Atomization and Excitation 43 1.5 VAPOUR GENERATION The number of abstracts reviewed i n this Section has decreased considerably compared t o those i n previous years. This should not be judged as r e f l e c t i n g a decline i n the popularity o f the techniques since Sections 1 . 2 , 3.1.1.3 and 3.1.1.4 cover vapour generation w i t h plasmas as we1 1 as new methods of sample preparation and reduction.In t h i s Section, the more fundamental advances i n atomization and instrument systems a r e reviewd. The more noteworthy advances t h i s year have included non-dispersive fluorescence systems coupled t o hydride generation, which whilst not new, have now a t t r a c t e d commercial a t t e n t i o n . 1.5.1 Hvdride Generation44 Analytical A tomic Spectroscopy Although not a new technique, the use of atomic fluorescence, i n p a r t i c u l a r non- dispersive AF, f o r the detection of hydride forming elements has undergone a modest revival.This i s principally because of i t s simplicity and i t s applic- a b i l i t y t o multi-element analysis. Braun e t a l . (377, 1506) have described a commercial non-dispersive atomic fluorimeter and reported detection l i m i t s f o r As, B i , Sb and Se which were about ten-fold b e t t e r than could be obtained w i t h equivalent hydride AA methods. Similarly Kuga and Tsujii (1055) have reported on the determination of As by non-dispersive AF.generated by sodium borohydride reduction, was swept i n t o a graphite furnace maintained a t a temperature of 1200 OC.claimed. c e l l was used t o determine Te i n high-purity copper (416). ference from copper on hydride generation, the dissolved sample was passed through a Chelex-100 ion-exchange column. The increased s e n s i t i v i t y of AF compared t o AA was exploited by Ebdon e t a l . (1169). By using a continuous hydride generation system w i t h a miniature H2/Ar diffusion flame, As and Se were determined, yielding detection l i m i t s of 0.34 ng m1-' and 0.13 ng ml-l, respectively. ation procedures have again been described.This year sees the publication of Astrom's work on a FI system f o r hydride generation (1450), which was reported l a s t year as a conference a b s t r a c t (see ARAAS, 1981, 17, Ref. C772). determination of Bi by injection i n t o a continuously flowing stream of HC1 was described.After reaction w i t h sodium borohydride i n a mixing c o i l , the evolved hydride was swept i n t o an e l e c t r i c a l l y heated quartz tube f o r convention- al AA measurement. accomplished i n continuously flowing systems and t h i s theory finds support i n a paper by Crock and Lichte (2266), who have employed a conventional AutoAnalyzer system t o determine t r a c e levels of As and Sb i n geological materials.ference suppressants were added, and two 40-foot delay c o i l s were used t o allow equilibrium conditions t o be established so t h a t no interferences from C u , Fe, U and V were observed. i n hydride AA, Welz and Melcher (C113, C256, 1453) proposed two possible pro- cesses. After reduction t o the hydride, the analyte may react with the i n t e r - f e r a n t t o form an insoluble compound, o r the i n t e r f e r a n t p r e f e r e n t i a l l y may be reduced t o the f r e e metal, on t o which the hydride may adsorb.Dedena (1453, see ARAAS, 1981, 11, Ref. C769) concluded t h a t improvement in atomizer design could reduce gas phase interferences by 2-3 orders of magnitude.t o explain the influence of the condition of the quartz substrate on the atomiz- a t i on of hydri des , Verl i nden (221 7 ) observed t h a t cl osed-end s i 1 i ca tubes showed In t h e i r system, arsine, A detection l i m i t of 0.01 ng was To avoid the i n t e r - A non-dispersive AF system employing an H2/Ar flame as the atomization ~- Methods of automation aimed a t reducing the tedious nature of hydride gener- The Interference suppression has been reported t o be more e a s i l y Inter- In an attempt t o c l a r i f y the mechanism of interference f o r t r a n s i t i o n metals In an attemptAtomization and Excitation 45 severe internal deterioration and devi t r i f i c a t i o n of the quartz t o B-cristobal- i t e .The author a l s o noted t h a t no such problems occurred in open ended tubes. and co-workers (2347). Hydrides of As, S b , Se and Sn were passed i n t o a stream of ozone produced in a s i l e n t discharge ozoniser. erated by the reaction: The most novel hydride system reported t h i s year was t h a t used by Fujiwara Chemiluminescence was gen- MHn t O3 -+ H MO * --.* H MO t hv X Y X Y Detection was by a non-dispersive system.co-interference was observed which could not be resolved by separation and preferential v o l a t i l i z a t i o n from a liquid N2 t r a p o r by chromatographic means. Matsumoto and Fuwa (1457) have measured broad-band molecular emissions emanating from AsH3 introduced into an air/H2 flame. Two band heads were recorded, one a t 420-440 nm and a second a t 480-520 nm, postulated t o be due t o As0 and As2 species respectively. 10-nm band pass interference f i l t e r a t 500 nm and this yielded a detection l i m i t of 20 pg ml-1 f o r a 10 ml sample. Other references of i n t e r e s t - Since the detection was non-specific, A non-dispersive detection system was employed, w i t h a Determination of In by hydride generation : 330. 1.5.2 Mercury Generati on Probably the most novel methods currently proposed f o r mercury determination are those based on e l e c t r o s t a t i c and e l e c t r o l y t i c techniques. (1126) e l e c t r o s t a t i c a l l y captured Hg p a r t i c l e s on t o graphite substrates p r i o r t o ETA. A collection efficiency of >90% was claimed. plished by reduction of known amounts of Hg(I1) s a l t s t o generate Hg vapour which was collected under s i m i l a r conditions t o the samples.The apparatus had been previously described f o r the collection of Pb p a r t i c u l a t e s i n atmos- pheric samples (see ARAAS, 1981, lJ, Ref. 1601) and shows considerable potential f o r simple s e n s i t i v e atmospheric analysis. A thin layer electrodeposition flow cell was employed by Frick and Tallman (1129) t o determine Hg i n water.flow c e l l was designed t o force solution flowing through a graphite tube electrode into a t h i n layer adjacent t o the inner wall, thereby f a c i l i t a t i n g mass transport during electrodeposi t i o n . conventional ETA. Torsi e t a l . Calibration was accom- The The graphite tube was then removed f o r The use of chemical collection systems f o r Hg a r e s t i l l extremely a t t r a c t i v e methods f o r the separation and concentration of Hg vapour.Sub-nanogram amounts of Hg were determined by adsorption on t o s i l v e r sand (1863). poisoning of the s i l v e r sand by chlorides o r sulphides in the sample, combustion a t 600-700 OC with CuO c a t a l y s t was employed with a s i l v e r sand pre-column t o To prevent46 Analytical Atomic Spectroscopy scrub out deleterious vapours.Problems were encountered by Herano (1886) when c o l l e c t i n g Hg vapour on gold. High r e s u l t s were obtained compared t o wet oxid- a t i o n methods, and ashing aids such as Ca(OH)2 were said t o i n h i b i t atomization o f Hg from the combustion tube.A re-usable sampling tube based on s i l v e r e d alumina was described by Taylor (C284). suited f o r personal sampling applications. Collection e f f i c i e n c i e s o f 80-95% over the a n a l y t i c a l ranges o f 2 ng t o 10 ug Hg were claimed. lected and concentrated from seawater using a s p e c i a l l y synthesized d i t h i o - carbamate bonded s i l i c a - g e l (464).The pre-concentrated organo and inorganic mercurials were then thermally desorbed i n t o the quartz tube atomizer o f a Zeeman AA spectrometer. p a r t i c u l a r l y a t t r a c t i v e t o the analyst. Goto and colleagues (2029) described an automatic system f o r the determination of t o t a l and inorganic Hg. flow digestion, reduction, and e x t r a c t i o n i n small bore tubes, and a t slow flow rates were applied t o monitoring Hg i n sewage e f f l u e n t . 0.1 ppb was obtained when an 8 p1 f l o w c e l l was used f o r detection. ous m i n i t o r i n g o f Hg i n o i l - s h a l e gases was described by Girvan and Fox (352, see also ARAAS, 1981, 11, Ref. 257). Marshall and Midgley (1788) have determined SO2 i n ambient a i r u t i l i z i n g the reaction between SO2 and Hg' reagents. ambient a i r using t h i s method (see also ARAAS, 1981, 11, 46). A second i n d i r e c t method u t i l i z e d the interference e f f e c t of I2 on Hg t o determine down t o 2.5 pg o f I - i n seaweed (1539). s e l e c t i v e electrode methods especially since B r - and C1- d i d n o t i n t e r f e r e . The device was said t o be i d e a l l y Mercury was c o l - Automatic methods, especially those w i t h automated sample handling steps, are Continuous A detection l i m i t o f The continu- Two i n d i r e c t methods described t h i s year are worthy o f note. Concentrations a t the ppb l e v e l could be detected i n The author claimed t h a t the method was superior t o ion-