A demountable boosted-output spectral lamp for atomic absorption and fluorescence measurements

A demountable boosted-output spectral lamp is described that permits easy exchange of the cathode, which is in the form of a disc pressed from the appropriate powder or machined from rod. The new lamp overcomes to a large extent the major disadvantage of the conventional boosted hollow-cathode lamp, namely the interaction of the sputtering and boosting discharges. In flame atomic absorption spectrometry it yields calibration curves more nearly linear than those obtained with commercial hollow-cathode lamps. In non-dispersive flame atomic fluorescence it permits the attainment of detection limits rather better than those obtained with other high-intensity light sources.     

Evaluation of new high-frequency discharge lamps for atomic absorption and atomic fluorescence spectrometry of cadmium,lead and zinc

High-frequency discharge lamps with a hollow electrode are successfully utilized as the spectral line sources for atomic absorption and atomic fluorescence spectrometry of cadmium, lead and zinc. The sensitivities for atomic absorption spectrometry are superior to those obtained with commercially available hollow-cathode lamps by factors of 1.5 (Cd), 1.4 (Pb) and l.6 (Zn). Detection limits for non-dispersive atomic fluorescence spectrometry with graphite furnace atomization are 1 × 10^-13 g (Cd), 3 × 10^-11 g (Pb) and 2 × 10^-13 g (Zn). The linear analytical range covers over four (Cd, Zn) and three (Pb) decades of concentration above the detection limits.     

Investigation of a coaxial boosted-output hollow-cathode lamp for atomic absorption

A version of the boosted-output, hollow-cathode lamp has been studied as a possible light source for atomic absorption. Our version of this lamp utilizes a secondary electrical discharge to enhance the emission. passing axially through the center of an open cylindrical cathode. Eventually the increase in intensity is accompanied by a decrease in the absorbance of test solutions due to line-broadening in the lamp. Using the criterion of equivalent absorbance, lamps of this design provided ten to twenty times the intensity of commercial hollow-cathode lamps for the elements studied: aluminum, molybdenum, titanium vanadium and copper.     

Applications of the zeeman effect to analytical atomic spectroscopy--IV: capacitively-coupled radiofrequency spectral sources

A magnetically-stable spectral source is described in which a radiofrequency plasma is generated within a single hollow-cathode electrode. Power is coupled to the plasma by placing metal electrodes at the radiofrequency supply potential, around the outside of the lamp-casing. The sources are simple to build, and the capacitive power-coupling technique is convenient for generating a plasma at any desired point within the envelope. The performance of the sources is compared with that of the corresponding commercial hollow-cathode lamps driven from a direct current supply.     

Application of a demountable water-cooled hollow-cathode lamp to atomic-fluorescence spectrometry

A demountable water-cooled hollow-cathode lamp has been investigated as a primary source in atomic fluorescence spectrometry. The discharge current ranged from 300 to 500 mA, and the flowing argon pressure between 0.4 and 4 mbar. Sensitivities ranging from 0.03 to 2 mug ml were obtained for 12 elements. The performances of the hollow-cathode lamp and those of the customary metal vapour discharge lamps for thallium, indium and gallium are compared. The role of the narrowness of the exciting lines in increasing the signal-to-scattering ratios is stressed.     

Atomic line profile measurements on hollow-cathode and electrodeless discharge lamps using a high-resolution echelle monochromator

Commercial r.f.-excited electrodeless discharge lamps (EDLs) and hollow-cathode lamps (HCLs) of the elements As, Bi, Cd, Sb, Se, Sn, Te and Zn were studied using a 2.54-m scanning echelle monochromator. The variation of the widths of the resonance lines from these lamps was investigated for a range of power and current levels. In general, the tendency to self-absorption and self-reversal is greater for the more volatile elements, although the strong self-reversal of the Pb 217.0 nm line from a HCl is an exception. EDLs for the less volatile elements, which are incorporated as iodides, show relatively little variation in line width except at the highest powers.The extent of the overlap between the Bi and I atomic lines at 206.2 nm is demonstrated and, for As, a hyperfine structure splitting constant (A-value) of 0.016 cm⁻¹ was determined for the 5s⁴P energy level.     

High frequency excitation of vapours produced by hollow cathode sputtering

Using a hollow cathode discharge for producing a suitable atomic vapour, the spectral lines of elements were excited by a high frequency discharge of 2450 MHz. These lamps were used as primary light sources for atomic absorption spectroscopy and were compared with conventional hollow cathode lamps. Higher intensity of radiation as well as higher sensitivity was obtained with the high frequency discharge. The interaction of the microwave field with the hollow cathode discharge limits the ultimate intensity. The stability of radiation from these sources is good. Measurements of line halfwidths indicate gas temperatures of approximately 500°K for both the high frequency and conventional hollow cathode discharges.     

Roll-over of analytical curves in atomic absorption spectrometry arising from background correction with pulsed hollow-cathode lamps

A theoretical analysis of background correction systems in atomic absorption spectrometry reveals the interdependence of three phenomena: analytical sensitivity, roll-over of the analytical curve, and wavelength proximity of the background correction. The deuterium lamp system sacrifices wavelength proximity and the Zeeman technique is subject to roll-over. For the newly introduced correction technique using pulsed hollow-cathode lamps roll-over has also been observed, although the effect is reduced by sacrifices of both wavelength proximity and analytical sensitivity.     

Two different types of hollow-cathode discharges used for high resolution laser spectroscopy on copper

Two different techniques, Doppler-free saturation spectroscopy on a hollow-cathode discharge and fluorescence spectroscopy on a collimated atomic beam produced from a hollow-cathode discharge, have been used for high-resolution laser-spectroscopy measurements on the 3d ¹⁰ 4p and 5p states in neutral Copper. The relative merits of the two techniques are discussed.     

High-frequency discharge-lamp with hollow electrode

A new spectral-line source, which is a high-frequency discharge-lamp with a hollow electrode, is described. The lamp is designed for efficient operation using only high-frequency power. Absolute radiance of the high-frequency lamp is measured at operating frequencies of 20 and 85 MHz, at power levels of 2 to 30 W, and in the pressure range from 1 to 8 torr. The radiance of the high-frequency lamp is ten to a hundred times higher than that of hollow-cathode lamps under d.c. operation at maximum rating. The S/N ratio in element analysis utilizing coherent forward-scattering of resonance radiation is improved by the high-frequency lamp. The width of the spectral line emitted from the high-frequency lamp is comparable with that of the d.c. hollow-cathode lamp.     

Ultramicro atomic-absorption spectroscopy with a tungsten-filament atom-reservoir

The detection and measurement of traces of zinc, lead, copper and silver by atomic-absorption spectroscopy, with a tungsten-filament atom-reservoir (TFAR), hollow-cathode lamps and limited-field viewing is described. The performance of this atom cell is compared with that of the carbon-filament atom-reservoir for determination of lead. Greater sensitivity and fewer matrix effects are observed with the TFAR system. The lifetime of the tungsten filament is almost indefinite.     

The design and development of a multichannel atomic absorption spectrometer for the simultaneous determination of trace metals in hair

A multichannel atomic absorption spectrometer capable of analysing up to nine elements simultaneously in human hair has been designed. Light from an array of hollow-cathode lamps is passed through an electrically heated graphite tube into a direct reading spectrometer. The photomultiplier output is fed into a novel transient signalprocessing device which separates the absorption pulse from the continuous background and increases linear range and sensitivity. Solutions containing Ni, Co, Si, Mn, Al, Cu, Ag, Cr and Fe in nanogram and sub-nanogram amounts can be determined with reasonable precision.     

Thermostated radio-frequency excited electrodeless discharge lamps as primary sources in AFS

The performance of Cd and Zn thermostated electrodeless discharge lamps (EDL's) excited at 150 MHz radio-frequency through the inductively-coupled mode in a coil, have been studied with respect to the effect of lamp temperature, amount of material and RF power upon the source radiant output, atomic absorption, atomic fluorescence signals, spectral line width and line profile height of Cd 479.99 nm, Cd 228.8 nm, Zn 481.05 nm and Zn 213.9 nm. Although the lamps show similar behaviour to their microwave excited counterparts, they nevertheless offer several advantages that could renew the interest in EDL's as primary excitation sources in analytical spectroscopy.     

An application of the Zeeman elect to atomic absorption spectrometry: Development of spectral-line sources stable in magnetic field

A new atomic-absorption spectrophotometer using the Zeeman effect, in which the magnetic field is applied to the light source, is described. A steady magnetic field of 3.8 kG was applied to conventional hollow-cathode lamps, which were operated using a high frequency power of 100 MHz.The π-and σ-components of the Zeeman split atomic lines were observed alternatively after traversing a flame. The absorbance difference between of the two Zeeman components was proportional to the atomic-absorption and was not influenced by background absorption. Dependences of atomic absorption signals on magnetic field strengths which were in close relation to profiles of absorption lines were measured for elements Cd, Mg, Pb, Cr, Cu and Mn by scanning of magnetic field strength.     

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

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.     

Applications of the zeeman effect to analytical atomic spectroscopy-V use of commercial hollow-cathode lamps

The feasibility of using radiofrequency-excited commercial hollow-cathode lamps as Zeeman-modulated sources is examined. A supply frequency of 2.5 Mhz is found to be generally suitable. At this frequency the d.c. and Rf zero magnetic field lamp characteristics remain similar, and satisfactory magnetic stability is obtained. Suitable choice of magnetic field strength is found to give partial discrimination between analyte atomic-absorption and self-absorption within the lamp for emission lines showing an anomalous multiples.     

ICP emission spectrometer relative response by the branching-ratio method: branching ratios for Fe, Se, Te, Ge and Pd

The relative spectral response of a commercially available inductively coupled argon plasma (ICP) emission spectrometer has been determined over a wide spectral range (approx. 190 to >900 nm) using overlapping sets of radiative branching ratios of several atomic and ionic species. Response curves were determined in two ways. In the first, calibrations were based on Ar II and Ar I lines emitted by Ar-filled hollow-cathode lamps used as line sources instead of the plasma torch. In the second, the ICP emission of selected lines of Ni and Fe was used. Branching ratios determined from the ICP emission of lines of Fe I, Se I, and Te I, using Ar lines for the intensity calibrations, were compared with previously published branching ratios or f-values for these atoms, and good agreement was found. The calibrations based on Ar II and Ni I were used to measure further branching ratios, and application to the measurement of branching ratios from selected levels of Ge I and Pd I is shown.     

The performance of boosted output hollow cathode lamps in flame atomic absorption spectrometry

A study has been made of boosted output hollow cathode lamps, including (a) the relative increase in the intensity of the resonance line on boosting, (b) the effect of boosting on the spectrum of the emitted radiation, (c) the shape of the calibration graphs in flame atomic absorption spectrometry, and (d) the characteristic concentrations and detection limits found using boosted and unboosted lamps. The relative increases in the intensities of the various resonance lines on boosting is much less for modern lamps than was previously reported for early lamps, and reasons for this are discussed. For flame atomic absorption spectrometry the most useful effects of boosting appear to be a sharpening of the resonance line and a reduction in its background. The chief benefit to the analyst of using boosted output lamps is the increased linearity of the calibration graphs and the consequent extension of the range of concentrations that can be measured accurately.     

High-resolution continuum source atomic absorption spectrometry: a review of current applications

Atomic absorption spectrometry (AAS) is one of the most widely used and available methods for analysis of substances and materials. It allows one to determine about 70 elements from the periodic table and is characterized by rapidity, high accuracy and sensitivity, as well as simplicity of analytical techniques. A feature of AAS is simultaneous determination of only one element due to the use of a measurement design with a line source (hollow-cathode lamps, high-frequency electrodeless lamps, optical quantum generators, etc.). To make AAS more competitive, the first commercially available continuum source atomic absorption spectrometer was designed in 2004. Unique analytical capabilities of the new instruments found application first of all in the analysis of food, pharmaceuticals, waste and drinking water, oil and petrochemicals, biological objects, etc. This review covers publications on the application of continuum source AAS in analytical chemistry and provides a development outlook of the method.

     

A continuum source vs. line source on the way toward absolute graphite furnace atomic absorption spectrometry

The main achievements in the development of the methods of absolute analysis in atomic absorption spectrometry during 40 years are based on the electrothermal atomization of samples and measurement of absorption coefficient in the centre of resonance lines with line-spectra sources as it was proposed by Walsh in 1955. Three main problems with this procedure are the following: (1) a non-homogeneous distribution of analyte vapours in the vertical direction of the graphite tube and its potential redistribution in the presence of matrix; and (2) much higher variations of sensitivity than expected due to the age and individual characteristics of line sources and operating conditions and (3) the deviation from a proportional relation between the absorbance and atomic vapour concentration. To eliminate the first problem, it has been suggested to use a linear photodiode array detector instead of a photomultiplier and to summate absorbances over the height of spectral slit of monochromator. To eliminate the second and third problems, it has been proposed to use a continuum source instead of line sources and to measure a total (wavelength integrated) absorption of resonance line with a high-resolution echelle spectrometer. The advantages of this last proposal are not so obvious as might be expected from some recent publications. From the analysis of different approaches to linearization and stabilization of calibration curves, it was concluded that the most simple and efficient way consists in implementation of the boosted-output hollow-cathode lamps in commercial instruments.