No abstract

No abstract

No abstract

A three-aperture gas dynamic vacuum interface for ICP-MS has been developed which reduces the ion current within the ion optics. The effect on performance limitations previously associated with space charge were determined. The gas and ion dynamics within the first stage of the vacuum interface are similar to those of current ICP-MS instruments and allow delineation of the relative effects of space charge in the interface region and within the ion optics. The sensitivity of the instrument to trace elements is similar to that of current commercial instruments. The instrument shows an improvement in the discrimination against low mass ion transmission. It also shows a dramatic improvement in both the magnitude and analyte-ion mass dependence of the signal suppression induced by a high concentration of a heavy concomitant element (Tl). The new design results in more uniform ion kinetic energies as a function of ion mass-to-charge ratio. The performance improvements are ascribed to the reduction of space charge effects resulting from both the reduction of the ion current within the ion optics and the reduction of the mass dependence of the ion kinetic energies. It is concluded that the discrimination against low-mass ions and the magnitude and analyte mass dependence of the signal suppression induced by concomitant heavy elements observed with current ICP-MS instruments derive from space charge effects within the ion optics. These effects are less significant within the first stage of the vacuum interface or within the mass analyzer.

The high-energy collision-induced dissociation (CID) mass spectra of C&, C&, C g , C:: and C g are reported. In all cases, fragmentation occurs by loss of an even number of carbon atoms, in agreement with photodissociation studies of C& and CA. No charge-separation reactions are observed for the multiply charged ions. Collision-induced dissociation of C& leads to a slight preference for formation of C&, while dissociation of C& and C: : shows a more pronounced preference for formation of C& and C g , respectively. Under electron-capture chemical-ionization conditions the fullerenes readily capture an electron to form the molecular anions. Collision-induced dissociation of C, and C, leads to elimination of 1, 2 and 4 carbon atoms; the elimination of one carbon is unique among larger carbon cluster ions. Charge inversion of the molecular anions leads to formation of the respective molecular cations and fragmentation of these cations by loss of an even number of carbon atoms. Formation of C& is slightly preferred in the C, case, while C& is the most abundant ion in the charge inversion mass spectrum of C,.Following the recent reports'-4 of the efficient preparation of macroscopic amounts of the fullerenes, C," and C7,,, there have been several reports of the mass spectra of these fullerenes. 1-6 The electron-ionization mass spectra of both C," and C70 are characteristic of aromatic molecules in showing the molecular ion as the base peak and intense doubly charged molecular ions, with little fragmentation of either species. In addition, weak triply charged molecular ion signals have been observed by Luffer and Schram6 for C60, while we have observed a similar triply charged molecular ion for C7". The electron affinity of C6" has been reported as 2.8 eV7 and we observe, under electron-capture chemicalionization conditions, that both C6,, and C70 readily form molecular anions with no fragment ions observed.Since the extent of fragmentation of these molecular ions is very small,6 it appeared desirable to examine the high-energy collision-induced dissociation (CID) reactions of the molecular ion species, as well as the collisional charge-inversion mass spectra' of the molecular anions in order to characterize more completely the fragmentation reactions occurring. The results of this examination are reported here; for C& and C,+, the results are compared with the photodissociation results reported by Smalley and co-workers.' EXPERIMENTAL All experimental work was carried out using a ZAB-2FQ mass spectrometer (VG Analytical, Manchester, UK) which has been described in detail previously." The features of the instrument that are essential to the present work are that it is a reversedgeometry (BE) double-focusing mass spectrometer with a collision cell located at the focal point in the second field-free region between the magnetic (B) and electric (E) sectors. In the collisional studies of C& and C& the ion beam of interest was selected by the magne-* Author to whom correspondence should be addressed. tic sector and underwent...