使用飞秒镱 (Yb) 激光器的第五次谐波 (206 nm) 和第四次谐波发射 (257 nm) 作为电离源，通过质谱法在线测量人类呼出气中的各种有机化合物。通过共振增强、双色、双光子电离，分子离子显着增强，这对于在背景下区分分析物非常有用。空气中丙酮的检测限为 0.15 ppm。经测定，三名受试者呼出气中的丙酮浓度平均为 0.31 ppm，处于正常健康受试者的范围内，明显低于糖尿病患者的范围​​。在呼出的空气中还观察到许多其他成分，可归属于乙醛、乙醇、异戊二烯、苯酚、辛烷、丁酸乙酯、吲哚、辛醇等。因此，本方法显示出可用于糖尿病在线分析以及各种疾病（例如 COVID-19 和癌症）诊断的潜力。

A variety of organic compounds in human exhaled breath were measured online by mass spectrometry using the fifth (206 nm) and fourth (257 nm) harmonic emissions of a femtosecond ytterbium (Yb) laser as the ionization source. Molecular ions were enhanced significantly by means of resonance-enhanced, two-color, two-photon ionization, which was useful for discrimination of analytes against the background. The limit of detection was 0.15 ppm for acetone in air. The concentration of acetone in exhaled breath was determined for three subjects to average 0.31 ppm, which lies within the range of normal healthy subjects and is appreciably lower than the range for patients with diabetes mellitus. Many other constituents, which could be assigned to acetaldehyde, ethanol, isoprene, phenol, octane, ethyl butanoate, indole, octanol, etc., were observed in the exhaled air. Therefore, the present approach shows potential for use in the online analysis of diabetes mellitus and also for the diagnosis of various diseases, such as COVID-19 and cancers.