Flow analysis-hydride generation-gas phase derivative molecular absorption spectrophotometric determination of antimony in oral homeopathic products ("AntimoniumTartaricum") formulated under alcoholic medium

In this work, a flow analysis-hydride generation-gas phase derivative molecular absorption-(UV) spectrophotometric method has been developed for the direct determination of antimony in aqueous and hydro-alcoholic samples. Antimony (III) from undiluted samples is directly transformed into the gaseous stibine (SbH₃) form by on-line reaction with sodium tetrahydroborate (NaBH₄) in acidic medium (HCl). The gaseous phase generated is separated from the liquid phase using a commercial gas-liquid separator, and swept - with the help of a carrier gas (N₂) stream - into a quartz gas cell (10 cm pathlength); where the corresponding absorption spectrum is acquired in a continuous mode over the 190-300 nm wavelength range, using a conventional spectrophotometer. A derivative strategy was selected in order to avoid the strong spectral interference of the ethanol vapor on the gaseous SbH₃ absorption spectrum. In this way, the peak height at 223 nm of the second order derivative spectrum appears as a clear, clean and interference free analytical signal, which allows the direct determination of antimony. The recovery values obtained from homeopathic formulations (prepared in alcoholic medium) spiked with know amounts of antimony ranged between 97.5 and 103%. The method provides a dynamic range from 0.20 to 30 mg Sb l⁻¹. The precision (RDS), evaluated by replicate analysis (n = 5) of samples and standard solution containing between 2.5 and 15 mg Sb l⁻¹ was in all cases lower than 1.2%. The proposed method was applied to the determination of antimony in commercial homeopathic products (“Antimonium Tartaricum”) prepared in hydro-alcoholic medium; and showed to be simple, precise, and accurate.