An automatically triggered digital integrator and the specific electronic circuits to measure the aspiration time was constructed and applied to flame atomic absorption spectrometry with discrete nebulization. The integrated signal was proportional to the absolute amount of the element in the sample solution injected. The ratio on the integrated signal to the aspiration time was proportional to the concentration of element in the sample solution irrespective of the volume injected. The reproducibility of the ratio method was 0.5%–1% for the sample volume ≳40 &mgr;l of 5 ppm Cu solution.