Cordycepin, which has great immunomodulatory activities such as anticancer, antifungal, antivirus, antileukemia and lipid-lowering ones, is the secondary metabolite of Cordyceps militaris (C. militaris). Liquid submerged fermentation is the common cultivation process to produce cordycepin. To optimize the fermentation process and improve production, monitoring the cordycepin secretion in the fermentation is essential. The measurement based on chromatography-mass spectrometry methods is generally involved in the complex sample pretreatments and time-consuming separation, so more rapid and convenient methods are required. Matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) is more attractive for faster and direct detection. Therefore, MALDI-MS detection combined with isotope-labeled internal standard was applied to the measurement of cordycepin content in the fermentation broth and mycelium. This method made accurate quantification of cordycepin in the range of 5–400 μg/mL with a relative standard deviation of 5.6%. The recovery rates of fermentation samples after the 1, 13, and 25 days were 90.15%, 94.27%, and 95.06%, respectively. The contents of cordycepin in the mycelium and fermentation broth were 136 mg/g and 148.39 mg/mL on the 20th culture day, respectively. The cordycepin secretion curve of the liquid fermentation of C. militaris was real-time traced over 25 days.

虫草素具有抗癌、抗真菌、抗病毒、抗白血病、降脂等免疫调节活性，是蛹虫草( C. militaris )的次级代谢产物。）。液体深层发酵是生产虫草素的常见培养工艺。为了优化发酵过程并提高产量，监测发酵过程中虫草素的分泌是必不可少的。基于色谱-质谱法的测定通常涉及复杂的样品前处理和耗时的分离，因此需要更快速、更方便的方法。基质辅助激光解吸电离质谱 (MALDI-MS) 对更快、更直接的检测更具吸引力。因此，将MALDI-MS检测结合同位素标记内标应用于发酵液和菌丝体中虫草素含量的测定。该方法可准确定量 5–400 μg/mL 范围内的虫草素，相对标准偏差为 5.6%。1、13、25天后发酵样品的回收率分别为90.15%、94.27%和95.06%。培养第20天菌丝体和发酵液中虫草素的含量分别为136 mg/g和148.39 mg/mL。液体发酵的虫草素分泌曲线C. militaris被实时追踪超过 25 天。