Robert I. McCrindle

Spectroscopic and electrical studies of a solution-cathode glow discharge

A glow discharge using a solution as the cathode was investigated to add to the understanding of the operating mechanism and characteristics of such systems. The intensities and vertical distributions of emission from several analytes and background species were observed and compared with the vertical distribution of Fe excitation and OH rotational temperatures, as well as to electrical characteristics. The effects of the discharge gap size, the pH and conductivity of the solution, the applied current and the solution flow rate on these distributions were also studied. Detection limits for this system were found to be comparable to those of similar systems and mostly in range of tens of parts per billion.

Use of a furnace with a graphite filter for electrothermal atomic absorption spectrometry

The development of an atomization technique for electrothermal atomic absorption spectrometric (ETAAS) analysis, based on the filtration of the analyte vapour through heated graphite, is presented in its historical context. Initially the method was applied to the analysis of solids. Despite the effectiveness of atomization, the time taken to prepare each solid sample and graphite tube arrangement made single-element determinations impractical using the ETAAS technique. The proposed new version of the furnace with a graphite filter was designed for the analysis of liquids using commercial ETAAS instruments equipped with an autosampler, programmable power supply and a system for background correction. The main advantages of the atomizer were discovered in the course of the determination of Al, Bi, Cd and Cu for different sample volumes, and Cd, Pb and Bi in the presence of NaCl and CuCl2 matrices. These advantage include: a 1.6–2.8-fold increase in sensitivity; the possibility of increasing the volume of doped solutions up to 100 µl, and at the same time reducing the drying period to 15 s; and obtainment of a lower level of spectral background and chemical interferences without chemical modification. The accuracy of the method was verified by the determination of Cd and Pb in whole blood and steel.

Excitation temperature and analytical parameters for an ethanol-loaded inductively coupled plasma atomic emission spectrometer

The effect of ethanol concentrations on the excitation temperature of an inductively coupled plasma was determined from hydrogen emission signals. Increasing the ethanol concentration resulted in an initial increase in excitation temperature. This temperature reached a maximum when 15% v/v ethanol was nebulized, then decreased with further increase in ethanol concentration. The analytical parameters of sensitivity, detection limits and background equivalent concentration for Pb, Cd, Al, Cr, Fe, Na, Mn, Mo and V were correlated to the effects caused by the ethanol within the plasma. The sensitivity in the determination of all the elements increased with increasing ethanol to a maximum of 15% ethanol, the amount of increase depending on the element. The flow rate of the aerosol carrier gas was of greater importance when ethanol was present in the solvent than when pure water was the solvent. Improved detection limits were obtained when the plasma was operating under optimum conditions and the samples were in 15% ethanol solutions.

The graphite filter furnace: a new atomization concept for atomic spectroscopy

A new atomization concept for electrothermal atomic absorption spectroscopy (ETAAS) is proposed and discussed. The basic idea is to form within part of an atomizer a large surface over which the collection of fine particles of the sample is to be distributed, and to constrain the vapor exit from that part to the analytical zone. For the amounts of analyte which are in the range of ordinary ETAAS, these techniques do not affect the character of atomic vapor release because the surface area for the analyte is smaller than that of the vapor passage. However, when there is an excess of matrix, this technique creates the conditions for matrix vapor saturation which impedes the evaporation. This in turn restricts the concentration of matrix vapor in the analytical zone and, respectively, limits spectral background and gas-phase chemical interferences. The concept is realized in the design of a graphite filter furnace. The principle of operation of the atomizer and practical methods to obtain analytical advantages are discussed and compared, using experimental data.

The determination of antimony in lead–antimony alloys using ICP-OES and internal standardisation

Lead–antimony alloys are used in certain applications where ductile alloys are required. The physical properties of the alloy will depend primarily on the chemical composition, in this case, the amount of antimony present. Antimony will inhibit corrosion, change the density, and also increase the hardness of the alloy. An analytical test procedure making use of an inductively coupled plasma optical emission spectrometer (ICP-OES) was needed for the accurate and precise determination of the antimony content of lead–antimony alloys. The sample for analysis was prepared with an internal standard and quantified using an ICP-OES. Cadmium was selected as internal standard because it emits at a wavelength close to antimony and it has a first ionisation potential almost the same as antimony. Three certified reference materials were analysed. The results obtained for three reference materials were precise and accurate. Day-to-day repeatability was better than 1.4% m/m. Within-day repeatability of an alloy was 0.016% m/m.

Analysis of cobalt, tantalum, titanium, vanadium and chromium in tungsten carbide by inductively coupled plasma - optical emission spectrometry.

Inductively coupled plasma optical emission spectroscopy (ICP-OES) was used to measure the concentrations of cobalt, tantalum, titanium, vanadium and chromium in solutions of tungsten carbide. The main advantage of the method described here lies in the speed, convenience and effectiveness of the dissolution procedure. Aliquots of powdered tungsten carbide were dissolved in a solution of 5% aqua regia in 30% hydrogen peroxide. Complete dissolution was usually achieved within 10 min. The accuracy of the method was assessed by the analysis of certified reference materials, secondary reference materials and matrix spiking. The method was successfully applied to commercial type samples with differing compositions. Slightly more emphasis was placed on the measurement of vanadium, since no information on the measurement of this element in solutions of tungsten carbide, by ICP-OES, has been published. Investigation of the interference effects of the elements in the sample matrix on each other was essential for accurate results comparable to other published analytical methods.

Applications of a two-step atomizer and related techniques for investigating the processes of sample evaporation and atomization in electrothermal atomic absorption spectrometry

A review of the results obtained with special experimental apparatus developed for the investigation of high-temperature processes taking place in the course of atomizing analytes are presented and discussed. The apparatus provides the means for monitoring the evaporation process of elements from various matrices and the interaction of metals with substrate materials and gases within the atmosphere of the furnace. Using molecular vapour absorption spectra the composition of vapours in the analytical zone can be identified. Basic elements of the apparatus include a two-channel spectrometer and a two-step atomizer. The atomizer consists of a sample vaporizer and a tube furnace that can be heated to, and held at, a pre-set temperature. The temperature of the vaporizer is controlled automatically by analytical signal feedback. The evaporation characteristics of Ag, Au, Bi, Cd, Co, Cu, Ga, Ge, Pb, Sn, Te, Tl and Zn in the presence of halide and oxygen containing matrices and Ag, Bi, Cd, Co, Ga, In, Mn, Pb, Sb, Sn, Te, Tl and Zn in both inert and hydrogen atmospheres are presented. Molecular spectra of the halides of Ga, In, Tl, Mg, Ag and oxides of Ga and Al are specified. The atomization mechanism of In, Ga and Al in an inert atmosphere containing oxygen impurities is clarified. An unknown spectrum, probably belonging to AlO molecules, was observed. An explanation of the results obtained, based on Langmuirs theory of evaporation, and developed for the experimental conditions of electrothermal atomic absorption spectrometry, is put forward. The thermodynamic criteria to predict the behaviour of an element in the presence of a reagent are suggested. Calculations of the vapour composition of the oxides of Cd, Zn, Pb, In, Tl, Ga, Ge, Ba and Al in the presence of oxygen in the protective gas, were made. Suggestions are made for ways in which the instrument could be further developed.

Reductive separation and slurry nebulization of converter matte for ICP-OES analysis of some platinum group metals and gold

A new method that involves slurry nebulization–ICP-OES analysis and permits accurate estimation of platinum group metals (PGMs) and gold in converter matte has been developed. The method involves reduction of the PGMs and Au with SnCl2 in concentrated HCl medium by heating on a laboratory hotplate and subsequent filtration of the hot mixture through a 0.45 µm membrane filter to separate the accompanying base metals. The resulting metallic precipitate of Au and PGMs was quantitatively transferred into a micronizing mill, ground for 30 min, diluted to 1000 ml with distilled-de-ionized water, and placed in an ultrasonic bath for 15 min to ensure homogeneity. An aliquot of this concentrated slurry was diluted to give a slurry of 0.005% m/v concentration prepared in 5.0% v/v hydrochloric acid and 1.0% m/v Triton X-100 as a dispersant and was directly nebulized into the ICP-OES for the determination of Au, Ir, Pd, Pt, Rh and Ru. The concentrations of Au and PGMs determined using ICP-OES were validated employing the standard additions method and by comparing with literature values that were obtained utilizing reductive separation and conventional dissolution procedure. The method, which allows separation of the PGMs and Au from a complex matrix offers the advantage of reduced analysis time (by ∼60%) and minimized contamination from additional sample preparation steps involved in the traditional procedure.

Diffusion of molecular vapors through heated graphite

Abstract The reasons for the elimination of interferences in a filter furnace used as an atomizer in electrothermal atomic absorption spectroscopy (ETAAS), are examined theoretically and experimentally. The results of observations of stepped or multipeak background absorption signals for NaCl, NaI, KCl, KBr, KI, CaCl 2 and MgSO 4 , which are characteristic for each matrix and different types of graphite used, leads to hypotheses about the formation of molecule-graphite intercalation composites. These are treated as stable compounds of different stoichiometry having substantial specific enthalpy of formation. The validity of the idea is confirmed with the measurements of the rate of NaCl vapor release through a graphite filter as a function of temperature, and comparison with the literature data for similar compounds of alkali metals. The effect of implantation of molecular particles into a crystalline lattice leads to reduction of their diffusion rate through graphite, which in turn provides time-resolved background and atomic absorption signals. Further investigations and development of the idea to understand the analytical effect are proposed.

Electron density and hydrogen distribution in an ethanol-loaded inductively coupled plasma

The effect of an ethanol-loaded sample solution when aspirated into an inductively coupled plasma was investigated. It was found that increasing concentrations of ethanol resulted in a proportional increase in the intensity of the Hα line. The electron density, as calculated both with and without Abel inversion, also increased with increasing ethanol concentration. Mass flow rates of the aerosol increased with an increase in the ethanol concentration. This resulted in a relative mean drop-size distribution which increased from 2 µm for water to 4.5 µm for 25% ethanol. A mechanism is suggested to explain the increases encountered.