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.     

Experimental characteristics of direct current and high frequency boosted hollow cathode lamps

Two types of boosted output hollow cathode lamps, viz. direct current and high frequency boosted lamps, were investigated and the characteristics compared. Both lamps are demountable and use the same water-cooled cathode holder. Remarkably similar results were obtained for both types of booster discharges with respect to intensity enhancement of various spectral lines of a number of elements, and with respect to line widths, which were measured with a Fabry-Perot interferometer for strontium only. The interferometer measurements also revealed that although the gain in total intensity for Sr is only about a factor of 8, the gain in intensity at line centre is approximately a factor 40. Although the intensity enhancement caused by the booster discharges is relatively small (～ a factor of 10) for resonance lines in the visible region, the absolute intensities of these lines are much higher than those of lines in the ultraviolet.     

Investigation of a high-intensity spectral lamp for atomic absorption spectrometry—I: High-intensity combined-discharge spectral lamps

The design of lamps with a combined discharge is described in this work. The lamps reveal high emission intensity and small resonance line width, in comparison with conventional hollow cathode and high-intensity Walsh-type lamps. The performance and operating lifetime of the lamps for 26 elements have been investigated. The design also realizes some significant advantages for creating multielement spectral light sources. The paper further describes the design of a high-intensity lamp with a selective modulator providing a modulation depth of 50–70%. The modulator-signal to modulated-signal ratio is shown to be 5–6%. It is demonstrated that application of lamps with selective modulation leads to an increase in the linear range in the high absorbance region of the analyte.     

Application of a modulated Grimm-type glow discharge plasma as primary light source for simultaneous reading atomic absorption spectrometry

Summary The Grimm-type glow discharge lamp (GDL) working in a modulated way can be used as primary light source for atomic absorption measurements. The number of element radiations is given by the composition of the target (sample on GDL) which becomes sputtered. Its composition can be adopted to the analytical problem to be solved. It is easy to change the target.The glow discharge source generated at relatively low power (10–24 W) is burning stable for >20 min on the same spot. This is time enough to operate atomic absorption measurements of 10 samples simultaneously, for example, by using the normal flame technique or the graphite tube furnace or the atomsource sputter method to generate atoms of the sample material. The monochromator device of an AA spectrometer has to be replaced by a polychromator one.The spectral behaviour of the glow discharge source compared to that of the hollow cathode lamps of the elements studied is described here by using a double beam two channel AA spectrometer for simultaneous reading of both the signals. In most cases the glow discharge source is the better one. Home-made targets are used to measure first analytical results.

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Einsatz einer modulierten Glimmentladungslampe als Primärlichtquelle zur simultan messenden Atomabsorptionsspektrometrie

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We have to thank the Spectruma company and Bernhard Bogdain especially for supporting this work.     

Baseline shifts in inverse Zeeman-effect graphite furnace atomic absorption spectrometry ascribed to the Zeeman effect of the CN molecule

The background-corrected Zeeman absorbance baseline shows shifts for lines of several hollow cathode lamps up to tenths of an absorbance unit with firings of an empty graphite furnace atomiser and clear differences in the sizes of the shifts according to whether the furnace is purged with nitrogen or argon. Baseline shifts are seen for hollow cathode lines close to listed rotation lines of the (0,0) and higher bands of the CN violet system. Such shifts, it is suggested, are caused by overlap of the hollow cathode lines with Zeeman-shifted CN lines and in support of this suggestion the known behaviour of CN lines in magnetic fields (spin doublet contraction) is cited. Evidence is presented for the existence of interfering CN lines near the main atomic absorption line of Cr (357.9 nm), as a spectral interference occurs in both the inverse Zeeman configuration (with lamps containing iron) and with continuum source correction.     

Some intense sources of radiation for the alkali and alkaline earth elements

Five new methods are described for the preparation of intense narrow line sources of resonance radiation for the alkali and the alkaline earth elements. Optimum conditions for their preparation and operation are described and their suitability for atomic fluorescence spectrometric purposes has been investigated. The most successful method involves a discharge in flowing atmospheric pressure argon in a quartz tube. A small quantity of the element (or element halide) of interest is suspended in a quartz cup in the discharge stream. The resulting source is applicable to a wide range of relatively involatile elements and, although it is somewhat short lived, it may be recharged readily. Microwave excitation of hollow cathode lamps was not found to be very useful for analytical purposes.     

Coherent forward scattering spectrometry of manganese and chromium using a xenon lamp and a tellurous oxide acousto-optic tunable filter

Coherent forward scattering spectrometry has capabilities of simultaneous multielement analysis and simple instrumentation. Considering these features the authors used a xenon lamp as a continuous excitation light source and a tellurous oxide acousto-optic tunable filter as a scanning monochromator. This simple system was applied to the simultaneous determination of manganese and chromium. An analytical procedure for the determination of manganese in steels was developed and applied to standard reference materials. It was further shown that the dynamic range for both elements can be apparently extended by the use of various exciting lines and combinations of hollow cathode lamps, the xenon lamp, the tunable filter and a spectrometer.     

A simple,low cost,multielement atomic absorption spectrometer with a tungsten coil atomizer

An inexpensive, multielement atomic absorption spectrometer utilizing a tungsten coil atomizer has been developed. The novel optical arrangement employs three 60° beam combiners to blend the spectral output from four light sources such as electrodeless discharge lamps, or hollow cathode lamps, and then direct that output over an atomizer. This instrument uses an inexpensive tungsten coil atomizer that is extracted from a standard 150 W projector bulb. The temperature of the coil is computer-controlled by changing the voltage across the coil. A low voltage is first used to dry the sample then a higher voltage is used to atomize the sample. Simultaneous detection of the analyte absorption signals is accomplished using a charge-coupled device. The elements of interest in this study were Cd, Pb, and Cu. Near-line background correction was used to correct for nonspecific analyte absorption.     

Instrumentation for simultaneous multielement atomic absorption spectrometry with graphite furnace atomization

Graphite furnace-atomic absorption spectrometry (GF-AAS) is restricted to the determination of 4 to 6 elements simultaneously due to the limitations of hollow cathode lamps. However, a consideration of prototype continuum source instruments and recent advances in the fields of spectrometer and detector technology suggests that a multielement GF-AAS instrument, with the multielement versatility associated with atomic emission spectrometry, is possible. Such a multielement instrument would employ a continuum source and provide 1.) multielement determinations for 30 to 40 elements, 2.) wavelength and time integrated absorbance measurements which are independent of the source width, 3.) detection limits comparable to line source AAS with the potential for another order of magnitude improvement using atomization at elevated pressures, 4.) extended calibration ranges limited only by the memory of the atomizer, and 5.) high resolution inspection of the spectra surrounding the analytical wavelength. Such an instrument could provide figures of merit comparable to inductively coupled plasma-mass spectrometer with considerably less complexity.     

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.