Portable Laser Ablation Sampling Device for Elemental Fingerprinting

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Portable Laser Ablation Sampling Device for Elemental Fingerprinting of Objects Outside the Laboratory with Laser Ablation Inductively Coupled Plasma Mass Spectrometry Reto Glaus, Joachim Koch, and Detlef Günther* Laboratory of Inorganic Chemistry, ETH Zürich, Wolfgang-Pauli-Strasse 10, 8093 Zürich, Switzerland S Supporting Information *

ABSTRACT: Laser ablation-inductively coupled plasma mass spectrometry (LA-ICPMS) is a powerful method for elemental fingerprinting of solid samples in a quasi-nondestructive manner. In order to extend the field of application to objects outside the laboratory, a portable laser ablation sampling device was assembled using a diode pumped solid state laser and fiber-optics. The ablated materials were sampled on membrane filters and subsequently quantified by means of LAICPMS. The analytical performance of this approach was investigated for glass and gold reference materials. Accuracies of better than 20% were reached for most elements and typical limits of detection were found to be in the range of 0.01−1 μg/g. In summary, this approach combines spatially resolved sampling with the detection power of ICPMS and enables elemental fingerprinting of objects which cannot be transferred to the laboratory, e.g., archeological artifacts in museums.

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the dimensions of the ablation cell (maximal up to a few decimeters in size). In order to analyze larger objects, attachable ablation cells have been developed, which can be placed directly onto the sample surface.15−17 Furthermore, an open noncontact cell has been reported by Asogan et al.,18 which can be applied to large planar samples. Recently, an atmospheric sampling strategy has been proposed allowing to ablate samples without the need of any ablation cell.19 However, in either of these cases, the object of interest has to be transferred to the laboratory in order to be analyzed. A laser-based in situ sampling strategy for the elemental analysis of paintings was reported by Smith et al.,9 but a detailed description of the sampling prototype has not been given. In the proposed procedure, the ablated materials were sampled on membrane filters and were analyzed subsequently in the laboratory by LA-ICPMS in a qualitative manner. Another laser-based analytical method suitable for elemental fingerprinting is laser induced breakdown spectroscopy (LIBS). LIBS is well applicable for portable analyses,20 e.g., for environmental monitoring and geological exploration. The method found as well applications in archaeometric research but rarely for in situ analyses of archeological artifacts.21 Similar to LA, small amounts of material are removed during LIBS measurements and spatially resolved analysis can be performed. However, unlike in LA-ICPMS, the laser induced plasma is directly used as a source for the analytical information, i.e., its atomic, ionic, and molecular emission. The ablation process is a

he coupling of laser ablation (LA) as a direct sampling technique for solids with inductively coupled plasma mass spectrometry (ICPMS) allows for trace elemental as well as isotopic analysis with no or minimal sample preparation.1 Spatially resolved sampling by LA causes no damage on the macroscale and thus the integrity of the analyzed object is preserved almost entirely. Therefore, LA-ICPMS is often termed to be quasi-nondestructive. One growing field of application for LA-ICPMS is archaeometric research, where quantitative elemental and isotopic data are crucial in solving questions concerning provenance, age, and authenticity.2,3 In fact, elemental fingerprinting with LA-ICPMS has already been applied to various types of archeological samples such as ceramics,4 glasses,5 gold artifacts,6,7 obsidians,8 and paintings.9 Furthermore isotopic analyses by LA-ICPMS have been performed such as determination of lead isotopes in ancient ceramic,10 copper and silver artifacts,11 and osmium isotopes in gold coins.12 Quantification procedures for LA-ICPMS typically require an external standard material with a similar type of matrix as the sample, either dielectric or metallic, depending on the sample to be analyzed. Even though the utilization of femtosecond (fs)LA-ICPMS allows one to extend the range of matrixes that can be accurately quantified, nonmatrix-matched calibration is not always applicable.13 In order to correct for different ablation rates of sample and standard, an element with known concentrations in both materials is required as an internal standard. Alternatively, if all major elements can be accessed, normalization procedures can be applied, e.g., 100% oxide normalization for oxide matrixes.14 A limitation of a conventional LA-ICPMS setup is the restricted sample size given by © 2012 American Chemical Society

Received: March 28, 2012 Accepted: May 8, 2012 Published: May 8, 2012 5358

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Figure 1. Assembled portable laser ablation sampling device (A) and details of the LA module (B).

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EXPERIMENTAL SECTION Portable LA Sampling Device. The portable LA sampling device basically consists of a pulsed laser, an optical fiber attached to a hand-held LA module, a sampling filter mounting, and a membrane pump. Picture and schematic of the system are shown in Figure 1. An air-cooled diode pumped solid state (DPSS) laser with an output wavelength of 532 nm (Wedge HB 532, Bright Solutions SRL, Cura Carpignano, Italy) was used due to its compact dimensions, while providing sufficient pulse energy for LA purposes and offering a short pulse duration (technical details are given in Table 1). Portable LA

complex event involving material release in a variety of forms and time regimes.22 A major drawback of LIBS analysis is therefore the dependency of the analyte response on the sample matrix, which generally makes matrix-matched calibrations necessary.23 If semiquantitative information suffices, alternatively, calibration-free (CF)-LIBS can be applied by assuming the plasma to obey local thermodynamic equilibrium conditions. Furthermore, even quantitative data can be obtained by CF-LIBS in some cases which, however, are only reliable for major elements whereas the accuracy achievable for minor and, especially, trace elements usually remains insufficient.24 A further element-specific analytical technique suitable for portable applications relies on energy dispersive X-ray fluorescence spectrometry (XRF). This method is inherently nondestructive and therefore interesting for the in situ analysis of archeological objects.25 Portable XRF systems have typical Xray spot size larger than 1 mm; however, with portable micro XRF instrumentations spatial resolutions in the submillimeter scale can be achieved.26 A limitation of the technique is the rather poor detection capability for light elements. Because of the absorption of low-energy X-rays in air, elements lighter than silicon cannot be quantified, except when a vacuum chamber equipped instrument is used.27 Quantification for in situ XRF analysis is usually complex and strongly prone to matrix effects (i.e., absorption and enhancement effects of X-rays in the sample material), dependence on physical properties (e.g., surface irregularity and mineralogy), and spectral interferences.28 Both portable XRF and LIBS devices can reach typical limits of detection in a range of 10−1000 μg/g. As a consequence, applicability to elemental fingerprinting is limited and potentially meaningful trace elements cannot be accessed, such as the rare earth elements. The main objective of this study was to design, construct, and test a portable LA sampling device, which allows in situ sampling of arbitrarily sized objects in the field. Furthermore, a strategy for the subsequent elemental quantification of sampled materials with LA-ICPMS is described. The element analytical capabilities of this approach are demonstrated on the example of glass, gold, and ceramic samples.

Table 1. Specifications of the DPSS Laser and Properties of the Laser Radiation at the Sample Side wavelength maximal output energy pulse duration beam diameter ablation frequency maximal energy on the sample surface crater size maximal fluence

532 nm 1.3 mJ 100 μm 9 J cm−2

with laser radiation in the UV range would be desirable to ablate transparent materials and to reduce potential elemental fractionation effects. However, lasers with UV radiation with similar pulse energies result in larger dimensions and require usually water cooling. Furthermore the beam delivery through fibers is more affected by absorptions. Our own efforts using the fifth harmonic (213 nm) of the fundamental Nd:YAG laser radiation failed because of moderate light transmissions through the fiber smaller than 10%. The radiation of the DPSS laser was coupled into an optical fiber (core diameter 450 μm; length 2 m; Ocean Optics Inc., Dunedin, FL) using an aspheric lens (effective focal length (EFL), 7.5 mm). The lens was mounted on a x/y translation stage positioned at the laser exit, and the distance to the fiber was adjusted such that the laser light went through its focus point before reaching the fiber entrance, in order to avoid damage to the fiber.20 The fiber exit was connected to a lens tube (2.54 cm diameter) containing a collimation lens (EFL, 75 mm) and another aspheric focusing lens (EFL, 20 mm). At the 5359

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end of the lens tube, a custom built cell equipped with a glass window and a tubing connection for aerosol extraction was mounted (Figure 1B). The focal plane of the fiber output radiation was adjusted to the open end of the cell. The theoretical spot size in the focus point is given by the fiber diameter and the ratio of the numerical apertures of collimating and focusing lens and corresponds to approximately 120 μm. For sampling, the LA module was applied to the sample surface and the produced aerosol particles were collected on membrane filters (pore size, 0.4 μm; diameter, 13 mm; HTTP01300, Millipore, Billerica, MA). For this purpose, ambient air carrying the aerosol was sucked through the filter by a membrane pump (NMP 05, KNF Neuberger AG, Balterswil, Switzerland) with a flow of about 0.15 L/min. The sampling area on the filter was restricted to a cross section of about 7 mm2 by a modified filter holder in order to increase the material density for the following reablation in the laboratory. Membrane filters with submicrometer pore size are suitable to efficiently collect LA generated aerosol particles.9,29 However, elements like carbon and sulfur, which preferentially form gas species during the ablation in air, would pass through the filter30 and can therefore not be sampled. In this study, aerosol from 1000 laser pulses was generally sampled on a filter corresponding to a typical number of pulses applied for a LAICPMS analysis. Higher numbers of pulses may compromise the sampling efficiency due to an increased backpressure at the filter as well as the loss of the focus point. Glass and ceramic materials were ablated for 10 s with 100 Hz and the maximal fluence. The gold standards were sampled with 1 kHz for 1 s with a reduce fluence of 4.5 J cm−2 due to the far lower ablation threshold and in order to reduce the debris around the crater pit. Quantification by LA-ICPMS. After the sampling procedure, each filter was placed upside-down onto a carbon pad. This allowed for remobilizing the sampled material in a controlled way by ablating through the membrane filter (about 10 μm thickness). It turned out that LA of the sampling side would have led to nonuniform material removal due to the shockwave formed during the LA process and, thus, to strong signal fluctuations. Reablation of filters was performed by a commercial LA system (Nd:YAG, λ = 213 nm; pulse duration, 5 ns; LSX-213, CETAC Technologies, Omaha, NB) using a fast scanning routine (parameters are given in Table 2). Prior to the sampling area, a filter blank area (about 3 mm2) was ablated to account for the elements present in the filter and support material. The signals were detected with a quadrupole ICPMS Elan 6100 DRC plus (PerkinElmer Inc., Woodbridge, Canada). A scheme of the filter reablation and a representative transient signal of an ICPMS analysis can be found in Figure S-1 in the Supporting Information. LAMTRACE software was used for data reduction and quantification according to Longerich et al.31 Solid standard reference materials (SRMs) ablated in hole drilling mode (parameter given in Table 2) were used as external standards for the LA-ICPMS quantification of the filter sample materials. However, the large amount of carbon transported into the plasma due to ablation of filter material caused polyatomic interferences (e.g., 40Ar13C on 53Cr) and led to an element dependent degree of sensitivity enhancement, especially pronounced for main group elements with high ionization potentials.32−34 Therefore, in an alternative strategy, aerosols produced by LA of SRMs were collected on filters (transparent glass materials were ablated with the 213 nm

Table 2. Experimental Operating Conditions for LA-ICPMS Analyses of Filters (Scanning) and Reference Materials (Hole Drilling) LA parameters

scanning

spot diameter repetition rate scan speed fluence

200 μm 20 Hz 350 μm/s 18 J cm−2

carrier gas flow (He) ICPMS parameters rf power nebulizer gas flow auxiliary gas flow plasma gas flow detector mode dual (pulse and analog) dwell time isotopes monitored

1.0 L/min

hole drilling 100 μm 10 Hz 18 J cm−2 (for glass and ceramic), 9 J cm−2 (for gold) 1.0 L/min

1400 W 0.78−0.83 L/min 0.75 L/min 17.5 L/min

10 ms gold: 13C, 47, 48Ti, 53Cr, 55 Mn, 57Fe, 59Co, 60Ni, 63, 65 Cu, 66, 68Zn, 75As, 78Se, 105Pd, 107Ag,a 111Cd, 118, 120 Sn, 121Sb, 195Pt, 197Au,a 208Pb, 209Bi glass and ceramic: 7Li, 9Be, 13C, 23Na,a 25 Mg, 27Al, 29 Si, 39K, 42Ca, 45Sc, 47Ti, 51V, 53Cr, 55 Mn, 57Fe, 59 Co, 60Ni, 63Cu, 66Zn, 69Ga, 85Rb, 88Sr, 89Y, 90Zr, 137 Ba, 139La, 140Ce, 141Pr, 146Nd, 147Sm, 153Eu, 157Gd, 159 Tb, 163Dy, 165Ho, 166Er, 169Tm, 172Yb, 175Lu, 208 Pb, 232Th, 238U

a

Signal suppressed (about 1 order of magnitude) using a custom resolution on the quadrupole.

system) and reablated in the same way as sample materials. This approach, hereinafter referred to as filter standard approach, allowed one to supply a constant amount of carbon to the ICP and therefore to match the conditions during the analyses of samples and external standard material. An alternative to LA-ICPMS quantification of the filter sampled material would be digestion of the sampling filter and subsequent quantification with solution nebulization ICPMS as described by Kuhn et al.29 However, taking the high dilution factors during the sample preparation (e.g., 10 million-fold dilution for 1 μg of sample material in a final amount of 10 g of solvent) and more severe blank contributions into account, trace element quantification in the submicrogram/gram range could not be achieved by this strategy. Samples. The analytical performance of the quantification approach was tested on basalt glass USGS SRM BHVO-2G (United States Geological Survey, Reston, VA) and gold materials NA1 and NA2 (Norddeutsche Affinerie AG, Hamburg, Germany).7 An ancient Chinese ceramic rod (octagonal stick, 4 cm length, colored with han blue) was analyzed as the test object. For both glass and ceramic samples, the NIST SRM 610 (National Institute of Standards and Technology, Gaithersburg, MD) was used as external standard for quantifications. Reference values for the glass SRMs were taken from the GeoReM database35 (preferred values). For system characterization, test measurements were initially performed on stainless steel SRM JK37 (Swedish Institute for Metal Research, Stockholm, Sweden). Electron Microscopy. The morphology of filter-sampled particles was studied by scanning electron microscopy (SEM; Gemini 1530, Carl Zeiss Inc., Germany). Each one steel (JK37) and glass (BHVO-2G) sample were ablated by 1000 laser pulses using the portable LA system (carrier gas, air) as well as 5360

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Figure 2. Left column: Microscopic images of ablation craters on a steel surface (A; 100 pulses, 4.5 J cm−2) and a glass surface (B; 1000 pulses, 9 J cm−2) produced using the portable LA system. Right columns: SEM images of filter-sampled particles produced with portable LA (C, D), by reablation of filter-sampled materials (E, F), and with 213 nm LA (G, H) for steel and glass samples, respectively.

of metallic samples. The formation of these large particles with the 532 nm system cannot be excluded, but they are probably lost on the sample surface, due to the ablation under air or less of these large particles are produced due to the 5-fold lower pulse duration of the portable laser compared to the 213 nm system. While the ablation of the glass sample with 213 nm led exclusively to the production of nanoparticle agglomerates (Figure 2H), numerous large spherical particles were found for the LA of the glass sample with the portable system (Figure 2D). After reablation of filter sampled glass material and recollecting on filters, still some of these large particles could be found (Figure 2F). However, the reablation seems to reduce the relative number of these large particles, compared to the initial aerosol produced with the 532 nm system and lead therefore to more favorable conditions for the ICPMS measurements. Micrometer sized particles may differ in their elemental composition from the bulk material and are potentially depleted in volatile elements.29,37 Therefore, loss of these larger particles on the sample surface or during the aerosol transport and incomplete vaporization of large particles in the ICP are potential sources of elemental fractionation. The ablation efficiencies of the portable LA system were estimated by comparing the signal intensities of filter ablation to the ones of a standard LA-ICPMS setup. Relative signal intensities were found to be dependent on the sample matrix ranging from 10 to 35% for opaque glass samples, 20% for gold samples, and about 80−120% for ceramic samples. The sampling efficiency of the system was found to be not significantly different for ablation frequencies ranging from 10 to 1000 Hz. Therefore, the use of high ablation frequencies is suitable for the sampling, and sufficient amounts of material can be collected within seconds for the subsequent trace element analysis in the laboratory. The limits of detection (LODs) for the portable LA sampling followed by LA-ICPMS quantification were calculated by taking the filter blank signals into account. Figure 3 shows the

the LSX-213 system (carrier gas, helium), and the aerosol particles were collected on membrane filters (on the full area, 13 mm diameter). Additionally filters with high material densities were ablated, as described for the filter quantification, and were recollected on filters for morphology studies by SEM.

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RESULTS AND DISCUSSION Characterization of the System. LA of a steel surface using the portable laser allowed to produce well-defined craters with a diameter of about 110 μm and a flat bottom (Figure 2A). In fact, the beam delivery through large-core optical fibers lead to spatial dispersion of the initial Gaussian beam profile and therefore to some extent to a beam homogenization.36 The ablation of the steel sample with 1000 pulses resulted in a crater depth of 50 μm, which corresponds to an ablated mass of about 2.5 μg assuming a cylindrical crater shape. Compared to this, LA of glass samples resulted in reduced craters sizes of 100 μm (Figure 2B) but an increased crater depth of about 75 μm. Furthermore, craters appeared to be slightly tapered, which is related to the higher ablation threshold of glass samples compared to metals and a not fully homogenized beam profile. Melt formations at crater rims and particle depositions around the ablation pits were observed for both materials. LA with a wavelength of 532 nm and the use of air as a transport gas are not favorable conditions regarding aerosol formation and elemental fractionation.13 To address possible sources of elemental fractionation, filter sampled aerosol particles produced under the different applied LA conditions were studied by SEM. When ablating the steel sample with the portable LA system, exclusively agglomerates of nanoparticles were found on the filter surface (Figure 2C). Such agglomerated were as well observed for the reablation of the filter sampled material (Figure 2E); however, a large part of them can be assigned to the ablated filter material itself. In contrast, the ablation with the 213 nm system resulted in a mixture of agglomerates and few micrometer-sized spherical particles (Figure 2G), which are typical for the nanosecond LA 5361

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Figure 3. LODs determined for a ceramic sample analyzed using the portable LA sampling with subsequent LA-ICPMS quantification and literature values of LODs for portable LIBS20 and portable XRF.38

Figure 4. Relative error compared to the reference values for the quantified elemental concentrations in the basalt glass BHVO-2G (A) and in the gold sample NA2 (B) using the offline sampling approach and subsequent analysis by LA-ICPMS. Elements are plotted in concentration descending order. The error bars represent the standard deviation of four replicates each.

ablation properties of the loaded filter and the filter blank were found to be not exactly the same. The concentration of sodium was too high in the support material under the filter and could therefore not be quantified in the sampled material. The elements zinc and zirconium were also affected by background signals occurring form the support material, which led to an overestimation of the concentrations and to higher uncertainties. The suitability of the offline sampling approach for metallic samples was tested on the example of gold standards, as archeological gold artifacts are in the scope of the presented method. The gold material NA2 was quantified using NA1 as an external standard and 197Au+ as an internal standard. A total of 16 of the 19 elements certified in the gold standards could be quantified with a bias less than 30% (Figure 4B). The concentrations of titanium, chromium, and selenium were below their respective LODs in the NA1 and were therefore not quantified. Relative to 197Au+, the concentrations of all minor and trace elements were underestimated, except for arsenic and antimony. Both elements are probably affected by a pronounced sensitivity enhancement due to the large amounts of carbon in the plasma. Antimony could as well be affected by the isobaric interference with 109Ag12C+. Appling the filter standard approach for the calibration allowed correcting for some pronounced fractionation effects of, e.g., lead and cadmium to a large extent and improves accuracy of quantifications for elements with carbon enhanced sensitivities. The discrepancy in the calculated concentration of bismuth with the two quantification strategies can probably be explained by the isobaric interference 197Au12C+. In contrast to the glass samples, lower accuracies of the quantification results have to be taken into account for the gold samples. Guerra et al.39 stated that (nanosecond) LA-ICPMS is not suitable for quantification of gold samples, whereas Watling

estimated LODs for the portable LA approach in comparison with literature values of other portable element specific techniques. The LODs of the portable LA sampling approach depend on the ablation efficiencies of the sample and on the number of laser pulses applied. Typical LODs range from 1 μg/ g for light elements down to 0.01 μg/g for heavy elements. Numerical values of LODs for the analysis of ceramic, glass, and gold are provided in Table S-1 in the Supporting Information. Elements which are present in the filter material or the underlying carbon pad (like Sr, Zr, Ba, and Pb) as well as elements measured on minor isotopes (Ca, Cr, Fe) or those suffering from severe isobaric interferences (Si, K) have an increased LOD compared to other elements in the respective m/z range. Compared to portable XRF and LIBS, the LODs observed in this study are up to 3 orders of magnitude lower. Quantification of Standard Reference Materials. The analytical performance of the quantification approach regarding precision and accuracy was tested by comparing different SRMs. The quantification of the filter-sampled BHVO-2G using NIST SRM 610 as an external standard and 42Ca+ as an internal standard yielded accuracies better than 20% for most of the measured elements (Figure 4A). The obtained precisions were in the range of a few percent for elements with concentration well above the LOD and which were not affected by interferences. The concentration of lithium, for example, was close to its LOD and resulted in a higher bias and lower precision of 30% and 15%, respectively. The concentrations of beryllium and lead were below their limits of detection of 7 and 1 μg/g, respectively. Potassium and chromium, which were both affected by interferences (38Ar1H+ and 40Ar13C+) could be determined accurately only when the calibration was performed with filter-sampled external standards. For most of the other elements, no significant difference in the quantification results was found using the solid or filter standard approach. The 5362

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et al.40 and Outridge et al.41 have shown that even with unfavorable laser conditions meaningful elemental data can be obtained. For accurate quantification of metals and especially gold samples, femtosecond LA-ICPMS was proposed if no matrix-matched standard is available.7,13 Despite the fact that not the most suitable laser conditions were used for the sampling, valuable data were obtained for elemental fingerprinting purposes. Trace Element Quantification of a Ceramic Sample. A ceramic rod with a size suitable for ablation in a standard cell was quantified using a standard LA-ICPMS setup as well as the offline sampling strategy with subsequent LA-ICPMS analysis. For both methods, 100% oxide normalization was applied for the quantification.14 Figure 5 shows the result of both

macroscopic scale. This approach is, in particular, useful for bulk analyses, as variation with depth are averaged during the filter sampling. The LA sampling device allows for in situ sampling of arbitrary sized objects, which cannot be transported to the laboratory, e.g., archeological artifacts in museums. Subsequent analyses of the sampled materials by LA-ICPMS allow quantification of major, minor, and trace elements with similar performance as a standard LA-ICPMS setup. Elemental quantification with accuracies better than 20% is achievable for most elements. Metallic samples, however, were found to be more affected by elemental fractionation. Compared to other portable techniques, like LIBS and XRF, far lower limits of detection in the range of 0.01−1 μg/g can be reached, and therefore a broader range of trace elements can be quantified for fingerprinting purposes. Future developments will mainly focus on the design modifications of the sampling module. In this context, a variable crater size, a fast filter changing, and an integrated, CCD camera-based sample observation appear necessary to further enhance the operational convenience. It should be emphasized that, currently, portable LA systems based on fiber optics hardly allow the application of wavelengths in the UV spectral range or ultra short laser pulses accessible, which would be desirable to analyze highly transparent materials and reduce potential elemental fractionation effects. Another advantage of mass spectrometric analyses over XRF and LIBS, which was not addressed in this work, is the possibility to determine isotope ratios. The combination of the offline sampling and isotopic ratio determination with a multicollector ICPMS could provide further valuable information regarding origin of the sample and raw materials used during the manufacturing process.2

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Figure 5. Comparison of the quantified elemental concentrations (in weight percent of the corresponding oxide) of a ceramic sample analyzed by a standard LA-ICPMS setup and by the offline sampling strategy. The error bars represent the standard deviation of five replicates each. The numerical values are provided in Table S-2 in the Supporting Information.

ASSOCIATED CONTENT

S Supporting Information *

Additional information as noted in text. This material is available free of charge via the Internet at http://pubs.acs.org.

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approaches and illustrates the capabilities of the portable system to determine elemental composition in a broad concentration range over 7 orders of magnitude. The results of both measurements were in good agreement with each other. Some of the elements were affected by heterogeneities in the ceramic material and their concentrations were therefore determined with lower precisions compared to the homogeneous glass standards. The results of zinc, zirconium, and chromium, which signals were affected by filter background and carbon interferences, respectively, had larger uncertainties and their concentrations were overestimated with the filter approach. Lithium, on the other hand, was close to its LOD and had therefore a large uncertainty. All rare earth elements could be quantified, giving valuable information for fingerprinting of the sample. The experiment showed that with the filter sampling approach similar analytical performance can be reached as with a standard LA-ICPMS setup.

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Fax: +41 44 6331071. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors wish to thank Philipp Trüssel and Roland Maeder for manufacturing of parts of the sampling device and Frank Krumeich (EMEZ) for the electron microscopic measurements. Igor Gornushkin, Jens Riedel, and Alexander Kadenkin at BAM Federal Institute for Material Research and Testing are thanked for the opportunity to test DPSS lasers for LA purposes. This work was financially supported by the Swiss National Science Foundation (Project ID 200020-124628/1) and ETH Zurich.

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REFERENCES

(1) Russo, R. E.; Mao, X. L.; Liu, H. C.; Gonzalez, J.; Mao, S. S. Talanta 2002, 57, 425−451. (2) Resano, M.; Garcia-Ruiz, E.; Vanhaecke, F. Mass Spectrom. Rev. 2009, 29, 55−78. (3) Giussani, B.; Monticelli, D.; Rampazzi, L. Anal. Chim. Acta 2009, 635, 6−21. (4) James, W. D.; Dahlin, E. S.; Carlson, D. L. J. Radioanal. Nucl. Chem 2005, 263, 697−702.

CONCLUSIONS The portable laser ablation device described in this work was shown to be suitable for the sampling of metals and opaque nonmetallic samples. Drilling of well-defined craters removes a minimal amount of sample material required for the subsequent quantification and preserves the integrity of the objects on a 5363

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dx.doi.org/10.1021/ac3008626 | Anal. Chem. 2012, 84, 5358−5364