Use of multiphoton ionization of molecules for the determination of neptunium traces in solution

The possibility of detecting trace amounts of neptunium atoms and molecular compounds by laser resonance ionization spectroscopy has been investigated in acetylene-air and acetylene-nitrous oxide flames. Experimentally evaluated atomization coefficients of neptunium in the process of thermal dissociation in flames (10^–4% for C₂H₂-air and 10^–2% for C₂H₂–N₂O) do not allow to use atomic ionization signal for determination of neptunium microamounts in solutions. High yield multiphoton ionization of NpO molecule has been realized in fuel rich C₂H₂–N₂O flame. This pehnomenon has been used for determination of trace quantities of Np in solution. The detection limit was 2·10^–9 g/ml.     

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.     

Some observations on the interdependence of cyanide concentration and atomization efficiency in the nitrous oxide-acetylene flame

A relationship is derived between CN concentration and atomization efficiency in the C₂H₂-N₂O flame. The relationship is examined under various experimental conditions and β values are estimated for a number of elements. The possibility of complex vapour phase oxide formation by U is considered.     

Optimization of thermostated electrodeless discharge lamps for analytical atomic spectrometry

Thermostated and unthermostated electrodeless discharge lamps (EDL's) operated at 2450 MHz with either an A-antenna or a $\text{3}\text{4}$-wavelength Broida cavity have been critically studied with respect to the effect of type and pressure of fill gas, lamp temperature, microwave power and the form of element and/or compound within the lamp, upon the source radiant output, atomic absorption and atomic fluorescence signals of Zn-213·8 nm, Pb-283·3 nm, Mn-279·5 nm, Hg-253·7 nm and Tl-377·6 nm. Temperature control of electrodeless discharge lamps eliminates most of the problems which have previously plagued their operation. Also as a result of these studies, certain misconcepts in the operation and characteristics of electrodeless discharge lamps have been clarified; e.g., the ‘skin effect’ is present in many electrodeless discharge lamps, but all lamps also exhibit a homogeneous glow discharge; at high microwave powers and/or at high lamp temperatures, spectral lines apparently exhibit little self-absorption and self-reversal; and most important, control of lamp temperature is the most critical parameter controlling spectral output because atomization within the lamps is predominantly thermal in origin. Also, contrary to the conclusions reached by some workers evaluating the analytical usefulness of atomic fluorescence flame spectrometry, it is shown that detection limits one-to-three orders of magnitude lower result when thermostated EDL's are used in atomic fluorescence spectrometry with C₂H₂-air flames.     

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.     

Internal standard method in flame atomic absorption spectrometry

Some selection criteria and experimental considerations for selecting an internal standard in flame atomic absorption spectrometry were studied. Rational criteria for the selection of internal standards include the atomization efficiencies of the elements. An experimental study of the variation of the atomization degree due to a temperature decrease can be made with the help of plots of absorbance against the rate at which the sample solution is introduced. The temperature decrease produced by increasing the rate at which water was introduced using a heated chamber without water-cooled condenser was estimated to vary from 2420 K to 2218 K with 1.0 ml water per minute. Curves for the alkali, alkaline earth, and several other metals were obtained in the air-acetylene flame. The shapes of the curves are critically dependent on the degree of atomization of the metal itself. Elements with curves that have similar slopes can be used as mutual internal standards. Some of the other factors which affect the atomization efficiencies—i.e. changes in fuel and air flow, and matrix composition—were also studied.     

Detection and assignment of inorganic aqueous polymers relevant to environmental nanogeoscience by direct infusion electrospray ionization mass spectrometry

Inorganic polymers in aqueous solutions are being proposed as essential components in new theories concerning nonclassical nucleation and growth of nanominerals relevant to environmental nanogeosciences. The study of those complex natural processes requires multi‐technique analytical approaches able to characterize the solutions and their constituents (solutes, oligomers, polymers, clusters and nanominerals) from atomic to micrometric scales. A novel analytical approach involving an electrospray ionization source (ESI) coupled to time‐of‐flight mass spectrometry (TOF/MS) was developed to identify inorganic polymers in aqueous solution. To this end, the presence of initial Al oligomers and their polymerization processes was studied during a nanomineral aqueous synthesis (hydrobasaluminte, Al₄SO₄(OH)₁₀·12‐36H₂O). Ensuring the feasibility and robustness of the methodology as well as the stability of the polymers under study (avoiding undesirable fragmentation), a meticulous study of the ESI‐TOF MS working conditions was performed. Precision of the methodology was evaluated obtaining relative standard deviations below 3.3%. For the first time in the study of inorganic polymers in the earth sciences, the mass accuracy error (ppm) has been reported and the use of significant decimal figures of the m/z signal has been taken into account. Complementary to this, a four‐step polymer assignment methodology and a database with the Al^? and Al‐SO₄^2? polymers assigned were created. Several polymers have been assigned for the first time, including Al (SO₄)⁺·H₂O, Al₂O(SO₄)²⁺·H₂O, Al₅O₄(OH)₅²⁺·2H₂O, and Al₃O₅(OH)^2?·4H₂O, among others. The results obtained in the present study help create a foundation to include mass spectrometry as a routine analytical technique to study mineral formation in aqueous solution.     

Atomic distributions in acetylene-air flame using hydraulic high-pressure nebulization with direct (100%) introduction of solutions Applications to speciation analysis

One of the fundamental factors of the performance of atomic spectrometric methods is the efficiency of sample introduction into flame or plasma. By utilization of the formerly developed hydraulic high-pressure nebulizer, a nebulizer/burner system with solution uptake efficiency of 100% have been worked out. Optimizing operation parameters of nebulizer/burner system, an improvement of 2-12 times was achieved for the signal-to-noise ratio in the flame emission and flame atomic absorption spectrometry, depending on sample flow rate. This nebulizer is especially suitable for development of liquid chromatography-AAS/FES coupled technique for speciation analytical tasks.     

Plasma afterglow atomization in electrothermal atomic absorption spectrometry

Potentialities of an Ar/H₂ microwave induced plasma afterglow at 8.2 mbar as an atomization source in electrothermal atomic absorption spectrometry have been examined. More specifically the atomization efficiency, as shown from appearance temperatures, and the reaction mechanisms of the atomization of the oxides and chlorides of alkaline earth and transition metals have been investigated and compared with conventional electrothermal atomization. For all the investigated metal chlorides and alkaline earth oxides, a considerable decrease in appearance temperature (some 500 K), is observed in the plasma afterglow. Such enhanced atomization is believed to be linked to reactions with H atoms. No plasma enhancement, however, is measured for the atomization of the transition metal oxides. All metal oxides are effectively reduced to free metal in the solid state by the Ar/H₂ afterglow, and as a consequence the supply rate is governed by the metal sublimation for these compounds. For metal chlorides, however, strong evidence is found for the atomization process to proceed via gas phase reactions.     

SEM-EDXRF Study of Two Chemical Modifiers Based on Platinum and Tungsten and Their Effect on ET-AAS Atomization of Lead

 The behavior of two chemical modifiers based on platinum and tungsten, is studied in the two parts of this work. At first, the chemical and morphological alterations of these during pyrolysis and atomization stages in electrothermal atomic absorption spectrometry are studied. The compounds were H₂PtCl₆ and Na₂WO₄. A cylindrical graphite tube was used, and fixed shaped rectangular graphite plates were put inside as platforms to prepare the specimens. The crystalline formations on the platforms were studied by scanning electron microscopy and the energy dispersive X-ray spectra allowed the estimation of the chemical composition changes of the modifiers and the graphite surface. According to the spectra and the images obtained, both modifiers where found to change their crystalline form at temperatures between 500–1250 °C. Severe corrosion of the graphite surface was observed in case of H₂PtCl₆ at temperature higher than 750 °C, while minor damages were observed in case of Na₂WO₄. In the second part of this work, the efficiency of these modifiers was tested for maximum loss-free pyrolysis temperature and atomization of lead by electrothermal atomic absorption spectrometry. The optimum results, concerning these parameters, obtained for medium concentration of the modifiers. The effect of each modifier on the atomization signal is discussed, and the optimum concentration of each one is estimated.     

Indirect hydrogen analysis by gas chromatography coupled to mass spectrometry (GC–MS)

Gas chromatography (GC) is an analytical tool very useful to investigate the composition of gaseous mixtures. The different gases are separated by specific columns but, if hydrogen (H₂) is present in the sample, its detection can be performed by a thermal conductivity detector or a helium ionization detector. Indeed, coupled to GC, no other detector can perform this detection except the expensive atomic emission detector. Based on the detection and analysis of H₂ isotopes by low‐pressure chemical ionization mass spectrometry (MS), a new method for H₂ detection by GC coupled to MS with an electron ionization ion source and a quadrupole analyser is presented. The presence of H₂ in a gaseous mixture could easily be put in evidence by the monitoring of the molecular ion of the protonated carrier gas. Copyright © 2013 John Wiley & Sons, Ltd.     

Assessment of three digestion procedures for Zn contents in Pakistani soil by flame atomic absorption spectrometry

Evaluation of three different digestion procedures for accurate determination of elemental concentration in soils was undertaken. The digestion procedures, two leaching and a total dissolution processes were compared for twenty-one soil samples. The soil standard reference materials (SRMs), IAEA Soil-5 and IAEA Soil-7 were analysed for quality control purposes. Zinc (Zn) was analysed using flame atomic absorption spectrometry (FAAS). Precise analysis was accomplished in the SRM and soil samples, which was better than 4.7% for leaching and total dissolution procedure. Compared with the elemental concentration in soil samples, HF–HClO₄ procedure achieved greater accuracy, where as HNO₃–H₂O₂ and HNO₃–H₂SO₄–HCl procedures were comparable with slight variation in a few samples.     

N-Hydroxysuccinimidyl phenylacetate as a novel derivatizing reagent for aliphatic amines in gas chromatography

A new succinimidyl ester amine-reactive reagent, N-hydroxysuccinimidyl phenylacetate (SIPA), has been synthesized for analytical derivatization of aliphatic amines, such as methylamine, ethylamine, propylamine, butylamine and pentylamine in gas chromatography (GC). The derivatiation conditions were investigated in detail. The experimental results showed that SIPA was a useful reagent with the advantages including mild derivatization condition, rapid reaction time and selectivity to amino group. In a pH 8.5 H₃BO₃-Na₂B₄O₇ buffer solution and dichloromethane, the derivatization and extraction can be accomplished at the same time and excess reagent need not be removed before analysis, which greatly simplified the sample preparation. The derivatives were analyzed by gas chromatography-mass spectrometry (GC-MS) and gas chromatography/flame ionization detector (GC/FID). The detection limits (S/N=3) were in the range of pmol level.     

A possible steady state kinetic model for the atomization process during flame atomic spectrometry: Application to atomization interference effects of aluminum on Group II elements

The atomization interference effects of AlCl₃ on MgCl₂ and CaCl₂ during flame atomic absorption spectrometry were studied in terms of a steady state kinetic model which takes into account relative rates of thermal dissociation of analyte and interferant metal salts, recombination of counter atom and analyte and interferant atoms, charge transfer between analyte and interferant species, and ion/electron collisional de-ionization within the plasma. Data are presented showing that the interference of AlCl₃ on the atomization of MgCl₂ and CaCl₂ in an air-acetylene flame is due (a) to interference effects due to AlCl₃ which occur prior to complete atomization of the Group II metal chlorides, and (b) to the recombination of the Group II metal and the chlorine atom which is enhanced by the increased density of the chlorine atom as a result of the dissociation of the AlCl₃ interferant.     

The relation of double peaks, observed in quartz hydride atomizers, to the fate of free analyte atoms in the determination of arsenic and selenium by atomic absorption spectrometry

The mechanism at the origin of double peaks formation in quartz hydride atomizers were investigated by continuous flow hydride generation atomic absorption spectrometry. Arsenic and selenium were used as model analytes. The effect of atomization mode (flame-in-gas-shield (FIGS), miniature diffusion flame and double flame (DF)) and some experimental parameters as oxygen supply rate for microflame and the distance from atomization to free atoms detection point, were investigated on the shape of both analytical signals and calibration graphs. Rollover of calibration graphs and double peak formation are strictly related each to the other and could be observed only in FIGS atomizer mode under some particular conditions. A mechanism based on incomplete atomization of hydrides cannot explain the collected experimental evidences because the microflame of FIGS is able to produce quantitative atomization of large amount of hydrides even at supply rate of oxygen close to extinction threshold of microflame. The heterogeneous gas–solid reactions between finely dispersed particles, formed by free atom recombination, and the free atoms in the gaseous phase are at the origin of double peak formation.     

The study of C1?C3 monosubstituted alkyl benzenes by the inverse convolution of first differential ionization efficiency curves

The electron impact ionization efficiency curves for the parent ions and the [C₇H₇]⁺ fragment ion formed from monosubstituted alkyl benzenes (R?CH₃? n-C₃H₇) have been studied by applying the inverse convolution technique of Vogt and Pascual to the first derivative ionization efficiency curves of the ions. Ionization and appearance energies measured for the ions at threshold are in good agreement with recently published photoionization values. Structures in the ionization efficiency curves (higher energy processes) are also reported for about 4 e V above threshold. The heats of formation calculated for [C₇H₇]⁺ fragment ions obtained from toluene and ethyl benzene at threshold are equal to 864 and 865 kJ mol^?1 respectively, and are consistent with the tropylium structure. However, for the [C₇H₇]⁺ fragment ion obtained from n-propyl benzene at threshold the calculated heat of formation is equal to 923 kJ mol^?1 and probably corresponds to a benzyl structure.     

Optimization and comparison of two digestion methods for multi-element analysis of certified reference plant materials by ICP-AES. Application of Plackett-Burman and central composite designs

Two open-vessel wet digestion methods using mixtures of (i) HNO₃ and H₂SO₄ (WD I), and (ii) HNO₃, H₂SO₄ and H₂O₂ (WD II) were developed and optimized for determination of a wide range of elements in plant reference materials by inductively coupled plasma atomic emission spectrometry. A Plackett-Burman fractional factorial experimental design with eight experiments for seven variables was used for the evaluation of the effects of several digestion variables at once. From these studies, certain variables showed up as significant, and they were further optimized by using a star-type central composite experimental design, which involved fourteen experiments. Instrumental variables such as radio-frequency incident power, nebulizer argon gas flow rate and sample uptake flow rate were also optimized. The analytical performance was assessed statistically. Nine elements in total can be simultaneously determined at the concentration levels usually found in plant materials. The agreement between measured and certified values with respect to NIST-SRM 1568a (rice flour), IAEA-331 (spinach leaves) and IAEA-359 (cabbage) proved that the developed methods are well suited for routine elemental analysis of plants or foods of plant origin. Correspondence: George A. Zachariadis, Laboratory of Analytical Chemistry, Department of Chemistry, Aristotle University, GR-54124 Thessaloniki, Greece     

A possible steady state kinetic model for the atomization process during flame atomic spectrometry: Application to atomization interference effects of aluminum on Group II elements

The atomization interference effects of AlCl₃ on MgCl₂ and CaCl₂ during flame atomic absorption spectrometry were studied in terms of a steady state kinetic model which takes into account relative rates of thermal dissociation of analyte and interferant metal salts, recombination of counter atom and analyte and interferant atoms, charge transfer between analyte and interferant species, and ion/electron collisional de-ionization within the plasma. Data are presented showing that the interference of AlCl₃ on the atomization of MgCl₂ and CaCl₂ in an air-acetylene flame is due (a) to interference effects due to AlCl₃ which occur prior to complete atomization of the Group II metal chlorides, and (b) to the recombination of the Group II metal and the chlorine atom which is enhanced by the increased density of the chlorine atom as a result of the dissociation of the AlCl₃ interferant. Received: 23 February 1998 / Revised: 18 December 1998 / Accepted: 25 December 1998     

Direct measurement of the C2H5C(O)O2 + NO reaction rate coefficient using chemical ionization mass spectrometry

The rate coefficient for the reaction of the peroxypropionyl radical (C₂H₅C(O)O₂) with NO was measured with a laminar flow reactor over the temperature range 226–406 K. The C₂H₅C(O)O₂ reactant was monitored with chemical ionization mass spectrometry. The measured rate coefficients are k(T) = (6.7 ± 1.7) × 10⁻¹² exp{(340 ± 80)/T} cm³ molecule⁻¹ s⁻¹ and k(298 K) = (2.1 ± 0.2) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹. Our results are comparable to recommended rate coefficients for the analogous CH₃C(O)O₂ + NO reaction. Heterogeneous effects, pressure dependence, and concentration gradients inside the flow reactor are examined. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet: 31: 221–228, 1999