Techniques of sample preparation of milligram-sized samples for C determinations by tandem accelerator mass spectrometry are reported. precisions of better than ± 2% in measurement of ₁₄C/₁₃C on a single target, an iron-carbon bead containing about a milligram of carbon can be achieved in about one hour's actual measurement time on the target. Standard materials with known ₁₄C/₁₃C ratios are measured in the same way. High precision data can be achieved by much longer counting times up to 4 hours, often on several targets. Higher count rates could be achieved by use of graphite targets and preliminary studies of graphitization of small samples are also reported. -- AATA