GENERATION OF CADMIUM ATOMS AT ROOM-TEMPERATURE USING VESICLES AND ITS APPLICATION TO CADMIUM DETERMINATION BY COLD VAPOR ATOMIC SPECTROMETRY

The only metal recognized as able to form a monoatomic vapor at room temperature is mercury (''cold vapor'' generation). This property has been widely used in many analytical techniques, particularly in atomic spectroscopy, to increase the efficiency of the transport of the metal to the measurement cell. In fact, cold vapor atomic absorption spectrometry (CV-AAS) has become the most common method for the determination of trace and ultratrace levels of mercury in the most varied samples. Evidence is shown here demonstrating that cadmium appears also to be able to form cold atomic vapor under appropriate reaction conditions. Experimental results show that some types of volatile cadmium species (most probably hydrides) can be produced by reduction with sodium borohydride of Cd2+ in an aqueous solution of vesicles of didodecyldimethylammonium bromide. Such volatile species are able to transport the metal to the atomic absorption measurement cell, where Cd-0 cold vapor has been detected. The absorption profile of the absorbing species at room temperature has been measured in a typical absorption quartz cell by using a spectrograph/charged coupled device arrangement. Results demonstrate the presence of monoatomic cadmium vapor in measurable concentrations in the absorption cell, the magnitude of the AAS signal being proportional to the metal concentration in the aqueous solution. This vesicular volatile species generation facilitates cadmium transport to the atomizer cell, thereby improving by about 20 times the detectability of cadmium by the cold vapor inductively coupled plasma atomic emission spectrometry technique (detection limit, 1 ng/mL Cd). Moreover, a highly sensitive determination of the metal based on these facts can be carried out by CV-AAS (detection limit, 0.O8 ng/mL), and sensitivity can be further improved by working at lower temperatures for volatile species generation and transport to the absorption cell.