Jeffrey H. Macedone

Factors affecting analyte transport through the sampling orifice of an inductively coupled plasma mass spectrometer

Abstract Laser-excited ionic fluorescence has been used to study the effects of sample matrix, operating conditions, and load coil shielding on analyte ion transport efficiency through the sampling orifice of an inductively coupled plasma mass spectrometer. Significant changes in ion transport efficiency result from changes in sample composition, RF forward power, nebulizer flow and torch shield configuration. The changes in ion transport efficiency correlate well with changes in the potential recorded on a single floating probe placed 1 mm upstream from the sampling orifice.

Optical measurements of ion trajectories through the vacuum interface of an inductively coupled plasma mass spectrometer.

A flexible laser excited fluorescence system has been used to trace ion trajectories in the first vacuum stage of an inductively coupled plasma mass spectrometer. The system has been used to record the spatial distributions of ions immediately upstream from the sampling cone and in the 10 mm downstream from the cone for a variety of positions of the plasma with respect to the sampling cone. The data were used in turn to test the efficacy of scanning the plasma across the sampling cone to generate maps of ion distributions in the plasma. The maps generated by scanning the plasma across the cone are close approximations of the ion distribution immediately upstream from the sampling cone, but are not representative of distributions in an unperturbed plasma.

Source gas kinetic temperatures in an ICP-MS determined by measurements of the gas velocities in the first vacuum stage

Gas kinetic temperatures in the inductively coupled plasma ion source of a plasma-source mass spectrometer were determined for a range of instrument conditions by diode laser spectroscopy. Centerline velocities of argon atoms in the supersonic expansion in the mass spectrometer’s first vacuum stage were calculated from Doppler shifts in the excitation spectra of the probe atoms. Source stagnation temperatures were in turn calculated from the atom velocities. Among the conditions studied were a set typical of “cold” plasmas, with a measured temperature of 5080 ± 40 K, and conditions typical of “hot” plasmas, with a measured temperature of 7380 ± 30 K. Addition of 100 mg L−1 of lithium lowered the temperature in the plasma significantly, while increasing the water load delivered to the plasma raised the temperature.

Educational demonstration of a spherically propagating acoustic shock.

Exploding gas-filled balloons are common chemistry demonstrations. They also provide an entertaining and educational means to experimentally verify nonlinear acoustical theory as described by the Earnshaw solution to the lossless Burgers equation and weak-shock theory. This article describes the theory, the demonstration, and the results of a propagation experiment carried out to provide typical results. Data analysis shows that an acetylene-oxygen balloon produces an acoustic shock whose evolution agrees well with weak-shock theory. On the other hand, the pressure wave generated by a hydrogen-oxygen balloon also propagates nonlinearly, but does not approach N-wave-like, weak-shock formation over the propagation distance. Overall, the experiment shows that popular demonstrations of chemical reactions can be extended from chemistry classrooms to a pedagogical tool for the student of advanced physical acoustics.