Flow injection on-line preconcentration coupled to hydride generation atomic fluorescence spectrometry for ultra-trace amounts of cadmium determination in seawater

A simple flow injection on line separation and preconcentration system coupled to hydride generation atomic fluorescence spectrometry (HG-AFS) was developed for ultra-trace cadmium determination in seawater. With the sample pH kept at 3.0, the preconcentration of cadmium on the inner walls of the knotted reactor was carried out based on the retention of cadmium complex with 1-phenyl-3-methyl-4-benzoylpyrazol-5-one. A 0.2 mol L⁻¹ HCl was introduced to elute the retained analyte complex and merge with KBH₄ solution for HG-AFS detection. Under the optimal experimental conditions, an enhancement factor of 12 was obtained with a sample consumption of 12.0 mL. The limit of detection was 3.2 ng L⁻¹ with a sample frequency of 24 h⁻¹. The developed method was validated by the analysis of cadmium in certified reference materials, and was applied to the determination of cadmium in four seawater samples with R.S.D. of around 10%. Correspondence: Hong Wu, Department of Chemistry, Xuzhou Normal University, Xuzhou 221116, P.R. China     

A novel method for the determination of Pb2+ based on the quenching of the fluorescence of CdTe quantum dots

A novel method for the determination of Pb²⁺ has been developed based on quenching of the fluorescence of thiol-capped CdTe quantum dots (QDs) by Pb²⁺ in aqueous solutions. Under optimum conditions, the relative fluorescence intensity was linearly proportional to the concentration of Pb²⁺ between 2.0 × 10⁻⁶ and 1.0 × 10⁻⁴ mol L⁻¹ with a detection limit of 2.7 × 10⁻⁷ mol L⁻¹. The relative standard deviation (RSD) was 4.6% for a 4.0 × 10⁻⁵ mol L⁻¹ Pb²⁺ solution (N = 5). As an application, the proposed method was successfully applied to the analysis of Pb²⁺ in food samples, and the results were satisfactory, i.e. consistent with those of flame atomic absorption spectrometry (FAAS). Correspondence: Heyou Han, College of Science, Institute of Chemical Biology, State Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan 430070, P.R. China     

Application of full factorial design for the preconcentration of chromium by solid phase extraction with Amberlyst 36 resin

The preconcentration of chromium(III) by solid phase extraction and its determination from aqueous solutions by flame atomic absorption spectrometry (FAAS) is investigated by applying an experimental design. The optimization of the preconcentration variables such as pH of the sample solution, flow rate of the sample solution and concentration of elution solution was carried out using 2³ full factorial design. The most important parameter affecting the preconcentration of chromium is the concentration of eluent. In the established experimental conditions, chromium can be determined with a relative standard deviation of 2.0% (N = 7) for a chromium concentration of 100 μg L⁻¹. The detection limit for chromium was 1 μg L⁻¹ (N = 20). The adsorption capacity of Amberlyst 36 is found to be 90.9 mg g⁻¹ for chromium. Effect of other ions on the procedure was also evaluated. The method was validated by the analysis of certified reference materials (tea leaves GBW 07605 and fish tissue IAEA-407). The method was applied to the determination of chromium in waste water, dam water, carrot, parsley and lettuce. Correspondence: Ali Rehber Türker, Department of Chemistry, Faculty of Science and Arts, Gazi University, TR-06500 Ankara, Turkey     

Multisyringe Flow Injection Analysis for Determination of 1-Naphthylamine in Water Samples

1-Naphthylamine (NPA) is one of the main degradation products of pesticides derived from naphthalene, and a well-known bladder carcinogen in men. The Griess assay is used for NPA determination because of its high sensitivity and selectivity. The azo dye 4-(sulphophenylazo)-1-naphthylamine is formed, which shows a peak maximum at 540 nm. After optimizing multisyringe flow injection analysis (MSFIA) parameters, the analytical characteristics of the method were obtained, with a working linear range of 0.5 to 14 mg L⁻¹, according to the equation A = 0.0738±0.0019 [NPA] + 0.0028 ± 0.0042, r = 0.9997. Values for RSD (%) and E_rel (%) were calculated for the concentration levels of 0.5, 6 and 12 mg L⁻¹; values obtained were 1.1, 0.4 and 0.3% for RSD and 0.8, 0.3 and 0.2% for E_rel, respectively. LD was 0.01 mg L⁻¹ and LQ was 0.04 mg L⁻¹ NPA. The MSFIA procedure for the determination of NPA was applied to different water samples (well water, tap water, seawater, and wastewater from the EDAR-1, Palma de Mallorca water treatment plant), with satisfactory results and a throughput of 90 samples per hour.     

Direct electrochemistry and electrocatalysis of hemoglobin on an indium tin oxide electrode modified with implanted carboxy ions

A flow injection on-line preconcentration system was developed for the determination of lead by hydride generation atomic fluorescence spectrometry (HG-AFS). It is based on a simple micro-column filled with multiwalled carbon nanotubes (MWCNTs). The preconcentration of lead on the MWCNTs was carried out based on the adsorptive retention of analyte via on-line introducing the sample into the micro-column system. A 0.3 mol L^?1 HNO₃ was introduced to elute the retained analyte and merged with KBH₄ solution for HG-AFS detection. Under the optimal experimental conditions, an enhancement factor of 26 was obtained with a sample consumption of 14.4 mL. The limit of detection was 2.8 ng L^?1 and the precision (RSD) of 11 replicate measurements of 0.2?μg L^?1 Pb was 4.4%. The method was validated by analyzing three certified reference materials, and was successfully applied to the determination of trace lead in natural water samples.     

Kinetic-potentiometric assay of formaldehyde in pharmaceutical and industrial samples, monitored by copper solid ion selective electrode, after its reaction with the copper(II)-bis-(ethylenediamine) complex

A kinetic-potentiometric method is described for the quantitative assay of formaldehyde (HCHO) in pharmaceutical and industrial preparations. It is based on the reaction of HCHO with (ethylenediamine)-Cu(II)-sulfate [Cu(CH₂NH₂)₂(H₂O)₂] · SO₄. The changes in potential, resulting from the release of the Cu(II) cations, are monitored with a Cu(II)-ion selective electrode. The calibration curve for the HCHO is linear in the concentration range 50–250 mg L⁻¹, with a limit of detection of 8.5 mg L⁻¹. The method shows very good reproducibility with an RSD of 2.6% for successive injections (n = 5) of 150 mg L⁻¹ HCHO primary solution, while it is interference free. The method was successfully tested in various industrial and pharmaceutical preparations.     

Solid Phase Extraction of Lead(II) by Sorption on Grinded Eucalyptus Stem and Determination with Flame Atomic Absorption Spectrometry

A sensitive and simple solid‐phase preconcentration procedure for the determination of trace amount of lead by flame atomic absorption spectrometry (FAAS) is developed. The method is based on the adsorption of Pb²⁺ on the column of fine grinded eucalyptus stem adsorbent, elution of the column by nitric acid and subsequent determination by FAAS. The effect of different variables such as pH, eluent type, flow rate and interfering ions on the recovery of the analyte was investigated and optimum conditions were established. The adsorption of lead onto fine grinded eucalyptus stem can formally be described by a Langmuir equation with a maximum adsorption capacity of 4.49 mg g^?1. A preconcentration factor of 50 was achieved using the optimum conditions. The calibration graph was linear in the range 10–125 ng mL^?1 of lead in the initial solution with r = 0.9982. The limit of detection based on 3S_b criterion was 4.5 ng mL^?1 and the relative standard deviation for eight replicate measurements of 30 and 80 ng mL^?1 of iron was 3.6 and 2.8%, respectively. The method was successfully applied to the determination of lead added to well, tap and wastewater samples.     

Design of a field flow system for the on-line spectrophotometric determination of phosphate, nitrite and nitrate in natural water and wastewater

This study describes the design and optimisation of a field flow system for the in-situ collection and on-line determination of phosphate, nitrate and nitrite by flow injection analysis-spectrophotometry. The method is based on the initial determination of phosphate as its phosphoantimonylmolybdenum blue complex which is then oxidized on-line by nitrite and the decrease in absorbance is monitored at 880 nm. Nitrate is determined as the difference between total and initial nitrite content in a separate flow after reduction to nitrite in a cadmium reductive column. The calibration curves were linear in the range 0–2.00 mg L⁻¹ P-phosphate, 0–10.00 mg L⁻¹ nitrite and 0–7.00 mg L⁻¹ nitrate with correlation coefficients of 0.9979, 0.9993 and 0.9995, respectively. The detection limits, calculated as 3S/N, were 0.15 mg L⁻¹ for P-phosphate, 0.17 mg L⁻¹ for nitrite and 0.09 mg L⁻¹ for nitrate. The reproducibility was below 3.0% (n = 7). Method validation in the analysis of natural water and wastewater samples revealed that it can efficiently be applied to the determination of the target analytes, with recoveries in the range of 92–108%. Correspondence: Athanasios G. Vlessidis, Laboratory of Analytical Chemistry, Department of Chemistry, University of Ioannina, Ioannina 45110, Greece     

Flow and Sequential Injection Manifolds for the Spectrophotometric Determination of Captopril Based on its Oxidation by Fe(III)

 Two new simple and rapid methods are reported for the accurate and precise spectrophotometric determination of captopril (CPL) using flow (FI) and sequential injection (SI) analysis. The methods are based on the fast oxidation of CPL by Fe(III). The produced Fe(II) reacts with 2,2′-dipyridyl-2-pyridylhydrazone (DPPH) in acidic medium to form a colored complex which is monitored spectrophotometrically at 535 nm. Both methods allow the determination of the analyte up to 1000 mg L⁻¹ at a sampling rate of 120 and 60 injections per hour for FI and SI, respectively. The methods are very precise [s _r=0.8 and 1.2% at 500 mg L⁻¹ CPL (n=12) for FI and SI, respectively] and the 3σ detection limits (c _L=4.0 and 7.0 mg L¹, respectively) are quite satisfactory. Their application to a variety of anti-hypertensive commercial pharmaceutical formulations showed excellent results (relative errors, e _r, < ± 1.6% in all cases compared to an official HPLC method), while common pharmaceutical excipients were found not to interfere. Recovery experiments further verified the accuracy of the developed methods, as the percent recoveries were in the range of 98.1–102.5%. Author for correspondence. E-mail: themelis@chem.auth.gr Received May 9, 2002; accepted January 8, 2003 Published online May 5, 2003     

Determination of cobalt in biological materials by RNAA via induced short-lived 60mCo

A chemiluminescence (CL) micro-flow system is presented for rapid determination of chemical oxygen demand (COD) in water at room temperature. In this system, potassium dichromate is reduced to Cr³⁺ in 2 mol L⁻¹ H₂SO₄ during the chemical oxidation of COD substances in the sample, and Cr³⁺ can be measured with the help of the luminol-H₂O₂ CL system. The polymethyl methacrylate micro-flow chip with discrete microdroplet sampling was used here. Effects on COD determination (such as pH, concentrations, the channel length, and interference) were investigated. The linear range for COD determination was 0.27–10 g L⁻¹, and the detection limit was 100 mg L⁻¹. The method was successfully applied to the determination of COD in wastewater samples. The data obtained with the present method were in fairly good agreement with those obtained by the titrimetric method. Correspondence: Zhujun Zhang, Key Laboratory of Analytical Chemistry for Life Science of Shaanxi Province, School of Chemistry and Materials Science, Shaanxi Normal University, Xi’an 710062, P.R. China; Department of Chemistry, Institute of Analytical Science, Southwest University, Beibei, Chongqing 400715, P.R. China     

A solid-contact Pb2+-selective polymeric membrane electrode with Nafion-doped poly(pyrrole) as ion-to-electron transducer

Conducting polymer poly(pyrrole) (PPy) doped with Nafion was successfully used as ion-to-electron transducer in the construction of a solid-contact Pb²⁺-selective polymeric membrane electrode. The Nafion dopant can effectively increase the capacitance of the conducting polymer and improve the mechanical robustness of the coating. The transducer layer, PPy-Nafion, characterized by cyclic voltammetry and electrochemical impedance spectroscopy, exhibits a sufficiently high bulk (redox) capacitance and fast ion and electron transport process. The new Pb²⁺-selective polymeric membrane electrode, based on PPy-Nafion film as solid contact, shows stable Nernstian characteristics in Pb(NO₃)₂ solution within the concentration range of 1.0 × 10⁻⁷–1.0 × 10⁻³ M, and the detection limit is 4.3 × 10⁻⁸ M. The potential stability of the electrode and the influence of the interfacial water layer were also evaluated by chronopotentiometry and potentiometric water layer test, respectively. The results show that the solid-contact Pb²⁺-selective electrode, based on PPy-Nafion film as ion-to-electron transducer, can effectively overcome the potential drift and reduce the water layer between the PPy-Nafion transducer layer and the ion-selective membrane.     

Determination of trace amounts of lead in mussels by flow-injection flame atomic-absorption spectrometry coupled with on-line minicolumn preconcentration

A minicolumn packed with poly(aminophosphonic acid) chelating resin incorporated in an on-line preconcentration system for flame atomic-absorption spectrometry was used to determine ultratrace amounts of lead in mussel samples at μg L^–1 level. The preconcentrated lead was eluted with hydrochloric acid and injected directly into the nebulizer for atomization in an air-acetylene flame for measurement. The performance characteristics of the determination of lead were: preconcentration factor 26.8 for 1 min preconcentration time, detection limit (3σ) in the sample digest was 0.25 μg g^–1 (dry weight) for a sample volume of 3.5 mL and 0.2 g sample (preconcentration time 1 min), precision (RSD) 2.3% for 25 μg L^–1 and 2.0% for 50 μg L^–1. The sampling frequency was 45 h^–1. The method was highly tolerant of interferences, and the results obtained for the determination of lead in a reference material testify to the applicability of the proposed procedure to the determination of lead at ultratrace level in biological materials such as mussel samples. Received: 1 November 2000 / Revised: 8 January 2001/ Accepted: 11 January 2001     

Electrochemical determination of lead(II) using a montmorillonite calcium-modified carbon paste electrode

Utilizing the fascinating properties of montmorillonite calcium (MMT-Ca), such as huge cationic exchange capacity, strong adsorptive ability, high chemical and mechanical stability, an MMT-Ca modified carbon paste electrode (CPE) was constructed for the sensitive determination of Pb²⁺. In 0.01 mol·L⁻¹ HCl, Pb²⁺ was firstly exchanged and accumulated on an MMT-Ca modified CPE surface and secondly reduced to Pb at −0.90 V. In the following potential sweep from −0.90 to −0.50 V, reduced Pb was oxidized, resulting in an obvious stripping peak at −0.58 V. After optimizing the parameters, such as determining medium, content of MMT-Ca, accumulation potential and time, an electrochemical method was developed for the analysis of Pb²⁺. Compared with bare CPE, the MMT-Ca modified CPE significantly enhances the sensitivity of Pb²⁺ analysis. The limit of detection is evaluated to be 6.0 × 10⁻⁹ mol L⁻¹ Pb²⁺. Finally, this method was successfully employed to determine trace levels of Pb²⁺ in water samples. The first two authors contribute equally do this work     

Electrochemical Study of 4-Nitrophenol at a Modified Carbon Paste Electrode

 A zeolite-modified carbon paste electrode (CPE) has been used for the determination of 4-nitrophenol by differential pulse voltammetry (DPV). The electrochemical reduction of 4-nitrophenol at −1.0 V is carried out in a Britton-Robinson medium at pH 3.5. The cyclic voltammetric (CV) behaviour has been investigated to study the nature of the process. Studies on the effect of pH were carried out over the pH range 2–9 with the Britton-Robinson buffer solution, and the influence of pH on peak height and peak potential was analyzed. A linear relationship between peak intensity and concentration is obtained in the range 0.2–10 mg L⁻¹, with a detection limit of 0.04 mg L⁻¹; a relative standard deviation of 1.5% for a 5 mg L⁻¹ 4-nitrophenol concentration and a relative error of 2.6% were also obtained (n=11). Received March 3, 1998. Revision December 10, 1998.     

Development of a sequential injection–square wave voltammetry method for determination of paraquat in water samples employing the hanging mercury drop electrode

This work describes the development and optimization of a sequential injection method to automate the determination of paraquat by square-wave voltammetry employing a hanging mercury drop electrode. Automation by sequential injection enhanced the sampling throughput, improving the sensitivity and precision of the measurements as a consequence of the highly reproducible and efficient conditions of mass transport of the analyte toward the electrode surface. For instance, 212 analyses can be made per hour if the sample/standard solution is prepared off-line and the sequential injection system is used just to inject the solution towards the flow cell. In-line sample conditioning reduces the sampling frequency to 44 h⁻¹. Experiments were performed in 0.10 M NaCl, which was the carrier solution, using a frequency of 200 Hz, a pulse height of 25 mV, a potential step of 2 mV, and a flow rate of 100 μL s⁻¹. For a concentration range between 0.010 and 0.25 mg L⁻¹, the current (i _p, μA) read at the potential corresponding to the peak maximum fitted the following linear equation with the paraquat concentration (mg L⁻¹): i _p = (−20.5 ± 0.3)C _paraquat − (0.02 ± 0.03). The limits of detection and quantification were 2.0 and 7.0 μg L⁻¹, respectively. The accuracy of the method was evaluated by recovery studies using spiked water samples that were also analyzed by molecular absorption spectrophotometry after reduction of paraquat with sodium dithionite in an alkaline medium. No evidence of statistically significant differences between the two methods was observed at the 95% confidence level.     

开叉毛细管HG-FAAS测定地质样品中的锑、铋

氢化物发生原子吸收法(HG-FAAS)广泛应用于冶金、地质、环境、医药和食品分析等领域中。研究表明,氢化物发生法的检出限、测定精度以及干扰等情况与原子化器和氢化物发生器的结构以及传输过程有关[1]。郭小伟等[2-4]研制了用于火焰原子吸收光谱分析的双毛细管喷雾器,并利用其测     

Flow-Injection Spectrophotometric Determination of Diclofenac or Mefenamic Acid in Pharmaceuticals

 Two flow injection (FI) spectrophotometric methods are proposed for the determination of diclofenac (DCF) or mefenamic acid (MF) in bulk samples and pharmaceuticals. Both methods are based on the reaction of DCF or MF with potassium ferricyanide in a sodium hydroxide medium. The absorbance of the orange products obtained is measured at 455 nm for DCF and 465 nm for MF. The corresponding calibration graphs are linear over the range 0.20–20.0 mg L⁻¹ for DCF and 1.00–100 mg L⁻¹ for MF, while the limits of detection were 0.05 and 0.18 mg L⁻¹, respectively. Received March 27, 2000. Revision November 15, 2000.     

Electrochemical behaviour of a lead electrode in phosphoric acid

 A lead electrode was studied in 6 and 12 M H₃PO₄. Oxidation of a freshly polished electrode occurred in the −0.5 to −0.3 V vs. SCE range, and led to PbHPO₄ growth on the electrode surface. The dissolution of this layer by electrochemical reduction occurred between −0.5 and −0.7 V. The influence of temperature (20 °C and 65 °C) was investigated and showed that the anodic and the cathodic peaks were increasing, and more markedly for the 12 M H₃PO₄. The ratio Q _cathodic/Q _anodic (Q=electrical charge flowing through the electrode) was equal or close to the unity at 20 °C and decreased as the temperature was increased. The influence of Cl⁻, Br⁻ and I⁻ ions was also evaluated. The addition of Cl⁻ and Br⁻ predominantly led to Pb₅(PO₄)₃Cl and Pb₅(PO₄)₃Br, respectively, while I⁻ led to a mixture of PbI₂ and PbHPO₄. Received: 18 July 1999 / Accepted: 2 November 1999     

Exploiting Sulphide Generation and Gas Diffusion Separation in a Flow System for Indirect Sulphite Determination in Wines and Fruit Juices

A flow system for sulphite determination in wines and fruit juice samples has been developed exploiting H₂S generation and gas diffusion separation. The composed sandwich gas diffusion cell was coupled in the flow manifold to permit sulphite reduction to H₂S and H₂S diffusion through a microporous PTFE membrane to produce methylene blue resulting from the reaction with N,N-dimethylphenylene diamine (DMPD) and Fe³⁺. The flow parameters were optimized, and the best results were obtained by using NaOH solution for H₂S collection. Interferences of H₂S, CO₂ and ascorbic acid were evaluated. Limits of detection (3σ) for the free and total sulfite were calculated at 0.12 and 0.25 mg L⁻¹, respectively. The results obtained by the proposed process were in agreement with the reference methods for a 95% confidence level.     

Simultaneous Voltammetric Determination of Cd2+ and Pb2+ in Gasoline Samples Employing a Chemically Modified Acrylonitrile-Butadiene-Styrene (ABS) Composite Electrode

A composite electrode based on acrylonitrile-butadiene-styrene and graphite chemically modified with a bismuth film (AGCE-BiF) was applied for the simultaneous determination of Cd²⁺ and Pb²⁺ in gasoline samples. Extraction induced by microemulsion breaking (EIMB) was used for the first time in the preparation of the samples for electroanalysis. AGCE-BiF was characterized by SEM, AFM, CV, and SWASV. The sensor showed an increase in sensitivity via in situ modification with bismuth film. The LOD was 4 μg L⁻¹ for Cd²⁺ and 2 μg L⁻¹ for Pb²⁺. The results showed satisfactory recoveries and precision, being statistically compatible to those obtained with FAAS.