The antlmony specles antimony( 111), antimony(V), methylstlbonic acld, and dimethyistlbinic acid are reduced in aqueous matrlx by sodlum borohydrlde to stlbine, methylstlbine, and dimethyistibine. Sb(II1) and Sb(V) are reduced together to stlbine under hlghly acldlc condltlons in a solutlon containing Iodide. Sb(II1) Is selectlveiy reduced at near-neutral pH, where no reductlon of Sb(V) takes place. Sb(V) Is then obtained by subtraction. The methylantimony acids are reduced at acld pH without addltlon of iodlde. The stlblnes are collected on a Iiquld-nitrogen-cooled trap and separated chromatographically after heatlng the trap. They elute Into a quartz cuvette burner or graphite furnace mounted In the beam of an atomic absorption spectrophotometer; the resulting absorbance signals are recorded as chromatographic peaks. The absolute detectlon limit is 30-60 pg of Sb, depending on species and operating conditions; the concentration limit of detection is 0.3-0.6 ng L-' for a lOOmL sample. Analytical results from river and estuarlne waters are presented. Sb(III), Sb(V), methyistibonlc acld, and dlmethylstlblnic acid were found In natural waters.Antimony enters the aquatic environment as a result of the weathering of rocks (which contain an average of 0.16 ppm Sb), from soil runoff, through effluents from mining and manufacturing, and from municipal discharges. Typical concentrations in unpolluted waters are in the sub-partsper-billion range ( I , 2), but in leachates from secondary lead smelters levels of several parts per million have been observed (S. Johnston, Department of Environmental Regulation, Tallahassee, FL, personal communication, 1981). Antimony and its compounds have been listed as priority pollutants by the U.S. Environmental Protection Agency.The determination of antimony in aqueous solutions by reduction to stibine with sodium borohydride was first suggested by Braman et al. (3). Detection of the stibine was by atomic emission from a dc discharge. The combination of hydride generation and atomic absorption detection (without cold-trapping of the stibine) was described by Fernandez (4). As will be discussed below, these procedures and similar ones in the literature are applicable only to solutions containing Sb(III), inasmuch as Sb(V) is not completely reduced under the conditions described. The reduction of this species requires the presence of iodide ion in an acid reaction medium (5). This effect has been used for the selective determination of Sb(II1) and Sb(V) (6); at low pH and in the presence of zirconium(IV), the reduction of Sb(II1) is suppressed less than that of Sb(V), so that under these conditions only Sb(II1) is determined. Total inorganic antimony is then measured by DBpartement d'Environnement, Universit6 reduction in acid solution in the presence of iodide, and Sb(V) is calculated as the difference. This method is not highly selective; interference of Sb(V) in the determination of Sb(II1) starta to become significant at a ratio of 41. As will be shown below, most natural waters have S...
