Direct detection of optical radiation through a sampling orifice for inductively coupled plasma atomic emission spectroscopy

The direct optical viewing of an argon inductively coupled plasma (ICP) through a sampling orifice inserted directly into the plasma has been accomplished. A copper cone with a sampling orifice is attached to the entrance slit chamber of a monochromator and inserted directly into an ICP to obtain optical spectra in the vacuum ultraviolet (VUV). With solar-blind photomultiplier tube (PMT) detection, detection limits are 50 ng mL[superscript]-1 for the resonance lines of Br and Cl during injection into the plasma of aerosols of aqueous solutions generated by pneumatic nebulization. With ultrasonic nebulization, the detection limits improve to 8 ng mL[superscript]-1 for Br and 15 ng mL[superscript]-1 for Cl. Detection limits for Br and Cl in the form of an aqueous sample were superior to the best reported values in the Ar and He ICP, and in the microwave-induced plasma atomic emission spectroscopy (MIP-AES) literature. Another significant breakthrough in the present work includes the determination of nonmetals in gases by their direct injection into the ICP by a device called a direct injection probe (DIP). This low dead volume interface (\u3c 40[mu] L) is used for the introduction of gaseous samples directly into the axial channel of the ICP. Injection of a gaseous mixture of compounds containing the elements Br, Cl, S, and C results in detection limits of 0.1, 0.3, 0.05, and 1 ng, respectively. These detection limits are by far the best obtained for these elements in a gaseous form by ICP-AES. The extension of ICP-AES analysis to the determination of nonmetals, metalloids, and/or selected metals in aqueous and gaseous samples illustrates the value of this optical sampling approach in the VUV;Because this optical viewing system does not use any lenses, mirrors, or windows, VUV radiation can be detected down to 78.7 nm, the wavelength corresponding to the ionization energy of Ar. This ICP-VUV-AES system can therefore be beneficially applied as a diagnostic tool in the examination of excitation mechanisms in the ICP, especially with the observation of the Ar resonance lines at 104.8 and 106.7 nm. ftn[superscript]†DOE Report IS-T-1310. This work was performed under Contract W-7405-Eng-82 with the U.S. Department of Energy