Microanalysis of carbonate rocks using APDC-MIBK extraction and atomic absorption can be accomplished through the use of a sodium hydroxide ammonium chloride buffer. The sensitivity of the method is in the part-per-billion range and the potential extension of the method to allow the simultaneous extraction of up to 20 elements is indicated. Analyses of 3 samples of Millepora sp. from the Coral Sea for Co, Cd, Cu, Ni, Zn, Fe, and Pb are presented. The APDC-MIBK extraction system can be used for ultra-trace element analysis of freshwater, sea water, sediment interstitial water, briny groundwater, granite, and carbonate sediment and rock.