Exploration of Microwave Plasma Source Cavity Ring-Down Spectroscopy for Elemental Measurements

Abstract

We are exploring sensitive techniques for elemental measurements using cavity ring-down spectroscopy (CRDS) combined with a compact microwave plasma source as an atomic absorption cell. The research work marries the high sensitivity of CRDS with a low-power microwave plasma source to develop a new instrument that yields high sensitivity and capability for elemental measurements. CRDS can provide orders of magnitude improvement in sensitivity over conventional absorption techniques. Additional benefit is gained from a compact microwave plasma source that possesses the advantages of low power and low-plasma gas flow rate, which are of benefit for atomic absorption measurements. A laboratory CRDS system consisting of a tunable dye laser is used in this work for developing a scientific base and demonstrating the feasibility of the technique. A laboratory-designed and -built sampling system for solution sample introduction is used for testing. The ring-down signals are monitored using a photomultiplier tube and recorded using a digital oscilloscope interfaced to a computer. Lead is chosen as a typical element for the system optimization and characterization. The effects of baseline noise from the plasma source are reported. A detection limit of 0.8 ppb (10(-)(10)) is obtained with such a device.

Application of atmospheric pressure dielectric barrier discharge plasma for the determination of Se, Sb and Sn with atomic absorption spectrometry

“…It has become a favored detection technique in elements analysis since the detection limits of ICP-atomic emission spectrometry (ICP-AES) and especially ICP-mass spectrometry (ICP-MS) are low. However, using ICP as an atomization cell for AAS measurement has some limitations [21]. Another plasma for the elements analysis is MIP; low detection limits also can be obtained [22].…”

Cavity Ringdown Laser Absorption Spectroscopy

“…(192) Duan et al have investigated coupling an microwave induced plasma cavity ringdown spectroscopy (MIP-CRDS). (23) In that study, lead was chosen as a typical element for the system demonstration so that the results could be directly compared to those from an ICP-CRDS system. A detection limit of 0.8 ng mL −1 for Pb was obtained in that initial feasibility study.…”

Diode laser microwave induced plasma cavity ringdown spectrometer: Performance and perspective

“…Advantages of using a MIP instead of an ICP have been discussed extensively in our previous work. 28,29 Briefly, the MIP requires less electrical power and operating gas and also does not require a cooling system, important advantages when fieldability and portability are needed. We have also found that the MIP source is more stable than the ICP source for CRDS measurements.…”

“…The center wavelength for the mirrors is specified to be 620 nm with a reflectivity of 99.99%. For the 680 nm wavelength used in this effort, the maximum reflectivity of the mirrors is 99.9% and the effective reflectivity 26,29 is 99.85% when the plasma is on. The spacing between the longitudinal modes of this cavity is 0.0064 cm Ϫ1 , or 192.3 MHz.…”

“…36 More recently, an atmospheric-pressure compact microwave induced plasma ͑MIP͒ has been introduced as the atomization/ionization source coupled with CRDS ͑MIP-CRDS͒. 29 For applications requiring portability, the replacement of the pulsed laser system with a compact light source is an essential next step.…”