A growing number of recent publications on clusters reflect a tremendous interest in these particles. These studies reveal new fundamental physical and chemical aspects of matter. Clusters are called the fifth state of matter: liquid, solid, cluster, gas and plasma. In this work, a carbon cluster was generated by a spark cluster source and detected by single focusing mass spectrometer in situ. We examined the effects of cluster source parameters on the generation of carbon cluster and report our initial results. This method should be useful for studying the mechanism of fullerene formation. In the case when carbon clusters generated in plasma arc are carried by the Ar or H2 gas flow downstream through a vacuum chamber to the ion source of mass spectrometer, we obtained a small binary carbon cluster C28H4 (hydrogenated fullerene). The empty fullerene is tetravalent and strongly binds four hydrogen atoms, which significantly weakens two different sets of bonds and leads to an open-shell electronic structure. Conclusion is that endohedral C28H4 are hypervalent. We have demonstrated how in situ mass spectrometry has led to the rapid development of an important branch of synthetic fullerene chemistry that has yielded many new small fullerenes and related derivatives with novel structures and properties. The impact of mass spectrometry on the synthesis of fullerene derivatives is the subject of this paper. Significantly, a large fraction of products could be condensed on a specially designed collection plate, which allows further spectroscopic characterization of new derivatives.