6 1.2 PLASMAS Analytical Atomic Spectroscopy 1 . 2 . 1 Inductively Coupled Plasmas Inductively coupled plasma optical emission spectrometry continues t o follow the familiar development curve, c h a r a c t e r i s t i c of analytical techniques. Following the period o f rapid growth, there i s some evidence t h a t the period of consolid- ation has been reached. reporting new developments has increased and, as often happens, there i s an apparent separation between "users" and researchers.now almost e n t i r e l y related t o developments i n commercially available instruments. The r a t i o of papers describing applications t o those Progress f o r the users i sAtomization and Excitation 7 1.2.1.1 Plasma Characteristics Mechanistic studies o f the I C P continue t o be reported w i t h chemical engineering groups concentrating on the physico-chemical c h a r a c t e r i s t i c s , and a n a l y t i c a l spectroscopists concerning themselves mainly w i t h e x c i t a t i o n mechanisms. Boulos -- e t a l .(C141, C1304) used l a s e r Doppler anemometry f o r studying v e l o c i t i e s i n a 50 mm diameter 3 MHz plasma a f t e r seeding i t w i t h e i t h e r C o r S i p a r t i c l e s .For a 3.2 mm i n j e c t o r operated a t between 4.8 and 7.4 1 min-l, a x i a l v e l o c i t i e s i n the plasma i n the range 5-20 m s - l were recorded. Meubus (C1305) reported an a1 t e r n a t i v e v e l o c i t y measurement technique based on recording the time/intensi t y curves o f spectral l i n e s emitted during the decay period o f plasma e x t i n c t i o n .These were used t o monitor the decay o f plasma temperature and through an energy balance equation, the plasma v e l o c i t y . and co-workers (C81, C146, C1351, C2060) have continued t h e i r work on the e x c i t a t i o n mechanism of the plasma and have proposed r a d i a t i o n trapping as the p r i n c i p a l mechanism of energy storage i n the plasma.Previously i t was considered t h a t the metastable states provided the p r i n c i p a l energy store, b u t they pointed out t h a t , a t the high c o l l i s i o n rates o f an atmospheric pressure plasma, these states would be expected t o be i n c o l l i s i o n a l equilibrium w i t h nearby r a d i a t i v e states and could therefore only s t o r e energy i f the e f f e c t i v e l i f e t i m e s o f the r a d i a t i v e states were themselves greater than expected.To demonstrate r a d i a t i o n trapping, & self-absorption o f the A r l i n e s , the e f f e c t i v e excited s t a t e l i f e t i m e s were measured f o r plasmas operated a t various pressures i n sealed tubes. By modulating the r.f.power a t various frequencies, i t was possible t o observe the e f f e c t i v e damping o f the o s c i l l a t i o n by the excited s t a t e l i f e t i m e s (C81). For the A r 811.53 nm l i n e , upper s t a t e l i f e t i m e s o f 1 ms, 100 us and 33 US were obtained a t pressures o f 1 atm, 10 Torr and 0.1 Torr respectively. r a d i a t i o n trapping model.mental evidence supports the "recombining plasma" model as described by Fujimoto ( J . Phys. SOC. Japan, 1980, 49, 1569). Penning i o n i z a t i o n o f analyte species by both metastable l e v e l s and also those l e v e l s involved i n r a d i a t i o n trapping, followed by three body ion-electron recombination. Results on the s p a t i a l d i s t r i b u t i o n s o f temperature, electron density, and A r metastable concentration l e d Fuwa and co-workers (420, see also C197) t o favour metastable A r atoms, having an e f f e c t i v e i o n i z a t i o n p o t e n t i a l o f 4.21 eV, as the i n t r i n s i c i o n i z a t i o n b u f f e r i n the I C P .t h e o r e t i c a l and measured e x c i t a t i o n and i o n i z a t i o n rates f o r the a l k a l i n e earth elements has been reported (C2059). described an energy balance model f o r the I C P based on the supposition o f LTE, b u t reported t h a t i n the s k i n zone both the electron concentration and temperature were higher than predicted.H e i f t j e These values were considered t o be consistent w i t h the Boumans (1376) has commented t h a t the available experi- The dominant mechanisms i n t h i s model are A comparison o f the On the macroscopic scale, Eckert (1306)8 Analytical Atomic Spectroscopy A d d i t i o n a l reference on t h e preceding t o p i c - C1346. E x c i t a t i o n temperatures continue t o be determined f o r various plasma c o n f i g u r - a t i o n s b u t , i n i s o l a t i o n , such r e s u l t s are o f l i m i t e d value unless they a r e r e l a t e d t o t h e known s p a t i a l p r o p e r t i e s o f t h e I C P and t h e c u r r e n t t h e o r i e s on plasma mechanism.One study (C142), f o r example, r e p o r t e d t h e e f f e c t o f i n j e c t o r gas f l o w r a t e on e x c i t a t i o n temperatures a t a f i x e d viewing h e i g h t , using Ca and Fe as t h e thermometric species.p a t t e r n t h a t as t h e f l o w r a t e increased t h e temperature f e l l . Temperatures o f 6700 K, 5800 K, 4000 K and 3300 K were obtained a t f l o w r a t e s o f 0.5, 1.0, 1.5 and 2.0 1 min-' r e s p e c t i v e l y . Abdallah and Mermet (C1364) compared e x c i t a t i o n temperatures f o r Fe and r o t a t i o n a l temperatures f o r N2' and OH i n A r and He ICPs and i n A r and He MIPs generated w i t h a Surfatron. non-LTE n a t u r e o f t h e A r I C P , t h e various temperatures were i n agreement (4500 K), whereas f o r t h e He I C P and t h e MIPs t h e e x c i t a t i o n temperature o f Fe (4500 K) exceeded t h e r o t a t i o n a l temperatures, 2000 K.The g e n e r a l l y observed increase i n e x c i t a t i o n temperature w i t h energy o f t h e upper e x c i t e d s t a t e was t h e s u b j e c t o f comment by Kornblum and Smeyers- Verbeke (1377), who p o s t u l a t e d t h a t t h e temperature increase i s a continuous f u n c t i o n o f t h e e x c i t e d s t a t e energy r a t h e r than a step f u n c t i o n associated w i t h i n d i v i d u a l s t a t e s .E x c i t a t i o n , v i b r a t i o n a l , and r o t a t i o n a l temperatures have been determined (369) i n A r cooled and N2 cooled plasmas and used t o show d i f - ferences i n plasma s t r u c t u r e . temperatures i n molecular gas plasmas and found t h a t t h e order o f e x c i t a t i o n temperatures i s nitrogen<air<oxygen. temperatures (7000-10000 K) were i n c l o s e agreement ( w i t h i n 400 K) w i t h t h e r o t a t i o n a l temperatures, c o n f i mi ng t h e LTE n a t u r e o f t h e a i r plasma.a n a l y t i c a l f i g u r e s o f m e r i t f o r A r cooled and a i r plasmas, t h e same group (C1688) r e p o r t e d t h a t t h e a i r plasma a t l e a s t equalled t h e performance o f t h e A r cooled plasna and exceeded i t when used i n c o n j u n c t i o n w i t h u l t r a s o n i c - n e b u l i z a t i o n w i t h o u t d e s o l v a t i on.These conclusions were supported i n another study (C1267) which showed t h a t w i t h mixed N 2 / A r cooled plasmas, t h e v e r t i c a l p o s i t i o n s o f t h e emission maxima are s t r o n g l y dependent on t h e N 2 / A r r a t i o , and t h a t f o r pure N2 c o o l i n g most maxima occur a t o n l y 2 t o 4 mm above t h e l o a d c o i l .The dependence o f plasma temperature on pressure f o r N2 plasmas was s t u d i e d by E l k a t t a n (C204) who showed t h a t v i b r a t i o n a l and r o t a t i o n a l temperatures increased (Tvib 4230-5570 K, Trot 4030-5150 K) s t e a d i l y w i t h increase i n gas pressure (65-265 Pa).Montaser e t a l . (C35, 1568) used t h e s e r i e s - l i m i t line-merging technique, w i t h A1 as t h e t e s t element, t o determine e l e c t r o n d e n s i t i e s i n A r cooled and N2 cooled plasmas. Under s i m i l a r o p e r a t i n g c o n d i t i o n s , e l e c t r o n concentrations were h i g h e r The r e s u l t s obtained f o l l o w e d t h e expected Unexpectedly, i n view o f t h e i n t h e case o f t h e OH group by as much as Barnes and co-workers (C2055, C2434) have determined e x c i t a t i o n and r o t a t i o n a l It was noted t h a t f o r a i r , t h e e x c i t a t i o n ComparingAtomization and Excitation 9 i n the A r cooled plasma than i n the N2 cooled plasma, b u t when both plasmas were operated t o favour the e x c i t a t i o n o f high energy l i n e s , the electron concentra- t i o n s were s i m i l a r .power 400-3000 W, ne = 8 . 5 ~ 1 0 ~ ~ - 1 . 4 ~ 1 0 ~ ~ ~ m - ~ ; N2 cooled plasma: height 5 mn, power 1-3 kW, ne = 8 . 5 ~ 1 0 ~ ~ - 4 x l O ~ ~ (C2061) , using mass spectra and i o n i z a t i o n temperatures, confirmed the physical transport o f energetic species such as NO' from t h e induction r i n g t o the c e n t r a l channel where they may i o n i z e neutral analyte atoms.I o n i z a t i o n temperatures i n the N2 cooled plasma (5750-6700 K a t 1.2 kW) were s i g n i f i c a n t l y lower than those i n the A r cooled I C P operated under s i m i l a r conditions. The recorded values were A r cooled plasma: height 15 mm, Further studies by t h e same group Understanding the s p a t i a l c h a r a c t e r i s t i c s @f t h e I C P i s a key t o understanding i t s properties as an a n a l y t i c a l source, including matrix interferences which are o f t e n caused by changes i n the s p a t i a l emission patterns.workers (C47, C145, 433, 434, C1267, 1375) have continued t h e i r extensive work on t h i s subject and have now published t h e i r r e s u l t s (433) describing the behaviour o f " s o f t " and "hard" l i n e s (see ARAAS, 1981, lJ, 8) w i t h respect t o plasma temperature and s p a t i a l p o s i t i o n .S i m i l a r conclusions, regarding d i s t i n c t regions o f e x c i t a t i o n i n the I C P , were a r r i v e d a t by Kawaguchi e t a l .(412), based upon t h e measurement o f a x i a l p r o f i l e s o f e x c i t a t i o n temperatures (Fe) and r o t a t i o n a l temperatures (OH). I n addition, H o r l i c k ' s group have now produced data on h o r i z o n t a l emission p r o f i l e s (C145, 1375) and on the v e r t i c a l d i s t r i b u t i o n o f atomic and i o n i c concentrations f o r the analyte species Cay Cd and Mg (C47).The h o r i z o n t a l p r o f i l e s show c l e a r l y t h a t emission from ions i s concentrated i n the boundary region between the c e n t r a l column and t h e upper-end o f the induction zone. sample (434) produced s i g n i f i c a n t s p a t i a l s h i f t s i n the emission patterns which can r e s u l t i n both enhancements and depressions when t h e emission i s viewed a t a f i x e d height.plasma, both CaI and CaII l i n e s were enhanced whereas higher i n the "non-thermal" zone they were depressed. Radial p r o f i l e s revealed t h a t low down i n the plasma the enhancements occurred i n the boundary region between the c e n t r a l column and the induction zone. A t higher l e v e l s i n the plasma, CaI emission was generally depressed, b u t CaII emission was depressed on the c e n t r a l a x i s and enhanced i n the boundary region.It w i l l be i n t e r e s t i n g t o see i f t h i s mechanism applies equally t o other elements since the balancing o f depression and enhancement explains the known a n a l y t i c a l advantages o f using i o n i c l i n e s emitted from t h e "non-thermal" region.The authors i n f e r r e d from the data t h a t t h e low a x i s enhancement resulted from increased c o l l i s i o n a l e x c i t a t i o n whereas ambipolar d i f - fusion may influence analyte behavious higher i n the plasma. I n s i m i l a r work (2039), which included r e s u l t s on molecular spectra, i t was demonstrated t h a t the r a d i a l displacement of molecular emission from t h e analyte w i t h increasing H o r l i c k and co- The a d d i t i o n o f e a s i l y ionizable concomitants t o the I n p a r t i c u l a r f o r Cay i n t h e low a x i s "thermal" region o f the10 Analytical Atomic Spectroscopy height i n the plasma i s a f u n c t i o n o f the ease o f atomization o f the sample.Spatial studies o f the a x i a l atomic and i o n i c concentrations o f Ca, Cd and Mg i n the plasma have shown t h a t i n a l l cases the AAS signal peaked lower i n the plasma than d i d the emission signals (C47). This i s i n agreement w i t h the r e s u l t s o f Koirtyohann e t a l . (2228) who have published s p a t i a l data on i n t e r - element e f f e c t s i n the low region o f the plasma.alkali-metal matrix elements on the atomization, e x c i t a t i o n and i o n i z a t i o n be- haviour o f a l k a l i n e earth elements, i t was found t h a t there was no e f f e c t on atomization, t h a t i o n i z a t i o n was suppressed, b u t t h a t the emission i n t e n s i t i e s o f both atomic and i o n i c l i n e s were enhanced.than on atoms. E x c i t a t i o n temperature measurements indicated t h a t a l i t h i u m matrix d i d n o t a f f e c t the temperature, and the authors concluded t h a t the mechanism was non- thermal. A novel approach t o mapping discharge c h a r a c t e r i s t i c s (C2058) was the use o f f r e e Cd atoms produced from a furnace and introduced i n t o e i t h e r the outer o r sample flow gas streams.C2368. Observing the e f f e c t o f The e f f e c t on ions was l a r g e r The data were n o t affected by p r i o r desolvation of the aerosol. Additional references on the preceding t o p i c - C18, C144, C202, C2354, Abel-inversion i s widely used t o convert l a t e r a l i n t e n s i t y data t o r a d i a l i n t e n s i t y data.and two papers (860, 1492) have discussed improved computational forms. The use o f AFS f o r plasma diagnostics (C2057) overcomes t h i s problem and has been used t o show differences i n the atomic and i o n i c d i s t r i b u t i o n s i n an I C P . ICP-OES has been recognised and several groups are engaged i n the preparation o f atlases o f spectral l i n e s .Winge e t a l . (1673) have surveyed the information t o be presented i n t h e i r forthcoming "Atlas of Spectral Information f o r I n d u c t i v e l y Coupled Plasma Atomic Emission Spectroscopy". It w i 11 provide data on 70 elements including wavelength scans, wavelength scans o f concomitant elements, and a l i s t i n g o f 973 prominent l i n e s w i t h estimated detection l i m i t s .A more comprehensive l i s t i s under preparation by Wohlers and Ward (C10, C182) who reported t h a t so f a r 10000 l i n e s i n the range 185-850 nm had been recorded i n t h e i r data base which covered most elements except the r a r e earths. _ - e t a l . (1564, 2323) have used a computer-controlled scanning echelle spectro- meter t o produce high r e s o l u t i o n background spectra and spectra o f the a l k a l i n e earth elements over the wavelength range 207-601 nm.A study (1380) o f the Fe spectrum i n the 200-300 nm range reported 100 l i n e s n o t y e t l i s t e d i n e x i s t i n g tables. because o f the d i f f e r e n t e x c i t a t i o n conditions , d i f f e r e n t l i n e s were needed t o provide optimum performance, which then equalled o r exceeded t h a t o f the A r cooled There are e r r o r s associated w i t h the technique, however, The importance o f comprehensive and we1 1 documented wavelength tables f o r Parsons A spectral study o f the N2 cooled plasma (C183) showed t h a tAtomization and Excitation 1 1 ICP.Additional reference on the preceding t o p i c - 2380.The use of vacuum and N2 purged spectrometers has enabled analysts t o determine important elements such as As, B , Br, Hg, I , P, S , and Se u s i n g vacuum u l t r a v i o l e t l i n e s . and i t i s encouraging t o see reports (C238, C2470) of new work in this area. the other end of the spectrum, Fry e t a l . (C1269) have employed photodiode arrays t o study red and near infrared l i n e s of non-metals such as Br, C , C 1 , F, H , N, 0, and S.accuracy of analyses by ICP-OES and these may r e s u l t from the overlap of adjacent spectral l i n e s and from apparent overlap caused by instrumental broadening of the l i n e profile. l i n e profiles assuming Van der Waals potentials todescribe collisional broaden- i n g by neutral Ar or He, and obtained half-widths in the range 0.001-0.01 nm, an order of magnitude larger than those predicted by the kinetic theory.The e f f e c t of the various types of broadening and instrument resolution (see a l s o C2472) on line-overlap and analytical performance was discussed. The 1 ine- widths of f i f t e e n spectral l i n e s of ten elements have been measured using a Fabry-Perot interferometer (2238), values f o r the half-width ranged from 0.001-0.005 nm with "a" values of the Voigt integral i n the range 0.2-0.7. Fassel e t a l .(546) demonstrated the f e a s i b i l i t y of determining isotope abund- ances of Pb and U from ICP emissions, obtaining s a t i s f a c t o r y resolution f o r the 206Pb, 207Pb and 208Pb isotopes and f o r the 235U, 236U and 238U isotopes.rules regarding the allocation of broadcast frequencies. however, t h a t this may not be the optimum frequency f o r ICP-OES a s demonstrated in a study by Robin e t a l . (1206). 40, 50 and 56 FlHz showed t h a t as the frequency increased, both the excitation temperature and electron density decreased i n a l i n e a r manner. The resulting decrease in background continuum was greater than the reduction in l i n e intensity resulting i n improved SBRs, and hence detection limits, f o r a number of elements - e.g. BI, CoII, CuI, NiI and VII, p a r t i c u l a r l y f o r h i g h e r wavelength l i n e s .appeared t o be no d i f f i c u l t y w i t h atomization of refractory elements such as Al, Ti and W. f o r both pure Ar and Ar/H2 plasmas, the continuum below 500 nm i s due t o radiative recombination but t h a t above 500 nm, Bremsstrahlung radiation makes a s i g n i f i c a n t contribution. introduction of water, increased the electron density and excitation temperature This region of the spectrum i s not well documented A t Spectral interferences represent the major source of uncertainty i n the Mermet and Batal (130, C2180) have calculated The almost universal use of 27 MHz power f o r ICPs resulted mainly from the I t i s becoming apparent, A comparison of plasmas operated a t 5, 27, In s p i t e of the lower plasma temperature (4000 K ) a t 56 MHz, there Spectrometric studies (129, 1371) o f a 40 MHz plasma showed t h a t I t was a l s o demonstrated t h a t the presence o f H2, e .~ .from the1 2 Analytical Atomic Spectroscopy and hence the continuum i n t e n s i t y , whereas the i n t r o d u c t i o n o f e a s i l y ionizable elements such as K and Na had no e f f e c t on these parameters. The electron temperature was found t o be 10000 K. Additional references on the preceding t o p i c - C21 , C201 , C2108. The e f f e c t s o f sol vent loading on plasma performance have been investigated by Browner and co-workers (C2080).Water as both aerosol and vapour was investigated w i t h respect t o signal magnitude and SBR. Optimum aerosol i n t r o - duction conditions were recommended. A s i m i l a r study (1743) on the e f f e c t s o f 30 common organic solvents on a low powered (1.75 kW) A r I C P showed t h a t solvent vapour loading i s the main f a c t o r influencing the plasma s t a b i l i t y .magnitudes were compared f o r aqueous and organic solvents, and f o r the Cu atomic l i n e enhancements were obtained, whereas f o r C r and Fe the i o n l i n e s were suppressed. increasing the power, mixing the solvent w i t h water, o r increasing the nebulizer gas flow-rate. Signal Toleration o f the plasma t o organic solvents was increased by 1.2.1.2 SamDle Introduction Sample i n t r o d u c t i o n has been one o f the less well developed aspects o f ICP-OES, but from the considerable number o f reports t h i s year i t i s apparent t h a t increasing e f f o r t s are being devoted t o t h i s subject.s o l i d s cause problems w i t h the nebulizer, the f l o w - i n j e c t i o n technique o f f e r s a possible solution.Indeed, some would claim t h a t the greater speed o f analysis f a c i l i t a t e d by the technique makes i t useful i n a l l applications, except those r e q u i r i n g the highest s e n s i t i v i t y and precision. The advantages are less when a scanning spectrometer i s used because m u l t i p l e i n j e c t i o n s may be required f o r each element and the time available f o r peak f i n d i n g and automatic background correction i s 1 i m i ted.Greenfield (C215, C1229) demonstrated the application o f F I t o ICP-OES, and has shown how the technique may be used t o implement a v a r i e t y o f c a l i b r a t i o n procedures. methods o f measurement (C1246) indicated t h a t i n e i t h e r case l i n e a r i t y and precision were good and comparable t o those obtained w i t h continuous nebulization. Alexander e t a1 .(1540) reported the determination o f Cay Fe, K, Mg, and Na i n serum using up t o 500 p l i n j e c t i o n s i n a c a r r i e r stream flowing a t r a t e o f 7.5 1 o f less than 2% (RSD). aliquots, using A r as the d r i v i n g gas, and w i t h water f l u s h between samples, was described by Mizuike e t a l .(977). For the analysis o f small sample volumes, o r where high l e v e l s o f dissolved A study o f peak height versus peak area the high A device which allowed segmented i n j e c t i o n s o f 40 p1 min-l. This gave r a p i d clean-out o f the chamber and a precision Additional reference on the preceding t o p i c - C1319.Nebulizers continue t o be the weakest l i n k i n I C P instrumentation and althoughAtomization and Excitation 13 p r a c t i c a l improvements have been made, t h e b a s i c o p e r a t i o n and design c r i t e r i a a r e n o t w e l l understood. Sharp (C269) has s t u d i e d t h e gas dynamics o f t y p i c a l gas j e t s used i n nebulizers, and has shown how j e t s t r u c t u r e , and r e l a t i v e p o s i t i o n i n g o f t h e j e t and uptake tube, a f f e c t t h e uptake r a t e and d r o p l e t s i z e d i s t r i b u t i o n o f a cross-flow n e b u l i z e r .Strasheim and Human (C2073, C2458) used l a s e r s c a t t e r i n g t o c h a r a c t e r i z e t h e d r o p l e t s i z e d i s t r i b u t i o n s produced by various n e b u l i z e r s and t h e i r associated chambers.It was found t h a t t h e SNR was d i r e c t l y p r o p o r t i o n a l t o t h e narrowness o f t h e d r o p l e t - s i z e d i s t r i b u t i o n and t h a t t h e SBR was d i r e c t l y r e l a t e d t o t h e number o f p a r t i c l e s i n t h e 0.5-8 p m range. An empi r i c a l model o f t h e nebul i zer-chamber combi n a t i on has been d e r i v e d by Gustavsson (C277).It employs t h e Nukiyama-Tanasawa equation t o provide an estimate o f t h e mean d r o p l e t diameter produced by t h e nebulizer, and uses t h i s t o compute a log-normal d i s t r i b u t i o n o f d r o p l e t s i z e s t h a t i s f i l t e r e d by t h e chamber, as c h a r a c t e r i z e d by i t s d r o p l e t c u t - o f f diameter dc.o f t h e e f f e c t o f surface t e n s i o n on d r o p l e t s i z e d i s t r i b u t i o n s , i t was shown t h a t many organic solvents produce d r o p l e t s l a r g e r , r a t h e r than smaller, than those produced from aqueous s o l u t i o n s (C2086). Hulmston (C293) has described a concentric-nebulizer/spray chamber combination t h a t allowed t h e waste s o l u t i o n t o be r e c i r c u l a t e d .A 1 m l sample could be sprayed f o r 10 minutes by t h i s method. It was necessary, however, t o f l o o d and wash t h e chamber between samples, w h i l s t p r o v i d i n g a bypass f o r t h e i n j e c t o r gas. r e s i d u a l 100 ~1 o f wash water had a s l i g h t d i l u t i o n e f f e c t on successive samples.A t o t a l consumption nebul i z e r / t o r c h combination has been r e p o r t e d (C2433) and t h e j e t - i m p a c t n e b u l i z e r has again received a t t e n t i o n (C1335). I n a study An estimated A d d i t i o n a l reference on t h e preceding t o p i c - C225. Babington n e b u l i z e r s have proved capable o f re1 i a b l y n e b u l i z i n g s o l u t i o n s having h i g h d i s s o l v e d s o l i d s contents o r c o n t a i n i n g suspended p a r t i c l e s .o f these devices a r e 1 aboratory f a b r i c a t e d . Wol c o t t and Sobel (C1318, 1574) have described i n d e t a i l t h e p r o d u c t i o n o f t h e i r modified o f f - c e n t r e i n j e c t i o n "V-groove" nebulizer.device f o r d i l u t e s o l u t i o n s were comparable w i t h those produced by a cross-flow n e b u l i z e r . A commercial v e r s i o n o f t h e Babington n e b u l i z e r i s t h e "GMK" neb- u l i z e r which has r e c e n t l y been i n c o r p o r a t e d i n t o a h y d r i d e generation system f o r t h e determination of As, Pb and Se (C218).Ebdon (C267, C2089) described a PTFE Babington-type n e b u l i z e r which was subsequently used f o r s l u r r y nebul- i z a t i o n o f coal samples i n t o b o t h A r cooled and N2 cooled plasmas. work ( 1 51 5) , two c o n c e n t r i c and two "V-groove" nebul i z e r s were compared when used w i t h a "cyclone" and a "double-pass" spray chamber. Comparable performance was obtained from t h e nebulizers, b u t t h e double-pass chamber was s u p e r i o r i n p r a c t i c a l a p p l i c a t i o n , t o t h e cyclone design.F r y e t a l . (C1336, C2307) have a l s o constructed a PTFE n e b u l i z e r and used i t f o r t h e s l u r r y n e b u l i z a t i o n o f Most P r e c i s i o n s and d e t e c t i o n l i m i t s obtained w i t h t h i s I n f u r t h e r14 Analytical Atomic Spectroscopy food samples prepared by sonic cavi tation/homogenization.employed t o investigate p a r t i c l e s i z e e f f e c t s . S l u r r i e s , produced from a i r p a r t i c u l a t e samples, w i t h diameters o f 10 pm o r less were introduced i n t o an I C P by a conventional concentric nebulizer (2264), and s u r p r i s i n g l y no problems o f blockage were reported.The g l a s s - f r i t nebulizer (see ARAAS, 1979, 9, 10) has been shown (871) t o give a mean p a r t i c l e s i z e diameter o f 5 0.1 um leading t o high transport e f - f i c i e n c i e s , b u t i t s performance i s l i m i t e d by long sample e q u i l i b r a t i o n times, a need t o wash the frit between samples, loss o f analyte by surface adsorption, and occasional contamination by leaching from the frit.attacks the glass and quartz o f t e n used f o r I C P nebulizers, chambers and torches. To overcome t h i s problem, several groups have investigated t h e use o f corrosion r e s i s t a n t materials f o r these components. For example, workers from one instrument company (C25, C220, C2074, C2438) used "Ryton", a carbon f i l l e d polymer, f o r the spray chamber and cross-flow nebulizer, and coupled these t o a demountable t o r c h assembly.as the wetted surfaces i n the nebulizer/chamber system (C74) and again coupled these t o a demountable torch. system using a P t / I r a l l o y f o r the nebulizer uptake tube with, once again, a demountable torch.(C25, C213). c h a r a c t e r i s t i c o f the spray chamber than the nebulizer, as the former acts as a f i l t e r r e j e c t i n g about 98% o f the sample. Browner and co-workers (C216, C262, 775, 1745, C2072) have continued t h e i r extensive studies on aerosol transport and have published (1745) a semi-theoretical model which estimates the e f f e c t s o f impaction, turbulence, c e n t r i f u g a l g r a v i t a t i o n a l and evaporation processes.Turbulence loss was shown t o be the f a c t o r dominant i n I C P nebulizer/chamber systems. favoured c o l l e c t i o n i n a cascade impactor f o r an AA nebulizer/spray chamber, whereas f o r an I C P nebulizer/spray chamber, c o l l e c t i o n on a f i l t e r proved equally e f f e c t i v e .e l e c t r o s t a t i c e f f e c t s i n spray chambers and have shown t h a t these can modify the transport e f f i c i e n c y and produce noise i n the emission signal. clean-out times are one o f the l i m i t i n g f a c t o r s i n the sample throughput r a t e . Dobb and Jenke (C83) reported t h a t on t h e i r system a time o f 130-270 s was required t o reduce the analyte signal t o 0.1% o f i t s i n i t i a l value when the concentration was l o 4 times the detection l i m i t .the signal could be modelled by a hyperbolic curve and t h a t the equation o f the curve could be used t o c o r r e c t a n a l y t i c a l data f o r memory e f f e c t s . Laser s c a t t e r i n g was Wet digestions o f materials containing s i l i c a require the use o f HF which Another company employed polypropylene and sapphi r e A t h i r d manufacturer described (C219) a PTFE Two o f the torches employed high p u r i t y alumina i n j e c t o r s It has long been r e a l i z e d t h a t the spray entering the plasma i s more A comparison (775) o f methods f o r measuring transport e f f i c i e n c y Tracy e t a l .(1509) have drawn a t t e n t i o n t o the presence of Chamber It was shown t h a t the decay of A heatedA to miza tion and Excita ti0 n 15 spray chamber/desolvation system was coupled w i t h a conventional pneumatic neb- u l i z e r t o produce improved detection 1 i m i t s f o r t h e determination o f t r a c e elements i n freshwaters (1855).nebulization and improves detection l i m i t s .however, can produce a t r a n s i e n t change i n the background emission, and t h e t r a n s i e n t signal renders r e l i a b l e background correction d i f f i c u l t . The thermal evaporators are e i t h e r heated by i n s e r t i o n i n t o the plasma o r by e l e c t r i c current. Broekaert and Leis (1362) used a graphite furnace t o introduce micro- amounts o f b i o l o g i c a l samples i n t o a plasma and reported detection l i m i t s 2-5 times lower than those obtained by continuous nebulization f o r the elements Cd, Co, C r , Cu, Fe, Pb, Mg, Mn, N i , T1, and Zn.an e l e c t r i c a l l y heated graphite cup t o determine Cay Cd, Cu, Ga, Mg, Pb, and Zn i n envi ronmental and botanical materi a1 s . Other reports i n c l uded : a modified commercial furnace(2285) , t h e determination o f t r a c e elements i n s a l t water and organic solvents using a p y r o l y t i c a l l y - c o a t e d graphite cup overcoated w i t h TaC (C2068, 2216), and the use o f an e l e c t r i c a l l y heated Ta boat (C85). Prack and Bastiaans (C24, C2090) have claimed t h a t w i t h c a r e f u l l y c o n t r o l l e d heating cycles, speciation measurements are possible. These authors described both electrothermal vaporization and a probe vaporizer t h a t was inserted i n t o the base o f the plasma.It w i l l be i n t e r e s t i n g t o see t h i s approach evaluated f o r r e a l samples, i.e. complex mixtures. K i r k b r i g h t e t a l . (C271, 1519, 1553, 1562, 1633, C2454) have also investigated both kinds o f vaporization device, applying them t o both inorganic and organic sample matrices.f o r the probe i n s e r t i o n vaporizer, a d d i t i o n o f 0.1% Freon 23 t o the i n j e c t o r f l o w reduced problems of carbide formation f o r t h e elements Mo, T i , U, and Z r , b u t no improvements were observed f o r B and C r . An automated system capable o f sequentially i n s e r t i n g sample-carrying cups i n t o the plasma and performing drying, ashing and vaporization cycles was described by Horlick, P e t i t and Todd (C2433).coolant. Thermal evaporation o f samples i n t o the I C P overcomes the i n e f f i c i e n c y o f The heating o f t h e i n j e c t o r gas flow, S i m i l a r l y H u l l (C1231) employed the use o f It was shown t h a t , The system was coupled t o a water cooled t o r c h employing a mixed Ar/02 Laser vaporization o f samples was one o f t h e f i r s t methods, other than nebulization, t o be used f o r sample i n t r o d u c t i o n i n t o the I C P and new work con- tinues t o be reported (see also Section 1.1.2).employed a ruby l a s e r i n both Q-switched and f r e e running modes, f i n d i n g the l a t t e r t o be more s u i t a b l e f o r the analysis o f Al-based a l l o y s and brass.Because o f sample inhomogeneity, the area o f the l a s e r focal p o i n t proved c r i t i c a l i n obtaining r e l i a b l e r e s u l t s . Kawaguchi e t a l . (471) used a Nd:YAG l a s e r t o vaporize low a l l o y s t e e l s i n t o t h e plasma and found t h a t the length and diameter o f the aerosol transport tube affected both t h e magnitude and s t a b i l i t y o f the signal.Attempts t o analyse Cu-based a l l o y s were unsuccessful owing t o H o r l i c k and Carr (550)16 Analytical Atomic Spectroscopy variable amounts o f material being evaporated from d i f f e r e n t sample compositions.A microprobe system has been coupled t o an I C P (976), and once again the import- ance of sample homogeneity f o r obtaining r e l i a b l e c a l i b r a t i o n s was stressed. Several groups have i n the past used arcs o r sparks as a means o f introducing s o l i d / l i q u i d samples i n t o the I C P . This year a commercial instrument has been introduced which employs an e l e c t r o n i c a l l y c o n t r o l l e d waveform spark as the sampling device (C40, C41, C42, C43, C222, C1232, C1316, C2210; see also C1273 and Sections 2.5.1 and 3.1.4.3).H e i f t j e and co-workers (C80, C2106) used t h e i r d.c. micro-arc vaporization system (previously used i n conjunction w i t h a MIP) t o introduce 111 a l i q u o t s i n t o both conventional (C80) and mini (13 mm i .d . ) ((2106) ICPs. A d.c. a r c was preferred f o r s o l i d sampling by Sing and S a l i n (C82), who used a dual wavelength system t o f a c i 1 i t a t e background correction o f the t r a n s i e n t signals. A novel r.f. arc sampling device has been described (C2203) i n which the sample i n j e c t o r tube o f the t o r c h i s f l a r e d a t i t s base t o form a small b e l l j a r which contains a water cooled Cu counter electrode.An r.f. arc i s struck between the plasma and the electrode sustaining a current o f 4A when the forward power t o the plasma i s 1.5 kW. The a r c length was mini- mized by keeping the t o r c h tubes as s h o r t as possible, the whole assembly having a length o f only 8.5 cm.An unusual device f o r introducing powders i n t o the I C P used a high frequency discharge t o produce suspended dust clouds from powdered samples, which were then swept i n t o the I C P i n j e c t o r (1148). f i c i e n c y o f 30-95% f o r various powders was claimed. obtained w i t h nebulization. e i t h e r continuous-flow o r those i n v o l v i n g condensation o f the hydride w i t h subsequent r a p i d release.r a t e o f hydride f l u x i s l i m i t e d by the tolerance o f the plasma t o H2 and water vapour. the problems o f measuring a t r a n s i e n t signal must be overcome. and Cooley (C221, C2481) have reported f u r t h e r work on a 3 channel continuous- flow hydride generation system (see ARAAS, 1981, 11, Ref. 31) and showed t h a t the formation o f PbH4 was g r e a t l y enhanced by m i l d oxidation o f the sample w i t h H202 p r i o r t o the reduction step.Instrument companies have been p a r t i c u l a r l y concerned w i t h designing equipment t h a t allows nebulization and hydride gener- a t i o n t o be performed without physical rearrangement o f the equipment, and two such systems have been described (C2081, C2179).mounted t h i s problem by connecting a hydride generator t o the uptake tube o f the nebulizer. Satisfactory r e s u l t s were obtained f o r As, b u t SeH2 was retained on the untreated walls of the glass spray chamber. was preferred by Hahn e t a l . (1122) f o r the determination o f As, B i , Ge, Sb, Se and Sn i n foods, w i t h detection l i m i t s ranging from 0.02 ng m1-l f o r As t o A transport e f - Hydride-generation provides detection 1 i m i t s 50-200 times lower than those Two types o f system are c u r r e n t l y being employed, The former enjoy convenience o f operation, but the The l a t t e r are capable o f providing the lowest detection l i m i t s , but Carr, Goulter Steig and Dennis (776) sur- The condensation type systemAtomization and Excitation 17 0.8 ng m l - ' f o r Sn.A d d i t i o n a l reference on t h e preceding t o p i c - 854. 1.2.1.3 Optimization, C a l i b r a t i o n and I n t e r f e r e n c e s Obtaining t h e b e s t r e s u l t s from a n a l y t i c a l techniques r e q u i r e s n o t o n l y an understanding o f t h e fundamental p r i n c i p l e s , b u t a c a r e f u l and considered ap- p l i c a t i o n o f a n a l y t i c a l methodology. It i s encouraging t o see r e p o r t s on these t o p i c s , n o t a b l y on o p t i m i z a t i o n , which enables n o t o n l y optimal performance t o be obtained b u t a l s o allows systems which a r e i n t r i n s i c a l l y d i f f e r e n t t o be compared.The v a r i a b l e s t e p Simplex method now seems firmly e s t a b l i s h e d as t h e p r e f e r r e d method f o r o p t i m i z a t i o n o f I C P systems.o b j e c t i v e v a r i a b l e , i t i s g e n e r a l l y more important f o r a n a l y t i c a l purposes t h a t i n t e r f e r e n c e s be minimized b e f o r e p r e c i s i o n o r s e n s i t i v i t y a r e optimized.Ebdon (C161) has l e d t h e way i n demonstrating t h e value o f Simplex techniques t o ICP-OES. I n a study o f optimum c o n d i t i o n s f o r various l i n e s , t h e l i n e a r r e l a t i o n s h i p between optimum power and " d i f f i c u l t y o f e x c i t a t i o n " , as r e p o r t e d by G r e e n f i e l d and Burns (ARAAS, 1980, 10, Ref. 477) f o r atom and i o n l i n e s i n the N2 cooled plasma was observed.It was f u r t h e r shown t h a t no such r e l a t i o n s h i p e x i s t s f o r t h e A r cooled plasma. o b j e c t i v e v a r i a b l e , i t was shown t h a t optimal SBR conditions, f o r e . ~ . Mn i n d i s t i l l e d water, corresponded t o very poor c o n d i t i o n s f o r minimizing i n t e r - ferences from t h e e a s i l y i o n i z a b l e elements.Re-optimization t o minimize i n t e r f e r e n c e s could be achieved w i t h no more than an o r d e r o f magnitude l o s s i n SBR. Cave e t a l . (C162) have compared t h e m e r i t s o f various Simplex procedures and G o l i g h t l y e t a l . (553) described an o b j e c t i v e f u n c t i o n f o r Simplex optim- i z a t i o n based on t h e r e c i p r o c a l s o f SBRs which provides optimized compromise condi t i ons .Although SBR i s u s u a l l y used as t h e On t h e question o f s e l e c t i n g an a p p r o p r i a t e A d d i t i o n a l reference on t h e preceding t o p i c - 1416. The least-squares method o f f i t t i n g data f o r t h e p r e p a r a t i o n o f c a l i b r a t i o n curves can produce gross e r r o r s a t low concentrations i f a l a r g e dynamic range i s used because t h e absolute variances a t h i g h c o n c e n t r a t i o n may be orders o f magnitude l a r g e r than those near t h e d e t e c t i o n l i m i t .v a r i a b l e s t o l o g a r i t h m i c q u a n t i t i e s , f o r example, produces a weighting which can overcome t h i s problem.r a t i o n curves, showed t h a t f o r t h e lower 3 orders o f magnitude, t h e standard d e v i a t i o n of the l i n e i n t e n s i t y i s constant, whereas i n t h e upper ranges, i t i s t h e r e l a t i v e standard d e v i a t i o n which remains constant. Under these c o n d i t i o n s l i n e a r scales a r e p r e f e r r e d f o r low c o n c e n t r a t i o n ranges and l o g scales f o r t h e upper ranges.o f t h e f u n c t i o n minimizes e r r o r s . Transformation o f t h e Maessen and Balke (549), i n a d e t a i l e d study o f c a l i b - Where functions a r e f i t t e d t o c a l i b r a t i o n data, c o r r e c t s e l e c t i o n Appropriate forms f o r various techniques e . ~ .18 Analytical A tomic Spectroscopy I C P , AAS, l a s e r OES, surface a n a l y s i s and XRF were described by Bubert and Klockenkamper (1374), see Section 3.2, w h i l s t Walters (C1430) discussed sources of v a r i a b i l i t y i n I C P c a l i b r a t i o n s .The s t a b i l i t y o f c a l i b r a t i o n curves depends on numerous f a c t o r s , b u t B o t t o (1794) has suggested t h a t s e t t i n g the instrument c o n d i t i o n s t o reproduce t h e r a t i o o f t h e CuI 324.75 nm/MnII 257.61 nm l i n e s e f f e c t i v e l y standardizes plasma c o n d i t i o n s thereby s t a b i l i z i n g c a l i b r a t i o n s I n view o f the known s p a t i a l v a r i a t i o n o f e x c i t a t i o n mechanisms, t h i s approach may be we1 1 founded.The presence o f improperly c o r r e c t e d background emission causes c a l i b r a t i o n s t o be n o n - l i n e a r near t h e d e t e c t i o n l i m i t . spectrographers have known t h i s f o r many years, i t i s now being re-discovered f o r ICPs (C78). been described by Gabarino and T a y l o r (872). Although An automatic mixing system f o r producing c a l i b r a t i o n curves has A d d i t i o n a l references on t h e preceding t o p i c - C52, 1311, C1320.Noise determines t h e a t t a i n a b l e p r e c i s i o n , and Boumans e t a l . (134) have shown t h a t ( a ) l i g h t f l u x i s t h e l i m i t i n g f a c t o r i n t h e low U.V. r e g i o n (190-250 nm), t h e r e f o r e , spectrometers w i t h h i g h o p t i c a l conductance, e f f i c i e n t entrance o p t i c s , and photomul t i p l i e r s w i t h h i g h s p e c t r a l s e n s i t i v i t y and low dark c u r r e n t a r e required, ( b ) t h e r e l a t i v e standard d e v i a t i o n o f t h e background comprises a constant source f l i c k e r n o i s e and shot noise, and t h a t ( c ) m a t r i x i n t e r e f e r e n c e s ( w i t h no s p e c t r a l l i n e coincidence) do n o t degrade d e t e c t i o n l i m i t s by more than a f a c t o r o f 2.An i n v e s t i g a t i o n o f n o i s e power spectra o f t h e I C P (1372) showed an approximate l / f c h a r a c t e r i s t i c , w i t h t h e components below 5Hz being determined by t h e type o f n e b u l i z e r used. spectrum i n t h e r e g i o n between 200-400 Hz was a t t r i b u t e d t o plasma r o t a t i o n and i n d i c a t e d s l i g h t a x i a l asymmetry (see a l s o ARAAS, 1981, 11, 10).authors (583) s t u d i e d the e f f e c t o f i n t e g r a t i o n p e r i o d on measurement p r e c i s i o n and s u r p r i s i n g l y showed t h a t f o r c o n c e n t r i c and cross-flow n e b u l i z e r s no improvement was obtained as t h e i n t e g r a t i o n p e r i o d was increased from 10 ms t o 30 s.For an u l t r a s o n i c n e b u l i z e r t h e longet. i n t e g r a t i o n periods produced poorer p r e c i s i on. f i c a l l y r e l a t e d t o a p a r t i c u l a r system and may n o t t r a n s l a t e t o others. papers noted i n t h i s s e c t i o n a r e those which i n t h e r e v i e w e r ' s o p i n i o n make statements o f general importance.Maessen e t a l . (C223, 1439 and 1488) a f t e r c o l l e c t i ng extensive data on a system optimized f o r reproduci b i 1 i t y concluded t h a t ( i ) the n e t l i n e i n t e n s i t y a t a l l wavelengths s t u d i e d showed a depression when measured i n the presence o f m a t r i x elements (Ca, K, Mg, Na), ( i i ) t h e m a j o r i t y o f l i n e depressions proceed i n the sequence K<Na<Mg<Ca, ( i i i ) t h e back- ground i n t e n s i t y showed an enhancement i n t h e presence o f m a t r i x elements and ( i v ) the m a t r i x e f f e c t of composite matrices was l e s s than t h e summed e f f e c t s o f A peak i n t h e noise The same This was a t t r i b u t e d t o t h e s i g n a l being s o u r c e - f l i c k e r noise l i m i t e d .Reports of i n t e r f e r e n c e s a r e o f t e n of l i m i t e d value because they a r e speci- TheAtomization and Excitation 19 the individual matrices. The authors a l s o demonstrated an "adaptation" e f f e c t showing t h a t washout and equilibrium times were longer when acid concentrations were changed, o r new acids introduced, than when repeated sprayings of the same acid were employed.Another study (C448), concerned with the e f f e c t s of Cs, K, L i , Na and Rb as chloride, n i t r a t e and perchlorate s a l t s , showed a depression of the background emission. spectroscopic c h a r a c t e r i s t i c s , the authors concluded t h a t the observed e f f e c t was non-spectral i n nature and was related t o sample introduction processes.The most common source of non-spectral interference i s the so-called acid-effect which has again been the subject of discussion (C224, C1260). Kawalski (595) have proposed the use of a generalized standard additions method for the characterization and elimination o f matrix interferences , whereas Thompson e t a l .(1522) described a d i l u t i o n device t h a t allowed automated matrix matching through linking the level of the matrix element t o the level monitored i n the appropriate channel of the spectrometer. After attempts t o c o r r e l a t e the r e s u l t s w i t h Kalivas and Additional references on the preceding topic - 323 , 1257 , 1493 , C1694 , 1804. 1.2.1 .4 Chromatographic Detection Atomic spectrometric techniques of analysis have t r a d i t i o n a l l y been confined t o determining the t o t a l elemental content of samples. Coupling these techniques t o separation procedures, however, has greatly expanded t h e i r scope and import- ance, particu a r l y i n the environmental and medical f i e l d s .(1456) invest gated the placement of the nebul izerlspray chamber r e l a t i v e t o the column i n high pressure liquid chromatography. They found t h a t when the spray chamber was d i s t a n t from the end of the column, peak broadening and dis- t o r t i o n occurred, but t h a t i f the chamber was placed close t o the end of the column, aerosol transport over a comparable distance resulted i n some loss of signal.independent of the mobile phase flow r a t e . various modes of separation have been reported, including the speciation of As and Se (C176), Cr(II1) and Cr(V1) (1657), organically bound metals i n natural waters (2224) , metal 1 i c components and pyri di ne i n coal refining sol vents (C2091) and rare earth elements (2455).o f an ICP as a fluorescence detector f o r HPLC. Browner e t a l . The l a t t e r arrangement did have the advantage of producing peak heights A number of applications u s i n g Lynch and Barry (C121) described the adaptation Additional references on the preceding topic - 1150, 1774, 1799. - Gas chromatographic detection by ICP-OES continues t o receive a t t e n t i o n .Yates and Kapila (C53, C54, C173), f o r example, described a system incorporating an in-line photoionization detector t o monitor GC performance and used the s p e c i f i c i t y o f ICP-OES t o determine alkyl lead and t i n compounds, metalocenes and organo-phosphorus compounds. has been used as a common component i n a system featuring e i t h e r MIP o r ICP-OES A dedicated mi ni-di rect-readi ng spectrometer20 Analytical A tomic Spectroscopy detection (C169).monochromator, r a t h e r than a mu1 ti -channel spectrometer, i n the detection equip- ment. The GC gas flow was shut-off while the spectrometer slewed t o successive wavelengths. Ge and Sb y i e l d i n g detection l i m i t s of 0.004 ug f o r Ge and 0.05 pg f o r As and Sb. I n contrast, Eckhoff e t a l .(1449) employed a slew scanning This system was applied t o the separation o f the hydrides o f As, 1.2.1.5 Instrumentation Perhaps the most important advance i n instrumentation has concerned coup1 i n g of an I C P t o a ma^^ spectrometer. Two groups, namely those o f Gray (see ARAAS, 1981, lJ, Ref. C2131) and Fassel (see ARAAS, 11, Ref. 2202) are pioneering t h i s work and t h i s year has seen the i n t r o d u c t i o n o f a comnercial instrument (C22, C160).A comparison o f I C P and M I P sources on the instrument showed that, whereas detection l i m i t s were 20 times lower w i t h the MIP, the l a t t e r suffered from c l a s s i c a l matrix interferences (s P043- on Ca), whereas the I C P d i d not. The instrument uses a high speed d i f f e r e n t i a l l y pumped i n t e r f a c e employing large (0.5 and 1.0 m) o r i f i c e s t o sample the plasma d i r e c t l y without formation o f a boundary layer.Date and Gray (C159, C292, 404) have discussed the advan- tages and disadvantages o f sampling w i t h and without boundary-layer formation, and reported r e s u l t s on t h e i r system showing detection l i m i t s o f less than 1 ng m1-l.nitude and some problems o f i o n i z a t i o n suppression were noted, both r e l a t e d t o boundary- 1 aye r format i on . The use o f atomic fluorescence spectrometry w i t h I C P atomization continues t o receive a t t e n t i o n and not unexpectedly the commercial instrument and i t s potenti a1 applications have been p l e n t i f u l l y described both i n the l i t e r a t u r e and a t conferences (C92, C140, 452, 729, 1089, C1333, C2482, see also Section 2.5.3).Recent developments include the extension o f the technique t o elements having t h e i r resonance l i n e s i n the V.U.V. e . ~ . P and S (2482), use i n combination w i t h hydride generation, use o f thermal gradient lamps f o r e x c i t a t i o n , and a t o r c h w i t h a glassy-carbon i n j e c t o r tube s u i t a b l e f o r use w i t h HF (C92).(C139, see also C2116) has reviewed AFS i n the I C P and Fredeen and Bastiaans (C108) have reported the determination o f C1 using l a s e r e x c i t a t i o n of non- resonant t r a n s i t i o n s . A novel approach employed a skimmed plasma (C2440) i n which only the central channel was used as the atom reservoir.The improved SBR yielded detection l i m i t s 5-20 times lower than w i t h conventional ICPs. Matrix interferences such as Ca/P04 and Ca/A1 were n o t encountered but i o n i z a t i o n type interferences were more severe (see also Section 1.3.5.1). Work continues on t h e development of t o r c h designs, the main aims being t o reduce gas consumption and operating power, while r e t a i n i n g a n a l y t i c a l perform- ance.Careful a t t e n t i o n t o the design of conventional sized torches can produce The dynamic range was however 1 imited t o less than 3 orders o f mag- WinefordnerAtomization and Excitation 21 s i g n i f i c a n t reductions i n gas consumption (C143, C1335, C1431 , 1570, C2109, C2453) allowing operation on 5-8 1 min-’ o f A r o r 5-7 1 min-’ o f N2.Such high e f f i c i e n c y torches can be sustained a t powers down t o 450 W and can be run a t even lower powers (250 W ) i f a higher frequency i s used (40.68 MHz). I n t h i s l a t t e r configuration, however, matrix interferences were more severe than f o r higher power operation (C2109).Ripson e t a l . (1508) have now published a description o f t h e i r water-cooled mini-torch which runs on only one 1 min-’ o f A r (see ARAAS, 1981 , 11, Ref. C2128). been used i n the emission mode (2001) and s i m i l a r conclusions were reached as f o r fluorescence detection. b e t t e r w i t h organic solvents have been reported by Boumans e t a1 . (1379) and Nobile e t a l .(382). I n the l a t t e r device, the i n j e c t o r diameter was decreased t o 0.56 m. The authors noted a s i g n i f i c a n t pressure b u i l d up (0.5 p.s.i.g.) i n the spray chamber w i t h the organic l i q u i d present, which required some 50 s t o s t a b i l i z e . Additional references on the preceding t o p i c - C1295, C1691. Other references o f i n t e r e s t - The skimmed t o r c h described above has also Modifications t o torches t o allow them t o cope Automated I C P spectrometer system: C182.On-line d i l u t i o n system f o r ICP-OES: 2241. Peak search routines: C2182. Separate impedance matcher/load coi 1 assembly: 2322. Vacuum u l t r a - v i o l e t ICP-OES instrument: 1223. 1 . 2 . 2 M i crowave-exci t e d Plasmas 1.2.2.1 Fundamental Studies There appears t o have been some r e v i v a l o f i n t e r e s t i n MIPs during the past year, w i t h new methods of generating discharges and new discharge geometries being reported. A review on the M I P has been given by Dahmen (1258).Plasmas generated i n a device c a l l e d a Surfatron (a section o f coaxial trans- mission l i n e terminated a t one end by a s h o r t c i r c u i t and a t the other by a capaci t a t i ve gap) have been described (1494).by A r MIPs i n resonant c a v i t i e s t h a t increasing power increases plasma length r a t h e r than diameter. introduced using u l trasonic-nebulization followed by desolvation. Because o f the low power (200 W ) and low residence times, atomization was r e l a t i v e l y i n - e f f i c i e n t .These e x h i b i t the property shown A He plasma was sustained i n a Surfatron w i t h samples Additional reference on the preceding t o p i c - C2123. The TMOIO c a v i t y o f Beenakker has been widely adopted because o f i t s a b i l i t y t o generate plasmas i n He a t atmospheric pressure. improvements and modifications have been advanced.This year a number o f For example, Matus e t a l .22 Analytical Atomic Spectroscopy (C57) employed capaci t a t i v e coup1 i n g o f the resonator, and a quarter wave trans- former t o match the c a v i t y and l i n e impedance. This resulted i n lower losses i n the matching device and less p u l l i n g o f the c a v i t y frequency, because the trans- former contains no capacitative elements.(128, C1271) modified t h e i r c a v i t y t o use capacitive coupling, b u t employed a more conventional double-stub tuner. A d d i t i o n a l l y they increased the c a v i t y depth from 1 cm t o 3 cm t o produce a longer discharge, and used a threaded i n s e r t i n the discharge tube t o produce a tangential f l o w which s t a b i l i z e d the plasma away from the tube w a l l .A t r u e t o r o i d a l M I P , analogous t o an I C P , has been described, and i n the same paper (1378), a 3 filament plasma t h a t yielded detection l i m i t s i n the range 10-30 ng m l - 1 f o r the elements Cay Cd, Co and Mg. Increased electron densities and emission i n t e n s i t i e s have been obtained i n sealed tube MIPs using a magnetic c o i l t o induce the theta-pinch e f f e c t (437, C2122).Additional references on the preceding t o p i c - 728, 729, 1747. Spectroscopic studies o f MIPs have been undertaken w i t h the aims o f f i n d i n g useful a n a l y t i c a l l i n e s , and of elucidating e x c i t a t i o n mechanisms. A study o f non-metal emission i n A r , He and Ne plasmas (C2129) l e d the authors t o conclude t h a t e x c i t a t i o n by rare-gas molecules i n the t r i p l e t s t a t e was the dominant mechanism.Carnahan e t a l . (C39) found t h a t by increasing the power i n t h e i r TMOIO c a v i t y t o 400 W , enhanced emission from the halogens was obtained without increase i n the background noise, thereby y i e l d i n g lower detection l i m i t s .Emission l i n e s i n the near i.r. (700-2000 nm) emitted from B r , C, C1, N, 0 and S i n a He M I P have been proposed f o r GC detection (C198, C2124). l i f e t i m e s i n the M I P were measured using time-resolved fluorescence induced by a synchronously pumped dye-laser (C200). S i m i l a r l y , Codding and Bollo-Kamara Excited s t a t e Additional reference on the preceding t o p i c - 862, C1696.Factors a f f e c t i n g atomization i n the M I P were investigated by Baughman and Goode (C203, C2121) using mass-spectral examination o f the plasma fragments. strong c o r r e l a t i o n between fragmentation and electron density was observed and t h i s was confirmed by boosting the electron density using a magnetic pinch.Introduction o f s o l i d s i n t o the afterglow o f a M I P (1905) produced atomization from the s o l i d a t temperatures o f <800 K by i n t e r a c t i o n w i t h atoms o f H, N and 0. Atomic absorption measurements on the r e s u l t i n g vapour showed f r e e atom densities o f 1010-1012 atoms i n e f f i c i e n t because of the low thermal temperature. Microwave e x c i t a t i o n o f the vapour produced by a GDL, however, overcame t h i s problem (1585), and produced enhanced emission from Ag, A l , Au, Cu and Ga and, s u r p r i s i n g l y , reduced emission from the A r f i l l - g a s , compared w i t h normal lamp operation.A Atomization by MIPs i s known t o be r e l a t i v e l y Additional reference on the preceding t o p i c - 327. 1.2.2.2 Sample Introduction D i r e c t nebulization i n t o MIPs i s n o t usually possible because o f t h e i r s e n s i t i v -Atomization and Excitation 23 i t y t o water. sample introduction i s possible i n a Beenakker cavity by raising the power coupled t o a He plasma above 300 W. MIP have preferred electrothermal vaporization as the method of sample intro- duction.Thus Aziz, Broekaert and Leis (1363) used a graphite furnace t o introduce micro-amounts of biological samples i n t o the plasma, reporting detection l i m i t s f o r Cd, Coy Cr, C u , Fey Mg, Mn, Ni, T1 and Zn i n the range 1-50 ng m1-l. as the noble metals, Bi, Cd, Co, C u , Fe and Zn onto a graphite tube which was then heated i n the He plasma gas stream. yielded detection l i m i t s down t o 0.05 ng m1-l.S have been determined i n aqueous solutions u s i n g a He MIP following vapor- ization from a Ta furnace (1596). Other references o f i n t e r e s t - Haas e t a l . (C38, C2071) have demonstrated t h a t this method of Most workers seeking t o analyse inorganic materials and solutions u s i n g the Vallard e t a l . (435) e l e c t r o l y t i c a l l y deposited elements such T h i s e l e c t r o l y t i c preconcentration The halogens (Br, C1 and I ) and Chemical generation of vapours f o r sample introduction: C300.Micro-arc sample introduction i n t o an atmospheric pressure N2 plasma: Sequential spectrometer f o r use w i t h MIP: C2187. C2070. 1.2.2.3 Gas-chromatoaraohic Detection This i s undoubtedly the most established and successful application of the MIP and i s now used routinely i n many laboratories.plasma operated i n the TMOIO Beenakker cavity i s most commonly employed b u t instrument modifications and new designs continue t o be reported. Budding (C69) compared the performance of the conventional design with t h a t of an ICP torch placed within a tapered wave-guide and operated a t 2450 MHz and powers up t o 400 W .Similarly, Carnahan and Caruso ((2127, see a l s o C39 i n Section 1.2.2.1) used up t o 400 W of power with a modified Beenakker cavity and obtained improved detection l i m i t s f o r the halogens. The Surfatron device (C2128, see also Section 1.2.2.1) has been used t o generate a He plasma f o r GC detection, as has the tangential flow torch of Bollo-Kamara and Codding (see 128, C1271 Section 1.2.2.1) (C2125).An axially-viewed He plasma was coupled t o an echelle spectrometer, equipped with a vibrating quartz plate f o r back- ground correction, and the plasma optimized f o r GC detection u s i n g a Simplex procedure (C170). rection i n a system described by Mulligan and Caruso (C167). cessful due t o the high Si background from the quartz plasma tube (C172).plasma detector was therefore used f o r S i , although the MIP was superior f o r B y C , P and halogen detection (see a l s o 719). The atmospheric pressure He For example, A vibrating mirror was preferred f o r rapid background cor- Attempts t o determine Si components i n pyrolized polymer samples were unsuc- A & ~~ Uden e t a l .(C71) compared the24 Analytical Atomic Spectroscopy He M I P w i t h the three electrode DCP and the I C P f o r high r e s o l u t i o n GC and reported t h a t t h e M I P was superior i n most cases. i n t e r n a l volume enables the M I P t o be placed closer t o the column thereby s i m p l i f y i n g the i n t e r f a c e and minimizing band spreading.I t s geometry and minimal Additional reference on the preceding t o p i c - 413. The determination o f empirical formulae (C166, C174, C2126) i s one o f the unique features o f M I P detection a r i s i n g from the independence o f the elemental signal and the molecular form. An unusual application o f t h i s p r i n c i p l e was the determination o f chlorinated and brominated a n i l i n e s (C171), which were f i r s t acylated and then "tagged" w i t h f l u o r i n e , and t h i s f a c i l i t a t e d both i d e n t i f i c - a t i o n and q u a n t i t a t i o n .paper, i s commonly used t o improve both the separation and detector response. Thus boronation has been employed t o f a c i l i t a t e the determination o f catechol (C72) ( t h i s paper also describes the determination of s t e r o i d a l carboranes) , and metallation t o improve the s e n s i t i v i t y f o r a l k y l halides (C2130).Other a p p l i c - ations reported included the determination o f u l t r a - t r a c e l e v e l s o f F i n u r i n e and d r i n k i n g water (875), o f f l u o r i n a t e d compounds i n r a t and human blood plasma (C168), and of Group I V organo-metallic compounds (1193).D e r i v a t i z a t i o n , such as t h a t described i n the previous 1 .2.2.4 Capaci ti v e l y Coup1 ed Microwave P1 asmas The c a p a c i t i v e l y coupled M I P has been used f o r a number o f years b u t has shown no signs o f acquiring wide-spread adoption. the determination o f W i n a N2-CMP f i n d i n g the atomic l i n e a t 400.875 nm t o be the most s e n s i t i v e (detection l i m i t 1.5 ppm).The operating conditions were optimized using a Simplex procedure which reduced interferences from e a s i l y ionizable elements. desolvation system (470) w i t h the CMP provided an improvement i n s e n s i t i v i t y o f 7-10 f o l d , compared w i t h the use of a pneumatic nebulizer. improvement i s obtained when u l t r a s o n i c nebulization w i t h desolvation i s used w i t h the I C P .sheath t o the plasma provided improved s t a b i l i z a t i o n and b e t t e r e x c i t a t i o n con- d i t i o n s , p a r t i c u l a r l y i n the presence o f high matrix concentrations. described the a n a l y t i c a l properties o f high power (2.5 kW) plasmatrons operating a t 2600 MHz.o f a c y l i n d r i c a l d i e l e c t r i c chamber i n t o which the power i s coupled, w i t h a concentric hollow counter-electrode protruding i n t o it, through which the sample i s introduced. Powders o r l i q u i d s can be introduced and t h e maximum temperature o f an a i r plasma was reported t o be 500-5100 K. WUnsch e t a l .(1098, 1681) , studied No i o n i c l i n e s were observed. Use o f an u l t r a s o n i c nebulizer/ A s i m i l a r Disam e t a l . (1047) reported t h a t adding an a d d i t i o n a l N2 gas Russian workers (C1293 , C1296 , C1297 , C1300, C1301 , C1302) have r e c e n t l y These devices, which can be run on a i r and other gases, consist The temperatureAtomization and Excitation 25 reported included the analysis o f pulverized rocks and minerals (C1296, C1300) , the determination o f B, C1, F, and S i n powder samples (C1301), and the deter- mination o f t r a c e elements (1 ppm l e v e l ) i n aqueous acids (C1302). 1.2.3 D i r e c t Current Plasmas 1.2.3.1 Fundamental Studies Most fundamental studies have been aimed a t elucidating the matrix e f f e c t s associated w i t h the DCP.Coleman and Williams (C164) have concluded t h a t some o f the contradictory statements i n the l i t e r a t u r e concerning enhancements o r depressions by matrix elements can be a t t r i b u t e d t o the sample i n t r o d u c t i o n process, p a r t i c u l a r l y the diameter o f the i n j e c t o r chimney. t h a t the i n t r o d u c t i o n o f e a s i l y ionizable elements produces v e r t i c a l s h i f t s i n the e x c i t a t i o n region, thereby causing interferences w i t h a f i x e d height measure- ment.A study o f the enhancement o f l i n e s o f t r a n s i t i o n elements by the presence o f Na (1355) l e d the authors t o conclude t h a t the DCP i s n o t i n LTE b u t may approach p a r t i a1 thermodynami c equi 1 i brium. and I C P sources and observed t h a t i n the DCP the e x c i t a t i o n conditions were s t r o n g l y dependent on the vapour composition, i o n i z a t i o n p o t e n t i a l , chemical state, and concentration o f the atomic vapour, whereas no such dependence occurred i n the I C P . o f 17 elements studied, only A1 and Cd exhibited lower detection l i m i t s i n the presence o f N2, and f o r most o f the other elements the detection l i m i t s were i n f e r i o r . has also been shown t o produce an upward v e r t i c a l s h i f t o f the e x c i t a t i o n region. This was a t t r i b u t e d t o increased vaporization o f the solvent, causing an increase i n the e f f e c t i v e sample stream f l o w rate, thereby p h y s i c a l l y pushing the plasma upwards. determination o f t r a c e elements i n organi c sol vents (C229 , C1253). selection and background correction were the subjects o f conference reports by Frank and Peterson (C165), and Johnson and Sisneros (C1240). They f u r t h e r showed Zucheng e t a1 . (1 744) compared DCP An i n v e s t i g a t i o n of mixed Ar/N2 DCPs (1597) showed t h a t The i n t r o d u c t i o n o f organic solvents i n t o the DCP (C1230, C2211) I n s p i t e of t h i s apparent d i f f i c u l t y , the DCP has been used f o r the L i ne Additional reference on the preceding t o p i c - C 1.2.3.2 Instrumentation Sample i n t r o d u c t i o n t o the DCP by s l u r r y nebulizat and K i nsey (C33). Refractory carbi des were chosen authors claimed s a t i s f a c t o r y r e s u l t s compared w i t h 243, 1955. on was reported by Comptois as the t e s t analytes and the c e r t i f i e d values, although they indicated t h a t the precision needed improvement. a detector f o r HPLC was described by Gardiner and B r a t t e r (C175), who deter- mined Cu, Fe and Zn i n the p r o t e i n f r a c t i o n o f human sera and intravenous f l u i d s . The detection l i m i t f o r the three elements was 5 pg 1 - l . Various groups have discussed automation and data processing procedures f o r Coupling o f the DCP as26 Analytical Atomic Spectroscopy DCP spectrometric systems. spectrometer which used a mi cro-computer as the control element , and particularly emphasized i t s a b i l i t y t o correct f o r d r i f t and rogue r e s u l t s produced by events such as mains voltage t r a n s i e n t s . A data processing programme capable of cor- recting f o r baseline and s e n s i t i v i t y changes and matrix e f f e c t s was reported by Bankston (973). Johnson e t a l . (C2168) described a procedure f o r characterizing spectral interferences occurring i n the determination o f rare earth elements i n geological materials. Olear e t a l . (C8, C1241) described an automated DCP Other references o f i n t e r e s t - Applications: C1236, C1237, C1250, C1252, C1254. Low frequency argon plasma arc: C2202. Spectrographic analysis w i t h a DCP: C27.