A study was carried out on the negative ion thermospray liquid chromatography/mass spectrometry and liquid chromatography/tandem mass spectrometry of a group of bile acids and their glycine conjugates. The liquid chromatographic/tandem mass spectrometric experiments were performed using low-energy collisions on a triple-quadrupole mass spectrometer. It was found that relatively high collision energies and collision gas pressures were required to produce fragmentation and that some unusual fragments were produced.

Tandem mass spectrometric (MS/MS) techniques have been widely used for the differentiation of isomeric compounds, since their spectra may show differences sufficient to distinguish between them. There are several different ways by which the MS/MS data can be obtained depending on the energies of the ions and the collisions. In this paper MS/MS spectra have been obtained for a group of isomeric bile acids using: 1, low-energy ions and low-energy collisions in a triple quadrupole mass spectrometer by liquid chromatography/MS/MS; 2, highenergy ions and low-energy collisions in a hybrid mass spectrometer by fast-atom bombardment MS/MS. Liquid chromatography combined with tandem mass spectrometry (LC/MS/MS) has also been used to identify the bile acids present in biological matrices such as bile extracts.

No abstract

The stability of the ion beam in a thermospray interface is largely dependent on the control of the vaporizer temperature. The original time-proportional vaporizer control circuit provides inadequate temperature stabilization. Modification of the circuit by repositioning the thermocouple amplifier and replacing the timeproportional part of the circuit with a phase-angle controller greatly improves the temperature stability and hence the ion-current stability. The improvement in performance was demonstrated using terbutaline as a test substance.A number of factors affect the ion-current stability on a thermospray interface, namely the vaporizer temperature stability, the flow rate and flow stability, the vaporizer exit nozzle diameter, the solvent composition and the source-block temperature and geometry. These parameters all interact. However, precise vaporizer temperature control is paramount in obtaining good ion-current stability.The need for good control of vaporizer temperature' and the influence of flow-rate' have previously been reported. The modifications reported in this paper are based on the work of Genuit and Bin~bergen.~ They demonstrated the advantages of using a phase control thyristor circuit rather than the original timeproportional circuit. Their modifications involved complete replacement of the vaporizer circuit with two new units. This paper deals with modification of the original controller at significantly lower cost, whilst maintaining the original features such as push-button temperature entry and vaporizer temperature programming.