Cd analysis by Atomic Absorption

Introduction

Cadmium is mainly produced as cadmium sulfide in the natural environment. In the industrial sphere, however, it is mostly produced as a by-product when producing zinc from zinc sulfide ore. Zinc ore normally contains about 0.01% of cadmium. Cadmium is widely used in a variety of fields. Its applications include a soldering material (due to it’s low melting point), electrodes in nickel-cadmium batteries, a bearing material, a plating material with stronger anticorrosive effect than that of zinc plating, and an alloy component for neutron control rods of light-water reactors that substitutes the expensive hafnium. However, it has been long known that cadmium is a harmful metal. Cadmium is chemically similar to zinc, which is one of essential elements for human body, and hence cadmium is easily absorbed into the body. First it accumulates in the liver, and then is sent to the kidneys. One third of the cadmium entering the body accumulates in the kidneys, and one sixth in the liver. In human body, metallothionein, a type of sulfur- containing protein, combines with cadmium to reduce its toxicity. The half-life of metallothionein is a few days, and cadmium freed from the decomposed metallothionein repeatedly combines with newly produced metallothionein. Cadmium freed during this process is toxic, and when accumulating in the kidneys, it combines with protein or enzymes those contain thiol group (-SH), and they are denatured then run into renal damage. This leads to abnormality in the metabolism of calcium and phosphorous, calcium loss from the bones, and finally symptoms such as deformation or softening of bones. Substances that render heavy metals non-toxic, like metallothionein, are also found in plants. One such substance is phytokeratin that is contained in plants resistant to cadmium and other heavy metals. Recently there has been a strong trend towards regulating harmful heavy metals. For example, the RoHS directive bans the use of specified harmful substances in electrical and electronic products marketed in the EU from the 1st July 2006. The harmful substances under the RoHS directive include organic halides (brominated flame retardants) and metals such as mercury, lead, hexavalent chromium, and cadmium. Analysis of cadmium is carried out in various occasions, including the quality monitoring of tap water and wastewater, environmental analysis of groundwater and soil, as well as quality control of food, pharmaceutical, and industrial products. Here we present examples of analyzing a nickel solution using the flame method, and plastic using the furnace method.

July 21, 2004 GMT