Application of a simple photoionization detector for non-dispersive atomic spectrometry in the vacuum ultraviolet region

The construction and operation of a simple, solar-blind photoionization detector which responds to incident radiation between 125 and 140 nm is described. The detector, the response characteristics of which are controlled by the ionization potential of the ethylamine filler gas and the calcium fluoride window employed, is shown to provide for efficient detection of atomic line emission from carbon, oxygen and chlorine in this wavelength region. The spectral sources employed for non-dispersive work with this detector are a microwave-excited argon plasma and a demountable hollow-cathode lamp.     

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.     

Pulsed discharge in a hollow cathode with the detection of ions in a time-of-flight mass spectrometer: Analytical capabilities in the analysis of solid samples

The results of a study of a new analytical system that includes an ion source with a hollow-cathode pulsed gas discharge and a time-of-flight mass spectrometer are reported. It was found that such a system can be successfully used for the direct analysis of metal and dielectric solid samples. The results of the optimization of various ionizer parameters, such as the delay of an ejecting pulse with respect to a discharge pulse and the bias voltage of the anode-cathode pair, are given. It was proposed to use an additive of hydrogen as a reaction gas for a considerable decrease in the intensities of gas components in the mass spectrum, and the effectiveness of this approach was demonstrated. The possibility of the rapid and efficient direct analysis of solid samples with the use of a hollow-cathode pulsed glow discharge was demonstrated using an example of the analysis of high-purity copper samples and the glassy slag of molten lead.     

A spectral study of charge transfer and Penning processes for Cu,Zn, Ag,and Cd in a glow discharge

The occurrence of charge transfer and Penning process in glow discharge atomic emission sources can have a profound effect on the specific and overall spectral emission line characteristics of analyte species in these sources. A detailed spectral illustration of several of these effects is presented in this study for Cu, Zn, Ag and Cd with a particular focus on the ionic emission characteristics (i.e. II lines) of these elements. Charge transfer and Penning processes in glow discharge devices are driven by ionic and metastable species generated from the filler gas. Comparison of spectra obtained utilizing different filler gases is particularly effective for revealing the unique and specific excitation pathways for the analyte ions. Detailed high resolution spectra are presented and compared for Cu and Zn (brass) with Ar, Ne or He filler gases and for Ag and Cd with Ar or He as the filler gas illustrating several charge transfer and Penning processes. Unambiguous identification of spectral lines for specific transitions was facilitated by the acquisition of all spectral data utilizing a UV–visible Fourier transform spectrometer. This spectrometer provided complete and continuous coverage of the spectral region from 200 to 650 nm and allowed spectral lines to be identified with an accuracy of 1–2 pm.     

An investigation into the role of metastable argon atoms in the afterglow plasma of a low pressure discharge

An investigation into the behaviour of metastable argon atoms in a low pressure (250 Pa) pulsed electrical discharge was undertaken in an effort to find the cause of the persisting emission from sputtered metal atoms in the afterglow of an atomic fluorimeter. Results obtained by time-resolved emission and absorption measurements of several argon and copper spectral lines indicate that low energy electrons in the afterglow are converted to high energy electrons via the recombination of electrons with argon ions and the subsequent collisions of pairs of metastable argon atoms. The high energy electrons excite the sputtered metal atoms to give rise to a slow decaying emission tail in the afterglow. A probable change in the electron energy distribution in the afterglow may also have an effect on the observed emission. This phenomenon may be reduced by the use of a suitable quenching gas.     

Distribution of metastable argon atoms in the modified Grimm-type electrical discharge

The absorbance by metastable argon atoms of the Ar 696.543 nm line in the modified Grimm-type electrical discharge source was measured at different discharge conditions and at distances varying from 0.25 to 6 mm from the cathode. A uranium/argon hollow cathode lamp was used as primary source, which gave an argon gas temperature of 850 K when run at 12 mA. A maximum absorbance of 0.57 was found 3 mm from the cathode at 600 V, 80 mA. The magnitude of absorbance increases with discharge current while the position of maximum absorbance shifts away from the cathode with increase in discharge voltage. The quenching of metastable atoms by nitrogen is demonstrated.The spatial distribution of the intensity of four different types of spectral lines is shown. The approximate number densities of the different particles are 10¹²cm^?3 for metastable argon atoms, 10¹⁶cm^?3 for neutral argon atoms, 10¹³ cm^?3 for sputtered copper atoms and 10¹⁴cm^?3for electrons.     

Glow discharge excitation and matrix effects in the Zn–Al–Cu system in argon and neon

Matrix effects and other deviations from the standard model of glow discharge optical emission spectroscopy (GD-OES) have been investigated in the Zn–Al–Cu system in a Grimm-type discharge in argon and neon. In ionic spectra of the elements that can be ionized by asymmetric charge transfer with ions of the discharge gas, most observed deviations from the standard model can be explained by variations of the number density of ions of the discharge gas, caused by asymmetric charge transfer reactions with the matrix element. Similar mechanism, but involving metastables of the discharge gas, was observed for the Cu II spectrum in neon. Some matrix effects in atomic spectra of aluminium and possibly also copper suggest that three-body recombination of ions of the discharge gas, assisted by an analyte atom, is responsible for excitation of certain atomic levels of the analyzed elements. Excited atomic states of the analyzed elements have higher fractional populations in neon than argon, by factors that are similar for all three elements and the median of which is slightly less than 3. It is shown which lines are free of matrix effects and suitable for highly accurate analysis of Zn–Al–Cu alloys by GD-OES and how to optimize the calibration model. Neon can be a reasonable alternative to argon as the discharge gas for some applications.     

Real-time analysis of CuO by inductively coupled plasma emission without external calibration

The study of a method, devoted to real-time detection of metallic pollutants present in stack gas, is investigated. This method is based on spectroanalysis using an inductively coupled plasma (ICP) emission system without external calibration. The fluidized bed technology is employed to inject metallic species into the ICP emission. The mass fluxes of copper oxide (CuO) are then determined by using the intensity ratios of the metallic element spectral lines with those of the plasma gas element (argon or dry air). These ratios and the plasma characteristics (atomic excitation temperature, degree of thermal disequilibrium θ=T_e/T_h) are inserted into a calculation code of plasma composition to determine the mass flux. The results are in good agreement using either argon plasma or dry air plasma. A study of the fluidized bed properties is made to compare our values with those resulting from the elutriation calculation of the copper oxide.     

A contribution to the study of matrix effects in the analysis of solid samples by D. C. glow discharge mass spectrometry

Relative Sensitivity Factors (RSF) for the analysis of 22 elements by glow discharge mass spectrometry have been determined from the multiple determination of 19 reference materials representing steels, Ni-based heat resisting alloys, copper, aluminium, molybdenum and indium by using an Ar/0.2 vol. % H₂ mixture as a filler gas. The measurements were made by using the VG 9000 glow discharge mass spectrometer. For all the materials analyzed, the relative variations of these factors were reduced by more than a factor of 2 when the Ar/H₂ mixture was substituted to the pure argon. In addition, the proposed technique greatly decreases the matrix effects, thus allowing the determination of the elemental composition of metallic samples without needing to use standard reference materials.     

Using the van der Waals broadening of the spectral atomic lines to measure the gas temperature of an argon microwave plasma at atmospheric pressure

The ro-vibrational emission spectra of the molecular species are usually used to measure the gas temperature of a discharge at atmospheric pressure. However, under some experimental conditions, it is difficult to detect them. In order to overcome this difficulty and obtain the temperature, there are methods based on the relation between the gas temperature and the van der Waals broadening of argon atomic spectral lines with a Stark contribution negligible. In this work, we propose a method based on this relation but for lines with a Stark broadening comparable with the van der Waals one.     

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.     

Emission topography of a stable spark discharge train

Time and space resolved spectroscopy are used to photograph the emission from a stable spark discharge train attacking a rotating copper beveled disk in flowing argon. The spark is generated at 60 Hz with a Bardocz type adjustable waveform source. Photographic density over background of sets of lines in the Cu I and Cu II term system is plotted as a function of lateral displacement from the vertical interelectrode axis and time at discrete horizontal distances away from the copper cathode surface to form spatially connected sets of lateral emission profiles. Data from secondary cathodes of silver and gold are presented, along with spectral evidence for radial compression of the cathode jets accompanying their charge transfer ionization and excitation. Spectrochemical applications utilizing time-space structural details are discussed.     

The determination of neon and argon in helium by atomic absorption spectrophotometry

An atomic absorption spectrophotometric technique is described for the determination of neon and argon, respectively, in helium. The accuracies obtained for nanomoles of neon and argon, respectively, were +2.1 and -1.5%. Two Geissler-type discharge tubes containing neon and argon, respectively, were used as emission sources; the absorption source was a quartz cell which contained the sample and related standards that were excited by a high-frequency oscillator. The spectral lines that were employed were neon 6402 Å and argon 8115 Å. Because the spectral lines used had transitions to metastable energy levels, instead of ground levels, a conventional monochromator was suitable.     

Hydrogen effects on copper,zinc and nickel atomic emission lines in argon radiofrequency glow discharge optical emission spectrometry

The effect of hydrogen (0.5%, 1% and 10% v/v) added to the argon plasma gas on the emission spectra of selected atomic lines for copper, zinc and nickel has been studied by radiofrequency glow discharge optical emission spectrometry (rf-GD-OES). Conductive homogeneous samples containing different concentrations of the elements under study in different matrices have been investigated. Results show different trends of the emission intensity lines with increasing hydrogen concentration in the rf-GD, depending on the line characteristics. In most cases, the emission yields of the lines under study did not change or increased when hydrogen was added to the discharge (no decreases were observed). The emission yields of certain lines showed much higher increases than other lines of the same element (for example, lines 213.86 nm of Zn and 231.10 nm of Ni). Our experiments indicate that such notorious increases could be related with the possible decrease of the self-absorption when hydrogen is added to the discharge. Overall, the results obtained for the emission yield changes of certain lines of a given element in different matrices (with different analyte content) showed that while for resonance emission lines very notorious increases are observed, the values for non-resonance lines do not change significantly (specially if the matrices employed are similar).     

Emission spectral characteristics of Cu,Ag, Zn,and Cd neutral atoms in a glow discharge

Detailed spectra highlighting the neutral atom emission characteristics (i.e. I lines) for Cu, Zn, Ag and Cd in a glow discharge device are presented in this study. A particular focus is the presentation of spectra that document the many high excitation energy neutral atom lines that are observed in these spectra. For Cu, several spectral lines originating from levels close to the ionization potential of copper are observed including lines from the so-called autoionizing levels which are actually just above the ionization potential for copper. Generally similar results are seen for Ag, Zn and Cd, including the observation of many high excitation energy neutral atom lines of Zn originating from the upper levels on the triplet side of the energy level diagram. The spectral data point to ion–electron recombination processes followed by stepwise de-excitation and radiative decay as a key mechanism in setting the spectral character of neutral atom emission in a glow discharge device. Unambiguous identification of spectral lines for specific transitions was facilitated by the acquisition of all spectral data utilizing a UV–visible Fourier transform spectrometer. This spectrometer provided complete and continuous coverage of the spectral region from 200 to 650 nm and allowed spectral lines to be identified with an accuracy of 1–2 pm.     

Determination of Nd,Ho, Er,Tm and Y in Solutions by Hollow Cathode Discharge with Copper Cathodes

Abstract

A hollow cathode discharge has been applied to the determination of Nd, Ho, Er, Tm and Y in solutions using copper cathodes and argon as a carrier gas. The solutions were evaporated to dryness in the cathodes without a pretreatment. Absolute detection limits for the elements studied here were found to be lower in the copper cathode by about one order than those obtained in previous studies in graphite hollow cathodes.     

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.     

Study of some excitation characteristics of the discharge in a hot hollow cathode

Some excitation characteristics of the discharge in a hot hollow cathode were investigated. A graphite cathode coated with evaporated films of copper, iron, manganese or titanium, and argon or helium fill gas were applied. The dependence of spectral-line intensities on fill gas pressure and discharge current were studied. At 0.4 A discharge current and various fill gas pressures, the excitation temperatures for iron, manganese and titanium were determined.     

Stark broadening for simultaneous diagnostics of the electron density and temperature in atmospheric microwave discharges

In this paper we delimitate the use of the Stark broadening of lines spontaneously emitted by atmospheric-pressure plasmas as an indirect method to determine both the electron density and temperature in discharges produced by microwaves. This method, previously presented in a recent paper (J. Torres et al., J. Phys. D: Appl. Phys. 36 (2003), L55-59), allows us to obtain experimental results for these two parameters in argon discharges in good agreement with other experimental results previously reported. The possibility of extending its use to a plasmogenic gas other than argon is discussed, and the limitations of the method are pointed out.     

A study of the medium voltage and high voltage controlled waveform spark sources for the spectrometric analysis of aluminium alloys

A medium voltage and a high voltage controlled waveform spark source were investigated as light sources for the analysis of aluminium alloys in an argon atmosphere using a sequential spectrometer. Burn-off curves are given for all six elements investigated and a scanning electron microscope was used to study the discharge areas on the samples. It was found that the argon purity was critical and that for the spectral lines used the high voltage source generally yielded better precision and stability.