Headspace sequestration of arsine onto a Pd(II)-containing aqueous drop as a preconcentration method for electrothermal atomic absorption spectrometry

A new method based on arsine preconcentration onto a single drop (3 μl) containing a Pd(II) solution (30 mg/l) is combined with electrothermal atomic absorption spectrometry (ETAAS) for the determination of As. Hydride generation is carried out in a vial containing an As solution (20 ml) in hydrochloric or citric acid medium. The drop was suspended at the tip of a microsyringe fixed above an extraction vial with a septum such that the tip of the needle was located in a consistent position in the headspace. The presence of Pd2+ in the hanging aqueous drop was seen to be highly effective for sequestration of the arsine formed, a preconcentration factor of 70 being achieved for As(III). The preconcentration method was fully characterized through optimisation of the following variables: Palladium concentration in the drop, sample volume, extraction time, stirring rate, extraction temperature, sodium tetrahydroborate (III) concentration, hydrochloric and citric acid concentration, drop volume and sample temperature. Preconcentration of other hydride-forming elements such as Se and Sb proved also effective under the conditions optimised for arsine. The limit of detection (LOD) (3σ criterion) of As(III), Se(IV) and Sb(III) were 0.1 (As), 0.15 (Se) and 0.2 (Sb) ng/ml. The relative standard deviations (RDS) (%) for As, Se and Sb were 3.5%, 2.5% and 3.0%, respectively.