Various artificial diamonds, graphite and vitreous carbon were atom-by-atom mass analyzed by a scanning atom probe (SCAP). Carbon clusters were detected in all specimens and the abundance of the clusters was found to be high for graphite and vitreous carbon. Nearly 90% of the carbon atoms field evaporated from 99.99% pure graphite were detected as clusters up to C11. After soaking in acid (H2SO4:HNO3:H2O=1:1:1) for 15 min no clusters were detected in the high-pressure high-temperature (HPHT) diamond which exhibited mass peaks of the clusters up to C6. The number of clusters formed by odd numbers of carbon atoms was larger than that formed by even numbers. The hydrogen concentration in chemically vapor deposited diamonds appeared to be related to the percentage of hydrogen in the mixed reaction gas while growing the diamonds. Few hydrogen ions were detected in the HPHT diamond and vitreous carbon. The hydrogen and oxygen distributions in the 99.8% graphite were rather uniform while those in the 99.99% graphite were localized. The present results suggest that the mass analysis by the SCAP may shed light on even the binding state of the analyzed materials. © 2000 American Vacuum Society.