Techniques of Atomic Absorption: Direct Determination of Cadmium in Biological Materials and Metal Speciation by Differential Atomization.
Date of Award
Doctor of Philosophy (PhD)
A method was developed for the direct determination of cadmium in biological materials. Determination of metals in biological samples was made difficult by the low concentration, the complex matrix, and the small amount of sample generally available. Current methods for this type of analysis involve either a wet-ashing or a dry-ashing step to break down the organic matrix and concentrate the metals present. These procedures often cause positive and/or negative errors due to contamination of the sample or loss of the metal of interest. The described method avoided these sources of error by eliminating sample pretreatment steps. The method made use of a unique carbon bed atomizer for electrothermal atomic absorption spectroscopy. A sample introduced onto the heated carbon bed was completely decomposed and atomized before being drawn through the lightpath, where atomic absorption was recorded. Use of the carbon bed atomizer efficiently broke down the organic matrix of biological samples, thereby reducing background absorption and eliminating the need for previous ashing steps. The sensitivity of the method (approximatly 10('-13) g) was sufficient so that preconcentration of the sample was unnecessary. Use of the carbon bed atomizer was applied to a study of the cadmium concentrations in whole blood, urine, perspiration, hair, and breath samples collected from a population not occupationaly exposed to the metal. Liquid samples were introduced into the atomizer by placing 1 (mu)l on a 6-mm filter paper disk. This technique immobilized the sample and promoted complete degradation of the matrix. Background signals were reduced to approximately 6-8% absorption. Hair samples were analyzed by dropping 1-cm segments onto the surface of the hot carbon bed. Breath samples were collected by pulling the sample through a bed composed of activated carbon. Data were collected indicating the average cadmium concentration and the range and distribution of cadmium values in blood, urine, sweat, and hair. Comparisons were made between the cadmium concentrations of two or more of these excretory tissues for individuals. Estimates of the average daily excretion of cadmium through each of these tissues were calculated. The total daily excretion of cadmium from the body was estimated to be 180 (mu)g/day, which was approximately equal to the daily intake. The results indicated that the half-life of cadmium in the human body is considerably less than 20-40 years, as is reported in the literature. There has been an increasing demand for analytical techniques which provide not only total metal analysis, but also differentiate between various metal compounds. Such techniques would provide information on the chemical form of a metal in a sample, which has particular significance in toxicological and environmental studies. A technique was developed which used a dual-stage atomizer for atomic absorption spectroscopy to distinguish between different chemical forms of metals. The first stage, consisting of a platinum wire loop, was gradually increased in temperature to vaporize different forms of a metal at their characteristic temperatures. The second stage, which was the carbon bed, was maintained hot to atomize the vaporous metallic species. Absorption traces were obtained for solutions of various lead and cadmium compounds using the platinum loop apparatus. Traces also were obtained for lead and cadmium in whole blood. Differences were observed in the absorption spectra of the various samples.
Weiss, Susan Deborah, "Techniques of Atomic Absorption: Direct Determination of Cadmium in Biological Materials and Metal Speciation by Differential Atomization." (1980). LSU Historical Dissertations and Theses. 3543.