Collection and Determination of Metal Contaminants in Gases A Review URSULA TELGHEDER*a AND VLADIMIR A. KHVOSTIKOVb aUniversity of Duisburg, Department of Instrumental Analytical Chemistry, L otharstrasse, 1, D-47057 Duisburg, Germany bInstitute ofMicroelectronics T echnology and High Purity Materials RAS, Chernogolovka, Moscow distr., 142432 Russia SUMMARY OF CONTENTS In some cases, particle counters are used for the determination of particulates in gases.7,20 Introduction The most suitable methods for collection are filtration, Determination of Solid Contaminants in Gases impaction and impingers.Further possibilities are electrostatic Filtration precipitation and nuclear condensation.21 Dissolution of the Particles on Filters Impactors Filtration Impingers Analytical Methods Filtration is the most frequently used method because of the References ease of operation, low cost, and the availability of pure filter materials. Different filter materials have been investigated.Keywords: Metal contamination; gases; analytical methods; Usually, membrane filters with a pore size ranging from review 0.0511,22 to 5 mm23–31 and cellulose filters32 have been used. Other materials used are PTFE and polycarbonate. Because of their high mechanical strength, and despite their high chemical blanks, glass-fibre filters have been widely INTRODUCTION applied.33–38 Polystyrene-fibre filters,26 quartz fibres34,39 and In dealing with the problem of the determination of metal silver membranes27 have also been investigated.contaminants in gases it is important to consider the following The advantages of membrane filters are the good separation points: Which gases will be analysed? What type of trace of particles of different sizes, a high pore density and a rapid metals are the contaminants? How can the different types of filtration. On the other hand, the disadvantages are the low metal contaminants be collected, enriched and separated? loading capacity and the rapid clogging.The element contents Which analytical methods will be used? of the blanks are lower, but trace element determinations by Most publications deal with the determination of contami- ETAAS andNAA have shown that the purity of the membranes nants in air. Additionally, other gaseous components have can vary from box to box, even if the filters are from the same been analysed such as HCl,1–5 Cl2,6,7 high-purity volatile manufacturer.29 inorganic hydrides (SiH4, GeH4), halogenides (SiCl4, GeCl4, The glass-fibre filters have a high loading capacity and are POCl3, BBr3 , BCl3), organometallic compounds (Et2Zn, Et2Te, inexpensive.However, the pore size is not defined and the Me2Cd), and organochlorosilanes (Me2SiCl2, MeSiHCl2),8–13 filters have a low strength. pure gas dust from coal power stations14 and incinerators, or All filters for the measurement of particles in air have to waste gas.15–17 Nevertheless, the determination of particles in fulfil particular requirements. Apart from the degree of depos- air is the most important and will be systematically and ition, the flow resistance of the uncovered filter and its change extensively pursued because of the guidelines18 in Germany.with increasing coverage must also be taken into consideration. Generally, in gaseous compounds metals could be solid Furthermore, attention must be paid to the factors leading to particles, liquids and gaseous contaminants.The following changes in the filter material caused by the measuring object, expressions have to be defined: (i) Particulate compounds: e.g., the humidity, the amount of air, or particles of aggressive among these all dusty compounds passing the filter system compounds. Finally, the filters should be selected for a good will be subsumed. (ii) Compounds that are able to pass the prior interpretation. filter system: by this definition, all compounds passing the filter system are included as well as gaseous and liquid Dissolution of the Particles on Filters compounds. For chemical analysis the particulate matter collected on the filter has to be dissolved, except for some physical methods DETERMINATION OF SOLID CONTAMINANTS such as X-ray fluorescence28,40 and NAA.24,29,36 Membrane IN GASES filters have to be decomposed by different mixtures of acids in closed and open systems. The most commonly used mixtures A large number of measuring methods exist for the registration of the suspended-particulate concentration in gases due to the are those of hot HNO3 and HCl,22,23 or HNO3 , HClO4 and HF (with a temperature programme from 80 to 230 °C),41 or VDI-Guideline 246318 in Germany. The procedure mainly used in practice is the high-volume sampler principle.19 This is a HNO3 and HF.After digestion, the acids are evaporated and the residue is dissolved in diluted HNO325 and concentrated sampling method with a very high rate of air flow for the determination of particulates in ambient air.In this process HNO3 only.29 If glass-fibre filters are used, the sample may be digested by the air is sucked from below by a diffuser working as an aerodynamic rectifier. Thus, a regular, distributed, laminar a mixture of HNO3 and HClO4, followed by heating, evaporation, and dissolution of the residue in HCl33 or in a mixture current of air impinges on the filter element. The amount of sample is sufficient to carry out a gravimetric of HNO3, HF, HCl and H2O2 .34,38 The digestion can also be carried out using potassium chlorate and HNO3 with gentle determination of mass as well as specific analysis.Journal of Analytical Atomic Spectrometry, January 1997, Vol. 12 (1–6) 1boiling on a hot-plate followed by the addition of HCl,35 In addition, a special Venturi separator for small amounts of dust has been investigated.66 The TU� V Rheinland sampling dissolution in HNO3,39 and the extraction of the metals using a Soxhlet apparatus.42 Polystyrene filters have been dissolved system67,68 was developed with parts of well known measuring techniques.Field tests with frit wash bottles as absorption in xylene.26 devices showed a good and in some cases a better efficiency than more complicated absorption apparatus such as the jet Impactors absorber or Venturi scrubber. The passing compounds are sucked through a heated tube and divided into several by-pass Size-fractionated aerosol samples were obtained by using a Battelle cascade impactor.43 streams.The compounds are then supplied to parallel absorption systems. A mixture of 5% HNO3 with 3% H2O2, and Wagner and Georgii44 developed a five-stage impactor which separates the particulate matter into five fractions (diameter aqua regia [HCl–HNO3 (3+1)] have been used as absorption solutions for metallic compounds. For the determination of 6.3–1.0 mm). Each stage is made of a PVC funnel connected to a brass tube.Nozzles with different diameters are located at mercury, a 3% KMnO4 solution in 10% H2SO4 has been found to be more efficient. the bottom of the tube. Sneddon and co-workers45–52 have described an impactor, directly connected to a commercial Bruckmann et al.69 used two impingers cooled to -12 °C and filled with 25% HNO3 as well as a further impinger for electrothermal atomizer. The sampling process is often performed with cascade impactors of various designs.15,53–55 The condensation.The impingers were connected by glass pipes to sampling equipment following VDI 2463 Sheet 7.70 most widely used cascade impactor is the Anderson sampler, which has the advantage of being simple and inexpensive.53,54 In order to precipitate suspended particles, Scharf71 suggested a procedure and described an instrument to determine The collecting discs, for example, are made of Plexiglas; the back-up filters are deep bed filters of glass fibre.The back-up the content of the suspended particles quantitatively. The amount of precipitated suspended particles was increased by filters of each fraction are extracted with HNO3 followed by acid filtration through XAD-4 amberlite resin. The solutions the addition of lightly condensing solvents to the gas being analysed followed by cooling the mixture. The particles were are then analysed by ETAAS. Weiswler and Gund55 described the chemical analysis of separated by a cooled impinger made of high-purity quartz.single aerosol particles collected on a nine-stage cascade impactor. The separate parts (sulfate, nitrate, chloride and ammonium ions) were characterized by a combination of ANALYTICAL METHODS microchemical precipitation and subsequent interpretation by scanning electron microscopy. Several methods for the analysis of particles for metals have been described, including AAS,4,15,22,23,25,29,30,33–35,41,42,44–53,70 AFS,47,72 XRF,28,40,43,55 NAA,22,24,29,36 ICP- Impingers AES,15,26,27,34,37,38,41 including sealed ICP-AES5–7,9–11,73–76 as well as ICP-MS,77 MIP,78 anodic stripping voltammetry,32,79 Filters have been mainly used for the precipitation of suspended particles in gases.Unfortunately, the amounts of elements in ion chromatography (IC),31 differential-pulse polarography, energy dispersive X-ray spectrometry (EDX) and laser micro- the blank solution of the filters were sometimes found to be high and varied from filter to filter.29 Therefore, the detection mass analysis (LAMMA).14 The most frequently used technique for the determination limit of the procedure involving gas filtration is limited by the quality of the filters.Impingers are more suitable for an of trace metals is atomic absorption, especially ETAAS. This method possesses the extreme sensitivity that is required extensive precipitation of suspended particles without contamination, especially for a low flow rate gas stream.In this section, without the need for time-consuming preconcentration methods. It is reasonably rapid and does not require excessively different sampling systems are exemplary characterized. (i) The single-line sampling system, based on the US expensive instrumentation. Pickford and Rossi25 constructed an automatic laboratory sampling system for the determination Environmental ProtectionAgency (EPA) method.56–59 Initially, the sample, which is sucked through, passes a cyclone lying of Pb in atmospheric particulates by ETAAS after acid dissolution. This system permits a large number of samples to be outside the exhaust channel and then a plane filter for the precipitation of particles, after which the compounds are analysed in the minimum time without operator attendance.A passive sampler designed to simulate pulmonary retention caught in several wash bottles. A similar system is the WEP (Wet-Electrostatic-Precipitator)-Sampling-Train. Here, a Wet- of sub-micrometre particles was described by Tennant and Rees.30 The device can accumulate lead from ambient air over Electrostatic-Precipitator is used instead of the cyclone followed by a plane filter.60 a period of 4 weeks.The analysis is carried out by ETAAS. A major advantage of the electrothermal atomizeris the feasibility (ii) The condensation nucleus collector developed by the Technical University of Lyngby (Denmark).This collector uses of the direct analysis of metal compounds collected by impaction. 45–52 There are several applications using ETAAS connec- a filter holder (following the guidelines in the German VDI 2066 Sheet 261 and a separator for compounds that are able ted with cascade impactors.44,80 Liang et al.47 reported the use of an impactor–ETAAS system for the direct determination of to pass the filter system (condensation nucleus collector57). The measuring arrangements described by Gutberlet62 and Cu, Fe, Mg, Pb, Sn and Tl in air at ng m-3 levels as well as a laser atomic fluorescence system for determination at pg m-3 Mu�ller63 consist of a filter holder, also following VDI 2066 Sheet 2.61 The outlet pipe is connected to many wash bottles.levels. The potential of atomic fluorescence with a tantalum coil For the precipitation of metals which may pass the filter system, a beam absorber has been developed at the University atomizer for direct analysis of gases was demonstrated for Fe determination in Ar.72 The detection limit obtained was of Hamburg.64 The sample gas is absorbed in a liquid using a pump and a Venturi tube which allows an extensive mass 4 ng l-1.Baaske and co-workers4,81 described the introduction of transfer between the gaseous and liquid phase. Two other prototype separators65 for such compounds are also based on gaseous samples into an electrothermal atomizer using a modified by-pass–back-flush–balancing injection system and this model: the first is the condensation origin absorber, which consists of a wash bottle with a frit, and the second is the later using an automated sampling system.The detection limit of Fe in gaseous hydrogen chloride was found to be electro-absorber, which is based on the origin absorber but also contains two platinum electrodes. 0.7 ng ml-1. 2 Journal of Analytical Atomic Spectrometry, January 1997, Vol. 12Table 1 Survey of measurements of metals in air and gases Element Matrix Sample collection Sample treatment Technique Ref.Air Impaction–ETAAS 49 Cd Fe Air High-volume sampler, low-volume Dissolution of the filter in xylene ICP-AES 26 sampler, polystyrene-fibre filter Fe HCl Direct introduction of the HCl into ICP-AES 3 the ICP-AES system Fe HCl ETAAS 4 Fe Ar AFS with Ta coil 72 Fe Ar MIP-AES 78 Fe Air Impaction–ETAAS 51 Hg Air Adsorption on PbS AES 80 Hg Air Impaction–ETAAS 50 P Ar Sealed ICP-AES 76 Pb Air Polycarbonate filters coated with a Atomization and excitation in the ICP-AES 27 thin film of high-purity Ag high-temperature plasma produced by the electrical vaporization of the Ag film Pb Air Impaction–ETAAS 52 Pb Suspended Membrane filters Acid digestion in 50% HNO3 , ETAAS 25 particles heating at 100 °C for 30 min Pb Air Membrane filters with a pore size of Membrane filters wet-ashed in HNO3 ETAAS 30 1.45 mm Pb Air Nuclepore filters with a pore size of Digestion in crucibles with a mixture AAS 23 5 mm of 8 mol l-1 HNO3 and concentrated (12 mol l-1 ) HCl (5+1) at 90 °C As, P Ar Sealed ICP-AES 75 Te, Se Atmospheric High-volume sampler, collection on Removal of interfering elements by ETAAS 33 aerosol glass-fibre filters cation exchange, digestion in samples concentrated HNO3 and 60% HClO4 , dissolution of the residue in 0.05 mol l-1 HCl As, Hg, Se Waste gas Nuclepore filters with a pore NAA 84 diameter of 0.4 mm Cd, Cu, Mn Aerosols Impaction–ETAAS 48 Cd, Cu, Mn Air Impaction on an electrothermal ETAAS 45 atomizer Cr, Mn, Pb Suspended High-volume sampler, glass-fibre ETV–ICP 37 particles filters As, Cd, Co, Suspended Glass-fibre and quartz filters Dissolution in a mixture of HNO3 , ETAAS 34 Tl particles HF, HClO4 and H2O2 Al, Fe, Pb, Air Impaction on glass-fibre filters XRF 21 Si Cd, Cu, Pb, Waste gas The sampler is based on The sampler is led to a vaporizer and Differential-pulse 39 Zn vaporization/condensation mixed with a strong oxidizing acid polarography principles (65% HNO3 ) Cd, Cu, Pb, Air Celotate cellulose filters Ashing in a high vacuum at low Anodic stripping 32 Zn temperature, adding concentrated voltammetry HNO3 and HF, heating for 1 h at 120 °C Cr, Fe, Mn, HCl ETAAS 81 Ni Cu, Mn, Ni, Fog; Fan collector; Zn Fog droplets Impact on PFTE strings (diameter HPLC 31 0.3 mm) Cd, Fe, Mn, Air Five-stage impactor ETAAS 44 Pb Al, C, Ca, Cl2 Sealed ICP-AES 7 Cu, Sn Al, Fe, Mg, Semiconductor- Adsorption of the trace metals on an Elution with a mixture of HCl, ICP-AES 85 Si, Zn grade gases adsorbing material HNO3, H2O As, Cd, Cu, Suspended High-volume sampler, various types Digestion with KClO3, 20% HNO3 , Flame AAS 35 Pb, Zn particles of glass-fibre filters simmering for 15 min on a hot-plate Ca, Mg, Na, Fog Ion chromatography 31 NH4+, K Cd, Cu, Fe, Airborne High-volume sampler, glass-fibre Soxhlet extraction; acid digestion Flame AAS 42 Mn, Pb particulates filters with a mixture of HNO3, H2SO4 , HClO4 , at 120°C for 2 h; autoclave digestion, HNO3 at 50°C for 1 h Cr, Cu, Fe, HCl Polycarbonate filters Digestion with HCl–HNO3 ETAAS 22 Mn, Ni As, Cd, Cr, Air Impinger, filling solution: 25% Digestion in a mixture of HNO3, ETAAS 69 Cu, Ni, HNO3 ; membrane filter, 1.2 mm HClO4 , HF with increasing Pb pore size tempetures, 80–200°C Journal of Analytical Atomic Spectrometry, January 1997, Vol. 12 3Table 1 (continued) Element Matrix Sample collection Sample treatment Technique Ref.Air Precipitation on glass-fibre and Cr, Cu, Fe, XRF 28 Mn, Ni, Zn membrane filters Cu, Fe, Mn, Air Impaction–ETAAS 47 Pb, Sn, Tl or LAFS As, Cd, Cr, Air Impinger, different procedures 84 Hg, Ni, Pb, Se Al, C, Ca, Cr, HCl Sealed ICP-AES 5 Fe, Ni, Sn Cd, Co, Cr, Airborne Cascade impactor, collection on Extraction with 1 mol l-1 HNO3 at ETAAS 53 Cu, Ni, Pb, particulates Plexiglas 80 °C for 1 h, filtration over Zn Amberlite XAD-4 C, Fe, Ge, AsCl4 Sealed ICP-AES 10 Mg, Mo, Ni, Sn, V Al, Ca, Cr, Cl2 Sealed ICP-AES 6 Cu, Fe, Mg, Mo, Ni, Sn Al, Ca, Cr, Suspended Glass-fibre and quartz filters ICP-AES 34 Cu, Fe, Mg, particles Ni, Pb, Zn Al, Cd, Cr, Filter Millipore filters Dissolution in concentrated HNO3 in ETAAS 29 Cu, Fe, Mn, a PTFE screw-cap dissolution bomb Ni, Pb, Zn Br, Mg, Mn, HCl Polycarbonate filters NAA 22 Na, Sb, Sn, Te, Ti, Zn Co, Cr, Fe, Filter Millipore filters NAA 29 Mn, Na, Sb, Sc, Se, Zn Be, Cd, Cr, Airborne High-volume sampler; low-volume HNO3–H2O2 digestion; aqua regia ICP-AES 38 Cu, Fe, Mn, particulates sampler; glass-fibre filters and quartz- digestion; HNO3–HClO4 digestion Ni, Pb, V, fibre filters Zn Ag, Co, Mn, Pure gas dust Cascade impactor LAMMA 14 Mo, Nb, Ni, Pb, Sn, Ti, V, Zn As, Cd, Cr, Waste gas Impinger, filling solution: quartz Digestion: HNO3–HF, heating ETAAS 15 Cu, Hg, Ni, cotton, two-steps: acid washing ICP-AES Pb, Sb, Se, solutions, absorption solution: 5% V, Zn HNO3+3% H2O2 , aqua regia Al, Au, Co, NAA 24 Cr, Cs, Cu, La, Mn, Sc, Se, V, Zn As, Al, Bi, Suspended Filter made of air filter cardboard XRF 40 Ca, Cd, Cu, particles Cr, Fe, K, Mn, Ni, Sb, Sn, Si, Ti, Pb, Zn Al, Ca, Cd, Air High-volume sampler; membrane Digestion with a mixture of HNO3 , ICP-AES 41 Co, Cr, Cu, filters with a pore size of 1.2 mm HClO4 ; temperature programme ETAAS Fe, Mg, Mn, 80–230 °C Ni, Pb, Sb, Sr, Ti, V, Zn As, Ba, Ca, Air High-volume sampler; glass-fibre NAA 36 Cd, Ce, Co, filters Cr, Cs, Fe, La, Lu, Mo, Ni, Rb, Sb, Sc, Se, Sm, Sn, Ta, Yb, Zn Al, As, Ca, Air Battelle cascade impactor in six EDXRF PIXE 43 Cu, Fe, K, particle-size fractions Mn, Si, Ti, Pb, Rb, Sr, Zn Ag, Al, Bi, Gases Concentration of the metals on a Dc-arc 8 Ca, Cd, Co, carbon collector by vacuum spectrographic Cr, Cu, Fe, distillation method Mg, Mn, Mo, Na, V, Zn, Ni, Pb, Sb, Ti 4 Journal of Analytical Atomic Spectrometry, January 1997, Vol. 12Table 1 (continued) Element Matrix Sample collection Sample treatment Technique Ref.Air Nine-stage cascade impactor AAS Metals 55 IC Many Semiconductor- The gas is carried by an argon stream ICP-MS 2 elements grade gases into the ICP-MS system Chiou and Manuel33 determined, for example, Te and Se comparison of the impulse sequence of the spectral lines with calibrating filters. after removing interfering elements by cation exchange. Flame AAS has also been used.23,35,42 A disadvantage of PIXE can also be used for the determination of trace contaminants43 because of the detection sensitivity obtained flame AAS is that direct analysis of solids is difficult.On account of its multi-element capability, AES has been widely by the higher ‘signal-to-bremsstrahlung’ relationship; X-rayinduced photoelectron spectroscopy has been used for the used to determine a number of different elements in a sample. Because of high sensitivity, fewer interferences and multi- chemical analysis of single aerosol particles.The main advantage of NAA is the simple sample prep- element capability, ICP-AES has become an ideal technique5 –7,9–11,15,26,27,34,37,38,41,73–76 for trace element aration. Faix et al.22 have determined particle-bound trace metals in highly pure hydrogen chloride by NAA. Trace determination. Standardized techniques have been mostly used. Sugimae elements in ambient air24,36 and the concentrations of several elements in the vapour-phase in the stack of a coal-fired power and Mizoguchi26 described the direct determination of Fe in airborne particulate matter by direct nebulization of suspen- plant83 have been determined in the same way.Occasionally, electrochemical procedures, such as differen- sions into the ICP. A similar procedure for the direct determination of Pb in urban particulate material has been carried tial-pulse polarography and, particularly, anodic stripping voltammetry, have been used for the determination of metals.39 out using thin silver films electrically vaporized from membrane filters.27 A number of workers have used simultaneous multi- Larjava and Kauppinen39 developed a sampler to collect gaseous metals and to fractionate the particles into three element analysis by conventional ICP-AES.15,34,38,41 Schram3 described a method for direct introduction of reactive gases classes.The sampler is based on vaporization/condensation principles. into an ICP-AES system. The gaseous sample is led into a mixing chamber, positioned under the aerosol tube of the ICP- Table 1 gives a general survey of the field of analysis of air and gases for metals and their compounds including AES torch.Regulation of the gas flow is effected by the by-pass–back-flush method or the peristaltic pump. applications. The method of sealed ICP, developed by Jacksier, Barnes and co-workers5–7,9–11,73–76 seems very promising for the direct analysis of reactive gases. The main advantage of this method REFERENCES is that the plasma is excited inside a closed container so that the direct contact of aggressive gases with the parts of the 1 Yin, I.H., Denyszyn, R. B., and Bandy, T., paper presented at Microcontamination, West Conference, Anaheim, 1989. analytical system is excluded. These workers demonstrated the 2 Hutton, R. C., Bridenne, M., Coffre, E., Marot, Y., and possibilities of the method for the analysis of arsine, silane, Simondet, F., J. Anal. At. 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Received April 29, 1996 58 Schwitzgebel, K., Coleman, R. T., Collins, R. V., Mann, R. M., and Thompson, C. M., T race Element Study of a Primary Copper Accepted September 17, 1996 6 Journal of Analytical Atom