This paper is comprised of 4 chapters describing; the observations of atomic distributions in the flame, atomic absorption in the aqueous phase, ozone chemiluminescence with hydride generation technique, and techniques for enhancing sensitivity in absorption spectrometry.<BR>In the second chapter, distribution of atoms in atomic absorption flames (air-acetylene and nitrous oxide-acetylene flames) is discussed, where atomic absorption intensities of several elements were observed in different parts of flame under various conditions. These distributions were presented as coordinates of which abscissa and ordinate express fuel (acetylene) flow rate and observation height above the burner, respectively. This presentation makes it possible to illustrate the effects of chemical factors influencing the atomic distribution in the flame, i.e., dissociation energies of mono-oxides and mono-halides of the analytes are one of the essential factors in determining the atomic distribution in the flame. Also, 50 inorganic complexes of Cr, Mn, Fe, Co, Ni, and Cu were nebulized into the air-acetylene flame and ligand effects on the atomic distributions of these elements are discussed.<BR>In the third chapter, the possibility of observing atomic absorption in the aqueous solution was discussed. Spectroscopic observation made on the surface of the electrode during the reduction of metal ions by electrolysis did not give any atomic absorption spectrum, which has been previously suggested by Tyson and West. Thus we tried to measure the absorption spectrum in the aqueous solution of Hg(I) and Hg(II) just after the addition of reducing agents such as Sn²⁺, SO₃^2-, and NaBH₄. A transient absorption spectrum appeared, which gave a peak located around 243.7 nm. This spectrum provided a doublet structure. These characteristics are successfully explained as a absorption spectrum of hydrated mercury atom.<BR>The fourth chapter discusses gas-phase chemiluminescences for the detection of arsenic, antinomy, tin, and selenium. The hydride generation technique, which has been developed for atomic absorption spectrometry of these elements, was combined with the ozone chemiluminescence which has been originally used for detecting NO_x. This combination resulted in a sensitive analytical method especially for arsenic (detection limit of arsenic is 0.15 ng or 3 ppt). In addition, the hydride generation technique was also mentioned for the quantitative generation of phosphine from phosphate ion, which has been previously difficult to be executed. Phosphate solution was mixed with NaBH₄ and dried at 40°C on a quartz boat, and then heated at 430°C in the helium flow. This technique gives a consistent conversion of phosphate to phosphine (conversion rate : 43%). Coupling with a FPD-gas chromatography, 100 pg of P as phosphate can be analyzed.<BR>The fifth chapter discribes the techniques which bring about the high sensitivity in absorption spectrometry. Laser induced thermal lensing colorimetry was applied to the determination of nitrite and phosphate ions, where a single cw laser was doubly used as a probe and a source. The accumulation and averaging of the photo-signals were done by a handmade system with a commercial computer or by a transient recorder/signal averager system.<BR>Furthermore, a long capillary cell(LCC) technique was mentioned. In Lambert-Beer's law, extension of the light pathlength provides an increase in absorbance. Therefore, we constructed a 1 m linear shaped LCC, which gave up to 300 times the amplification in absorbance compared to ordinary cells.