Taketoshi Nakahara

Continuous-Flow Determination of Trace Iodine by Atmospheric-Pressure Helium Microwave-Induced Plasma Atomic Emission Spectrometry Using Generation of Volatile Iodine from Iodide

A simple continuous-flow generation of volatile iodine by oxidation of aqueous iodide is described for the determination of low concentrations of iodine by atmospheric-pressure helium microwave-induced plasma atomic emission spectrometry (MIP-AES) in the normal ultraviolet (UV) and vacuum ultraviolet (VUV) regions of the spectrum. For measuring spectral lines in the VUV region, the monochromator and the enclosed external optical path between the MIP source and the entrance slit of the monochromator have both been purged with nitrogen to minimize oxygen absorption below 190 nm. Iodine atomic emission lines at 206.16 and 183.04 nm have been selected as the analytical lines. Of various oxidation reactions examined, an oxidizing solution of 1.0 mM sodium nitrite in 5.0 M sulfuric acid is the most favorable for the generation of elemental iodine. The gaseous iodine is separated from the solution in a simple gas/liquid separator and swept into the helium stream of a microwave-induced plasma for analysis. The best attainable detection limits (3σ criterion) for iodine at 183.04 and 206.16 nm were 2.3 and 3.2 ng/mL, respectively, with the corresponding background equivalent concentrations of 60 and 118 ng/mL in iodine concentration. The typical analytical working graphs obtained under the optimized experimental conditions were rectilinear over approximately 4 and 3 orders of magnitude in concentration for the 206.16- and 183.04-nm iodine lines, respectively.

Use of a Prior-Oxidation Procedure for the Determination of Iodine by Inductively Coupled Plasma-Atomic Emission Spectrometry

A simple prior-oxidation procedure is described for the determination of low concentrations of iodine by inductively coupled plasma-atomic emission spectrometry (ICP-AES) in the ultraviolet and vacuum ultraviolet (VUV) regions of the spectrum. For measuring spectral lines in the VUV region, the monochromator and the enclosed external optical path between the ICP source and the entrance slit of the monochromator have both been purged with nitrogen to minimize oxygen absorption below 190 nm. Iodine atomic emission lines at 206.16 and 183.04 nm have been selected as the analytical lines. The ICP-AES intensity is enhanced by a factor of up to 50 by prior oxidation of the iodide to elemental iodine using several oxidizing additives, presumably because of increased sample-transport efficiency between the nebulizer and the plasma. The best attainable detection limits (3-σ criterion) for iodine at 183.04 and 206.16 nm were 2.00 and 13.9 ng/mL, respectively, in the presence of 3.5-M perchloric acid or 0.2-M hydrogen peroxide, while the corresponding detection limits were 0.088 and 0.56 μ/mL in the absence of an oxidizing additive. The typical analytical working graphs obtained under the optimized operating conditions were rectilinear over approximately five orders of magnitude in concentration.

Determination of trace concentrations of bismuth by inductively coupled plasma-atomic emission spectrometry with hydride generation

Abstract A simple, rapid and sensitive method is described for the determination of trace concentrations of bismuth, based on continuous reduction of bismuth with sodium tetrahydroborate followed by introduction of the generated bismuth hydride (BiH 3 ,“bismuthine”) into an inductively coupled plasma (ICP) source where the atomic emission from the element can be measured. The operating conditions have been optimized for the continuous generation of bismuthine and its determination by atomic emission spectrometry (AES) in the ICP source. The effects of several inorganic and organic acids and inter-element interference effects have been examined. Hydrochloric acid (1.0 M) is the most suitable reaction medium for bismuthine generation. Compared with a conventional solution nebulization the present system gives a sensitivity increase of a factor of approximately three orders of magnitude. The method has a detection limit of 0.35 ng Bi ml , and the linear dynamic range spans nearly five orders of magnitude from 0.5 ng Bi ml . The precision values at 2 and 200 ng Bi ml are 2.8 and 1.3% relative standard deviation ( n = 10), respectively. Bismuthine generation in the presence of potassium iodide and either potassium dichromate or hydrogen peroxide has been improved greatly; a good correlation between bismuth emission intensity ratio (i.e. bismuth emission enhancement) and iodine emission intensity has been observed. This indicates that the liberated iodine may play a significant role in the atomization and/or excitation of bismuth atoms within the ICP. Most of the interference effects can be minimized by the addition of thiourea, but the method of standard additions is recommended for accurate determinations. The present method is applied to the determination of bismuth in wastewaters, copper metals, aluminum alloys and geological reference standards (NBS, BCS and JSS). The results, except for wastewaters, are in good agreement with the certified or reported values.

Indirect determination of iodine in seawater and brine by atmospheric pressure helium microwave induced plasma atomic emission spectrometry using continuous-flow cold-vapor generation of mercury

Abstract An indirect method for the determination of iodine as iodide by continuous-flow cold-vapor generation of mercury and atmospheric pressure helium microwave induced plasma atomic emission spectrometry (MIP-AES) is described. The method is based on the decrease of mercury emission intensity in highly acidic solutions due to the interference effect of iodide, i.e., the formation of stable mercury(II) iodide complexes. Under the optimized experimental conditions, analytical working graphs have been linear over the concentration range of 2–100 ng/ml of iodide. The best attainable detection limit by the indirect MIP-AES method is 0.74 ng/ml of iodine. The present method has successfully been applied to the determination of total iodine in seawater and brine.

Determination of tin by non-dispersive atomic fluorescence spectrometry coupled with a hydride generation technique

A method is described for the determination of tin by generation of its hydride using sodium tetrahydroborate(III). This is followed by the introduction of the hydride into a pre-mixed argon (entrained air)-hydrogen flame where all of the atomic fluorescence lines of tin are simultaneously detected by the use of a non-dispersive measuring system with a microwave-excited electrodeless discharge lamp for atom excitation. The best attainable detection limit is 1.2 ng (equivalent to 0.6 ng ml–1) and analytical calibration graphs obtained by measuring peak heights and integrated peak areas of the atomic fluorescence intensities are linear over a range of approximately four orders of magnitude with a precision of 3–6%. Optimisation of the experimental parameters and interference studies are reported. The method is illustrated by the determination of tin in JSS and NBS low-alloy steels with good accuracy.