Ion association by time-of-flight mass spectrometry: a study of V-P-O catalysts.

The oxidation catalysts (VO2)P207 and ß-VOPO4 are studied by laser desorption time-of flight mass spectrometry. Mass spectra of both positive and negative ions are reported for these compounds. Individual scans are tested for ion association, that is, the consistent appearance of a given pair of ions in many scans. The structurally simpler [Symbol: see text]-VOPO4 shows fewer associations than either (VO)2P207 or an (18)O-substituted analogue of ß-VOPO4 even though the overall spectra from the three compounds do not differ greatly. These results indicate that the associations observed between ions may be sensitive to small differences in structure in the original specimen. Thus, the identification of ion association may provide information to supplement the mass spectrum of the sample.

An automatic electrometer ranging circuit for a spark-source mass-spectrometer.

An auto-ranging circuit which accommodates the erratic nature of the electrometer output signals from a spark-source mass-spectrometer is described briefly.

Simultaneous ion-beam collection for precise measurement of nuclidic ion-current ratios in spark-source mass spectrometry.

Simultaneous ion-beam collection techniques make significant improvement possible in the precision of measurements when electrical ion-detection is used with the spark ion-source. The advantage of reference of specific ion-current signals only to those from desired regions of the mass spectrum is that reproducible measurements may be made on heterogeneous samples such as oxide-graphite pellets. For example, isotopic ratio measurements from separate samplings of an oxide (pelleted with graphite) are reproducible to better than +/-0.5%. The technique is also advantageous when sparking dissimilar electrodes, such as a gold probe and a metal bar.

Relative sensitivity coefficients for rare earths in spark-source mass spectrometry.

Relative sensitivity coefficients have been computed for rare earth elements according to empirical models which have been proposed in the literature. Explanations concerning differences between the computed and observed values are based upon possible instrumental discrimination effects which negate some processes occurring in the ion source. Computations relating elemental physical constants to observed results in a semi-random manner are shown which support this contention.

Automatic control of the ion-illumination angle in a spark-source mass spectrometer.

Automatic adjustment of only the spark-gap width in a spark-source mass spectrometer does not ensure that optimum conditions of electrode geometry are maintained with respect to the ion-optics system. A device has been developed which simultaneously maintains a constant gap width and also a more constant z-axis ion-illumination angle. This is the first development to utilize ion-optics parameters to adjust the sparking electrodes automatically. The system maintains the electrodes in an optimum configuration such that higher and more constant instrument sensitivity is maintained automatically. In addition, a significant improvement in the precision of instrumental response is demonstrated. It appears that relative isotopic abundances can be determined directly by the spark-source method which are comparable to those obtained in some cases by surface ionization or by electron bombardment. Results are given that support this contention.

A semi-automatic system for operation of electrical detection for a spark-source mass-spectrometer.

A semi-automatic control system has been developed for a spark-source mass-spectrometer, which permits close interaction between the operator, the instrument via electrical ion-detection and a computer via time-sharing (remote terminal) facilities.

Determination of rare earths in selected rare earth matrices by spark source mass spectrometry.

Three methods of preparing rare earth samples for mass spectrographic analysis are presented. Techniques for adding appropriate internal standards are described and relative sensitivity factors for rare earth impurities in rare earths, lanthanum, yttrium and scandium matrices are presented. Although indium has some value as an internal standard in rare earth samples, best analytical results are obtained when selected rare earths are used as internal standards.

Application of low-cost operational amplifiers to electrical detection in spark-source mass spectrometry.

An electrical detection system for spark-source mass spectrometry has recently been developed. This brief addendum describes an improvement in the signal amplification and its conversion to digital output which has important implications in the future development of electrical detection.

An electrical detection system for a spark-source mass spectrograph.

An electrical detection system has been developed which can be used with the high-frequency spark-source mass spectrograph. Details of the system are discussed and examples are given illustrating its advantages (rapidity and precision). One distinct advantage of electrical detection is that a constant volume of sample material is used for each impurity determination. The system can also be used to assess sample inhomogeneities.