Capillary zone electrophoresis with indirect UV detection: Determination of sodium dodecyl sulfate in simulated stream water

SDS (sodium dodecyl sulfate) has been quantitatively determined by capillary zone electrophoresis using a fused silica capillary and a 5 mM dihydroxybenzoic acid / sodium hydroxide buffer in 5% methanol solution at a pH of 8.1. The ion was detected by indirect UV absorption at 250 nm. Detection range was from 0.8 to 50 mg SDS/L. This rapid method requiring only small sample volumes was developed in support of an aquatic toxicology study in a simulated stream water and is applicable to waters containing common inorganic ions.     

Reverse flow injection spectrophotometric determination of iron(III) using chlortetracycline reagent

A simple reversed flow injection colourimetric procedure for determining iron(III) was proposed. It is based on the reaction between iron(III) with chlortetracycline, resulting in an intense yellow complex with a suitable absorption at 435 nm. A 200 μl chlortetracycline reagent solution was injected into the phosphate buffer stream (flow rate 2.0 ml min⁻¹) which was then merged with iron(III) standard or sample in dilute nitric acid stream (flow rate 1.5 ml min⁻¹). Optimum conditions for determining iron(III) were investigated by univariate method. Under the optimum conditions, a linear calibration graph was obtained over the range 0.5–20.0 μg ml⁻¹. The detection limit (3σ) and the quantification limit (10σ) were 0.10 and 0.82 μg ml⁻¹, respectively. The relatives standard deviation of the proposed method calculated from 12 replicate injections of 2.0 and 10.0 μg ml⁻¹ iron(III) were 0.43 and 0.59%, respectively. The sample throughput was 60 h⁻¹. The proposed method has been satisfactorily applied to the determination of iron(III) in natural waters.     

Flow-injection determination of sodium and potassium by separationon a silica column and extraction-spectrophotometry with benzo-18-crown-6 and tetrabromophenolphthalein ethyl ester

Sodium and potassium ions in waters are determined by flow-injection extraction-spectrophotometry. The ion-association complexes formed between the metal/crown ether cations and the tetrabromophenolphthalein ethyl ester anion (TBPE^-) are extracted into chlorobenzene/benzene (1:3) and the absorbance of the organic phase is measured after phase separation with a porous membrane. Sodium and potassium are separated on-line with a column (1 mm i.d.×30 cm) packed with silica gel (100-200 mesh). The manifold comprises four streams, each at 0.8 ml min^?1. The sample is injected into a water stream and mixed with a reagent stream containing lithium acetate and benzo-18-crown-6 before entering the silica gel column; after the separation, the stream is mixed with EDTA (trilithium salt) and lithium hydroxide, and then with the extraction solution containing TBPE.H. Extraction proceeds in a 2-m coil; the absorbance of the organic phase is measured at 620 nm. CAlibration graphs are linear inthe ranges 0–×10^?3 M sodium and 0–2×10^?4 M potassium. The sample throughput is 15 h^?1. The procedure is applicable to river and tap waters.     

Determination of cyanide by an indirect spectrophotometric method using 5-Br-PADAP

Complexation of Ni(2+) with cyanide inhibits its colour reaction with 5-Br-PADAP and this reaction is used in the spectrophotometric determination of cyanide at the ug level. Cyanide in industrial waste waters is determined after an initial transfer as hydrogen cyanide from the sample into sodium hydroxide solution with a stream of air.     

Low-level mercury determination with thiamine by fluorescence optosensing

A sensitive fluorescence optosensing method for the determination of Hg(II) in water samples is described. The method, using a flow injection technique, is based on the immobilization on a non-ionic-exchanger solid support (packed in a flow cell placed in a conventional fluorimeter) of the thiochrome formed by the oxidation of thiamine with Hg(II) in a continuous flow carrier at pH 8.1. Experimental parameters such as the solid support, the carrier pH, the thiamine concentration and the flow-rate were investigated to select the optimum operating conditions. The proposed optosensor showed a relative standard deviation of + 3.0% for ten replicates analysis of 100 ng ml(-1) of mercury(II). A detection limit of 3 ng ml(-1) for mercury(II) was achieved for 4-ml sample injections. A detailed study of interferences (possible elements present in natural waters) demonstrated that this optosensing method is virtually specific for this metal, because it allows the determination of mercury in the presence of relatively large amounts of other heavy metals and compounds present in natural waters, such as Mg(II) or Ca(II). The method was successfully applied to the determination of Hg(II) in spiked samples of mineral, tap and sea water.     

Turbidimetric determination of sulphate in plant digests and natural waters by flow injection analysis with alternating streams

An improved flow injection system with alternating streams of reagents is described for the turbidimetric determination of sulphate. Samples are injected into an inert carrier stream which is mixed with barium chloride to form a barium sulphate suspension. The range of the method can be extended to low concentrations by continuously adding sulphate to the sample carrier stream. System performance is improved by automatic alternate pumping of the reagent stream and an alkaline EDTA solution at high flow rate. All operations are controlled by an electronically-operated proportional injector-commutator. Even after routine analysis of 3000 samples of natural waters and plant digests, baseline drift was not observed. The proposed method is suitable for 120 samples per hour with a relative standard deviation less than 1% for sulphate concentrations in the range 1–30 ppm (waters) or 5–200 ppm (plant digests). The results compare well with those obtained by standard manual procedures.     

Gas diffusion with preconcentration for the determination of fluoride in water samples by flow injection

The preconcentration of fluoride is achieved on-line by converting it to trimethylsilane which then diffuses through a gas permeable membrane to be absorbed in a stationary sodium hydroxide acceptor stream. This stream is enclosed in the sample loop of an injection valve and after preconcentration, the fluoride sample is flushed into a flow injection manifold for spectrophotometric analysis by the zirconium/alizarin S procedure at 520 nm. The method is suitable for fluoride analysis in the range 0.1-10 mg/l at a sampling rate of 17/hr. Phosphate does not interfere and aluminium and iron can be tolerated at 200 and 500 times the fluoride concentration, respectively. The LOD was calculated to be 0.055 mg/l and LOQ was found to be 0.18 mg/l.     

Segmented-flow analysis: On-line microwave sample processing for the analysis of natural waters

 A flow system including an on-line coated capillary column for the determination of traces of metal ions in natural waters is proposed, employing a manifold of flow microwave sample processing. This method eliminates the noise caused by the organic matrix, i.e. humic and fulvic acids. The system was applied to the determination of Pb, Co, Mn(II), and Fe(III) in swamp water. The proposed technique can be useful for routine analysis of natural and waste waters. Received: 29 January 1996/Revised: 17 July 1996/Accepted: 20 July 1996     

Flow injection analysis-flame atomic absorption spectrometry system for indirect determination of cyanide using cadmium carbonate as a new solid-phase reactor

A new and simple flow injection system procedure has been developed for the indirect determination of cyanide. The method is based on insertion of aqueous cyanide solutions into an on-line cadmium carbonate packed column (25% m/m suspended on silica gel beads) and a sodium hydroxide with pH 10 is used as the carrier stream. The eluent containing the analyte as cadmiumcyanide complexes, produced from reaction between cadmium carbonate and cyanide, measured by flame atomic absorption spectrometry. The absorbance is proportional to the concentration of cyanide in the sample. The linear range of the system is up to 15 mg L⁻¹ with a detection limit 0.2 mg L⁻¹ and sampling rate 72 h⁻¹. The method is suitable for determination of cyanide in industrial waste waters with a relative standard deviation better than 1.22%.     

Biosorption of heavy metals on Aspergillus fumigatus immobilized Diaion HP-2MG resin for their atomic absorption spectrometric determinations

A solid phase extraction procedure based on biosorption of copper(II), lead(II), zinc(II), iron(III), nickel(II) and cobalt(II) ions on Aspergillus fumigatus immobilized Diaion HP-2MG has been investigated. The analytical conditions including amounts of A. fumigatus, eluent type, flow rates of sample and eluent solutions were examined. Good recoveries were obtained to the spiked natural waters. The influences of the concomitant ions on the retentions of the analytes were also examined. The detection limits (3sigma, N = 11) were 0.30 μg l⁻¹ for copper, 0.32 μg l⁻¹ for iron, 0.41 μg l⁻¹ for zinc, 0.52 μg l⁻¹ for lead, 0.59 μg l⁻¹ for nickel and 0.72 μg l⁻¹ for cobalt. The relative standard deviations of the procedure were below 7%. The validation of the presented procedure is performed by the analysis of three standard reference materials (NRCC-SLRS 4 Riverine Water, SRM 1515 Apple leaves and GBW 07605 Tea). The procedure was successfully applied for the determination of analyte ions in natural waters microwave digested samples including street dust, tomato paste, black tea, etc.     

Influence of water sample storage protocols in chemiluminescence detection of trace elements

This paper shows the influence of different sample storage protocols, on the chemiluminescence signal of some metal ions. The storage protocols studied were: acid addition (HCl or HNO(3)) and no reagent addition to filtered and refrigerated (T=4 degrees C) samples. Light emission was produced for the chemiluminescence reaction between luminol and hydrogen peroxide in buffer carbonate conditions (pH 10.8) catalysed by Cr(III), Co(II) and Cu(II). Batch and/or flow modes in different conditions were tested. Fe(II), Fe(III), Ni(II) and Mn(II) did not give chemiluminescence in the studied conditions. A parallel study of sensitivity and selectivity was performed. Then the presence or absence of the masking agent EDTA, added to samples or used in the carrier stream, is assayed. If the samples are acidified with HNO(3), a previous neutralisation is needed using batch mode. The determination of Cr(III) is independent of storage protocol by flow injection (FI) method; however, the determination of Co(II) or Cu(II) or total determination of three metals requires the conditioning of standards. Detection limits achieved are ranged between 0.5 and 2 mug l(-1). For batch mode, detection limits are better for unacidified samples and worse for carbonate-neutralised samples. The influence of storage protocols was validated using standard metal mixtures and calibration solutions. The use of standard reference material (SRM(c) 1640) (Trace elements in natural water) corroborates the previous statements and validates the accuracy of the different approaches underlined. This paper demonstrates that it is possible to determine Cr(III) selectively in natural waters.     

Simultaneous determination of nanomole amounts of sulphur dioxide and hydrogen sulphide by flow injection analysis with on-line preconcentration by means of capillary denuder tubes

A simple and rapid method for trace determination of SO2 and H2S in gaseous samples by using a flow injection system with on line preconcentration on capillary denuder is described. The gaseous samples are led through a 0.4 M sulphamic acid solution, retaining nitrogen dioxide, ammonia and hydrogen chloride. The sulphur dioxide is collected from the carrier gas stream (250 cm3 min-1) as sulphuric acid in a capillary denuder tube coated with a thin layer of 0.01-0.03 M hydrogen peroxide solution of 0.05 mM sulphuric acid; hydrogen sulphide passes into a second tube coated with 0.075 mM sodium sulphide solution of 0.1 M aqueous sodium hydroxide. The films containing the sulphuric acid and the sodium sulphide, respectively, are eluted with the corresponding circulating absorbent streams and pass through the detectors. Sulphuric acid is detected by conductimetry and sulphide is determined spectrophotometrically at 230 nm. If nanoequivalent amounts of H2S are present in the sample containing a large concentration of SO2 (SO2/H2S concentration ratio > 20), the sulphur dioxide is filtered out of the sample gas stream by solid sodium hydrogen carbonate. A limit of detection of 3.5 micrograms m-3 is obtained.     

气动毛细管微滴进样-化学发光法测定酚磺乙胺

传统的化学发光(CL)分析有分立式取样和流动注射式两种方式,各有优缺点,目前国内外的仪器都采用手动进样或电动进样方法,速度和进样量均很难精确控制,对微升级的样品尤为困难,另外也无法实现在线分析。本文提出的气动毛细管微滴进样化学发光(AFCM-CL)检测法是以气体压力作为     

Electrosynthesis of a new selective chelating agent for solid phase extraction of Ni(II) from water samples: characterisation and analytical applications

A new polymer as a selective chelating agent for separation and preconcentration of nickel ions from water samples was prepared by electropolymerisation of 4-nitrophenol. Electrosynthesis was carried out on the lead cathode in aqueous sodium acetate solution. The electrode-product is a dark-brown powder, insoluble in water but soluble in methanol, N,N-dimethylformamide (DMF) and tetrahydrofuran (THF). The electrode-product was characterised by differential scanning calorimetry (DSC), gel permeation chromatography (GPC), FT-IR, ¹H-NMR, cyclic voltammetry (CV) and UV-Vis spectrometry. A proper mechanism and structure of the prepared polymer was suggested. A few drops of methanolic solution of electrode-product formed a blue complex with nickel ions in an aqueous medium in the pH range of 6 to 10. This new chelating reagent was used as a coating material on activated charcoal and applied for solid phase extraction of trace amounts of nickel ions from natural and waste waters. The effect of different parameters such as type of eluent, elution conditions, sample volume and sample flow rate and mass of coating material were studied. In the presence of co-existing ions, no significant interferences were observed. Under the optimal conditions, limits of detection (LOD) and quantification (LOQ) were 0.32 and 1 µg L^?1 Ni(II), respectively. The proposed method was used for determination of Ni(II) in some lagoons south of the Caspian Sea and waste waters of factories. The validity of this method was confirmed by the comparison of the obtained results with the results of ICP-OES.     

Preconcentration of inorganic mercury with an anion-exchange resin and direct reduction—aeration measurements by cold-vapour atomic absorption spectrometry

Inorganic mercury ions (5–50 ng l^-1) present in natural waters (500 ml) are concentrated on anion-exchange resin (0.2 g; chloride form) in a batchwise operation. The resin is filtered off and introduced into a bubbler containing tin(II) solution. The adsorbed mercury ions are reduced to the metal and vaporized with a stream of air in a closed system. Satisfactory recoveries are obtained for sea waters made 0.1 M in nitric acid, and for river and spring waters also made 0.1 M in nitric acid or 0.01 M in ammonium thiocyanate. The method preconcentrates traces of inorganic mercury ions by an order of magnitude, and is also effective in preventing mercury loss during sample storage.     

Flow-injection fluorimetric determination of mercury(II) with calcein

A flow-injection spectrofluorimetric method for the determination of Hg(II) is described. The method is based on the complex that is formed between Hg(II) and calcein at pH 11-12. This reagent was not used before for determining Hg(II). The excitation wavelength is 324 nm and the emission wavelength is 522 nm. The calibration graph shows a linear range between 7.7 and 128 microg l(-1) (relative standard deviation 2.0%), the sampling rate was 90 h(-1). The effect of several interferents has been examined. Trace mercury in natural waters were determined satisfactorily using a modified manifold, which has an EDTA stream in order to minimize the calcium and magnesium interference.     

Fluorimetric flow injection analysis of trace amount of formaldehyde in environmental atmosphere with 5,5-dimethylcyclohexane-1,3-dione

A simple and sensitive flow injection method with fluorimetry and 5,5-dimethylcyclohexane-1,3-dione (dimedone) was developed for the determination of formaldehyde. Formaldehyde reacted with dimedone in the presence of ammonium acetate to form a fluorescence compound, which has an excitation wavelength at 395 nm and an emission wavelength at 463 nm. A two-channel flow system was assembled. Distilled water and 0.3% dimedone buffered at pH 5.5 were delivered at 0.7 ml min⁻¹ and 100 μl of sample was injected into the carrier stream. The reaction was done in the reaction system designed newly, which consists of heating and cooling devices. The chemical reactivity with formaldehyde was excellent in the reaction system and selective. The calibration graphs were linear in the range of 25–100 and 5–10 ppb. RSDs (n=10) for 50 and 10 ppb formaldehyde were 0.6 and 3.4% and the LOD (S/N=3) was 0.9 ppb. The sample throughput was 20 h⁻¹. The method was applied to the determination of formaldehyde in gas sample evolved from adhesive agents and in living environmental indoor. The sensitive and selective method is useful for monitoring trace of formaldehyde in the environmental atmosphere.     

Determination of nanomolar concentrations of phosphate in freshwaters using flow injection with luminol chemiluminescence detection

A simple and rapid flow injection (FI) method is reported for the determination of phosphate (as molybdate reactive P) in freshwaters based on luminol chemiluminescence (CL) detection. The molybdophosphoric heteropoly acid formed by phosphate and ammonium molybdate in acidic conditions generated chemiluminescence emission via the oxidation of luminol. The detection limit (3× standard deviation of blank) was 0.03 μg P l⁻¹ (1.0 nM), with a sample throughput of 180 h⁻¹. The calibration graph was linear over the range 0.032–3.26 μg P l⁻¹ (r²=0.9880) with relative standard deviations (n=4) in the range 1.2–4.7%. Interfering cations (Ca(II), Mg(II), Ni(II), Zn(II), Cu(II), Co(II), Fe(II) and Fe(III)) were removed by passing the sample through an in-line iminodiacetate chelating column. Silicate interference (at 5 mg Si l⁻¹) was effectively masked by the addition of tartaric acid and other common anions (Cl⁻, SO₄²⁻, HCO₃⁻, NO₃⁻ and NO₂⁻) did not interfere at their maximum admissible concentrations in freshwaters. The method was applied to freshwater samples and the results (26.1±1.1–62.0±0.4 μg P l⁻¹) were not significantly different (P=0.05) from results obtained using a segmented flow analyser method with spectrophotometric detection (24.4±4.45–84.0±16.0 μg P l⁻¹).     

Repetitive determination of chloride using the circulation of the reagent solution in closed flow-through system

The precipitation reaction of silver chloride (AgCl) is carried out in a large amount of ammonia (NH₃). This makes possible to adopt a closed-loop flow injection (FI) system and to determine chloride repetitively. A solution of 30 mmol l⁻¹ silver nitrate and 80 mmol l⁻¹ NH₃ in a single reservoir (250 ml) is continuously circulated through the flow cell at a flow rate of 2.0 ml ml⁻¹. The chloride containing sample (100 μl) was introduced into this reagent solution by means of six-way valve. AgCl precipitates formed in the sample zone are monitored spectrophotometrically (at 500 nm) in the flow system. After passing through the flow cell, the excess NH₃ in the circulating reagent solution dissolves AgCl precipitates and the stream then returns to the reservoir. Various variables of the FI system were optimized and a study of interfering ions was also carried out. A linear calibration graph was obtained from 3.0 to 30 mg l⁻¹ chloride. Two hundred repetitive injections of 5.0 mg l⁻¹ chloride into the circulating reagent solution have shown unchanged base-line and good reproducibility. The method was successfully applied to the determination of chloride in tap, natural and the reference waters.     

Ferrozine colorimetry and reverse flow injection analysis (rFIA) based method for the determination of total iron in aqueous solutions at nanomolar concentrations

Iron is one of the most microbiologically and chemically important metals in natural waters. The biogeochemical cycling of iron is significantly influenced by the redox cycling of Fe(II) and Fe(III). Because of the unique chemistry of iron, it is often needed to analyze iron at nano-molar concentrations. This article describes a reverse flow injection analysis (rFIA) based method with ferrozine spectrophotometric detection to quantify total iron concentration in stream water at nanomolar concentrations. The rFIA system has a 0.65 nM detection limit and a linear dynamic range up to 1.40 μM for the total iron analysis. The detection limit was achieved using a 1.0 m long liquid waveguide capillary flow cell, 1.50 m long knotted reaction coil, 87.50 μL injection loop and a miniature fiber optics spectrophotometer. The optimized colorimetric reagent has 1.0 mM ferrozine, 0.1 M ascorbic acid, 1.0 mM citric acid and 0.10 M acetate buffer adjusted to pH 4.0. The best sample flow rate is 2.1 mL min^?1 providing a sample throughput of more than 15 samples h^?1. The linear dynamic range of the method can be adjusted by changing the volume of the injection loop. The rFIA manifold was assembled exclusively from commercially available components.