DTPA (diethylenetriammine-N,N,N′,N″,N″-pentaacetic acid) complexes on a hanging mercury drop electrode, followed by a stripping voltammetric measurement of the catalytic reduction current of the adsorbed complex in the presence of sodium nitrite in case of cobalt or in the presence of sodium nitrate in case of chromium determination. In the CAdSV procedure UV-photolysis was used for the sample pre-treatment; the ET-AAS determination did not require any separate preliminary decomposition of the analyte urine samples. The accuracy of the procedures was checked by the analysis of commercially available quality control urine samples. The detection limits (3σ) were 0.13 μg l⁻¹ for Co and 0.18 μg l⁻¹ for Cr in ET-AAS determination and 0.007 μg l⁻¹ for Co and 0.002 μg l⁻¹ for Cr in CAdSV measurements. Precision (R.S.D.) was less than 5% for both methods. The study has shown that the CAdSV is a more reliable and sensitive technique for the determination of very low cobalt and chromium contents in urine, the detection of which is not possible when using the AAS technique.     

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.     

Voltammetric behaviour of the synthetic pyrethroid lambda-cyhalothrin and its determination in soil and well water

The pyrethroid lambda-cyhalothrin is a common insecticide which is widespread in the environment. A study of the electrochemical reduction of the pesticide on a hanging mercury drop electrode (HMDE) was performed as basis for the development of a sensitive analytical method for determination of lambda-cyhalothrin in natural samples. Two electrochemical techniques—cyclic voltammetry (CV) and differential pulse voltammetry (DPV)—were applied. The study was performed in the pH range 2-13 using Britton-Robinson (B-R) buffer to control the pH of the measuring solutions and tetrabutylammonium chloride (TBAC) salt as supporting electrolyte. In DPV, a single reduction peak was observed at both pH<4.0 and pH>10.5 while two cathodic peaks were produced in the pH range 4.0-10.5. The results showed that the reduction of lambda-cyhalothrin in the measuring solution is irreversible. The limiting current was found to be diffusion-controlled and free of adsorption of the electroactive species to HMDE over the whole pH range tested. For the analytical DPV method running at pH 2 the relationship between peak current and lambda-cyhalothrin concentration was linear up to 500 μg l⁻¹ (1.1×10⁻⁶ mol l⁻¹) with a detection limit of 2.5 μg l⁻¹. The repeatability in terms of relative standard deviation (n=10) was in the order of 3.5% at concentration levels of 5 and 10 μg l⁻¹. A DPV method for determining lambda-cyhalothrin in the agrochemical formulation Karate, spiked soil and well water was developed. The recovery was about 94% in well water and 92% in soil samples at concentration range of 0.05-0.5 μg l⁻¹ and 0.05-0.5 μg g⁻¹, respectively.     

Direct determination of lead in produced waters from petroleum exploration by electrothermal atomic absorption spectrometry X-ray fluorescence using Ir-W permanent modifier combined with hydrofluoric acid

The present work reports the development of a methodology for the direct determination of lead in high saline waters derived from petroleum exploration employing electrothermal atomic absorption spectrometry with permanent Ir-W and HF as modifiers. These waters, so-called produced waters, have complex composition containing several types of organic and inorganic substances. In order to attain best conditions (highest analytical signal besides lowest background) for the methodology studies about the effect of several variables and the convenient calibration strategy were performed. Also, the efficiency of other modification approaches was evaluated. At best conditions, pyrolysis and atomization temperature were 800 and 2200 °C, respectively, when the modifiers cited above were utilized. Obtained results indicate that, in this kind of sample, lead can be determined by standard addition method or employing external calibration with standard solutions prepared in 0.8 mol l⁻¹ NaCl medium. In order to evaluate the accuracy of the procedure, a recovery test was performed with six spiked samples of produced waters. The detection limit, quantification limit and the relative standard deviation in 0.8 mol l⁻¹ NaCl were also calculated and the values are 1.5 μg l⁻¹, 5.0 μg l⁻¹ and 5.0% (at 10 μg l⁻¹ level), respectively.