A rapid and efficient method was developed for the determination of a fluorinated gas in a lipid microbubble contrast agent, by ultrasound-mediated microbubble destruction (UMD) and gas chromatography-mass spectrometry (GC-MS). UMD was performed using bath sonication. The microbubble destruction was assessed according to the change in the microbubble size, measured by dynamic light scattering (DLS). The results indicated that 20 min bath sonication at 40 kHz was sufficient for disruption of 25 μL of a microbubble agent [octafluoropropane (OFP)-containing lipid microbubbles] in 1 mL saline. The released OFP was then determined by GC-MS with electron impact ionization in the selected-ion-monitoring (SIM) mode using external standardization. A limit of quantification of 9.22 ng OFP and a linearity range of 30.74 to 30 742.24 ng were obtained. Validation of the method showed satisfactory specificity, precision and accuracy. Its validity was further supported by its application in the analysis of real samples with determined values consistent with those by the US Pharmacopeia method. In particular, the sample preparation time was shortened from 3 h to 20 min. In this study, an alternative sample preparation method has been established for microbubble gas content determination, which is rapid and as accurate as classic methods.