Methods for Improving the Sensitivity in Atom Trapping Flame Atomic Absorption Spectrometry: Analytical Scheme for the Direct Determination of Trace Elements in Beer HENRYK MATUSIEWICZ* AND MARIUSZ KOPRAS Politechnika Poznan�ska, Department of Analytical Chemistry, 60–965 Poznan� , Poland. E-mail: Henryk.Matusiewicz@fct.put.poznan.pl A method is described for the atomic absorption (AA) cally result in a further improvement in both sensitivity and determination of Ag, Cd, Cu, Fe, In, Mn, Pb, Tl and Zn in detection limit.Surprisingly, the possibility of combining these beer using an ‘integrated atom trap’ system mounted on a techniques has only recently been independently investigated.8,9 standard AA air–acetylene flame burner. A new design of The investigation by Turner and Roberts8 into the use of a atom trapping technique that would exceed the operational single silica tube atom trap at high tube obscuration resulted capabilities of existing arrangements (a water-cooled single or in the introduction of a new type of hybrid atom trap, the dual silica tube or a double-slotted quartz tube) and permit slotted tube water-cooled atom trap (STWCAT), which conconstruction of an ‘integrated trap’ was investigated.A sists of a commercially available slotted tube atom trap (STAT) significant improvement in detection limit was achieved and a single silica tube water-cooled atom trap (WCAT), compared with that obtained using either of the above atom fabricated in-house. It was found that the STWCAT performed trapping techniques separately.Rapid, accurate analyses can very well in comparison with the other two tubes, showing be achieved using continuous aspiration. The concentration very high sensitivity with excellent precision. The analytical detection limits were 3.0, 5.0, 1.2, 4.0 and 0.1 ng ml-1 for Cu, sensitivities were discussed for Cd and Pb in river water and Fe, Mn, Pb and Zn, respectively, using a 2 min in situ sewage eZuent samples.In a previous paper,9 we described preconcentration time. The relative standard deviations are of the use of a laboratory-made quartz ‘integrated atom trap’ the order of 3.0–6.0% for this technique. Basic analytical (IAT) structure to enhance the sensitivity in flame atomic performance characteristics are also given for Ag, Cd, In and absorption spectrometry (FAAS). Tl using various designs of atom trap. The designs studied ‘Conventional’ atom trapping AAS involves the collection include both slotted tube and single silica tube water-cooled and in situ preconcentration of the analyte in a flame system atom traps.containing a silica tube cooled by water circulation followed by an atomization period when gas (air, argon, nitrogen, etc.) Keywords: T race element determination; integrated atom trap is forced into the silica tube to remove the water and thus system; flame atomic absorption spectrometry; sensitivity cause heating of its surface.In this study, an alternative means increase; beer of atomization for some elements is suggested, involving a change in flame composition by altering the gas5acetylene The most common form of atom trapping technique employs ratio prior to re-atomization of the analyte, so that the hot a tube with an aperture, often a slot to admit the vaporized and reducing tip of the blue zone touches the silica surface, sample (analyte), mounted above the burner of a flame atomic eVecting atomization of the analyte. This is termed the ‘flame absorption spectrometer and on its optical axis.The sample is alteration technique’. nebulized into the flame. There are two modes of operation of The importance of several metals (As, Cd, Cu, Fe, Pb, Zn) atom trapping systems where the analyte is concentrated ‘onin beer is now well recognized. Many governmental organiza- line’. In the most commonly used mode, the vaporized sample tions have established maximum concentration limits for many flows continuously through an atom trapping slotted quartz trace elements. Several atomic spectrometric techniques have tube.1 The gain in sensitivity over a conventional long-path been studied and recommended for the determination of trace burner is of the order of 3- to 5-fold for easily atomized elements in beer samples, including FAAS,10–13 electrothermal elements.This improvement is attributable to the increased atomic absorption spectrometry (ETAAS)12–18 and inductively residence time of the atoms in the optical path.The alternative coupled plasma atomic emission spectrometry (ICP-AES).19 approach depends on first collecting the analyte atoms on the Trace amounts of Cd, Cu, Pb and Zn have been determined exterior wall of a water-cooled single or dual silica tube by in beer by AAS with the use of slotted quartz tubes.20 The condensation over a period of time; this is then followed by same technique has been used to determine Pb in beer.21 The their rapid release when the tube temperature is raised.2 In the main advantage of ICP-AES is its multi-element capability. latter mode, the gain in sensitivity can be of the order of ETAAS has the advantage of lower detection limits for many 10- to 50-fold.elements in comparison with the other techniques mentioned, This technique has attracted considerable interest over the and thus preconcentration steps may not be required.However, years and the enhancement eVect using two main types of ICP-AES and ETAAS equipment is more costly to purchase atom trapping was subsequently confirmed by several workand to maintain for many laboratories than FAAS systems. A ers.3,4 More recently, Turner et al.5 optimized parameters for convenient and inexpensive method of preconcentration of determining Pb and Cd by a dual ‘bent’ water-cooled silica trace elements with minimal analyst intervention would enable tube.This was further developed by Ellis and Roberts6,7 for trace elements in beer liquids to be measured fairly rapidly by As, Sb, Cu, Mn and Hg. means of FAAS. A combination of the advantages of the water-cooled silica tube with those of a double-slotted quartz tube should theoreti- This paper reports on the results from a number of experi- Journal of Analytical Atomic Spectrometry, November 1997, Vol. 12 (1287–1291) 1287ments using the IAT system with the flame alteration technique for solutions containing several metals.For comparison, the same solutions were also analyzed without the IAT system, but with various designs of atom trap. The purpose of this work was to develop a practical and sensitive method for the direct determination of trace amounts of Ag, Cd, Cu, Fe, In, Mn, Pb, Tl and Zn in beer by atom trapping FAAS using an IAT. The sensitivities obtained with the use of this system coupled with FAAS were similar to those obtained by ETAAS.EXPERIMENTAL Apparatus A Carl Zeiss Jena (Jena, Germany) Model AAS 3 flame atomic absorption spectrometer was used with an IBM-PC compatible computer. The sampling rate for the PMT signal was 10 Hz. Signals were processed with in-house software (Turbo Pascal Version 7.0) to extract the transient peak heights, areas and Fig. 1 Integrated atom trap (IAT) structure attachment on the burner peak times. The operating conditions for the analysis are listed head: 1, slotted tube atom trap (STAT); 2, single silica tube; 3, water– in Table 1.Hollow cathode lamp currents and slit-widths argon control system; 4, burner; 5, modified holder (holder arm); 6, were as recommended by the manufacturer. Deuterium lamp handle; 7, clamping screw; 8, mounting peg; and 9, burner clamp background correction was used throughout. (bracket). Three designs of atom trap were investigated. A watercooled single or dual silica tube atom trap was arranged as previously described3 and mounted on a 10 cm burner in such dimensions (8 cm×2 mm wide).The length of the quartz tube is limited by the atomizer compartment. To prevent the AAS a manner as to permit the system to be vertically and laterally adjusted in the flame. The tubes had an od of 3 mm and an id quartz optics from contacting hot gases escaping from the quartz tube, the quartz tubTAT) has two slots on both of 1 mm for water cooling. The distance between the two tubes was 1 mm.A four-way rotary glass valve allowed water or sides so that the hot gases are vented vertically instead of horizontally towards the quartz windows. With both clamps argon (or nitrogen) to pass through the silica tubes. A double-slotted quartz tube (modified metal holder–clamp- in position, the observation (analytical) section of the single or dual silica tube can be held inside the slotted quartz tube. ing system Model ACT-80 atom concentrator tube, Varian Associates, Palo Alto, CA, USA)3 was installed on a standard The height of the silica tube(s) could be raised or lowered inside the STAT.The IAT system was mounted over an air– 10 cm air–acetylene burner. The design permits changeover from analysis with the modified ACT-80 to that for a acetylene burner on a mounting bracket, which permitted calibrated movement both vertically and horizontally. conventional flame in a few seconds. An IAT was designed and constructed in this laboratory; it The automatic flame ignition system was disabled for this study. The fixed position of the modified ACT-80, single consisted of a combination of a single or dual silica tube and a double-slotted quartz tube atom trap (STAT) (Fig. 1). A or dual silica tube trap and IAT interfered with the autoignition probe. 10 cm pathlength burner head was slightly modified and fitted with two rigid metal clamps. One clamp was capable of holding A cooling thermostat was used for cooling the water, its internal pump circulating water via PVC tubes connected to the modified holder of the ACT-80 within the flame used for the STAT, the other was designed to hold a single or dual the single or dual silica tube atom traps.The continuously flowing cooling water kept the surface of the silica tube(s) at silica tube on to the burner head. The ACT-80 had two lengthwise cuts on opposite sides of the tube angled at 120° below 100 °C, which allowed the analyte atoms to condense on the surface of the tube.to each other, relative to the axis of the tube. The longitudinal slot under the tube (flame entrance slot) was enlarged The single or dual silica and slotted quartz tubes were coated with lanthanum to prevent devitrification and to (12.5 cm×8 mm wide) and the upper slot had the original Table 1 Standard operating conditions for the integrated atom trap (IAT) system Parameter Ag Cd Cu Fe In Mn Pb Tl Zn Wavelength/nm 328.1 228.8 324.8 248.3 304.0 279.5 217.0 278.8 213.9 Spectral bandpass/nm 0.3 0.3 0.3 0.2 0.3 0.2 0.3 0.2 0.2 Background correction Yes Yes Yes Yes Yes Yes Yes Yes Yes Lamp current/mA 4 4 4 5 5 5 5 5 5 Flame type* Air–C2H2 Air–C2H2 Air–C2H2 Air–C2H2 Air–C2H2 Air–C2H2 Air–C2H2 Air–C2H2 Air–C2H2 Flame conditions† Preconcentration Stoichiometric Lean Lean Stoichiometric Stoichiometric Stoichiometric Lean Lean Lean in situ Atomization Stoichiometric Rich Rich Stoichiometric Stoichiometric Stoichiometric Rich Rich Rich Water-cooled silica tube atom trap position Above the burner/mm 5 5 5 5 5 5 5 5 5 Tube obscuration (%) 30 30 30 30 30 30 30 30 30 STAT tube–burner 5 5 5 5 5 5 5 5 5 gap/mm * Nebulizer uptake rate for all elements, 5 ml min-1.† Air flow rate 475 l h-1, acetylene flow rate 50 l h-1 (fuel-lean flame); air flow rate 475 l h-1, acetylene flow rate 80 l h-1 (fuel-rich flame); air flow rate 475 l h-1, acetylene flow rate 70 l h-1 (stoichiometric flame); 10 cm slot burner. 1288 Journal of Analytical Atomic Spectrometry, November 1997, Vol. 12improve the silica surface properties (increasing the surface Determination of Ag, Cd, Cu, Fe, In, Mn, Pb, Tl and Zn Levels Present in Beer Samples area) by continuous aspiration via the burner nebulizer of 0.5 and 1% m/v lanthanum solutions, respectively, for 15 min. All samples were analyzed for levels of Ag, Cd, Cu, Fe, In, The tubes were then conditioned by allowing them to heat up Mn, Pb, Tl and Zn using the STAT, the single and dual silica for 15 s.The tubes were re-coated after approximately 50 runs. tubes discussed in earlier work3 and the IAT apparatus. The results obtained from the three diVerent atom traps were then compared and contrasted. The accuracy of the method was Reagents checked by calculating the percentage recovery of elements added to the beer sample solution. Standard solutions of the elements were prepared from Titrisol solutions (Merck, Darmstadt, Germany), containing 2 g l-1 of the element.Serial dilutions were made with high-purity dis- RESULTS AND DISCUSSION tilled water from a Heraeus Bi18 (Heraeus, Hanau, Germany) system in order to prepare working solutions. The lanthanum The results of this study relate to two distinct aspects of the chloride solution used to coat the quartz tubes (0.5 and 1% overall investigation: atom trapping techniques to increase the m/v) was prepared from a 10% m/v lanthanum chloride sensitivity of FAAS, and its application to practical analysis.solution supplied by Alfa Inorganics (Ward Hill, MA, USA) Although these are related, there are developmental details for as a releasing agent for use in atomic absorption. each that are independent. Hence, it is convenient to discuss the development of the atom trap and analysis technique separately. Sample Preparation Samples of commercial beers were purchased at local stores Evaluation of Atom Trap Designs and were de-gassed by filtration (Whatman No.4 filter-paper) The initial study consisted of varying some parameters to find and analyzed undiluted.The samples were treated with the optimum sensitivity for each of the three designs of atom HNO3 and H2O2 to avoid clogging the burner by direct trap. However, substantial optimization of the preconcen- aspiration of the samples into the flame. Beer solutions were tration parameters was not undertaken, as this information subjected to UV irradiation for 4 h in the presence of HNO3 was readily available from a review paper4 (and references and H2O2, which were added to the beer solutions prior to cited therein) pertaining to trace metal detection by atom UV digestion.22 A UV digester, Model R-6 (Mineral, Warsaw, trapping and in situ preconcentration for FAAS. Poland), was used for all digestions.The parameters used for the optimization of the IAT for the Four diVerent commercial brands of beer were investigated. determination of trace elements are shown in Table 1.The height of the silica tube above the burner, the percentage obscuration of the light beam and fuel flow rate were found Principle of the Atom Trapping Procedure to have significant eVects on the sensitivities of the elements studied. One general conclusion was that, while the conditions In order to collect (trap) the analyte, each sample solution was conventionally aspirated via the nebulizer/burner directly into for diVerent elements were optimized at diVerent heights of the silica tube above the primary reaction zone within the flame, the flame for a pre-determined collection time (1–5 min) in which an IAT system had been installed above the burner slot.in all cases the highest signals were obtained when the light path was close to the tube surface. Increased sensitivity was The lower edge of the silica tubes (both the water-cooled and STAT) was fixed 5 mm above the burner top. The height of also achieved by lowering the tube closer to the burner slot.In this work, 5 mm was the lowest height that could be used, the burner was adjusted so that the tubes obscured 10–50% of the incident light beam. Sample solutions were aspirated given the present tube clamping device on the burner for the single silica tube and STAT. In addition, despite the higher into the flame using the flame alteration technique. During the trapping process, a fuel-lean flame was used; flow rates of air enhancement factors for the smaller gaps, distances closer than 5 mm cannot be recommended, at least when the burner system (475 l h-1) and acetylene (50 l h-1) were adjusted.During this collection period, a continuous flow of cooling water permitted used in this study was allowed to heat the tube continuously, owing to the danger of overheating the burner head. In analyte atoms to condense (adsorb) on the surface of the tubes during solution aspiration. After this collection period, argon agreement with Turner and Roberts,8 we also observed that the sensitivity of all the elements studied using the single silica was passed through the tubes to remove the cooling water rapidly and a pulsed fuel-rich flame was immediately used for tube was similar to that obtained using the dual silica tube system. No analytically useful results were obtained with the releasing; flow rates of acetylene (80 l h-1) were adjusted (the hot and reducing tip of the blue zone touches the silica surface dual tube design and, consequently, it was not investigated further.The single silica tube was therefore chosen for further eVecting volatilization/atomization of the analyte), so that no soot deposited on the cooled silica tubes during the atomization study. It was demonstrated that although the relationship is not, in general, particularly linear, a longer aspiration time period (a rich flame at flow rates of acetylene above 80 l h-1 caused soot formation, wherein the signal-to-noise ratio increased the analytical signal.A reasonable aspiration time per sample in a routine laboratory would be about 2 min. This became unacceptably high). The tubes rapidly heated in the rich flame, generating a transient atomic absorption signal as time was chosen to investigate the analytical performance of the IAT system with respect to linearity, sensitivity, precision the analyte atoms were released (volatilized) from the surface.Peak height absorbance was measured during a 15 s read and detection limit. No diVerent tube coating materials were examined, but the lanthanum coating was applied primarily period. Peak area measurements gave poor precision, which could be attributed to the relatively large width of the signals as a result of practical laboratory experience. A comparison of detection limits is given in Table 2 for (2–8 s). Deuterium lamp background correction was applied to eliminate non-atomic absorption and scattering.conventional FAAS, ETAAS and with three atom trap designs. For the elements studied, the IAT technique improved detection Under the same conditions, a series of standard solutions were aspirated and analyzed. The concentrations of metals in limits considerably when a 2 min collection time was used. Detection limits obtained with a 2 min collection time the samples were obtained by the regression equation of the calibration graphs. are low enough to suggest that this procedure provides a Journal of Analytical Atomic Spectrometry, November 1997, Vol. 12 1289Table 2 Comparison of detection limits (DL)* for elements obtained using various atom traps (ng ml-1) Conventional FAAS STAT Silica tube atom trap† IAT‡ ETAAS§ Precision,|| Precision, Precision, Precision, Element DL X¶ % RSD DL X % RSD DL X % RSD DL X % RSD DL X Ag 30 1 5.8 10 3 5.0 2.0 15 6.3 0.6 50 5.5 0.2 150 Cd 15 1 6.1 5 3 6.2 1.0 15 6.3 0.5 30 5.1 0.08 187 Cu 40 1 4.3 16 2.5 3.3 7.0 5.7 4.5 3 13.5 3.9 0.6 67 Fe 55 1 4.9 22 2.5 4.1 11 5 5.0 5 11 4.7 0.4 137 In 350 1 7.3 110 3.1 6.5 50 7 7.8 10 35 5.9 6 58 Mn 20 1 3.2 10 2 3.0 2.5 8 3.9 1.2 16.5 3.0 0.3 67 Pb 150 1 6.3 55 2.7 5.9 15 10 6.6 4.0 37.5 6.0 1 150 Tl 300 1 8.1 150 2 7.1 20 15 8.5 10 30 6.1 5 60 Zn 12 1 5.4 3.0 4 4.9 0.5 25 6.1 0.1 120 5.0 0.05 240 * Detection limit defined by 3 blank criterion (n=9).† 2 min collection time for water-cooled single silica tube atom trap.‡ 2 min collection time for IAT technique. § 10 ml. ¶ Enhancement (improvement) factor. || RSD of nine replicate aspirations at analyte concentrations 20-fold above calculated detection limit. viable alternative to the use of ETAAS methodology for the Analysis of Beer Samples determination of these (volatile) trace metals. To illustrate the use of the IAT system in practical application and to assess the quality of the results obtained with the Flame Alteration Technique developed methodology, real beer samples were analyzed.Samples of beer of diVerent brands from Poland purchased in The eVect of flame conditions on the trapping and release of glass bottles in the retail market were analyzed in duplicate. the elements was studied by varying the fuel flow rate. In these The accuracy of this method of analysis can only be assessed experiments, the richness of the flame was restricted to a level by an examination of the recovery data, as no certified reference such that no carbon deposited on the tube.In the lean flame, materials were available. For this purpose, calibration was the fuel supply was reduced until the primary reaction zone achieved using the method of standard additions. The results became small and was bright blue, as opposed to the situation for the beer samples analyzed using the IAT are given in where the blue zone touches the silica surface in the fuel-rich Table 3. Comparison of standard additions with the slope of experiments.The same air flow rate (475 l h-1) was maintained the calibration graphs showed that there were no significant in both series of experiments. The sensitivities of atom-trapping interferences from the sample matrices, and element spikes AAS for Cd, Cu, Pb, Tl and Zn appeared to be dependent on added before the UV digestion procedure were quantitatively the flame conditions; therefore, a marked increase in signals recovered. Therefore, analyses can be performed using a direct was obtained when the flame was altered.The best sensitivity calibration graph. Although no interference study was under- was obtained when a lean flame (acetylene flow rate of taken, to eliminate possible matrix eVects, only the method of 50 l h-1) was used for trapping (collecting) these elements and standard additions was used to obtain accurate results. The a fuel-rich flame (acetylene flow rate of 80 l h-1) was used for precision of replicate determinations is typically better than releasing (atomizing).In this novel case the signal is sharp 10% RSD (n=2). and rapid. The detection limits obtained with a 2 min collection time The sensitivity of the atom-trapping AAS technique for Ag, are low enough to suggest that the procedure for the determi- Fe, In and Mn appeared to be virtually independent of the nation of trace elements in beer using the IAT is a viable flame conditions. The use of a fuel-rich flame when analyte alternative to the standard ETAAS method for this determi- species are being released is apparently not very important.nation. The usual advantage of the high sample throughput of The results for collection in a lean flame and release in a rich the conventional FAAS technique cannot be claimed for the flame were not very diVerent from those observed when both IAT procedure; the time per sample is similar to that of the trapping and release were carried out in a stoichiometric flame (acetylene flow rate of 70 l h-1).ETAAS procedure. In a 3 month period of intensive work, not Table 3 Analysis of commercial beer samples* Concentration†/ng ml-1 Description Ag Cd Cu Fe In Mn Pb Tl Zn Pils Premium ND‡ ND 80±3 16±1 ND 164±6 95±6 ND 70±4 Premium ND ND 90±4 45±2 ND 110±4 101±6 ND 92±5 10,5 ND ND 105±5 30±2 ND 100±4 105±6 ND 105±6 BCC ND ND 70±3 15±1 ND 135±5 65±5 ND 65±4 * Polish beer: LECH Browary Wielkopolski S.A. † Mean±standard deviation (n=2).‡ ND=Not detected. 1290 Journal of Analytical Atomic Spectrometry, November 1997, Vol. 12Table 4 Polish legislation, literature values and results of this work Financial support by the Poznan� University of Technology is for the levels of elements studied gratefully acknowledged (Grant No. BW31–524/97). Polish legislation*/ Literature This work/ Element ng ml-1 values/ng ml-1 ng ml-1 REFERENCES Cd 4 ND† 1 Watling, R. J., Water SA, 1977, 3, 218. Cu <100 11–130 70–105 2 Lau, C., Held, A., and Stephens, R., Can.JSpectrosc., 1976, Fe <5000 70–700 15–45 21, 100. Mn 100–164 3 Matusiewicz, H., Sturgeon, R., Luong, V., and MoVatt, K., Pb <200 9–68 65–105 Fresenius’ J. Anal. Chem., 1991, 340, 35, and references cited Zn <1000 7–70 65–105 therein. 4 Matusiewicz, H., Spectrochim. Acta Rev., 1997, 52B, in the press. * Polish Norm, Beer, No. PN-89 A-79098. 5 Turner, A. D., Roberts, D. J., and Le Cor, Y., J. Anal. At. † ND=Not detected.Spectrom., 1995, 10, 721. 6 Ellis, L. A., and Roberts, D. J., J. Anal. At. Spectrom., 1996, 11, 259. 7 Ellis, L. A., and Roberts, D. J., J. Anal. At. Spectrom., 1996, one tube failed, so the inference is that the apparatus is 11, 1063. 8 Turner, A. D., and Roberts, D. J., J. Anal. At. Spectrom., 1996, reasonably robust. 11, 231. Table 4 compares the results obtained in this work with 9 Matusiewicz, H., and Kopras, M., paper presented at XXIX literature values. The Cu, Fe, Pb and Zn levels in the Polish Colloquium Spectroscopicum Internationale, Leipzig, Germany, beers are comparable to other published values.All of the 1995, p. 297 (Tu-B 239). samples are well below the maximum levels allowed by Polish 10 Borriello, R., and Sciaudone, G., At. Spectrosc., 1980, 1, 131. legislation. 11 Hergenreder, R. L., At. Spectrosc., 1991, 12, 74. 12 Skurikhin, I. M., J. Assoc. OV. Anal. Chem. Int., 1993, 76, 257. 13 Li, Y., Van Loon, J. C., and Barefoot, R.R., Fresenius’ J. Anal. CONCLUSIONS Chem., 1993, 345, 467. 14 Wagner, H. P., Dalglish, K., and McGarrity, M. J., J. Am. Soc. The IAT system has been evaluated for analytical applications Brew. Chem., 1991, 49, 28. to real beer samples. This approach is considerably more 15 Srikanth, R., Ramana, D., and Rao, V., Bull. Environ. Contam. sensitive than conventional FAAS for the determination of T oxicol., 1995, 54, 783. 16 Cervera, M. L., Navarro, A., Montoro, R., and Catala, R., trace elements and provides a viable alternative to the conven- J. Assoc. OV. Anal. Chem., 1989, 72, 282. tional ETAAS technique. Therefore, this method can be 17 Cervera, M. L., Navarro, A., Montoro, R., de la Guardia, M., recommended and widely used when ETAAS is not available. and Salvador, A., J. Anal. At. Spectrom., 1991, 6, 477. The types of sample most suited to analysis by this procedure 18 Wagner, H., J. Am. Soc. Brew. Chem., 1995, 53, 141. are relatively simple aqueous matrices and those where a 19 Matsushige, I., and de Oliveira, E., Food Chem., 1993, 47, 205. reasonable volume (5–10 ml ) of solution is available. The 20 Li, H., Lian, J., and Du, J., Fenxi Ceshi T ongbao, 1991, 10, 51. 21 Lee, M., and Brown, A., Brewers’ Guardian, 1985, 13. method is restricted to elements atomized in an air–acetylene 22 Wahdat, F., and Neeb, R., Fresenius’ Z. Anal. Chem., 1989, flame and, in particular, to the more volatile elements such as 335, 748. Cd, Pb or Zn. The major advantages of this procedure are its relative simplicity, low cost and that the IAT system is also Paper 7/04407K readily decoupled. The main disadvantages of the IAT system Received June 23, 1997 and, in general, the atom trapping FAAS technique, are Accepted August 5, 1997 that they are limited to relatively few elements and there is significant consumption of sample during the trapping step. Journal of Analytical Atomic Spectrometry, November 1997, Vol. 12 1291