On-line separation for the speciation of mercury in natural waters by flow injection-cold vapour-atomic absorption spectrometry

Inorganic mercury and methylmercury are determined in natural waters by injecting the filtered samples onto a low cost commercial flow injection system in which an anion exchange microcolumn is inserted after the injection loop (FIA-IE). If hydrochloric acid is used as the carrier solution, the HgCl4(2-) species (inorganic mercury) will be retained by the anion exchanger while the CH3HgCI species (methylmercury) will flow through the resin with negligible retention. Four anion exchangers and seven elution agents were checked, in a batch mode, to search for the best conditions for optimal separation and elution of both species. Dowex M-41 and L-cysteine were finally selected. Mercury detection was performed by cold vapour-electrothermal atomic adsorption spectrometry (HG-ETAAS). Both systems were coupled to perform the continuous on-line separation/detection of both inorganic mercury and methylmercury species. Separation and detection conditions were optimized by two chemometric approaches: full factorial design and central composite design. A limit of detection of 0.4 microg L(-1) was obtained for both mercury species (RSD < 3.0% for 20 microg L(-1) inorganic and methylmercury solutions). The method was applied to mercury speciation in natural waters of the Nerbioi-lbaizabal estuary (Bilbao, North of Spain) and recoveries of more than 95% were obtained.     

Ion chromatography in the analysis of natural waters

Ion chromatography is a new method for the determination of cations and anions in solution, based on ion-exchange separation of the analysed ions on a separator column, suppression of the background eluent signal on a suppressor column and finally, conductometric detection. Ion chromatography is characterized by high sensitivity, selectivity and reproducibility. This method now is widely applied to the determination of inorganic and organic ions in natural waters.     

On-line introduction of high-pressure gas-liquid sample for capillary gas chromatographic analysis

An on-line sample introduction technique in capillary gas chromatograph (CGC) for the analysis of high-pressure gas-liquid mixtures has been designed and evaluated. A sample loop of 0.05 microL and a washing solvent loop of 0.5 microL are mounted on a 10-port switching valve, which serves as the injection valve. A capillary resistor was connected to the vent of sample loop in order to maintain the pressure of the sample. Both the sample and the washing solvent are transferred into the split-injection port through a narrow bore fused silica capillary inserted into the injection liner through a septum. The volume of the liner is used both as the pressure-release damper and evaporation chamber of the sample. On-line analysis of both reactants and resultants in ethylene olimer reaction mixture at 5 MPa was carried out, which demonstrated the applicability of the technique.     

On-line sample cleanup in the liquid chromatographic analysis of pharmaceuticals for citrate content

Matrix interferents are removed from pharmaceutical samples via an on-line, automated column switching process in which the difference in hydrophobicity between the analyte and the interferents allows these species to be isolated in different parts of the chromatographic system. In this case, the interferents are trapped on a cleanup column and are flushed to waste as the analyte undergoes additional separation on an analytical column. The utility of this approach is demonstrated by the quantitation of citrate in pharmaceutical samples by ion suppression, reversed-phase liquid chromatography. The performance of this system is statistically equivalent to that of a manual pretreatment method employing disposable, solid-phase extraction cartridges.     

Advances in on-site analytical sample preparation for analysis of environmental waters: A review

The collection, storage, and transportation of water samples from far-off places to the labs is a pretty challenging task. It can cause contamination, degradation, or losses of the analytes, leading to errors in the analysis. On-site sample preparation provides an opportunity to extract the analytes into suitable extraction media that preserves the analytes and is easy to handle in terms of storage and transportation. However, the required equipment for on-site sample preparation should be simple, portable, and energy-efficient. Solvent- and sorbent-based microextraction approaches and the modern variants of solid-phase extraction have shown great potential for on-site sample preparation because of reduced consumption of solvents and low energy requirement. This review provides an overview of the application of different extraction techniques in on-site sample preparation, their advantages, and their limitations. The recent advances combining on-site extraction and analysis have also been critically discussed.     

微波催化显色反应分光光度法测定天然水中的磷

研究了用抗坏血酸作为还原剂磷钼蓝分光光度法测定磷时微波对于显色反应的催化作用和测定的适宜条件。试验表明:微波(高档,800W)可以使显色反应在3min内快速完成并稳定48h。线性范围:0~1.0mg/L,ε700nm=1.7×104L.mol-1.cm-1。对天然水样进行7次平行测定,其结果的RSD≤2.5%,回收率在98.6%~103%之间。与国家标准方法比较,无显著性差异。     

On-line microwave sample pretreatment for the determination of mercury in blood by flow injection cold vapor atomic absorption spectrometry

A method for on-line treatment of whole blood in a microwave oven and determination of mercury by flow injection cold vapor atomic absorption spectrometry was developed. After dilution of the whole blood and addition of oxidant, all further treatment and measurement were performed automatically, on-line. Recoveries of five mercury compounds were complete. Good agreement between measured and recommended values of mercury in whole blood reference materials was obtained. Measured mercury values also agreed with results from other accepted methods. Sample throughput was about 45 measurements/hr. Detection limit (3s) in diluted sample was 0.1 μg/l corresponding to 1μg/l Hg in whole blood. The RSD value at 0.5 μg/l Hg in the diluted sample was 6–7% (11 measurements and 0.5 ml sample volume). Mercury concentrations between 1 and 150 μg/l in whole blood can be measured using this method. For three replicate measurements, 0.5 ml of whole blood is required.     

Voltammetric methods for speciation analysis of trace metals in natural waters

Trace metals play an important role in the regulation of primary productivity and phytoplankton community composition. Metal species directly affects the biogeochemical cycling processes, transport, fate, bioavailability and toxicity of trace metals. Therefore, developing powerful methods for metal speciation analysis is very useful for research in a range of fields, including chemical and environmental analysis. Voltammetric methods, such as anodic stripping voltammetry (ASV) and competing ligand exchange-adsorptive cathodic stripping voltammetry (CLE-AdCSV), have been widely adopted for speciation analysis of metals in different natural aquatic systems. This paper provides an overview of the theory of voltammetric methods and their application for metal speciation analysis in natural waters, with a particular focus on current voltammetric methods for the discrimination of labile/inert fractions, redox species and covalently bound species. Speciation analysis of typical trace metals in natural waters including Fe, Cu, Zn, Cd, and Pb are presented and discussed in detail, with future perspectives for metal speciation analysis using voltammetric methods also discussed. This review can elaborate the particular knowledge of theory, merits, application and future challenge of voltammetric methods for speciation analysis of trace metals in natural waters.     

Non-chromatographic speciation analysis of chromium in natural waters

The difference in toxicity between Cr(III) and Cr(VI) species is one of the main reasons for the recent developments in analytical procedures for their differentiate. Non-chromatographic methods offer highly convenient tools for this purpose and can be used as a fast and cheap alternative to the chromatographic processes. The present work overviews and discuss different non-chromatographic procedures for speciation of chromium in natural water samples such as coprecipitation, dialysis, solvent and solid phase extraction. This survey will attempt to cover the state of-the art from 2005 to 2010.     

Potentiometric stripping analysis for manganese(II) in natural waters

Potentiometric stripping analysis (p.s.a.) methods for the measurement of manganese(II) in natural waters are described; batch and flow approaches are discussed. The more versatile flow p.s.a. technique is suitable for concentrations in the range 2 nM–30 μM. Application of these techniques is illustrated by measurements in a variety of natural waters. Interferences arising from manganese—copper interactions in the mercury electrode can be suppressed by the addition of zinc or gallium depending on the concentration of the interfering copper. The relative merits of the batch and flow p.s.a. techniques are discussed.     

On-line microwave oven digestion flame atomic absorption analysis of solid samples

A manifold has been developed for on-line microwave oven digestion and flame atomic absorption spectrometric (FAAS) determination of metallic elements in solid samples. The use of a closed flow system permits sample treatment before analysis by FAAS, the direct injection of slurries avoids a filtration step and the interconnection of two conventional rotary injection valves allows the rapid introduction of samples and standards. The determination of lead in sewage sludge was employed as a test system for the proposed on-line sample digestion manifold. The procedure has a limit of detection of 0.2 μg Pb g^?1.     

On-line mass spectrometric analysis of hydrothermal reactions for biomass model sample containing sulfur compounds

Biomass gasification using supercritical water is a promising way to produce hydrogen gas. However, this method might release toxic heteroatomic compounds. It is therefore important to clarify reaction pathways for efficiently obtaining hydrogen gas and suppressing environmental burden. L-cysteine was adopted for a test reagent containing sulfur and determination of the sulfur compound reaction pathways was studied by Li⁺-ion attachment mass spectrometry. It was found that H₂S, CO, CO₂, SO, SO₂ and SO₃ gasses were released at high concentrations in the gas phase during the hydrothermal reaction. By adding Ca(OH)₂ as alkali, the pathway of these gasses were, however, suppressed into the liquid phase so that the toxic emissions to the gas phase could be avoided.     

Lab-on-valve in the miniaturization of analytical systems and sample processing for metal analysis

In the past decade, the lab-on-valve (LOV) system, as the third-generation of the flow-injection analysis technique, has exhibited powerful capability in instrument miniaturization and on-line sample pretreatment.This review presents and discusses the state of the art in the progress of the LOV system in the determination of metal species in two parts:

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miniaturization of analytical instrumentations; and,

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sample-processing front-ends.

As a miniaturized analytical set-up, LOV incorporates detection techniques for the determination of metal species (e.g., spectrophotometry, electrochemical detection and atomic spectrometry). However, coupling LOV sample pretreatment with atomic or mass spectrometric detectors provides high-sensitivity determination or speciation of metal species.We also discuss future perspectives of the LOV system in metal determination and/or speciation.     

On-line sample processing involving microextraction techniques as a front-end to atomic spectrometric detection for trace metal assays: A review

Within the last decade, liquid-phase microextraction (LPME) and micro-solid phase extraction (μSPE) approaches have emerged as substitutes for conventional sample processing procedures for trace metal assays within the framework of green chemistry. This review surveys the progress of the state of the art in simplification and automation of microextraction approaches by harnessing to the various generations of flow injection (FI) as a front end to atomic absorption spectrometry (AAS), atomic fluorescence spectrometry (AFS) or inductively coupled plasma atomic emission spectrometry or mass spectrometry (ICP-AES/MS). It highlights the evolution of flow injection analysis and related techniques as vehicles for appropriate sample presentation to the detector and expedient on-line matrix separation and pre-concentration of trace levels of metals in troublesome matrices. Rather than being comprehensive this review is aimed at outlining the pros and cons via representative examples of recent attempts in automating green sample preparation procedures in an FI or sequential injection (SI) mode capitalizing on single-drop microextraction, dispersive liquid-phase microextraction and advanced sorptive materials including carbon and metal oxide nanoparticles, ion imprinted polymers, superparamagnetic nanomaterials and biological/biomass sorbents. Current challenges in the field are identified and the synergetic combination of flow analysis, nanotechnology and metal-tagged biomolecule detection is envisaged.     

Speciation analysis of heavy metals in natural waters: a review.

Metal speciation in natural waters is of increasing interest and importance because toxicity, bioavailability, environmental mobility, biogeochemical behavior, and potential risk in general are strongly dependent on the chemical species of metals. This paper provides an overview of the need for speciation of heavy metals in natural waters, the chemical and toxicological aspects of speciation, and the analytical procedures for separation and the different techniques for final determination that are used today. The trends and developments of speciation are also discussed. Finally, the case of chromium (Cr) was selected for a detailed presentation because the speciation of this metal has attracted a great deal of interest in view of the toxic properties of Cr(VI).     

Sampling, sample treatment and quality assurance issues for the determination of phosphorus species in natural waters and soils

Phosphorus is an important macronutrient and the accurate determination of phosphorus species in environmental matrices such as natural waters and soils is essential for understanding the biogeochemical cycling of the element, studying its role in ecosystem health and monitoring compliance with legislation. This paper provides a critical review of sample collection, storage and treatment procedures for the determination of phosphorus species in environmental matrices. Issues such as phosphorus speciation, the molybdenum blue method, digestion procedures for organic phosphorus species, choice of model compounds for analytical studies, quality assurance and the availability of environmental CRMs for phosphate are also discussed in detail.     

Determination of nitrate in natural waters by flow-injection analysis

Summary Nitrate was determined in natural water samples by flow-injection spectrophotometry. It was reduced to nitrite with copperized cadmium and the nitrite thus produced reacted with p-aminoacetophenone and m-phenylenediamine. The limit of detection was about 1.5 g l^–1 for sample injections of 650 l. The sampling rate was about 40 samples h^–1 and the relative standard deviation was above 1% for 0.1–0.3 mg l^–1 nitratenitrogen. Nitrite present in the sample was determined separately and subtracted.

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Nitratbestimmung in natürlichen Wässern mit Hilfe der Fließinjektions-Analyse

Zusammenfassung Nitrat wird bei dieser Methode mit Hilfe einer Cu/Cd-Reduktionssäule zu Nitrit reduziert, das mit p-Aminoacetophenon und m-Phenylendiamin zur Reaktion gebracht wird. Die gebildete Verbindung wird spektral-photometrisch gemessen. Die Nachweisgrenze beträgt etwa 1,5 g/l bei injizierten Probevolumina von 650 l. Der Probendurchsatz beträgt 40/h. Die relative Standardabweichung liegt über 1% bei 0,1–0,3 mg/l Nitrat-Stickstoff. Vorhandenes Nitrit wird gesondert bestimmt und abgezogen.

     

On-line coupling of electrochemical preconcentration in tungsten coil electrothermal atomic absorption spectrometry for determination of lead in natural waters

A flow injection system was coupled to a tungsten coil electrothermal atomizer (150 W) for on-line separation and preconcentration of lead based on its electrochemical reduction on the atomizer surface. The electrochemical cell is built up inside the furnace by using a Pt flow-through anode and the atomizer itself as the flow-through cathode. The manifold and the tungsten coil power supply were controlled by a computer running a program written in Visual Basic, which was utilized in synchronism with the original software of the atomic absorption spectrometer. The flow-through anode (50 mm long, 0.7 mm i.d.) was inserted in tip of the autosampler arm by replacing the last section of the PTFE sample delivering tube. The tungsten coil atomizer and the counter electrode were easily connected to a d.c. power supply. An enrichment factor of 25 was obtained for lead after a 120-s electrodeposition for a sample flowing at 1.0 ml min⁻¹. The method detection limit was 0.2 μg l⁻¹ Pb and the R.S.D.<5% (n=10 for 5 μg l⁻¹ Pb). Up to 2% m/v NaCl or KCl and 5% m/v CaCl₂ or MgCl₂ did not interfere on the separation and atomization of 5 μg l⁻¹ Pb.     

On-line sample preconcentration with chemical derivatization of bacterial biomarkers by capillary electrophoresis: a dual strategy for integrating sample pretreatment with chemical analysis

Simple, selective yet sensitive methods to quantify low-abundance bacterial biomarkers derived from complex samples are required in clinical, biological, and environmental applications. In this report, a new strategy to integrate sample pretreatment with chemical analysis is investigated using on-line preconcentration with chemical derivatization by CE and UV detection. Single-step enantioselective analysis of muramic acid (MA) and diaminopimelic acid (DAP) was achieved by CE via sample enrichment by dynamic pH junction with ortho-phthalaldehyde/N-acetyl-L-cysteine labeling directly in-capillary. The optimized method resulted in up to a 100-fold enhancement in concentration sensitivity compared to conventional off-line derivatization procedures. The method was also applied toward the detection of micromolar levels of MA and DAP excreted in the extracellular medium of Escherichia coli bacterial cell cultures. On-line preconcentration with chemical derivatization by CE represents a unique approach for conducting rapid, sensitive, and high-throughput analyses of other classes of amino acid and amino sugar metabolites with reduced sample handling, where the capillary functions simultaneously as a concentrator, microreactor, and chiral selector.