Annual tritium exposures can be reconstructed for long time periods by analyzing radioactive concentrations in tree rings near nuclear facilities that can release tritiated water (HTO) to the environment. Since the mass of analyzed samples is on the order of milligrams, usual methods such as liquid scintillation counting cannot be applied. The recommended method comprises thermal decomposition of the milligram-sized samples, reduction of the resulting HTO to tritiated hydrogen, quantitative absorption of titanium hydride (TiHT) in titanium powder, and determination of the H/T ratio using an accelerator mass spectrometer method. This paper describes the method for obtaining TiHT standards with different H/T isotopic ratios for calibration of a mass spectrometer detector.