ISSN:0306-1353    

DOI:10.1039/AA98313FX001

出版商:RSC    

年代:1983

数据来源: RSC

ISSN:0306-1353    

DOI:10.1039/AA98313BX003

出版商:RSC    

年代:1983

数据来源: RSC

摘要:

Atomization and Excitation 7 1.2 PLASMAS 1 . 2 . 1 Inductively Coupled Plasmas The most important recent development in the use of the ICP f o r elemental deter- mination has been the replacement of optical detection by mass spectrometric detection. spectra, thereby leading to fewer 1 ine interferences compared with optical emission detection. to the ppb level, and of using the isotope dilution method when the highest preci s i ons and accuracies are required.There remai n problems, however, with the precision, the effect of total s a l t loading on the interface, some incon- venient spectral coincidences and double ionization of some elements. Never- theless, there are two commercial instruments in production and considerable interest from users who cannot achieve the required performance with optical detection.This offers improved limits of detection and greatly simplified Further, i t i s capable o f providing isotopic analysis down8 Analytical A tom ic Spectroscopy 1.2.1.1 Plasma Characteristics Plasma modelling i s useful i n d e f i n i n g the boundary conditions under which plasmas operate and i n providing global views o f t h e i r s t r u c t u r e and dynamics.Boulos e t a l . (C1781) presented a r e f i n e d mathematical model which was used t o study the e f f e c t o f the a x i a l i n j e c t i o n o f a stream o f f i n e Cu p a r t i c l e s i n t o a plasma. l o c a l i z e d cooling and could a t high concentrations a f f e c t the transport mechanisms, tending therefore t o quench the discharge.H i e f t j e and co-workers (1882, C2271) have continued t h e i r work on determining rates o f energy t r a n s f e r i n the plasma using modulation o f the applied r.f. power (see ARAAS, 1982, 12, 7). I n a d d i t i o n t o the " r a d i a t i o n trapping" mechanism described previously, they now r e p o r t t h a t electron ambipolar d i f f u s i o n may also contribute t o t h e energy transport process.Further support f o r t h i s mechanism was given by Aeschbach (79) who concluded t h a t r a p i d energy t r a n s f e r o f t h i s kind would contribute t o non-LTE conditions i n the a x i a l channel o f the plasma. Ripson and de Galan (1021) c a r r i e d out power balance studies on a conventional I C P and on low power miniature ICPs e x t e r n a l l y cooled by a i r o r water.It was found that, depending upon the torch design, the generator i n c i d e n t power exceeded t h a t absorbed by the plasma by 2540%. (1 kW) was convected away by t h e large A r f l o w and, f o r the water cooled torch, the power was conducted away by the water. most e f f i c i e n t , operating on as l i t t l e as 300 W.It was shown t h a t the vapour produced by the p a r t i c l e s gave r i s e t o For the conventional torch, the power The air-cooled torch proved t o be Additional referenceon the preceding t o p i c - 934. Elucidating the e x c i t a t i o n mechanisms o f the I C P continues t o occupy the e f f o r t s o f researchers. Batal and Mermet (235) c l a s s i f i e d analyte l i n e emis- sions from the I C P according t o t h e i r e x c i t a t i o n energy and concluded t h a t charge transfer from A r ions i s the dominant e x c i t a t i o n mechanism.having e x c i t a t i o n energies o r combined ionization-exci t a t i o n energies approaching t h a t o f the ground s t a t e A r i o n (15.76 eV) were found t o be p a r t i c u l a r l y intense.This explains why i o n l i n e s are o f t e n observed t o be more intense than atomic l i n e s emitted from the I C P . The dominance o f the charge-transfer mechanism o f e x c i t a t i o n was supported by Boumans e t a l . (1020, C1974, C1985). Theoretical and p r a c t i c a l studies indicated t h a t , providing departures from col l i s i o n a l dominated equilibrium (LTE) (see also C2064) are not too great, the plasma can be considered as being i n p a r t i a l LTE w i t h respect t o i t s electrons. from t h i s t h a t the plasma may be described by a s i n g l e parameter, the electron concentration.Calculations based on t h i s assumption confirmed t h a t nearly resonant charge t r a n s f e r from A r ions t o analyte atoms i n the ground s t a t e i s the dominant e x c i t a t i o n mechanism. The reverse process i s blocked because o f f u r t h e r e x c i t a t i o n / d e - e x c i t a t i o n o f the ionized species.Blades (67) postulated Lines It followsAtomization and Excitation 9 that the population of Ar ions i n the analyte channel i s enhanced by rapid exchange of Ar between the axial channel and the plasma core.Rate models enable s t a t e populations t o be determined, without reliance on assumptions about the nature of the equilibrium, provided that the appropriate cross-sections are known. Lovett (78, C1787) employed a rate model t o demon- s t r a t e that radiative processes (decay, recombination and absorption) signific- antly affect the energy level populations o f col lision-dominated plasmas.In addition, i t was shown that Penning ionization has a negligible effect on spectrally derived temperatures except for elements of h i g h second ionization potential. The same author (C2272) concluded that the lack of evidence for "resonance broadening" of spectral lines in the ICP indicated a rather low upper limit t o inelastic collisional rates.In contradiction, Winefordner e t a l . (806, C2018) determined excited s t a t e lifetimes in the ICP and showed t h a t , for elements having closely spaced energy levels, quenching collisions significantly decreased the effective s t a t e lifetimes, and that the rate coefficients for quenching approached those of radiative processes. The study of the spatial properties of the ICP has done much t o clarify the origins of the observed matrix interferences, and t o explain the existence of parametric optima as identified by procedures such as the sequential Simplex.Furata and Horlick (80) have now published (see ARAAS, 1981, fly Ref. 690) a description of t h e i r spectrographic technique for surveying spatial emission patterns in the ICP.Winefordner e t a l . (1080) used a variety of techniques t o compare the temperatures and number densities of electrons, and Ar and Ca atoms, ions and excited species. As might be expected, i t was found that a t 15 mn above the load c o i l , the Ca ion population extended t o greater radial distances than the atomic population and was less influenced by the presence of an easily ionizable element ( K ) . array spectrometer to study spatial properties of the plasma.Blades and Caughlin (C1785) produced axial and radial excitation temperature maps of plasmas operated a t various powers, axially fed w i t h water o r xylene. In gen- eral , the introduction of organic solvents lowered the plasma temperature, b u t t h i s could be restored by raising the power.Lichte and Layman (C1926) ob- served modifications of the plasma spatial structure resulting from extending the outer torch tube. The exclusion of a i r reduced emission from molecular species such as NO, O2 and OH, caused a narrowing and lengthening of the plasma and caused the central channel t o become eventually fully mixed with the plasma core. solute vaporization interferences.Two groups used the now familiar photodiode The resulting increase i n sample residence time was shown t o reduce The effect of operating frequency on plasma performance continues t o be investigated. Gunter e t a l . (1038) determined excitation temperatures and10 Analytical A tom ic Spectroscopy e l e c t r o n number d e n s i t i e s i n plasmas operated a t 9, 27 and 50 MHz.were i n accordance w i t h others r e p o r t e d p r e v i o u s l y (ARAAS, 1982, 12, l l ) , showing t h a t both e x c i t a t i o n and e l e c t r o n number d e n s i t y decreased w i t h increase i n o p e r a t i n g frequency. Wallace and Morrisroe (C2025) s t u d i e d t h e o p e r a t i n g c h a r a c t e r i s t i c s o f plasmas r u n a t 27 and 40 MHz.temperatures obtained a t t h e higher o p e r a t i n g frequency, t h e optimal i n j e c t o r f l o w r a t e was some 30% lower f o r t h e 40 MHz plasma. The r e s u l t s Consistent w i t h t h e lower Temperature data and measurement techniques have been r e p o r t e d by several groups. An i n t e r e s t i n g study by Tracy and Myers (737) presented data on t h e absolute s p e c t r a l radiance o f t h e A r continuum from a 27 MHz plasma operated a t 1250 W and viewed a t 15 mn above t h e l o a d c o i l .o f 1.2 x lo1' photons s-' mm" s r " nm-' was observed a t a wavelength o f 450 nm. A t 200 nm the radiance was reduced by a f a c t o r o f 60. For wavelengths below 400 nm, t h e plasma was found t o approximate a greybody w i t h a temperature o f 5480 K and an e m i s s i v i t y o f 4 x by Abel i n v e r s i o n , have been determined u s i n g conventional (467) and photodiode a r r a y (1377) spectrometers.Novotny Gal. (C1954) demonstrated t h e use o f a conventional mu1 tichannel spectrometer f o r t h e determi n a t i o n o f plasma temper- a t u r e from t h e Doppler w i d t h o f t h e A r 549.5 nm l i n e and e l e c t r o n d e n s i t y from t h e Stark w i d t h o f t h e Hg l i n e .The maximum s p e c t r a l radiance Radial e x c i t a t i o n temperatures, d e r i v e d A d d i t i o n a l references on t h e preceding t o p i c - 398, 1697. Molecular gas-cool ed p l asmas have gai ned i n p o p u l a r i t y , p a r t i c u l a r l y i n those c o u n t r i e s where A r i s expensive.p o s i t i o n and i o n i z a t i o n temperature o f mixed gas plasmas (Ar/N2 a t r a t i o s o f 0-1). 1000 K), and t h a t N c o n t a i n i n g species migrate from t h e plasma core i n t o t h e c e n t r a l channel. The c o o l i n g e f f e c t was confirmed by Ho (1701, C1883) who a l s o r e p o r t e d t h a t a mixed N 2 / A r ICP provided s u p e r i o r SBRs f o r atomic l i n e s o f medium e x c i t a t i o n energy, b u t poorer SBRs f o r i o n i c l i n e s than d i d an A r ICP.A i r and O2 cooled plasmas have a l s o been s t u d i e d (C1796, C2318), and both r e p o r t s p o i n t e d o u t t h e improved sample decomposition obtainable, which a l l o w s higher sampl i ng r a t e s . Houk e t a l .(1382) used MS t o study t h e com- I t was shown t h a t t h e presence o f N2 s u b s t a n t i a l l y cools t h e plasma (by Other references o f i n t e r e s t - E f f e c t o f a magnetic f i e l d on t h e I C P : Plasma diagnostics using l a s e r - e x c i t e d AF: Spectrographic method f o r c h a r a c t e r i z i n g ICPs: C2045. C1802, C2188, C2347. C2245. 1.2.1.2 Sample I n t r o d u c t i o n The recognized weaknesses o f t h e pneumatic n e b u l i z e r have once again promotedAtomization and Excitation 11 i n t e r e s t i n developing a l t e r n a t i v e techniques of sample introduction.e f f o r t has been directed a t thermal vaporization o f the sample. introduction of large q u a n t i t i e s of water, greatly increases the efficiency of sample introduction and permits the use of small sample volumes.Unfortunately, however, i t i s a commn feature of many of t h e a l t e r n a t i v e methods of sample introduction t h a t they produce t r a n s i e n t emission s i g n a l s , thereby adding t o the d i f f i c u l t y of accurate background correction. Most This avoids the The optimization and selection of appropriate nebulizers has been discussed by several workers (943, 1455).necessity of constant checking of nebul izer/sample introduction performance, e i t h e r using v i s i b l e observation o f Na o r Y emission, o r by the monitoring of line-pair i n t e n s i t y r a t i o s f o r l i n e s which behave d i f f e r e n t l y t o changing excitation conditions, 5, Zn(I1) 206.189 nm/Ca(I) 422.667 nm.study of nine d i f f e r e n t pneumatic nebulizer systems (C1831) showed t h a t the mass flux t o the plasma remained remarkably constant between systems, and t h a t the SNR varied only by a f a c t o r of 3 from the best t o worst systems used. Barnes e t a l . (1620) compared the performance of f i v e pneumatic nebulizers of d i f f e r i n g designs (adjustable cross-flow, fixed high pressure cross-flow, concentric and two Babington types) f o r the determination of C u i n a 5% alum- i n i u m solution.yielded the lowest detection l i m i t (3.4 ng ml-I), but the worst RSD (6.6% a t 2 ppm). detection l i m i t s (14 ng m1-I) with an RSD of 6.4% ( a t 2 ppm). Sobel version of the Babington nebulizer (see ARAAS, 1979, 9, 10) yielded an intermediate detection l i m i t of 10 ng ml-1 but combined t h i s with an RSD of 2.1% ( a t 2 ppm), and was therefore recommended as being most s u i t a b l e f o r alum- i n i um matrix determinations.In p a r t i c u l a r , Wallace (1302) commented on the A comparative I t was found t h a t the fixed h i g h pressure cross-flow nebulizer The variable cross-flow and concentric nebulizers gave the poorest The Wolcott and In s p i t e of their many drawbacks, nebulizers continue t o be the preferred device f o r liquid sample introduction.work previously reported a t conferences (see ARAAS, 1982, 12, 1 3 ) . Notably, Olsen and Strasheim (1041, C1957) on optimum droplet s i z e f o r introducing samples i n t o the ICP, Gustavsson (1286) on a s t a t i s t i c a l model of concentric nebulizer/chamber operation and Hulmston (755) on a recirculating nebulizer f o r small volumes. Gustavsson (1343) has also published a review of the theory of compressible flow as i t applies t o nebulizer design.nebulizer has been described (C2151) t h a t operated on 300 111 min-’ of solution and was used f o r d i r e c t injection of l i q u i d i n t o the ICP.considered t o be appropriate f o r nebulizing the e f f l u e n t from HPLC columns where the highly f i l t e r e d solvent would not block the f i n e c a p i l l a r i e s used i n the device. This year, several groups have published A micro-concentric The device was12 Analytical Atomic Spectroscopy Additional reference on the preceding topic - C2316.Babington nebulizers a r e the preferred choice f o r s l u r r y nebulization and f o r sol u t i ons contai n i ng very hi gh 1 eve1 s of di ssol ved sol ids (>5%). e t a l . (C1819) analysed titanium dioxide s l u r r i e s f o r trace elements and found t h a t calibration w i t h simple aqueous standards was possible. Use of a T i l i n e a s an internal standard improved the accuracy of the method.Similarly, Ebdon (C1848, 2088) determined trace elements i n coal s l u r r i e s using aqueous calib- ration standards. S i l i c a t e rocks were a l s o studied, b u t were not amenable t o simple calibration. Improved aerosol generation and a reduction i n viscosity e f f e c t s , i n the d i r e c t nebulization of o i l s , has been achieved by pre-heating the sample (1281).Improvements i n the design of the commercial GMK nebulizer were claimed t o reduce short term noise and memory e f f e c t s , and t o shorten the analysis time (C1755). Broekaert The most e f f i c i e n t nebulizers a r e the glass f r i t (see ARAAS, 1982, 12, 14) and ultrasonic designs. Both permit nebulization and sample introduction a t extremely low gas flow rates.Layman (C2156) investigated vertical Ca atom and ion l i n e s p a t i a l p r o f i l e s using a f r i t nebulizer operated a t 0.2 and 0.6 1 min-l. Ultrasonic nebulizers a r e known t o produce noisier optical signals than pneumatic types and i n a device designed t o nebulize 300 p1 samples (30), internal standardization was necessary t o improve the precision of determination In current nebulizer based systems, the spray chamber, mcre than the nebulizer, determines the c h a r a c t e r i s t i c s of the aerosol injected i n t o the plasma.p a r t i c u l a r problem associated w i t h spray chambers i s the r e l a t i v e l y long time required t o "wash" them out between samples. Thompson e t a l ; (1174) reduced sample changeover time by reducing dead volume i n the sample uptake tube and reducing the volume of a Scott-type double-pass spray chamber.(1248, see a l s o ARAAS, 1982, 12, 14) found t h a t the washout time was element dependent, being longest f o r the alkaline earths and heavy metals. A Dobb and Jenke The acid dissolution of s i l i c e o u s materials requires the use of HF which attacks glass sample introduction systems.research groups have produced desi gns fabricated i n corrosion r e s i s t a n t mater- i a l s . A system has been described (47) t h a t makes use of an a l l PTFE nebulizer and spray chamber, coupled t o a graphite i n j e c t o r tube. Recently, both manufacturers and Additional reference on the preceding topic - 232.Depending upon the physical and chemical properties of the solvent, the nebulizer/spray chamber introduces, i n varying r a t i o , a mixture of dry partic- ulate, wet aerosol and water vapour t o the plasma. The excitation and s p a t i a l properties of the plasma are accordingly modified by the sample stream and this probably accounts f o r many of the observed matrix interferences.Browner'sAtomization and Excitation 13 group have attempted t o define optimum c r i t e r i a f o r sample i n t r o d u c t i o n (C1824, C2152, C2207). Thus they investigated the e f f e c t s on "hard" and " s o f t " l i n e s o f varying p a r t i c u l a t e , solvent aerosol and vapour loads i n the plasma. Sample i n t r o d u c t i o n by various forms o f thermal evaporation has a t t r a c t e d considerable a t t e n t i o n t h i s year, although some o f the reports are published versions o f previously given conference papers (see ARAAS, 1982, 12, 15).Notable among these were K i r k b r i g h t ' s group on graphite rod vaporization (484) and graphite rod d i r e c t sample i n s e r t i o n (833, C1745, C1832, C2087); and Ng on carbon cup vaporization o f synthetic sea water (1158), o f organic solutions (1314) and o f r e f r a c t o r y elements (977); and Prack and Bastiaans (1252) on metal speciation by thermal evaporation.Barnes e t a l . (1400, C1797) described the use o f a modified c o m e r c i a l rod device f o r the vaporization o f b i o l o g i c a l materials, and Browner and Long (C2334) studied the transport phenomena and e x c i t a t i o n mechanism o f d r y aerosol sample i n t r o d u c t i o n .The d i r e c t analysis o f s o l i d s i s a p o t e n t i a l application o f thermal vaporization and Van Loon e t a l . (C1930) employed a commercial graphite furnace vaporizer t o introduce 1 5 7 5 mg samples o f both inorganic and organic materials.A P t o r W loop atomizer has been used (56) f o r vaporization o f 10 111 samples i n t o an I C P . Caruso Additional references on the preceding t o p i c - 799, C1783, C1907, C1977, C2157. The d i r e c t i n t r o d u c t i o n o f powdered s o l i d s t o the plasma has been considered The a t t r a c t i o n s and t r i e d almost since the inception o f the ICP-OES technique.o f removing the necessity o f dissolution, however, appear t o be outweighed by the d i f f i c u l t i e s of producing r e l i a b l e i n t r o d u c t i o n devices, segregation o f the sample, and c a l i b r a t i o n problems. who continue t o r e p o r t new methods (509, 576, 870, 1175, C2352) t h a t may have s p e c i f i c value, b u t are u n l i k e l y t o come i n t o general use. This does not seem t o deter researchers, Additional references on the preceding t o p i c - 1505, C1830.Arc and spark vaporization continue t o be investigated and there has been a r e p o r t (C2199) of the application o f spark sampling t o non-conducting s i l i c a t e materials. powder t o form a p e l l e t . Calibration was achieved using only two reference samples, the a n a l y t i c a l curve being assumed t o be l i n e a r over the c a l i b r a t i o n range.Spark sampling has also been employed f o r aluminium (1456) and high temperature a l l o y s (954). - 12, 16) papers describing a micro-arc sampling device (1374), and a plasma derived r.f. a r c sampling device (932). The materials were rendered conductive by pressing w i t h graphite H i e f t j e e t a l .have now published (see ARAAS, 1982, Laser a b l a t i o n o f f e r s the a b i l i t y t o remove materials from large substrates,14 Analytical Atomic Spectroscopy o r from those t h a t a r e t o o r e f r a c t o r y t o be t h e r m a l l y vaporized. Thus, Ishizuko and Uwamino (805) a b l a t e d various p o l i s h e d metal surfaces, b u t r e p o r t e d t h a t the technique could n o t y e t be used q u a n t i t a t i v e l y .M a r t i n and Thompson (854) vaporized samples from p e l l e t i z e d s o i l s and were a b l e t o d i f f e r e n t i a t e q u a n t i - t a t i v e l y s o i l s o f d i f f e r i n g o r i g i n . A recent t r e n d has been t o combine h y d r i d e generation and continuous n e b u l i z - a t i o n i n a s i n g l e device i n o r d e r t o a v o i d t h e necessity o f changing the sample i n t r o d u c t i o n systeni' t o determine t h e h y d r i d e forming elements.Preston (1394) replaced t h e impact bead o f a V-groove n e b u l i z e r w i t h an angled tube through which e x t e r n a l l y generated hydrides c o u l d be introduced i n t o t h e path o f the n e b u l i z e r gas.S i m i l a r l y , Lancione and Drew (C2146) introduced hydrides through a "T" j o i n t placed between t h e n e b u l i z e r chamber and t h e t o r c h i n j e c t o r . It i s known t h a t c a r e f u l c o n t r o l o f a c i d concentration and the presence o f an oxidant a r e p r e r e q u i s i t e s f o r t h e formation o f a v o l a t i l e Pb species t h a t may be PbH4.c a t a l y s i s i s the c r i t i c a l f a c t o r determining t h e r e a c t i o n conversion e f f i c i e n c y . Summerhays e t a l . (470) have demonstrated t h a t the conversion o f an analyte t o a v o l a t i l e species i n s o l u t i o n , 5, 0s t o Os04 o r Hg(I1) t o Hg(O), can enhance the s i g n a l by 24 t o 55 times.It was suggested t h a t t h e increased s e n s i t i v i t y a r i s e s from r a p i d v o l a t i l i z a t i o n o f t h e analyte from the d r o p l e t cloud, thereby increasing t h e sample i n t r o d u c t i o n e f f i c i e n c y t o as h i g h as 100%. Hutton and Montaser (C2191), however, suggested t h a t surface The advantages o f f l o w i n j e c t i o n have been p r e v i o u s l y described (see ARAAS, 1982, 12, 12) and an i n c r e a s i n g number o f a p p l i c a t i o n s papers a r e now appearing t h a t use t h i s technique.G r e e n f i e l d has now published h i s r e s u l t s on t h e a p p l i c a t i o n of F I t o ICP-OES (935, see a l s o ARAAS, 1982, 2, Ref. C215, C1229). The standard a d d i t i o n s method i s a u s e f u l way o f d e a l i n g w i t h m u l t i p l i c a t i v e i n t e r f e r e n c e s ; element determinations.t h e increased speed o f implementing the standard a d d i t i o n method renders i t ap- p r o p r i a t e f o r ICP-OES determinations. Van Loon e t 2 1 . (C1931) combined hydride generation o f AsH3 w i t h F I and reduced t h e consumption o f borohydride and the generation o f H2 which elevates t h e background l e v e l a t the As wavelength and quenches the plasma a t h i g h concentrations. McLeod, Worsfold and Cox (C2089) used F I f o r t h e i n t r o d u c t i o n o f serum samples t o the I C P , determining Cay Cu, Fey K, L i , Mg, Na and Zn.- a l . (C2153) t o implement F I f o r t h e a n a l y s i s o f b i o l o g i c a l m a t e r i a l s .however, i t i s g e n e r a l l y t o o t i m e consuming t o use f o r m u l t i - Two groups have demonstrated (567, C2333) t h a t w i t h FI, An HPLC pump and i n j e c t i o n valve was used by Faske et A d d i t i o n a l reference on the preceding t o p i c - C2155. Other references o f i n t e r e s t - Reviews on sample i n t r o d u c t i o n f o r ICP-OES: 1167, 1205, 1624, C2217.Atomization and Excitation 15 1.2.1.3 Optimization, Calibration and Interferences Optimization has been the subject o f numerous reports, but unfortunately many authors confuse the term "optimum", which should apply t o a unique s e t o f conditions, o r a t l e a s t sets o f such conditions t h a t r e a l i z e the optimal response of the objective variable, w i t h a r b i t r a r y sets o f conditions t h a t hap- pen t o f u l f i l l a p a r t i c u l a r c r i t e r i o n .t h a t i t allows unequivocal comparison o f f i g u r e s o f m e r i t f o r systems t h a t are d i f f e r e n t i n d e t a i l . A t present, f u l l f a c t o r i a l design experiments, o r the more e f f i c i e n t v a r i a b l e step-sire Simplex approach are the only methods capable of determining t r u e optima. P a r t i a l parametric searches, though incapable o f guaranteeing t r u e optima, provide p a r t i a l mapping o f the response surface i n d i c a t i n g t h e e f f e c t o f various parameters.Thus, Bamiro e t a l . (1635) i n - vestigated conditions f o r achieving good SBRs while minimizing matrix i n t e r - ferences and found t h a t t h i s was best achieved when operating under conditions appropriate t o the e x c i t a t i o n o f "hard" 1 ines. were reported by Marquardt e t a l .(352). De Galan e t a l . (1640) used the Simplex technique f o r optimizing the precisions o f determinations i n b i o l o g i c a l materials and demonstrated i n another r e p o r t (C1912) t h a t i t i s possible t o optimize for minimization o f interferences without serious loss o f detection power.An advantage o f t r u e optimization i s S i m i l a r parametric studies The use of i n t e r n a l standardization t o improve the precision o f determin- a t i o n should n o t be necessary w i t h an i n h e r e n t l y stable source such as the ICP.It i s , however, becoming increasingly apparent t h a t because low frequency pro- p o r t i o n a l ( f l i c k e r ) noise i n the plasma i s dominated by variations i n the nebulizer performance, i n t e r n a l standardization does improve the precision, p a r t i c u l a r l y of determinations i n concentrated solutions. It i s important t h a t the chosen i n t e r n a l standard and analyte l i n e s have a strong c o r r e l a t i o n o f i n t e n s i t y v a r i a t i o n . Belchamber and H o r l i c k (759) investigated various analyte and i n t e r n a l standard l i n e s and obtained an improvement i n the precision by a f a c t o r o f 2.i n t e r n a l standards as they exhibited poor c o r r e l a t i o n s o f i n t e n s i t y w i t h analyte l i n e s .and Schmidt ( 4 ) who obtained a 25-fold improvement i n precision when determining Not s u r p r i s i n g l y argon l i n e s were found t o be unsuitable as Examples of improvements i n precision and accuracy were given by Slavin Mn i n 5% sodium c h l o r i d e solutions, and by Larber and Goldbart (1621) who reduced d r i f t from 10% t o 0.1% using an i n t e r n a l standard.Myers and Tracy (1403) commented on the importance o f selecting appropriate conditions f o r implementing i n t e r n a l standardization. Notably, the signal must be proport noise l i m i t e d , the signals must be sampled nearly a t the same i n s t a n t , and careful regulation o f power and the i n j e c t o r f l o w r a t e are essential, A va able application o f i n t e r n a l standardization was i t s use w i t h an ETA sample ona U-16 Analytical Atomic Spectroscopy introduction system (1392).mentation of internal standardization was described by Moore e t a l . (507). An on-line dilution system f o r e f f i c i e n t imple- The a t t a i n a b l e precision i s determined by the noise associated w i t h measure- ment of the optical signal.Two groups have used f a s t Fourier transform spectrum analysers t o determine the sources of noise i n ICP-OES signals. and Belchamber (751 ) showed positive correlations between pressure fluctuations in the spray chamber and the optical signal. water flow t o the drain which was replaced by a sand soak-away bed (see a l s o ARAAS, 1981, 11, 1 0 ) .Benetti e t a l . (765) commented on the excessive noise power a t low frequencies which has previously been reported by other workers (ARAAS, 1982, 12, Ref. 1372) and has i n p a r t been a t t r i b u t e d t o operation of the nebulizer. A novel method f o r investigating noise sources i n the frequency range 0.1 t o l o 4 Hz, employed simultaneous measurement of several internal standard l i n e s u s i n g a photo-diode array spectrometer.I t was concluded t h a t short term fluctuations were largely a t t r i b u t a b l e t o changes i n the nebulizer uptake r a t e , and longer term d r i f t was due t o changes i n the outer and nebulizer gas flow r a t e s . source and detection equipment power l i n e s has been shown (927) t o reduce r .f . interference i n ICP detection systems substantially (20-fold). Kornblum e t a1 . (1415), rather surprisingly, found t h a t the temperature of the cooling water in the r . f . coil affected l i n e i n t e n s i t i e s s i g n i f i c a n t l y , -, 3%/OC f o r Cd(I1) and 1.5%/OC f o r Mg(I1). Horlick These were a t t r i b u t e d t o uneven The use of r .f . f i l t e r s and t r a n s i e n t suppressors on both Additional reference on the preceding topic - C1849. Spectral interferences remain the principal source of uncertainty in ICP-OES Reliable wavelength tables a r e therefore of great value t o the determinations. analyst in avoiding unsuspected l i n e overlaps and i t i s encouraging t o note t h a t work on characterizing ICP spectra i s continuing (1024, C1966, C2235, C2283).Several authors have given accounts of spectral interferences encoun- tered in particular matrices including biological materials (C2253). surface waters (1040), zirconium and zirconium alloys (134), iron and s t e e l s (440, 673), and petroleum and industrial products (941). The injection of organic materials i n t o the plasma can increase the background emission of species such as C2 and CN and produce luminous graphite p a r t i c l e s .The introduction of a small quantity of O2 t o the i n j e c t o r gas combusts the carbon containing species, and has been found both t o reduce the background emission i n t e n s i t y (223, 1726, C2319) and i n certain cases t o enhance the s e n s i t i v i t y (C2058).Other references of i n t e r e s t - Determination of alcohol i n water: 1186. Inter-element e f f e c t s i n ICP-OES: C1914. Interference due t o presence o f phosphoric acid: 955.Atomization and Excitation 17 1.2.1.4 Instrumentation The early work of Date and Gray u s i n g mass spectrometric detection w i t h the ICP has now been published (264, 810, 993, 1587), a s has the work of Houk, Fassel and Svec (268). Recent conference reports by Date and Gray (C1834, C2098) have detailed applications o f the "ICP-MS" technique including the determination of r a r e earths, hydride forming elements, the noble metals, t r a c e elements i n Ca rich solutions, Pb isotope r a t i o s i n minerals and Zn isotope r a t i o s i n e x t r a c t s of blood and faeces.Electrothermal vaporization has been employed f o r sample introduction (C1872). T h i s removes the h i g h background from water fragments, thereby resulting i n lower l i m i t s of detection and allows the determination of elements such as S , the spectral peaks of which a r e obscured by background peaks from aqueous seeded plasmas.Two commercial ICP-MS systems have been introduced and t h e i r performances and potential appl ications have been reviewed (C1773 , C1786, C2134, C2195, C2286). Additional reference on t h e preceding topic - C2094. Atomic fluorescence spectrometric detection i s another a l t e r n a t i v e t o the emission technique and solves most of the problems of spectral interference associated w i t h the l a t t e r .The a v a i l a b i l i t y of s u i t a b l e sources i s limited, b u t t h i s problem has been overcome (C1873, 563) by using two plasmas, one as the atomizer and the other as an excitation source. A modified plasma termed a "pencil plasma", produced by lowering the coupling coil w i t h respect t o the torch, decreasing the outer gas flow r a t e and increasing the nebulizer gas flow r a t e , was used as the atomizer by Long and Winefordner (C2346). fluorescence (see Section 1.3.5.1) has been used both a s a diagnostic and analytical technique.Ionic fluorescence, excited by a tunable dye-laser (250), confirmed mass-spectrometric observations t h a t ionic concentrations peak on the a x i s , although emission i n t e n s i t i e s peak off-axis lower in the plasma.have been reports of modifications t o plasmas designed t o reduce background emission including a mechanically skimmed plasma (C2341), and a torch w i t h an extended and constricted outer tube t h a t produces a mixing o f the core and the centtal channel (C2343). Omenetto e t a1 . described a method f o r simultaneous s c a t t e r i n g correction (790) in ICP excited AF, and determined A1 in nuclear wastes (777) by t h i s technique.Laser excited There Additional reference on the preceding topic - 219, C1901 , C2220, C2340. Developments i n spectrometers a r e often slow in reaching the analyst because of the great cost of the engineering required t o convert research devices i n t o robust routine instruments.An example i s the Fourier transform spectrometer which has been coupled t o an ICP by Faires, Palmer and Engleman (C2194, C2196, C2197, C2198). T h i s type of spectrometer has many advantages, most notably,18 Analytical Atomic Spectroscopy h i g h and s e l e c t a b l e r e s o l u t i o n , t h e a b i l i t y t o monitor the e n t i r e spectrum simultaneously, and extreme wavelength accuracy.e x c e l l e n t multi-element c a p a b i l i t y , p o s i t i v e l i n e i d e n t i f i c a t i o n , accurate back- ground c o r r e c t i o n and h i g h inter-element s e l e c t i v i t y when t h e e n t i r e s i n g l e - element spectrum i s used i n the d e t e c t i o n scheme. There are, however, some serious drawbacks. The whole spectrum i s simultaneously monitored by t h e detec- t o r , i m p l y i n g a l i m i t e d dynamic range when s t r o n g l i n e s a r e present and a reduc- t i o n i n the SNR f o r weak l i n e s because t h e h i g h l e v e l s o f p r o p o r t i o n a l n o i s e from s t r o n g l i n e s a r e spread o u t over t h e e n t i r e spectrum.High r e s o l u t i o n i s t h e most a t t r a c t i v e p r o p e r t y o f t h e e c h e l l e spectrometer (66, C2279) and t h e increased commerci a1 avai l a b i 1 i t y o f these devices has l e d t o severe1 r e p o r t s o f t h e i r use f o r ICP-OES.f a c i l i t a t e background c o r r e c t i o n (402) , o r t h e determination o f s p e c t r a l l i n e - widths (655, C1876). t h a t even w i t h e c h e l l e spectrometers, t h e instrument f u n c t i o n p r i m a r i l y deter- mines t h e observed l i n e - w i d t h and t h a t h i g h e r s l i t - w i d t h s a r e o f t e n r e q u i r e d t o o b t a i n s a t i s f a c t o r y SNRs.A novel form o f e c h e l l e spectrometer t h a t makes use o f a pre-disperser, as opposed t o t h e normal cross-dispersion order s o r t e r , has been described by Boumans and Vrakking (C1814, C2130). Several authors have discussed wavelength s t a b i 1 i ty requirements f o r spectrometers and methods o f l o c a t i n g and measuring analyte l i n e peaks (113, 1649, C1902, C2133, C2238, C2239, C2270, C2280, C2284).There have been r e p o r t s o f developments o f con- ventional spectrometers , n o t a b l y a vacuum f a c i 1 i ty f o r a scanning spectrometer (C2247, C2278, C2353), a d d i t i o n o f a moveable e x i t s l i t t o a monochromator t o f a c i l i t e l i n e measurements (C2249), and conversion o f a polychromator i n t o a quasi-scanning spectrometer (C1990).These should t r a n s l a t e t o I n c r e a s i n g l y , wavelength modulation i s being added t o McLaren and Berman (C1770, C1784, C2282) have claimed A d d i t i o n a l references on t h e preceding t o p i c - 738, 1530, C2248.Improvements i n t o r c h design continue t o be reported. The s o - c a l l e d m i n i - torches, o f diameter l e s s than 18 mm, can operate a t very low gas f l o w rates, down t o 1-2 1 m i n - l , b u t a t some l o s s o f a n a l y t i c a l performance. More s i g n i f i - cant t o t h e a n a l y s t are t h e h i g h e f f i c i e n c y 18 mm t o r c h designs which can oper- a t e on gas flows of g. 6 1 min-’, and r e t a i n t h e a n a l y t i c a l performance o f t h e conventional designs, High e f f i c i e n c y torches have been described by He e t a l . (472), and a Simplex optimized design by Montaser e t a l .(C2269). a l 18 mm t o r c h has been modified (1410, C1909) by removing t h e o u t e r tube and r e p l a c i n g i t w i t h a water cooled s i l i c a j a c k e t . This t o r c h c o u l d be operated a t gas flows o f 5 1 min-’ and e x h i b i t e d performance s i m i l a r t o conventional torches, C2083, C2268) o f t h e i r e x t e r n a l l y cooled mini-torches (see ARAAS, 1982, 12, 21).A n a l y t i c a l performance has been assessed, and i t i s claimed t h a t f o r t h e a i r - cooled torch, i t i s s i m i l a r t o t h a t o f c u r r e n t l y used commercial designs. Sobel A convention- There have been f u r t h e r r e p o r t s from Ripson and de Galan (C1980,Atomization and Excitation 19 (627) has now published a description of an extended outer torch which by excluding a i r entrainment, allowed the determination of N, using the 174.27 nm l i n e , down t o 27 ppm.improve t h e i r performance f o r the introduction of organic solvents. - a l . (C1801, C2317) found t h a t by reducing the diameter of the i n j e c t o r tube below 2.0 nun, i t was possible t o introduce v o l a t i l e , low density organic solvents such a s methanol and MIBK.coil assembly (381) allowed convenient mounting of the torch on optical bench t r a n s l a t i o n mounts. I t has been noted t h a t modifications t o torches can Barrett et The design of a separated impedance matcher/load Additional reference on the preceding topic - C1881. The recent advances i n torch design lead t o lower power requirements f o r ICP operation. have appeared.Bozarth e t a l . (C2131) have described a commercial a l l s o l i d s t a t e r e f . power u n i t capable of giving up t o 1.5 kW of output a t 40.68 MHz. T h i s u n i t incorporates microcomputer control of i t s operating parameters and many s a f e t y features. In contrast t o the sophistication of t h i s s o l i d s t a t e device, Wohlers and Bernier (C2254) described a simple and inexpensive free- r u n n i n g design based on a Hartley o s c i l l a t o r t h a t used only two inexpensive glass vacuum power valves.The performance of t h i s device was claimed t o be equivalent t o t h a t of modern commercially available units. I t i s timely, therefore, t h a t two reports of new low power generators Other references of i n t e r e s t - Atomic fluorescence instrument patent: 370.Detection systems f o r ICP-OES, review o f : 234. E l e c t r o s t a t i c preconcentrati on device: C2100. Laser excited AF: C1960. Quartz f i b r e o p t i c f o r coupling of an ICP: C1869. Resonance monochromators f o r ICP-OES: C1959. 1 .2.1.5 Chromatographic Detection Use of the ICP f o r chromatographic detection i s becoming an established tech- nique and i t will surely not be long before commercial instruments a r e intro- duced.MIP cannot compete as i t does f o r GC. f o r ICP-OES are impressive, the absolute detection l i m i t s f o r sample intro- duction by nebulization, w i t h i t s low efficiency, a r e not adequate f o r many applications, p a r t i c u l a r l y those involving c a p i l l a r y column separations.Jinno e t a l . (835) used the ICP as a detector f o r c a p i l l a r y column HPLC, b u t found i t necessary t o mix the column eluent w i t h c a r r i e r solvent t o feed the nebulizer. This resulted in lower detection limits than f o r conventional HPLC- The ICP i s perhaps most s u i t e d t o liquid chromatography (967) where the Although the r e l a t i v e detection limits Thus,20 Analytical Atomic Spectroscopy ICP.been reported by two groups. Bushee e t a l . (C2190) combined hydride generation and cold vapour techniques f o r the separation and determination of As and Hg compounds. A combination of fraction collection, followed by carbon cup vapor- ization i n t o the ICP was used by Caruso e t a l .(C2335) f o r the determination of organometallics separated by HPLC. Efforts t o improve s e n s i t i v i t y by avoiding the nebulization step have Additional reference on the preceding topic - C2325. 1.2.2 Mi crowave-i nduced P1 asmas 1.2.2.1 Fundamental Studies Over the years there have been many publications o f experiments aimed a t phys- i c a l characterization of MIPs.There does not y e t , however, appear t o be a generally accepted view on the excitation mechanisms of these devices. measurement of various physical parameters continues, one of the most important being the electron number density. number densities (n,) i n Ar MIPs operated a t 1 1 min-’ and 0.1 1 rnin-”with and without the addition of 1000 ppm KC1. For the 1 1 min-’ plasma, ne = 1 x 1015 cm-3 compared w i t h 0.6 x 1015 cm-3 i n the 0.1 1 min-’ plasma.Seeding w i t h KC1 increased the electron density t o 1.5 x 1015 cm-3 i n the 1 1 min-’ plasma, e t a1 . (1081 , C2356, C2370, see a l s o ARAAS, 1982, 12, 22) have continued t h e i r studies of the MIP and reported the use of a l e a s t squares data f i t t i n g method t o determine ne from broadening of the He l i n e .of electron number density and various temperatures have been reported f o r Ar (C1944) and He (1601) discharges. postulated t h a t excitation occurs primarily through c o l l i s i o n s w i t h metastable He atoms o r h i g h energy electrons. (1354) concluded t h a t spectral data indicated t h a t sequential ionization and excitation was the principal mechanism w i t h the energy being transferred from the metastable rare gas molecule.produce metastable 0 atoms (1652). Various r a r e gases were used as d i l u e n t s , b u t He proved most effective in enhancing the concentration of the metastable atoms. An atmospheric pressure plasma in N2 has been described and i t s noise power density spectrum characterized (C2375). Thus, Outred e t a l .(C1963) determined electron but decreased i t t o 0.3 x 1015 ~ m ’ ~ in the 0.1 1 min-’ plasma. Goode Spatially resolved measurements For the He discharge, the authors In contradiction, Bauer and Skogerboe A low pressure O2 MIP has been used t o Additional rererence on the preceding topic - 1622. Efficient and r e l i a b l e coupling of the microwave power t o the plasma i s an important design consideration and various authors have described methods of tuning and impedance matching.description (see ARAAS, 1982, 12, 23) of t h e i r water cooled Beenakker cavity/ Carnahan and Caruso (508) have now published aAtomization and Excitation 21 tuner combination which i s capable o f e x c i t i n g A r o r He discharges a t powers o f between 150-500 W.detection l i m i t f o r Ca o f 4 ppb was obtained. the Beenakker c a v i t y has been developed (C2385) which allows the impedance matching c h a r a c t e r i s t i c s o f the c a v i t y t o be predicted. inserted i n t o the c a v i t y f o r tuning t h e device t o the generator. Jansen (1349, C1891, C1900) commented t h a t the small diameter r a t i o o f the s i l i c a tube t o the c a v i t y causes i n e f f i c i e n t use o f the microwave energy.They preferred a two electrode plasma configured t o s u i t the p a r t i c u l a r application. For example, a concentric electrode device was used as a GC detector, a s t a i n - less s t e e l extension tube attached t o the column acting as the centre electrode.Aqueous aerosols were introduced i n t o the plasma and a An e l e c t r i c a l c i r c u i t model o f A quartz rod was Huf and Other reference o f i n t e r e s t - Spectra o f molecular compounds: C1899. 1.2.2.2 Sample Introduction The low k i n e t i c temperature and thermal capacity o f the M I P renders i t most s u i t a b l e f o r the atomization and e x c i t a t i o n o f vapours o r gases.(C1800) reviewed appropriate methodologies including h y d r i de generation, halogen generation and GC. Thermal evaporation o f materials from metal f i l a - ments was one o f the e a r l i e s t methods used f o r sample introduction. Kamamaru e t a l . (126) determined Zn i n metalloproteins by desolvation, ashing and vaporization o f the Zn-containing samples from a tungsten filament device.Selby e t a l . (C1757) used a carbon furnace vaporizer and found strong enhance- ments o f a n a l y t i c a l signals when e a s i l y ionizable elements were present i n the sample. were introduced separately i n t o the plasma i n d i c a t i n g , as expected, t h a t the interferences are associated w i t h the e x c i t a t i o n process r a t h e r than the vapor- i z a t i o n step.micron range has been used (C2386) f o r introducing aqueous samples i n t o an MIP. Barnett e t a1 . The same enhancements occurred when samples and e a s i l y ionized elements A glass frit nebulizer producing very f i n e droplets i n the sub- A novel i n t e r f a c e design (1309) f o r HPLC used a wire, onto which the column eluent was run, allowing 5% o f the eluent t o be evaporated i n t o the plasma by passing the He/02 plasma gas over the w i r e surface. estimate the r e t e n t i o n time o f the deuteriated mobile phase by monitoring the ‘H 656.10 nm l i n e .The device was used t o Additional references on the preceding t o p i c - 1313, C2373. 1.2.2.3 Gas-chromatographic Detection The great v a r i e t y i n gas-chromatographic techniques requires t h a t detectors be22 Analytical A torn ic Spectroscopy t a i l o r e d t o individual requirements and so modifications and developments of instrumentation cont nue t o be reported.l i n e s a r e used in chromatographic detection, and because the separation reduces spectral interferences , spectrometers of modest performance are adequate.Several groups have reported the use of small polychromator spectrometers (C2374), sometimes adding a quartz refractor plate, driven by a stepper motor (783) o r torque motor (C2037), f o r background correction. comments, i t seems surprising t h a t Cerbus e t a l . (945) chose t o use a high performance echel l e spectrometer i n t h e i r detector system. face i s c r i t i c a l as poor design can r e s u l t i n peak broadening, condensation, or extinction of the plasma i f the solvent loading i s too high.Jordan e t a l . (896) described an open-split, solvent venting interface t o pyrolize compounds p r i o r t o introduction i n t o the plasma. Only a limited number of spectral In view of the above The GC-MIP i n t e r - There have been f u r t h e r reports (1384, C2371) of the use of the tangential flow torch, f i r s t described by Bollo-Kamara and Codding (see ARAAS, 1982, 12, 22).I t was found t h a t the tangential torch produced a 25-fold enhancement in SNR f o r the detection of C compared w i t h a conventional torch. The determination of empirical formulae by MIP-OES depends upon the indep- endence of the emission intensity and the molecular s t r u c t u r e .reports on the limitations imposed by t h i s assumption. (1025) found t h a t measured and theoretical values of empirical formulae agreed well f o r low molecular weight molecules excited i n a low pressure He plasma, b u t the discrepancies became greater as the number of atoms i n the molecule increased.A study of organic micro-pollutants i n water (142) revealed t h a t the r e l a t i v e molar response, f o r the range of compounds studied, varied by only 210%. An investigation of the e f f e c t on emission i n t e n s i t y of d i f f e r e n t functional groups was published by Qing-Yu e t a l . (974). Koirtyohann (354) has shown t h a t the presence of traces of N2 i n the He gas greatly decreases the excitation efficiency of C1 and F when a Beenakker cavity i s used as a GC detector.For maximum response, N2 must be kept t o less than 0.001% of the t o t a l volume. Above t h i s concentration and up t o a level of 0.1%, the signals f o r F and C1 are inversely proportional t o N2 concentration, and above 0.1% the discharge changes colour t o the c h a r a c t e r i s t i c blue of a N 2 plasma.There have been Dingjan and de Jong Derivatization can be used t o improve the s e n s i t i v i t y of a determination o r t o label compounds t o improve the s e l e c t i v i t y of determination. For example, trialkyl-lead compounds i n aqueous media were extracted i n t o benzene, following saturation of the aqueous phase w i t h NaC1, and converted t o t h e i r n-butyltri- alkyl-lead derivatives prior t o determination by GC-MIP ( 3 ) . Delaney and Warren (975) discussed derivatization techniques and the labelling of functional groups with 2 H , the halogens, P , S , Se and S i .Atomization and Excitation 23 Other references o f i n t e r e s t - Capacitively coupled plasmas: 14, 940, 1058, 1355.Determination o f , alkylmercury i n seawater: 460. organometallics and inorganic halides: C2163. s t e r o i d a l carboranes : 525. Pyrolysis GC: 1101. Review o f GC-MIP: 674. 1.2.3 D i r e c t Current Plasmas The e f f e c t o f e a s i l y ionizable elements on the e x c i t a t i o n mechanism o f the DCP has been the subject o f extensive i n v e s t i g a t i o n and new studies continue t o be reported.Coleman e t a l . (C1788) separated sample i n t r o d u c t i o n e f f e c t s from the e x c i t a t i o n mechanism by introducing Hg vapour i n t o the plasma and con- cluded t h a t s h i f t s occur i n the emission p r o f i l e s and t h a t the extent o f the s h i f t s and the magnitude o f the enhancement o f both atom and i o n l i n e s depended upon the i o n i z a t i o n p o t e n t i a l and the concentration o f the e a s i l y ionizable element.I n addition, i t was found t h a t e a s i l y ionized elements d i d not i n f l u - ence the over-all electron concentration, b u t g r e a t l y affected electron density gradients. concentrations i n DCPs has now been reported (1397). Unfortunately the values reported contain l a r g e e r r o r s as the low r e s o l u t i o n monochromator and uncooled array used yielded measurements o f hydrogen l i n e broadening o f i n s u f f i c i e n t accuracy . The use o f a photodiode array t o measure s p a t i a l l y resolved electron Additional reference on the preceding t o p i c - C2314. A d r o p l e t generator has been used by Boyko and Keliher (233) t o study vapor- i z a t i o n e f f e c t s i n the DCP. The generator produced droplets o f 2&50 ~1 and i t was found t h a t 18 p1 droplets produced signals 77% o f the continuous nebulization signal, 27 p1 droplets produced signals a t the 97% l e v e l , and 48 u l droplets gave signals a t the 104% l e v e l . Other papers dealing w i t h aspects o f sample i n t r o d u c t i o n included a r e p o r t by Margold and Bastiaans (C2154) on s u b s t i t u t i o n o f N2 f o r A r as the nebulizer gas. upon performance, p a r t i c u l a r l y i n respect t o background emission, atomization e f f i c i e n c y and plasma s t a b i l i t y . the DCP, b u t d i l u t i o n i s sometimes necessary. suggested a novel way o f dealing w i t h d i f f i c u l t solvents i n v o l v i n g the use o f an e m u l s i f i e r t o form a f i n e suspension i n an aqueous c a r r i e r phase. (C2338) employed f l o w i n j e c t i o n f o r sample i n t r o d u c t i o n using an HPLC sampling valve w i t h e i t h e r an HPLC o r a p e r i s t a l t i c pump. This appeared t o have a deleterious e f f e c t Organic solvents (96.2) may be introduced i n t o Kinsey and Comptois (C2158) Boorn The atomization properties o f24 Analytical Atomic Spectroscopy the DCP were exploited by Wirz e t a1 , (1402, C2036) who used the plasma as an atomizer for Zeeman AAS, using either nebulization or electrothermal vaporiz- ation for sample introduction. Only two reports of chromatographic detection using the DCP have been received t h i s year. Cr(II1) and Cr(V1) down t o the 10-50 ppb level, and Gardiner e t a l . (1087) used gel-filtration chromatography t o speciate protein bound C u , Fe and Zn in serum and intravenous fluids. Krull e t a l . (C2221) used paired-ion HPLC t o determine Other references of interest - Applications of the DCP t o metals analysis: 412, 413. Pulsed discharge in liquid: C1975. Three-electrode concentric a.c. plasma: 746, C2281.

ISSN:0306-1353    

DOI:10.1039/AA9831300007

出版商:RSC    

年代:1983

数据来源: RSC

摘要:

24 Analytical Atomic Spectroscopy 1.3 FLAMES In the reference l i s t of previous volumes of ARAAS, papers which describe the use o f flames outnumber those f o r any other means of 3tomization and the dist- ribution of references collected i n Volume 13 presents no exception to t h i s pattern. as well as the large number of papers describing applications that continue t o appear in the literature.of flame atomization in 1983, b u t the year did see a striking increase in papers describing the use of flow injection f o r sample introduction, and i n the nebul- ization of samples i n the form of slurries and emulsions. that FI will gain the attention of the instrument manufacturers before long, b u t there i s s t i l l no sign of recent research efforts in FAFS or continuum source atomic absorption being similarly taken up.This reflects the past and current status of FAAS in routine analysis Very few novel developments appeared i n the area I t seems certain 1.3.1 Fundamental Studies Two new burner concepts have been applied in FAES. described the use of tandem flames t o increase molecular dissociation. A secondary flame was operated independently of the normal primary flame, and was introduced into the primary flame a t heights and angles which were independently controllable.Emission from Ca was enhanced when the secondary flame was fuel rich. I n a new burner design called the Merensky burner, dry aerosols from solutions o r powdered samples were introduced into air/CzHp or Nz0/C2Hz flames independently of the flame gas mixture (1036).Nebulization was achieved by a versionof the Babington nebulizer and the aerosol was introduced into the central section of the burner. Edwards and Boss (C2390) Spectroscopic studies on the premixed NO/C2H2Atomization and Excitation 25 flame (918), and the effects of dichloromethane on an air/CH4 flame (390) have been reported and may be of passing interest t o analytical chemists.also been suggested that the air/natural gas flame i s acceptable, and preferable t o air/C2H2 on safety grounds, for teaching the principles of AAS (688). I t has Another new type of burner has been designed for the measurement of HPO emis- sion (C1955). diameter, respectively. a t a temperature of 7 7 0 4 O O 0 C , which was shown t o give optimum sensitivity for the measurement of HPO emi ssi on.I t consists of two concentric pyrex tubes of 25 mm and 10 mn An air/H2 flame i s used and burns on the inner tube A cross-correlation study of excess low frequency fluctuations (over the range 5-100 Hz) of the background and Na emission from a sheathed, premixed, laminar air/C2H2 flame has produced some analytically useful results (1018).High correlation of noise characteristics was observed between different locations in the flame, and the background and Na signal noises were also fully correlated with each other. flame noise which was identified as fluctuations in the flame thickness, originating in i n s t a b i l i t i e s a t the outer edges of the flame. The results have consequences for the optimum choice of frequency of intensity modulation i n AAS and AFS, and suggest that figures of merit such as precision and detection limit depend not only on the location of the measurement zone in the flame, b u t also on the size of the measurement volume.These measurements suggested a common source of The errors which can be introduced i n AAS by variations in isotopic compo- The authors sition have been studied by a computer simulation model (C2377).report that the larger the isotope s h i f t of the spectroscopic energy levels, and the greater the hyperfine structure separations, the greater will be the isotopic error. speci f i c isotope HCLs (C1760). The measurements are i nfl uenced by excessive broadening and line s h i f t s , caused by b o t h thermal and pressure broadening effects, which were studied in detail for the air/C2H2 flame using a high resolution scanning echelle monochromator. Cr t r i p l e t lines a t 425.435, 427.480 and 428.972 nm using an air/C2H2 flame have also been studied, and collisional cross-sections for N2 perturbers cal- culated (1019).Isotopic r a t i o measurements of Pb have been reported using Line broadening parameters for the Two research groups are now promoting mathematical methods for the use o f non-linear portions of working curves i n AAS.Formulation of the analyte con- centration as a non-linear function of the response was achieved by adaptation of the least squares regression technique, and the results were used t o demon- s t r a t e the advantages of computer calculations compared t o manual interpretation (C1916).Alternatively, curvature can be interpreted as resulting simply from stray light using a modified form of Beer's Law (C2326). I f the incident light26 Andy tical A to mic Spectroscopy I. consists o f two parts, primary r a d i a t i o n (XI,) and s t r a y l i g h t ( l - x ) I o , then the absorbance o f an analyte a t concentration c i s given by: A = - log(xlO-klc t ( l - ~ ) l O - ~ 2 ~ ) Working AAS curves have been described by t h i s equation using optimized values o f the variables kl, k2 and x.r a p i d enough f o r real-time processing o f experimental data and hence the use o f non-linear portions o f working curves i n r o u t i n e analysis. c a l c u l a t i o n o f the apparent amount and e f f e c t o f s t r a y l i g h t , and i t s dependence on instrument parameters such as HCL current, and monochromator s l i t width.This approach appears t o be useful as i t i s It also allows the P r a c t i c a l measurements o f precision functions have been used t o optimize the conditions f o r the determination o f high concentration constituents o f a1 loys (767, 1469, C1732).It i s shown f o r example t h a t the RSD f o r the determination o f N i a t concentrations up t o 2000 ug m1-l i n solutions o f s t e e l samples depends on sample weight, resonance wavelength, absorption path length, type and stoicheiometry o f the flame. precision o f determination o f high concentrations o f a number o f elements by AAS i n an a i r / C 2 H 2 flame (140).o f the AAS determination deteriorated when the burner head was rotated b u t n o t when the HCL current was increased. Analyte emission noise was shown t o e f f e c t the Owing t o analyte emission noise, the precision The d i f f i c u l t y i n selecting compromise flame conditions i n simultaneous multi-element analysis f o r continuum source AAS remains one o f the more s i g n i f - i c a n t deterrents t o the wider use o f t h i s method.e t a l . (see ARAAS, 1982, 72, Ref. 1572) showed t h a t f o r the determination o f Cay Coy C r y Cu, Fey K, Mg, Mn, Na and Zn, a l l elements except Ca and Mg could be determined simultaneously under a s i n g l e s e t o f air/C2H2 flame conditions, b u t Ca and Mg required the use o f lanthanum as a releasing agent. It has now been demonstrated t h a t Cay Cu, Fey K, Mg, Na and Zn can be determined simultaneously i n blood serum by using continuum source AAS and an air/C2H2 flame (C2177).Samples (0.5 ml) were d i l u t e d 1:5 w i t h a d i l u e n t containing 0.1% La (as c h l o r i d e ) and 5% glycerol. venient compromise conditions has been the incorporation o f up t o 60% N20 i n t o an air/C2H2 flame gas mixture (C2329).Fey K, Mg, Mn, Na and Zn were achieved by using optimized conditions f o r a number of CRMs. been subjected t o d e t a i l e d investigations and f i g u r e s o f m e r i t compared t o those f o r concentional l i n e source AAS (747). concentrations f o r continuum source AAS were 3 - f o l d poorer and detection l i m i t s between 4 - f o l d (> 250 nm) and 20-fold (< 250 nm) poorer.below 250 nm was a t t r i b u t e d t o the much smaller s l i t height used on the echelle monochromator compared t o conventional AAS systems. I n an e a r l i e r paper Harnly An a l t e r n a t i v e approach t o the i d e n t i f i c a t i o n o f more con- Accurate r e s u l t s f o r 8 elements, Cay Cu, The performance c h a r a c t e r i s t i c s of continuum source AAS have I n general , c h a r a c t e r i s t i c The poor performance Examples o f OH and CNAtomization and Excitation 27 absorption interferences on A1 a t 309.271 nm (N20/C2H2), B i a t 306.772 nm (air/C2H2) and C r a t 357.869 nm were also described.Performance i s degraded and the use of a l t e r n a t i v e wavelengths f o r these elements i s recommended (see also Section 2.2.1). 1.3.2 Atomization and Interference Studies While nothing r e a l l y innovative has been reported on t h i s subject i n 1983, there have been several publications o f genuine i n t e r e s t , p a r t i c u l a r l y those on the study o f the generation and properties o f aerosol p a r t i c l e s .optimum flame stoicheiometry f o r the N20/C2H2 flame has been shown t o be r e l a t e d t o the dissociation en=y (Do) of the monoxide o f the analyte element (C2019). For D0<5.5 eV, analyte signals are l a r g e l y independent o f flame stoicheiometry, b u t elements w i t h D0>6.0 eV require a s l i g h t l y fuel r i c h flame, as i s we11 known. Platinum metals require the h o t t e s t possible flame, &, lean flame conditions, as the s e n s i t i v i t y i s dependent on the low v o l a t i l i t y o f the metals themselves.The atomization e f f i c i e n c y o f I n has been determined i n an a i r / C 2 H 2 flame and yielded a value o f 0.085 t 0.007 (111). Choice o f The AAS s e n s i t i v i t y f o r B i n a N20/C2H2 flame has been compared t o t h a t i n a d.c.argon arc (C1969). would be expected owing t o the low e f f i c i e n c y o f atomization o f boron caused by the formation o f i n v o l a t i l e metal and carbide p a r t i c l e s . added t o the c a r r i e r gas o f the arc, the signal was also reduced i n t h i s source, suggesting t h a t carbide formation may be s i g n i f i c a n t .plexing ligand has been shown t o have a s i g n i f i c a n t influence on the AAS sensi- t i v i t i e s o f Cu (362) and Ru (C1971). Chelating agents enhance the Cu response, b u t the e f f e c t s on Ru are more serious and may be enhancing o r depressing. Fortunately the authors s t a t e t h a t the interferences can s t i l l be control l e d by a d d i t i o n o f Cu o r Cu + Cd sulphates (C1971).The s e n s i t i v i t y f o r B i n the flame i s much lower than When C2H2 was The nature o f the com- Kono and Kojima (21) studied the e f f e c t s o f organic solvents on dry p a r t i c l e formation by c o l l e c t i n g the dry p a r t i c l e s on a polished Mg p l a t e and examining them w i t h SEM and analysing them w i t h an electron probe microanalyser.It was found t h a t solvent composition effected the porosity, p a r t i c l e s i z e and the c r y s t a l 1 i n i ty o f the dry p a r t i c l e s , and i t was concl uded t h a t these properties are a major f a c t o r i n the established e f f e c t s o f organic solvents on AAS sensi- t i v i t y i n flames. High speed colour cinematography was also used t o study the changes i n the p r o f i l e o f flames f o l l o w i n g t h e i n t r o d u c t i o n o f organic solvents (C2001).It was shown t h a t flames can be sub-divided i n t o more than the t r a d - i t i o n a l three regions o r zones and t h a t the geometry o f the regions changes w i t h the composition o f t h e solvent. sample solutions has a l s o been investigated (1061, 1667) and i s said t o reduce The suspension o f carbon powders i n28 Analytical A tomic Spectroscopy interferences of phosphate anions on alkaline earth metals (1667).SEM and electron probe microanalysis of dry p a r t i c l e s trapped on Mg plates a s described above, i t has been demonstrated t h a t the s e n s i t i v i t y enhancement of a graphite powder suspension i s related t o the increase i n the number of f i n e (< 0.1 pm) dry p a r t i c l e s produced (1061).By u s i n g The horizontal displacement of p a r t i c l e s i n an air/C2H2 flame has been studied by high speed cinematography, and a l s o by microphotography of dry p a r t i c l e s deposited on surfaces i n close proximity t o the flame (C2000).t h a t p a r t i c l e s leaving the flame are d i f f e r e n t t o those found on the inside surface of the burner, and t h a t p a r t i c l e s i n flames move w i t h a major hori- zontal component of velocity. I t was shown Inevitably, studies of calcium interferences were reported again t h i s year. The N,0/C2H2 flame has been recommended as a means of removing interferences o f inorganic acids i n AAS and AES (482). The matrix e f f e c t of aluminium on Ca has been described by means of a simplified mathematical model and an empirical f i t t i n g procedure (68, 1546). The interference of phosphine on calcium has been explained as a condensed phase interference (5, C2208, see also ARAAS, 1982, 12, 29).droplet t o form a refractory Ca-POx compound.of Ca by PH3 i s thus the same as t h a t f o r H3P04. the interference e f f e c t i s reduced as the s i z e of the analyte droplet i s decreased (C2208). Combustion products of PH3, POx,diffuse into the desolvating The mechanism of the depression I t has a l s o been shown t h a t The enhancement of the chromium atomic absorption s e n s i t i v i t y by surfactants has been shown t o be dependent on flame stoicheiometry, purity of C2H2, con- centration of Cr and surfactant, and the pH of the analyte solution (C2210, see also ARAAS, 1982, 12, 29).In addition, use of a uniform-droplet generator yielded d i f f e r e n t r e s u l t s from a conventional nebulizer system. 1.3.3 Devices f o r Sample Introduction As mentioned e a r l i e r , 1983 has seen a s t r i k i n g increase i n the number of papers devoted t o the development and application of flow injection sample introduction.I t appears l i k e l y t h a t FI will become a s conventional as d i r e c t aspiration, and the number o f application papers suggests there i s potential f o r instrument manufacturers t o o f f e r FI accessories f o r their flame instruments. To allow f o r this increased interest, the usual section of t h i s chapter on micro-sampling devices has been s p l i t i n t o two separate sections covering micro-sampling via the nebulizer (1.3.3.2) and micro-sampling d i r e c t l y i n t o the flame (1.3.3.3).Atomization and Excitation 29 1.3.3.1 Nebulizers Smith and Browner (C2206) have pointed out t h a t the nebulizer/impact bead/spray chamber configurations t h a t produce the highest o v e r a l l transport e f f i c i e n c i e s and hence best s e n s i t i v i t i e s , are o f t e n the most prone t o severe v o l a t i l i z a t i o n interference effects.efficiency, i t i s possible t o s e l e c t appropriate operating configurations f o r a p a r t i c u l a r analysis e i t h e r t o maximize s e n s i t i v i t y o r t o minimize i n t e r f e r - ences.I n another conference presentation, Pearce and Boss (C2209) have des- cribed f u r t h e r experiments w i t h e l e c t r o s t a t i c a l l y charged aerosols (see ARAAS, 1982, 12, 31). A t h e o r e t i c a l i n t e r p r e t a t i o n o f d r o p l e t movement i n the mixing chamber was based on the s i z e and charge o f the droplet, the i n t e n s i t y o f the applied e l e c t r i c f i e l d and the speed and v i s c o s i t y o f the flowing gases.The data can be used t o calculate the magnitude o f the e l e c t r i c f i e l d required t o produce a defined d r o p l e t size. eagerly awaited. the simple i n t r o d u c t i o n o f standards f o r the standard additions method (505). A PTFE Babington type nebulizer has been described f o r the i n t r o d u c t i o n o f By using information on d r o p l e t s i z e and transport Publication o f the d e t a i l s o f these studies i s A branched c a p i l l a r y nebulizer system has again been used f o r s l u r r i e s (834).s i m i l a r droplet-size d i s t r i b u t i o n s t o conventional nickel-plated brass nebulizers.Some useful investigations o f s l u r r y atomization have also been reported t h i s year. Atomic absorption signals f o r T i from Ti02 s l u r r i e s w i t h p a r t i c l e d i - ameters claimed t o be as low as 0.16 pm were s t i l l lower than those from solutions o f the same T i concentrations (C2213). Although t h e loss o f signal could be due t o changes i n nebulization-transport e f f i c i e n c y o r the vaporization e f f i c i e n c y , i t was shown t h a t the l a t t e r e f f e c t was dominant, Since c r y s t a l - l i t e s as small as 0.16 pm are known t o agglomerate i n t o l a r g e r p a r t i c l e s , these r e s u l t s are n o t unexpected, but the conclusions o f the study were supported by a novel experiment i n which the A1 AAS signal from A1203 coatings on Ti02 p a r t i c l e s was found t o be the same as the A1 signal from a s o l u t i o n a t the same concentration. A j l e c and Stupar (761, C7735, C1790) have studied the factors which a f f e c t the e f f i c i e n c y o f sample transport, nebulization and atomization when suspensions o f p a r t i c l e s o f d i f f e r e n t size are sprayed i n t o a flame.It was shown t h a t p a r t i c l e size has a major influence on the transport e f f i c i e n c y , p a r t i c l e s l a r g e r than 15 pm being completely retained i n the spray chamber. d i s t r i b u t i o n o f the suspended material i n the flame i s s t r o n g l y influenced by l a t e r a l d i f f u s i o n and the r a t e o f vaporization, g i v i n g apparently high atomiz- a t i o n efficiency values i n the central zone o f the flame.Rotation o f the burner was suggested t o overcome t h i s problem. S l u r r y suspension methods have been proposed f o r the r a p i d determination o f A1 and Fe i n red mud (761 , C1735) and f o r many constituents o f p l a n t material (1089, see also ARAAS, 1982, 12, The nebulizer i s said t o be easy t o construct and t o give The30 Analytical Atomic Spectroscopy Ref. 952). I n the l a t t e r case, a carbonaceous s l u r r y was formed by p a r t i a l wet ashing o f samples w i t h conc. H2S04. Sequential background measurement and s u b t r a c t i o n was necessary as the D2-arc background c o r r e c t o r c o u l d n o t compen- s a t e a c c u r a t e l y f o r the l a r g e background s i g n a l from the s l u r r y .Some a p p l i c - a t i o n s o f t h e emulsion technique have a l s o been described d u r i n g 1983 (494, 541, C2042, C2078). These a l l r e l a t e t o t h e determination o f metals i n l u b r i - c a t i n g o i l s and f u r t h e r i n f o r m a t i o n can be obtained from Section 4.1.The atom t r a p p i n g method (see ARAAS, 1982, 12, 31) has been used f o r t h e determination o f Cd and Pb i n a c e t i c a c i d e x t r a c t s o f s o i l s (592, 1042, C2080). Coating t h e s i l i c a tube w i t h A1203 by a s p i r a t i o n o f an A1 s o l u t i o n , reduced i n t e r f e r e n c e l e v e l s , b u t an i r o n oxide c o a t i n g was necessary i f t h e samples contained h i g h concentrations o f Fe o r Na.Two i n t e r e s t i n g developments i n coupled chromatography-flame spectrometry have been reported. A flame AAS system has been coupled t o a h i g h performance gel chromatographic apparatus f o r haemoglobin determination i n blood (534) and flame photometric L i d e t e c t i o n has been used as an i n d i r e c t method f o r t h e determination o f anions by replacement i o n chromatography (1541).l a t t e r experiment, t h e counter c a t i o n o f an e l u t i n g anion from an i o n chromato- graph was s t o i c h e i o m e t r i c a l l y replaced by L i on a c a t i o n exchange column. L i t h i u m determination i n the f i n a l e l u a t e gave a s e n s i t i v e d e t e c t i o n o f anion concentrations.I n t h e 1.3.3.2 Micro-samDle I n t r o d u c t i o n v i a t h e Nebulizer This s u b - d i v i s i o n o f micro-sampling devices includes d i s c r e t e sample n e b u l i z a t i o n and F I sample i n t r o d u c t i o n . The continued p o p u l a r i t y o f the simple d i s c r e t e sample n e b u l i z a t i o n technique i s demonstrated by t h e appearance o f automated systems (1116, 1702), an automatic photocoupled t r i g g e r (607), and a review i n the Chinese l i t e r a t u r e (271).A s p e c i a l PTFE micro-sampler has a l s o been described (252). twelve small c o n i c a l holes o f capacity 700 111 f o r t h e samples. Samples are added by m i c r o p i p e t t e and are subsequently aspi r a t e d completely from each h o l e v i a conventional n e b u l i z e r tubing.Improved s e n s i t i v i t y has been achieved by p l a c i n g a s l o t t e d q u a r t z tube i n t h e flame (997, 1431) as o r i g i n a l l y described f o r continuous n e b u l i z a t i o n by Watling (see ARAAS, 1977, 1, 24 and 1978, 8, 21).The s l o t s a r e 50 mm and 40 mm i n l e n g t h and c u t a t 180' t o each o t h e r i n an 8 mm i . d . tube. A p o r t i o n o f t h e flame enters t h e tube t h e longer s l o t s and increases the residence time o f atoms i n the l i g h t path. A useful 4 - f o l d improvement i n s e n s i t i v i t y f o r Pb i n blood was obtained i n combination w i t h t h e d i s c r e t e n e b u l i z a t i o n procedure (997). This has a c e n t r a l wash-solution r e s e r v o i r surrounded byAtomization and Excitation 31 Flow i n j e c t i o n i s r a p i d l y becoming accepted as a convenient means o f i n t r o - ducing micro-samples i n t o a flame AAS system.i s unavoidable, as the sample becomes dispersed i n the flowing stream before entering the nebulizer, the method i s applicable t o a wide range o f analyses and o f f e r s a simple implementation of t h e standard additions technique (744, 1047).A s i m p l i f i e d model has been used t o describe the dispersion o f a sample i n the flowing stream (560, 744, C2017, C2077). I n t h e model, dispersion i s ascribed t o a s i n g l e hypothetical mixing chamber located immediately p r i o r t o the measure- ment stage. The dispersion model can be used t o generate c a l i b r a t i o n curves f o r flame AAS by two d i f f e r e n t procedures.the c o n t r o l l e d dispersion o f a d i s c r e t e volume o f a s i n g l e concentrated stand- ard, o r by production o f concentration-time gradients by including a small well- s t i r r e d mixing chamber j u s t before t h e flowing stream i s introduced i n t o the nebul i zer .Although a loss o f s e n s i t i v i t y Calibration can e i t h e r be achieved by Incorporation o f an anion exchange column i n t o the F I system has been used t o remove the interference e f f e c t s o f P043- and S042- on Ca (1555). Extracts o f metals produced by automatic e x t r a c t i o n i n t o MIBK/APDC have been introduced i n t o a flame AAS system by FI (606, 1196, C2107).The loop o f the i n j e c t o r was f i l l e d w i t h the MIBK s o l u t i o n , and t h i s was transferred as a slug t o the nebul- i z e r , i n an aqueous flowing stream w i t h no dispersion. When a sample i n an organic solvent i s i n j e c t e d i n t o an aqueous flowing stream, the background absorption changes a t the precise time o f sample i n t r o d u c t i o n t o the flame.Correction f o r t h i s has been demonstrated using a Zeeman AAS system (C2040). Preconcentration o f t r a c e elements i n sea water using Chelex 100 has also been coupled t o flame AAS by F I methods (990). O f the many other papers on flow i n j e c t i o n flame spectrometry, many r e l a t e t o the analysis o f c l i n i c a l materials (125, 533, 683, 684, 685, 1513, C2223), s i l i c a t e rocks (1073), and s t e e l s (1543) and a l l demonstrate the advantages o f the method (small sample volume, speed, p r e c i s i o n ) . 1.3.3.3 D i r e c t Micro-samle Introduction i n t o the Flame I n ARAAS, Volume 12, extensive publications on the loop microsampling technique were reported.No new work has been described i n 1983, b u t a useful review o f the use o f the loop method i n flame AAS and AES was prepared by Brandt and Messerschmidt (891). o f Pb i n o i l s (542), b u t i n t e r e s t i n t h i s method now seems t o be decreasing r a p i d l y . The Delves' Cup method has been used f o r t h e determination Another form o f d i r e c t micro-sample i n t r o d u c t i o n i n t o the flame i s the furnace-in-flame atomizer.This method f i r s t described by L'vov e t a l . i n 1969 (V.P. Borzov, B.V. L'vov and G.V. Plyuschch, Zh. P r i k l . Spektrosk., 1969, 11,32 Analytical Atomic Spectroscopy 217) has never caught the imagination o f other workers, but o f f e r s considerable p o t e n t i a l p a r t i c u l a r l y f o r t h e analysis o f s o l i d samples. One o f the problems o f the Delves' Cup method was the f a i l u r e t o atomize a l l b u t the most v o l a t i l e elements, but t h i s problem can be overcome i f the atomization cup i s heated electrothermally l i k e a graphite furnace.i n 1983 (775, C1810) one o f which described an automated furnace-in-flame atomizer based on a commercial power supply (C1810).a motor t o a p o s i t i o n below the atomization cup a t the beginning o f the ashing step and removed when atomization was complete. claimed t o be as simple and convenient t o operate as advanced ETA systems. p o t e n t i a l f o r s o l i d sample and o i l analysis using matrix f r e e aqueous standard solutions has been demonstrated.Two papers on t h i s method appeared The burner was moved by This new automatic system i s I t s A useful review o f the p r a c t i c a l applications o f MECA appeared recently (236), b u t the only new work on t h i s t o p i c described the determination o f S i (1545). The method i s based on generation o f SiF4 and t r a n s f e r t o a MECA oxy-cavity i n a stream o f N2. 1.3.3.4 Sample Introduction by V o l a t i l i z a t i o n Kantor has produced two excellent review papers on the application o f combined atomic absorption methods (C1746, and i n Spectrochim. Acta, Part B, 1983, 38, 1483). The application o f FAAS t o the study o f aerosols generated i n graphite furnaces as a means o f studying atomization and interference phenomena i n ETAS i s w e l l known (793).Kantor has also pointed out the analogous nature o f t h i s procedure t o those used f o r the study o f high temperature v o l a t i l i z a t i o n pheno- mena i n other s c i e n t i f i c d i s c i p l i n e s such as high temperature chemical technol- ogy, and has used information from such sources t o provide an improved descrip- t i o n o f aerosol transport e f f i c i e n c y .One GC application which has appeared concerns the determination o f a l k y l - selenides i n the environment (727). t r a p and then analyzed by coupled gas chromatography-atomic absorption. A i r samples were collected on a cryogenic 1.3.4 Flame Atomic Fluorescence Spectrometry Very l i t t l e novel work has been described on t h i s t o p i c i n 1983, b u t there does appear t o be a modest increase i n the number o f analysts taking advantage o f the p o t e n t i a l o f AFS i n i t s various forms - l i n e source, continuum source and non- dispersive.A method has been described f o r the detection o f v o l a t i l e sulphur compounds i n which a Xenon lamp i s used as spectral source (707).Detection o f sulphides and sulphites i n aqueous solutions (buffered w i t h Na ascorbate) was achieved by sequential evolution o f H2S and SO2, and detection o f S by AFS i n aAtomization and Excitation 33 H2-diffusion flame. Since no detectable signal was obtained f o r a flow of pg hexane s-’, the potential f o r use as a GC detector i s obvious, although s e n s i t i v i t y may have t o be improved f i r s t .Use of AFS as a metal s p e c i f i c detector f o r HPLC has a l s o been reported, both as a s p e c i f i c system f o r Cd 600 the (C2242), and i n a 4-channel non-dispersive system used variously f o r C u , Fey Mg, Mn, Ni and Zn i n complexes (1524). A description of the l i n e source AFS method reported l a s t year (ARAAS, 1982, - 12, Ref.C306) f o r the determination of lead i n blood has now been published (813); the method has been extended t o the determination of Pb i n urine and water (1634). background s c a t t e r correction. w i t h greater s e n s i t i v i t y by u s i n g a N2-separated air/H2 flame. continuum source AFS method has been used f o r the determination of Coy C u , Ni and Zn in manganese nodules (1013).air/C3H8 flame was preferred t o air/C2H2 on grounds of s e n s i t i v i t y . A simul- taneous l i n e source non-dispersive AFS system was developed f o r the determination of As, Hg, Pb, Se and Sn i n which an entrained air/Ar/H2 flame was used t o atomize hydrides of these elements generated i n the normal way (1629). taneous detection was obtained by modulation of the r .f . EDLs used as l i g h t sources f o r each element a t d i f f e r e n t frequencies , w i t h separate lock-in- amp1 i f i e r s tuned t o each corresponding frequency. A N2-separated air/C2H2 flame was used w i t h a xenon a r c f o r Water samples could be analysed s a t i s f a c t o r i l y A sequential No background correction was used, and an Simul- Further work has been described on the use of wavelength modulation f o r back- ground correction i n continuum source AFS (473, 1048).Two double modulation systems have been described which remove the AE component from the t o t a l AF plus AE signals obtained by wavelength modulation (1048). In flame AFS, the i n t e n s i t y modulation system also helps t o remove spectral interferences from concomitant AE signals.length modulation i n AFS have now been investigated and described in more detail (473). magnitudes of transmission losses , r e f l e c t i o n losses and defocussing losses a t large modulation i n t e r v a l s (>1 .O nm) were i d e n t i f i e d . Some of the special features of sectored wheel wave- E f f i c i e n t square wave modulation a t 160 Hz was demonstrated, and the 1.3.5 Applications of Lasers Compared t o previous years, there is this year a s i g n i f i c a n t increase in the number of investigations of real sample analysis by techniques based on l a s e r excitation of atoms.This appears unlikely t o herald the development of new commercial laboratory based instruments, but i t might lead t o a range of sophis- t i c a t e d on-line analysis instrumentation based on l a s e r s and f i b r e optics (see Section 1.3.5.3).Hieftje (387, C2219) has produced useful overviews of the potential of l a s e r based methods, and has c l e a r l y indicated directions i n w h i c h34 Analytical Atomic Spectroscopy f u t u r e research on these methods should be aimed.Omenetto (81) attempted t o d e f i n e a number o f common terms used i n t h e l a s e r fluorescence f i e l d , and h i s paper w i l l undoubtedly be o f wide general i n t e r e s t . 1.3.5.1 Laser-exci t e d Atomic F1 uorescence Spectrometry ( LAFSl I n an i n t e r e s t i n g conference paper, H i e f t j e (C2219) p r e d i c t e d t h a t s i g n i f i c a n t gains i n s e n s i t i v i t y i n atomic spectrometry a r e o n l y l i k e l y t o be achieved i f s a t u r a t e d l a s e r - e x c i t e d atomic fluorescence spectrometry i s employed.o u t t h a t , f o r t h i s p r e d i c t i o n t o hold, i t would be necessary t o have a v a i l a b l e high-power l a s e r s , which can be r a p i d l y tuned o r which emit simultaneously, a t wavelengths from 200-800 nm.I n a d d i t i o n , atom sources must be developed t h a t have low background r a d i a t i o n and which are capable o f r e t a i n i n g atoms f o r extended periods. Measured a g a i n s t these c r i t e r i a , advances reported d u r i n g 1983 appear modest, b u t nevertheless some s i g n i f i c a n t steps have been taken.He p o i n t e d Two approaches t o the e l i m i n a t i o n o f l i g h t s c a t t e r i n t e r f e r e n c e i n LAFS have Omenetto (C2293) described t h e use o f an excimer-pumped tunable been reported. dye-laser t o e x c i t e atomic and i o n i c fluorescence i n flames, carbon furnaces and an I C P . The l a s e r system could be tuned from 217 nm t o t h e near i.r.w i t h a s p e c t r a l bandwidth o f 0.015 nm a t a peak power o f 10-50 kW (u.v.) o r 200-500 kW (fundamental). s i g n a l s from the m a t r i x , and on-resonance r e f l e c t i o n s (presumably s t r a y l i g h t ) o f l a s e r r a d i a t i o n . The d e t e c t i o n l i m i t s f o r A l , B y Bay Mo, Pb, S i , V, Y and Z r i n an I C P were i n the range 0.6 t o 5 ng m1-l.The Pb d e t e c t i o n l i m i t i n an air/C2H2 flame o f 0.3 ng m1-l allowed t h e determination o f t h i s element i n blood, f o l l o w i n g d i l u t i o n o f t h e sample (1 : l o ) . was used by Goff (1532) t o improve s i g n i f i c a n t l y the d e t e c t i o n l i m i t f o r Ba i n a premixed flame. t h i s system, and off-resonant e x c i t a t i o n was claimed t o open up t h e p o s s i b i l i t y o f multielement LAFS.Non-resonance fluorescence was used t o a v o i d overlapping s c a t t e r A wavelength modulated CW dye-laser The LAFS o f Fey Na and Ni i n an I C P was a l s o s t u d i e d w i t h Non-resonance fluorescence has a l s o been used t o advantage i n LAFS w i t h electrothermal atomization (C1730, C1854).A narrow band dye-laser which c o u l d be tuned from 260 t o 750 nm w i t h o u t p u t powers ranging from 1 t o 50 kW was used by F a l k and co-workers t o achieve a Pb d e t e c t i o n l i m i t o f 5 f g and a T1 d e t e c t i o n l i m i t o f 10 f g . l i m i t i n g source o f noise was s t r a y l i g h t emanating from the thermal emission o f the g r a p h i t e cup.determination w i t h an electrothermal atomizer (257, see a l s o ARAAS, 1981, 11, Ref. 1521) has been extended t o I n (C2244). Bolshov e t a l . (220) have given more d e t a i l s o f t h e i r a p p l i c a t i o n s t u d i e s o f LAFS u s i n g ETA (see ARAAS, 1982, S a t u r a t i o n could n o t be achieved f o r a l l elements, and the The double resonance e x c i t a t i o n method reported f o r Pb - 12, 34).Atomization and Excitation 35 Laser AFS studies of atomic and ionic vapours produced by cathodic sputtering o r hollow cathode type discharges have been used t o estimate excited s t a t e l i f e - times (1696) and s p a t i a l atom d i s t r i b u t i o n s (926).inductively coupled plasma have a l s o continued, but despite investigations of an extended sleeve torch (250), and l a s e r excitation of atoms i n excited s t a t e s (C2243), s e n s i t i v i t i e s reported t o date are unlikely t o stimulate much further a c t i v i t y i n this f i e l d (250, 1585).Laser AFS studies with the Further studies of the thermally a s s i s t e d fluorescence method f o r the measure- ment of s p a t i a l l y and temporally resolved temperatures i n b o t h flame (1399, C2345) and ICP (1585), have revealed t h a t a p a r t i a l Boltzmann equilibrium i s not reached i n e i t h e r case during the 5 ns l a s e r pulse.N2/02/C2H2 o r Ar/02/C2H2 flames i ndi cated t h a t Val id 1 ocal temperatures coul d not be obtained by the method (1399). Excitation of C atoms from the lowest metastable s t a t e of 1.26 eV, using an ArF l a s e r (x = 193 nm), allowed the deter- mination of C impurities i n nuclear fusion reactor plasmas by measurement of the resulting AF a t 248 nm (170, 466).Laser AFS has a l s o been used t o study the s p a t i a l d i s t r i b u t i o n of atoms from individual solute p a r t i c l e s i n flames (C2342). No r e s u l t s were given, b u t the advantages of t h i s method compared t o the Abel inversion of emission data a r e c l e a r .Studies of Na i n nine 1.3.5.2 Laser Enhanced Ionization (LEI) By f a r the most i n t e r e s t i n g paper on this subject i n the past year i s t h a t by Berthaud e t a l . (1310) on the temporal c h a r a c t e r i s t i c s of LEI signals. Their measurements were made w i t h two-step l a s e r excitation of Na using two tunable dye-lasers a t 588.99 nm and 498.28 nm respectively.studied, b u t two electron current peaks were observed which varied with the applied voltage and the distance between the burner electrode and the point of focus of the l a s e r beams. The mechanism proposed was ( i ) atoms are excited by the two-step process during the 6 ns pulse; aneously ionized ( i n p s ) ; ( i i i ) electrons and ions are separated by the e l e c t r i c f i e l d s e t up between the burner and the electrode; ( i v ) electron and ion currents a r e observed through ( a ) d i r e c t charge collection and ( b ) by the capacitive reaction of the burner-flame-electrode system t o the instantaneous creation and separation of charges.The f i r s t and immediate L E I signal a r i s e s from ( b ) , and the second peak coincides with the a r r i v a l of electrons a t the positive electrode. of K g i v i n g an enhancement of peak height ( b u t constant t o t a l ion current) due t o shorter pulse duration. Ion currents were not ( i i ) excited atoms are instant- I t was a l s o shown t h a t pulse shapes change i n the presence There has been a s i g n i f i c a n t increase in analytical applications o f LEI during 1983 (1002, 1007, 1328, 1602, C2016, C2049).Many of these attempts t o analyse36 Analytical Atomic Spectroscopy r e a l samples have produced i n t e r e s t i n g i n s i g h t s i n t o p r a c t i c a l features o f the technique. Thus K was determined i n the range 5 t o 10000 ng m l - 1 i n an a i r / C3H8/C4Hlo flame w i t h a N i / C r sensor a t 600 V, b u t K could not be determined i n the products o f the s i l i c o n e rubber industry as the sensor was r a p i d l y de- activated by organosilicon compounds (1602).Both d i r e c t a s p i r a t i o n and loop evaporation were used t o introduce Cs i n t o an air/C3H8/C4H10 flame (1002, 1007, C2049).interference o f Na was a t t r i b u t e d t o an increase i n the p o s i t i v e - i o n space charge around the cathode. e x c i t a t i o n energy t r a n s f e r between close energy l e v e l s o f Cs and Rb through v i b r a t i o n a l l e v e l s o f molecules (1002), but the LEI pulse shape e f f e c t mentioned above (1310) appears a more l i k e l y explanation. Despite t h i s problem, the Cs content o f Rb s a l t s was determined (1007, C2049).Broad band spectral i n t e r - ferences have been observed by Turk e t a l . (C2016), and background correction was accomplished by tuning the dye-laser across the a n a l y t i c a l absorption l i n e . A high power CW dye-laser (pumped by a Kr' l a s e r ) has been used t o measure A Cs detection l i m i t o f 4 pg m l - 1 was reported, and the depressive The i n i t i a l enhancement by Rb was said t o be due t o the LEI o f Cay Gay I n , L i , Na and S r i n an air/C2H2 flame and K and Pb i n an air/H2 flame (112). b e t t e r f o r others than those w i t h a pulsed dye-laser, matrix e f f e c t s are said t o be much less w i t h the CW laser.Interferences from e a s i l y ionized elements are claimed t o be much less w i t h the dual l a s e r i o n i z a t i o n approach (1379, see also ARAAS, 1982, 12, 36), and can also be reduced by using optimized high voltage electrodes (804) o r pulsed signal c o l l e c t i o n (784). Although detection l i m i t s were poorer f o r some elements and Green and co-workers (C2389) have continued t o promote the use o f t o t a l con- sumption burners f o r LEI (see ARAAS, 1982, 12, 36). o f electrode configurations and interferences were reported t h i s year, and a low detection l i m i t for Cu o f 1.8 ng m l - 1 was claimed.t h a t on the determination o f H r a d i c a l s i n an air/H2 flame w i t h optogalvanic detection (389).More d e t a i l e d investigations An i n t e r e s t i n g r e p o r t was A new technique which involves LEI o f atoms i n a vacuum chamber has been described and has been used f o r the determination o f Na i n cadmium sulphide crystals, A1 i m p u r i t i e s i n germanium, and trace elements i n water and human blood (713). chamber where the atoms were subjected t o l a s e r stepwise photo-ionization.The sample was thermally evaporated and atomized i n the vacuum Other references o f i n t e r e s t - Optogalvanic and absorption p r o f i l e s f o r A r , Cu and Ne : 345. Optogalvanic Zeeman spectroscopy o f Ca, Cu and Ne i n a hollow cathode discharge : 171.Atomization and Excitation 37 1.3.5.3 Gther Studies Three papers dealing w i t h t h e p o t e n t i a l o f resonance i o n i z a t i o n spectroscopy have appeared i n 1983.resonance i o n i z a t i o n detection i n laser-excited AFS t o lower t h e detection l i m i t s o f many elements t o the s i n g l e atom l e v e l , The most promising methods involve atom e x c i t a t i o n t o the Lorentz curve wing, e x c i t a t i o n o f f i n e Zeeman and Stark s p l i t t i n g l e v e l s , and multiphoton e x c i t a t i o n . hand, described several p o s s i b i l i t i e s o f using the s e l e c t i v e m u l t i - s t e p e x c i t - a t i o n and i o n i z a t i o n o f atoms f o r AAS and AES analysis. Matveev (936, C1942) discussed t h e p o t e n t i a l o f using Donofeev e t a1 . (864) on the other I n t r a c a v i t y atomic absorption spectroscopy has been applied t o the determin- a t i o n o f A1 and Ca (60), C r and Fe (572), and Mo (832). I n two o f these cases (60, 572) atomization was achieved by an electrothermal atomizer furnace made o f a Ta/Re a l l o y placed i n the c a v i t y o f a dye-laser. A1 could be detected by using the resonance l i n e s a t 394.5 and 396.2 nm, b u t the detection l i m i t f o r Ca a t 393.4 nm was t o 3100 K, b u t vapour phase temperatures estimated from absorption measurements o f Fe l i n e s between 382 and 386 indicated t h a t the vapour temperature was 480 K lower than the w a l l temperature under t h e conditions used (572). Atomization o f Mo was achieved by a second l a s e r applied t o a sample i n d i s c form placed i n s i d e the c a v i t y o f the primary dye-laser (832). As l i t t l e as 5 x g o f g. The Ta/Re furnace could be heated An i n t e r e s t i n g application o f atomic and molecular fluorescence has appeared which may be of i n t e r e s t t o many atomic spectroscopists. have been used t o c a r r y o u t remote measurements o f molecular species i n combust- i o n gases (254). fluorescence l i g h t beams, were a l l conducted t o o r from the measurement zone using fused s i l i c a o p t i c a l f i b r e s o f up t o 37m i n length, Measurements o f both Na and OH i n combustion gases by fluorescence and absorption processes were described. F i b r e - o p t i c probes Energy from one of two dye-lasers, and transmitted and Other references of i n t e r e s t - A r t and K r t l a s e r fluorescence o f CN i n a N2/N20/CH4 flame : 1082. Fluorescence spectra o f OH molecules : 255.

ISSN:0306-1353    

DOI:10.1039/AA9831300024

出版商:RSC    

年代:1983

数据来源: RSC

摘要:

Atomization and Excitation 37 1.4 ELECTROTHERMAL ATOMIZATION The trends i n the year under review d i f f e r subtly from those in previous years. The move towards isothermal atomization, noted before, has now brought researchers together t o advance with some unity of purpose. This r e f l e c t s a growing matur- i t y in the technique, and i s i l l u s t r a t e d in excellent review a r t i c l e s by Koirt- yohann and Kaiser ( 2 ) , and also by Slavin e t a l .(1206). For t h i s reason fewer38 Analytical Atomic Spectroscopy papers are now appearing on i 11 -defined i n t e r f e r e n c e phenomena, w h i l e more are based on t h e a p p l i c a t i o n o f w e l l researched mechanistic models. It would a l s o be appropriate a t t h i s stage i n ETA development t o acknowledge t h e g r e a t c o n t r i - b u t i o n t o t h e s u b j e c t made by t h e l a t e Professor Ray Woodriff, who always stood firmly behind t h e o r i g i n a l concept o f isothermal atomization, even when i t was n o t fashionable t o do so.With t h e c u r r e n t awareness o f t h e multielement c a p a b i l i t i e s o f t h e I C P , t h e use o f ETA f o r simultaneous multielement a n a l y s i s has now gained considerable momentum.has proved t o be an e x c e l l e n t device f o r t h i s work and t h e c a p a b i l i t i e s o f these systems f o r both absorption and emission a n a l y s i s are described i n Section 1.4.4.3. ual l y a t t r a c t some commercial a t t e n t i o n . The h i g h r e s o l u t i o n e c h e l l e spectrometer It i s hoped t h a t t h e continued developments on t h i s theme w i l l event- 1.4.1 Atomizer Design This y e a r again sees t h e achievement o f isothermal atomization i n ETA as the most important growth area, although t h e techniques a l l u d e d t o here have been o u t l i n e d before. achieving isothermal atomization, &, platforms , plugs and probes, was pre- sented by Ottaway e t a l .(C1753, C2090, C2129). They concluded t h a t , t o date, t h e p l a t f o r m method o f f e r e d the simplest and cheapest r o u t e t o improved anal- y t i c a l performance w i t h c u r r e n t commercial instruments. The same group (980) a l s o showed how improvements i n s e n s i t i v i t y i n AES c o u l d be achieved by t h e use o f platforms. t h e use o f platforms and probes i n l a r g e r furnaces, Siemer and Lewis (404, 471, 565) have modified a commercial carbon cup type atomizer. Two designs were described; i n one (404, 471) t h e electrodes o f the carbon cup were p o s i t i o n e d h i g h e r i n the cup g i v i n g an increase i n the atomic vapour temperature.The second design (565) was s i m i l a r t o t h a t described by L i t t l e j o h n and Ottaway (see ARAAS, 1979, 9, Ref. 2074) where the cup was f i x e d below t h e tube.devices were more t o l e r a n t o f vapour phase i n t e r f e r e n c e s than l y a v a i l a b l e system, provided t h a t i n t e g r a t e d s i g n a l measurements were made. Another furnace w i t h dual heating, r e p o r t e d by Frech and Jonsson l a s t y e a r i n conference papers (see ARAAS, 1982, 12, Refs.C2192, C2424), has now been described i n a more complete form (750). A comparison o f t h e advantages o f d i f f e r e n t systems f o r I n an attempt t o achieve c o n d i t i o n s s i m i l a r t o those created by Both t h e commercial- The p h y s i c a l and e l e c t r i c a l c h a r a c t e r i s t i c s o f atomizer substrates have u n t i 1 The use o f p y r o l y t i c r e c e n t l y been much neglected features o f atomizer design.g r a p h i t e coatings has o f course been w e l l documented and now several groups of workers are d i r e c t i ng t h e i r resources towards a1 t e r n a t i ve substrates. The use o f glassy carbon t o f a b r i c a t e g r a p h i t e furnace tubes was i n v e s t i g a t e d by de Galan e t a l .(754, 1028, C1933, C2111, C2265). These tubes o f f e r e d s i m i l a r l i m i t sAtomization and Excitation 39 of d e t e c t i o n t o p y r o l y t i c a l l y coated tubes , b u t provided a more uniform heating. T h e i r s u p e r i o r r e s i s t a n c e t o chemical a t t a c k r e s u l t e d i n l i f e t i m e s o f several thousand f i r i n g s a t an atomization temperature of 2350 K w i t h no appreciable loss i n s e n s i t i v i t y .Commercial atomizer power s u p p l i e s w i l l r e q u i r e s l i g h t m o d i f i c - a t i o n t o accommodate the d i f f e r e n t e l e c t r i c a l and thermal p r o p e r t i e s o f glassy carbon, and, w i t h o u t such m o d i f i c a t i o n , t h e i r f u l l temperature and d e t e c t i o n l i m i t c a p a b i l i t y w i l l n o t be r e a l i z e d .Another a l t e r n a t i v e t o p y r o l y t i c a l l y coated tubes i s t h e use of tubes f a b r i c a t e d t o g i v e a s t r u c t u r e t h a t c o n s i s t s e n t i r e l y o f p y r o l y t i c g r a p h i t e .cuvettes were described by L i t t l e j o h n e t a l . (C1928), and i t was shown t h a t g r e a t e r h e a t i n g r a t e s and h i g h e r temperatures were achieved f o r a given a p p l i e d power, and tube l i f e t i m e and t h e a n a l y t i c a l s e n s i t i v i t y were claimed t o be s u p e r i o r t o cornmeVcia1 e l e c t r o g r a p h i t e o r pyrocoated g r a p h i t e tubes.The temperature c h a r a c t e r i s t i c s o f such a furnace tube were described i n a German p a t e n t (1192). by Whiteside e t a l . (C2033, C2173). They considered a v a r i e t y o f p h y s i c a l and e l e c t r i c a l parameters and r e l a t e d these t o t h e performance c h a r a c t e r i s t i c s required.A method o f t e s t i n g p y r o l y t i c a l l y coated tubes was described i n another p a t e n t by G l a i s e r (1191). By using Cs as a t e s t element, t h e r e s i s t - ance t o t h e formation o f i n t e r c a l a t i o n compounds w i t h t h e g r a p h i t e was judged as a measure o f t h e e f f i c i e n c y o f t h e coated tube. Experiments w i t h t o t a l p y r o l y t i c g r a p h i t e A l t e r n a t i v e m a t e r i a l s t o e l e c t r o g r a p h i t e have a l s o been s t u d i e d There are two popular atomizer modifications f o r enhancing s e n s i t i v i t y and The use o f a tube l i n e d w i t h Ta-W a l l o y reducing c a r b i d e formation f o r c e r t a i n r e f r a c t o r y elements.i s t h e use o f coated o r l i n e d tubes. was claimed by Wu and Ma (510) t o improve s e n s i t i v i t y by a f a c t o r o f twenty f o r r a r e e a r t h elements and U.The second a l t e r n a t i v e i s t h e use o f metal atomizers. Although these have gained l i t t l e commercial a t t e n t i o n , they do appear t o have some l i m i t e d a p p l i c a b i l i t y i n s p e c i a l i z e d circumstances.A commercial W tube atomizer has r e c e n t l y been described by Sychra e t a l . (1504, 1740, C1847, C2008). i v i t i e s f o r r e f r a c t o r y elements were claimed t o be s u p e r i o r t o those obtained w i t h g r a p h i t e atomizers. The f i r s t o f these This apparatus incorporates temperature c o n t r o l l e d heating, and sensi t- Two novel atomizer c o n f i g u r a t i o n s have been described.c r i b e d by Shishido and Yamaka (1171), a carbon tube atomizer was r o t a t e d through 90' so t h a t the l i g h t source focussed above t h e sample i n j e c t i o n p o r t . degraded t h e s e n s i t i v i t y b u t allowed C r , Pb and Zn t o be determined i n b i o - l o g i c a l samples w i t h o u t t h e need f o r complex chemical procedures.The second c o n f i g u r a t i o n was a l a b o r a t o r y f a b r i c a t e d atomizer (based on a mini-Massmann furnace) which was designed t o a l l o w atomization t o take place w i t h o u t t h e need f o r d r y i n g o r ashing steps (756, see a l s o ARAAS, 1982, 12, Ref. 1983). The i n c o r p o r a t i o n o f such an atomizer i n a Zeeman based AA system has a l s o been I n t h e f i r s t , des- This40 Analytical Atomic Spectroscopy investigated (C1835) and preliminary experiments were conducted t o examine the e f f e c t of an a.c.magnetic f i e l d on the performance of the atomizer. 1.4.2 Fundamental Processes Investigations by L'vov and Ryabchuk (469, C1728, see a l s o ARAAS, 1982, 12, Ref. 1502) have demonstrated t h a t the p a r t i a l pressure of oxygen i n the graphite furnace i s several orders of magnitude higher than could be explained on purely thermodynamic grounds. These conclusions have stimulated Cedergren e t a1 . (C2275) t o examine the relevance of this w i t h regard t o their own high temper- ature equilibrium calculations of the oxygen levels present during atomization (see ARAAS, 1977, 7 , Ref. 358). attempted t o measure the actual oxygen content by u s i n g a chemiluminescent reaction between P vapour and molecular 02. experimentally derived values reported by L'vov and Ryabchuk. Sturgeon and co-workers (C2005, C2266) have Their measurements confirmed the I t may appear obvious t h a t i n graphite furnace ETA the carbon plays an important role in the atomization mechanism.Chakrabarti e t a1 . (313) r e i t e r a t e d t h i s , s t a t i n g t h a t , especially a t high temperatures, the role of carbon was c r i t i c a l in determining the p a r t i a l pressures of 02(g) and O(g) through equi- l i b r i a involving CO(g), C02(g) and other species. The e f f e c t of carbon black (32) on the atomization of Mo and V was demonstrated.black i n the sample solution, the absorbances of these elements were increased by a f a c t o r of s i x . Similar e f f e c t s on the AA signals of Be were demonstrated (972) f o r carbon black and other powder reductants such as sulphur and a l k a l i metal hydrides. In both these cases, the authors concluded t h a t the enhance- ments were due t o the reduction effects,of the powders and the suppressed vaporization of the oxides.refractory elements viz the formation of involati l e carbides, was examined by Muller-Vogt e t a1 , f o r the atomization of Mo (1126) and Si (948) , and by Wend1 (C2031) f o r Cry Mo and V. slow t h a t a t f a s t furnace heating rates both carbides would be present during atomization. explained by t h e i r influence on the decomposition of the Mo carbide phases. I n t e r s t i t i a l compound formation between Ag and carbon was shown (1661) t o be responsible f o r the gradual degradation in precision w i t h increasing use o f a pyrolytic graphi te-coated tube.radiological measurements were made , and the distance between carbon layers was observed t o increase as a r e s u l t of the Ag inclusion compounds.By dispersing the carbon The detrimental e f f e c t of carbon on certain The transformation of Mo2C t o MoC was shown t o be so The interference of other carbide forming elements could be X-ray d i f f r a c t i o n , neutron activation and The importance of accurate temperature measurements i n ETA has been high- lighted by the realization t h a t conditions close t o isothermal atomization are now a prerequisite f o r optimum atomizer performance.A discussion of the s p a t i a lAtomization and Excitation 41 and temporal temperature d i s t r i b u t i o n i n a platform furnace was presented by Welz and Schlemner (C2300). they reached the obvious conclusion t h a t the platform temperature lagged behind t h a t of the wall, b u t a l s o showed t h a t the vapour phase temperature was higher than the platform temperature.Very s i m i l a r conclusions were reached by Chak- rabarti e t a l . (C2263, C2393) u s i n g a predictive computer program t o calculate temperature variations between platform and probe atomization modes. workers f u r t h e r i 11 ustrated (C2394) differences in temperature between the walls and the platform o r probe of 200 and 250 K respectively, measured when the wall temperature had attained equi 1 i b r i um.heated by gaseous convection and radiation, the f a c t t h a t the probe and platform temperatures are so close is indeed surprising. Measuring wall , platform and gas phase temperatures, These Considering t h a t the probe i s probably Studies of atomic spectral l i n e profiles are recognized as being of consider- able importance when assessing the practical limitations of an absorption or emission technique.Such information i s often theoretically derived. The increased use of echel l e spectrometers , however , presents the researcher w i t h a means of making accurate measurements d i r e c t l y .Harshall e t a1 . (C1940) have used such a system t o investigate s e l f absorption and reversal e f f e c t s in carbon furnace AES, and t o assess t h e i r importance on the analytical curves of growth. A s i m i l a r system was used by Miller-Ihli e t a l . (1383) t o study time resolved AA spectra. Information regarding spectral l i n e overlaps and the temporal variations i n background was obtained. This is a potentially powerful system f o r deriving important spectral information and i t allows an optimization of the measurement time-window f o r background f r e e analysis.Rather unusual spec- t r a l e f f e c t s were reported by Fazakas (73, 418, 800) u s i n g an atomizer operating under positive pressure. A red-shift i n the spectral l i n e s was observed and i t was claimed t h a t Ga could be determined a t 403.298 nm by using the Mn 403.307 nm l i n e (resonance), and t h a t Cd a t 228.802 nm could be determined by using the A s 228.812 nm (non-resonance) l i n e .Also, while resonance l i n e s were adversely affected by pressure, the s e n s i t i v i t i e s of non-resonance 1 ines were considerably enhanced.Linearity of calibration i n both peak height and peak area absorption modes was a l s o considerably improved by the use o f pressure, t h i s being explained by the Lorenzian broadening of the absorption p r o f i l e . Other references of i n t e r e s t - Effect of analog-to-digi t a l converter resolution on absorption measure- ments : 7. Vapour expulsion from a graphite tube furnace : 794. 1.4.3 Interferences I t i s perhaps a r e f l e c t i o n o f the maturity of a technique, when eventually l e s s42 Analytical Atomic Spectroscopy l i t e r a t u r e i s devoted t o s p e c i f i c i n t e r f e r e n c e r e p o r t s and more i s devoted t o t h e understanding and o p t i m i z a t i o n o f t h e processes as a whole.This was p a r t - i c u l a r l y e v i d e n t i n 1983 when t h e advantages o f isothermal atomization t o provide b e t t e r c o n t r o l over t h e atomization environment made a more s i g n i f i c a n t impact. The minimal vapour phase i n t e r f e r e n c e s o f the s t a b i l i z e d temperature p l a t f o r m furnace were claimed by S l a v i n e t a l . (1206, C2056, C2273) t o p e r m i t almost absolute, &, "standardless" a n a l y s i s .s i g n a l o f 0.0044 A s-' was claimed by S l a v i n t o have been constant t o b e t t e r than 20% f o r each element studied. However, i t w i l l be a l o n g time before t h i s concept becomes p r a c t i c a l l y v i a b l e f o r r o u t i n e analysis, The mass o f analyte t h a t produced a The most s i g n i f i c a n t problem i n furnace analysis i s the c o n t r o l o f m a t r i x background i n t e r f e r e n c e .The use o f a commercial Zeeman background c o r r e c t i o n system was shown by V o l l k o p f e t a l . (C2022) t o be capable o f c o r r e c t i o n o f up t o 2.0 A u n i t s and allowed c o r r e c t i o n f o r both broad band and s t r u c t u r e d background.The measurement o f background spectra from organic solvents was r e p o r t e d by GUcer and Massmann (792). The aromatic molecules were, i t was claimed, so firmly bound t o t h e surface o f t h e g r a p h i t e atomizer t h a t they remained even a f t e r ashing a t 800 OC. f i e d i n a furnace atmosphere by observation o f t h e i r v i b r a t i o n a l absorption spectra.u l a r spectrum o f germanium sulphide has a l s o been recorded (1727). sate f o r background spectra, de Galan e t a l . (1295) modified a commercial spectrometer data s t a t i o n t o accommodate t h e simultaneous measurement o f both analyte and background absorption, w h i l e Baranov and co-workers (400) used an a l t e r n a t i v e t o t h e continuum source c o r r e c t i o n technique by employing a l i n e source which gave two primary source modes which s i g n i f i c a n t l y changed t h e absorption l i n e shape and the absorption c o e f f i c i e n t .Molecules o f benzene, toluene and xylene were i d e n t i - It was shown t h a t t h i s severely degraded AA measurements. The molec- To compen- (See a l s o Section 2 . 3 ) . Another approach t o t h e minimization o f m a t r i x i n t e r f e r e n c e s i s m a t r i x modi- f i c a t i o n . as whole blood has been r e p o r t e d by Holcombe and Eaton (676, 1276, see a l s o ARAAS, 1981, 11, 40). a r b i t r a r y basis (see ARAAS, 1980, 10, 57, 60). This contention was supported by S l a v i n e t a l . ((2169) who s t a t e d t h a t the mechanisms behind m a t r i x m o d i f i - c a t i o n a r e n o t f u l l y understood and t h e use o f these m o d i f i e r s o f t e n confused t h e a p p l i c a t i o n o f l i t e r a t u r e t h e o r i e s o f atomization.base was r e q u i r e d t o p r e d i c t t h e choice of m a t r i x m o d i f i e r and t o a l l o w optimum c o n d i t i o n s f o r each metal t o be found.This conclusion i s viewed by t h i s reviewer as a p a r t i c u l a r l y encouraging s i g n o f a more r e a l i s t i c a t t i t u d e . The e f f e c t o f i n s i t u oxygen ashing t o remove organic matrices such The s e l e c t i o n o f m a t r i x m o d i f i e r s has t o date been on an A b e t t e r t h e o r e t i c a lAtomization and Excitation 43 1.4.4 Developments i n Technique 1.4.4.1 Magneto-optics A s i g n i f i c a n t r e d u c t i o n i n t h e number o f development type papers on magneto- o p t i c a l e f f e c t s has occurred t h i s year.This may w e l l be due t o t h e widespread commercial a v a i l a b i l i t y o f various Zeeman systems which are now being g e n e r a l l y eval uated.One Zeeman d e r i v e d v a r i a n t , the V o i g t e f f e c t , has been s t u d i e d by Kankare and Stephens (1351, 1408). The SNR c h a r a c t e r i s t i c s were observed when t h e V o i g t e f f e c t was used t o determine atomic species. L i n e a r i z a t i o n o f response was found t o improve SNR e s p e c i a l l y i n t h e presence o f background emissions, however corn- p a r i s o n o f SNR w i t h conventional AA favoured t h e l a t t e r .Comparison o f t h e V o i g t e f f e c t w i t h AAS and AFS was made by L i e t a1 . (1184) and t h e f a c t o r s which govern o p t i c a l o u t p u t and l i n e a r i t y were discussed w i t h reference t o t h e d e t e r - mination o f t r a c e l e v e l s o f Ag, Pb and Rb.Kitagawa e t a l . (C1910) have used t h e i r experience o f t h e features o f the Faraday e f f e c t (coherent forward s c a t t e r i n g ) (see a l s o ARAAS, 1981, 11, 42) t o c o n s t r u c t a mobi l e atomi zer/spectrometer system f o r i n - s i t u t r a c e a n a l y s i s . t h e power f o r t h e e l e c t r o n i c s f o r t h e atomizer, l i g h t source and s i g n a l proces- s i n g were s u p p l i e d by two c a r b a t t e r i e s which, when f u l l y charged, allowed more than 100 atomizations.was attempted; magnetic f i e l d s t r e n g t h were observed. Faraday e f f e c t (see ARAAS, 1980, 10, Ref. 1723) was used by Hirokawa and co- workers (485) t o determine t r a c e s o f Ag and Pb. A1 1 O p t i m i z a t i o n o f t h e l i n e p r o f i l e o f t h e source r a d i a t i o n however, complex e f f e c t s between t h e t r a n s m i t t e d i n t e n s i t y and t h e An a l t e r n a t i v e c o n f i g u r a t i o n o f t h e 1.4.4.2 Sample I n t r o d u c t i o n The advantages o f isothermal atomization can be r e a l i z e d when p r e - d r i e d samples are i n t r o d u c e d i n t o a heated furnace by means o f a g r a p h i t e probe (see ARAAS, 1982, 12, 37).Ottaway and h i s group have c o n t r i b u t e d t o t h i s p a r t i c u l a r devel- opment and the r e d u c t i o n i n vapour phase i n t e r f e r e n c e s r e s u l t i n g from t h e h o t t e r atomization environment has been demonstrated (877 , C1927). a l s o automated t h e probe method o f sample i n t r o d u c t i o n (989), b r i n g i n g i t more i n t o l i n e w i t h c u r r e n t philosophies on i n s t r u m e n t a t i o n .The p r a c t i c a l u t i l i t y o f t h e probe method was demonstrated i n t h e determinations o f Pb i n blood (812), and Cd i n various b i o l o g i c a l matrices (C2076). I n both cases, good agreement w i t h c e r t i f i e d values was obtained by u s i n g o n l y aqueous c a l i b r a t i o n standards.These workers have The use o f s o l i d sampling, although p o t e n t i a l l y a t t r a c t i v e i n terms o f s e n s i t i v i t y , has never r e a l i z e d i t s i n i t i a l promise, p r i m a r i l y because o f poor44 Analytical Atomic Spectroscopy speed o f analysis, sample inhomogeneity and c a l i b r a t i o n problems.circumventing these d i f f i c u l t i e s i s t o introduce s o l i d samples as f i n e suspen- sions o r s l u r r i e s (see ARAAS, 1981, lJ, Ref. 41). Jackson e t a l . (772, C1897) have devised such a procedure f o r the determination o f Cd and Pb i n s o i l , f i n d i n g good c o r r e l a t i o n w i t h r e s u l t s obtained by digestion procedures. The s l u r r y formed i n t h i s case, however, required continuous a g i t a t i o n , which o f course would be a severe disadvantage i n automated batch analysis.The use o f Mg and Ni matrix modifiers w i t h coal s l u r r i e s was found by Pearce (C2070) t o allow s t a b i l i z a t i o n o f As and Se. A strong c o r r e l a t i o n between As l e v e l s and the presence o f p y r i t i c sulphur was found, and the author suggested t h a t t h i s was due t o the presence o f arsenopyrite (see also ARAAS, 1982, 12, Ref. 1545). s o l i d sampling was used t o advantage by Takada and Hirokawa (246) i n determining pg l e v e l s o f Cd and Pb i n high p u r i t y t i n . An a l t e r n a t i v e method o f s o l i d sampling w i t h use o f a l a s e r t o evaporate the sample p r i o r t o ETA-AAS, was described by Wennrich and D i t t r i c h (72).required the use o f closely matched standards. One method o f The high s e n s i t i v i t y o f However, c a l i b r a t i o n was d i f f i c u l t and The manual sampling o f l i q u i d s i n t o atomizers requires a high degree o f operator s k i l l t o avoid imprecision.A more elegant and v e r s a t i l e a l t e r n a t i v e t o d i s c r e t e sampling i s the i n t r o d u c t i o n o f aerosols i n t o the furnace (779). The performance o f such a commercially available device was described by Sotera et - a l . (359), who showed how the combination o f aerosol deposition w i t h platform type atomization was superior t o discrete sampling i n eliminating interferences i n the determination o f Bi, Pb, Te and T1 i n high temperature a l l o y s .Studies o f the nebulization e f f i c i e n c y w i t h such a system, presented by Dulude e t a l . (C2205) , i l l u s t r a t e d how the u l t i m a t e s e n s i t i v i t y o f the technique was determined by t h e deposition time and n o t by the nebulizer e f f i c i e n c y .aerosol arrangement was described by Jenke and Woodriff (401, 385). I n combin- a t i o n w i t h t h e i r constant temperature furnace (ARAAS, 1974, 4, Ref. 954), t h i s system produced detection l i m i t s only f i v e times b e t t e r than w t h flame AAS. A more cumbersome Introducing the eluate from a chromatographic column i n t o a graphite furnace Sampling has added a new dimension i n s e n s i t i v i t y t o metal speciation studies.the HPLC stream eluate every 43 s and summing the absorption measurements allowed Woolson (1132) t o determine trimethylarsine oxide, arsenite, dimethyl- arsonic acid, methylarsonic acid and arsenate i n e x t r a c t s o f a i r , s o i l and water samples, To study the association of Cu w i t h organic compounds i n s o i l pore waters, Haswell e t a l .(C2110) d i r e c t l y interfaced HPLCto U.V. and ETA-AAS systems. An automatic sample i n j e c t i o n system was used which resulted i n improved pre- c i s i o n i n the determination. thermal conductivity detector i n t o a graphite furnace (417). This allowed Se species t o be determined i n C1- and SO:- r i c h "synthetic r i v e r water" samples f o r which the conductivity signals were o b l i t e r a t e d by the high concentrations Eluate from an ion-chromatograph was routed from aAtomization and Excitation 45 o f these ions.Fingerprinting o f V porphyrin and non-porphyrin species both i n terms o f molecular weight and p o l a r i t y was performed by Komlenic e t a1 .(1198) (see also Section 4.1.1.1). By using HPLC w i t h both s t e r i c exclusion and p o l a r columns, information was obtained r e l a t i n g t o such d i s t r i b u t i o n s i n heavy crude petroleum products. 1.4.4.3 Multi-element Analysis The u l t i m a t e development i n ETA must be i t s use f o r simultaneous multi-element analysis. P a r a l l e l developments by two groups using echelle spectrometers have r e a l i z e d t h i s p o t e n t i a l f o r ETA i n both absorption (C2091, C2224, C2273) and emission (770) analysis.I n the former, the combination o f a continuum source, an echelle polychromator modified f o r wavelength modulation and a dedicated minicomputer, afforded comparable detection l i m i t s t o conventional l i n e source AA while the background correction c a p a b i l i t i e s were superior t o Zeeman AA.l i n e a r dynamic range f o r each element was extended t o 5 6 orders o f magnitude, and the use o f "curtained" tubes w i t h a d d i t i o n a l gas holes a t each end reduced memory e f f e c t s . C r y Cu, Fey Mo, N i , Pb, V and Zn i n blood serum (C2364) and i n human d i e t samples (C2303) over concentration l e v e l s from sub UCJ 1-1 t o mg 1 - l . spectrometer system f o r emission measurements was also demonstrated (770). The detection l i m i t s obtained were s i m i l a r t o those obtained by the same qroups o f workers using an echel l e monochromator and sectored wheel background correction system (980). A p p l i c a b i l i t y t o p r a c t i c a l analysis was demonstrated by t h e analysis o f NBS reference materials and the determination o f C r i n u r i n e (1088). By combining the Falk e x c i t a t i o n source (C1855) (see ARAAS, 1982, 12, Ref. 425) w i t h an echelle spectrometer, Falk and colleagues (1632) achieved detection l i m i t s f o r elements o f high e x c i t a t i o n p o t e n t i a l which were superior t o those obtained by carbon furnace AES. The complexity o f the background spectra i n t h i s techni que , furnace atomization w i t h non-thermal e x c i t a t i o n , degraded detection l i m i t s f o r elements o f lower e x c i t a t i o n p o t e n t i a l s . Delsus e t a l . (758, C1836) have used combinations o f a deuterium lamp, xenon lamp, 500 channel vidicon and 1000 channel photodiode arrays i n order t o study the p o t e n t i a l o f coherent forward s c a t t e r i n g f o r multielement analysis. The The technique has been applied t o determinations o f A l , Co, The use o f t h i s (See also Section 2.6.2). Other references o f i n t e r e s t - A new graphite tube r a d i a t i o n source f o r AES : 1401. Inexpensive spectrometric t r a c e analyses : C1794.

ISSN:0306-1353    

DOI:10.1039/AA9831300037

出版商:RSC    

年代:1983

数据来源: RSC

摘要:

Atomization and Excitation 1.5 VAPOUR GENERATION In this s e c t i o n , t h e more fundamental advances i n atomization and instrumental 4546 Analytical Atomic Spectroscopy systems a r e discussed. 1.2.1.2, 3.1.1.3 and 3.1.1.4 t o g i v e a f u l l e r p i c t u r e o f the s t a t e - o f - t h e - a r t i n vapour generation. It i s p a r t i c u l a r l y encouraging t h i s y e a r t o see several mechanistic studies o f h i g h q u a l i t y which may b r i n g an a i r o f enliahtenment t o t h e clouded area o f h y d r i d e generation.The importance o f s p e c i a t i o n i s emphas- i z e d b o t h i n Sections 1.5.1 and 1.5.2, as s t u d i e s on t h e environmental chemistry o f these h y d r i de-formi ng elements and Hg a r e advanced. This Section should be read i n conjunction w i t h Sections 1 .5.1 Hydr-i-de geneyacon Although h y d r i d e generation i s n o t a new technique, considerable confusion s t i l l e x i s t s over atomization mechanisms.t h e r e i s a resurgence o f i n t e r e s t i n e l u c i d a t i n g such mechanisms. blelcher (745, C2029) have continued t h e i r e x c e l l e n t s t u d i e s (see ARAAS, 1982, - 12, Refs.C113, C256, 1453) and t h e y have now demonstrated t h a t t h e atomization o f As i n a heated q u a r t z tube i s n o t caused by thermal decomposition, b u t by c o l l i s i o n w i t h H f r e e r a d i c a l s . excess H2 w i t h O2 ( e i t h e r r e s i d u a l O2 i n t h e system o r purge gas a d d i t i o n ) a t elevated temperatures.the i n f l u e n c e o f the temperature and t h e n a t u r e o f t h e q u a r t z substrate were much more c r i t i c a l . b u t t h e r m a l l y decomposed t o o t h e r molecular species. accord w i t h work by Akman e t a l . (71). As, i t was concluded t h a t when As was generated as t h e hydride, t h e a r s i n e was decomposed on t h e g r a p h i t e surface b e f o r e t h e atomization temperature was reached, and t h a t t h e m e t a l l i c As was vaporized as dimers and tetramers which were subsequently atomized by gas-phase d i s s o c i a t i o n .Thermodynamic c a l c u l - a t i o n s were used by Agterdenbos and co-workers (C1789) t o suggest t h a t a t a l l c o n d i t i o n s d u r i n g p r a c t i c a l analysis, Se would be v o l a t i l i z e d t o some degree i n the d i m e r i c form Se2 and hence would n o t absorb Se l i n e r a d i a t i o n .t h a l e r (C2191) has attempted t o e l u c i d a t e the unusual mechanisms behind t h e hydride generation of Pb. successful h y d r i d e formation. and t h e presence of an oxidant ( e i t h e r H202 o r Cr2072-)in t h e Pb(1I) s o l u t i o n .Experiments i n d i c a t e d t h a t t h e product o f t h e i n i t i a l r e a c t i o n was Pb(O), b u t t h a t t h e h i g h hydrogen o v e r p o t e n t i a l o f Pb(0) prevents f u r t h e r r e a c t i o n w i t h BH; and t h e oxidants must a c t as d e p o l a r i z i n g agents t o a l l o w nascent Pb(0) t o r e a c t f u r t h e r . Surface e f f e c t s on the w a l l s o f the r e d u c t i o n vessel were a l s o found t o be s i g n i f i c a n t .It i s heartening t o r e p o r t t h a t t h i s y e a r Welz and These H r a d i c a l s a r e formed by r e a c t i o n o f Under c o n d i t i o n s where t h e concentration o f O2 was low, When no hydrogen was present, a r s i n e was n o t atomized These conclusions a r e i n I n a study o f mechanisms f o r t h e ETA o f Morgen- Two p e c u l i a r c o n d i t i o n s had t o be f u l f i l l e d f o r These were, extremes o f low and h i g h a c i d i t y , An understanding o f t h e mechanisms o f i n t e r f e r e n c e i s t h e f i r s t step towards t h e i r c o n t r o l .Melcher and Welz (C2030) have shown how t h e i n t e r f e r e n c e o fAtomization and Excitation 41 copper and nickel on the determination of Se were due t o preferential reduction and precipitation of the f r e e t r a n s i t i o n metal on t o which the hydride will adsorb.By working w i t h an acid environment which provided b e t t e r s o l u b i l i t y f o r the metal, the interference could be delayed o r reduced. One a l t e r n a t i v e approach t o the a l l e v i a t i o n of an interference i s t o i s o l a t e the analyte from the i n t e r f e r i n g matrix.To t h i s e f f e c t , Maher (778) devised a s e r i e s of pre- treatment procedures f o r d i f f e r e n t analytical conditions t o eliminate i n t e r - ferences on the generation of H2Te. Another a l t e r n a t i v e i s the use of masking agents, and although the mechanisms by which these operate i s s t i l l not c l e a r , some workers s t i l l find them e f f e c t i v e in d i f f i c u l t analytical s i t u a t i o n s .Kellerman (326) favoured the use of thiosemicarbazide t o eliminate the i n t e r - ferences of noble metals on As, B i , Sb, Se and Te, whereas thiocyanate and ferrocyanide were both found by Broekman (C2050) t o be e f f e c t i v e i n eliminating interferences of copper, s i l v e r and t i n on Se.A great deal of importance i s now being placed on the determination of the naturally occurring oxidation s t a t e s and molecular species of hydride forming elements, since t h e i r toxicological properties are dependent on t h e i r chemical forms. technique was described by Yu e t a l .(238, 731, 734, 855) f o r the determination of traces of As, Sb, Se and Te i n various oxidation s t a t e s in natural waters. Cotton impregnated with t h i o g l y c o l l i c acid was used f o r quantitative adsorption of the lower oxidation s t a t e s , w i t h the higher s t a t e s being determined i n the percolate. Temperature-programmed GC was used by Andreae (856) t o separate the inorganic and organometallic hydrides of As, Ge, Sb and Sn formed from seawater samples.Comparable s e n s i t i v i t i e s were found f o r electron-capture detection and quartz-tube hydride-generation AA. Ion-exchange chromatography was favoured by Love11 and Farmer (C2094) f o r the separation of A s ( I I I ) , As(V), and mono- and di-methylarsonic acid i n various aqueous environmental samples and i n human uri ne.Various separation techniques have been reported t h i s year. A novel Methods of automation which reduce the tedious nature of practical hydride generation are always of i n t e r e s t . unsegmented FI technique (782) f o r hydride generation reported in previous volumes of ARAAS (see ARAAS, 1982, 12, Ref. 1450 and 1981, lJ, Ref. C772). other automatic systems have been described t h i s reviewing year and are worthy of mention. For instance L i u e t a l . (564) described a f u l l y automated computer controlled system f o r both hydride generation and Hg determination, and an automated module t o determine As in urine was described by Renoe (270). This year sees the patenting of Astrom's Two A novel method f o r the determination of 0s by AFS was described by Rigin (776).Osmium tetroxide generation was achieved by oxidative fusion and was followed by trapping on a cooled s i l i c a column. The Os04 was then thermally desorped i n t o a48 Analytical Atomic Spectroscopy stream of H2/He and passed i n t o the heated c e l l of a non-dispersive AF spectro- meter.The hazardous nature of the compound makes the general applicability of t h i s method doubtful. Ni and Pb was described by Ming e t a l . (2046). S e n s i t i v i t i e s a t sub ng levels were reported and the apparatus was useable w i t h commercial AA instrumentation. A chloride generation method f o r the determination of Cd, 1.5.2 Mercury Determination Considerable attention has been focussed on the importance of mercury speciation i n naturally occurring samples.Several chromatographic systems have been des- cribed. Fujita (447) has described a glass reduction and phase separation vessel t o link a HPLC t o a cold vapour AA detection system, and Yao e t a l . (98) separ- ated inorganic and organic-Hg on two silica-gel-packed micro-columns.These columns contained immobilized iminoacetate groups ( f o r inorganic Hg compounds) and dithiocarbamate groups ( f o r organic Hg compounds). After separation and precon- centration, the packings were dried then placed i n t o an electrothermal atomizer. The improvements i n s e n s i t i v i t y afforded by the use of chemical collection systems have been used f o r some years.Pre-concentration of Hg on t o gold has been shown by Welz and Melcher (C2324) t o be capable of yielding detection limits below 50 pg, but only i f careful control i s exercised over a number of experi- mental variables which influence precision, s e n s i t i v i t y and blanks. A new type of s o l i d phase collector, prepared by i m e r s i n g Chromosorb in chloroauric acid solutions, was shown by Hasegawa and co-workers (456) t o be highly e f f i c i e n t a t collecting and releasing Hg from the a i r .completely released when the c o l l e c t o r was heated t o 600 OC f o r 90 s , but was retained a t room temperature. Studies of the factors affecting adsorption of Hg on t o carbonaceous materials such as carbon black, f l a k e , graphite and glassy carbon were made by Koshima and Onishi (17).The presence of oxygen and oxi- dizing agents was shown t o be detrimental t o e f f i c i e n t Hg recovery. Mercury adsorbed on t o this was The ingenuity of the human mind i s indefatigable and several novel modific- ations t o Hg determinations have been reported. The simplest, and arguably the most useful, was reported by Hon e t a l . (613) who described a long path absorp- tion c e l l through which Hg laden a i r was forced by water displacement. apparatus required no heating o r c a r r i e r gas and a s e n s i t i v i t y of 0.08 ng m1-l was Quoted. A FI procedure was described by Van Loon e t a l . (1411) u t i l i z i n g commercially available Teflon tape as a membrane phase separator. The use of ascorbic acid as reductant f o r Hg generation was described by Pikhart (1229). The 5% solution o f ascorbic acid was claimed t o give r e s u l t s comparable w i t h those obtained by u s i n g the conventional t i n ( I 1 ) chloride i n HC1 reductant and i t had the advantage of being non-corrosive. I t will be i n t e r e s t i n g t o see how widely accepted t h i s modification becomes. This

ISSN:0306-1353    

DOI:10.1039/AA9831300045

出版商:RSC    

年代:1983

数据来源: RSC

摘要:

CHAPTER 2 Instrumentation 2.1 LIGHT SOURCES R e l a t i v e l y few new developments i n l i g h t sources were r e p o r t e d i n 1983 and most pub1 i c a t i o n s merely gave supplementary i n f o r m a t i o n on t o p i c s presented a t con- ferences h e l d d u r i n g t h e previous year. c h a r a c t e r i s t i c s of s p e c t r a l lamps was made by Bezlepkin e t a l . (1699), b u t t h i s must be considered a minor c o n t r i b u t i o n i n comparison w i t h S u l l i v a n ' s author- i t a t i v e t r e a t i s e (263) on lamps and sources.A b r i e f review o f t h e design and A new s p e c t r a l source was described (C1920) f o r a p p l i c a t i o n i n source s h i f t e d Zeeman-effect AAS (see Section 2.2.1 ) . The ENL (Elektroden-Niederfrequenz-Lampe) consisted o f a sealed q u a r t z U-tube w i t h a lamp b u l b t h a t contained metal, o r halogen s a l t s o f e i t h e r As, Cd, Pb, T1 o r Zn.The temperature o f t h e lamp was r e g u l a t e d by an e x t e r n a l heater, and a metal vapour discharge was generated by a s t a b i l i z e d low frequency a.c. passed between two e l e c t r o d e s i n s e r t e d i n t o the lamp b u l b .Although a s t a b l e , i n t e n s e discharge was produced when t h e lamp was placed i n a magnetic f i e l d , i t was suggested t h a t i n e f f i c i e n t vapour t r a n s p o r t i n t h e lamp may be a l i m i t a t i o n o f t h e ENL desicy. S u l l i v a n and co-workers (787, 893, C1953, C2007, C2225) continue t o expound t h e advantages o f t h e boosted discharge lamp w i t h demountable cathode f o r AAS and AFS (see ARAAS, 1982, 12, 47).g r e a t e r l o n g term s t a b i l i t y than do EDLs and g i v e resonance l i n e r a d i a t i o n f o r As, Cd, Cu, Fe, Mg, Ni , Pb, Sb and Zn t h a t i s 10 times more i n t e n s e than HCLs and 2-3 times more i n t e n s e than EDLs (787). The authors claimed t h e lamps e x h i b i t The e l e c t r o n i c c i r c u i t t h a t a u t o m a t i c a l l y sets t h e r e q u i r e d o p e r a t i n g c u r r e n t o f h o l l o w cathode lamps i n the Pye Unicam PU 9000 AA spectrometer was described i n a UK Patent (1273).O f 7 p l u g t e r m i n a l s t h a t p r o t r u d e from t h e lamp base, 2 supply a v o l t a g e t o t h e electrodes, and 5 a r e connected t o a 4 - r e s i s t o r network and a common lead.r e s i s t o r s , and t h e o t h e r 2 r e s i s t o r s determine t h e c u r r e n t . deduced an equation which r e l a t e s t h e i n t e n s i t y o f a HCL t o c u r r e n t . The depend- ency i s i n f l u e n c e d by pressure, dimension, s e l f - a b s o r p t i o n and the r e l a t i v e importance o f two- o r one-stage c o l l i s i o n a l e x c i t a t i o n , and c o l l i s i o n a l and r a d i - a c t i v e d e - e x c i t a t i o n (see a l s o ARAAS, 1982, 12, 47).The atomic element o f t h e lamp i s i d e n t i f i e d v i a 2 o f t h e Howard e t a l . (811) S i m i l a r l y , t h e design and - 4950 Analytical A tomic Spectroscopy a p p l i c a t i o n o f temperature g r a d i e n t lamps f o r AFS and AAS, p r e v i o u s l y discussed i n conference papers, have now been described (251, 503; ARAAS, 1982, 12, 48).see a l s o C1952 and The successful f a b r i c a t i o n o f i n t e n s e microwave e l e c t r o d e l e s s discharge lamps depends on t h e o p t i m i z a t i o n o f numerous interdependent experimental v a r i a b l e s (see ARAAS, 1979, 2, Ref. 1182). A simplex scheme developed f o r production o f v o l a t i l e element EDLs was modified (1253) t o i n c l u d e two a d d i t i o n a l parameters r e q u i r e d f o r the p r e p a r a t i o n o f a Mn lamp, Optimum v o l a t i l i z a t i o n o f Mn12 was achieved by a d d i t i o n o f 30 mg o f s i l i c o n c h i p s t o t h e EDL b u l b which was maintained i n a h o t a i r environment a t 464 OC p r i o r t o and d u r i n g t h e sublim- a t i o n process on a vacuum l i n e .Emission sources normally employed f o r a n a l y t e e x c i t a t i o n i n OES have occas- i o n a l l y been used w i t h some success as s p e c t r a l sources f o r AFS (see ARAAS, 1980, 10, Ref. 1186 and 1208). Recent examples o f t h i s concept have i n c l u d e d t h e generation o f analyte fluorescence i n a lower power ICP by l i n e r a d i a t i o n from a h i g h power I C P (C1873), and the c o n s t r u c t i o n o f a fluorescence spectro- meter (C1827) based on t h e p r o d u c t i o n o f resonance fluorescence i n a HCL by r a d i a t i o n from a GDL (see Section 2.6.3).

ISSN:0306-1353    

DOI:10.1039/AA9831300049

出版商:RSC    

年代:1983

数据来源: RSC

摘要:

50 Analytical A tomic Spectroscopy 2.2 OPTICAL SYSTEMS AND DETECTORS 2.2.1 Optics Strasheim e t a l . (1035, C2004) have developed two computer-controlled d i r e c t reading spectrometers based on a 1.5 m Paschen-Runge polychromator. l i g h t i n the i n i t i a l instrument (1035) was divided by a semi-transparent mirror i n t o two beams which were d i r e c t e d towards two i d e n t i c a l holographic g r a t i n g s .Each g r a t i n g gave a dispersed spectrum, i n t h e range 120-500 nm, on opposite s i d e s of the Rowland c i r c l e , which increased t h e number of l i n e s t h a t could be measured simultaneously with the spectrometer. ment (C2004) produced t h r e e i d e n t i c a l s p e c t r a on the Rowland c i r c l e by means of t h r e e g r a t i n g s and e i t h e r two remotely positionable beam s p l i t t e r s o r one beam s p l i t t e r and one remotely positionable mirror.e i t h e r instrument could a l s o function as a dual scanning monochromator by location of a r e f r a c t o r p l a t e behind t h e entrance s l i t . wavelength coverage o f a 1.5 m Rowland mount spectrometer was improved (1409) by location of a c y l i n d r i c a l mirror a t t h e zero order image of t h e spectrum produced by the f i r s t g r a t i n g ( 1 2 M 7 5 n m ) .the Rowland c i r c l e t o ensure best r e s o l u t i o n , d i r e c t e d r a d i a t i o n t o a second g r a t i n g which produced a 450-950 nm spectrum on an unused position of t h e Rowland c i rc 1 e . The i n c i d e n t A second version of t h e instru- The authors claimed t h a t The resolution and The mirror, positioned 10 mm fromInstrumentation 5 1 Improved o p t i c a l c o u p l i n g o f an ICP emission source and a polychromator was achieved by means o f a 1 mm diameter q u a r t z o p t i c a l f i b r e (1430, C1869).One end o f the f i b r e was f i x e d t o the entrance s l i t o f t h e polychromator and t h e o t h e r end mounted 3 mm from t h e o u t e r zone o f t h e plasma. f i b r e r e l a t i v e t o t h e plasma could be v a r i e d t o t r a n s m i t r a d i a t i o n from t h e optimum r e g i o n o f t h e discharge f o r any element.compromise p o s i t i o n was selected. The p o s i t i o n o f t h e I n simultaneous analyses, a A h i g h speed slew-scanning spectrometer has been developed (C1915, C2160) which can measure 50 a n a l y t i c a l l i n e s , perform background c o r r e c t i o n and c a l i b - r a t i o n w i t h i n 1 minute.Two separate monochromators were suspended Q e r t i c a l l y i n t h e spectrometer and s p e c i a l screws w i t h small i n e r t i a mechanisms were employed i n t h e s i n e b a r systems. 5-phase stepping motor, a scan speed o f 36000 steps s - l c o u l d be a t t a i n e d i n 70 ms. A wavelength range o f 190 t o 540 nm c o u l d t h e r e f o r e be scanned w i t h i n 20 s a t a step s i z e o f 0.0005 nm. Through a combination o f t h e screws and a A r a p i d scanning spectrometer o f l i m i t e d wavelength coverage was described by M u l l i g a n e t a1 .(944) f o r measurement o f t h e M I P emission spectra o f non-metals. A scanning range o f 10 nm was achieved by l o c a t i o n o f an o s c i l l a t i n g m i r r o r (10 Hz) between the entrance s l i t and g r a t i n g o f a 0.5 m monochromator. l i m i t s obtained w i t h t h e r a p i d scan technique were comparable t o those obtained by slow scan o r s i n g l e wavelength measurement (see ARAAS, 1982, 12, Ref. 1449). Detection Other references o f i n t e r e s t - Reduction of s p e c t r a l i n t e r f e r e n c e e f f e c t s i n I C P emission spectrometry w i t h an e c h e l l e spectrometer : 941. S t r a y l i g h t from holographic and r u l e d g r a t i n g s : 1311, 1312. 2.2.2 Detectors I n a t u t o r i a l review, Busch and Benton (556) explained t h a t t h e a p p l i c a t i o n o f m u l t i p l e x approaches i n atomic spectroscopy was o f t e n l i m i t e d by u n s a t i s f a c t o r y d e t e c t o r c h a r a c t e r i s t i c s .I n s i n g l e element systems , frequency-division and Hadamard transform methods have n o t been e n t i r e l y s a t i s f a c t o r y due t o t h e shot- noise behaviour o f p h o t o m u l t i p l i e r tubes.d e t e c t o r systems based on wavelength-divi s i o n mu1 ti p l e x i n g w i t h a r r a y d e t e c t o r s show most promise, provided d e t e c t o r s a t u r a t i o n and blooming can be avoided. McGeorge e t a l . (234) reviewed the s t a t u s o f d e t e c t i o n systems f o r multielement I C P analysis.The advantages and l i m i t a t i o n s o f photographic emulsions and PMT detectors were compared t o those o f photo-emission and semi-conductor imaging systems, l i n e a r photodiode arrays and v i d i c o n d e t e c t o r s . The PMT remains t h e most s u i t a b l e and w i d e l y used d e t e c t o r f o r s p e c t r o m e t r i c a n a l y s i s , b u t o f the The authors concluded t h a t m u l t i p l e5 2 Analytical Atomic Spectroscopy various optical image detectors currently available, application of photodiode arrays i s growing in importance, especially for ICP studies.array i s often preferred t o other image detectors mainly because i t has better U . V . response than silicon vidicons and charge-coupled devices (1289).The photodiode Silicon intensified target (SIT) vidicons have been successfully applied in molecular cavity emission analysis (1249) and for spatially resolved spectral studies (C2392). The SIT image intensifier developed by Ishida e t al. (C1895) had a microchannel plate and a MgF2 window that allowed operation t o 120 nm. The authors claimed that the detection sensitivity was equal t o or better than that of a PMT.Poor noise characteristics have previously limited the applic- ation of S I T detectors in trace ICP analysis (see ARAAS, 1980, 10, Ref. 844). However, Brockaert and co-workers (C1818) have shown that ICP detection limits can be improved by a factor of 5 on average i f the SIT i s cooled t o -20 OC. wavelengths above 26C-270 n m , detection limits were similar t o or only slightly poorer than those obtained with an EM1 9789 QB PMT.however, the SIT detection limits were u p t o an order of magnitude worse t h a n the PMT. For A t lower wavelengths, Improvements in the operation of an AF resonance detector (see ARAAS, 1980, - 10, Ref. 1208) were reported by Human e t a1 . (C1893). The detector was based on the selective absorption and fluorescence o f atomic spectral lines in the after- glow of a pulsed low pressure discharge.elements was achieved by use of a f l a t cathode in the sputtering cell instead of a hollow cathode. Optimum signal t o background ratios for emission from the afterglow were obtained through careful control of the discharge gas flow. The pressure and nature of the f i l l e r gas were found t o influence the magnitude of Mo fluorescence in a hollow cathode resonance detector (1529) developed for intracavi ty spectroscopy.A continuum source AA spectrometer was described (802) that employed a N2-sheathed circular air/C2H2 flame or air/H2 flame as a resonance detector. The fluorescent radiation was measured with either a solar- blind PMT or a broad response PMT f i t t e d with a Scholt UG 1 f i l t e r , depending on whether the resonance l i n e was below or above 300 nm. Enhanced atomization of refractory Other references of interest - Carbon rod atomizer as a resonance detector for ICP emission : C1959. Interface for Reticon diode array : 797. Photoelectric image dissector for measurement of vertical spectral distr- bution in an ICP : 1538.

ISSN:0306-1353    

DOI:10.1039/AA9831300050

出版商:RSC    

年代:1983

数据来源: RSC

摘要:

52 Analytical Atomic Spectroscopy 2.3 BACKGROUND CORRECTION More information on the characteristics o f the Smi th-Hieftje background correct-Instrumentation 53 - ion procedure f o r AAS (351, 786, C1776, C2122, C2212) was provided by workers from Instrumentation Laboratory Inc. (see ARAAS, 1982, 12, 48). Correction f o r background absorbance up t o 3 was i l l u s t r a t e d by the atomization of 50 pg Cd i n the presence o f 200 pg NaCl (786, 1381), and simultaneous measurement of Cd and Pb in seawater (C2212).accurately compensate f o r spectral -1 ine overlap. measurement of Sb (786) and Se (1381) i n solutions t h a t contained per cent levels of nickel. ly a loss i n s e n s i t i v i t y of about 50% f o r most elements (C1381). A similar approach t o the S m i t M i e f t j e system was reported by Baranov e t a l .(52). making spectral measurements a t HCL currents of 10 mA and 30 mA s a t i s f a c t o r y background correction was achieved f o r the determination of A u , Fe and Zn i n nickel potassium and sodium s a l t solutions. I t was claimed t h a t the Smith-Hieftje system can a l s o Examples given included the The main disadvantage of the correction procedure i s apparent- By Besides the publication of patent applications from Hitachi (1502) and Perkin- Elmer (445, 579), few papers on Zeernan-effect background correction instrument- ation appeared in 1983.An i n t e r e s t i n g development from Grun-Optik (C1920) was the design of a new lamp f o r saurce-shifted Zeeman-effect AAS (see Section 2.1).Preliminary studies indicated t h a t optimization of the d.c. transverse magnetic f i e l d was necessary t o achieve best s e n s i t i v i t y . evaluation of the time-resolved AAS s i g n a l , i t was possible t o estimate the degree of Zeeman self-absorption. I t was claimed t h a t , by I n plasma emission spectrometry, the nature of the spectrum close t o an analyte line must be known f o r s a t i s f a c t o r y selection of background correction points.In spectrometers without a slew-scanning monochromator , d i s c r e t e spectral scans can be obtained i f an optical beam s h i f t i n g system i s located behind the entrance s l i t . Eckhoff and co-workers (783) used a stepper motor- control led quartz r e f r a c t o r plate f o r single point, off-peak background cor- rection with a 4-channel MIP spectrometer.A similar device has been applied f o r background correction w i t h an echelle polychromator (402). rotation torque motor i s used t o give rapid o s c i l l a t i o n of a r e f r a c t o r p l a t e , wavelength modulation background correction can be achieved w i t h a phase- s e n s i t i v e lock-in detection system (see a l s o Section 1.4.4.3).of this procedure f o r background correction i n simultaneous mu1 tielement analysis by ETA-AES have been i l l u s t r a t e d (815; approach was a l s o applied i n MIP-GC (C2037) t o give a 100-fold improvement i n analyte s e l e c t i v i t y , but w i t h a corresponding degradation i n detection l i m i t due t o a decrease in SNR.of the emission i n t e n s i t y next t o the analyte l i n e , measured by means of a multiple e x i t - s l i t system, was preferred since i t gave similar s e l e c t i v i t y t o wavelength modulation, b u t w i t h b e t t e r detection l i m i t s . When a limited The advantages see also ARAAS, 1982, E, 51). The An a l t e r n a t i v e procedure which involved subtraction54 Analytical Atomic Spectroscopy Further development o f a square-wave wavelength modulation system (see ARAAS 1979, 9, 35) has enabled frequencies up t o 160 Hz t o be u t i l i z e d f o r e f f e c t i v e background correction i n continuum source-excited FAFS. i n t e n s i t y modulation, the square-wave chopper provided two methods o f double modulation (1048) t h a t could adequately compensate f o r the spectral interference o f K emission a t 404.4 nm on Pb fluorescence a t 405.8 nm. I n combination w i t h

ISSN:0306-1353    

DOI:10.1039/AA9831300052

出版商:RSC    

年代:1983

数据来源: RSC

摘要:

54 Analytical Atomic Spectroscopy 2.4 AUTOMATED SAMPLE INTRODUCTION Several novel procedures f o r the automatic i n t r o d u c t i o n o f l i q u i d s have been described. generator was used t o deposit samples as 150 pm diameter d r o p l e t s . The formation o f small c r y s t a l s when the microdrops were d r i e d reduced the chemical i n t e r f e r - ence o f c h l o r i d e s a l t s on Pb determination and sulphate s a l t s on Au determination.An aerosol-deposition method was a l s o used (562) f o r sample i n t r o d u c t i o n i n an o n - l i n e analyser developed f o r t h e measurement o f Au i n the process l i q u o r s o f a g o l d recovery p l a n t . An automatic g r a p h i t e probe sample i n t r o d u c t i o n system f o r ETA-AAS was devised by L i t t l e j o h n e t a l .(989) (see a l s o Section 1.4.4.2). A conventional auto-sampler deposited volumes up t o 20 p1 on t o t h e probe head i n s i d e t h e atomizer tube f o r d r y i n g and ashing o f samples. Removal o f the probe from the tube p r i o r t o t h e atomization stage, w i t h subsequent r e i n t r o d u c t i o n a f t e r a constant temperature was a t t a i n e d , allowed sample v a p o r i z a t i o n i n a h i g h temperature environment.c o n t r o l l e d via t h e furnace programmer. I n ETA-AAS improved p r e c i s i o n was achieved (779) when a microdrop A c t i v a t i o n o f t h e probe, by means o f a solenoid, was A m o d i f i c a t i o n t o t h e procedure f o r operation o f the GMK pueumatic n e b u l i z e r (C1755) i n ICP a n a l y s i s s u b s t a n t i a l l y improved l o n g term d r i f t and reduced memory e f f e c t s between samples.Production o f t h e aerosol was stopped f o r a p e r i o d t o p r e c o n d i t i o n t h e g a s - l i q u i d i n t e r f a c e p r i o r t o a n a l y s i s o f a new sample. It was a l s o p o s s i b l e t o s e l e c t a backflush stage and a u t o m a t i c a l l y i n t r o d u c e i n t e r n a l standards when required.Since t h e performance o f t h e stop-flow GMK n e b u l i z e r was s i m i l a r t o t h e o r i g i n a l n e b u l i z e r w i t h respect t o d e t e c t i o n l i m i t s , p r e c i s i o n and p a r t i c l e handling, s i g n i f i c a n t advantages i n t h e a n a l y s i s o f con- c e n t r a t e d and t u r b i d samples were expected w i t h t h e modified o p e r a t i n g regime.Considerable savings i n a n a l y s i s time were achieved (507) through t h e a p p l i c a t i o n o f an automatic o n - l i n e d i l u t i o n system developed f o r use w i t h a GMK n e b u l i z e r . The d i l u e n t and sample streams were transported and mixed by a two-channel p e r i - s t a l t i c pump p r i o r t o formation o f t h e aerosol.A semi-automatic procedure f o r d i s c r e t e sample n e b u l i z a t i o n i n FAAS was described (1116) t h a t allowed e i t h e r a i r o r a s u i t a b l e s o l v e n t t o pass through t h e system between samples. The l a t t e r mode gave b e t t e r SNR f o r organic solvents.Instrum en tatio n 5 5 An e l e c t r o n i c photocoupler was used (607) t o i n i t i a t e the i n t e g r a t i o n sequence o f an AA spectrometer during d i s c r e t e sample i n t r o d u c t i o n .t o be s u i t a b l e f o r any sample s o l u t i o n regardless o f o p t i c a l transparency. generator was developed (233) f o r r e p e t i t i v e i n t r o d u c t i o n o f 20-50 111 droplets i n t o the nebulizer o f a 3-electrode d.c.plasma, An i n d i v i d u a l drop s i z e d e l i v - e r y precision o f 5% o r b e t t e r was obtained. analyte emission i n t e n s i t y was equivalent t o continuous nebulization. The authors suggested t h a t the r e p e t i t i v e drop generator reduced the tedium o f measuring nebulization e f f i c i e n c y i n the d i s c r e t e sampling mode when a l a r g e number o f small volumes must be reproducibly introduced i n t o the plasma.precision s i m i l a r t o t h a t obtained w i t h continuous nebulization was achieved (755) when a r e c i r c u l a t i n g nebulizer and spray chamber were used t o transport 1 m l samples i n t o an I C P .I n contrast, poor s i g n a l s t a b i l i t y was encountered (30) w i t h an u l t r a s o n i c nebulizer constructed f o r batchwise i n t r o d u c t i o n o f 300 111 samples. The t r i g g e r was found A For droplets greater than 27 u l , Signal A flow i n j e c t i o n manifold was modified (606) t o permit automatic e x t r a c t i o n o f metal ions i n aqueous samples i n t o MIBK w i t h APDC (see ARAAS, 1981, 11, Refs. 1346 and 1835). i n j e c t o r loop. No dispersion o f the e x t r a c t volume (110 ~ 1 ) occurred and increases i n s e n s i t i v i t y o f 15- t o 20-fold were claimed f o r Cu, N i , Pb and Zn. An automatic f l o w i n j e c t i o n e x t r a c t i o n system was also described by Yasuda e t a l . (C2040) f o r Zeeman-effect FAAS.i n t o the main aqueous sample stream. hydride generation system (782 and see ARAAS, 1982, 12, Ref. 1450) was a l t e r e d by Van Loon and co-workers (C1931) (see also Section 1.5.1) t o avoid high con- sumption o f borohydride and excessive production o f H2. mixing the reductant w i t h acid, NaBH4 and sample solutions were i n j e c t e d i n t o water streams which passed t o a mixing block f o r hydride production.The organic phase was vented i n t o an air/C2H2 flame an The organic solvent and dithizone were i n j e c t e d A previously described flow i n j e c t i o n Instead o f c o n t i n u a l l y A microprocessor-controlled graphite rod f o r i n t r o d u c t i o n o f l i q u i d o r s o l i d samples i n t o an I C P was described (833, C1832). Programs w r i t t e n i n BASIC and Machine Code were used t o p o s i t i o n the rod a t d i f f e r e n t heights below the I C P c o i l f o r drying, ashing and atomization o f samples.Other references o f i n t e r e s t - Apparatus f o r measuring the weight o r volume of solutions atomized i n AAS o r ICP-OES : 1503. Aspects o f f l o w i n j e c t i o n methods f o r AAS : 1047. ETA cup f o r preconcentration and vaporization o f HPLC e f f l u e n t i n t o I C P : C2335. HPLC-ETA i n t e r f a c e f o r AAS determination o f Cu complexes : C2110. Improvement i n I C P spectrometer response time f o r signals produced by ETA56 Analytical A tomic Spectroscopy sample i n t r o d u c t i o n : C2322. Modified Babington nebulizer f o r hydride generation and l i q u i d sample i n t r o d u c t i o n i n t o I C P : 1394. Patent f o r sample i n t r o d u c t i o n f o r AAS and LC : 1473. Serni-automatic module f o r hydride generation-AAS : 270. S o l i d sampler f o r Zeeman AAS : 566.

ISSN:0306-1353    

DOI:10.1039/AA9831300054

出版商:RSC    

年代:1983

数据来源: RSC