ANALYTICAL CHEMISTRY, VOL 50, NO. 4 , APRIL 1978
649
Volatilization of Arsenic(II1, V), Antimony(II1, V), and Selenium(IV, VI) from Mixtures of Hydrogen Fluoride and Perchloric Acid Solution: Application to Silicate Analysis Sixto Bajo Swiss Federal Institute for Reactor Research, 5303 Wurenlingen, Switzerland
The possible volatilization of As(II1, V), Sb(II1, V), and Se(IV, V I ) from mixtures of HC104/HF is investigated. I t is shown that there are no losses with Sb and Se irrespective of the Initial oxidation state, and with As(V). As(II1) is partially or totally lost by volatilization; this can be avoided by oxidizing As with HCIO,. The oxidation state of all three elements after the HCI04/HF treatment is determined. These results lead to a recommended procedure for the dissolution of siliceous materials in which As, Sb, or Se are to be determined.
Silicates are often dissolved for analytical purposes by a mixture of HF and HCIOl ( I , 2 ) . However, it is not clear from t h e literature (3, 4 ) if in t h e course of this operation, which comprises partial or total evaporation of the solution, there are losses of traces of As, Sb, and Se. The usefulness of some existing literature data is restricted, because (a) the oxidation state and t h e weight of the elements used in a n experiment are not stated ( 5 ) ,(b) the possibility of absorption by platinum vessels-which was demonstrated for Se (6)-is often not taken into account (5, 7,8), (c) it is often not possible to decide if the observed losses are really due to volatilization and not t o some other step in the procedure used. The volatilization of Se from different solutions was studied by Bock and Jacob (9),but the system HF/HC104 has received little attention. T h e determination of As after dissolution of silicates with HF, HCI04, H N 0 3 , and KMnO, was described by Terashima ( I O ) , and after vapor phase attack by H F and H N O Bby Feldman ( 1 1 ) . I t was the purpose of the present investigation to establish reliable data on the volatilization of As, Sb, and Se from a mixture of HF and HC104 under conditions t h a t are representative for the dissolution of silicates. T h e elements were studied in the range of 1p g to 1 mg, and great care was taken to use them in well defined oxidation states. The experiments were done in the presence of silicates (as granite) and without silicates. Losses were determined by the radiotracer method, and t h e oxidation state was determined again after the experiment.
EXPERIMENTAL Reagents and Apparatus. The acids used were HN03 (65%), HCIOl (60%), and H F (40%). The solution of zinc bis(diethyldithiocarbamate) (Zn(DDC)2)was 1.7 X M in CHC13 (22). The grain size of the granite used was
