Abstract: The longitudinal distribution of Se free atoms in externally heated quartz tube hydride atomizers was studied under analytical conditions, i.e. selenium concentrations of 10^-100 µg L-1 and argon flow rates of 25-400 mL min-1. The selenium signal was measured through the walls of the optical tube with the tube perpendicular to the radiation beam at various positions along the tube length. The highest concentration of free atoms was found near the middle of the optical tube, where atomization proceeds. Under typical analytical conditions, all free atoms disappear before they reach the ends of the atomizer. The free atom decay rate is greatly enhanced at higher analyte concentrations. This is a major source of calibration graph curvature. The atomization efficiency was influenced much less. The presence of zones where once reacted free atoms are reatomized at the optical tube ends was proven by the spatially resolved observation. Using the measures originally meant to prevent flame ignition on the tube ends, such as quartz windows or prolonged unheated parts of the tube, no reatomization takes place. The effect of reatomization on the analytical performance of the atomizer was shown: the sensitivity is improved and the non-linearity of the calibration graph is substantially reduced, while the baseline noise remains at the same level. Recommendations concerning the quartz tube atomizer design and dimensions are given.

Abstract: The characteristics of the K+-doped glass-slab optical waveguide are discussed in terms of effective path length and relative sensitivity. The waveguide was coated with octadecylsilane and used in the spectrophotometric detection of methylene blue (C. I. Basic Blue 9) by FIA. The coated waveguide could be used for the detection of methylene blue when an ion pair was formed with dodecyl sulfate.

Abstract: Light (632.8 nm) from a linearly polarized 2-mW He - Ne laser was focused by a 2.5-cm-focal length lens to traverse an Ortho model 300-051100 sheath-flow cuvette in which the sample stream was injected along the axis of a sheath stream under laminar-flow conditions, and was detected by a 1-mm2 Si photodiode connected through a current-to-voltage converter to a digital voltmeter. The cuvette was located ~1.5 cm past the beam waist (waist spot size ~15 µm) and near the centre of the beam axis. A set of diffraction fringes was formed at the extremities of the field by interaction of the beam with the body of the cuvette, the intensity at the centre of the fringe system being markedly perturbed by the presence of the sample stream. The detection limit for a 20 µm-radius sample stream corresponded to a refractive index difference of 3 x 10^-6, i.e., ~15 pg for glycerol. Application to flow injection analysis and gradient-elution HPLC is envisaged.