Analysis Of Natural Water Samples Research Articles

The use of a polymer inclusion membrane for separation and preconcentration of orthophosphate in flow analysis

A highly sensitive flow analysis system has been developed for the trace determination of reactive phosphate in natural waters, which uses a polymer inclusion membrane (PIM) with Aliquat 336 as the carrier for on-line analyte separation and preconcentration. The system operates under flow injection (FI) and continuous flow (CF) conditions. Under optimal FI conditions the system is characterised by a linear concentration range between 0.5 and 1000μgL−1P, a sampling rate of 10h−1, a limit of detection of 0.5μgL−1P and RSDs of 3.2% (n=10, 100μgL−1) and 7.7% (n=10, 10μgL−1). Under CF conditions with 10min stop-flow time and sample solution flow rate of 1.32mLmin−1 the flow system offers a limit of detection of 0.04μgL−1P, a sampling rate of 5h−1 and an RSD of 3.4% (n=5, 2.0μgL−1). Interference studies revealed that anions commonly found in natural waters did not interfere when in excess of at least one order of magnitude. The flow system, operating under CF conditions, was successfully applied to the analysis of natural water samples containing concentrations of phosphate in the low μgL−1P range, using the multipoint standard addition method.

Multi-residue method for the determination of 16 recently used pesticides from various chemical groups in aqueous samples by using DI-SPME coupled with GC–MS

A simple and solvent-free multi-residue method has been optimized to determine 16 currently used pesticides from different chemical groups in aqueous samples. The extraction of analytes was carried out with direct immersion solid-phase microextraction (DI-SPME) and for the identification and quantitative determination gas chromatography coupled with mass spectrometry (GC–MS) was applied. Two commonly used adsorbent coatings have been applied and compared: 100μm of polydimethylsiloxane (PDMS) and 85μm of polyacrylate (PA). The method development parameters of DI-SPME, analyte desorption and GC–MS analysis have been outlined along with the final experimental conditions. When the optimum extraction conditions were applied (extraction time 60min, 10% (w/v) NaCl solution, 45°C) the limits of detection (LODs) were in the range of 0.015–0.13μgL−1 and the relative standard deviations (RSDs) were between 1.9 and 9.6%. The developed analytical method was successfully applied to the analysis of natural water samples from the following sources: river, sea, canal and rain.

A novel extractant-impregnated resin containing carminic acid for selective separation and pre-concentration of uranium(VI) and thorium(IV)

The present work proposes the use of a novel extractant-impregnated resin (EIR) as an adsorbent in trace separation and pre-concentration of U(VI) and Th(IV) ions. The new EIR was prepared by impregnating carminic acid onto Amberlite XAD-16 resin beads. The morphology of new EIR was studied by BET surface area measurements and SEM micrographs. A column packed with CA/XAD-16 was used for selective separation and pre-concentration of the metal ions. Maximum adsorption of Th(IV) and U(VI) ions occurred at pHs of 3.50–5.75 and 3.75–6.50, respectively. The adsorbed metals could be eluted sequentially using 0.55 mol L−1 HCl for U(VI) and 2.25 mol L−1 HCl for Th(IV). The dynamic capacity of EIR was found to be 0.832 and 0.814 mmol g−1 for Th(IV) and U(VI), respectively. The tolerance limit of some foreign ions was also studied. The proposed method showed a good performance in analyzing geological reference materials and a synthetic seawater sample. Furthermore, the above procedure was successfully employed for the analysis of natural water samples.

Separation and Preconcentration of Trace Amounts of Manganese and Nickel from Natural Water Samples by a Diimine Derivative Schiff Base-Coated Silica-Gel Minicolumn

An efficient method for preconcentration of trace amounts of Mn (II) and Ni (II) ions by using a minicolumn (10 mm × 30 mm i.d.) filled with a diimine derivative Schiff base on silica-gel has been reported. The retained analytes on the column were recovered with 5 mL of mixture of nitric acid 5 mol L−1and methanol (1 : 1) and were determined by a flame atomic absorption spectrometer. Different factors including pH of sample solution, sample volume, amount of sorbent, eluent volume, and interference of other ions have been studied and the optimized conditions developed were utilized for the trace determination of Mn (II) and Ni (II) in natural water samples. The recoveries for the analytes under the optimum working conditions were higher than 98%. The relative standard deviations of the determinations (10 replicate analyses) at 25 μg L−1of Mn (II) and Ni (II) were 2.5% and 2.3%, respectively. The limit of the detection (3s,n=10)for analytes were found to be 0.20 μg L−1for Mn (II) and 0.15 μg L−1for Ni (II). The proposed method was applied to the analysis of natural water samples with satisfactory results.

Study of silica-manganese oxide hybrid material as a new solid phase for on-line continuous flow enrichment of Cd(II) ions coupled to flame atomic absorption spectrometry

The main purpose of the present work is to synthesize and characterize a new sorbent material, which contains manganese oxide particles finely dispersed in a silica matrix, and evaluate its ability to improve the detectability of flame atomic absorption spectrometry (FAAS) for on-line determination of trace Cd(II) in aqueous and biological samples. The surface area, pore volume and micropore size of the sorbent were found to be 232m2g−1, 0.0303cm3g−1 and 1.7nm, respectively. To accomplish the on-line sorbent preconcentration, 20.0mL of a pH 9.0 Cd(II) solution at a flow rate of 10.0mLmin−1 were preconcentrated onto 320mg of the SiO2/MnOx material packed into a mini-column and then eluted with 1.0molL−1 HNO3 toward the FAAS detector. The following analytical features were obtained: linear responses to Cd(II) ions in the range of 1.0–50.0μgL−1 (r=0.9968), detection limit of 0.20μgL−1, preconcentration factor of 39.4, concentration efficiency of 19.7min−1, consumptive index of 0.51mL, and analytical frequency of 20h−1. The dispersion of manganese oxide in the SiO2 matrix promoted a 2.15-fold improvement on detectability of Cd(II) ions in comparison with an analytical curve built with SiO2 as sorbent. The accuracy of the preconcentration method was verified through the analysis of natural water samples employing addition/recovery tests and GF AAS as reference technique, and analysis of certified reference materials — Lobster Hepatopancreas (TORT-2) and NIST SRM 1643e (“Trace elements in natural waters”).

Determination of Total Phosphorus and Nitrogen in Water by Ion Chromatography

An ion chromatography combined with ultraviolet-ozone oxidation procedure was proposed for detecting total phosphorus(TP) and total nitrogen(TN) simultaneously in water samples.The mixed solution of Na2CO3/NaHCO3 was used as eluent,and the samples were injected with 1 mL large volume loop directly.Under the optimal conditions,TP concentration displays linear relationship in the range of 0.05-5.00 mg/L and TN concentration in the range of 0.10-10.00 mg/L.The correlation coefficient of curve was 0.9999 and 0.9998 respectively.The detection limit of TP was 3.60 μg/L and that of TN was 4.57 μg/L.The relative standard deviations(RSD) of TP and TN were less than 4.9 and 4.1% respectively.The standard addition recoveries of TP were from 95.0% to 105.0%,and those of TN were from 93.0% to103.0%.The relative error for the analysis of natural water samples to the standard were less than 4.2%.The method proposed has good selectivity and high sensitivity,as well as precision.The determination results agree well with those obtained by the National standard method.

Chemical analysis of sulfur species in geothermal waters

Analytical methods have been developed to determine sulfur species concentrations in natural geothermal waters using Reagent-Free™ Ion Chromatography (RF™-IC), titrations and spectrophotometry. The sulfur species include SO42−, S2O32−, and ∑S2− with additional determination of SO32− and SxO62− that remains somewhat semiquantitative. The observed workable limits of detections were ≤0.5μM depending on sample matrix and the analytical detection limits were 0.1μM. Due to changes in sulfur species concentrations upon storage, on-site analyses of natural water samples were preferred. Alternatively, the samples may be stabilized on resin for later elution and analysis in the laboratory. The analytical method further allowed simultaneous determination of other anions including F−, Cl−, dissolved inorganic carbon (DIC) and NO3− without sample preservation or stabilization. The power of the newly developed methods relies in routine analysis of sulfur speciation of importance in natural waters using techniques and facilities available in most laboratories doing water sample analysis. The new methods were successfully applied for the determination of sulfur species concentrations in samples of natural and synthetic waters.

High Sensitivity Arsenic Analyzer Based on Liquid-reagent-free Hydride Generation and Chemiluminescence Detection for On-site Water Analysis

In this work, a portable and reliable instrument based on manual hydride generation and subsequent ozone induced chemiluminescence analysis was developed and optimized for measurement of aqueous arsenic in drinking water. The aim was to develop a system for use in the field in villages in developing countries where water treatment systems have been installed. Consequently, it is beneficial that the system could be operated without reagent solutions or purified water. Arsenic trihydride (arsine) was generated by reaction with solid acid and solid borohydride, and then introduced to a chemiluminescence cell where the arsine was mixed with ozone to generate chemiluminescence. The measurement could be repeated with the throughput of 60 times h(-1), and the limit of detection was 0.4 µg L(-1). The measurable arsenic concentration was up to 1 mg L(-1) for 2 mL samples. The system was evaluated for analysis of natural water samples, and the obtained data agreed well with those from ICP-MS and sequential hydride generation flow analysis. We expect this small and inexpensive instrument will be used in developing countries.

Comparison of sorption behavior of Th(IV) and U(VI) on modified impregnated resin containing quinizarin with that conventional prepared impregnated resin

This paper reports the results obtained by studying the ion-exchange properties of a new solvent impregnated resin (SIR), which was prepared by impregnation of quinizarin (1,4-dihydroxyanthraquinone, QNZ) on Amberlite XAD-16 after nitration of the benzene rings present in its structure. The sorption behavior of Th(IV) and U(VI) on/in the modified SIR was compared with that of the SIR prepared via the conventional method. It was observed that sorption capacity and sorption rate of the modified SIR are significantly greater than the conventional one. The modified SIR was then applied to the extraction of Th(IV) and U(VI) ions at the presence of many co-existence metal ions. The results obtained denote on successful application of this new SIR to analysis of natural water samples spiked to Th(IV) and U(VI) ions.

Sequential injection determination of orthophosphate as ion associate of 12-molybdophosphate with Astra Phloxine

A simple and fast reaction between 12-molybdophosphate heteropoly anion and the polymethine dye Astra Phloxine was used for the development of a new SIA method for the determination of orthophosphate. The suggested method has higher sensitivity and a broader calibration range than existing SIA methods. It can be used to detect phosphate in the range from 0.2 to 10μmolL−1 with a detection limit of 0.1μmolL−1 and an acceptable throughput of 20 samples h−1. The comparably low molybdate (5.6mmolL−1) and dye (0.1mmolL−1) concentrations led to an improvement in the stability of the base line. Inter-day reproducibility was better than 5%, while the intra-day RSD was in the range 0.8–3.5%. The method was used for the analysis of natural water samples and phosphorus-containing chemicals having a low content of orthophosphate.

Selective extraction of Th(IV) over U(VI) and other co-existing ions using eosin B-impregnated Amberlite IRA-410 resin beads

A new chelating polymeric sorbent as an extractant impregnated resin (EIR) has been developed using eosin B and Amberlite IRA-410 resin. The impregnation process was characterized by FT-IR spectroscopy. The eosin B-impregnated resin showed superior binding affinity for Th(IV) over U(VI) and many co-existing ions. The influence of various physicochemical parameters on the recovery of Th(IV) were optimized by both static and dynamic methods. The Langmuir adsorption isotherm gave a satisfactory fit of the equilibrium data. The kinetic studies performed for Th(IV) sorption revealed that <20 min was sufficient for reaching equilibrium metal ion sorption. A preconcentration factor of 100 was found for the column-mode extraction. The accuracy of the developed method in conjunction with Arsenazo III procedure was tested by analyzing geological reference materials and seawater sample, which are prepared, synthetically. Furthermore, the above procedure has been successfully employed for the analysis of natural water samples.

Automatic sequential injection liquid–liquid micro-extraction system for on-line flame atomic absorption spectrometric determination of trace metal in water samples

An automatic sequential injection (SI) liquid–liquid micro-extraction system incorporating a dual-conical micro-gravitational phase separator is proposed as versatile approach for on-line metal preconcentration and/or separation. Coupled to flame atomic absorption spectrometry (FAAS) the potentials of this novel schema are demonstrated for lead determination in water samples at the μg l −1 level. The non-charged lead complex with ammonium pyrrolidine dithiocarbamate (APDC) was extracted on-line into 300 μl isobutyl methyl ketone (IBMK) through the extraction coil. The organic phase containing the extracted metal complex is collected in the upper cavity of the phase separator and then forwarded to the nebulizer. All the critical parameters were optimized and offered good performance characteristics and high preconcentration ratios. A sample consumption of 10.5 ml enabled the determination of Pb(II) in the range of 3.0–250.0 μg l −1 with an enhancement factor of 120 and a sampling frequency of 25 h −1. The detection limit and the precision were 1.4 μg l −1 and 2.9% (at 50.0 μg l −1 concentration level), respectively. The proposed method was evaluated by analyzing certified reference material and was applied successfully to the analysis of natural water samples.

Rapid quantification of humic and fulvic acids by HPLC in natural waters

A simple method based on high-performance size-exclusion chromatography (HPSEC) has been developed for rapid quantification of humic and fulvic acids (HA and FA) in stream waters. A Tsk-gel column was used to separate natural dissolved organic matter (DOM) into two components: peak A and B. In terms of HPSEC chromatograms and fluorescence patterns, peak A and B were similar to the corresponding XAD-extracted HA and FA, respectively. It is suggested that peak A fraction mainly consisted of HA, and peak B fraction FA. The similar separation of HA and FA using HPSEC and a conventional XAD method suggests the consistency of molecular size distribution and physical–chemical properties of DOM. HPSEC offers a simple and rapid method for the quantification of HA and FA instead of tedious extractions of humic substances. Analyses of natural water samples show that the calculation of HA/FA based on UV absorbance was under- or over-estimated, the calibration using the extracted HS allows a more accurate quantification. The fast screening of HA and FA provides useful quantitative and qualitative information that can be used in environmental or monitoring studies.

Iron speciation by solid phase extraction and flame atomic absorption spectrometry using N,N′-bis-(2-hydroxy-5-bromobenzyl)-2-hydroxy-1,3-diiminopropane

A new Schiff base, N,N′-bis-(2-hydroxy-5-bromobenzyl)-2-hydroxy-1,3-diiminopropane, has been synthesized for the very sensitive determination of iron(III) and iron(II) in natural water samples. It enabled a very selective and rapid method for iron determination to be developed. The method has also been applied to total iron determination in sediment samples. In the preconcentration system, the Schiff base reagent is mixed with the samples and chelates containing iron(III). The complexes are then adsorbed on silica gel within a column system. Elution of the adsorbed chelate from the silica gel was performed with a small volume of acetone containing 2.5% nitric acid. The iron is measured off-line by flame atomic absorption spectrometry. The method can be applied to the preconcentration, separation and speciation of iron. The effects of parameters such as pH, sample flow rate, eluent flow rate, foreign ions and ligand concentration have been investigated. The effect of humic acid that can produce complexes with metal ions in natural systems has also been investigated. The results obtained indicate that the method is not affected by the presence of up to 10 ppm humic acid, which would be a very high concentration to be present in natural systems. The solid phase extraction method developed has been applied to the determination of iron in both natural water samples and sediment samples. The LOD was found to be 0.17 mg L−1 when no preconcentration was used, although preconcentration factors of 100 could be achieved. The recovery values for spiked samples were between 100 and 104%. The results were compared statistically with those from the standard 1,10 phenanthroline method used for iron speciation in water systems. A Student’s t-test indicated no significant difference between the two methods. In addition, this method was applied to the analysis of a certified sediment sample, LGC 6156. Generally, a 10-fold preconcentration factor was required for the analysis of natural water samples.

Determination of Copper at a Glassy Carbon Electrode Modified with Langmuir–Blodgett Film of p‐tert‐Butylthiacalix[4]arene

AbstractA new type of voltammetric sensor, Langmuir–Blodgett film of p‐tert‐butylthiacalix[4]arene modified glassy carbon electrode, was advanced and used for determining copper at trace levels by differential pulse stripping voltammetry. Calibration plot was found to be linear in the range of 2×10−8 M to 5×10−6 M; the detection limit was 2×10−9 M. Possible recognition mechanism was also discussed. From determination of Copper in real samples (river, lake and tap water) it can be concluded that the method is rapid, sensitive in determining of copper and can be used in the analysis of natural water samples.

Study of Factors Affecting the Performance of Voltammetric Copper Sensors Based on Gly‐Gly‐His Modified Glassy Carbon and Gold Electrodes

AbstractThis paper reports a study of the factors affecting the analytical performance of gold and glassy carbon electrodes modified with the tripeptide Gly‐Gly‐His for the detection of copper ions. Gly‐Gly‐His is attached to a glassy carbon (GC) surface modified with 4‐carboxyphenyl moieties or a gold surface modified with 3‐mercaptopropionic acid by the reaction of the N‐terminal amine group of the peptide with the carboxylic acid groups of the monolayer via carbodiimide activation. X‐ray photoelectron spectroscopy was used to characterize the steps in the biosensor fabrication. It was found that the analytical performance of a sensor prepared with Gly‐Gly‐His on a GC electrode was similar to that on a gold electrode under the same conditions. The performance was greatly enhanced at higher temperature, no added salt during copper accumulation and longer accumulation time within a pH range of 7–9. Interference studies and investigations of stability of the Gly‐Gly‐His sensor are reported. Analysis of natural water samples show that the sensors measure only copper ions that can complex at the sensor surface. Strongly complexed copper in natural water is not measured. Despite greater stability of diazonium salt derived monolayers on carbon surfaces compared with alkanethiols self‐assembled monolayers on gold, the stability of the sensors was essentially the same regardless of the modification procedure.

Simultaneous determination of lead and cadmium at a glassy carbon electrode modified with Langmuir–Blodgett film of p- tert-butylthiacalix[4]arene

A glassy carbon electrode (GCE) modified with a Langmuir–Blodgett (LB) film of p- tert-butylthiacalix[4]arene (TCA) has been investigated as a disposable sensor for measuring the trace levels of lead and cadmium. The possibility of determining lead and cadmium at trace levels was examined with differential pulse stripping voltammetry in the measurement step. The electrochemical response was characterized with respect to supporting electrolyte, pH of solution, accumulation time, accumulation potential, layers of the LB films, and possible interferences. Calibration plots were found to be linear in the range 2 × 10 −7 to 5 × 10 −5 mol l −1 (Cd 2+) and 1 × 10 −7 to 2.5 × 10 −5 mol l −1 (Pb 2+); the detection limits were 2 × 10 −8 mol l −1 (Cd 2+) and 8 × 10 −9 mol l −1 (Pb 2+). Possible recognition mechanism was also discussed. From the analysis of real samples (river, lake and tap water) it can be concluded that the method is sensitive and reproducible in determining of these elements and can be used in the analysis of natural water samples.

Electroanalytical method for determination of the pesticide dichlorvos using gold-disk microelectrodes

This paper reports the use of laboratory-prepared gold microelectrodes and square-wave voltammetry for analytical determination of low concentrations of the pesticide dichlorvos in pure and natural water samples. After optimization of the experimental and voltammetric conditions, the best voltammetric responses-current intensity and voltammetric profile-were obtained in 0.1 mol L(-1) NaClO4 with f=100 s(-1), a=50 mV, and DeltaE(s)=2 mV. The observed detection and quantification limits in pure water were 7.8 and 26.0 microg L(-1), respectively. The reproducibility and repeatability of the method were also determined; the results were 1.4% (n=5) and 1.2% (n=10), respectively. Possible interfering effects were evaluated in natural water samples collected at different points with different levels of contamination from agricultural, domestic, or industrial waste from an urban stream. Results showed that the detection and quantification limits increased as a function of the quantity of organic matter present in the samples. Nonetheless, the values observed for these method characteristics were below the maximum value allowed by the Brazilian code for organophosphorus pesticides in water samples. Recovery curves constructed using the standard addition method were shown to be satisfactory compared with those obtained from high-performance liquid chromatography, confirming the suitability of the method for analysis of natural water samples. Finally, when the method was used to determine dichlorvos in spiked cows' milk samples, satisfactory recovery and relative standard deviations were obtained.

Determination of Cr(VI) by Catalytic Adsorptive Stripping Voltammetry with Application of Nitrilotriacetic Acid as a Masking Agent

AbstractA selective and sensitive method for determination of traces of Cr(VI) in the presence of a large excess of Cr(III) by differential pulse catalytic adsorptive stripping voltammetry is presented. For minimization of Cr(III) interference nitrilotriacetic acid was used as a masking agent. The determinations were performed in a flow system. The calibration plot was linear from 1×10−10 to 1×10−8 mol L−1 for accumulation time 60 s. The relative standard deviation for 3×10−9 mol L−1 Cr(VI) was 4.1% (n=5). The detection limit for an accumulation time of 60 s was 4×10−11 mol L−1. The influence of common foreign ions is also presented. The performance of the method was verified by analysis of certified reference material for Cr(VI) and comparing the results of analyses of natural water samples with those obtained by another accepted electrochemical method.

Solid Phase Spectrophotometric Determination of Traces of Arsenate and Phosphate in Water Using Polyurethane Foam Sorbent

A simple and sensitive method for the determination of arsenate and phosphate in the µg L−1 concentration range using solid phase spectrophotometry has been developed. The method utilizes the quantitative sorption of the heteropoly blue species of arsenomolybdic and phosphomolybdic acids by polyurethane foam (PUF) sorbent prior to direct spectrophotometric measurement of the solid phase. In the same time the difference in formation behavior between the arsenomolybdic and phosphomolybdic acids at different pH values of sample solution has allowed their determination in the presence of each other. A preconcentration factor of 150 has been achieved for 100 mL samples. The detection limits are 5.4 and 1.66 µg L−1 for arsenate/As and phosphate/P, respectively and the working analytical ranges are from 5.4–54 µg L−1 and 1.6–40 µg L−1 respectively. The different experimental parameters such as rate of color development, acidity of solution and the analyte concentration have been thoroughly investigated. Analysis of natural water samples has been performed.