Fluorine was determined by molecular absorption spectrometry (MAS) in a graphite tube furnace, and fluorine, chlorine, and bromine were determined in a flame. For the fluorine work, aluminum nitrate was added as a reagent to produce aluminum fluoride molecules whose absorbance was monitored with emission from a platinum hollow cathode lamp ((\mathrm{HCL})) at (227.45 \mathrm{~nm}). A deuterium arc lamp was employed for background correction. For the furnace work, barium nitrate was used as a chemical modifier to increase the absorption signal. After optimization of the chemical and furnace conditions, a detection limit of (160 \mathrm{pg}) (F) was obtained, with a linear dynamic range of two orders of magnitude. Graphite furnace MAS was used to accurately determine fluoride in dental rinse and National Institute of Standards and Technology oyster tissue, but the precision was between 21 and (23 %). Low recoveries were obtained for the determination of trifluoroacetic acid and 1,2,2,3-tetrafluoropropan-1-ol by graphite furnace MAS. The detection limit for F by flame MAS was 13 (\mathrm{mg} \operatorname{liter}^{-1}), which is a factor of 5 lower than the best reported flame MAS detection limit. Chlorine was determined by flame MAS with the aluminum chloride molecule. Excitation was done at (261.4 \mathrm{~nm}) with a lead (\mathrm{HCL}), and a detection limit of (180 \mathrm{mg} \mathrm{liter}^{-1}) was obtained. Flame MAS of bromine was done by use of (\mathrm{AlBr}) (excitation at (279.0 \mathrm{~nm}) with an arsenic (\mathrm{HCL}) ) and (\mathrm{InBr}) (excitation at (284.3 \mathrm{~nm}) with a chromium (\mathrm{HCL}) ), but very poor detection limits were obtained: (24.5 \mathrm{~g} \mathrm{liter}^{-1}) and (500 \mathrm{mg} \mathrm{liter}^{-1}), respectively. E 1993 Academic Press. Inc.