L. de Galan

The electronic partition functions of atoms and ions between 1500°K and 7000°K

Abstract Electronic partition functions of the atoms and first ions of 73 elements have been calculated over the temperature range of 1500–7000°K. The results are presented in the form of a fifth order polynomial expression which has been fitted to the data by a method of least squares.

Spatial distribution of the temperature and the number densities of electrons and atomic and ionic species in an inductively coupled RF argon plasma

Abstract A survey of the literature shows that the values found for the excitation parameters (temperature and electron number density) in an inductively coupled radio-frequency argon plasma at atmospheric pressure (ICP) depend on the plasma configuration and the measuring procedure. The present study proposes a novel method for measuring excitation temperatures that does not require a knowledge of transition probabilities. The experimental work concerns measurements of the spatial distributions of the temperature, the number densities of the electrons and various atomic and ionic species in a low-power (∼0.5 kW) ICP for analytical purposes operated at either of two extreme carrier gas flow rates. Observations were made at three different heights above the induction coil. At high flow rate (∼51/min) the familiar hollow configuration of the plasma is demonstrated by off-axis maxima for the temperature and the number densities of electrons and atomic species at all observation heights. At low flow rate (∼1 l./min), the radial atom number density distributions are parabolically shaped and constricted to a smaller channel at all observation heights. The authors conclude from the results that both the plasma configurations are not in a state of complete local thermal equilibrium at observation heights used for analytical work (i.e., above the coil).

A study of the interference of cesium and phosphate in the low power inductively coupled radiofrequency argon plasma using spatially resolved emission and absorption measurements

Abstract The literature on interferences in the radio frequency inductively coupled atmospheric argon plasma (ICP) is reviewed. Even for the most extensively investigated interferences of aluminium, phosphate and alkali elements on calcium, the studies are mostly descriptive. Interpretation of these data is impeded by conflicting results, the absence of thermal equilibrium and the lack of radially resolved observations. The present study of a low-power ICP (0.5 kW) utilizes the Abel inversion technique for emission and absorption measurements of atom and ion lines to clarify the mechanism of interferences on calcium and magnesium due to phosphate and cesium. Under conditions of large carrier gas flow (4.5 1/min) the pronounced interferences are the result of three combined effects: volatilization interference, a change in excitation temperature and a shift in the ionization equilibrium. At lower carrier gas flow (1.4 1/min) the interferences are markedly reduced but still due to the same three effects. The relative preponderance of a particular type of interference depends upon the height of observation and upon the particular combination of analyte and interferent considered.

Measurement of the free atom fraction of 22 elements in an acetylene-air flame

Abstract The ratio of the free atom concentration and the total concentration of an element in a fuel-rich premixed acetylene-air flame is measured experimentally for 22 elements. The atom concentration is derived from the integrated absorption measured with a continuous source; the total concentration of an element is calculated from the flow rates of solution and flame gases. Because copper is found to be completely atomized, this element is proposed as a standard of reference for the acetylene-air flame.

Comparison of line and continuous sources in atomic absorption spectrophotometry

Abstract Expressions are given for the absorption signal (absorbance or fraction absorbed) in atomic absorption spectrophotometry with a line source and a continuous source, respectively. A theoretical and experimental comparison is made between the shape of the working curves, the magnitude of the signals, and the limits of detection in both cases. The significance of the spectral bandwidth of the monochromator and the absorption line profile is discussed. With a good medium-dispersion monochromator, a continuous source offers several distinct advantages and yields detection limits which are approximately the same as those obtained with a hollow-cathode discharge tube.

Arrangement for measuring spatial distributions in an argon induction coupled RF plasma

Abstract An experimental arrangement is described that permits the measurement of axial and radial distributions of temperature, electron concentration and element concentrations in an induction coupled RF plasma at atmospheric pressure (2 kW, 50 MHz). Special attention is given to the sample introduction system and plasma stability. The optical arrangement allows measurements in emission and absorption. Preliminary results are given.

Interferometric measurements of atomic line profiles emitted by hollow-cathode lamps and by an acetylene-nitrous oxide flame

Abstract Source line profiles for eighteen atomic transitions of nine elements emitted by low-current hollow-cathode lamps and by an acetylene-nitrous oxide flame have been measured with a Fabry-Perot interferometer. Distortions caused by instrument broadening are shown to be negligible. Contribution of self-absorption to the profile widths is estimated. In nearly all cases hyperfine structure has a decisive influence upon the observed profile. For thirteen transitions of known hyperfine structure the experimental curves are compared with computer simulated spectra using Gaussian functions to derive the Doppler temperature of hollowcathode lines and Voigt functions to calculate the collision broadening of flame lines. The results show that the Doppler temperatures of hollow-cathode lines range from 400 to 700°K, that flame lines are significantly shifted to the red and that collision broadening in the flame is fully comparable to Doppler broadening, i.e. the a-parameter varies between 0.5 and 1.5.

The influence of hollow-cathode lamp line profiles upon analytical curves in atomic absorption spectroscopy

Abstract Analytical curves of Ca, Al, Mn, Ga and In in the acetylene-nitrous oxide flame are calculated using line profiles measured with a pressure-scanned interferometer. The effects of hyperflne structure, flame Une shift and finite hollow-cathode lamp line width are determined and found to decrease sensitivity by 10 to 20% and to bend the curves towards the concentration axis according to a quadratic function that causes deviations from a straight line between 2 and 7% at absorbance one. An increase of the lamp current from 5 to 25 mA d.c. enhances the effects mentioned above. It is shown that cooling the hollow cathode raises the sensitivity by only a few per cent and in some cases even reduces sensitivity. The use of a tunable laser as a primary source can improve sensitivity, especially when the atomic line profile consists of several widely spaced hyperfine components.

Line profiles emitted by Cu and Ca hollow cathode lamps pulsed to one ampere

Abstract Interferometrically measured emission resonance line profiles are presented for commercial copper and calcium hollow cathode lamps, pulsed at frequencies from 10 to 300 Hz with pulses having a constant current-duration product. Pulses ranged from 7.8 mA at 1280 μs to 1000 mA at 10 μs. Time integrated profiles show that self-reversal increases with repetition frequency and that the lines broaden with increased current. Time resolved profiles show that self reversal developes during a pulse. A simple transport model is proposed to account for the observed blue shifts in the emission profile and in the self-reversal dip of the copper resonance line. The analytical significance of the results is briefly discussed.

The influence of line profiles upon analytical curves for copper and silver in atomic absorption spectroscopy

Abstract Analytical curves for copper (324 and 327 nm) and silver (328 and 338 nm) have been calculated by using experimental hollow cathode lamp profiles and profiles of the absorption coefficient in the air-acetylene flame. Lamp line profiles were recorded with a Fabry-Perot interferometer and corrected for instrumental distortion by an iterative pseudo-deconvolution technique. Gas-temperatures in the hollow cathode between 410 and 450 K were calculated from profiles recorded at low lamp current. An analysis was made of the changes of the lamp line profile when the lamp radiation is partly absorbed by metal atoms in the flame. It was found that the asymmetry in the transmitted profile caused by absorption in the flame, can yield accurate values of the flame line shift, particularly when the lamp line is self-reversed. The influence of hollow cathode lamp current upon sensitivity and linearity of analytical curves was studied. It was calculated that a tunable dye laser emitting narrow lines and used as a primary source, can raise sensitivity relative to a low current operated lamp by 35% at maximum in the case of copper and 10 % in the case of silver. If such a laser line is simulated by reducing the source line width with an interferometer, the results are found to agree with calculations. At low lamp current the curves for silver appear to be straight whereas the curves for copper are bent due to hyperfine structure. Self-reversal at high current enhances curvature, so that at 25mA the curves deviate by 15% from a straight line at absorbance one. Straightforward atomic absorption measurements yield experimental curvatures that agree with the calculated values within the experimental error.