Determination of trace level bromate and perchlorate in drinking water by ion chromatography with an evaporative preconcentration technique

A simple sample preconcentration technique employing microwave-based evaporation for the determination of trace level bromate and perchlorate in drinking water with ion chromatography is presented. With a hydrophilic anion-exchange column and a sodium hydroxide eluent in linear gradient, bromate and perchlorate can be determined in one injection within 35 min. Prior to ion chromatographic analysis, the drinking water sample was treated with an OnGuard-Ag cartridge to remove the superfluous chloride and concentrated 20-fold using a PTFE beaker in a domestic microwave oven for 15 min.The recoveries of the anions ranged from 94.6% for NO2- to 105.2% for F-. The detection limits for bromate, perchlorate, iodate and chlorate were 0.1, 0.2, 0.1 and 0.2 microg/l, respectively. The developed method is applicable for the quantitation of bromate and perchlorate in drinking water samples.     

Spectrophotometric determination of trace aluminium content in parenteral solutions by combined cloud point preconcentration-flow injection analysis

A cloud point preconcentration and flow injection (FI) analysis methodology for aluminium(III) determination has been developed. The analyte in the initial aqueous solution was complexed with Chrome Azurol S (CAS) in the presence of the cationic surfactant benzyldimethyltetradecylammonium chloride (BDTAC). The absorption spectroscopic characteristics of the ternary complex [Al(III)-CAS-BDTAC] were examined in detail. The preconcentration step was carried out by means of the non-ionic surfactant polyethylene glycol p-nonylphenyl ether (PONPE 7.5). The enriched analyte solution was injected into an FI system using an HPLC pump. The chemical variables affecting the analytical performance of the combined methodology were studied and optimised. The developed approach was successfully applied to the determination of trace amounts of aluminium in parenteral solutions without previous treatment. Under the optimum experimental conditions, 99.9% extraction was achieved for a preconcentration factor of 50. The limit of detection was 1.12 x 10(-7) mol(-1). The calibration plot was linear over at least two orders of magnitude of aluminium concentration. The developed coupled methodology, which thoroughly satisfies the typical requirements for pharmaceutical control processes, is appropriate for monitoring the aluminium concentration in parenteral nutrition.     

Determination of bromide ion in raw and drinking waters by capillary zone electrophoresis.

A new capillary zone electrophoretic method was developed for the determination of bromide ion in raw and drinking waters. An NaCl-based low-pH buffer caused a reduction of electroosmotic flow (EOF) in the buffer zone, whereas injected water sample resulted in higher EOF in the sample zone thus pumping out the neutral water plug. Sample stacking was used for the preconcentration. The method was applicable for waters from low to intermediate ionic strengths, i.e., the concentration of chloride should preferably be less than 40 mg/l. The method had a limit of detection of 15 micrograms/l at a signal-to-noise ratio of three (S/N = 3) and a limit of quantitation of 20 micrograms/l. CZE results obtained with real samples were compared with ion chromatography--inductively coupled mass spectrometric results.     

微波浓缩-离子法测定饮用水中的痕量溴酸根和高氯酸根

 建立了一种简便的用于浓缩水中痕量BrO3 -和ClO4 -的样品前处理方法。水样经OnGuardAg柱过滤 ,用微波炉在 15min内可浓缩 2 0倍 ,所测离子的回收率均高于 90 %。又采用IonPacAS16型亲水性柱 ,用 15 0 μL定量环 ,以NaOH为流动相、梯度淋洗方式 ,在 35min内测定了包括BrO3 -和ClO4 -在内的 8种离子。BrO3 -和ClO4 -的检测限分别为 0 10 μg/L和 0 2 0 μg/L。该方法在实际应用中有较大的参考价值。     

Immobilized DNA switches as electronic sensors for picomolar detection of plasma proteins

The sensing principle of a new class of DNA conformational switches (deoxyribosensors) is based on the incorporation of an aptamer as the receptor, whose altered conformation upon analyte binding switches on the conductivity of an adjacent helical conduction path, leading to an increase in the measured electrical signal through the sensor. We report herein the rational design and biochemical testing of candidate deoxyribosensors for the detection and quantitation of a plasma protein, thrombin, followed by surface immobilization of the optimized sensor and its electrochemical testing in both a near-physiological buffer solution and in diluted blood serum. The very high detection sensitivity (in the picomolar range) and specificity, as well as the adaptability of deoxyribosensors for the detection of diverse molecular analytes both small and macromolecular, make this novel sensing methodology an extremely promising one. Such synthetic and robust DNA-based electronic sensors should find broad application in the rapid, miniaturized, and automated on-chip detection of many biomedically relevant substances (such as metabolites, toxins, and disease and tumor markers) as well as of environmental contaminants.     

Simultaneous determination of trace oxyhalides and haloacetic acids using suppressed ion chromatography-electrospray mass spectrometry

A new analytical procedure for the simultaneous determination of trace oxyhalides and haloacetic acids (HAs) in drinking water and aqueous soil extracts is described. The method uses micro-bore ion chromatography (IC) coupled with suppressed conductivity (SC) and electrospray ionization mass spectrometric detection (ESI-MS). The IC-SC-ESI-MS system included a secondary flow of 100% MeOH, which was added to the column eluate (post-suppressor) and resulted in a significant increase in sensitivity for all analytes. All ESI-MS parameters were optimized for HA analysis and sensitivity quantitatively compared to suppressed conductivity. Full analytical performance characteristics for the developed method are presented for monochloro-, monobromo-, dichloro-, dibromo-, trichloro-, bromochloro, chlorodifluoro-, trifluoro-, dichlorobromo- and dibromochloroacetic acid, as well as the oxyhalides iodate, bromate, chlorate and perchlorate. In the case of the HAs, an optimised 25-fold SPE preconcentration method meant all analytes could be readily detected well below the USEPA 60 μg/L regulatory limit using conductivity and/or ESI-MS. The IC-ESI-MS method was applied to the determination of oxyhalides and HAs in both soil extracts and drinking water samples. Soil samples were extracted using ultra pure water with subsequent determination of perchlorate at 1.68 μg/g of soil. A drinking water sample containing HAs was preconcentrated using LiChrolut EN solid phase extraction cartridges with subsequent sulphate and chloride removal. Total HAs were determined at 13 μg/L.     

Preconcentration method for the determination of thorium in natural water by wavelength dispersive X-ray fluorescence spectrometry

The preconcentration of thorium from natural water and its determination directly by wavelength dispersive X-ray fluorescence spectrometry (WDXRF) were attempted. The first step consists of thorium preconcentration from slightly acid solutions on polyurethane foam (PUF) loaded with 2-etilhexylphosphonic acid (EHPA) reagent as solid phase. PUF held up to 50% (w/w) of the reagent and the preconcentration was maximum at the acidity of 0.25 mol^.l^-1 hydrochloric solution. Sorption on PUF had fast kinetics and 4.0 and 10 mg^.l^-1 detection and quantitation limits of thorium were achieved, respectively, as well as a R.S.D. of 4.2% at 21.7 mg^.l^-1. This method was successfully applied to natural water analyses. The results were in good agreement with reference values of water samples at 95% confidence level.     

The quantification of potassium using a quartz crystal microbalance

N,N'-dibenzyl-4,13-diaza-18-crown-6 (A) and bis[(benzo-15-crown-5)-4'-ylmethyl] pimelate (B) were tested as coatings for two piezoelectric crystals for potassium quantification. Both sensors showed stability, reversibility and sensitivity characteristics that allowed their use in quantitative analysis. However, compound A is much more sensitive to potassium than B. Compound A also shows a larger relative sensitivity for potassium with regard to sodium than B. A pharmaceutical sample of known composition was analysed both by an acoustic wave sensor with a crystal coated with compound A and by conductivity. No statistically significant difference in the median of the results was found (alpha = 0.05), although precision is superior for the conductivity methodology. Performance of the sensor in terms of frequency stability and selectivity was improved by the incorporation of PVC, a plasticizer and a lipophilic salt in the coating composition. Limits of detection found for potassium were 1.92 ppm, or 1.75 ppm for a crystal with a frequency decrease due to coating of 2.9 kHz or 3.9 kHz, respectively. Selectivity coefficients (fixed interference 80 ppm) for potassium over Na, Ca, Al, Zn, Mg, and Fe ranged from 0.103 to 0.332.     

Solid-phase extraction and sample stacking-capillary electrophoresis for the determination of quaternary ammonium herbicides in drinking water

Conditions for the simultaneous determination of paraquat, diquat and difenzoquat by capillary zone electrophoresis were established by combining two preconcentration procedures. Off-line solid-phase extraction was used for the isolation and preconcentration of quats in drinking water. Quats were then analysed by capillary electrophoresis using sample stacking with matrix removal as on-column preconcentration procedure. Two different porous graphitic carbon cartridges were compared. The breakthrough volumes of the three herbicides were calculated and the loading capacity of the sorbents was compared. Recoveries higher than 80% for difenzoquat and around 40% for paraquat and diquat were obtained when a sample volume of 250 ml was percolated. For the stacking-capillary electrophoresis analysis of quats, 50 mM acetic acid-ammonium acetate (pH 4.0), 0.8 mM cetyltrimethylammonium bromide with 5% (v/v) methanol as carrier electrolyte was used. Detection limits, based on a signal-to-noise ratio of 3:1, were lower than 0.3 microg l(-1) for standards in Milli-Q water, and lower than 2.2 microg l(-1) for drinking water samples. Run-to-run and day-to-day precision of the method were established. The two preconcentration procedures used together was successfully applied to the analysis of the three herbicides in spiked drinking water at concentrations below the maximum admissible US Environmental Protection Agency levels.     

Simultaneous determination of Cd(II), Cu(II) and Pb(II) in surface waters by solid phase extraction and flow injection analysis with spectrophotometric detection

A method for heavy metal monitoring using spectrophotometric detection is presented. Traces of Cu(II), Pb(II) and Cd(II) at the low microg l(-1) level can be determined simultaneously after both selective removal of metal interferences and preconcentration using 'extraction chromatographic resins'. Lewatit TP807'84, which contains di(2,4,4-trimethylpentyl)phosphinic acid as active component, was used as solid adsorbent. Two minicolumns containing this resin were used: one at pH 3.2 for the removal of interferences, such as Zn(II) and Fe(III), and the other at pH 5.5 for the selective preconcentration of the target analytes. Spectrophotometric determination used FIA methodology with sulfarsazene as chromogenic reagent and partial least-squares multivariate calibration. The method was successfully applied to the analysis of surface waters from the Llobregat river and ground water samples from wells in the Guadiamar basin. Accuracy, expressed in terms of recoveries, was in the range 80-120% and relative standard deviations were below 10%.     

Use of cloud point extraction methodology for the determination of PAHs priority pollutants in water samples by high-performance liquid chromatography with fluorescence detection and wavelength programming

The cloud point extraction methodology has been used to develop a new procedure for the preconcentration of polycyclic aromatic hydrocarbons in water samples (bottled and network supply). Triton X-114 was used as extractant agent. The procedure, consisting of three steps (preconcentration into the surfactant, clean-up and concentration of the eluate), allows good detection limits to be reached (from nanograms per liter to even sub-nanograms per liter in some cases). Determination was carried out by HPLC, with fluorimetric detection and wavelength programming.     

Voltammetric Determination of 5‐Aminoquinoline at Carbon Film Electrode and Carbon and Gold Screen Printed Electrodes – A Comparative Study

Aminoquinolines are widely used as antimalarial drugs and thus there is an ever increasing demand for their determination. In this paper, non‐traditional carbon film electrode developed in our laboratory (CFE) with easily replaceable carbon film was used for the determination of 5‐aminoquinoline (5‐AQ) and compared with well‐established commercially available carbon screen printed electrode (CSPE) and gold screen printed electrode (AuSPE). Electrochemical behavior of 5‐AQ was characterized by cyclic and differential pulse voltammetry. Differences in electrochemical behavior of 5‐AQ at different electrodes were evaluated. Determination of 5‐AQ was carried out by differential pulse, square wave, and direct current voltammetry. Practical applicability of the method was verified by direct determination of 5‐AQ in model samples of drinking and river water. Achieved limits of quantitation were in submicromolar concentrations. It was found out that novel CFE in terms of overall performance is in most aspects superior to routinely used commercially available CSPE and AuSPE.     

Surface acoustic wave sensor system applied to the kinetic study of urease in plant seeds

A new type of the surface acoustic wave (SAW) sensor system was delivered. Ure-ase from several kinds of plant seeds was extracted with different extracting solvents. The urease activity, Michaelis constant and other kinetic parameters were estimated for the first time by means of the new device-SAW sensor system. Some factors such as pH, temperature, activators and inhibitors are also discussed. The method can be applied to the determination of urea content in human urine and the experimental results consist with those reported.     

The use of silica-immobilized brown alga (Pilayella littoralis) for metal preconcentration and determination by inductively coupled plasma optical emission spectrometry

The brown alga Pilayella littoralis was used as a new biosorbent in an on-line metal preconcentration procedure in a flow-injection system. Al, Co, Cu and Fe were determined in lake water samples by inductively coupled plasma optical emission spectrometry (ICP-OES) after preconcentration in a silica-immobilized alga column. Like other algae, P. littoralis exhibited strong affinity for these metals proving to be an effective accumulation medium. Metals were bound at pH 5.5 and were displaced at pH<2 with diluted HCl. The enrichment factors for Cu^II, Fe^III, Al^III and Co^II were 13, 7, 16 and 11, respectively. Metal sorption efficiency ranged from 86 to 90%. The method accuracy was assessed by using drinking water certified reference material and graphite furnace atomic absorption spectrometry (GFAAS) as a comparison technique. The column procedure allowed a less time consuming, easy regeneration of the biomaterial and rigidity of the alga provided by its immobilization on silica gel.     

Linear Scan Stripping Voltammetry at Glassy-Carbon Based Thin Mercury Film Electrodes for Determination of Trace Aluminium in Dialysis Fluids.

Abstract

Linear scan cathodic stripping voltammetry at glassy-carbon based thin mercury film electrodes is a simple and inexpensive alternative for determining trace Al(III) in dialysis fluids.

The efficiency of a variety of ligands (SVRS, Cupferron and Blue Black Eriochrome R) was evaluated comparing their voltamperometric response by application of a linear scan mode, after preconcentration into the mercury film electrode as Al(III) complexes.

The best results were obtained when Cupferron was used as ligand, since its stripping current compares favourably in terms of sensitivity and resolution. The sharply defined cathodic peak at -1.3 V, corresponding to the reduction of the interfacial accumulated complex, could be used for quantitation. The response is linear up to 50 μg/l; correlation coefficient, 0.995. The relative standard deviation (at 20 μg/l level) is 3.5%, a detection limit of 0.5μg/l was estimated from the signal to noise characteristics of the response for 5 μg/l, which compares favourably among the reported electroanalytical methods for aluminium.

We calibrated the method under conditions of use estimating the trace aluminium exposure in patients undergoing dialytic treatment.     

Polyethylene powder as an absorbent for preconcentration of aluminium, beryllium and thallium

Polyethylene powder has been shown to function effectively as an adsorbent for the preconcentration of complexing agents and their metal complexes. The adsorbed trace compound can easily be eluted from the polyethylene by use of polar organic solvents and subsequently be determined by AAS or spectrophotometry. In this paper, the adsorptivity of chrome azurol S and rhodamine B and their complexes with aluminium, beryllium and thallium (as [Tl Br₄]^–) on polyethylene was investigated. The influence of the pH and the effect of the saline concentration of the solution were studied. From the preconcentration of aluminium and beryllium with chrome azurol S, enrichment factors up to 10 and 20, respectively, could be achieved. For thallium with rhodamine B the factor was 50. With this analytical procedure, recoveries of 92–110%, 94–103% and 96–104% with relative standard deviations of 3.4–5.4%, 2.6–5.3 and 1.6–7.2% for aluminium, beryllium and thallium respectively, were achieved. The method was used for the preconcentration of trace amounts of the metals from tap water, dialysis solutions and solid salts.     

Fluorimetric determination of aluminium in water by sequential injection through column extraction

A fluorimetric procedure for the determination of aluminium with matrix removal in drinking water is proposed. The system is based both on the solid phase extraction of aluminium on a new chelating resin (XAD-4 modified by grafting salicylic acid) and the fluorimetric detection of a complex formed between 8-hydroxyquinoline-5-sulfonic acid (HQS) and Al(III), after elution of the resin by hydrochloric acid. The sorption and elution of aluminium were studied in both competitive and non-competitive conditions, varying pH, flow-rates, volume and concentration of reagents, as well as time contact. The optimised procedure allows determination of Al³⁺ at the sub-ppb level (LOD: 0.2 g L^–1 for 1 ml of sample) within a working range of 0.2–500 g L^–1. The analytical procedure was successfully employed for the determination of aluminium in drinking water during and after flocculation/coagulation treatment processes.     

Simultaneous detection of cadmium, copper, and lead using a carbon paste electrode modified with carbamoylphosphonic acid self-assembled monolayer on mesoporous silica (SAMMS)

A new sensor was developed for simultaneous detection of cadmium (Cd²⁺), copper (Cu²⁺), and lead (Pb²⁺), based on the voltammetric response at a carbon paste electrode modified with carbamoylphosphonic acid (acetamide phosphonic acid) self-assembled monolayer (SAM) on mesoporous silica (Ac-Phos SAMMS). The adsorptive stripping voltammetry (AdSV) technique involves preconcentration of the metal ions onto Ac-Phos SAMMS under an open circuit, then electrolysis of the preconcentrated species, followed by a square wave potential sweep towards positive values. Factors affecting the preconcentration process were investigated. The voltammetric responses increased linearly with the preconcentration time from 1 to 30 min or with metal ion concentrations ranging from 10 to 200 ppb. The responses also evolved in the same fashion as adsorption isotherm in the pH range of 2-6. The metal detection limits were 10 ppb after 2 min preconcentration and improved to 0.5 ppb after 20 min preconcentration.     

Column-switching linked to large sample volumes to preconcentrate β-blockers at trace levels in environmental water

This paper describes about an automated on-line enrichment method for the simultaneous determination of seven β-blockers in river water using a short liquid chromatography column for preconcentration coupled with LC-DAD. The method performs the preconcentration of 30 mL of river water samples (5% organic modifier) using a 50 mm × 4.6 mm C18 column for enrichment and a 150 mm × 4.6 mm C18 column for separation, allowing the determination of β-blockers at trace levels in river water. The analytical procedure was developed by optimizing the breakthrough parameters (flow rate, time of preconcentration and percentage of organic modifier added to the sample) in order to achieve the maximum sensitivity, and by optimizing the mobile phase (composition and flow rate) to get adequate separation of the components in a reasonable analysis time. Under the optimized conditions, the method was validated with respect to linearity, precision, limits of detection, limits of quantification and accuracy. Detection and quantitation limits ranged between 0.1 and 3.1 and between 1.0 and 5.0 ng mL⁻¹, respectively, whereas the RSD on inter-day precision was below 8%.To cope with the matrix effect in the determination of these drugs in river water samples, the standard addition methodology was successfully applied. Recoveries ranging from 81 to 115% proved the accuracy of the methodology proposed in this work.