| Spectroscopic instrumentation can be divided into three distinct groups: (1) sample introduction, (2) source (for emission or mass spectral detection), (3) detection. Each one of these areas is equally important and each division has shortcomings associated with it. This thesis describes improvements that were made in each of these three areas. A simple model was developed that can accurately predict the response profile of transient samples when ultrasonic nebulization is utilized. The practical limitations of ultrasonic nebulization as a sample introduction technique for discrete or transient samples are discussed. Secondly, source modification and development are addressed. These modifications were directed toward a Microwave Plasma Torch (MPT) which was developed in the mid 1980s. Until recently, only an argon MPT plasma exhibited the stability that is required for routine analysis. Several design improvements have been made to the MPT so a stable helium discharge can be formed. The modified MPT was first used as an emission source for the detection of tetraethyllead and later a helium MPT plasma was coupled to chromatography for the mass spectral detection of halogenated hydrocarbons. The MPT is a relatively new ion source for elemental mass spectrometry. In such applications, the MPT offers several advantages over conventional microwave sources and over the inductively coupled plasma (ICP). First, the plasma is not contained in a discharge tube but is anchored at the tip of a central conductor. This feature reduces memory effects and allows tuning to remain constant throughout operation. A flame-like plasma is formed, similar to but smaller than the ICP, that allows the sample vapor to be introduced through a central channel in the plasma. This attribute makes the MPT extremely tolerant to the introduction of foreign material (especially molecular species) and unusually robust, compared to other microwave plasmas. Finally, an ICP-MIP tandem source was investigated as an alternative source for atomic emission spectroscopy. The analytical performance of this "atomization-excitation" tandem source was improved through source modulation. |
