Electrodeless Discharge Lamps Research Articles

Flow Injection Analysis of Mercury/Cold Vapor Atomic Fluorescence Spectrophotometry

Abstract A new flow injection system for the determination of mercury by the cold vapor atomic fluorescence method is described. A sample solution (64 μ1) is injected into a stream of 0.1 M hydrochloric acid, which is mixed with a stream of 3% tin (II) chloride solution in a mixing joint. The combined stream is carried through a reaction coil for reduction of Hg (II) to Hg (0) and subsequently introduced into a specially designed gas-liquid separation vessel. Then the vaporized mercury is swept into a flow type fluorescence cell with a continuous flow of argon after removal of water in the gas phase through a condenser. Mercury is excited with an electrodeless discharge lamp as a source and the mercury fluorescence at both 184.9 and 253.7 nm is measured with a solar-blind photomultiplier. This method allows about 35 determinations of mercury in aqueous samples per hour. The calibration curve is linear over the 0–20 ppb range of mercury. The limit of detection (S/N = 3) is 0.008 ng (0.12 ppb × 64 μ1) and t...

Determination of lead in blood by flame atomic-fluorescence spectrometry.

A simple, rapid method is described for the determination of lead in blood. Dilution 1 + 4 with Triton X is the only sample preparation required and measurements are carried out using a purpose-built atomic-fluorescence spectrometer with a nitrogen-separated air - acetylene flame. The preparation and operation of the lead electrodeless discharge lamps used as the excitation source have been optimised by a ten-factor Simplex procedure. A detection limit of 6 µg l–1 has been achieved for lead in aqueous solution. No significant chemical interferences were observed from the major constituents of the blood matrix and a second continuum source is used to achieve automatic background correction for scattered radiation. Aqueous lead standards are used for calibration. Accuracy was established by satisfactory comparison with values reported for quality control blood samples.

Emission line profile studies of electronic modulated inductively-coupled excited rf-EDL plasmas

The evolution of emission line profiles emitted by an electronically modulated electrodeless discharge lamp plasma was studied with respect to the influence of modulation frequency, modulation amplitude and power input to the plasma. The 114Cd EDL was excited by a radio-frequency of 150 MHz through the inductively-coupled mode. The spectral lines of Cd studied have shown different degrees of self-absorption broadening in the beginning of the on-period of the modulation cycle. This broadening effect tended to disappear towards the end of the on-period. Line profiles were also found to be narrower in the case where the modulation factor is 100%. Increasing power led to increased half-widths without much increase in the profile height.

Capillary Discharge Lamp for the Direct Determination of Iodine by Flame Atomic Absorption Spectroscopy

A simple and inexpensive iodine capillary discharge lamp has been developed. The spectrum of iodine was produced by maintaining a current-limited alternating current discharge in a helium-iodine vapor mixture flowing through a quartz capillary discharge tube. The performance of this spectral lamp as a source of resonance radiation for atomic absorption spectroscopy was evaluated using both unshielded and argon-shielded air-acetylene and nitrous oxide-acetylene flames. Sensitivities and detection limits for iodine obtained using the reported spectral source were found to compare favorably with data reported by other workers who used an electrodeless discharge lamp and a modified hollow cathode lamp.

Determination of sub-nanogram amounts of mercury by cold-vapour atomic fluorescence spectrometry with an improved gas-sheathed atom cell

An improved gas sheathed cell for the cold-vapour determination of mercury by atomic fluorescence spectrometry is described. Mercury ions in aqueous solution are reduced by tin(II) chloride, and the mercury flushed from solution by argon is discharged from a tube situated adjacent to the spectrometer entrance slit and a mercury electrodeless discharge lamp. A second stream of argon is directed up small capillaries arranged around this outlet tube to provide a laminar sheath of argon around the atom cell. At optimised flow rates, the signal is about 10 times greater than when no laminar sheath is provided. Precision is also improved. The limit of detection (2σ) is 0.01 ng of mercury for a 0.5-ml aliquot of sample (i.e. 20 ng 1 -1). The accuracy of the system is demonstrated by the determination of mercury in NBS Orchard Leaves and in barley seeds. Typically relative standard deviations are in the range 0.6–3%.

Fabrication and Utilization of a High-Power Microwave Supply for Electrodeless Discharge Lamps and other Spectrochemical Emission Sources

A study of the factors influencing the performance of a microwave-induced discharge shows that the analytical utility generally increases as the applied microwave power is increased. The fabrication of an easily used high-power system (500 W) is described; the system is used to excite electrodeless discharge lamps of relatively high-boiling species, multielement lamps, and an atmospheric-pressure flowing plasma. The system has been used to study vaporization phenomena in a cadmium electrodeless discharge lamp. The ground-state atom population, as measured by absorption, appears to be directly related to the thermal (wall) temperature.

Performance and application of controlled temperature-gradient lamps in atomic absorption spectrometry

An improved design of controlled temperature-gradient lamp (CTGL) is suitable for arsenic, cadmium, phosphorus, potassium, rubidium, selenium, sodium, sulphur and zinc. Intensity and linewidth measurements indicate that the CTGL is significantly more intense than an electrodeless discharge lamp (EDL) at the same linewidth. CTGL's also compare favourably with EDL's when used as light sources for a.a.s. Arsenic and selenium can be determined at very low concentrations (ng ml -1) by the hydride generation technique. Sulphur and phosphorus can be detected in the vacuum ultra-violet region using nitrogen-separated flames; the limits of detection are 13 and 10 μg ml -1, respectively.

Novel instrumentation of a nondispersive vacuum ultraviolet atomic absorption spectrophotometer for mercury

A nondispersive vacuum ultraviolet atomic absorption spectrophotometer for mercury has been developed. A mercury electrodeless discharge lamp (EDL), which provided a significant radiant flux at both the main resonance line at 185.0 nm and the resonance-intercombination line at 253.7 nm, was utilized with a nitrogen-purged system and a CsI phototube. Because of its spectral response, the CsI phototube allowed it to measure effectively the mercury atomic absorption only at 185.0 nm. The dependence of the atomic absorption sensitivity on the EDL operational power was similar to that in a dispersive system. Since the nondispersive system allowed operation of the EDL with lower power compared with the dispersive system, better sensitivity could be obtained owing to less self-absorption of the resonance line. Furthermore, the low fluctuation noise of the light source led to a lower detection limit. The sensitivity and detection limit were 0.077 and 0.014 ng, respectively, and the relative standard deviation for 0.05 ng mercury was at most about 5.8%.

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.

The determination of tellurium by nondispersive atomic fluorescence spectrometry using the hydride generation technique

Atomic fluorescence spectrometry with a nondispersive measuring system is combined with a hydride generation technique for the determination of tellurium. Atomic fluorescence measurement is based on the reduction of tellurium by either metallic zinc or sodium borohydride, introduction of the generated tellurium hydride into a premixed argon (entrained air)-hydrogen flame, and excitation with a tellurium electrodeless discharge lamp. The comparison of the zinc and the sodium borohydride reduction methods is discussed in terms of detection limit, precision and interference. The best attainable detection limits for tellurium are 2ng (0.1 ng ml ) and 30 ng (1.5 ng ml ) with the zinc and the sodium borohydride methods respectively. Analytical working curves obtained from peak-height and peak-area measurements are linear over a range of approximately 4 orders of magnitude. Of the mineral acids examined in the range up to 2.0 m. nitric acid gives a depressing interference in the range greater than 0.5 m in the zinc method, whereas all of the acids greater than 1.0 m give a slight enhancement of the signal in the sodium borohydride method. The presence of several elements including other hydride-forming elements in 1000-fold ratio to tellurium causes a depressing interference, while enhancing interferences from tungsten and vanadium are observed in the zinc and the sodium borohydride methods, respectively. The present system coupled with the zinc method has been applied to the determination of tellurium in several samples of high-purity copper metal after separation of the analyte from copper by passing an ammoniacal solution of the sample through Chelex-100 resin. The results are in good agreement with those obtained by graphite furnace atomic absorption spectrometry.

Investigation of a high-intensity spectral lamp for atomic absorption spectrometry—II: Radio frequency electrodeless discharge lamps for alkaline earth metals and lithium

The design of RF electrodeless-discharge lamps for alkaline earth metals and Li with Mo-glass envelopes in discussed. A study of the emission characteristics of the lamps has been carried out. Operating conditions providing high intensity without significant broadening of resonance lines have been established. The emission instability of the lamps for the above mentioned elements was found to be 1–1.6% for a 30 min period. The lamps yield intensities a factor of 10–20 higher than the high-intensity combined-discharge lamps for the same elements. The minimum operating lifetime of the lamp is about 150 h.

Hyperfine structure and isotope shift of the 13-μm transition of ^129l

High resolution Fourier transform spectra of the 1.3-microm emission from (127)I and (129)I electrodeless discharge lamps are presented and analyzed. The hyperfine splitting constants of (129)I are: A = 18.35 +/- 0.01 mK and B = 26.55 +/- 0.07 mK for the J = 3/2 ground state and A = 146.32 +/- 0.02 mK for the J = (1/2) excited state. The validity of the theoretical intensity and isotope relationships is confirmed. The isotope shift between (129)I and (127)I for the 1.3-microm transition was measured to be <1 mK.

Precision isotope shifts for the heavy elements I Neutral uranium in the visible and near infrared

A Fourier transform spectrometer was used to obtain high-resolution spectra of a 234UI4/238UI4 electrodeless discharge lamp. Over 2000 uranium isotope shifts were measured in the visible and near-infrared regions. Level isotope shifts were determined by least squares for 183 odd and 518 even levels of U i with an overall standard deviation of 0.0036 cm−1.

A line profile study of the 193.76 nm arsenic emission line from lamps used in atomic absorption spectroscopy

The width of the 193.7 nm line of arsenic has been measured for a commercial hollow cathode lamp (HCL), a pumped hollow cathode lamp and a commercial electrodeless discharge lamp (EDL). The measurements were made using an echelle spectrometer and operating the lamps under a wide range of conditions. The line widths for the commercial HCL and for the EDL were found to be 0.91 pm (9.10 mÅ) and 0.895 pm (8.95 mÅ) respectively when operated under the recommended unpulsed operating conditions, and the EDL line was seven times as intense as that from the HCL. When the lamps were pulsed, the widths of the lines increased to 1.009 pm (10.09 mÅ) in the case of the HCL and to 0.904 pm (9.04 mÅ) for the EDL. The arsenic HCL, with neon as a carrier gas, suffers from severe spectral interference which arises from the presence of the 193.89 nm and 193.01 nm Ne II lines. This could account for most of the curvature of the absorbance-vs-concentration calibration curve.

Improved instrument for mercury determination by atomic fluorescence spectrometry with a high-frequency electrodeless discharge lamp

An instrument for the determination of mercury at nanogram levels is described. With aeration, collection on gold wool and a mercury radiofrequency electrodeless discharge lamp, high sensitivity is obtained with a detection limit of 0.01 ng. The system is used for analysis of sea water.

A contribution to the determination of “reactive” and “total” mercury in sea water

Abstract A method for the determination of “reactive” and “total” mercury in sea water by Atomic Fluorescence Spectroscopy with a Hg‐radiofrequency electrodeless discharge lamp to measure Hg levels below 0.05 ng is described. UV photo‐oxidation to degrade organic mercury compounds is used. Concentrations of reactive and total mercury respectively in the range of 0.4–9 and 1–30 ng [ are measured.

A radio frequency generator for exciting electrodeless discharge lamps

Important features of the instrument described are the simplicity of its design, the fact that no transmission cable is used between excitation coil and oscillator, and the ability to compensate for changes in the load, represented by the plasma in the discharge lamp. The generator operates at 149 MHz, which is much higher than the normal frequencies prescribed for the industrial, scientific and medical bands, but still allows coils to be used instead of cavities. The maximum power level of the generator is 192 W, while the typical power output to the discharge lamps is of the order of 60W.

Controlled temperature-gradient atomic spectral lamp

The lamps are based on excitation of a thermally-produced vapour in a low-pressure gas discharge. For arsenic and selenium, the resonance line intensities are five times higher than those emitted by electrodeless discharge lamps for the same line-widths. Limits of detection are 16 ng ml -1 for arsenic and selenium in non-dispersive atomic fluorescence measurements; sensitivities are also improved in atomic absorption.

A boosted-output spectral lamp with interchangeable cathode for atomic fluorescence spectrometry

The new type of boosted-output atomic spectral lamp described has a readily-interchangeable cathode that requires only a small quantity of pure material. The direction of argon flow-through is designed to enable the lamp to be used with cathodes of relatively volatile elements such as arsenic and selenium, without the element being deposited on the exit window. The high numerical aperture of the lamp makes it suitable for use in atomic fluorescence spectrometry. Its warm-up time is faster than that of commercially-available electrodeless discharge lamps and its performance in flame atomic fluorescence at least as good. For less-volatile metals the performance is equal to that of earlier types of demountable boosted-output lamp.

Building an inexpensive microwave source for electrodeless discharge lamps

We demonstrate that a microwave power source to operate electrodeless discharge lamps can be built by modifying an inexpensive microwave oven at about 1/3 the cost of a commercial unit.