Species-specific isotope-ratio measurements of volatile tin and antimony compounds using capillary GC–ICP–time-of-flight MS

The analytical performance of an axial inductively-coupled-plasma time-of-flight mass spectrometer (ICP–TOFMS) as a detector for fast transient chromatographic signals resulting from the coupling to capillary gas chromatography (CGC) was investigated. A cryotrapping GC–ICP–TOFMS method for the determination of volatile metal(loid) compounds (VOMs) in gases was used and the suitability of the TOF mass analyzer for multi-elemental speciation analysis and multi-isotope ratio determinations was studied in terms of accuracy and precision. Isotope ratios ¹¹⁸Sn/¹²⁰Sn and ¹²¹Sb/¹²³Sb have been determined in in-house gas standard atmospheres in Tedlar bags at two different levels (100 pg and 1 ng) for different elemental species (SnH₄, MeSnH₃, Me₂SnH₂, Me₃SnH, BuSnH₃, SbH₃, and MeSbH₂). A limitation arising from counting statistics in both detection modes could be shown. A solution containing rhodium (10 ng mL^–1) and cadmium (40 ng mL^–1) was introduced simultaneously to the GC outlet. Rhodium acts as a continuous internal standard and Cd is used for mass-bias correction (by measuring the ¹¹¹Cd/¹¹³Cd ratio). The detection system in both pulse counting and analog mode was examined. The best attainable precision was established for Me₂SnH₂ (analog mode, 12 replicates, 1 ng, RSD 0.34%, accuracy 0.31%) whereas most other species ranged between 0.4 and 0.5% RSD if higher concentrations were used. The limitations of the pulse counting system are clearly seen, with peak heights of more than 2000 counts reaching saturation (for an integration time of 100 ms), which reduces the accuracy of isotope ratio determinations. A dozen VOM could be detected in an aged landfill gas sample; several unidentified Sn compounds were present. Although their isotope ratios are within the confidence value of the standards, it is not yet clear if the acquired precision is good enough to identify isotopic fractionation of metal(loid)s through biovolatilization processes. With the precision achieved, the combination of cryotrapping GC and ICP–TOFMS is a powerful tool for monitoring volatile multi-element species in multi-tracer experiments and isotope dilution methodology. Received: 23 November 2000 / Revised: 19 February 2001 / Accepted: 24 February 2001     

A flow injection analysis system for monitoring silver (I) ion and iodine residuals in recycled water from recovery systems used for spaceflight

A laboratory-built flow injection analyzer is reported for monitoring the drinking water disinfectants silver (I) ion and iodine in water produced from NASA's water recovery system. This analyzer uses spectrophotometric detection with a custom made 10 cm optical flow cell. Optimization and interference studies are discussed for the silver (I) ion configuration. Subsequent results using the silver (I) configuration with minor modifications and alternative reagents gave promising results for iodine determinations as well. The estimated MDL values for Ag⁺ and I₂ are 52 μg L⁻¹ Ag⁺ and 2 μg L⁻¹ I₂; the mean percent recoveries were 104% and 96.2% for Ag⁺ and I₂ respectfully; and percent relative standard deviations were estimated at 1.4% for Ag⁺ and 5.7% for I₂. The agreement of this potentially multifunctional analyzer to reference methods for each respective water disinfectant is measured using Bland–Altman analysis as well as more traditional estimates.     

High-sensitivity methods for sequential injection determination of the main constituents of alloys

A sequential injection system with spectrophotometric detection was proposed for the determination of copper, zinc and lead in brass. In view of the high analyte concentrations and the sensitivity of the involved catalytic methods, optimization of the flow system was carried out aiming mild reaction conditions. Copper and lead determinations were based on the catalytic effects of Cu²⁺ and Pb²⁺ on the oxidation rates of resorcinol and pyrogallol red by H₂O₂, respectively, and zinc determination involved precipitate formation after oxidation of 1-nafthylethylenediamine by K₃Fe(CN)₆. The analytical procedures were designed with some common parameters such as pH=9.0 (borate system), λ=530 nm, and H₂O₂ as oxidizing agent; system geometry was maintained.The proposed system is rugged, and base line drift is not observed during 4 h operation periods. Twenty samples are run per hour (60 determinations) and reagent consumption is minimal, thus avoiding drawbacks related to waste management. Precise results (R.S.D.<1.0%; n=7) are obtained and a detection limit of 1% (w/w) was estimated for the three analytes. Results were in agreement with flame atomic absorption spectrometry.     

High-precision stopped-flow mixer for kinetic determinations

A highly automated, chemically inert, stopped-flow mixing system for rapid kinetic determinations is described. The reactant solutions are drawn into the drive syringes through novel double check valves, which are an integral part of the syringe block. The prime movers for the flow systems are pneumatic cylinders driven by compressed air; air flow is controlled by electromechanical valves actuated by optically isolated zero-crossing switches. The dead time of the flow system is 2–3 ms, depending on the drive pressure.The spectrophotometric detection system consists fo a high-intensity light source, a wavelength selector and a reference detector that are mechanically isolated from the flow system by a quartz fiber-optic light guide. The transducers are solid-state photodiodes. The sample photodiode is mounted adjacent to the output window of the cell to minimize light losses. The signal-to-noise ratio of the photometric system is from 2×10² to greater than 4×⁴, depending on wavelength, absorbance level, and amount of signal averaging.The reduction of Fe(CN)₆^3? by ascorbic acid was used as a test reaction. Accuracy and precision better than 0.3% were obtained for routine determination. A detection limit of 4.10×10^?7 M Fe(CN)₆^3?, or 134 μg kg^?1 K₃Fe(CN)₆, was found for this system.     

Enzymatic assay with detection by enhanced luminol chemiluminescence in a reversed micellar system: determination of l-amino acids and glucose

A detection system for hydrogen peroxide, i.e., luminol chemiluminescence (CL) in a hexadecyltrimethylammonium bromide (CTAB) reversed micellar system, was coupled to enzyme reactions. The use of CTAB reversed micellar medium allows one to conduct both the oxidase enzymatic and CL detection reactions simultaneously at mild pH (l-amino acid system, pH 8.7; glucose system, pH 8.5) in the absence of any co-oxidant or catalyst. Based on this result, simple and unique determinations of l-amino acids and glucose as substrates were developed. The calibration graph for a representative amino acid, l-phenylalanine, was linear in the concentration range 4.0×10^?6?200×10^?6M with a relative standard deviation of 5.78% (five determinations). The method established for l-phenylalanine was also applicable for the assay of fourteen other l-amino acids. The calibration graph for glucose was linear in the concentration range 5.4×10^??540×10^?6M with a relative standard deviation of 4.27% (eight determinations). This method was compared with a standard spectrophotometric method (hexokinase) and successfully applied to the determination of glucose in human serum.     

The selective determination of halogens and sulphur in solution by atmospheric-pressure helium microwave-induced plasma emission spectrometry coupled to an electrothermal introduction system

Instrumentation is described for the direct determination of Cl, Br, I and S in dissolved samples. A tantalum furnace is coupled directly to a TM₀₁₀ cavity, in which a helium microwave plasma is generated at atmospheric pressure. Samples (20 μl) are dried, ashed and atomized; the free atoms are transported by helium to the cavity, where they are excited. Detection limits are in the sub-mg l^-1 region. The effect of counter cations is removed by the addition of 50 mg l^-1 potassium hydroxide, which also helps to suppress interferences by large amounts of matrix constituents, but the standard addition technique remains necessary to permit determinations that are reliable to within 5%.     

Application of the interference standard method for the determination of sulfur, manganese and iron in foods by inductively coupled plasma mass spectrometry

The interference standard method (IFS) is evaluated to improve the accuracy of the determination of S, Mn and Fe in meat and grain samples by inductively coupled plasma quadrupole mass spectrometry (ICP-QMS). Due to ICP-QMS relatively low resolution, polyatomic interferences caused by ¹⁶O₂⁺, (¹⁶OH)₂⁺, ⁴⁰Ar¹⁴NH⁺, and ⁴⁰Ar¹⁶O⁺, for example, can compromise determinations at m/z 32, 34, 55, and 56, respectively. In IFS, differently from traditional internal standard methods, plasma naturally occurring species are used to correct for variations in the interference signal rather than the analyte signal. The method is based on the hypothesis that the interfering ion and the IFS probe present similar behaviors in the plasma, and that by using the analytical (analyte plus interference)/IFS signal ratio one could reduce variations due to interference and, consequently, improve accuracy. In this work, this strategy is evaluated in real sample applications and significant improvements on accuracy are observed for ³²S, ³⁴S, ⁵⁵Mn, and ⁵⁶Fe determinations. Recoveries ranging from 72% for Mn to 105% for Fe in two different standard reference materials are obtained using the ³⁸Ar probe. These analytes are successfully determined in meat and grain samples with concentrations ranging from 4.42 μg g⁻¹ for Mn in corn to 7270 μg g⁻¹ for S in chicken liver. The method is compared with other strategies such as internal standardization and mathematical correction. No instrumental modification or introduction of foreign gases is required, which is especially attractive for routine applications.     

Simultaneous Determination of Sodium,Potassium, and Ammonium Ions by Automated Direct Potentiometry

Abstract

Sodium, potassium and ammonium ions, in concentration ranges of natural and waste water samples, have been simultaneously determined by direct potentiometry, using sodium, potassium, and ammonia ion-sensitive electrodes. The results are printed out as concentration units directly from an automated continuous -flow system with on-line minicomputer and printer. The optimum sampling rate is 20 samples or 60 determinations per hour. Various water samples have been analyzed and the results compared to those obtained by the standard methods. The lower detection limits were 0.1 ppm for Na⁺ and NH₄ ⁺ and 1.0 ppm for K⁺. The values of standard deviation were < 10%, with the exception of the lowest concentrations. The relative error was in the range of ± 2%. The correlation of standard and proposed methods was very good.     

Simultaneous spectrophotometric flow-through measurements of pH, carbon dioxide fugacity, and total inorganic carbon in seawater

An autonomous multi-parameter flow-through CO₂ system has been developed to simultaneously measure surface seawater pH, carbon dioxide fugacity (fCO₂), and total dissolved inorganic carbon (DIC). All three measurements are based on spectrophotometric determinations of solution pH at multiple wavelengths using sulfonephthalein indicators. The pH optical cell is machined from a PEEK polymer rod bearing a bore-hole with an optical pathlength of ∼15 cm. The fCO₂ optical cell consists of Teflon AF 2400 (DuPont) capillary tubing sealed within the bore-hole of a PEEK rod. This Teflon AF tubing is filled with a standard indicator solution with a fixed total alkalinity, and forms a liquid core waveguide (LCW). The LCW functions as both a long pathlength (∼15 cm) optical cell and a membrane that equilibrates the internal standard solution with external seawater. fCO₂ is then determined by measuring the pH of the internal solution. DIC is measured by determining the pH of standard internal solutions in equilibrium with seawater that has been acidified to convert all forms of DIC to CO₂. The system runs repetitive measurement cycles with a sampling frequency of ∼7 samples (21 measurements) per hour. The system was used for underway measurements of sea surface pH, fCO₂, and DIC during the CLIVAR/CO₂ A16S cruise in the South Atlantic Ocean in 2005. The field precisions were evaluated to be 0.0008 units for pH, 0.9 μatm for fCO₂, and 2.4 μmol kg⁻¹ for DIC. These field precisions are close to those obtained in the laboratory. Direct comparison of our measurements and measurements obtained using established standard methods revealed that the system achieved field agreements of 0.0012 ± 0.0042 units for pH, 1.0 ± 2.5 μatm for fCO₂, and 2.2 ± 6.0 μmol kg⁻¹ for DIC. This system integrates spectrophotometric measurements of multiple CO₂ parameters into a single package suitable for observations of both seawater and freshwater.     

Direct and simultaneous determination of copper and manganese in seawater with a multielement graphite furnace atomic absorption spectrometer

The direct and simultaneous determinations of Cu and Mn in seawater using a multielement graphite furnace atomic absorption spectrometer (Perkin-Elmer SIMAA6000) are described. Three kinds of chemical modifier (Mg(NO₃)₂, Pd(NO₃)₂ and a mixture of these) were tested. The matrix interferences were removed completely so that a simple calibration curve method could be used to determine Cu and Mn in seawater from the open ocean using Pd or a mixture of Pd and Mg as the chemical modifier. The relative standard deviations (RSDs) for the simultaneous determination of Cu and Mn in seawater from open ocean are 10% or less, and the detection limits were 0.07 μg 1⁻¹ for Cu and 0.10 μg 1⁻¹ for Mn, using Pd as the chemical modifier. The accuracy of the method is confirmed by analysis of four kinds of certified reference saline waters.     

银（III）配合物-鲁米诺流动注射化学发光新体系测定肾上腺素

儿茶酚胺是一类非常重要的神经递质,在人体的心血管系统、神经系统、内分泌腺、肾脏、平滑肌等组织系统的生理活动中起着广泛的调节作用。肾上腺素为儿茶酚胺的一种,建立灵敏、高效的肾上腺素检测技术具有重要的临床意义。本文将银（Ⅲ）配合物与鲁米诺组成新的流动注射化学发光体系,利用碱性介质中肾上腺素对三价银配合物－鲁米诺化学发光体系有明显的增强效应来测定肾上腺素的含量,并据此建立了高效测定肾上腺素的流动注射化学发光新方法。在优化的条件下,该方法测定肾上腺素的线型范围为1.0×10－9～1.0×10－7 mol L-1,检出限为8.0×10－10 mol L-1,对1.5×10－8 mol L-1肾上腺素11次平行测定,其相对标偏差为2.9％。利用建立的分析方法测定了药物肾上腺素,并对三价银－鲁米诺化学发光新体系测定肾上腺素的反应机理进行了讨论。     

Maßanalyse und Katalyse

The application of the therinometric method to the catalytic endpoint indication in volumetric determinations by precipitation reactions is discussed. The direct titration of silver, mercury(II) and palladium(II) as well as the determination of several anions (Cl^?, Br^?, J^?, SCN^?, CN^?, [Fe(CN)₆]^4? and S^2?) by backtitration with iodide standard solution is described. The well known reaction between cerium(IV) and arsenic(III), catalysed by iodide, serves as an indicator. The ions mentioned can thus be determined in the microgram range with good accuracy.     

Determination of phenylglyoxylic acid in urine using a multi-pumping flow system

In this work a simple, fast and fully automated analytical methodology for the spectrophotometric determination of phenylglyoxylic acid is proposed. Phenylglyoxylic acid is a metabolite of styrene that is excreted in urine, being used as an indicator of styrene occupational exposure. The developed procedure was based on the phenylglyoxylic acid ability to inhibit the formation of the peroxovanadium cation produced by the reaction between vanadate and H₂O₂. The analytical process was implemented in a multi-pumping flow system that employs multiple solenoid actuated micro-pumps as the only active components. This enabled the reproducible insertion and efficient mixing of low volumes of sample and reagents as well as the transportation of the sample zone towards detection. Thus an easily controlled, low cost, compact and reliable analytical system was implemented. A linear working range for phenylglyoxylic acid concentrations up to 700?mg?L^?1 (r ^2?=?0.995, n?=?7), was obtained, with a detection limit of 37?mg?L^?1. The system handles about 43 determinations per hour yielding precise results (relative standard deviation?<?5%, n?=?10). The developed methodology was applied to the determination of phenylglyoxylic acid in urine samples and the obtained results were in agreement with those furnished by the comparison method with relative percentage deviations lower than 6.6%.     

“Stat” methods in continuous flow analysis : Determination of Copper,Iron, Iodide and Hydrochloric Acid

A continuous flow “stat” method is described in which a certain arbitrarily imposed state in the flowing stream is automatically maintained by regulating the rate of flow of one of the components. The electronic system is regulated by measuring a physical phenomenon in the flowing solution. The method is illustrated by the examples of a continuous flow absorptiostat [Fe(III)/S₂O₃^2-/Cu(II)]for determinations of copper(II) (1–10 μg ml^-1), iron(III) (25–250 or 12.5–125 μg ml^-1), as well as for determination of iodide (12.8–128 μg ml^-1). A continuous flow conductostat [HCl/NaOH] for determination of 1–2.5 × 10^-4 M HCl is also described. This analytical technique is intended for automatic continuous monitoring of sample streams.     

A new atomization cell for trace metal determinations by tungsten coil atomic spectrometry

A new metallic atomization cell is used for trace metal determinations by tungsten coil atomic absorption spectrometry and tungsten coil atomic emission spectrometry. Different protecting gas mixtures are evaluated to improve atomic emission signals. Ar, N₂, CO₂ and He are used as solvents, and H₂ and C₂H₂ as solutes. A H₂/Ar mixture provided the best results. Parameters such as protecting gas flow rate and atomization current are also optimized. The optimal conditions are used to determine the figures of merit for both methods and the results are compared with values found in the literature. The new cell provides a better control of the radiation reaching the detector and a small, more isothermal environment around the atomizer. A more concentrated atomic cloud and a smaller background signal result in lower limits of detection using both methods. Cu (324.7 nm), Cd (228.8 nm) and Sn (286.3 nm) determined by tungsten coil atomic absorption spectrometry presented limits of detection as low as 0.6, 0.1, and 2.2 μg L⁻¹, respectively. For Cr (425.4 nm), Eu (459.4 nm) and Sr (460.7 nm) determined by tungsten coil atomic emission spectrometry, limits of detection of 4.5, 2.5, and 0.1 μg L⁻¹ were calculated. The method is used to determine Cu, Cd, Cr and Sr in a water standard reference material. Results for Cu, Cd and Cr presented no significant difference from reported values in a 95% confidence level. For Sr, a 113% recovery was obtained.     

Determination of coenzyme Q10 by in situ EPR spectroelectrochemistry

A rapid and sensitive method is developed for the determination of coenzyme Q₁₀ (CoQ₁₀) on the basis of the measurement of the radical intermediate (ubisemiquinone) formed during the reduction reaction of CoQ₁₀ at a silver electrode by in situ EPR spectroelectrochemical techniques. At the potential of −0.55 V (versus SCE), the ubisemiquinone is formed and is stable in ethanol+water. Under optimal conditions, it was found that the proposed method provided a linear response over the CoQ₁₀ concentration range 5–100 μmol l⁻¹ with a detection limit of 3 μmol l⁻¹. The relative standard deviation of the results was 7.5% for six successive determinations at 10 μmol l⁻¹ CoQ₁₀. This method is a useful tool for improving the selectivity when other chemicals present in the sample do not interfere in the assay.     

Extractive spectrophotometric determination of trace amounts of nitrogen dioxide,nitrite, and nitrate

A sensitive extractive spectrophotometric method for the determination of nitrogen dioxide in air and nitrite and nitrate in water, soil and blood serum is described. Nitrogen dioxide in air is fixed as nitrite in a suitable trapping solution. The method is based on the diazo coupling reaction betweenp-nitroaniline andN-(1-naphthyl)ethylenediamme dihydrochloride [NEDA]. The azo dye formed under aqueous conditions is extracted with isobutyl methyl ketone [IBMK]. The system obeys Beer's law over the range 0–3 g of nitrite at 545 nm and the colour is stable for 3h. The molar absorptivity of the colour system is 5.7 × 10⁴ L mol^–1 cm^–1. The relative standard deviation is 1.3% for ten determinations at 2 ug of nitrite. Nitrate is determined as nitrite after reduction on a cadmium column. Negative interferences from SO₂, H₂S, Cu²⁺ and Cr³⁺ and positive interference from Fe²⁺ and Fe³⁺ can be simply masked.     

Evaluation and application of internal standardization in atomic absorption spectrometry with electrothermal atomization

A new dual-channel system developed for use in atomic absorption spectrometry is used to assess the internal standard technique for electrothermal atomization. Cobalt was found to be a suitable internal standard for iron determinations, and is used for determination of 7—330 ng Fe ml^-1 in water samples. With use of the internal standard technique, fluctuations caused by atomizer variables are reduced and interferences from many cations are also decreased.     

Underpotential Deposition Study and Determination of Bismuth on Gold Electrode by Using Voltammetry

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Electrochemical Enzyme‐Linked Immunoassay for the Determination of Estriol Using Methyl Red as Substrate

Abstract

A new electrochemical substrate for horseradish peroxidase, methyl red, is reported. In this reaction system, horseradish peroxidase can catalyze the redox reaction of methyl red and H₂O₂. Methyl red exhibits a sensitive voltammetric peak at?0.51 V vs. Ag/AgCl reference electrode, the decrease of the peak current of methyl red is in proportion to the concentration of horseradish peroxidase (HRP). The linear range for determination of horseradish peroxidase is 5.0×10^?8～5.0×10^?7 g mL^?1 and the detection limit is 1.8×10^?8 g mL^?1. The relative standard deviation is 3.3% when 2.0×10^?7 g mL^?1 HRP was sequentially determined 11 times. A voltammetric enzyme‐linked immunoassay method for the determination of estriol was developed, based on this electrochemical system. The linear range for determination of estriol is 1.0～1000.0 ng mL^?1, and the detection limit is 0.33 ng mL^?1. The relative standard deviation for 11 parallel determinations with 200 ng mL^?1 estriol is 4.8%. Some pregnancy serum samples were analyzed with satisfactory results.