Lower limits of detection for atomic absorption spectroscopy with direct aspiration of aqueous samples are commonly in the range o.og-I.0 p.p.m.1. These have been reported for iron and nickel as 0.05 p.p.m. by BARRAS". The purpose of the present study was a systematic attempt to lower considerably the limits of detection for these two metals in water and brines by using the advantages offered by solvent extraction. ALLEN~ was one of the first to apply solvent extraction to analysis by atomic absorption. He extracted zinc from water solutions at PH values between 2.5 and 5.0 with ammonium pyrollidine dithiocarbamate (APDC) in methyl isobutyl ketone (MIBK), and obtained a lower limit of detection of 0.006 p.p.m. SIBRAGUE AND SLAVING demonstrated that cadmium, cobalt, iron, manganese and nickel could be extracted from potassium chloride brine with APDC and MIBK. MANSELLS also investigated these same reagents in the extraction of manganese from water. DE-LAUGHTER~ used diphenylthiocarbazone and dithiol in the extractions of chromium and molybdenum, respectively, into MIBK. MULFORD~ has briefly reviewed the principle of solvent extraction as it applies to atomic absorption analysis. Even though several metals have been analyzed by atomic absorption spectroscopy in combination with selected complexing agents and organic solvents, an examination of the existing literature indicates that in many cases thoroug,h studies. to determine the PH, solvent, extraction time, and optimal complexing agent were not .performed. Only a systematic approach is likely to result in the greatest possible sensitivity. EYPERInIENTAL Instrumentation Analyses were performed with a Model 82-360 Jarrell-Ash .atomic absorption spectrometer, a HETCO total consumption burner, and a Leeds-Northrup recorder equipped with optional IO x scale expansion. Commercial hydrogen and dry, filtered air were used for supply gases. Chemicals Primary-standard or reagent-grade chemicals were used wherever possible. All solutions were prepared with distilled, deionized water. Solutions of iron and * Taken from the hl.S. thesis of Mr. RAYMOND D. EDDY.