I-129 has been successfully applied as tracer in environmental, geological, and oceanographic research. For samples with low stable iodine concentration and ultra low level I-129, the sample preparation technique to separate iodine prior to AMS measurement has been a bottleneck, limiting the applicability of I-129 We have reported a carrier-free method, using coprecipitation, to avoid the potential introduction of I-129 through the use of stable iodine carrier iodine. In this work, the detection limit and the analytical uncertainty of this method are investigated and minimum sample amount required to obtain reliable analytical results are estimated. The method is validated with a series of samples in ranges of known iodine concentrations and I-129/I-127 ratios. The results confirm our previous conclusion that an AMS target containing 5.0 mu g iodine can be used for analyzing samples with I-129/I-127 > 10(-12), and that for samples with I-129/I-127 < 10(-13) more than 25 mu g iodine is necessary.