Anal. Chem. 1998, 70, 2639-2645
Simultaneous Determination of Volatile Metal (Pb, Hg, Sn, In, Ga) and Nonmetal Species (Se, P, As) in Different Atmospheres by Cryofocusing and Detection by ICPMS Christophe Pe´cheyran,† Christophe R. Quetel,‡ Fabienne M. Martin Lecuyer,† and Olivier F. X. Donard*,†
Laboratoire de Chimie Bio Inorganique et Environnement, Universite´ de Pau et des Pays de l’Adour, EP 132, Helioparc, F64000, Pau, France, and Institute of Reference Materials and Measurements, European Commission, Retieseweg, B-2440 Geel, Belgium
A sensitive method for multielemental speciation analysis of volatile metal and metalloid compounds in air has been developed. The analytes are sampled simultaneously in the field by cryofocusing on a small glass wool-packed column at -175 °C. Detection is performed in the laboratory by low-temperature GC hyphenated with ICPMS. Oxygen addition in the carrier gas was used to reduce interferences originating from the presence of volatile carbon-containing species in the samples. Plasma stability during analysis was monitored continuously by internal standardization (Xe). This system provides routine absolute detection limits of 0.06-0.07 pg (as Pb) for tetraalkyllead species (Me4Pb, Et4Pb), 0.2 pg (as Sn) for tetraalkyltin species (Me4Sn, Et4Sn), 0.8 pg (as Hg) for mercury species (Hg0, Me2Hg, Et2Hg), and 2.5 pg (as Se) for selenium species (Me2Se). This instrumentation makes it possible to collect small air sample volumes and has been successfully applied to the determination of volatile metal and metalloid species in the atmosphere in urban and rural locations. Qualitative application in the semiconductor industry is also reported with regard to the detection of arsenic (ASH3, tert-butylarsine), phosphorus (PH3, tert-butylphosphine), alkylindium, and gallium species. It is now generally accepted that many volatile and nonvolatile metal compounds are distributed in the environment through the atmosphere.1 While trace metals usually enter the atmosphere in the form of aerosols, they can also be present in gaseous forms resulting from natural biogenic processes or direct anthropogenic inputs. Despite a sharp decrease in the use of leaded gasoline in recent years, volatile alkyllead species are still used as an antiknocking agent in some European countries and are still commonly present in both urban and rural areas.2,3 Elemental mercury vapors are emitted to the atmosphere by anthropogenic activities and natural †
Universite´ de Bordeaux I. Institute of Reference Materials and Measurements. (1) Nriagu, J. O. Nature 1989, 338, 47-49. (2) Hewitt, C. N.; Harrison, R. M. Anal. Chim. Acta 1985, 167, 277-287. ‡
S0003-2700(97)00961-X CCC: $15.00 Published on Web 05/15/1998
© 1998 American Chemical Society
processes. Both sources play a key role in the biogeochemical cycle of this element in urban and remote areas.4,5 Many metal and metalloid compounds may also form volatile species through natural biogenic processes and contribute to significant gaseous fluxes of metals and metalloids to the atmosphere. This has recently been illustrated for selenium after its volatile forms emitted by plants or oceanic environments were identified.6-8 The disposal of wastes in landfills may also lead to the formation of volatile species of tin, mercury, arsenic, antimony, tellurium, and bismuth.9 A growing area of interest concerns industrial hygiene-related aspects, particularly in the semiconductor industry, where highly toxic gases containing As, P, In, and Ga are used in the epitaxial growth of crystals. To better understand the biogeochemistry of trace elements and their effect on health, the concentrations of the volatile species in the atmosphere at trace levels must be measured. The most common technique for the determination of volatile metal species involves sampling on one or more solid sorbents at room temperature.2,10-14 The sorbents are usually species-selective and do not allow the simultaneous collection and later determination of several species from different metals. Cryogenic trapping of analytes has the advantage of collecting species without alteration,7,13,15-17 but this technique has been little developed (3) Hewitt, C. N.; Harrison, R. M. Environ. Sci. Technol. 1987, 21, 260-266. (4) Schroeder, W. H. In Mercury pollution Integration and synthesis; Watras, C. J., Huckabee, J. W., Eds; Lewis Publishers: Boca Raton, FL, 1994. (5) Gustin, S. M.; Taylor, G. E.; Leonard, T. L.; Keislar, R. E. Environ. Sci. Technol. 1996, 30, 2572-2579. (6) Amouroux, D.; Donard, O. F. X. Geophys. Res. Lett. 1996, 23, 1777-1780. (7) Jiang, S. G.; Robberecht, H.; Adams, F. Appl. Organomet. Chem. 1989, 3, 99-104. (8) Ko ¨lbl, G. Mar. Chem. 1995, 48, 185-197. (9) Feldmann, J.; Hirner, A. V. Int. J. Anal. Chem. 1995, 60, 339-359. (10) Bzezinska, A.; Van Loon, J.; Williams, D.; Oguma, K.; Fuwa, K.; Haraguchi, I. H. Spectrochim. Acta 1983, 38B, 1339-1346. (11) Schroeder, W. H.; Jackson, R. Chemosphere 1984, 13, 1041-1051. (12) Ballantine, D. S. Jr.; Zoller, W. Anal. Chem. 1984, 56, 1288-1293. (13) Bloom, N.; Fitzgerald, W. F. Anal. Chim. Acta 1988, 208, 151-161. (14) Nerin, C.; Pons, B.; Martinez, M.; Cacho, J. Mikrochim. Acta 1994, 112, 179-188. (15) Reamer, D. C.; Zoller, W. H.; O’Haver, T. C. Anal. Chem. 1978, 50, 14491453.
Analytical Chemistry, Vol. 70, No. 13, July 1, 1998 2639
because large volumes of air must be sampled and because of problems associated with ice-clogging of the trap. Nevertheless, this technique has been shown to successfully trap a large range of volatile metal species such as Pb, Sn, Hg and Se.9,17 Most successful speciation techniques combine gas chromatography and atomic spectrometry (AAS, AES, ICPMS) for the specific sensitive detection. The multielemental detection capabilities of plasma sources used for atomic emission detection or for elemental mass spectrometry have recently received increasing interest for the determination of organometallic species.18 GCICPMS has proved to be a highly effective tool for the determination of organometallic compounds,19-24 but very few applications are reported on the multielemental determination of volatile metal species in air by GC-ICPMS.9,25 To our knowledge, volatile metal species have never been determined simultaneously in the atmosphere in urban, rural, and industrial locations with a multielemental approach. This paper describes the analytical developments made to determine volatile metal and metalloid species in different atmospheres. An automated field cryotrapping device was developed to collect air samples at -175 °C. Samples are then flash-desorbed in the laboratory in a cryogenic trapping-gas chromatographyICPMS (CT-GC-ICPMS) system to determine volatile species. The analytical procedure combines the advantages of field preconcentration, gas sample introduction into the detector, and sensitive multielemental detection. Xe and O2 were added directly to the plasma of the ICPMS to act as an internal standard and reduce the interference originating from the presence of organic compounds in the samples. Optimization of the operating conditions is discussed. The technique was used to determine volatile metal species in urban and rural areas in and around Bordeaux, France, and results of qualitative applications in industrial environments of the semiconductor industry (Thomson CSF, Orsay, France) are given. EXPERIMENTAL SECTION Reagents. Individual stock solutions (10 µg of metal/mL) of organometallic standards of Se (Me2Se), Sn (Me4Sn and Et4Sn), Hg (Me2Hg and Et2Hg), and Pb (Me4Pb and Et4Pb) were obtained by diluting the pure organometals (Strem Chemicals, Octel France for the alkyllead species) in pure methanol (spectroscopy grade, Merck). Mixed working solutions were prepared daily in degassed methanol for a final concentration for each species ranging from 0.5 to 500 ng of metal/mL. Solutions were stored in Teflon septum-sealed glass vials and kept in ice at -4 °C during analysis to maintain stability of the species. (16) Radziuk, B.; Thomassen, Y.; Van Loon, J. C.; Chau, Y. K. Anal. Chim. Acta 1979, 105, 255-262. (17) Jiang, S. G.; Chakraborti, D.; Adams, F. C. Anal. Chim. Acta 1987, 196, 271-275. (18) Byrdy, A. A.; Caruso, J. A. Environ. Sci. Technol. 1994, 28, 528A-534A. (19) Van Loon, J. C.; Alcock, L. R.; Pinchin, W. H.; French, B. J. Spectrosc. Lett. 1986, 19, 1125-1135. (20) Chong, N. S.; Houk, R. S. Appl. Spectrosc. 1987, 41, 66-74. (21) Kim, A. L.; Foulkes, M. E.; Ebdon, L.; Hill, S. J.; Patience, R. L.; Barwise, A. G.; Rowland, S. J. J. Anal. At. Spectrom. 1992, 7, 1147-1149. (22) Prange, A.; Jantzen, E. J. Anal. At. Spectrom. 1995, 10, 105-109. (23) De Smaele, T.; Verrept, P.; Moens, L.; Dams, R.; Sandra, P. Fresenius’ J. Anal. Chem. 1996, 355, 778-782. (24) Moens, L.; De Smaele, T.; Dams, R.; Van Den Broeck, P.; Sandra, P. Anal. Chem. 1997, 69, 1604-1611. (25) Feldmann, J.; Cullen, W. R. Environ. Sci. Technol. 1997, 31, 2125-2129.
2640 Analytical Chemistry, Vol. 70, No. 13, July 1, 1998
Figure 1. Gas sampler used for volatile metal and metalloid species collection.
Calibration was done with elemental mercury standards by sampling, with an airtight microsyringe, the headspace above 100 g of Hg0 placed in a glass bottle fitted with a Teflon septum cap.13 All gases (Ar, He, O2, and Ar/Xe mixture) were 99.995% pure and were supplied by AGA (Toulouse, France). Sampling Device and Analytical Apparatus. (i) Field Air Sampling. Air samples were collected in the field on a routine basis with a portable, automated, laboratory-made gas sampler (Figure 1). Samples were filtered with a 0.1-µm filter to remove aerosols, dried with a cryogenic water trap set at -20 °C, and cryocondensed at -175 ( 1 °C in the sampling column (170 mm long, i.d. 5 mm) packed with silanized glass wool (Supelco, pesticide grade). The temperature of the sampling column was electronically controlled and selected to avoid trapping of oxygen (boiling point, -183 °C). The aspiration flow rate was 0.8 L/min. The volume of air required for quantitative analysis is directly related to the concentration of the analytes in the atmosphere and varied in our study from a few liters to 100 L. Due to the high sensitivity of our analytical apparatus (see below), air volumes ranging from 10 to 25 L were found to be sufficient for the quantitative determination of tetraalkyllead and mercury species in rural and urban areas. After cryocondensation, the field column was sealed with homemade Teflon stoppers and stored at -190 °C in a dry atmosphere cryocontainer (Voyageur 12, L’air Liquide). Quantitation of the analytes was performed by CT-GC-ICPMS (see below) after their flash desorption from the field column in a stream of helium and refocusing in a U-shaped chromatographic column immersed in liquid nitrogen (Figure 2). All tubes and connections in the air sampler are made of Teflon (PFA, Bioblock) and were washed with concentrated HNO3 and rinsed with Milli-Q water prior to use. New columns were soaked in a 10% HNO3 solution for 2 h under ultrasonic conditions and rinsed thoroughly with Milli-Q water. The traps were then dried under laminar bench flow for 2 days at ambient temperature and silanized with pure hexamethyldisilazane. Columns were then heated for 10 min at 300 °C while purified He flowed through them and stored in double clean plastic bags until field sampling. To test for the complete recovery of volatile species and the possibility of interconversion during storage, a mixed solution of the various alkylleads, Hg0, alkylmercury, -tin, and -selenium was vaporized and carried in a clean synthetic air stream (0.25-1.05 L/min) through the air sampler. The sampling tubes were then analyzed by CT-GC-ICPMS, and the results were compared with the signal produced by the direct injection of the same mixture
Table 1. Simultaneous Trapping Efficiency (%) of Hg0, Me2Hg, Et2Hg, Me2Se, Me2Se2, Me4Sn, Et4Sn, Me4-nEtnPb (n ) 0-4) (n ) 5) for Injections of 200 pg of Each Species as Metal air flow rate (mL/min)
Me4Pb
Et4Pb
Me4Sn
Et4Sn
Hg0
Me2Hg
Et2Hg
Me2Se
250 470 750 1050
104 ( 4 98 ( 4 103 ( 4 105 ( 4
101 ( 5 96 ( 5 100 ( 5 100 ( 5
100 ( 3 98 ( 3 101 ( 3 100 ( 3
100 ( 4 97 ( 4 100 ( 4 99 ( 4
98 ( 4 96 ( 4 99 ( 4 100 ( 4
109 ( 6 103 ( 6 108 ( 6 109 ( 6
100 ( 7 102 ( 7 109 ( 7 109 ( 7
100 ( 9 102 ( 9 104 ( 9 110 ( 9
Figure 3. Simultaneous detection of standards of volatile metal species by CT-GC-ICPMS (all amounts expressed on metal basis). (T) Temperature (°C) of the chromatographic column as a function of time during the desorption; (1) 208PbMe4, 100 pg; (2) 208PbEt4, 75 pg; (3) 120SnMe4, 75 pg; (4) 120SnEt4, 100 pg; (5) 202Hg0, 150 pg; (6) 202HgMe , 150 pg; (7) 202HgEt , 75 pg; (8) 78SeMe , 150 pg. 2 2 2
Figure 2. Schematic diagram of the cryogenic trapping-gas chromatography-ICPMS setup.
just ahead of the chromatographic column. Comparison with the two different sets of results indicated that all species are stable under these conditions, and the overall trapping process yields 100% recovery without any species interconversion between all the species processed simultaneously (Table 1). (ii) Analytical Instrumentation. The cryogenic trap-gas chromatography-ICPMS setup (Figure 2) involves three steps: the injection of the analytes and their cryocondensation on the top of a packed gas chromatography column, the gas chromatography separation of the analytes, and their detection in the ICPMS. Transfer lines are made of Teflon tubing (o.d. 1 mm) and are as short as possible and heated to prevent condensation. Gas flow rates are monitored with mass flow meters (Tylan). Gas flow is regulated with solenoid Teflon valves (ASTI). Volatile metal species are first injected into a 5-mL glass cell heated to approximately 200 °C, flushed by a helium flow (100 mL/min). A microscale volume of 2 µL of the mixed working solutions is used for calibration. The analytes are then volatilized, carried by the helium stream, and condensed on the top of a packed, U-shaped chromatographic column (Chromosorb W HP 60-80 mesh coated with 10% Supelco SP2100) immersed in liquid nitrogen. The injection of the volatile species into the cryotrap takes less than 5 min. This mode of injection of calibrants was used for the optimization of the different steps of this hyphenated system and for the quantitation of real samples. Species are separated and eluted after the column has been gently warmed and the cryogenic dewar has been removed. The
column is heated by a coaxial electrical wire wrapped around it. The heating system is grounded to the ICPMS to prevent any arcing from the radio frequency load coil in the torch box. A flow of helium (100 mL/min) is flushed through the column during the elution of the analytes. Compounds elute sequentially according to their boiling point and the chromatographic properties of the packing material.26 The heating program allows quantitative temperature cycles starting from the temperature of liquid nitrogen up to 250 °C in only 5 min (Figure 3) and provides a good separation of the species of interest. No degradation or memory effects for the various species investigated were observed during calibration tests. Before being injected into the plasma, the helium stream carrying the analytes eluting from the gas chromatography column is mixed with an Ar stream (900 mL/min). A flow of pure oxygen (15 mL/min) is mixed with the central Ar/He gas stream in order to minimize carbon sensitivity effects. To avoid intense oxidation of the cones, oxygen addition begins 1 min before data acquisition starts and is stopped at the end of the 5-min run. An Ar/Xe mixture (50 ppm as Xe, 2.5 mL/min) is also added to the central stream for continuous internal standardization. The mixture of the different gases is done with a five-way adapter made of PTFE, specially designed for this purpose. The inductively coupled plasma mass spectrometer used for these determinations is a Perkin-Elmer SCIEX Elan 5000 (Norwalk, CT). The operational parameters are given in Table 2. RESULTS AND DISCUSSION Optimization of the Instrumental Setup. In this hyphenated system, all of the analytes are introduced into the plasma in a (26) Donard, O. F. X.; Rapsomanikis, S.; Weber, J. H. Anal. Chem. 1986, 58, 772-777.
Analytical Chemistry, Vol. 70, No. 13, July 1, 1998
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gaseous form. This enhances the significant overall sensitivity compared to the common nebulization configuration, with which only a small percent of the analytes reach the plasma. Moreover, the desolvatation and large evaporation steps are avoided, and the plasma energy is used only for atomization and ionization.27 Mixed plasma can also significantly increase sensitivity for elements of high ionization potential. Murillo and Mermet have shown that the addition of a small amount of hydrogen in the central channel of the plasma, as sheathing gas or after premixing with the carrier gas, results in an overall significant ionization process by considerably improving thermal conductivity.28 At 5000 K, He thermal conductivity is 10 times greater than Ar thermal conductivity (1.3 and 0.1 W‚m-1‚K-1, respectively29). In our system, the introduction of He increases analyte ionization.30 (i) Optimization of the Torch Injector Position and Internal Standardization. An Ar/Xe mixture (2.5 mL/min) was added to the central Ar/He gas stream to optimize the torch injector alignment with the cones axis. Optimization of the sensitivity response on Xe isotopes enabled us to properly align the injector. Xe did not cause any isobaric interference for determinations and was, therefore, used on a routine basis.23 At the concentration used, three isotopess124Xe (isotopic abundance 0.096%), 128Xe (isotopic abundance 1.92%), and 130Xe (isotopic abundance 4.08%)scan be detected within a convenient detector range, which varies from 15 000 to 550 000 counts/s and offers good conditions
for the optimization of the injector. During routine analysis, this addition of Ar/Xe was also used for continuous internal standardization and to verify instrumental stability over time. (ii) Addition of Oxygen. Experiments were initially performed without oxygen addition. Under these conditions, repeated injections (2 µL) of methanol containing standard solutions resulted in poor reproducibility and sensitivity for all the volatile metal species considered. Large signal depression was also recorded on the Xe isotopes used as an internal standard when methanol eluted into the plasma. This signal perturbation continued up to 2 min longer than the elution of methanol and overlapped the elution of all the species of interest except Hg0, which eluted before methanol. Furthermore, there was important carbon deposition on the sampling cone. Similar effects have been reported by Van Loon et al.19 Similar problems also occurred with real air samples, since carbon-containing gases were also trapped with our sampling procedure. To overcome the effect of carbon on sensitivity, a continuous stream of O2 (15 mL/min) was added to the central gas flow to prevent carbon deposition on the cones and carbon introduction into the quadrupole.19 This resulted in a rapid recovery of the Xe profile after the elution of methanol and a relatively significant increase in sensitivity. The increase is similar for each series of organometallic compounds but differs with respect to the metal present in the chemical formulation (a 110% increase for lead species, 130% for tin species, only 30% for Me2Se, and 50% for mercury species). In the absence of oxygen, carbon deposits on the sampler cone and partially clogs the sampler inlet, decreasing ion extraction efficiency and resulting in a large and general decrease in sensitivity. The decrease in ion extraction efficiency might be partially counterbalanced by slightly better ionization conditions for poorly ionized elements. The carbon deposited on the cone may, indeed, serve as an active C+ source with a high ionization potential (IP ) 11.26 V) and may improve the ionization efficiency of elements with a lower ionization potential (Se, Hg) by electron transfer.31,32 Hg0 elutes before methanol and is, therefore, not affected by these processes. Elements already fully ionized, such as Pb and Sn, will not be affected by the improved ionization yield and will only be limited by the reduction of ion extraction efficiency. Therefore, oxygen-free conditions result in a smaller decrease in sensitivity for Se and Hg than for Pb and Sn. The addition of oxygen eliminates carbon deposition on the cones and preserves optimal extraction efficiency conditions of ions to the detector, yielding a general improved sensitivity for all elements. (iii) Optimization of the Central Ar Gas Flow Rate. Ion formation and extraction efficiency are strongly affected by the geometry of the plasma.33 The position of the ion formation area depends on the composition of the gas used in the plasma formation and on the central gas flow rates. Optimal ion extraction efficiency is obtained when this area is at the tip of the sampler cone.34
(27) Peters, G. R.; Beauchemin, D. Anal. Chem. 1993, 65, 97-103. (28) Murillo, M.; Mermet, J. M. Spectrochim. Acta 1989, 44B, 359-366. (29) CRC Handbook of Chemistry and Physics, 66th ed.; CRC Press: Boca Raton, FL, 1990. (30) Sheppard, B. S.; Shen, W. L.; Davidson, T. M.; Caruso, J. J. Anal. At. Spectrom. 1990, 5, 697-700.
(31) Larsen, E. H.; Stu ¨ rup ,S. J. Anal. At. Spectrom. 1994, 9, 1099-1105. (32) Alain, P.; Jaunault, L.; Mermet, J. M.; Delaporte, T. Anal. Chem. 1991, 63, 1497-1498. (33) Olesik, J. W. Anal. Chem. 1996, 68, 469A-474A. (34) Horlick, G.; Tan, S. H.; Vaughan, M. A.; Rose, C. A. Spectrochim. Acta 1985, 40B, 1555-1572.
Table 2. CT-GC-ICPMS Operating Conditions Cryotrapping sample desorption time into the cryotrap at 250 °C cryotrap temperature carrier gas
5 min -196 °C He, 100 mL/min
Chromatography packed column, Chromosorb W HP/10% Supelco SP2100 temperature -196 to 250 °C carrier gas He, 100 mL/min on-column injection 2 µL column
Ni cones Rf power gas flows Ar cooling Ar intermediate Ar carrier Ar/Xe makeup O2 dwell time sweeps per replicates resolution data acquisition isotopes monitored
ICPMS Perkin-Elmer SCIEX Elan 5000 1100 W 15 L/min 0.8 L/min 0.95 L/min 2.5 mL/min, 50 ppm as Xe 15 mL/min 20 ms 1 normal Chromafile MS software, Perkin-Elmer SCIEX 78Se, 77Se, 118Sn, 120Sn, 128Xe, 130Xe, 200Hg, 202Hg, 206Pb, 208Pb
2642 Analytical Chemistry, Vol. 70, No. 13, July 1, 1998
Figure 4. Optimization of the Ar carrier gas flow for lead (Me4Pb, Et4Pb), mercury (Hg0, Me2Hg, E2Hg), tin (Me4Sn, Et4Sn), and selenium (me2Se) compounds and xenon in an Ar-He-O2 mixed plasma.
To optimize our system, we studied the influence of the Ar gas flow rate on sensitivity. Optimization was done after injection of 100 ng/mL as metal of mixed organometallic solutions (Figure 4). The sensitivity response was normalized to the highest value obtained, and the Ar central gas flow rate was varied between 500 and 1300 mL/min. Maximum signal response was obtained for a flow rate of 950-1000 mL/min. No species-specific sensitivity within a given metal family response was observed, underlining that all species are equally atomized and ionized in the plasma. Xenon optimal signal response was obtained with a slightly lower flow rate. This difference may be related to the different modes of introduction in the plasma. Xenon is added continuously to the central gas flow, whereas the analytes elute from the column in a pulsed mode. Optimal Ar flow rate conditions for lead, tin, mercury, and selenium species were, therefore, always set 100 mL/min above the optimal value found for Xe. Daily working conditions could be obtained rapidly after optimization of the Xe response. (iv) Interferences. Isobaric interference can make species identification difficult. The isotopic distribution of at least two isotopes was systematically compared to theoretical values to verify the identification of new species. The precision obtained on the measured isotopic ratio depends on the concentration of the analytes. In general, we obtained an agreement better than 95% between the measured and calculated isotopic ratios to validate species identification. For low analyte concentration, we considered that the relative standard error on the isotopic ratio should be less than 20% with the set of acquisition parameters. This approach is limited, however, in the case of monoisotopic elements, such as 51V, 27Al, and 75As. Volatile metallic species were, therefore, identified by combining the information obtained between the retention time and the isotopic match with respect to reference compounds.
The only matrix effect observed was associated with the presence of atmospheric CO2 in air samples. There was a large decrease in signal, nonetheless corrected by the continuous monitoring of the Xe+ signal, when CO2 (bp -78.4 °C) was eluted from the column. The time slot affecting the species coeluting with CO2 is located between 0.65 and 1.05 min. This certainly affects the precision of the results obtained within this time slot on an accurate quantitative approach but still allows us to obtain quantitative information. Species likely to be affected by this effect are the very volatile hydride species, if they occur,35 such as AsH3, SeH2, and SnH4. (v) Analytical Performances. Analytical performances of the hyphenated setup are reported in Table 3. Relative standard deviations (RSDs) were calculated using either peak areas or peak height. The best reproducibility was obtained using peak areas. For each species, RSD was usually less than 4% for amount of 100 pg as metal injected. Absolute detection limits (3σ) are around 70 fg (as Pb) for lead species, 200 fg (as Sn) for tin species, 800 fg (as Hg) for mercury species, and 2500 fg (as Se) for selenium species. These are among the lowest reported to date.22 The linearity of calibration curves extends over 3 orders of magnitude (from 1 pg to 1 ng as metal). The precision on isotopic ratios was obtained after five injections of standard solutions (200 pg of each species as metal). An agreement better than 97% was generally obtained between the measured values and the theoretical isotopic ratio. In air, the detection limits based on 25-L samples were 0.004, 0.010, and 0.2 ng/m3 for lead, tin, and selenium species, respectively. Blanks from field columns did not contain any detectable amount of lead, tin, selenium, arsenic, indium, or gallium species. However, after storage for several days under the conditions (35) Donard, O. F. X.; Weber, J. H. Nature 1988, 332, 339-341.
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Table 3. Analytical Performances of the CT-GC-ICPMS System
(min)a
retention time peak width (s)a at half-height RSD (area)a (100 pg as metal injected) RSD (height)a (100 pg as metal injected) slope (area)b (counts pg-1) correl coeff r2b detection limitc (femtograms as metal)
Me4Pb
Et4Pb
Me4Sn
Et4Sn
Hg0
Me2Hg
Et2Hg
Me2Se
2.10 ( 0.01 3.25 ( 0.03 0.9 1.2 5200 0.9996 60
3.02 ( 0.04 9.16 ( 0.64 2.0 8.5 5150 0.9996 70
1.85 ( 0.01 2.85 ( 0.05 1.3 2.5 5350 0.9995 200
2.75 ( 0.02 5.68 ( 0.25 1.8 6.1 5400 0.9995 220
1.30 ( 0.01 2.15 ( 0.05 3.5 4.0 1200 0.9994 800
1.90 ( 0.01 3.06 ( 0.03 1.1 1.3 1150 0.9997 810
2.46 ( 0.01 4.17 ( 0.09 1.6 3.2 1200 0.9995 850
1.72 ( 0.02 1.44 ( 0.02 9.0 10.7 400 0.998 2500
208/206
208/206
120/118
120/118
202/200
202/200
78/77
isotopic ratios
theoretical a
202/200
2.14 ( 0.01 2.19 ( 0.02 1.37 ( 0.01 1.36 ( 0.01 1.30 ( 0.01 1.31 ( 0.01 1.29 ( 0.03 3.17 (0.12 2.22 2.22 1.37 1.37 1.29 1.29 1.29 3.10
measureda
200 pg of each species as metal, n ) 5. b Injections from 1 to 1000 pg as metal. c DL ) 3×SD/slope(area).
Table 4: Volatile Metal Species Concentrations in Air Samples Collected in Bordeaux City and above the Gironde Estuary siteb estuary kp 5 kp 15 kp 30 kp 53 kp 75 kp 93 kp 100 ocean Bordeaux site 1 site 2 site 3 site 4 site 5 site 6 a
Me4Pb
Me3EtPb
Me2Et2Pb
MeEt3Pb
Et4Pb
Me2Se
Me4Sn
Hg0
0.18 0.23 0.13 0.03 0.02 0.04 0.04 0.03
0.02
