Anal. Chem. 1907, 59, 2476-2479
2476
Radiotracer Investigation of the Interference of Hydrofluoric Acid in the Determination of Arsenic and Antimony by Hydride Generation Atomic Absorption Spectrometry Kilian Petriek and Viliam Krivan*
Sektion Analytik und Hochstreinigung, Universitat Ulm, Oberer Eselsberg, D- 7900 UlmlDonau, FRG
The Influence of hydrofluoric acid on the behavior of arsenic and antimony In hydrlde generation wlth NaBH, was Investigated by means of the radlotracers "As and 12,Sb. Slmuitaneously, the corresponding extlnctlons were measured. Up to a concentration of 1% hydrotluorlc acld present In hydrochlorlc acld sample soiutlons does not affect the hydrogenatlon of As(II1) and Sb(II1). I n soiutlons with higher HF concentratkn, As(V) forms [AOF,OHr ions whkh do not react with NaBH,. After the [AsF,OH]- ions are hydrolyzed, the Interference of hydrofiuorlc acld can be suff lciently reduced by complex formatlon wlth boric acid. Antlmony(V) Is not hydrogenated in the presence of hydrofiuorlc acld, which, in addlon, serlwsly hlnderr, the reductlon of Sb(V) to Sb( 111). Improved procedures are proposed whlch allow the ellminatlon of the Interference of hydrofiuorlc acld in both the hydrogenatlon and the absorption measurement stages and also In the reduction of Sb(V) to Sb(II1) In this medlum.
Hydride generation atomic absorption spectrometry (AAS) is one of the most important methods for the determination of trace concentrations of arsenic and antimony. However, serious interference problems may occur with analysis of samples that must be decomposed in solutions containing larger amounts of hydrofluoric acid. In addition to various metals and geological samples, this is the case in many environmental samples such as airborne particulate matter, sewage sludge, soil, sedimenb, and many plant materials. Welz (1) presented an overview on the interference of hydrofluoric acid for all common hydride-forming elements from which it can be seen that hydrofluoric acid causes detectable interferences in the determination of antimony already at a concentration of 0.0002% and in the determination of arsenic a t a concentration of 0.02%. In both cases, the signal depression is strongly increasing with the concentration of hydrofluoric acid reaching about 80% depression at 0.02% H F for antimony and about 50% depression at 1% H F for arsenic. However, no information was given on the valence states of the elements. On the other hand, Janousek (2)did not observe any significant interference by hydrofluoric acid in the determination of arsenic in tungsten and niobium and their alloys after their dissolution in a HN03-HCl-HF acid mixture. In all previous investigations, atomization was achieved a t temperatures between 900 and 1000 "C by using a quartz tube. The aim of the present work was to study the mechanism of the interference of hydrofluoric acid by means of the radiotracer technique complemented by conventional absorption measurements. The main aspect was to distinguish between the interference in the hydride-generation vessel and in the atomization device and to develop improved procedures which eliminate the interference of hydrofluoric acid. EXPERIMENTAL SECTION Instrumentation. A Perkin-Elmer MHS 20 mercury/hydride system and a Perkin-Elmer atomic absorption spectrophotometer,
Table I. Operating Parameter for the MHS 20 Using a Quartz Tube (Purge Gas Nitrogen) or Graphite Tube (Purge Gas Argon)
parameter
Sb
As
quartz tube purge I 25 reaction 10 purge I1 40 graphite tube 30 s at 25 "C purge I heating up to 2100 "C 45 s 10 s at 2100 O C reaction 10 s at 2100 "C purge I1
20 15 50
30 s at 25 "C
45 s 15 s at 2100 "C 10 s at 2100 "C
Model 400,equipped with electrodeless discharge lamps for arsenic (resonance line, 193.7 nm; slit, 0.7 nm; power, 8 W) and antimony (resonance line, 217.6 nm; slit, 0.2 nm; power, 8 W) were used. Atomizations were performed with a commercially available quartz tube at 900 "C and with a pyrolytically coated graphite tube (specialmanufacture by Ringsdorff-Werke GmbH, Bonn, FRG) at 2100 "C. The gaseous hydrides were introduced into the tubes via a T connection in the center. The graphite tube was 55 mm long, of 11.5 mm i.d. and 14.5 mm 0.d. For its heating, a Perkin-Elmer HGA 70 graphite tube furnace was used. The operating parameters for the spectrophotometer are given in Table I. Deuterium-lamp background correction was used for each measurement. The peak area was recorded during an integration time of 12 9. The y-rays of the radiotracers were counted with a well-type NaI(T1) scintillation detector of 23 cm i.d. and 28 cm length (Bicron, Newbury, CT) coupled with a single-channel analyzer (Berthold, Wildbad, FRG). In each experiment, a counting error
