Analysis of glass by UV laser ablation inductively coupled plasma atomic emission spectrometry. Part 2. Analytical figures of merit

Two lasers working in the UV part of the spectrum have been used for the direct analysis of glass samples by laser ablation ICP-AES. An XeCl excimer laser (308 nm) and a Nd:YAG laser operating at the third harmonic (355 nm) and the fourth harmonic (266 nm) have been selected. The energy was 70 mJ and 5 mJ for the excimer laser and the Nd:YAG laser, respectively, with a 10 Hz repetition rate. Figures of merit such as repeatability, reproducibility, accuracy and limits of detection have been studied. Si was used as an internal standard to improve the repeatability, the reproducibility and the accuracy. Use of internal standardardization led to an RSD of less than 1% for most elements and to a linear calibration graph irrespective of the colour of the glass samples. Limits of detection in the solid were of the same magnitude as those obtained using sample dissolution and pneumatic nebulization. Results confirmed that the XeCl laser provided the best results of detection whereas the Nd:YAG laser, particularly at 266 nm, was less sensitive to glass colour.     

Determination of additives in PVC material by UV laser ablation inductively coupled plasma atomic emission spectrometry

UV laser ablation inductively coupled plasma atomic emission spectrometry (LA-ICP-AES) has been applied to the direct determination of additives in solid poly(vinyl chloride) materials. A Nd:YAG laser, operating at its fourth harmonic (266 nm), was used with a beam masking device, in the most reproducible conditions, to introduce solid particles into the plasma torch of a simultaneous ICP-AES system. Emphasis was placed on both precision and accuracy in the analysis of PVC materials by LA-ICP-AES. A series of six in-house PVC reference materials was prepared by incorporating several additives in increasing concentrations. Three alternative methods were evaluated to certify the amount of incorporated elements: ICP-AES with sample dissolution, NAA and XRF. Satisfactory results and good agreement were obtained for seven elements (Al, Ca, Cd, Mg, Sb, Sn and Ti) among the ten incorporated. Sample homogeneity appeared to be satisfactory, and calibration graphs obtained by LA-ICP-AES for several elements are presented. Finally, the performance of the technique in terms of repeatability (1.6-5%), reproducibility (2–5%), and limits of detection was investigated.     

Bulk analysis by IR laser ablation inductively coupled plasma atomic emission spectrometry

Two laser ablation systems dedicated to bulk analysis were evaluated for steel and PVC samples, using inductively coupled plasma atomic emission spectrometry detection. These systems were characterized by the use of a Nd:YAG laser operating at 1064 nm, the absence of observation device and a large laser spot size. The 1064 nm wavelength was selected to avoid the use of frequency-multiplying optics, and to be less critical to the sampling position. Calibration graphs and limits of detection are given for both types of materials. LODs were in the range 3–120 μg/g for steel, and in the range 0.07–15 μg/g for PVC. In the case of steel samples, similar calibration graph slopes were obtained between polished and unpolished samples.     

Bulk analysis by IR laser ablation inductively coupled plasma atomic emission spectrometry

Two laser ablation systems dedicated to bulk analysis were evaluated for steel and PVC samples, using inductively coupled plasma atomic emission spectrometry detection. These systems were characterized by the use of a Nd:YAG laser operating at 1064 nm, the absence of observation device and a large laser spot size. The 1064 nm wavelength was selected to avoid the use of frequency-multiplying optics, and to be less critical to the sampling position. Calibration graphs and limits of detection are given for both types of materials. LODs were in the range 3-120 microg/g for steel, and in the range 0.07-15 microg/g for PVC. In the case of steel samples, similar calibration graph slopes were obtained between polished and unpolished samples.     

Depth profiling of tin-coated glass by laser ablation inductively coupled plasma emission spectrometry with acoustic signal measurement

A pulsed, frequency-quadrupled Nd:YAG laser (266 nm, 10 Hz) coupled to an inductively coupled plasma atomic emission spectrometer (ICP-AES) was employed for depth profiling by ablation of a pyrolytically deposited Sn layer (300 nm) on float glass. The procedure consisted of performing individual ablation cycles (layer-by-layer). A raster with stroke distance of either 50 microm or 200 microm (the raster density) was used as an ablation pattern. The ablation was stopped after each cycle and the peak area of the resulting transient optical signal of the ICP discharge was plotted against the cycle number. The ablation rate of 90 to 20 nm per cycle at a low-energy pulse (6 mJ to 1 mJ) was determined by profilometry. A beam masking was employed to attenuate the laser shot energy and to eliminate the peripheral irregularity of the beam profile. Almost uniform removal of the square area (1 mm x 1 mm) of the coating by ablation was achieved by combining the fitted raster density, beam masking, focusing and beam energy. Different ablation processes were distinguished in cases of the tin coating and the uncoated glass surface. While the coating was mainly evaporated, the uncoated glass surface exhibited a crumbling associated with production of glass powder. This was confirmed by electron microscopy observations. The measured acoustic signal followed the behavior of the emission intensity of the Sn line and was supposed to be proportional to the amount of Sn vapors. The emission intensity depth profile of the Sn coating with graded structure was obtained, which qualitatively corresponded with the depth profile measured by secondary ion mass spectrometry.     

Depth profiling of tin-coated glass by laser ablation inductively coupled plasma emission spectrometry with acoustic signal measurement

A pulsed, frequency-quadrupled Nd:YAG laser (266 nm, 10 Hz) coupled to an inductively coupled plasma atomic emission spectrometer (ICP-AES) was employed for depth profiling by ablation of a pyrolytically deposited Sn layer (300 nm) on float glass. The procedure consisted of performing individual ablation cycles (layer-by-layer). A raster with stroke distance of either 50 μm or 200 μm (the raster density) was used as an ablation pattern. The ablation was stopped after each cycle and the peak area of the resulting transient optical signal of the ICP discharge was plotted against the cycle number. The ablation rate of 90 to 20 nm per cycle at a low-energy pulse (6 mJ to 1 mJ) was determined by profilometry. A beam masking was employed to attenuate the laser shot energy and to eliminate the peripheral irregularity of the beam profile. Almost uniform removal of the square area (1 mm × 1 mm) of the coating by ablation was achieved by combining the fitted raster density, beam masking, focusing and beam energy. Different ablation processes were distinguished in cases of the tin coating and the uncoated glass surface. While the coating was mainly evaporated, the uncoated glass surface exhibited a crumbling associated with production of glass powder. This was confirmed by electron microscopy observations. The measured acoustic signal followed the behavior of the emission intensity of the Sn line and was supposed to be proportional to the amount of Sn vapors. The emission intensity depth profile of the Sn coating with graded structure was obtained, which qualitatively corresponded with the depth profile measured by secondary ion mass spectrometry.     

Calibration graphs for steels by IR laser ablation inductively coupled plasma atomic emission spectrometry

Infrared laser ablation (IRLA) was studied as a sample-introduction technique for the analysis of steels by inductively coupled plasma atomic emission spectrometry (ICP–AES). A comparison of two IRLA–ICP–AES systems based on Q-switched nanosecond Nd?:?YAG lasers was performed. The beam of the Lina-Spark atomizer (LSA Sarl, Cully, Switzerland) based on the Surelite I-20 laser (Continuum, USA) was moved along a circle. A Perkin–Elmer Optima 3000 DV ICP system was used both with lateral and axial viewing modes. A laboratory-made ablation system based on the Brilliant laser (Quantel) was coupled to a Jobin-Yvon 170 Ultrace ICP (lateral viewing, polychromator part employed). A sample was rotated along a circle during ablation. Linearity of calibration plots was verified at least up to 19% Cr and 12% Ni without internal standardization for both LA–ICP–AES systems. Other elements examined were Mo up to 3%, Mn up 1.5%, Si up to 1.7%, and Cu up to 0.15%. The reproducibility was in the range 5–1 %RSD for a mass percentage 0.5–20% of steel constituents. The relative uncertainty of the centroids of the calibration lines was in the range from ± 4% to ± 12% for Cr, Ni, Mn, Mo, and Si, and from ± 8% to ± 19% for Cu. The lowest determinable quantities were calculated for calibration dependencies. Performances of both the IR-LA–ICP–AES were comparable.     

Calibration graphs for steels by IR laser ablation inductively coupled plasma atomic emission spectrometry

Infrared laser ablation (IRLA) was studied as a sample-introduction technique for the analysis of steels by inductively coupled plasma atomic emission spectrometry (ICP-AES). A comparison of two IRLA-ICP-AES systems based on Q-switched nanosecond Nd: YAG lasers was performed. The beam of the LINA-Spark atomizer (LSA Sarl, Cully, Switzerland) based on the Surelite 1-20 laser (Continuum, USA) was moved along a circle. A Perkin-Elmer Optima 3000 DV ICP system was used both with lateral and axial viewing modes. A laboratory-made ablation system based on the Brilliant laser (Quantel) was coupled to a Jobin-Yvon 170 Ultrace ICP (lateral viewing, polychromator part employed). A sample was rotated along a circle during ablation. Linearity of calibration plots was verified at least up to 19% Cr and 12% Ni without internal standardization for both LA-ICP-AES systems. Other elements examined were Mo up to 3%, Mn up 1.5%, Si up to 1.7%, and Cu up to 0.15%. The reproducibility was in the range 5-1 %RSD for a mass percentage 0.5-20% of steel constituents. The relative uncertainty of the centroids of the calibration lines was in the range from +/- 4% to +/- 12% for Cr, Ni, Mn, Mo, and Si, and from +/- 8% to +/- 19% for Cu. The lowest determinable quantities were calculated for calibration dependencies. Performances of both the IR-LA-ICP-AES were comparable.     

Infrared laser ablation study of pressed soil pellets with inductively coupled plasma atomic emission spectrometry

Potential of infrared laser ablation (LA) coupled with ICP-AES as a technique suitable for the determination of trace elements (Zn, Cu, Ni, Cr, and V) in agricultural soils was studied. Operating parameters such as laser beam energy, laser beam focusing with respect to the sample surface, and velocity of the sample translation in the plane perpendicular to the laser beam were optimized. Soil samples were mixed with powdered Ag as a binder, and an internal standard (GeO(2)), and pressed into pellets. Calibration samples were prepared by adding known amounts of oxides of elements of interest into soils of known elemental composition and then processed in the same way as the analyzed samples. Calibration curves were found to be linear at least up to several hundreds of mg kg(-1) for the elements of interest. The elemental contents obtained by using LA-ICP-AES were compared with those obtained by analysis using wet chemistry followed by ICP-AES with pneumatic nebulization (PN). The results were in good agreement. Accuracy was also tested using certified reference soils with a bias not exceeding 10% relative.     

Characterization of acoustic signals produced by ultraviolet laser ablation inductively coupled plasma atomic emission spectrometry

A simple device was designed to measure the acoustic signal accompanying laser ablation. The potential use of this signal for laser ablation-inductively coupled plasma atomic emission was examined. A frequency quadrupled pulsed Nd:YAG laser radiation was used for the ablation of glass, steel and ceramic samples. The relation between the acoustic signal, the laser energy, the analyte signal and the amount of ablated material was studied and evidence of the use of the acoustic signal for the exact focusing of the laser beam onto the sample surface was given. A more intense acoustic signal was observed for the exact focusing with a formation of larger ablation craters in glass and ceramics. Received: 25 June 1998 / Revised: 25 September 1998 / Accepted: 30 September 1998     

Characterization of acoustic signals produced by ultraviolet laser ablation inductively coupled plasma atomic emission spectrometry

A simple device was designed to measure the acoustic signal accompanying laser ablation. The potential use of this signal for laser ablation-inductively coupled plasma atomic emission was examined. A frequency quadrupled pulsed Nd:YAG laser radiation was used for the ablation of glass, steel and ceramic samples. The relation between the acoustic signal, the laser energy, the analyte signal and the amount of ablated material was studied and evidence of the use of the acoustic signal for the exact focusing of the laser beam onto the sample surface was given. A more intense acoustic signal was observed for the exact focusing with a formation of larger ablation craters in glass and ceramics.     

Modelling of the evaporation behaviour of particulate material for slurry nebulization inductively coupled plasma atomic emission spectrometry

This paper is an electronic publication in Spectrochimica Acta Electronica (SAE), the electronic section of Spectrochimica Acta, Part B (SAB). This hardcopy text, comprising the main body and an appendix, is accompanied by a disk with programs, data files and a brief manual. The main body discusses purpose, design principle and usage of the computer software for modelling the evaporation behaviour of particles in inductively coupled plasma atomic emission spectrometry (ICP-AES). Computer software has been developed in FORTRAN 77 language in order to simulate the evaporation behaviour of particles of refractory materials such as encountered in the analysis of advanced ceramic powders by slurry nebulization inductively coupled argon plasma atomic spectrometry. The program simulates the evaporation of single particles in the inductively coupled plasma and also enable it to calculate on the base of a given particle size distribution the evaporation behaviour of all the particles contained in a sample. In a so-called “intensity concept”, the intensity is calculated as a function of the observation height in order to determine recovery rates for slurries compared with aqueous solutions. This yields a quick insight whether a calibration with aqueous solutions can be used for analysis of slurries of a given powder by slurry nebulization ICP-AES and also is a help in determining the optimal parameters for analyses of powders by means of slurry nebulization ICP-AES.Applications for the evaporation of Al₂O₃ and SiC powders document the usefulness of the model for the case of a 1.5 kW argon ICP of which the temperature at 8 mm above the load coil has been determined to be 6100 K. The model predicts the maximum particle size for SiC and Al₂O₃ that can be transported (10–15 μm) and evaporated for a given efficiency under given experimental conditions. For both Al₂O₃ and SiC, two ceramic powders of different grain size were investigated. The median particle sizes cover the range typical of ceramic powders. Investigations were made for SiC A 10 (median particle size 2.2 μm), SiC F1200 (4.3 μm) and Al₂O₃ AKP 30 (< 1.9 μm) and Al₂O₃ Cilas 715 (3.0 μm), respectively, in which particles with diameters of up to 23 μm still are found.     

Modified Babington nebulizer for inductively coupled plasma atomic emission spectrometry.

A PTFE Babingtonnebulizer equipped with a hood was investigated for inductively coupled plasma atomicemission spectrometry in conjunction with a PTFE cyclone chamber, in order to nebulize various sample solutions containing high salts, hydrofluoric acid and/or suspended solid. A hood of 3 mmphi (nozzle side) - 5 mmphi (outlet side) and 6 mm in length gave a comparable or higher sensitivity compared to a system with a commercially available concentric nebulizer and a glass cyclone chamber. Moreover, the present nebulizer was fully interchangeable with a concentric one at normal argon pressure, attaining sufficient stability, a short wash-out time and good nebulizing of high matrices solutions. The present system was successfully applied to the determination of trace impurities in highly pure silica powders.     

Interface for capillary electrophoresis coupled with inductively coupled plasma atomic emission spectrometry.

A modified concentric nebulizer was used as the interface to couple capillary electrophoresis (CE) to inductively coupled plasma atomic emission spectrometry (ICP-AES). The CE capillary replaces the central tube of the concentric nebulizer. The tip of the nebulizer tapers slowly to allow uncertainty in the position of the capillary. A platinum wire was inserted into the CE capillary to provide electrical connection to the CE power supply. pH changes inside the capillary due to electrolysis of the background buffer electrolyte was small and has minimal effects on the CE separation. The peak broadening effects due to the nebulizing gas flow, however, were significant. Resolution decreases quickly when the flow-rate of the carrier gas increases. Sample stacking technique was used to improve the resolution of species of opposite charge, e.g., Cr(VI) vs. Cr(III) ions. Detection limit of Cr based on peak area is approximately 10 ppb for the CE-ICP-AES system.     

Quality of calibration in inductively coupled plasma atomic emission spectrometry

Calibration is a crucial step during the whole analytical process. A procedure is suggested to assess the quality of linear regression used for the calibration graph, based on the use of confidence limits for the concentration, as the regression coefficient is not appropriate for this purpose. This procedure has been applied to inductively coupled plasma atomic emission spectrometry. It indicates that the use of only three standards should be discouraged because of unacceptably high confidence limits for the concentration. Moreover, use of weighted regression is more adequate in performing the least squares method and provides more constant confidence limits over the concentration range used to construct the calibration graph. This procedure could be easily added to any commercially available ICP system software.     

Applications of inductively coupled plasma mass spectrometry and laser ablation inductively coupled plasma mass spectrometry in materials science

Inductively coupled plasma mass spectrometry (ICP-MS) and laser ablation ICP-MS (LA-ICP-MS) have been applied as the most important inorganic mass spectrometric techniques having multielemental capability for the characterization of solid samples in materials science. ICP-MS is used for the sensitive determination of trace and ultratrace elements in digested solutions of solid samples or of process chemicals (ultrapure water, acids and organic solutions) for the semiconductor industry with detection limits down to sub-picogram per liter levels. Whereas ICP-MS on solid samples (e.g. high-purity ceramics) sometimes requires time-consuming sample preparation for its application in materials science, and the risk of contamination is a serious drawback, a fast, direct determination of trace elements in solid materials without any sample preparation by LA-ICP-MS is possible. The detection limits for the direct analysis of solid samples by LA-ICP-MS have been determined for many elements down to the nanogram per gram range. A deterioration of detection limits was observed for elements where interferences with polyatomic ions occur. The inherent interference problem can often be solved by applying a double-focusing sector field mass spectrometer at higher mass resolution or by collision-induced reactions of polyatomic ions with a collision gas using an ICP-MS fitted with collision cell. The main problem of LA-ICP-MS is quantification if no suitable standard reference materials with a similar matrix composition are available. The calibration problem in LA-ICP-MS can be solved using on-line solution-based calibration, and different procedures, such as external calibration and standard addition, have been discussed with respect to their application in materials science. The application of isotope dilution in solution-based calibration for trace metal determination in small amounts of noble metals has been developed as a new calibration strategy. This review discusses new analytical developments and possible applications of ICP-MS and LA-ICP-MS for the quantitative determination of trace elements and in surface analysis for materials science.     

Study of laser ablation of brass materials using inductively coupled plasma atomic emission spectrometric detection

A XeCl laser and a Q-switched Nd:YAG laser operating at 1064, 532, 355 and 266 nm were used to ablate brass materials with varying concentrations of Zn and Cu. The ablated material was transported to an inductively coupled plasma for further atomization, excitation and ionization with an atomic emission spectrometric detection. A Zn enhancement was observed, which could be suppressed by using a Nd:YAG laser working at 266 nm with fluences higher than 400 J cm⁻² (equivalent to 80 GW cm⁻²). In contrast, a lack of linearity was observed for Cu as a function of the concentration, regardless of the wavelength and the fluence. The Cu problem seemed to occur during the ablation and was related to the structure of the brass material. Lack of linearity was also observed for Zn and other contained elements when samples from different origins were used.     

Laser ablation inductively coupled plasma atomic emission spectrometry of a uranium-zirconium alloy: ablation properties and analytical behavior

The ablation properties and analytical behavior of a uranium-zirconium alloy have been examined using tandem laser ablation/pneumatic nebulization sample introduction in conjunction with inductively coupled atomic emission spectrometry (LA-ICP-AES). An apparent change in composition of the laser ablation aerosol (1–15 GW cm⁻² Zr deficient, 40–250 GW cm⁻² Zr rich) is observed. This phenomenon is independent of laser wavelength. After collection and bulk chemical analysis of the ablation product, this phenomenon is attributed to an atomization interference in the ICP.

Two distinct modes of laser ablation have been observed which depend upon the wavelength of the ablating laser (visible or near infrared). These two modes result in characteristic ablation crater types and analyte emission behavior. Ablation yields at 1064 nm are dependent upon laser power density only, whilst yields at 532 nm are dependent upon both laser power density and illumination area. The latter is considered to be symptomatic of direct interaction of the laser light with the surface, and the former, of indirect coupling of laser energy, via a micro-plasma, into the surface.     

Optimized microwave-assisted decomposition method for multi-element analysis of glass standard reference material and ancient glass specimens by inductively coupled plasma atomic emission spectrometry

A novel microwave-assisted wet-acid decomposition method for the multi-element analysis of glass samples using inductively coupled plasma atomic emission spectrometry (ICP-AES) was developed and optimized. The SRM 621 standard reference glass material was used for this purpose, because it has similar composition with either archaeological glass specimens or common modern glasses. For the main constituents of SRM 621 (Ca, Na, Al, Fe, Mg, Ba and Ti), quality control data are given for all the examined procedures. The chemical and instrumental parameters of the method were thoroughly optimized. Thirteen acid mixtures of hydrochloric, nitric, and hydrofluoric acids in relation to two different microwave programs were examined in order to establish the most efficient protocol for the determination of metals in glass matrix. For both microwave programs, an intermediate step was employed with addition of H₃BO₃ in order to compensate the effect of HF, which was used in all protocols. The suitability of the investigated protocols was evaluated for major (Ca, Na, Al), and minor (Fe, Mg, Ba, Ti, Mn, Cu, Sb, Co, Pb) glass constituents. The analytes were determined using multi-element matrix matched standard solutions. The analytical data matrix was processed chemometrically in order to evaluate the examined protocols in terms of their accuracy, precision and sensitivity, and eventually select the most efficient method for ancient glass. ICP-AES parameters such as spectral line, RF power and sample flow rate were optimized using the proposed protocol. Finally, the optimum method was successfully applied to the analysis of a number of ancient glass fragments.     

Modelling the temporal intensity distribution of laser ablation inductively coupled plasma mass spectrometry in single shot mode

A transport model is proposed that describes the temporal intensity distribution observed in laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) in single-shot mode using quantitative signal equations. Calculations aim on the deduction of the dispersion function describing the time-dependent part of the signal equation.

The dispersion function depends on transport time in the centre of the transport tube, as related to carrier gas flow rate and tube volume and on the relation between carrier gas flow rate and ablation chamber volume. The equations describing the signal shape standardize signals from different systems and allow quantitative optimization of the ablation chamber, the transport tube and the detector.

Application of the model to ICP-MS shows that only a part of the area filled by the transported vaporization product and thus only a part of the transported vaporization product can be observed at the detector. The model is able to quantify both fractions.

As was calculated, the observed fraction of analyte is always higher than the observed fraction of the sample containing cross section and depends on the chosen transport parameters characterising the dispersion function. Thus, the determination of the signal integrals in the usual way can lead to systematic errors if the parameters influencing the dispersion function are variable.

Therefore, a different method of analysis based on signal equations is proposed and demonstrated. By this method of data treatment, all important system parameters influencing the dispersion function could be calculated and matched with theoretical ones. Furthermore, a complete integral of the transient signal including its statistical variation can be generated from a limited number of measurement points. For example, this can be applied to signals detected incompletely because of detector saturation and enables the use of high-abundance elements as internal standards.

Furthermore, the method can be used to monitor system performance, to identify the flow regime inside the ablation chamber, to take into account the sample volume for quantitative analysis and finally, to detect anomalous signal distributions that would lead to systematic errors. The prospects and limitations of the model are discussed for LA-ICP-MS in single shot mode.