LIQUID-CHROMATOGRAPHY TIME-OF-FLIGHT MASS-SPECTROMETRY WITH A PULSED SAMPLE INTRODUCTION INTERFACE

Conventional high-performance liquid chromatography (LC) has been comb ined with time-of-flight mass spectrometry (TOFMS) with the use of a p ulsed sample introduction (PSI) interface. The ion chromatogram obtain ed by using LC/TOFMS is similar to that obtained with a UV detector. N o significant peak distortion is introduced by the PSI interface. Vari ous experimental parameters affecting the performance of the LC/TOFMS system are investigated. It is shown that the PSI LC/TOFMS system can handle liquid now rates ranging from 0.5 to 1.6 mL/min. Water and vari ous organic solvents can be used as the mobile phase. Volatile buffers and solvent modifiers can also be used. Several other parameters affe cting the system performance, including the temperature of the sample vaporizer and the capillary tube in the interface as well as the flow rate of the makeup gas, are also investigated. In addition, the effect ive sample transfer efficiency of the PSI interface is studied. It is shown that, by pulsing only 0.31%-0.61% LC effluent into the mass spec trometer with the interface, a chromatogram can be obtained with its p eak area equivalent to that obtained by introducing 37%-72% sample int o the system continuously. This represents an increase of sampling dut y cycle by a factor of 118 using the pulsed technique, although the ov erall detection duty cycle of the present LC/TOFMS system is still low . Finally, several examples of separation and detection by the PSI LC/ TOFMS system are given to illustrate its analytical capability. The ad vantages and limitations of the PSI interface in comparison with other interfacing techniques are briefly discussed.