Species In Water Samples Research Articles

Sensitive Mercury Speciation Analysis in Water by High-Performance Liquid Chromatography-Atomic Fluorescence Spectrometry Coupling with Solid-Phase Extraction.

An efficient method based on high-performance liquid chromatography coupled with atomic fluorescence spectrometry (HPLC-AFS) was successfully developed for the simultaneous determination of four mercury species including Hg2+, methylmercury (MeHg), ethylmercury (EtHg), and phenylmercury (PhHg) in water. Samples were enriched and cleaned up with a solid-phase extraction (SPE) pretreatment using a thiol cartridge. Some key parameters including the selection of a SPE cartridge, eluent type, eluent volume, and interference factors were systematically investigated. Chromatographic separation was achieved on a C18 column using a mobile phase consisting of methanol and 60 mmol L-1 ammonium acetate with 10 mmol L-1 L-cysteine by gradient elution. Under the optimized conditions, good linearity (r ≥ 0.9991) was observed between 0.20 to 10.0 μg L-1. The limits of detection were in the range of 0.001 - 0.002 μg L-1. High recoveries (87.2 to 111%) and good reproducibility (1.1 - 6.5%) were obtained. Such a method is sensitive, selective and accurate, which can be applied to the quantification of mercury species in water samples.

Fabrication of Functional Groups-Rich Monolith for Magnetic Field-Assisted In-Tube Solid Phase Microextraction of Inorganic Selenium Species in Water Samples Followed by Online Chromatographic Determination

Efficient separation and enrichment is a crucial step in the analysis of Se(IV) and Se(VI). In the present study, for the first time, online monolith-based magnetic field-assisted in-tube solid phase microextraction (MFA/IT-SPME) was applied to capture inorganic selenium species in water samples. In this connection, porous monolith mingled with magnetic nanoparticles was synthesized in silica capillary and employed as microextraction column (MEC) of MFA/IT-SPME. After that, a magnetic coil utilized to perform variable magnetic fields in adsorption and desorption steps was twined on the MEC. Se(IV) was coordinated with o -phenylenediamine to form coordination compound which was infused to the MEC to be captured. Results evidenced that application of magnetic field during extraction procedure assisted the capture of Se(IV)-OPA complex with the enhancement of extraction efficiency from 83% to 97%. Under the optimized conditions, MFA/IT-SPME was online combined with HPLC equipped with diode array detector (DAD) to perform quantification of Se(IV) and Se(VI) in environmental water samples. Total inorganic Se was quantified after pre-reduction of Se(VI) to Se(IV) prior to applying established approach, and subtraction method was adopted to calculate Se(VI) and Se(IV) contents. The limit of detection for Se(IV) was as low as 0.012 μg/L. Reliability of suggested method was investigated by assaying Se(IV) and Se(VI) species in real-life waters with satisfactory recoveries (81.1%-116%) and repeatability (RSDs below 9%).

Electrochemical analysis of nitrite contamination in water using SnTe@GO modified glassy carbon electrode

An electrochemically active tin telluride (SnTe) decorated graphene oxide (GO) (SnTe@GO) nanocomposite has been synthesized through simple experimental method and used the same for surface modification of glassy carbon electrode, thus developed a new efficient SnTe@GO/GCE which in turn has been demonstrated as a sensor for identification and quantification of nitrite species in water samples. Common analytical techniques are employed and established the physiochemical properties of SnTe@GO nanocomposite. The electrocatalytic activity of SnTe@GO/GCE has been examined towards sensing and quantification of nitrite through Cyclic Voltammetry and Differential Pulse Voltammetry techniques. The obtained results revel that SnTe@GO/GCE exhibited high sensitivity with wide linear range such as 9.8-162 mM and detection limit found to be 0.079 µM. In addition, in order to inspect the real time application of SnTe@GO/GCE, it is also employed and determined the concentration of nitrite in drinking water, pond water and well water samples which are collected from Rayapuram, Muttukadu and Guindy during the specific period. The LOD observed for drinking water collected from Rayapuram, Chennai are 1.63 μM, pond water collected from Muttukadu, Kanchipuram 2.5 μM, and the well water collected from Guindy, Chennai are 1.25 μM, and thus proves that the newly designed SnTe@GO/GCE is an excellent sensor for nitrite species even in real water sample analysis.

Ultrasound-assisted dispersive micro-solid phase extraction using molybdenum disulfide supported on reduced graphene oxide for energy dispersive X-ray fluorescence spectrometric determination of chromium species in water

Molybdenum disulfide (MoS2) was supported on graphene oxide (GO) by hydrothermal method. The resulting nanocomposite (MoS2-rGO) was characterized by X-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy. The experiments show that at pH 2, MoS2-rGO has a great affinity for adsorption of hexavalent chromium ions while Cr(III) ions remain in aqueous sample. In the adsorption process, the dominant role plays chemisorption. The determined adsorption capacity is 583.5 mg g−1. Parameters affecting the extraction process, namely sample pH, sample volume, contact time, and matrix ions, were investigated by sequential batch tests. Under optimal conditions (pH 2, sample volume 50 mL, sonication time 10 min, adsorbent mass 1 mg), the calibration curve covers the 1–200 ng mL−1 range with a correlation coefficient (R2) of 0.998. The recovery of the method is 97 ± 3%. Other data of merit include a relative standard deviation of < 3.5%, enrichment factor of 3350, and detection limit of 0.050 ng mL−1. The accuracy of the method was confirmed by analysis of the reference materials QC1453 (chromium VI in drinking water) and QC3015 (chromium VI in seawater). The method was successfully applied to chromium speciation in water samples, including high salinity ones. The concentration of Cr(III) was calculated as the difference between the total concentration of chromium (after oxidation of Cr(III) to Cr(VI) with potassium permanganate) and the initial Cr(VI) content.Graphical abstractSchematic presentation of a method for determination of chromium species by energy dispersive X-ray fluorescence spectrometry after preconcentration on molybdenum disulfide supported on reduced graphene oxide.

Selective collection of long fragments of environmental DNA using larger pore size filter

Environmental DNA (eDNA) can exist in water with various sizes and states. Among them, relative to extra-cellular DNA, intra-cellular DNA such as cell and tissue fragments can mainly be detected at larger size fractions, and may be protected from enzymatic DNA degradation processes. Here, we verified the hypothesis that the selective collection of such large-sized eDNA enhances the efficiency of capturing less-degraded eDNA, based on a tank experiment using Japanese Jack Mackerel (Trachurus japonicus) as a model species. We concentrated different volumes of rearing water using the filters with different pore sizes (0.7 μm and 2.7 μm), and quantified the copy number of short and long mitochondrial and short nuclear DNA fragments of target species in water samples. As a result, the ratio of long to short eDNA concentrations was higher in the larger pore size filter, which would support our stated hypothesis. In addition, the ratio of nuclear to mitochondrial eDNA was lower in the larger pore size filter. These results imply a difference in the persistence of nuclear and mitochondrial DNA between intra- and extra-cellular environments. Moreover, larger filter pore size did not necessarily decrease the yields of eDNA, and there was little difference in yields in smaller filtration volumes. The findings of this study indicate the potential to select information from eDNA signals by focusing on eDNA of specific size and state, which may contribute to efficient utilization of the information on species taxonomy and physiology in water samples.

Hollow fiber liquid phase microextraction combined with total reflection X-ray fluorescence spectrometry for the determination of trace level inorganic arsenic species in waters

In the present study, we investigated the possibilities and drawbacks of hollow fiber liquid phase microextraction (HF-LPME) combined with total reflection X-ray fluorescence (TXRF) spectrometry for the determination of low amounts of inorganic arsenic (As) species in water samples. The obtained results showed that a three-phase HF-LPME system was more suitable to be used in combination with TXRF than the two phase configuration, since lower detection limit and better precision for As determination can be attained. Relevant experimental parameters affecting As extraction (i.e. types of extractant, organic solvent, agitation speed, pH and extraction time) and TXRF analysis (deposition volume and drying mode) were systematically evaluated. It was found that As(III) was more efficiently extracted at pH 13, whereas, optimum pH for As(V) extraction was at pH 8.5. Limits of detection (LOD) achieved using the best analytical conditions meet the requirements of current legislation and allow the determination of inorganic As(V) and As(III) in water. The proposed method was also applied to different spiked environmental water samples for the preconcentration and subsequent determination of trace inorganic As species.

Ultrasonic-assisted Supramolecular Solvent Liquid-liquid Microextraction for Inorganic Chromium Speciation in Water Samples and Determination by UV-Vis Spectrophotometry

Ultrasonic-assisted Supramolecular Solvent Liquid-liquid Microextraction for Inorganic Chromium Speciation in Water Samples and Determination by UV-Vis Spectrophotometry

Capillary electrophoresis coupled to electrospray mass spectrometry for the determination of organic and inorganic arsenic compounds in water samples

Some compounds of arsenic are extremely toxic to the human body even at low levels. Long-term exposure from drinking contaminated water causes adverse health effects. This has led the European Union and other global organizations to reduce the maximum residue limit for the total arsenic up to 10 μg L−1 in water for human consumption. The toxicity of arsenic depends on the oxidation state, chemical structure and solubility in the biological environment. Main analytical procedures report on the determination of arsenic species in water samples which have been developed based on atomic spectroscopy –speciation performed in the sample treatment step– and inductively coupled plasma-mass spectrometry (ICP-MS). In such cases, speciation is performed by coupling to high-performance liquid chromatography (HPLC). As far as we know, the determination of arsenic species in water samples at low concentration levels by capillary electrophoresis (CE) coupled to electrospray mass spectrometry (ESI-MS) has not been described up to now. In this research CE-ESI(−)-MS is proposed for the identification and simultaneous quantification of organic and inorganic arsenic species in water samples for human consumption. The target compounds were dimethylarsinate (DMA), mono-methylarsonate (MMA), arsenite (i-As(III)) and arsenate (i-As(V)). Optimization of the composition and nature of both the electrophoretic separation medium –using hexafluoro-2-propanol (HFIP) as an additive– and the sheath liquid was performed and aimed at achieving the best sensitivity and separation efficiency for the CE-ESI(−)-MS coupling. Two simple sample treatments were proposed: one based on dispersive liquid-liquid micro-extraction (DLLME) intended for a rapid determination of the total content of inorganic arsenic in the water sample; and the second based on partial evaporation of the water sample to detect each of the four main arsenic species. For the second, limits of detection between 0.02 and 0.04 μg L-1 were found, which are similar results as the ones achieved with methods based on HPLC-ICP-MS.The DLLME + CE-ESI(−)-MS method was applied to the determination of total inorganic arsenic in eleven water samples in the province of Salamanca (Spain). Five of the analyzed samples had values close to, or superior to the maximum residue limit for the total of arsenic in water intended for human consumption (10 μg L-1). The validated method CE-ESI(−)-MS for arsenic speciation was applied with success to the analysis of the weakly mineralized water sample (dry residue < 50 mg L-1) of both groundwater and bottled water.

A Coupled Extraction/Re-Extraction Method for the Chemical Speciation of Nickel in Natural Waters

Chemical fractionation and speciation of metals species in natural waters and its relation with bioavailability have received increased attention in recent years. A simple liquid membranes method, based on coupled liquid extraction and re-extraction processes, is proposed to separate and quantify the species of nickel present in water samples. A simplex optimization of chemical variables, such as carrier concentration in the organic solution and nitric acid concentration in the receiving solution, was performed and, under optimized conditions, the extraction system was applied to determine nickel species in water samples at natural level concentrations. A linear relationship was established between extraction efficacy and the concentration of dissolved organic carbon in the samples, allowing the separation and determination of labile and non-labile nickel fractions, since the latter was not transported through the organic solution acting as liquid membrane. When the total and labile concentrations of metals were analyzed in real samples with different salinities, no significant differences were found between the results obtained and those from well-established methods. An average relative error of 1.50 and 2.37 was obtained for total Ni concentration and labile fraction, respectively. Finally, a comparison with the theoretical speciation data calculated with the software WinHumic V was successfully performed. Thus, the proposed method allows the simultaneous determination of labile and non-labile nickel fractions, presented as a simple alternative to nickel fractionation in natural waters.

Development and Optimization of an External-Membrane Introduction Photoionization Mass Spectrometer for the Fast Analysis of (Polycyclic)Aromatic Compounds in Environmental and Process Waters.

The development of sensitive analytical techniques for the real-time detection of aromatic hydrocarbons (AHs) and polycyclic aromatic hydrocarbons (PAHs) is of high importance, because of their impact on human health and the environment. A promising approach, regarding to direct determination of (P)AHs in aqueous samples, is resonance-enhanced multiphoton ionization (REMPI) coupled to external-membrane introduction mass spectrometry (eMIMS). In eMIMS, analytes are extracted from the water phase into the gas phase, which is supplied to the MS by using an external semipermeable membrane setup. As a result, no laborious enrichment techniques are needed. With REMPI, ions are formed by the subsequent absorption of two photons via an excited molecular state. The unique ionization scheme of REMPI provides selective and sensitive detection of (P)AHs. When combining the capabilities of REMPI and MIMS, direct measurements of sub-μg/L concentrations of small (polycyclic)aromatic compounds are feasible. In this study, we present an external sheet membrane probe (ESMP) for the determination of selected (polycyclic)aromatic species in water samples by using REMPI time-of-flight mass spectrometry (REMPI-TOFMS). This inlet design shows promising results with respect to the direct analysis of (P)AHs in aquatic environments. With this early stage system, concentrations down to tens of ng/L for selected small (polycyclic)aromatic compounds are accessible within minutes without any sample preparation.

Dynamics of trace metals in the system water – soil – plant – wild rats – tapeworms (Hymenolepis diminuta) in Maglizh area, Bulgaria

BackgroundThe impact of chemical elements on the biosphere is a function of their concentration and chemical form. Elucidation and prognosing of the latters in water basins and soil extracts is of particular significance for the assessment of their bioaccumulation in plants and animals. ObjectivesTrace metals dynamics in the system water – soil–plant–wild rats – Hymenolepis diminuta in two agro-industrial zones (East and West) around Maglizh city, Bulgaria were investigated through experimental studies and thermodynamic modelling of the chemical species. MethodsSamples from surface waters of rivers, their nearby uncultivated soils, meadow uncultivated vegetation (Ranunculus acris and Gramineae) and field rats were collected. In situ measurements and laboratory analyses were performed for the determination of the physico-chemical characteristics and total concentrations of Al, Fe, Mn, Ni, Cu, Zn and Pb. The distribution of their dissolved chemical species in water samples and in the aqueous soil extracts was calculated using a thermodynamic approach. The relationship chemical species - bioaccumulation was discussed. ResultsWaters and soils in the East zone of Maglizh area were found to be more polluted compared to those in the West one, regarding Ni, Mn, Zn, Pb and Cu, while Mn and Cu displayed the highest mobility in West zone soils. Trace metals contents in Ranunculus acris exceed that in Gramineae, since the highest accumulation factors were calculated for Cu and Zn. The highest accumulation in rats was found for Zn followed by Cu, being higher in the West zone. Thermodynamic modelling shows that Mn2+ free ions are dominant in both waters and aqueous soil extracts. Ni2+ and Zn2+ ions followed by metal-organic complexes are dominant in waters of East zone while metal-organic complexes followed by free ions are dominant in waters of West zone and both soil extracts. Metal-organic complexes are dominant for Fe, Cu and Pb in all samples studied, while mainly hydroxy forms (Al(OH)4−) followed by metal-organic complexes are typically for Al depending on pH. ConclusionsExperimentally established bioaccumulation of trace metals in the studied vegetation and rats is a consequence of the total concentration of trace metals in waters and soils, their mobility and chemical species. The dominance of organic complexes of trace metals is a prerequisite for their bioaccumulation in plants. Rats are in direct contact with the soil solution and therefore, of importance is the content of free ions of Mn2+, Ni2+, Zn2+, which are easily absorbed through the skin. The host-helminth system wild rat/H. diminuta could be used as a bioindicator for trace metals pollution.

Cloud point extraction and ICP-MS for titanium speciation in water samples

An analytical method for the separation and determination of titanium dioxide nanoparticles in water samples has been developed. The separation was performed by Cloud Point Extraction (CPE) with Triton X-114. Titanium dioxide nanoparticles and ionic titanium were analysed in the surfactant rich phase and surfactant poor phase respectively, by inductively coupled plasma-mass spectrometry (ICP-MS). Parameters related to the CPE procedure such as Triton X-114 and NaCl concentrations were evaluated. Optimum concentrations of 0.03% (w/v) and 2.5 mM of Triton X-114 and NaCl respectively, were selected to develop this study. The TiO2 nanoparticles extracted were digested using HNO3 and H2O2 in an ultrasonic bath for 10 min at 60 °C and analysed by ICP-MS. The analytical characteristics of the method (calibration, limits of detection and quantification, precision and recovery) were evaluated. The LOD and LOQ for Ti determination in the surfactant rich phase were 0.13 and 0.45 µg L−1, respectively. Finally, the method was applied for the determination of TiO2 nanoparticles in swimming pool water samples.

Spectrophotometric determination of iron species using ultrasound-assisted temperature-controlled deep eutectic solvent dispersive liquid–phase microextraction and multisimplex optimisation

ABSTRACT A simple, quick and disperser-solvent-free analytical method based on ultrasound-assisted temperature-control deep eutectic solvent dispersive liquid-phase microextraction (UA-TC-DES-DLPME) in combination with spectrophotometry was developed for the separation/preconcentration and determination of iron species. In this method, Fe(II) was complexed with 2,4,6-tri(2ʹ-pyridyl)-l,3,5-triazine (TPTZ), and extracted into a hydrophobic deep eutectic solvent (DES) consisting of choline chloride and 4-chlorophenol (ChCl/4-Chph). The dispersion of DES in aqueous phase was speeded up by ultrasound waves and temperature-control process without using any organic dispersive solvent. Total iron concentration was obtained after reduction of Fe(III) to Fe(II) with hydroxylamine hydrochloride, and the amount of Fe(III) was calculated according to the difference between the concentration of total iron and Fe(II). At optimum conditions that obtained using Multisimplex method, the calibration curve was linear over the range of 5.0–100.0 µg L −1 with the detection limit of 1.2 µg L −1. The intra- and inter-day relative standard deviations (RSDs) at 20 µg L−1 level of Fe(II) (n = 5) were 3.6 and 4.5.%, respectively. The proposed method was successfully applied to the determination of iron species in water samples.

Chromium speciation using paper-based analytical devices by direct determination and with electromembrane microextraction

In this study, we developed and compared three different methods for chromium speciation in water samples using microfluidic paper-based analytical devices (μPADs). In all methods, detection was based on the complexation reaction of Cr(VI) with diphenylcarbazide on the μPADs. Cr(III) ions were oxidized to Cr(VI) by Ce(IV) prior to colorimetric detection on the μPADs. In the first method, oxidization of Cr(III) to Cr(VI) in the solution containing both trivalent and hexavalent chromium was performed using a batch procedure to obtain total chromium. A dual electromembrane extraction (DEME) technique for simultaneous preconcentration and extraction of chromium species and a single electromembrane extraction (SEME) for preconcentration and extraction of Cr(VI)/total chromium [quantified as Cr(VI) content after oxidation of Cr(III) ions to Cr(VI)] were used in the second and third methods, respectively. The electromembrane extraction was based on the electrokinetic migration of cationic Cr(III) and anionic Cr(VI) toward the cathode and anode, respectively, into the two different hollow fibres. Octanol-1 and bis(2-ethylhexyl) phosphate (DEHP) in octanol-1 (0.7% v/v) were the most suitable supported liquid membranes for extraction of Cr(VI) and Cr(III), respectively. Among these methods, SEME showed the lowest limits of detection for both analytes.Under optimized conditions, linear calibrations were obtained for Cr(III) from 3 to 30 μg L−1 and for Cr(VI) from 3 to 70 μg L−1. The detection limits were 1.0 μg L−1 and 0.7 μg L−1 for Cr(III) and Cr(VI), respectively. Our developed method was applied to analyse water samples spiked with different concentrations of Cr(III) and Cr(VI) at the parts-per-billion (ppb) level. The statistical evaluation showed that the proposed method agreed well with the validation method, i.e., inductively coupled plasma atomic emission spectroscopy (ICP-AES).

Vortex-assisted supramolecular solvent microextraction based on solidification of floating drop for preconcentration and speciation of inorganic arsenic species in water samples by molybdenum blue method

A new vortex-assisted supramolecular solvent microextraction based on solidification of floating drop (VA-SSM-SFD) has been developed for preconsentration and spectrophotometric determination of inorganic arsenic (iAs) species in various water samples. The method is based on the formation of arsenomolybdenium blue complex followed by VA-SSM-SFD procedure and subsequent spectrophotometric determination in a microcell. The supramolecular solvents consisted of reverse micelles of 1-dodecanol in tetrahydrofuran (THF) which were formed by in-situ coacervation of 1-dodecanol micelles in aqueous samples. Under optimized conditions, iAs (V) formed hetroploy blue complex and was directly determined. The concentration of iAs (III) was determined by subtracting iAs (III) from the total iAs following the oxidation of iAs (III) to iAs (V) by permanganate in acidic medium. Under optimal conditions, the calibration curve for iAs determination showed good linearity in the range of 5.0–140.0 μg L−1(R2 = 0.9988) and detection limit was found to be 0.4 μg L−1, which is much lower than WHO guideline of 10 μg L−1 for iAs in drinking water. The repeatability and reproducibility for 20 μg L−1 were found to be 2.47 and 3.9%, respectively. The proposed method was successfully applied to speciation of iAs species in real water samples.

Electrochemical sensors as simple and cheap devices for rapid determination of various species in environmental samples

The electrochemical methods are very good tool for determination of trace concentrations of various species in water samples. The analysis carried out using these methods are usually simple, fast and also the cost of the required equipment is much lower comparing to other instrumental methods. Furthermore, the electroanalytical methods are easy to automate and computerize. Among five major groups of these methods (potentiometry, voltammetry, coulometry, conductometry and dielectrometry), potentiometry and voltammetry attract the greatest attention of researchers. In this paper, experimental results of research related to development of procedures (voltammetric and potentiometric) for the determination of elements in environmental water samples were presented. Due to their common occurrence in environment and possible toxic effects on living organisms, vanadium and nitrate ions were selected for investigation. Optimization of voltammetric procedure for V(V) determination were carried out in matrix containing different surfactants and humic acids, using lead film electrode as a working electrode. Results showed that only nonionic surfactant Brij-35 did not interfere with the voltammetric signal. Other surfactants as well as humic acids reduced the signal, and possibility of their elimination with suitable resins were also investigated. Potentiometric measurements were consisted of preparation and determination of analytical properties of nitrate ion-selective electrodes with solid contact. The results showed that among three different membrane composition, the best response was achieved by membrane containing: Ni(Phen)2, THTDPCl, PVC and NPOE in the ratio of 1:2:33:64 wt. %, respectively. With the detection limit of 2.8 × 10-6 mol L-1, the working concentration range from 5 × 10-5 to 1 × 10-1 mol L-1 and a slope of -55.1 mV per decade, this electrode showed good selectivity to sulfate, acetate, carbonate, dihydrogen phosphate, fluoride and chloride ions, and also good potential reversibility.

Ultrasensitive Colorimetric Chromium Chemosensor Based on Dye Color Switching under the Cr(VI)-Stimulated Au NPs Catalytic Activity.

In view of the high toxicity of Cr(VI), simple and rapid on-site analytical approaches are in high demand for environment monitoring. Herein, an innovative chemosensor is developed for on-site sensitive detection of Cr(VI) in minutes by the naked eye. The chemosensor consists of gallic acid-capped gold nanoparticles (GA-Au NPs), methylene blue (MB), and NaBH4. In the presence of Cr(VI) ions, the reduction of MB by NaBH4 is able to greatly accelerate due to the Cr(VI)-stimulated catalytic activity of GA-Au NPs, resulting in a color switching of MB from blue to colorless for the quantitative detection of Cr(VI). The chemosensor in solution exhibits excellent selectivity and ultrahigh sensitivity to Cr(VI), with the detection limits of 0.05 nM by UV-vis spectroscopy and 0.1 nM by the naked eye. Similarly, a paper-based chemosensor is obtained by immobilization of GA-Au NPs and MB onto a piece of filter paper, offering a more convenient approach for rapid on-site detection of Cr(VI). In addition, H2O2 as an oxidizing agent is employed to convert Cr(III) into Cr(VI), thus achieving speciation analysis of Cr. The applicability of a chemosensor is also validated by the detection of Cr speciation in water samples with satisfactory recoveries.

Development of a New Kinetic Spectrophotometric Method for the Determination of Chromium with an Optical Probe.

The aim of this work is the development, optimization, and validation of a new spectrophotometric kinetic method for the determination of dissolved chromium species in water samples with the use of the polymethine dye Astra Phloxine FF. The progress of the chemical reaction was simple, effective, and precisely monitored from the start of the reaction using an optical probe. The method is based on the impact of Cr(VI) concentration on the rate of decrease in the Astra Phloxine FF concentration. The experimental data were evaluated using four experimental data analysis methods, namely with the initial rate method, the average rate method, the fixed time method, and the absorption peak volume change method. Under the optimal reaction conditions, the best results were achieved using the method of the average rate constant for evaluating the experimental data. Using this data evaluation method for the determination of Cr(VI), the LoD was found to be 1.87 µg L-1 and RSD ( n = 6; 0.2 mg L-1 Cr) 3.59%. The presented work was used for the determination of chromium in model samples-CRM material and tap and waste water-and with the calibration line method and the standard additions method.

Chromium Speciation in Water Samples by Loading a New Sulfide-Containing Biodegradable Polymer Adsorbent in Tip of the Syringe System

A new adsorbent poly-3-hydroxybutyrate-2-(dodecylthiocarbonothioylthio)-2-methylpropionate triester (PH-DTT-MPT) was first time loaded in a micropipette tip for speciation of chromium in different water samples. Total chromium (Cr), trivalent chromium (CrIII), and hexavalent chromium (CrVI) in different natural water samples were determined by electrothermal atomic absorption spectrometry. Known concentration of CrIII and CrVI was passed through a biodegradable polymer for investigation of the behavior of the newly used adsorbent. The newly used copolymer absorbed the CrIII on surface of the PH-DTT-MPT at pH 7.0, while CrVI was not adsorbed in desired pH value. After passing the real and standard solutions through the micropipette, then 2.0 mol L−1 HCl was used for elution of CrIII from the biodegradable polymer. Total Cr was calculated after reducing CrVI into CrIII by specific concentration of hydroxy ammonium chloride (HONH2·HCl). The concentration of CrVI in different natural water samples was estimated after back calculation of CrIII from total chromium. Effect of analytical parameters like adsorbent, pH, eluent, sample volume, flow rates, and interfering ions was also studied. The LOD, LOQ, RSD, and EF of the developed method were calculated as 6.1 ng L−1, 20 ng L−1, 1.17%, and 90, respectively. Validation of developed method was checked by certified reference materials and spiking addition method. The developed method was successfully applied for determination of total Cr, CrIII, and CrVI in various natural water ecosystems.

Combination of sequential cloud point extraction and hydride generation atomic fluorescence spectrometry for preconcentration and determination of inorganic and methyl mercury in water samples

A sequential cloud point extraction method was established for the determination of trace mercury species in water samples by hydride generation atomic fluorescence spectrometry (HGAFS). The proposed extraction system consisted of two chief steps: isolation of inorganic mercury (Hg2+) by chelating with potassium-iodide and methyl green, and then isolation of methyl mercury (CH3Hg+) by chelating with ammonium pyrrolidinedithiocarbamate. The nonionic surfactant Triton X-114 was chosen as the extractant, while the brominating agent was applied to convert extracted CH3Hg+ into Hg2+. Before HGAFS detection, the two surfactant-rich phases obtained in the sequential process were separately diluted to 3 mL with 5% (v/v) HCl after the addition of antifoam (0.4 mL). The effects of experimental conditions, including pH and concentration of surfactant and chelating agents, on cloud point extraction were optimized. Under the optimum conditions, the limits of detection for Hg2+ and CH3Hg+ were 0.007 and 0.018 μg/L with the enrichment factors of 15.1 and 11.2, respectively. The proposed method was successfully used for the determination of trace Hg2+ and CH3Hg+ in water samples with satisfactory recoveries of 95–104%.