DC Arc Excitation Research Articles

Determination of trace metals in industrial boron carbide by solid sampling optical emission spectrometry. Optimization of DC arc excitation (current, atmosphere and chemical modifier)

Graphite arc emission spectrometry has become possible as a result of the invention of novel types of optical spectrometers with Echelle-optics and semiconductor array detectors, and by the application of electronically controlled, high current arc generators. An optimization of the excitation parameters to boron carbide analysis is reported here, measuring background corrected line intensities that were integrated for the time of total evaporation of 5 mg boron carbide sample with or without added chemical modifiers. The following set of experimental conditions were compared with respect of analytical sensitivity and precision: (A) no modifier, Ar + O2 (20%), 16 A; (B) sample + graphite powder (1 + 1), Ar + O2 (20%), 16 A; (C) sample + CaF2 (1 + 1), Ar, 25 A; (D) sample + CaF2 + graphite powder (1 + 1 + 1), Ar, 25 A. The graphite powder modifier resulted in improved precision in general, and the CaF2 was effective as a plasma ionization buffer and fluorinating agent. The best compromise was found under conditions B, when oxygen was present in the discharge atmosphere. This is likely due to the stepwise conversion of the boron carbide matrix to the more volatile boron oxide. Under conditions B, detection limits in the ranges of 0.3–9 µg g−1 for Al, Ca, Cr, Cu, Fe, Mg, Mn and Si and that of 18–38 µg g−1 for Ti, W, and Zr were attained. Average RSDs of 10.2 and 9.7% were found, respectively, without and with internal referencing to boron.

Dc arc spectrometry of solids: some new aspects of an old method

K. Flórián, J. Haßler and E. Surová, J. Anal. At. Spectrom., 1999, 14, 559 DOI: 10.1039/A807088A

Direct Spectrochemical Analysis of Solids: A Method for Characterization of Sediments

Techniques for the direct analysis of powdered samples provide an advantageous alternative to methods using wet digestion in sample preparation. The direct spectrochemical methods based on electrothermal vaporization (ETV-ICP-OES, solid-ETV-AAS, etc.) show a great similarity to the classical method of dc arc excitation, used in spectrography. Owing to this, the classical dc arc spectrographical method was used in parallel with ETV methods in the direct solid sampling analysis of river and basin sediments. The calibration procedure is the major difficulty of all techniques applied to direct solid sample analysis because of a lack of suitable reference materials. Consequently, it was necessary to verify the application of model calibration samples, preferentially using the simple dc arc OES system and both spectrographic and spectrometric evaluation. The performance parameters of the methods mentioned are compared with those published for the ETV-ICP-OES and SS-ETV-AAS methods.

DC arc excitation — is it obsolete?

The significance of direct current arc plasmas as radiation sources for optical emission spectroscopy is discussed. Their development is discussed in view of the other radiation sources such as flames, discharges under reduced pressure and high-frequency plasmas. It is shown, that the wall-stabilized arc as one of the current-carrying DC-plasma arcs is also today still of use, for instance, for the analysis of powder samples. Transferred arc plasmas also include a series of plasmajets of which the three-electrode DC arc plasma (DCP) is commercially available. The significance and use of these arc discharges are compared with those of other radiation sources such as the inductively coupled plasma (ICP) and the glow discharge lamp, by means of the number of publications made in the course of time. For the analysis of solid samples, DC arcs can be universally used; they have high power of detection and are simple and therefore cannot, up to now, be replaced. Because of the low investment and operation costs, the DCP is a viable alternative to the ICP for the analysis of solutions. Furthermore, the power of detection of the DCP is comparably high and is in some cases, because of the high tolerable salt concentrations, even higher than in the case of the ICP. Matrix effects, however, are high in the case of DCP, due to varying concentrations of easily ionized elements. The capabilities of high power arcs with respect to lower matrix effects and a possible increase of the dynamic range by use of different lines of the elements to be determined are discussed. It is also claimed that the availability of different commercial DC arc systems is prerogative for their further development.

Evaluation and suppression of the light emission instability in case of high-current dc arc excitation in a biological matrix

Evaluation and suppression of the light emission instability in case of high-current dc arc excitation in a biological matrix

Study of the effect of external rotating magnetic field on high-current DC arc excitation in a biological matrix

Study of the effect of external rotating magnetic field on high-current DC arc excitation in a biological matrix

Optimization of high-current DC arc excitation in controlled atmosphere for the spectrographic analysis of biological matrix

Optimization of high-current DC arc excitation in controlled atmosphere for the spectrographic analysis of biological matrix

Elemental characterisation of aluminium used in reactors by optical emission spectroscopic methods

Using AC spark, AC arc and DC arc excitations in optical emission spectroscopic systems, the Al metal used in reactors can be characterised for its minor or trace element composition. The best precision of ± 6% is obtained with an AC spark in which the rod sample is taken as a self electrode and elements Cu, Fe, Mn, Si and Ti are determined in the concentration range 0·01–1%. The oxide powder sample with DC arc excitation provides best minimum detection limits of 10 ppm in general and 21 trace elements are determined by it. The AC arc method also uses oxide powder standards prepared synthetically and determines B and Mg in addition to the elements determined in AC spark excitation with a precision of ±9%.

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%.

Arc Spectral Lines of Selenium and Tellurium

Several factors limit the detection of selenium by excitation in the dc arc. One, the most persistent lines (1960.9, 2039.9, and 2062.8 A) are in the spectral region that requires a photographic emulsion sensitive to short-wave radiation. Also, plane-grating spectrographs in common use have gratings blazed for maximum speed around 3000 A to take advantage of the sensitive lines of elements in that region, thus lines at shorter wavelengths, below 2500 A, are greatly attenuated. Arc lines of tellurium are more plentiful and favorably located than those of Se, however, the two most persistent lines (2383.3 and 2385.8 A) are weakened by the blaze angle. In prior analysis of Se and Te by the dc arc it was noted that spectral lines occur that can be utilized for the detection of these elements in various materials by conventional dc-arc excitation. In the present study, differences found are compared with published tables.

The Practical Analysis of High-Purity Chemicals. VI. Emission Spectrographic Analysis of High-Purity Acids

The spectrographic analysis of volatile acids in a high-purity form is reviewed and a procedure presented that involves evaporation of a 100-g sample under temperature controlled contamination-free conditions and emission spectrography using dc-arc excitation under controlled atmosphere. In the evaporation, graphite (10 mg) is added as a collector, sulfuric acid to convert to less volatile sulfates (with acetic, hydrochloric, and nitric acids), and also mannitol to retain boron (with hydrochloric and hydrofluoric acids). Indium is added as a internal standard. Spectra are examined for 33 elements against a multielement standard in graphite containing indium as an internal standard. For the concurrent analysis of three samples, the elapsed time is 4–10 h and the actual working time 3–5 h. Recovery studies are reported as well as the use of the procedure in the assessment of the leaching of borosilicate glass by concentrated mineral acids.

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%.

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.

Detection and Estimation of Some Trace Elements by dc-Arc Excitation Using the Vacuum-Cup Technique

The dc-arc excitation of aqueous hydrochloric acid solutions of various elements has been studied. Teflon cups of the Zink type were employed. By using the 3089-Å line of the OH band or gallium as an internal standard, boron, mercury, tin, chromium, iron, aluminum, manganese, copper, and zinc in the part-per-million range have been determined.

Comparison of dc Arc and Plasma Arc Excitation to Determine Rhenium in Molybdenite

The dc arc is considerably more sensitive than the plasma are in determining rhenium, using the rhenium emission line at 3460.5 Å and cobalt at 3453.5 Å as the internal standard. The plasma arc is twice as precise as the dc arc. The internal standard technique does not increase precision of the plasma arc for rhenium but is useful to indicate proper functioning of the arc aspirator assembly. Use of a 1:1 alcohol—ethanol solvent for rhenium increases sensitivity of plasma arc determinations by a factor or two. The extracting solvent used to remove rhenium from molybdenite, 4-methyl-2-pentanone, is not spectrographically useful in the plasma arc at the wavelengths used for rhenium determination.

Quantitative spectrochemical analysis of silicate rocks, silicate minerals, and allied materials: Preliminary report on a scheme of analysis

A system of quantitative spectrochemical analysis of silicates (rocks, minerals, soils, meteorites and allied material) using DC arc excitation, is outlined and discussed briefly. The object in devising this analytical scheme is to reach an effective compromise between so-called specific, accurate methods which handle a very limited number of elements in one procedure, and the general methods by means of which many elements are determined semi-quantitatively in one operation. In the simple analytical scheme outlined here, a complete quantitative analysis of a silicate involves a limited number of arcings. Volatilization is considered the most important property in the grouping of elements for each arcing and for choosing an internal standard for each group. Standard deviations invariably fall within the range of 2.5–8%. Included in the analytical scheme are fluorine, all alkali metals and the so-called major constituent elements.