Arc Excitation Research Articles

Untersuchungen zur atomspektroskopischen spurenanalyse in A IIIB V-halbleiter-mikroproben—IV : Vergleich der bestimmung von tellurspuren im GaP und GaAs durch AAS, AFS und AES

Methods are described for the determination of trace tellurium in acid solution in the absence and presence of the inorganic matrices As, P, Ga, GaP and GaAs and for the direct determination in solid GaP and GAs. The following methods were used: AAS with electrothermal atomization, AFS with electrothermal atomization, and AES with d.c. arc excitation. The conditions for each of the methods were optimized and the analytical results were compared. It is shown that AAS with electrothermal atomization gives the best absolute and also relative limit of detection for trace tellurium (90 pg Te, or 4 ppm Te in GaAs or GaP). Therefore this method is recommended for the determination of trace tellurium in very small samples of A IIIB V-semiconductors.

Interference effects in a capillary arc excitation source for emission spectrometry

The effects of major constituents (K, Zn, and phosphate) on the emission intensities of eighteen selected analytes in a d.c. capillary arc plasma provided with a nebulizerdesolvation apparatus, are reported. Potassium and zinc enhance the emission from most of the analytes, especially that from the elements of medium ionization potential. Cesium added in excess as a buffer reduces the cation interferences to negligible proportions. The presence of phosphate results in a marked decrease in the excitation temperature of the plasma. Depression effects of phosphate, observed for all the analytes tested but Mg, Se, and La, are probably due to the reduced temperature.

Bestimmung von spuren seltener erden in anderen seltenen erden durch atomabsorption mit elektro-thermischer atomisierung und durch emissions-spektrographie mit dem gleichstromdauerbogen

The determination of traces of rare earths in other rare earths by atomic absorption with electrothermal atomization and by d.c. arc emission spectrography The determination of traces of some rare earth elements (Yb, Eu, Tm, Sm, Dy, Ho, Er) in matrices of other rare earths by a.a.s. with electrothermal atomization (tantalum ribbon), and of traces of Tm and Dy by a.e.s. with d.c. arc excitation is described. The influence of the boiling points of the traces and matrices on the possibility and the sensitivity of the a.a.s. determinations is discussed. The results of the methods are compared. Better absolute, and in most cases also relative, detection limits can be achieved by a.a.s.

Effects of potassium chloride on the analytical characteristics of the capillary arc excitation source.

In emission spectrometry using a capillary arc as an excitation source, the effects of potassium chloride in solutions on the spectrum and background intensities, analytical curves, precision, and sensitivity have been investigated. Sample solutions were sprayed with a pneumatic glass nebulizer, passed through a modified desolvation device, and the desolvated aerosols were introduced into the arc plasma to be excited. The capillary arc operated satisfactorily at a low argon flow rate of 1.15l/min. The spectrum intensity of iron increased and the background emission decreased with increasing potassium chloride concentration. When spraying solutions with more than 0.5 M potassium chloride, potassium chloride deposited on the inside of the capillary, reducing the emission stability. The use of 0.1 M potassium chloride solutions resulted in the improvement in detection limits for all the elements tested but tungsten and zirconium without marked decrease in the slope of analytical curves and reduction in the precision of measurements.

Characterization of a capillary arc excitation source for emission spectrochemical analysis of solutions

A low power d.c. capillary arc source has been combined with a sample desolvation system for solution analysis. The dependence of excitation temperature and rotational temperature in the arc plasma on the arc current and additive gas is described. The arc operates well for several hours without resharping the cathode tip. The high stability of emission, which is satisfactory for operation with instantaneous photoelectric read-out, is maintained with economical argon flow rates of less than 21 min −1. Detection limits for nine elements (Al, Ba, Ca, La, Mo, Sn, V, W, Zr) are as good as or better than the reported arc emission and flame emission values.

Temperature determination and the distribution of relative line intensities in combined and arc excitation sources when the solution is introduced in the form of an aerosol

Temperature determination and the distribution of relative line intensities in combined and arc excitation sources when the solution is introduced in the form of an aerosol

A vidicon spectrometer and its application to the analysis of gold

A TV camera which is attached to a monochromator, is used for the photoelectric measurement of optical spectra. The properties of this detection system and its application to the analysis of trace metals in high purity gold with d.c. arc excitation are described. Problems which originate from this application are discussed and results are compared with those obtained with different analytical methods.

A Semiautomated Device for Controlled Atmospheres in Optical Emission Spectroscopy

In connection with the determination of trace heavy metals in animal and plant tissue by optical emission spectroscopy, the need arose for a device that could maintain controlled atmospheres at the analytical gap at steady state conditions during high current dc arc excitation periods in which relatively large amounts of matrix constituents were vaporized. Operational needs required precise and continuous adjustment of electrode position, minimal contamination risk, and suitability for routine use.

Emission Spectrographic Determination of Arsenic, Antimony, Cadmium, Lead, Copper, and Zinc in Airborne Particulates Collected on Glass Fiber Filter

Abstract A fast, simple, precise, and direct emission spectrographic method has been developed for the determination of arsenic, antimony, cadmium, lead, copper, and zinc in airborne particulates collected on glass fiber filter. Sample discs, punched out from the glass fiber filter, are packed in a boiler cap electrode. Fifty microliters of an internal standard solution containing 10 mcg/ml of indium are added drop wise on the discs. After evaporating the solution, the electrode is subjected to DC arc excitation (current: 15 A, analytical gap: 2 mm, exposure time: 30 sec with no preburn). The precision of the method is consistently better than ±12%.

Emission Spectrographic Determination of Trace Elements in Airborne Particulate Matter Collected on Silver Membrane Filter

An emission spectrographic method is described to determine the concentrations of aluminum, bismuth, cadmium, chromium, iron, lead, manganese, molybdenum, nickel, tin, vanadium, and zinc in airborne particulate matter collected on a silver membrane filter. The sample filter is dissolved with dilute nitric acid. Hydrochloric acid is added to precipitate silver ion as silver chloride. After the solution is evaporated to dryness, the residue is subjected to dc arc excitation. The precision of the method is better than ±18%.

Oxidation and reduction tendencies on the electrode surfaces during arc excitation

In this paper the existence of the oxidation and reduction tendencies in the polarized a.c. arc are proved. These tendencies are shown to change the spectral line intensities. The tendencies depend on the polarities of the electrodes and the arc current, on the absolute and relative reactivities of the reacting partners, on the amounts of the reactive gas components in the case of gas mixtures, and on the electrode temperature. The tendencies are explained by a simple model.

Relationship between the general laws of vapor-liquid equilibria and the analytical curve of emission spectrometry

The relationship between the vapor-liquid equilibrium and the analytical curve of emission spectrometry is discussed on the basis of H irata's equation, i.e., y 1 y 2 = α( x 1 x 2 ) β, where y is the mole fraction in the vapor phase, x in the liquid phase, α and β are constants for binary systems in a certain concentration range, and the indices 1 and 2 refer to the two components. Evaporation produced by different atomization-excitation systems can be characterized by apparent evaporation constants, α' and β', the values of which fall between the true values, α and β, of the normal distillation, and unity. Two powder techniques were selected representing the limiting cases: injection spark excitation (α' ≈ α, β' ≈ β) and controlled arc excitation (α' ≈ 1, β' ≈ 1). Using these excitation methods, the analytical curves of the impurities in industrial alumina and electrocorundum were studied using cup-electrode techniques with arc excitation. As a result, one of Hirata's rules could be selected for a given pair of elements. An unambiguous correlation between the properties of the analytical curves and Hirata's rules could be established.

Direct-reading d.c. arc spectrometry for rapid geochemical surveys

A technique developed for the rapid quantitative analyses of metals in large suites of silicate materials is described. A direct-reading emission spectrometer interfaced to a dedicated minicomputer is used with d.c. arc excitation. Sample, buffer and arc parameters were chosen to promote reproducible selective volatilization. By partial integration of the line emission for the volatile metals, the spectrum background contribution is reduced, improving line to background ratios and permitting both “volatile” and “nonvolatile” metals to be determined in one burn. Preformed electrode cups are used in a specially designed arc chamber which incorporates a gas jet for controlled atmosphere and arc stabilization, and permits automatic electrode alignment as well as rapid and efficient cleaning between samples. No adjustment of the electrodes is made during the burn. One standard only is required for calibration since the working curves are linear over the concentration ranges of interest and a method of background correction using this same standard is described. A high rate of analysis as well as good accuracy and precision is achieved for 21 metals.

Direct Spectrographs Determination of Boron in UF4

Abstract A method for the direct spectrographic determination of boron in uranium tetrafluoride, using d. c. arc excitation is described. Observations made on the choice of arc current, exposure time and the electrode type are presented. The sensitivity obtained for boron using B 2497. 7 A by the present method is 0. 07 ppm.

Time-dependent behaviour of a stable auroral red arc excited by an electric field

We examine the electric field hypothesis as a possible explanation of a stable auroral red arc. An electric field perpendicular to the geomagnetic field in the ionosphere heats the ambient F-region electrons and ions. Given large enough electric fields, the electrons can be heated sufficiently to excite the OI ( 1 D) term of atomic oxygen by electron impact, giving rise to the λ6300 emission characteristic of the red arc. The electron and ion heating rates are determined by the relative drift between the plasma and neutral gas. The electric field, acting through ion drag, accelerates the neutral gas in a time scale small compared to the observed lifetime of the arc. If the electron density within the red arc is high, the relative drift between the plasma and neutral gas is significantly reduced and the red arc excitation is effectively shut off because of the consequent lower electron and ion heating rates. For low electron densities, the electric field strength necessary to excite the red arc is far greater than any fields which have been observed. For all electron densities between these two extremes, the calculated features of a red arc excited by a perpendicular electric field cannot be made consistent with both satellite observations of electron temperature and ground-based observations of λ6300 emission. We conclude that it is not possible for a perpendicular electric field to excite a red arc such as observed, and thus support the contention that conduction of heat in the electron gas from the magnetosphere alone is sufficient to excite and maintain the stable auroral red arc.

Modulated mercury arc excitation sources in luminescence spectroscopy

The operation of HBO series mercury arcs from an unsmoothed, full wave rectified 50 Hz supply is described. The light output which is a 100 Hz sine curve provides a convenient excitation source for the measurement of luminescence by the lock-in technique.

Über die bestimmung kleinster konzentrationen chemischer elemente in der emissionsspektralanalyse mit photoelektrischer strahlungsmessung—II: Spurenbestimmung mit einem aastrittsspaltsystem aus lichtleitern

A new method for trace determination in emission spectrochemical analysis with photoelectrical recording has been developed and tested. in this method the intensities of the spectral line and of the spectral background on both sides of the line can simultaneously be measured. This is accomplished by means of an array of exit slits consisting of glass fibers. Up to 11 adjacing spectral regions each 50 mÅ wide can thus be covered. Two analytical examples are described which show the inherent possibilities of the method. Low concentrations of Cr (4254 Å) and Sr (4078 Å) in a graphite sample have been determined using arc excitation in different atmospheres. For Cr excited in air a light-source constant c U,∞ of 1,47 ppm has been obtained. With c U,∞ is meant the concentration where the intensity of the line equals the intensity of the spectral background, if a spectrograph of very high resolving power is used. The corresponding limit of detection was c = 0,2 ppm taking into account the actual experimental conditions as far as spectrograph and radiation detectors are concerned. It is determined by the noise of the radiation measuring device and agrees well with the expected and predicted value. in the case of Sr excited in an oxygen-argon atmosphere the corresponding values are c U,∞ = 0,08 ppm and c = 0,025 respectively. The latter one is considerably higher than expected. It could however, be proved that it is caused by noise of the light source i.e. fluctuations of an interfering line under the analysis line. For Cr the pertinent noise can be reduced and consequently the limit of detection can be considerably lowered with more powerful apparatus, e.g. higher resolving power of the spectrograph, better quantum efficiency of the photomultipliers etc. A limit of detection as low as 0,0036 ppm should be obtainable. In the case of Sr not much can be achieved in this way. A limit of detection of c = 0,01 ppm should be the minimum. A further decrease affords improvements in the light source, e.g. elimination of the interfering line.

Emission-spectrometric determination of trace rare earth elements in europium oxide

A dc arc excitation method in a controlled atmosphere was applied in the presence of CsCl-graphite (1∶9) buffer for the quantitative determination of traces of rare earth elements in europium oxide. The intensities of the cyanogen band spectra and the background could be reduced by the use of argon-oxygen (4∶1) mixed gas atmosphere and it was possible to obtain higher sensitivity than in the excitation in air. Addition of CsCl-graphite buffer causes an increase of the evaporation rate of the sample and of the number of atoms in the arc plasma, and the atoms and ions of rare earths distribute uniformly along the axis of the discharge gap. The buffer enhances the sensitivity and reproducibility and permits the determination of microquantities of 10 impurity elements within limits of detection from 3 to 11 ppm in high-purity europium oxide. The coefficients of variation are less than 13%.

Spectrographic Determination of Impurities in Molybdenum: Influence of a Diatomic Gaseous Reaction Product on the Arc Excitation in Argon

A spectrographic method has been developed for the determination of 24 trace elements in MoO3. The method is particularly effective for the refractory elements Nb, Ta, Zr, Ti, and V, which are difficult to determine by conventional spectrographic procedures. High sensitivity is achieved in a low amperage arc in argon as a consequence of certain thermochemical reactions which occur in the anode during the arcing process. Although it would appear that the discharge takes place in argon, in fact a small quantity of CO is evolved into the are when MoO3 is reduced in the anode. The evolution of CO changes the composition of the are gas and is essential to the ultimate vaporization and excitation of metal impurities. This paper presents time-resolved spectra, anode temperature, and arc gap voltage measurements which demonstrate the effect of CO.

The Use of the Direct Reading Spectrometer with dc Arc Excitation and Total Sample Combustion in the Analysis of High Purity Materials

When a dc arc is used for trace analysis on a spectrometer, calibration curves with a pronounced toe due to spectral background are found. For analysis of high purity materials it is most important that linear relationships should be established to ultra-trace levels when total impurity content is specified within the ppm level. A solution to this problem is outlined and the linear relationships obtained for copper, bismuth, and cadmium in high purity silver to 0.1 ppm are shown. An electronic circuit is described that enables these background corrections to be made.