Sample preparation methods for the determination of cadmium in urine by tungsten-coil electrothermal vaporization inductively coupled plasma atomic emission spectrometry.

摘要

The scope of this dissertation spans various sample preparation methods of clinical samples, specifically urine for the determination of cadmium by tungsten coil (W-Coil) electrothermal vaporization (ETV) inductively coupled plasma atomic emission spectroscopy (ICP-AES). These sample preparation methods include simple aqueous dilution, acid digestion, chelation and extraction, as well as permanent modification. When appropriate, the results yielded from W-Coil ETV-ICP-AES were compared to those from graphite furnace atomic absorption spectroscopy (GFAAS) due to the predominance of GFAAS as an analytical technique in trace metal analysis.; The W-Coil ETV is used as the means of sample introduction into the ICP in addition to acting as the vaporization source. Once extracted from the glass envelope, the W-Coil is housed in a glass vaporization cell that is purged with high purity argon gas to ensure the subsequent vapor is directly swept into the axially-oriented ICP. A 20 muL aliquot of sample is pipetted directly on the coil and is then subjected to a vaporization cycle controlled by a nearby PC. The vaporization cycle allows for a dry step, two ash steps, and vaporization step in which currents and their conjugate times are easily optimized according to analyte and sample matrix. The optical train is straightforward beginning with focusing the ICP image 1:1 with a focusing lens onto the entrance slit of a high resolution Czerny-Turner monochromator. The detection system is a thermo-electrically cooled charged coupled device (CCD) connected to a near by computer for spectral output. This system is capable of simultaneous multi-elemental detection within approximately a four nanometer window.; Real samples are prepared using aqueous dilution in conjunction with an internal standard and the standard additions method for data analysis. Cadmium concentrations determined by the W-Coil ETV-ICP-AES system and GFAAS are compared. Another set of real samples from the same lot are subjected to acid digestion, followed by chelation with ammonium pyrrolidine dithio-carbamate (APDC) and extracted into methyl iso-butyl ketone (MIBK). Cadmium concentrations determined by W-Coil ETV-ICP-AES with and without the use of an internal standard were compared. The W-Coil is permanently modified by Pd to minimize matrix interferences by assisting in thermal separation of the analyte from concomitants. Samples were prepared by a simple aqueous dilution and Cd concentration was directly determined. The same set of samples used in the chelation/extraction procedure are used here for comparison purposes.