Applicability of microwave induced plasma optical emission spectrometry (MIP-OES) for continuous monitoring of mercury in flue gases

The applicability of microwave-induced plasma optical emission spectrometry (MIP-OES) for continuous monitoring of the environmentally hazardous element mercury in flue gases has been studied. Microwave induced plasmas have been sustained using both a TM₀₁₀ cavity (Beenakker resonator) and a so-called Surfatron. The analytical figures of merit for mercury in argon and helium discharges with both types of low-power micro-wave discharges have been examined. To determine mercury in artificial stack gases non-mixed argon/nitrogen discharges have been tested using a tangential flow torch design which allows to introduce a metal-loaded nitrogen gas flow as external gas and argon as internal gas. The addition of main flue gas components such as water vapour (concentration <6 g/m³), oxygen (<4% v/v) and carbon dioxide (<15% v/v) decrease the mercury line intensities to a considerable extent. Trace gases (CO, HCl, SO₂, NO) in concentrations typical to waste incineration processes have been found to have no effect on the mercury and the argon line intensities. The detection limit of mercury in nitrogen is 8 g/m³ using the TM₀₁₀ MIP and 10 g/m³ using the Surfatron. As such low detection limits are below the emission limit values of present-day environmental legislation MIP-OES is useful for on-line monitoring of mercury.Dedicated to Professor Dr. Dieter Klockow on the occasion of his 60th birthday     

Comparative study of microwave-induced plasma atomic emission spectrometry and atomic fluorescence spectrometry as gas-chromatographic detectors for the determination of methylmercury in biological samples

In order to attain a lower detection limit with the HS GC MIP analytical method (Head-Space Gas Chromatography with Microwave-Induced Plasma detection) recently developed for the analysis of methylmercury in biological samples, the quarter-wave Evenson-type cavity used until now was replaced by a TM₀₁₀ Beenakker-type cavity, which was used with both argon and helium as carrier gas. With an argon plasma, an eightfold increase in detection limit was gained compared with the argon plasma sustained by the Evenson cavity, while only a four-fold increase was gained with the helium plasma. In a second step of the study, the MIP detector was replaced by an AFS (atomic fluorescence) detector (CVAFS Model-2, Brooks Rand Ltd, Seattle, USA). With this AFS detector a detection limit of 1 ng methyl mercury per g biological tissue could be reached; i.e. measurements were 40 times more sensitive than those using the Evenson cavity. This detector has some other advantages compared with MIP detection: it is less expensive and easier to manipulate, while the same precision and accuracy are obtained. The use of AFS as detector in the headspace gas chromatographic system is therefore an important improvement for the analysis of methyl-mercury in biological samples.     

A close-up of three microwave plasma sources in view of improved element-specific detection in liquid chromatography

Progress in the features of three types of microwave plasmas is discussed, in view of the development of successful methods for atomic spectrometric element-specific detection in liquid chromatography. For the low-power microwave induced plasmas the development of the toroidal plasma in a TM010 cavity according to Beenakker is mentioned as the break-through for the introduction of wet aerosols. Capacitively coupled microwave plasmas (CMP), which can be operated with helium, argon and even air as working gases, are robust and allow obtaining of detection limits for Fe, Cr, Ni and Co in aqueous solutions in the 0.02 to 0.06 μg/ml range and in light oils, as an example of organic liquids, between 0.08 and 0.13 μg/ml. Special attention should be given to the microwave plasma torch (MPT) in which aerosols from aqueous as well as from organic solutions produced by a Légère nebulizer can be introduced without desolvation. Here, detection limits for Cd, Cr, Li and Pb range from 0.02 to 0.5 μg/ml. For the case of chromium dissolved as dithiocarbamate complex in an acetonitrile/H₂O mixture (2:1), its detection limit is 0.12 μg/ml, being already below that obtained with UV spectrophotometry. The limits of detection achieved with the sources discussed in the case of atomic emission spectrometry show the prospective for further development.     

Determination of nanogram amounts of bromide and chloride by molecular emission cavity analysis based on gallium halide emission

By measuring the GaBr emission enhanced by iodide at 350 nm in a carbon cavity heated by a hydrogen/argon flame, 0–60 ng of bromide is determined with a detection limit of 0.5 ng μl^?1. In a similar way, gallium (0–20 ng) can be determined with a detection limit of 0.15 ng μl^?1. Interferences are reported. Chloride (0–1200 ng) is determined by means of GaCl emission; the detection limit is 50 ng μl^?1.     

Determination of aluminum and silicon in biological materials by inductively coupled plasma atomic emission spectrometry with electrothermal vaporization

An atomic emission spectrometric method is described for the determination of trace elements in microvolume samples especially of biological materials. Based upon the arrangement of a commercial electrothermal vaporizer and a 40-MHz inductively coupled plasma, the direct determination of aluminum and silicon in human body fluids such as urine and serum and aluminum in hemodialysis solution is performed. The instrumental system involves vaporizing the sample from a modified graphite electrode followed by atomization and excitation of the vapors in the ICP discharge. Compromise experimental conditions are reported and calibration functions compared. Limits of detection in 5-μl samples were 8 pg Al and 2.5 ng Si, and after preconcentration of Al with a poly(acrylamidoxime) resin, the detection limit was 1 pg Al. Recovery of 5 μg $\text{Si}\text{ml}$ and 10 ng $\text{Al}\text{ml}$ from aqueous and synthetic standards was 80–85% and 96–103%, respectively.     

The determination of tellurium by nondispersive atomic fluorescence spectrometry using the hydride generation technique

Atomic fluorescence spectrometry with a nondispersive measuring system is combined with a hydride generation technique for the determination of tellurium. Atomic fluorescence measurement is based on the reduction of tellurium by either metallic zinc or sodium borohydride, introduction of the generated tellurium hydride into a premixed argon (entrained air)-hydrogen flame, and excitation with a tellurium electrodeless discharge lamp. The comparison of the zinc and the sodium borohydride reduction methods is discussed in terms of detection limit, precision and interference. The best attainable detection limits for tellurium are 2ng (0.1 $\text{ng}\text{ml}$) and 30 ng (1.5 $\text{ng}\text{ml}$) with the zinc and the sodium borohydride methods respectively. Analytical working curves obtained from peak-height and peak-area measurements are linear over a range of approximately 4 orders of magnitude. Of the mineral acids examined in the range up to 2.0 m. nitric acid gives a depressing interference in the range greater than 0.5 m in the zinc method, whereas all of the acids greater than 1.0 m give a slight enhancement of the signal in the sodium borohydride method. The presence of several elements including other hydride-forming elements in 1000-fold ratio to tellurium causes a depressing interference, while enhancing interferences from tungsten and vanadium are observed in the zinc and the sodium borohydride methods, respectively. The present system coupled with the zinc method has been applied to the determination of tellurium in several samples of high-purity copper metal after separation of the analyte from copper by passing an ammoniacal solution of the sample through Chelex-100 resin. The results are in good agreement with those obtained by graphite furnace atomic absorption spectrometry.     

NMR spectroscopic study of noble gas binding into the engineered cavity of HPr(I14A) from Staphylococcus carnosus

Xenon binding into preexisting cavities in proteins is a well-known phenomenon. Here we investigate the interaction of helium, neon, and argon with hydrophobic cavities in proteins by NMR spectroscopy. 1H and 15N chemical shifts of the I14A mutant of the histidine-containing phosphocarrier protein (HPr(I14A)) from Staphylococcus carnosus are analyzed by chemical shift mapping. Total noble gas induced chemical shifts, Delta, are calculated and compared with the corresponding values obtained using xenon as a probe atom. This comparison reveals that the same cavity is detected with both argon and xenon. Measurements using the smaller noble gases helium and neon as probe atoms do not result in comparable effects. The dependence of amide proton and nitrogen chemical shifts on the argon concentration is investigated in the range from 10 mM up to 158 mM. The average dissociation constant for argon binding into the engineered cavity is determined to be about 90 mM.     

Eine mikromethode der flammen-atomabsorptions- und emissionsspektrometrie (platinschlaufen-methode)—II: Die bestimmung von As,Bi, Cd,Hg, Pb,Sb, Se,Te, Tl,Zn/Li,Na, K,Cs, Sr,Ba

This paper described the continuation of the work of Part I dealing with a microanalytical method in which the sample is introduced into a flame using an electrically heated platinum loop. This device is used in connection with an atomic absorption (AA) spectrometer. The detection limits are one to two orders of magnitude better than those of conventional flame AAS. The reproducibility depends on the element and is in general 3–5% (relative standard deviation) for concentrations in the $\text{ng}\text{ml}$ range. The platinum loop method can be also applied for flame emission analysis of small amounts of sample or the determination of low concentrations (alkalis). This application gives access to determinations in the lower ng or the pg range (detection limit of lithium: 0.6 pg).     

High-performance liquid chromatographic determination of the antitumor agent mitomycin c in human blood plasma

A high-performance liquid chromatographic method for the determination of the antitumor drug mitomycin C in blood plasma samples of cancer patients is described. The drug is extracted from the plasma with chloroform–2-propanol (1+1, $\text{w}\text{w}$) and chromatographed on a reversed-phase column with u.v. detection at 365 nm. The detection limit of the determination is 1 ng ml^-1 for 0.2–1.0 ml plasma samples. Preliminary results of a pharmacokinetic study show that the sensitivity and selectivity of the assay are adequate for drug monitoring in clinical practice. The results obtained from multiwavelength detection suggest the existence of metabolites.     

The optimization of an ICP injection technique and the application to the direct analysis of small-volume serum samples

The optimization and the analytical properties of an injection technique for the analysis of small-volume samples (50–200 μl) by inductively coupled plasma atomic emission spectroscopy (ICP-AES) are described. Samples are injected into a small funnel connected to a concentric glass nebulizer. A 3 kW argon/nitrogen ICP with power stabilization is used as excitation source. When operating the nebulizer at an argon pressure of 5 bar, relative detection limits for calcium, copper, iron, magnesium and zinc (0.2–50 $\text{ng}\text{ml}$) are a factor of 2 to 10 higher when compared with ICP methods using continuous nebulization. However, the full power of detection of the injection method is obtained at a 50 μl sampling volume. Matrix effects caused by sodium salt concentrations of 5 $\text{g}\text{l}$ are lower than 10%. Relative standard deviations s_r,(I_X) ranged from 0.03 to 0.07. The method was applied to the sequential determination of trace elements (copper, iron and magnesium) in human serum samples after a 1 + 4 dilution with Herrmann solution. The accuracy of the method is illustrated by the analysis results for calcium, copper, iron, magnesium and zinc in a series of test serum samples.     

Emission spectra of supersonically cooled methyldiacetylene cations

The ā²E → X?²E (Σ= + $\text{1}\text{2}$, - $\text{1}\text{2}$) electronic transitions of rotationally/vibrationally cooled CH₃CCCCH^- cation, as well as the d₁-/d₃-/d₄-substituted species, were studied by emission spectroscopy. Ion emission was obtained by electron impact on the neutral species seeded in a helium supersonic free jet. Vibrational frequencies in both electronic states are inferred to within ±1 cm^-1. Spin-orbit splittings are observed and interpreted on the basis of non-linear vibronic couplings. Rotational subbands are observed, yielding rotational and Coriolis parameters as well as rotational temperatures.     

Comparative study of a beenakker cavity and a surfatron in combination with electrothermal evaporation from a tungsten coil for microwave plasma optical emission spectrometry (MIP-AES)

Microwave induced plasmas, sustained in a Beenakker resonator and a surfatron, respectively, are used to excite vapours released by electrothermal evaporation of solutions from a tungsten coil. The analytical figures of merit of AES for two easily volatilized elements (Cu, Cd) are compared for argon MIP operated in the two resonators under optimized conditions. In the Beenakker resonator a 1-filament plasma was produced at an argon flow of 0.45 l./min and a forward power of 50 W. In the surfatron a 2-filament plasma with 2.44 l./min argon and a forward power of 130 W was used. The detection limits for Cu and Cd with the surfatron are lower than those obtained with the Beenakker resonator and are in the range 10-20 ng/ml. Also interferences arising from an easily ionized element such as Na are lower with the surfatron than with the beenakker resonator. The linear dynamic ranges in the case of the surfatron are also superior and extend over three decades of concentration.     

Studies of an inductively-coupled high-frequency argon plasma for optical emisson spectrometry—II: Compromise conditions for simultaneous multielement analysis

This paper deals with the experimental selection of conditions under which a low-power inductively-coupled plasma (ICP) can be operated so as to achieve a good compromise for simultaneous multi-element analysis. With the experimental facilities employed by the authors such conditions were found at a power of 0·7 kW, a carrier gas flow of $\text{1·31}\text{min}$ of argon, and an observation height of 15 mm. An outstanding detection power with detection limits below 1 $\text{ng}\text{ml}$ for 27 out of 32 representative elements and satisfactory suppression of ionization interference effects were simultaneously achieved.Modifications of a previously described ultrasonic nebulizer led to a higher rate of sample injection into the plasma, an improved overall reliability of the sample introduction device, and better reproducibility of spectral-line intensities (1·0–1·2% at concentrations 100 times the detection limits for 15-s integrations). Details of the construction of the ultrasonic nebulizer and its performance are provided and a simple theoretical treatment of the dependence of the aerosol ejection rate on the carrier gas flow and the size of the fog chamber is presented.Possible interelement interferences in the ICP are broadly classified.From the optimization experiments and application studies general conclusions regarding the usefulness of the ICP for both the accurate determination of a few elements and general overall analysis comprising a large number of elements are drawn.     

A sample introduction system for an inductively coupled plasma operating on an argon carrier gas flow of 0.1lmin

A sample introduction system is described for use with a water-cooled ICP torch described previously [Anal. Chem.51, 2378 (1979)]. It consists of a narrow bore (100 μm) stainless steel Babington nebulizer operating on 0.05 to 0.2 $\text{l}\text{min}$ argon inserted into a small (10 ml) nebulizer chamber. The solvent is force-fed continuously by gas pressure or with a peristaltic pump. Liquid samples can be supplied continuously or in discrete quantities using a sample loop between the pump and the nebulizer. In the latter case only 25 s are required for sample change. The nebulization efficiency for water and organic solvents is comparable to that of conventional pneumatic nebulizers operating on 1 $\text{l}\text{min}$ argon.     

Determination of tungsten by direct current plasma atomic emission spectrometry

The determination of tungsten in steels and alloys with the three-electrode direct current plasma (DCP) “spectrajet” was investigated. The relative intensities of 17 spectral lines of tungsten and several possible interfering lines of its concomitants are listed. WI 400.875 nm is normally best suited, because the background produced by iron and acid is low and easily compensated for by using a blank solution. The limit of detection c_l in steels is 2 × 10^?3% W for 10 $\text{mg}\text{ml}$ of sample. The line W I 407.436 nm is preferred in the presence of much titanium. For the purpose considered the DCP provides about the same power of detection as the more expensive inductively coupled plasma (ICP), but its observation zone is less well buffered against influences from the matrix.     

Determination of cadmium by an improved double chamber electrothermal vaporization inductively coupled plasma atomic emission spectrometry

An improved double chamber electrothermal vaporization (ETV) system was designed. A new inner chamber and its bottom plate made of quartz glass were attached with carrier support gas inlet port for the determination of cadmium by inductively coupled plasma atomic emission spectrometry (ICP-AES). The use of the inner chamber in combination with the plate played important roles to transport the metal vapor efficiently into argon ICP. Ten-μl sample aliquots were dried at 100 °C and subsequently heated at 1000 °C on the tungsten boat furnace. The evolved vapor was swept into the ICP source through PTFE tubing and the inner chamber by a 0.8 l/min H₂ (7%)-Ar carrier gas. The performance parameters of ETV-ICP-AES such as temperature program and gas flow rate were evaluated using cadmium standard solution. Under the optimized experimental conditions, the best attainable detection limit at Cd II 214.438 nm line was 0.2 ng/ml with linear dynamic ranges of 50 to 10,000 ng/ml for cadmium. The instrumental precision expressed as the relative standard deviation (RSD) from ten replicate measurements of 10,000 ng/ml for cadmium by ETV-ICP-AES was 0.85%. The present method has been successfully applied to the determination of cadmium in zinc-base materials.     

Structural Investigations of Argon Hydrates at Pressures up to 10 kbar

Neutron diffraction patterns of three argon hydrates which exist at the pressures up to 10 kbar has been studied; Rietveld refinement of their structures has been done. The phase which is stable from 1 bar to 4.6 kbar appears to be typical cubic structure II gas hydrate with variable degree of filling of the large cavities. Stoichiometry of this compound under high-pressure conditions has been determined for the first time and appears to be ArW4.5H₂O and Ar·4H₂O at 3.4 and 4.3 kbar, respectively. Gas hydrate existing in the pressure range of 4.6–7.7 kbar has a hexagonal structure (hexagonal structure III, so-called structure H). Refinement of the structure has shown that the best agreement between calculated and experimental pattern can be reached in the case of accommodation of five (!) argon atoms in the large cavity. Indexing of the neutron diffraction pattern of the hydrate stable in the 7.7–9.5 kbar range leads to the primitive tetragonal unit cell with parameters a = 6.342 Å, c = 10.610 Å at 9.2 kbar, which does not correspond to any known type of gas hydrates. The water framework of this structure was found by idealizing the structure of pinacol semiclathrate hydrate. This hydrate belongs to a new, earlier unknown, tetragonal structural type of gas hydrates. It contains only one type of polyhedral cavities with 14 faces. This type of polyhedrons are space-filling; two argon atoms occupy each cavity. This structure gives the first example of the gas hydrate water framework which contains only one type of polyhedral cavities.     

Determination of palladium in different samples by neutron activation after selective preconcentration with α-benzildioxime

A procedure is described for the determination of submicrogram quantities of palladium in sea water, biological and geological materials. Palladium is preconcentrated by coprecipitation with α-benzildioxime at pH 2 in the presence of citric acid followed by neutron activation. The method is highly selective and only traces of other metals are adsorbed on the surface of the precipitate. The instrumental variant of counting of long-lived ¹⁰⁹Pd (t$\text{1}\text{2}$ = 13.6 h) after 16-h irradiation gives a detection limit of 10 ng. A further decrease of the detection limit to 1 ng can be attained by removal of radioactive impurities (mainly ²⁴Na, ⁵⁶Mn and ⁸²Br) after washing the dichloromethane extract of dissolved precipitate with an aqueous solution of citric acid containing inactive carriers of bromide, manganese and sodium ions. Palladium (¹⁰⁹Pd) is finally measured by a NaI(Tl) well type scintillation detector. The method can be applied to most environmental samples.     

Rotational and vibrational temperatures of naphthalene in a naphthalene-argon supersonic jet

In the $\text{A}$¹B_2u-$\text{X}$¹A_g system of naphthalene in a supersonic jet, rotational contour calculations show rotational temperatures of 2–60 K for argon carrier gas pressures of 1520-120 Torr. The b_1u vibration v₂₄ shows a high vibrational temperature which corresponds to the seeding temperature for pressures <400 Torr.     

Comparison in the analytical performance between krypton and argon glow discharge plasmas as the excitation source for atomic emission spectrometry

The emission characteristics of ionic lines of nickel, cobalt, and vanadium were investigated when argon or krypton was employed as the plasma gas in glow discharge optical emission spectrometry. A dc Grimm-style lamp was employed as the excitation source. Detection limits of the ionic lines in each iron-matrix alloy sample were compared between the krypton and the argon plasmas. Particular intense ionic lines were observed in the emission spectra as a function of the discharge gas (krypton or argon), such as the Co II 258.033 nm for krypton and the Co II 231.707 nm for argon. The explanation for this is that collisions with the plasma gases dominantly populate particular excited levels of cobalt ion, which can receive the internal energy from each gas ion selectively, for example, the 3d⁷4p ³G₅ (6.0201 eV) for krypton and the 3d⁷4p ³G₄ (8.0779 eV) for argon. In the determination of nickel as well as cobalt in iron-matrix samples, more sensitive ionic lines could be found in the krypton plasma rather than the argon plasma. Detection limits in the krypton plasma were 0.0039 mass% Ni for the Ni II 230.299-nm line and 0.002 mass% Co for the Co II 258.033-nm line. However, in the determination of vanadium, the argon plasma had better analytical performance, giving a detection limit of 0.0023 mass% V for the V II 309.310-nm line.