Masao Umemoto

A study on detection limits of inductively coupled plasma-atomic emission spectrometry using a graphite cup direct insertion device

Abstract Concentration detection limits of the graphite cup direct insertion inductively coupled plasma (ICP) were investigated in comparison with those of the conventional pneumatic nebulization method. Several kinds of cups with relatively thin walls and approximately 1 mm diameter supporting rods were used. Effects of several factors such as the cup thickness, rf power, time constant etc., on the emission intensities of the graphite cup direct insertion ICP were studied to propose compromised operating conditions. The detection limits of the graphite cup direct insertion technique, which were measured by two methods, i.e. a direct detection method and a wavelength modulation method, were lower than those of the pneumatic nebulization method by one order of magnitude (e.g. Sb: 1.3, Bi: 0.85, Pb: 2.1, As: 4.4 ng ml ). The improvement is attributed to the higher emission intensities of the signals and lower background intensities.

Some characteristics of an inductively coupled plasma for atomic emission spectrometry with graphite cup sample introduction

Abstract Some characteristics of an inductively coupled plasma (ICP) using a graphite cup direct sample insertion technique (“DSIT plasma”) have been investigated in comparison with a plasma into which samples are introduced with a pneumatic nebulizer (“nebulization plasma”). The DSIT plasma had a doughnut structure, and the linear dynamic range was roughly four orders of magnitude, which is slightly smaller than that for the nebulization plasma. It did not have two distinct zones in the axial emission profiles, a thermal zone and a non-thermal zone, as observed in the nebulization plasma. The electron number density of the DSIT plasma, as observed laterally, was a factor of 4.5 lower than that of the nebulization plasma. The background intensities at 440 and 230 nm were inversely proportional to the outside diameter of the cup, while that for a cup with 0.5-mm wall thickness was a factor of 1.7 smaller than that of the nebulization plasma. For Pb and Cu, the intensity ratios of ionic to atomic lines for the DSIT plasma were close to those for the nebulization plasma, whereas, for Cd and Zn, these ratios were a factor of 3–4 smaller. The difference is related to the marked dependence of the ionic and atomic line intensities on the cup position for Cd and Zn in the DSIT. It is then advantageous to use atomic lines for the analysis of Cd and Zn.

Determination of arsenic and antimony in iron and steels by inductively coupled plasma-atomic emission spectrometry using a graphite cup direct insertion device

Abstract The development of an analysis based on inductively coupled plasma-atomic emission spectrometry using an improved graphite cup insertion device is reported for the determination of trace arsenic and antimony in iron and steel samples. In order to correct background change caused by rapid insertion of the graphite cup and eliminate spectral interferences due to matrices, a high resolution echelle spectrometer was used with wavelength modulation. The design of the graphite cup and the optimization of operating conditions were essential to rapid vaporization of analytes, resulting in sharper and more symmetric peak signals required for the improvement of sensitivity and precision. Detection limits obtained with 25 μl sample solutions were 45 ng ml for arsenic and 8 ng ml for antimony. The method was applied to the analysis of iron and steel certified reference materials and the results agreed well with the certified values.

Inductively coupled plasma-ionic absorption spectrometry using a xenon arc lamp and an echelle monochromator

Abstract Ionic absorption spectrometry using the inductively coupled plasma (ICP) as an ionization source and a 150 W stable xenon arc lamp as a light source has been investigated. A high-resolution echelle spectrometer was used for the absorption measurement. Ionic absorption lines in the wavelength region above 320 nm showed high sensitivity and detection limits of Y, Ti, Zr, Sc, Ce and La were of the same order of magnitude as those attained by ICP atomic emission spectrometry. Linear dynamic ranges of three orders of magnitude were observed for most elements tested. Effects of the measurement conditions such as rf power, outer gas flow rate, inner gas flow rate and observation height on the transmittance of the beam through the plasma and the absorbed radiation power of the analytes are also given.

Effect of outer gas flow rate on spectral line intensity and background intensity in inductively coupled plasma atomic emission spectrometry.

Effects of the outer gas flow rate on spectral intensities and SBRs were investigated for various excitation energies of spectral lines and observation heights. The influences of the outer gas flow rate on spectral intensities were unexpectedly great and markedly varies with excitation energies and observation heights. The influence at a lower observation height (e.g. 10 mm) above the load coil was especially severe and complicated.Effects of the outer gas flow rate on the background continuum intensity were also investigated. The background intensity increased with an increase in the outer gas flow rate at an longer wavelength (e.g. 400 nm) but decreased at an shorter wavelength (e.g. 220 nm). This phenomenon can be explained based upon both temperature dependence of the emissivity of radiative recombination as a function of wavelength and influence of the outer gas flow rate on the optical thickness for background emission.

Relation between rf power and signal profile in ICP-AES utilizing direct graphite cup insertion technique.

Atomization process and a model governing the rate of atom evaporation from the surface of the graphite cup inserted in the inductively coupled plasma are discussed. Several models proposed in graphite furnace atomic absorption spectrometry are reviewed and modified to be applicable to emission spectrometry. The relation between the number of atoms at the cup surface N and the number of atoms released by the surface in unit time n (t) is deduced to be given by an equation n (t) ∝N exp (-E/RT). The effect of rf power on time-dependent signal profiles has been also investigated and is discussed based on the equation. The atomization processes of Sn, Fe, Ni, Cr mainly proceed after the cup temperature reached the maximum, so that the temperature is regarded to be constant in the equation, resulting that the relation between n (t) and t is simple. Experimental results for those elements are well explained by the equation.

Measurements of radiation absorption by ground state atoms and ions in the center of the inductively coupled plasma (ICP) using a continuum source

Abstract Absorption in the inductively coupled plasma (ICP) was measured for the Mg I, Mg II and Cu I spectral lines using a stable 150 W mercury xenon lamp as a light source and a high resolution echelle spectrometer. The effects of rf power, carrier gas now rate and observation height on the absorption intensity (Δ I ) at the center of the plasma were investigated. For comparison the emission intensity ( I em ) was also measured. Examination of the relation between Δ I / I em and the plasma temperature demonstrated deviations from the Boltzmann distribution for both Mg atoms and ions at rf powers lower than 1.0 kW when the carrier gas flow rate was 0.61/min. Absorption was dominant at lower rf power and larger carrier gas flow rate, typically 0.8 kW and 0.601/min. The 150 W mercury xenon lamp provided a large absorption intensity under the absorption-dominant condition, which gave a deviation from the Boltzmann relation.