Gas flow dynamics of an inductively coupled plasma discharge

Temperature and velocity distributions within a low power (0.5–0.75 kW) inductively coupled plasma discharge operating in argon have ben determined for various operating parameters including aerosol gas now rate, plasma gas flow rate, aerosol nozzle diameter, and input power level. All measurements were made without samples. The channel formed in the discharge by the aerosol gas now exhibits temperature and velocity characteristics which distinguishes it from the plasma core and wall regions. Maximum plasma temperature of 8700 ± 300 K and channel gas velocity of 120 $\text{m}\text{s}$ were found.     

Temperature and velocity distributions in an inductively coupled plasma

Computer simulations of inductively coupled plasma discharges (ICP) with flow patterns similar to those found in spectrochemical analysis were reported previously. In this investigation temperature and velocity distributions are measured under conditions which allow direct comparison with computer calculations for pure argon central gas flows without solution aerosols. Based upon these comparisons, a refined ICP gas flow model is proposed and its application provides agreement within experimental error between measured and calculated velocity and temperature profiles in most regions of the discharge.     

Characteristics of the background emission spectrum from a miniature inductively-coupled plasma

The spectral characteristics of the background radiation emitted by a miniature inductively-coupled plasma (i.c.p.) are carefully examined and methods for reducing undesirable features discussed. The complex nature of the background emission spectrum for the mini-i.c.p. indicates that careful line selection criteria and background correction procedures should be employed. Extending the torch coolant tube to the bottom of the region being observed in the plasma proved to be the most effective method for reducing undesirable spectral band features. Acute changes in background emission levels with r.f. power and nebulizer gas flow rates emphasize the need for careful control of these parameters to achieve high precision. Comparison between mini-i.c.p. and conventional i.c.p. spectra reveals the basic similarity of the two sources.     

Ground state sigmatropic and electrocyclic rearrangements in some monoterpenes: The pyrolysis of α-pinene

Alloocimene 7, obtained via ocimene 6 by heating α-pinene 2, was further pyrolysed to a complex mixture of products derived primarily from antarafacial 1,7- and suprafacial 1,5-hydrogen migrations, and 6-eleetron disrotatory electrocyclizations.     

A computer program system for kinetic analysis of non-isothermal thermogravimetric data: I. Data acquisition and preparation for kinetic analysis

FORTRAN software is described which enables the generation of rate of weight change data (DTG) from percentage weight change measurements (TG), obtained under non-isothermal conditions. The program also transposes this information into the dimensionless extent and rate of reaction at unit temperature intervals by means of a cubic spline interpolation. A simple search routine identifies all DTG spikes in the thermogravimetric record, and the temperature and extent of reaction at which the rate attains its maximum value. This total information serves as input data for the kinetic analysis software to be discussed in part II of this communication. An example of the application of this program to the pyrolysis of bituminous coal is presented.     

A computer program system for kinetic analysis of non-isothermal thermogravimetric data: II. Generalized kinetic analysis and application to coal pyrolysis

A FORTRAN program is presented which enables the kinetic analysis of extent and rate of reaction data resulting from transposed experimental TG/DTG data obtained under non-isothermal conditions. This software allows one to perform Arrhenius, Friedman and Kissinger analyses for up to nine different solid-state rate-controlling reactions, including nth order, Avrami-Erofeev, phase boundary movement and diffusional models. Data from an investigation of the pyrolysis of a bituminous coal serve as an example of the application of the program.     

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.     

Modification and optimization of a 50 MHz inductively coupled argon plasma with special reference to analyses using organic solvents

The torch and nebulizer of an existing argon ICP system were modified and the system was (re-) optimized for aqueous and organic liquids. The paper describes the design considerations and construction of(1) a new, streamlined torch including a torch base used in this study, where a demountable rather than a prealigned version of the torch was preferred;(2) a cross-flow pneumatic nebulizer with adjustable teflon capillaries including a spray chamber with flow spoiler, concentric aerosol pick-up tube, and “U” tube with unequal legs to smooth the flow of wasted liquid to the drain.The (re)-optimization of the ICP system for analysis of aqueous solutions with inorganic matter or with both inorganic and organic matter is discussed in the light of earlier work in this laboratory regarding the selection of “compromise conditions” and the choice of representative spectral lines and measurement criteria for establishing such compromise conditions. In this context the authors consider the concepts of norm temperature and “hard” and “soft” lines, as well as recent results of measurements of spatial distributions in ICPs. The authors further describe experiments aimed at the optimization of the operating conditions of an “organic ICP” using methyl isobutyl ketone (MIBK) as organic solvent. Trends of net line and background signals and signal-to-background ratios with the ICP parameters (power; outer, intermediate and carrier gas flow; observation height; liquid feed rate) are reported, and a rational choice of compromise conditions for the ICP is argued.Performance characteristics of the modified ICP system, such as detection limits, precision and interference level, achieved under compromise conditions, have been communicated in a previous report [Spectrochim. Acta36B, 1031 (1981)] to demonstrate the capabilities of the system for analysis of aqueous solutions. Detection limits in MIBK and oil diluted in MIBK are reported in the present work as an illustration of the performance of the system when used for organic liquid analysis.     

Emission spectra of an argon inductively coupled plasma in the vacuum ultraviolet: background spectra from 85 to 200 nm

The background spectra emitted from an argon ICP discharge have been recorded over the spectral range 85 to 200 nm. These vacuum ultraviolet spectra were acquired by coupling the ICP to a 0.5-m Seya-Namioka vacuum monochromator, through a helium purged side-arm. Background features observed include emission from the resonance lines of ArI, and emission from gas impurities such as oxygen, nitrogen, carbon and hydrogen.     

Chemotaxonomy of the rutaceae—XII: The occurrence of severine in Atalantia monophylla and Hesperethusa crenulata. A revised structure for severine

Severine palmitate has been isolated from the fruit of Atalantiamonophylla and Hesptrethusacrenulata both of the family Rutaceae. NMR shift reagent and mass spectral studies suggest the need for revision of the structure of severine to 2. The revised structure is confirmed by the ¹³C NMR spectra of severine and its derivatives.     

A study of adsorption characteristics of traces of chromium(III) and (VI) on selected surfaces

The adsorption losses of chromium(III) or (VI) on the walls of Pyrex, flint glass and polyethylene beakers have been investigated. Chromium(III) or (VI) solutions were stored in beakers at different hydrogen ion concentrations, and losses due to adsorption were measured at various contact times by counting the γ-ray activity from chromium-51 radiotracer. At pH 6.95, chromium(III) solutions showed the greatest instability, particularly in polyethylene beakers, where losses up to 25% were observed at the end of the 15-day contact period. Chromium(VI) showed a completely different pattern; losses less than 1% were observed at the end of 15 days on all the three types of containers.     

Microwave spectrum of N2D4, 14N quadrupole coupling constants,and the barrier to inversion of the amino group

The microwave spectrum of N₂D₄ has been observed and analyzed. Based on five low-J rotational transitions the effective rotational constants are: A = 74712.9 ± 1.9 MHz, B = 18500.42 ± 0.46 MHz, and C = 18439.91 ± 0.46 MHz. The quadrupole coupling constants of the ¹⁴N nuclei are X_aa = 4.23 ± 0.04 MHz, X_bb = 1.98 ± 0.05 MHz, and X_cc = ?2.25 ± 0.05 MHz. Using the observed ground state inversion splittings for N₂D₄ and N₂H₄ the barrier to inversion of a single amino group is computed to be 5.00 kcal mol^?1.     

Molecular structure and conformation of 2,3-dichloro-1-propene as determined by gas-phase electron diffraction

The molecular structure and conformation of 2,3-dichloro-1-propene have been determined by gas-phase electron diffraction at nozzle temperatures of 24, 90 and 273°C. The molecules exist as a mixture of two conformers with the chlorine atoms anti (torsion angle ∠φ = 0°) or gauche (∠φ = 109°) to each other and with the anti form the more stable. The composition (mole fraction) of the vapor with uncertainties estimated at 2σ was found to be 0.55 (0.08), 0.49 (0.08) and 0.41 (0.10) at 24, 90 and 273°, respectively. These values correspond to an energy difference with estimated standard deviation ΔE° = E°_g-E°_a = 0.7 ± 0.3 kcal mol^?1 and an entropy difference ΔS° = S°_g-S°_a = 0.6 ± 0.9 cal mol^?1 K^?1. Some of the diffraction results, together with spectroscopic observations, permit the evaluation of an approximate torsional potential function of the form 2V = V₁ (1 - cos φ) + V₂ (1 - cos 2φ) + V₃ (1 - cos 3φ); the results are V₁ = 4.4 ± 0.5, V₂ = ?2.9 ± 0.5 and V₃ = 4.8 ± 0.2, all in kcal mol^?1. The results at 24°C for the distance (r_a) and angle (∠_α) parameters, with estimated uncertainties of 2σ, are: r(C_sp²-H) = 1.098(0.020)Å, r(C_sp³-H) = 1.103(0.020)Å, r(CC) = 1.334(0.009)Å, r(C-C) = 1.504(0.013)Å, r(C_sp²-Cl) = 1.752(0.021)Å, r(C_sp³-Cl) = 1.776(0.020)Å, ∠C-CC = 127.6(1.1)°, ∠C_sp³-C_sp²-Cl = 110.2(1.0), ∠C_sp²-C_sp³-Cl = 113.1(1.2)°, ∠H-C_sp³-H = 109.5° (assumed), ∠CC-H = 120.0° (assumed) and ∠φ = 108.9(3.4)°.     

Relative spatial profiles of barium ion and atom in the argon inductively coupled plasma as obtained by laser excited fluorescence

Relative ionic and atomic fluorescence profiles for barium have been obtained in an argon inductively coupled plasma by exciting different transitions with a nitrogen-laser pumped tunable dye laser and measuring the resulting fluorescence pulses with a boxcar averager. Spatially resolved profiles are directly obtained without the need of an Abel inversion procedure, with a volume resolution of approximately 0.2 mm³. The profiles are given along the excitation axis as well as along the observation axis, for different heights above the coil and different input powers. At low heights, the ion profile resembles a hollow pencil with a typical double-peaked, asymmetric distribution, while the atom profile seems to be complementary to the ion profile. Some scatter from water is also evident at low heights.     

Excitation of analytes and enhancement of emission intensities in a d.c. plasma jet: a critical review leading to proposed mechanistic models

Experimental data and theoretical criteria are used to critically review existing models for analyte emission enhancement in the 3-electrode d.c. plasma (DCP). The analytical zone is characterized as a non-optically thin recombining plasma in partial thermodynamic equilibrium (PTE). Spectrochemical excitation the authors ascribe largely to: (1) argon resonance line radiative transport; (2) inversion of optically pumped argon states; (3) inversion of analyte populations by Franck-Condon collisions with argon; (4) energy cascading in analytes via a multitude of channels. Adding an easily ionized element (EIE): (1) induces additional resonance line radiative transfer; (2) raises electron densities in cooler, analyte-rich plasma margins; (3) locally increases argon optical absorption cross sections via Stark broadening; (4) redistributes ohmic heating. Coupling between the proposed mechanisms is non-linear. Relationships between radiative transfer and collisional redistribution and (1) background suppression by EIE and (2) analyte emission enhancement by helium are also examined. Similarities between DCP and inductively coupled plasma (ICP) excitation mechanisms are noted and practical implications are addressed.     

Discovery of an electrical post-pulse in the surroundings of a high voltage spark discharge

In the vicinity of a high voltage spark, an electrical pulse of negative polarity was observed. The pulse's behavior with respect to spark cathode composition, gas flow, spatial distribution, and related parameters was characterized. Suggestions as to the origin of the pulse are made. Attempts at observing laser-enhanced ionization in the post discharge time period are described.     

The molecular structure and conformation of gaseous bis(chloromethyl)dimethyl silane as determined by electron diffraction

The molecular structure of bis(chloromethyl) dimethyl silane has been investigated in the gas phase at a nozzle temperature of 60° C. The molecules exist mainly in the GG form with the presence of 30% (+10%, ?20%) AG form. The values of the principal distances (r_a) and angles with estimated error limits of 2σ are r(C-H) = 1.093 (0.009) Å, r(C-Cl) = 1.801 (0.019) Å, r(Si-C) (the average Si-C bond) = 1.875 (0.009) Å, ∠(CSiC) = 109.5°, ∠(SiCCl) = 110.5° (0.4), ∠(CCH) = 112.5° (1.8) and φ (the gauche torsion angle relative to 0° for the anti form) = 117.4° (3.8).     

Molecular structure and conformation of gaseous bromoacetyl chloride and bromoacetyl bromide as determined by electron diffraction

Bromoacetyl chloride and bromoacetyl bromide are studied by gas phase electron diffraction at nozzle-tip temperatures of 70°C and 77°C, respectively. Both compounds exist as mixtures of anti and gauche conformers. The mole fraction anti, with uncertainties estimated at 2σ, was found to be 0.474(0.080) for bromoacetyl chloride and 0.615(0.069) for bromoacetyl bromide. The results for the distance (r_a)and angle (∠α) parameters, with parenthesized uncertainties of 2σ including estimated uncertainty in the electron wave length and correlation effects are as follows: (1) bromoacetyl chloride, r(C-H) = 1.086(0.062) Å, r(CO) = 1.188(0.009) Å, r(C-C) = 1.519(0.018) Å, r(C-Cl) = 1.789(0.011) Å, r(C-Br) = 1.935(0.012) Å, ∠C-CO = 127.6(1.3)°, ∠C-C-Cl = 111.3(1.1)°, ∠C-C-Br = 111.0(1.5)°, ∠H-C-H = 109.5°(assumed), $\text{}\text{?}$/o (gauche torsion angle relative to 0° for the anti form) = 110.0°(assumed); (2) bromoacetyl bromide, r(C-H) =1.110(0.088) Å, r(C=O) = 1.175(0.013) Å, r(C-C) = 1.513(0.020) Å, r(CO-Br) = 1.987(0.020) Å, r(CH₂-Br) = 1.915(0.020) Å, ∠C-CO = 129.4(1.7)°, ∠CH₂-CO-Br = 110.7(1.5)°, ∠CO-CH₂-Br = 111.7(1.8)°, ∠H-C-H = 109.5°(assumed), ∠ø (gauche torsion angle relative to 0° for the anti form) = 105.0°(assumed). The structural results are discussed in connection with the structures of related molecules.     

Structure,hydrogen bonding and vibrational spectra of pyruvic acid

The complete vibrational spectra of liquid pyruvic acid and the infrared spectrum of crystalline pyruvic acid at about 20 K have been recorded and analyzed. A vibrational assignment is proposed based on these spectra and comparison with spectra of derivatives of pyruvic acid.The spectra of pyruvic acid can best be interpreted in terms of a cyclic hydrogen-bonded dimer structure in which the two carbonyl groups are in a trans configuration in the pure liquid phase. A similar structure has been reported for crystalline pyruvic acid by X-ray diffraction. In dilute solution the structure appears to be monomeric with an internal hydrogen bond, in essential agreement with the structures of the monomer reported from microwave spectroscopic measurements.     

Non-aqueous quantitative determination of the carbonyl functional group by constant-current potentiometric titration

A non-aqueous direct titration procedure has been developed for the determination of aldehydes and ketones. It uses two platinum-wire indicating electrodes with a constant current of 0.5 muA. The solvent medium is 0.15M sodium perchlorate in tetrahydrofuran. The titrant is sodium fluorenyl in a mixture of 1,2-dimethoxyethane and tetrahydrofuran. All types of carbonyl compounds react with the sodium fluorenyl, but steric hindrance prevents complete reaction with certain ketones containing bulky groups. The lowest concentration of carbonyl that can be determined with acceptable accuracy and precision is 7.5 x 10(-3)M, the error being < 3% and the precision better than +/-2.5%. Most reducible compounds interfere, e.g., peroxides, acid halides, nitro-compounds, acids, and water, and cannot be differentiated potentiometrically. The method can be extended to other reducible functional groups, e.g., nitro groups and acid chlorides.