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.     

Atomemissionsspektroskopie mit laseranregung an graphit unter erhöhtem Druck—I. Plasmaeigenschaften

The paper describes the vaporization of graphite, the plasma form, the plasma properties and the interaction of laser radiation with the plasma for when the beam of a free running laser is focused on graphite in air at atmospheric pressure and in He, O₂, or Ar at pressures in a range from (1–40) × 10⁵ Pa.The power densities of the focused laser radiation (focal distances of condenser lens 150 to 50 mm) reach 10⁷$\text{W}\text{cm}{}_2$. The extent of vaporization depends on the pulse energy (under 40 × 10⁵ Pa not unambiguously, however) and the ambient pressure.The plasma is observed with normal, framing (to 10⁷ frames per second), and streak photography (to 25 $\text{mm}\text{μs}$). The plasma form depends, among other things, on the ambient gas, the power density of the laser pulse on the sample, and the ambient pressure. Increasing the pressure in the range from 25 × 10⁵ to 40 × 10⁵ Pa modifies the plasma form from a “plume” to a “fungus” with toroidal head. The average velocity of the plasma particles in air is about 3 × 10⁵$\text{cm}\text{s}$, which is 10 times higher than the velocity of the luminous plasma front. Under increased pressure a strong interaction between the laser radiation and the plasma takes place resulting in absorption by inverse bremsstrahlung (>50% in 40 × 10⁵ Pa He). In this way the luminosity of the plasma is enhanced by a factor of 100 (delay to the start of the laser pulse about 50 μs). This absorption of the laser beam by inverse bremsstrahlung becomes the dominating mechanism of excitation of the plasma and causes a strong temperature gradient from the point of absorption to the fringe.     

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.     

Characterization of noise in inductively-coupled plasma emission spectrometry

The nebulizing process in inductively-coupled plasma emission spectrometry is a major source of the instrumental variability; an attempt has been made to isolate this source so that its influence on the final result could be evaluated. Direct measurements of the time-dependent variations of the sample supply to the plasma were achieved by using a device based on the light-scattering property of nebulized test solutions. The noise from the nebulizer and of the emission signal was characterized by autocovariance functions and power spectral densities. The types of noise observed showed f^{-$\text{1}\text{2}$} and f^{-$\text{1}\text{4}$} character, depending on the concentration of the test elements employed. Cross-covariance revealed a strong correlation between the noise sources considered. The applicability and limitations of possible correction and electronic filtering procedures are indicated.     

Characteristics of Multi-Phase Alternating Current Arc for Glass In-Flight Melting

An innovative in-flight melting technology with multi-phase AC arc was developed for glass industry. The enthalpy probe and high speed video camera were used to characterize the temperature, velocity, and discharge behavior of multi-phase AC arc. The effects of input power and sheath gas flow rate on arc and melting behavior were investigated. Results show that the temperature and velocity on arc center are increased with input power or sheath gas flow increase. The fluctuation of luminance area ratio and coefficient of variation reflects the change of arc discharge behavior. High temperature of plasma enhances the melting of granulated raw particles during in-flight heating treatment. The shrinkage of particle and the volatilization degree of Na₂O increase under a larger flow rate of sheath gas. The characterized arc behavior agrees with the melting behavior of glass raw materials, which can provide valuable guidelines for the process control of glass melting.     

Gas chromatographic stationary phase properties of two room-temperature liquid organi salts

The gas chromatographic properties of two room-temperature liquid organic salts, triethyl-n-hexylammonium triethyl-n-hexylboride (TEHAB) and stearylmethyldipolyoxethyl(15)ammonium chloride (Ethoquad $\text{18}\text{25}$, are described. Triethyl-n-hexyl-ammonium triethyl-n-hexylboride could be used up to temperatures of 130°C but showed poor stability towards air and undesirable reactivity towards some dipolar and proton donor/acceptor solutes when used as a column packing material. In contrast, Ethoquad $\text{18}\text{25}$ had a maximum column operating temperature of 280°C, or 300°C after vacuum conditioning. From a calculation of mcReynolds' phase constants and the molar free energy, enthalpy, and entropy of solution for polarity test probes, it was established that Ethoquad $\text{18}\text{25}$ showed intermediate selectivity for dipolar and proton-donor solutes compared to results for conventional non-ionic phases. Ethoquad $\text{18}\text{25}$ is an excellent phase for the profiling of essential oils.     

Spectroscopic study of argon MIP discharge used for analysis of solutions

Microwave-induced plasma (MIP) is an attractive excitation source which seems to be competitive to ICP-AES discharge. Reduced requirements in power and amounts of carrier gas and solution are considerable in comparison with ICP-AES. However, some disadvantages (such as a partial atomization and instability of discharge) can arise from the reduced power. Fundamental studies of MIP could be a help for control and proper selection of operating parameters of this discharge type. The behavior of solutions sprayed into an argon plasma was studied in a commercial MIP under different experimental conditions (argon and aerosol flow rates, discharge power). Rotational and vibrational energy distributions on the basis of the OH A²Σ − X²π molecular spectra and electronic energy distributions on the basis of atomic spectra have been measured under operative conditions and discussed from the point of view of analytical applications of MIP.     

Elimination reactions of 1,2-dihalo-2,3,3-trifluorocyclobutanes

Elimination reactions on isomeric mixtures of $\text{cis}$ and $\text{trans}$ 1,2-dihalo-2,3,3-trifluorocyclobutanes are reported. In zinc-promoted dehalogenations a steady decrease in the relative amount of the $\text{trans}$ isomers compared to the $\text{cis}$ isomers occured, with 2,3,3-trifluorocyclobutene as the sole product. The $\text{cis}$ isomers reacted at a faster rate in potassium hydroxide induced eliminations to yield a slight predominance of 1-halo-2,3,3-trifluorocyclobutenes over 3-halo-3,4,4-trifluorocyclobutenes. However, with triethylamine as the inducing base, an increased rate of elimination from the $\text{trans}$ isomers was noted along with almost exclusive formation of 3-halo-3,4,4-trifluorocyclobutenes.     

Laser Doppler anemometry under plasma conditions. Part II. Measurements in an inductively coupled r.f. plasma

Laser Doppler anemometry is used for the measurements of the plasma and particle velocity profiles in the coil region of an inductively coupled r.f. plasma. Results are reported for a 50 mm i.d. induction plasma torch operated at atmospheric pressure with argon as the plasma gas. The oscillator frequency is 3 MHz and the plate power is varied between 4.6 and 10.5 kW. Plasma velocity measurements are obtained using a fine carbon powder as a tracer. Measurements are also given for larger silicon particles ( ) centrally injected into the discharge under different operating conditions.Nomenclature d _p particle diameter - P ₀ plasma power - Q ₁ powder carrier gas flow rate - Q ₂ plasma gas flow rate - Q ₃ sheath gas flow rate - r distance in the radial direction - V axial plasma velocity - V _p axial particle velocity - Z distance in the axial direction - standard deviation     

Synthesis of sterically hindered 1-arylpyrrolidines and 1-arylpiperidines by condensation of primary aromatic amines with cyclic ethers or diols

A variety of 1-($\text{o}$-alkylphenyl)- and 1-($\text{o}$-$\text{o}$'-dialkylphenyl)- pyrrolidines and -piperidines were prepared by the gas phase alumina mediated condensation of tetrahydrofuran (THF), tetrahydropyran (THP) or the corresponding diols with primary aromatic amines in fair to high yield. This methodology can also be used for the synthesis of 1-phenylhexahydroazepine from aniline. A mechanistic interpretation of the catalytic action of alumina is presented.     

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.     

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.     

The magnetic circular dichroism spectrum of matrix-isolated TaO

TaO has been matrix-isolated in an argon matrix at 14 K and 24 K and studied spectroscopically in the visible region (300–850 nm). Both adsorption and magnetic circular dichroism (MCD) spectra have been recorded and analyzed. A determination of the total angular momentum quantum numbers (ω) for fourteen excited electronic states has been made. The g factors for the ground ²Δ_{$\text{3}\text{2}$} and excited ²φ_{$\text{5}\text{2}$} states have been determined from a moment analysis of the MCD and absorption spectra of the 450.3 nm band. The present study indicates the power of the combination of magnetic circular dichroism and matrix isolation for the assignment of excited electronic states of high temperature molecules.     

The amperometric response of tubular electrodes applied to flow-injection determinations

The classical treatment by Taylor for the dispersion of mass injected into a fluid stream in a linear, tubular channel is applied for amperometric detection in flow-injection systems with a tubular, flowthrough electrode. Peak current is predicted to be dependent upon the $\text{l}\text{3}$rd root of flow rate for low dispersion and the —$\text{1}\text{6}$th root of flow rate for high dispersion. Agreement between experimental results and theory is excellent for flow rates of 0.5 ml min^-1 or less in a linear, tubular channel with an inner radius of 0.0483 cm. As examples, experimental and predicted currents agree to better than 0.1 μA throughout a peak with a maximum value near 2 μA, and effects of retention volume, sample volume, and flow rate on the ratio of peak current to steady-state current are predicted with errors of 9% or less.     

Implementation of acoustic, radiofrequency and microwave rotating fields in analytical plasma sources

Four helium plasma sources operating at atmospheric pressure have been developed for analytical emission spectrometry by applying a synchronically rotating field with three or more phases operating at 1 kHz, 27 MHz or 2.45 GHz. The plasma takes the form of a disk and has minimum field strength at the axis. Thus, a channel is formed at the center through which the sample in the form of wet aerosol or a chemically generated vapor of halogen may be introduced. A dual-flow concentric ceramic injector was used to supply helium plasma gas and the sample to the plasma. The helium plasma operated at low power levels (40-300 W) and low gas flow rates of below 3 L min^− 1 and was self-igniting. The acoustic, radio-frequency (rf) and microwave-driven plasmas can withstand wet aerosol loadings of 5, 30 and 100 mg min^− 1, respectively, generated by an ultrasonic nebulizer without a desolvation unit. The plasma physical characteristics were compared at these three frequencies under otherwise similar operating conditions. The helium excitation temperature, OH rotational temperature and electron number density increased with increasing frequency in ranges of 2800-4000 K, 1100-3200 K and 0.1-7 × 10¹⁴ cm^− 3, respectively. To demonstrate the effect of frequency on the plasma excitation efficiency the emission intensity from halogen ions was evaluated using chemical vapor generation with continuous sampling without desiccation. Using 3-phase microwave, 6-phase microwave, 4-phase rf and 1 kHz helium plasma sources the detection limits (3σ) for chlorine at 479.40 nm were 26, 60, 230 and 1200 ng mL^− 1, respectively. The microwave-driven plasma was the densest and had the highest excitation potential toward chlorine and bromine ions.     

Analyte response in laser ablation inductively coupled plasma mass spectrometry

The dependence of analyte sensitivity and vaporization efficiency on the operating parameters of an inductively coupled plasma mass spectrometer (ICPMS) was investigated for a wide range of elements in aerosols, produced by laser ablation of silicate glass. The ion signals were recorded for different carrier gas flow rates at different plasma power for two different laser ablation systems and carrier gases. Differences in atomization efficiency and analyte sensitivity are significant for the two gases and the particle size distribution of the aerosol. Vaporization of the aerosol is enhanced when helium is used, which is attributed to a better energy-transfer from the plasma to the central channel of the ICP and a higher diffusion rate of the vaporized material. This minimizes elemental fractionation caused by sequential evaporation and reduces diffusion losses in the ICP. The sensitivity change with carrier gas flow variation is dependent on m/z of the analyte ion and the chemical properties of the element. Elements with high vaporization temperatures reach a maximum at lower gas flow rates than easily vaporized elements. The sensitivity change is furthermore dependent on m/z of the analyte ion, due to the mass dependence of the ion kinetic energies. The mass response curve of the ICPMS is thus not only a result of space charge effects in the ion optics but is also affected by radial diffusion of analyte ions and the mismatch between their kinetic energy after expansion in the vacuum interface and the ion optic settings.     

Kinetic study on the system of FeOCl and pyridine

The layer compound FeOCl absorbs pyridine molecules into its interlayer regions. The kinetics of this intercalation were investigated in the temperature region from room temperature to 130°C. The reaction products had different compositions, $\text{FeOCl(pyridine)}{}_{\mathrm{<mtext>1</mtext><mtext>4</mtext>}}$ and $\text{FeOCl(pyridine)}{}_{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}$, in the temperature regions below and above 60°C, respectively. Reaction mechanisms were explained by nucleation and diffusion processes. The nucleation processes followed different rate equations in the respective temperature regions, the first-order rate law at lower temperatures, and the two-dimensional Avrami-Erofeev equation at higher temperatures. The diffusion processes were well described by two-dimensional Jander's diffusion equation. Activation energies of all processes were about 10 kcal/mole.     

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.     

Electrical conductivity in strontium titanate

The electrical conductivity of polycrystalline SrTiO₃ was determined for the oxygen partial pressure range of 10° to 10^?22 atm and temperature range of 800 to 1050°C. The data were found to be proportional to the $\text{?1}\text{6}\text{th}$ power of the oxygen partial pressure for the oxygen pressure range 10^?15–10^?22 atm, proportional to for the oxygen pressure range 10^?8–10^?15 atm, and proportional to for the oxygen pressure range 10⁰–10^?3 atm. These data are consistent with the presence of very small amounts of acceptor impurities in SrTiO₃.