Trace analysis of high-purity graphite by LA–ICP–MS

Laser-ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) has been established as a very efficient and sensitive technique for the direct analysis of solids. In this work the capability of LA–ICP–MS was investigated for determination of trace elements in high-purity graphite. Synthetic laboratory standards with a graphite matrix were prepared for the purpose of quantifying the analytical results. Doped trace elements, concentration 0.5 μg g^–1, in a laboratory standard were determined with an accuracy of 1% to ± 7% and a relative standard deviation (RSD) of 2–13%. Solution-based calibration was also used for quantitative analysis of high-purity graphite. It was found that such calibration led to analytical results for trace-element determination in graphite with accuracy similar to that obtained by use of synthetic laboratory standards for quantification of analytical results. Results from quantitative determination of trace impurities in a real reactor-graphite sample, using both quantification approaches, were in good agreement. Detection limits for all elements of interest were determined in the low ng g^–1 concentration range. Improvement of detection limits by a factor of 10 was achieved for analyses of high-purity graphite with LA–ICP–MS under wet plasma conditions, because the lower background signal and increased element sensitivity. Received: 4 January 2001 / Revised: 27 March 2001 / Accepted: 28 March 2001     

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.     

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS): comparison of different internal standardization methods using laser-induced plasma (LIP) emission and LA-ICP-MS signals.

The source of signal variations that governs the analytical performance of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) was investigated in this study. In order to specify the source of signal variations of LA-ICP-MS, laser-induced plasma (LIP) Fe emission, LA-ICP-MS Fe+ and LA-ICP-MS Ni+ signals were used as internal standards for the determination of trace elements in low-alloy steel certified reference materials (BS 50D and JSS 1005-1008). Fe 1373.5 nm emission signals from LIP were measured, while trace element LA-ICP-MS signals were collected. After that, the LIP emission signals, LA-ICP-MS Fe+ and LA-ICP-MS Ni+ signals were used as internal standards, and the analytical performance was evaluated by the RSDs and the correlation coefficients (r) of the calibration curves. The improvement factors were dependent on the internal standardization methods. Analytical precisions (RSDs) of trace element LA-ICP-MS signals were improved by factors of 1.5-3.3 using LIP Fe emission signals as an internal standard. The improvement factors of 2.5 - 5.9 and 4.1 - 17 were obtained by using LA-ICP-MS Fe+ and LA-ICP-MS Ni+ signals as internal standards, respectively. Better correlation coefficients (r) were also obtained using the LA-ICP-MS signal compensation (0.9985 by LA-ICP-MS Fe+ and 0.9996 by LA-ICP-MS Ni+) rather than the LIP Fe emission compensation (0.9932). In this paper we compare and discuss the analytical performance achieved by LA-ICP-MS using LIP Fe emission, LA-ICP-MS Fe+ and LA-ICP-MS Ni+ signals as internal standards.     

Improvements in calibration procedures for the quantitative determination of trace elements in carbonate material (mussel shells) by laser ablation ICP-MS

A better repeatability and accuracy in the quantitative determination of trace elements in mussel shells or carbonate-based materials by LA-ICP-MS was achieved by using a series of multielement calibration standards prepared by co-precipitation of twelve elements into a CaCO3 matrix in order to improve the homogeneity of the resulting powder samples. Pressed powder discs of good mechanical stability could be obtained at a pressure of 50 MPa, without the addition of a binder. An UV laser (modified Nd:YAG, 266 nm) was used in the Q-switched mode at a repetition rate of 10 Hz and an energy level of 3.5 mJ. Correlation coefficients (R) for the linear calibration graphs (concentration range: 1.5-400 microg/g) for Cr, Mn, Co, Cu, Zn, As, Cd, Sn, Ba, and Pb are generally better than 0.997. The detection limits for all elements investigated are in the sub-microg/g range. Incorporation of elements into the matrix by co-precipitation has shown as a superior method for producing calibration standards than the simple mixture of the analytes (in carbonate or oxide form) with the matrix (CaCO3) or addition of standard solutions to a carbonate powder base. Two examples of the quantitative determination of toxic elements in mussel shells will be presented.     

Determination of trace elements in zeolites by laser ablation ICP-MS

Laser ablation inductively coupled plasma mass spectrometry using a quadrupole-based mass spectrometer (LA-ICP-QMS) was applied for the analysis of powdered zeolites (microporous aluminosilicates) used for clean-up procedures. For the quantitative determination of trace element concentrations three geological reference materials, granite NIM-G, lujavrite NIM-L and syenite NIM-S, from the National Institute for Metallurgy (South Africa) with a matrix composition corresponding to the zeolites were employed. Both the zeolites and reference materials were fused with a lithium borate mixture to increase the homogeneity and to eliminate mineralogical effects. In order to compare two different approaches for the quantification of analytical results in LA-ICP-MS relative sensitivity coefficients (RSCs) of chemical elements and calibration curves were measured using the geostandards. The experimentally obtained RSCs are in the range of 0.2-6 for all elements of interest. Calibration curves for trace elements were measured without and with Li or Ti as internal standard element. With a few exceptions the regression coefficients of the calibration curves are better than 0.993 with internal standardization. NIM-G granite reference material was employed to evaluate the accuracy of the technique. Therefore, the measured concentrations were corrected with RSCs which were determined using lujavrite reference material NIM-L. This quantification method provided analytical results with deviations of 1-11% from the recommended and proposed values in granite reference material NIM-G, except for Co, Cs, La and Tb. The relative standard deviation (RSD) of the determination of the trace element concentration (n = 5) is about 1% to 6% using Ti as internal standard element. Detection limits of LA-ICP-QMS in the lower microg/g range (from 0.03 microg/g for Lu, Ta and Th to 7.3 microg/g for Cu, with the exception of La) have been achieved for all elements of interest. Under the laser ablation conditions employed (lambda: 266 nm, repetition frequency: 10 Hz, pulse energy: 10 mJ, laser power density: 6 x 10(9) W/cm2) fractionation effects of the determined elements relative to the internal standard element Ti were not observed.     

Imaging mass spectrometry in biological tissues by laser ablation inductively coupled plasma mass spectrometry

Of all the inorganic mass spectrometric techniques, laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) plays a key role as a powerful and sensitive microanalytical technique enabling multi- element trace analysis and isotope ratio measurements at trace and ultratrace level. LA-ICP-MS was used to produce images of detailed regionally-specific element distribution in 20 microm thin sections of different parts of the human brain. The quantitative determination of copper, zinc, lead and uranium distribution in thin slices of human brain samples was performed using matrix-matched laboratory standards via external calibration procedures. Imaging mass spectrometry provides new information on the spatially inhomogeneous element distribution in thin sections of human tissues, for example, of different brain regions (the insular region) or brain tumor tissues. The detection limits obtained for Cu, Zn, Pb and U were in the ng g(-1) range. Possible strategies of LA-ICP-MS in brain research and life sciences include the elemental imaging of thin slices of brain tissue or applications in proteome analysis by combination with matrix-assisted laser desorption/ionization MS to study phospho- and metal- containing proteins will be discussed.     

A new strategy of solution calibration in laser ablation inductively coupled plasma mass spectrometry for multielement trace analysis of geological samples

Because multielement trace analysis by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) is often limited by the lack of suitable reference materials with a similar matrix composition, a novel quantification strategy using solution calibration was developed. For mass spectrometric multielement determination in geological samples a quadrupole-based LA-ICP-MS is coupled with an ultrasonic nebulizer (USN). In order to arrange matrix matching the standard solutions are nebulized with a USN during solution calibration and simultaneously a blank target (e.g. lithium borate) is ablated with a focused laser beam. The homogeneous geological samples were measured using the same experimental arrangement where a 2% nitric acid is simultaneously nebulized with the USN. Homogeneous targets were prepared from inhomogeneous geological samples by powdering, homogenizing and fusing with a lithium borate mixture in a muffle furnace at 1050 degrees C. Furthermore, a homogeneous geological glass was also investigated. The quantification of analytical results was performed by external calibration using calibration curves measured on standard solutions. In order to compare two different approaches for the quantification of analytical results in LA-ICP-MS, measured concentrations in homogeneous geological targets were also corrected with relative sensitivity coefficients (RSCs) determined using one standard solution only. The analytical results of LA-ICP-MS on various geological samples are in good agreement with the reference values and the results of other trace analytical methods. The relative standard deviation (RSD) for trace element determination (N = 6) is between 2 and 10%.     

Spectrographic analysis of high-purity nickel oxide for twenty-one trace impurities, with use of a new buffer

A spectrographic method for the determination of twenty-one trace impurities in high-purity nickel oxide by the d.c. arc technique has been developed. A mixture of graphite and indium oxide in the ratio 2:1 is used as buffer. The lowest determination limits for various elements lie between 1 and 10 ppm with an average relative standard deviation of +/- 12%.     

Determination of Platinum Group Elements in Sulfide-Containing Minerals by Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry with Synthetic Calibration Standards

This paper develops sulfide calibration standards for quantitative determination of platinum group elements in natural sulfide-containing minerals by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). A series of sulfide calibration standards containing different concentrations of platinum group elements were prepared using a home-made high temperature furnace. Homogeneity of element distribution expressed as the RSD of signal intensity were less than 10%. The effective concentrations of platinum group elements in synthetic calibration standards were obtained both by pneumatic nebulization ICP-MS and by LA-ICP-MS. Relative percentage differences of these results obtained by two methods were mainly less than 11%. The synthetic calibration standards were then employed as calibrators for quantitative determination of platinum group elements in two natural chalcopyrite samples. The valid results demonstrated that our synthetic standards could be considered for quantitative microanalysis of platinum group elements in natural sulfide-containing minerals.     

Inorganic trace analysis by mass spectrometry

Mass spectrometric methods for the trace analysis of inorganic materials with their ability to provide a very sensitive multielemental analysis have been established for the determination of trace and ultratrace elements in high-purity materials (metals, semiconductors and insulators), in different technical samples (e.g. alloys, pure chemicals, ceramics, thin films, ion-implanted semiconductors), in environmental samples (waters, soils, biological and medical materials) and geological samples. Whereas such techniques as spark source mass spectrometry (SSMS), laser ionization mass spectrometry (LIMS), laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), glow discharge mass spectrometry (GDMS), secondary ion mass spectrometry (SIMS) and inductively coupled plasma mass spectrometry (ICP-MS) have multielemental capability, other methods such as thermal ionization mass spectrometry (TIMS), accelerator mass spectrometry (AMS) and resonance ionization mass spectrometry (RIMS) have been used for sensitive mono- or oligoelemental ultratrace analysis (and precise determination of isotopic ratios) in solid samples. The limits of detection for chemical elements using these mass spectrometric techniques are in the low ng g⁻¹ concentration range. The quantification of the analytical results of mass spectrometric methods is sometimes difficult due to a lack of matrix-fitted multielement standard reference materials (SRMs) for many solid samples. Therefore, owing to the simple quantification procedure of the aqueous solution, inductively coupled plasma mass spectrometry (ICP-MS) is being increasingly used for the characterization of solid samples after sample dissolution. ICP-MS is often combined with special sample introduction equipment (e.g. flow injection, hydride generation, high performance liquid chromatography (HPLC) or electrothermal vaporization) or an off-line matrix separation and enrichment of trace impurities (especially for characterization of high-purity materials and environmental samples) is used in order to improve the detection limits of trace elements. Furthermore, the determination of chemical elements in the trace and ultratrace concentration range is often difficult and can be disturbed through mass interferences of analyte ions by molecular ions at the same nominal mass. By applying double-focusing sector field mass spectrometry at the required mass resolution—by the mass spectrometric separation of molecular ions from the analyte ions—it is often possible to overcome these interference problems. Commercial instrumental equipment, the capability (detection limits, accuracy, precision) and the analytical application fields of mass spectrometric methods for the determination of trace and ultratrace elements and for surface analysis are discussed.     

A new strategy of solution calibration in laser ablation inductively coupled plasma mass spectrometry for multielement trace analysis of geological samples

Because multielement trace analysis by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) is often limited by the lack of suitable reference materials with a similar matrix composition, a novel quantification strategy using solution calibration was developed. For mass spectrometric multielement determination in geological samples a quadrupole-based LA-ICP-MS is coupled with an ultrasonic nebulizer (USN). In order to arrange matrix matching the standard solutions are nebulized with a USN during solution calibration and simultaneously a blank target (e.g. lithium borate) is ablated with a focused laser beam. The homogeneous geological samples were measured using the same experimental arrangement where a 2% nitric acid is simultaneously nebulized with the USN. Homogeneous targets were prepared from inhomogeneous geological samples by powdering, homogenizing and fusing with a lithium borate mixture in a muffle furnace at 1050?°C. Furthermore, a homogeneous geological glass was also investigated. The quantification of analytical results was performed by external calibration using calibration curves measured on standard solutions. In order to compare two different approaches for the quantification of analytical results in LA-ICP-MS, measured concentrations in homogeneous geological targets were also corrected with relative sensitivity coefficients (RSCs) determined using one standard solution only. The analytical results of LA-ICP-MS on various geological samples are in good agreement with the reference values and the results of other trace analytical methods. The relative standard deviation (RSD) for trace element determination (N = 6) is between 2 and 10%.     

Determination of trace elements in zeolites by laser ablation ICP-MS

Laser ablation inductively coupled plasma mass spectrometry using a quadrupole-based mass spectrometer (LA-ICP-QMS) was applied for the analysis of powdered zeolites (microporous aluminosilicates) used for clean-up procedures. For the quantitative determination of trace element concentrations three geological reference materials, granite NIM-G, lujavrite NIM-L and syenite NIM-S, from the National Institute for Metallurgy (South Africa) with a matrix composition corresponding to the zeolites were employed. Both the zeolites and reference materials were fused with a lithium borate mixture to increase the homogeneity and to eliminate mineralogical effects. In order to compare two different approaches for the quantification of analytical results in LA-ICP-MS relative sensitivity coefficients (RSCs) of chemical elements and calibration curves were measured using the geostandards. The experimentally obtained RSCs are in the range of 0.2-6 for all elements of interest. Calibration curves for trace elements were measured without and with Li or Ti as internal standard element. With a few exceptions the regression coefficients of the calibration curves are better than 0.993 with internal standardization. NIM-G granite reference material was employed to evaluate the accuracy of the technique. Therefore, the measured concentrations were corrected with RSCs which were determined using lujavrite reference material NIM-L. This quantification method provided analytical results with deviations of 1–11% from the recommended and proposed values in granite reference material NIM-G, except for Co, Cs, La and Tb. The relative standard deviation (RSD) of the determination of the trace element concentration (n = 5) is about 1% to 6% using Ti as internal standard element. Detection limits of LA-ICP-QMS in the lower μg/g range (from 0.03 μg/g for Lu, Ta and Th to 7.3 μg/g for Cu, with the exception of La) have been achieved for all elements of interest. Under the laser ablation conditions employed (λ: 266 nm, repetition frequency: 10 Hz, pulse energy: 10 mJ, laser power density: 6 × 10⁹ W/cm²) fractionation effects of the determined elements relative to the internal standard element Ti were not observed. Received: 7 April 2000 / Revised: 25 May 2000 / Accepted: 31 May 2000     

Improvements in calibration procedures for the quantitative determination of trace elements in carbonate material (mussel shells) by laser ablation ICP-MS

A better repeatability and accuracy in the quantitative determination of trace elements in mussel shells or carbonate-based materials by LA-ICP-MS was achieved by using a series of multielement calibration standards prepared by co-precipitation of twelve elements into a CaCO₃ matrix in order to improve the homogeneity of the resulting powder samples. Pressed powder discs of good mechanical stability could be obtained at a pressure of 50 MPa, without the addition of a binder. An UV laser (modified Nd:YAG, 266 nm) was used in the Q-switched mode at a repetition rate of 10 Hz and an energy level of 3.5 mJ. Correlation coefficients (R) for the linear calibration graphs (concentration range: 1.5–400 μg/g) for Cr, Mn, Co, Cu, Zn, As, Cd, Sn, Ba, and Pb are generally better than 0.997. The detection limits for all elements investigated are in the sub-μg/g range. Incorporation of elements into the matrix by co-precipitation has shown as a superior method for producing calibration standards than the simple mixture of the analytes (in carbonate or oxide form) with the matrix (CaCO₃) or addition of standard solutions to a carbonate powder base. Two examples of the quantitative determination of toxic elements in mussel shells will be presented. Received: 10 January 2000 / Revised: 16 March 2000 / Accepted: 26 March 2000     

Automated in situ trace element analysis of silicate materials by laser ablation inductively coupled plasma mass spectrometry

This paper describes the automated in situ trace element analysis of solid materials by laser ablation (LA) inductively coupled plasma mass spectrometry (ICP-MS). A compact computer-controlled solid state Nd:YAG Merchantek EO UV laser ablation (LA) system has been coupled with the high sensitivity VG PQII S ICP-MS. A two-directional communication was interfaced in-house between the ICP-MS and the LA via serial RS-232 port. Each LA-ICP-MS analysis at a defined point includes a 60 s pre-ablation delay, a 60 s ablation, and a 90 s flush delay. The execution of each defined time setting by LA was corresponding to the ICP-MS data acquisition allowing samples to be run in automated cycle sequences like solution auto-sampler ICP-MS analysis. Each analytical cycle consists of four standards, one control reference material, and 15 samples, and requires about 70 min. Data produced by Time Resolved Analysis (TRA) from ICP-MS were later reduced off-line by in-house written software. Twenty-two trace elements from four reference materials (NIST SRM 613, and fused glass chips of BCR-2, SY-4, and G-2) were determined by the automated LA-ICP-MS method. NIST SRM 610 or NIST SRM 613 was used as an external calibration standard, and Ca as an internal standard to correct for drift, differences in transport efficiency and sampling yield. Except for Zr and Hf in G-2, relative standard deviations for all other elements are less than 10%. Results compare well with the data reported from literature with average limits of detection from 1 ng x g(-1) to 455 ng x g(-1) and less than 100 ng x g(-1) for most trace elements.     

A new laser ablation system for quantitative analysis of solid samples with ICP-MS.

The laser ablation (LA) method is an effective technique for quantitative analysis. In the present work, a new LA system was developed for the high-sensitivity analysis of metal materials using inductively coupled plasma mass spectrometry (ICP-MS). This system consists of a high-frequency Q-switched laser and 2 scanning mirrors for scanning the ablation spot in an adequately large area of the specimen without vacant spaces. The influence of elemental fractionation (non-stoichiometric generation of vapor species) can be eliminated by repetitive irradiation of this pattern on the same area. Particles generated with an average laser power of 0.6 W with the developed LA system gave intensity and stability substantially similar to that of a 500 microg/ml solution steel sample in solution ICP-MS. The analytical performance of the developed LA-ICP-MS was compared with that of a solution ICP-MS using NIST steel SRMs. The performance of the newly-developed system is comparable to that of conventional solution ICP-MS in both accuracy and precision. The correlation coefficients between the contents and the intensity ratios to Fe were over 0.99 for most elements. The relative standard deviation (RSD) obtained by LA-ICP-MS revealed that this system can analyze iron samples with good precision. The results of ultra trace level analysis of high-purity iron showed that developed LA-ICP-MS is capable of analyzing ppm concentration levels with a 20 - 30 ppb level standard deviation. The detection limit was on the order of 10 ppb for most elements.     

Laser Ablation Inductively Coupled Plasma Mass Spectrometry for Determination of Trace Elements in Geological Glasses

 Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) was used as a powerful multielement analytical method for trace analysis of geological glasses which are useful as reference materials for geochemical in-situ microanalytical work. The quantification of the analytical results was carried out using the BCR-2G and NIST 612 glass standard reference material (SRM). The experimentally determined relative sensitivity coefficients (RSC) for both SRMs vary between 0.2 and 3 for most of the elements, with increasing mass an increasing of relative sensitivity coefficients was observed. The relative standard deviation (RSD) for determination of trace element concentration of most elements (N=3) are between 2 and 10%. The determination of trace elements in various geological glasses by LA-ICP-MS yielded a good agreement with the reference values and those results of other trace analytical methods. Received October 15, 1999. Revision April 14, 2000.     

Calibration of laser-ablation ICP-MS. Can we use synthetic standards with pneumatic nebulization?

An approach for the determination of trace element concentrations in high purity metals, using an inductively coupled plasma mass spectrometer (ICP-MS) with a laser-ablation system for direct solid sample introduction after calibration with nebulized liquid standards was made. Due to the inherent differences in the rate of sample introduction with laser-ablation and pneumatic nebulization, a matrix element must be used as an internal standard. This is problematical for elements that have no isotope with a relative abundance of less than 0.1 %, since the ion signals would be too high for direct measurement, and reduction of the ablation rate would compromise the sensitivity for trace elements. Due to the high stability of ICP-unit and mass filter of the instrument used, it was found that the tail of a mass-peak of the matrix element could be used as an internal standard. Therefore, a position at –0.5 amu from the matrix-isotope (e.g. ^62.5Cu in copper samples) was used for internal standardization. The standard deviation of this signal in a period of 2.5 h was 3.6% RSD with no notable drift when the laser ablation was used for sample introduction. The calibration of the matrix-element by nebulizing liquid standards showed that the ion signal measured on the peak-tail is directly proportional to the element concentration in the ICP. This indicates that the peak shape is not only stable, but also independent of the peak height. The advantages of this method lie in the easy preparation of calibration standards for quantitative measurements with a laser-ablation system and access to homogeneous standards for materials, that are difficult to homogenize in the solid state. The calibration of the traces is performed relatively to a fixed concentration of the matrix element. Calibrations were carried out for trace concentrations in high purity copper and good recoveries were obtained for high-purity reference standards. Received: 23 February 1998 / Revised: 20 July 1998 / Accepted: 25 July 1998     

Calibration of laser-ablation ICP-MS. Can we use synthetic standards with pneumatic nebulization?

An approach for the determination of trace element concentrations in high purity metals, using an inductively coupled plasma mass spectrometer (ICP-MS) with a laser-ablation system for direct solid sample introduction after calibration with nebulized liquid standards was made. Due to the inherent differences in the rate of sample introduction with laser-ablation and pneumatic nebulization, a matrix element must be used as an internal standard. This is problematical for elements that have no isotope with a relative abundance of less than 0.1 %, since the ion signals would be too high for direct measurement, and reduction of the ablation rate would compromise the sensitivity for trace elements. Due to the high stability of ICP-unit and mass filter of the instrument used, it was found that the tail of a mass-peak of the matrix element could be used as an internal standard. Therefore, a position at –0.5 amu from the matrix-isotope (e.g. ^62.5Cu in copper samples) was used for internal standardization. The standard deviation of this signal in a period of 2.5 h was 3.6% RSD with no notable drift when the laser ablation was used for sample introduction. The calibration of the matrix-element by nebulizing liquid standards showed that the ion signal measured on the peak-tail is directly proportional to the element concentration in the ICP. This indicates that the peak shape is not only stable, but also independent of the peak height. The advantages of this method lie in the easy preparation of calibration standards for quantitative measurements with a laser-ablation system and access to homogeneous standards for materials, that are difficult to homogenize in the solid state. The calibration of the traces is performed relatively to a fixed concentration of the matrix element. Calibrations were carried out for trace concentrations in high purity copper and good recoveries were obtained for high-purity reference standards. Received: 23 February 1998 / Revised: 20 July 1998 / Accepted: 25 July 1998     

Studies of LA-ICP-MS on quartz glasses at different wavelengths of a Nd:YAG laser

The capability of LA-ICP-MS for determination of trace impurities in transparent quartz glasses was investigated. Due to low or completely lacking absorption of laser radiation, laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) proves difficult on transparent solids, and in particular the quantification of measurement results is problematic in these circumstances. Quartz glass reference materials of various compositions were studied by using a Nd:YAG laser system with focused laser radiation of wavelengths of 1064 nm, 532 nm and 266 nm, and an ICP-QMS (Elan 6000, Perkin Elmer). The influence of ICP and laser ablation conditions in the analysis of quartz glasses of different compositions was investigated, with the laser power density in the region of interaction between laser radiation and solid surface determining the ablation process. The trace element concentration was determined via calibration curves recorded with the aid of quartz glass reference materials. Under optimized measuring conditions the correlation coefficients of the calibration curves are in the range of 0.9-1. The relative sensitivity factors of the trace elements determined in the quartz glass matrix are 0.1-10 for most of the trace elements studied by LA-ICP-MS. The detection limits of the trace elements in quartz glass are in the low ng/g to pg/g range.     

冷焰ICP-MS法测定高纯稀土氧化物中铁和钙的研究

用冷焰技术对高纯稀土氧化物中Ｆｅ和Ｃａ的分析方法进行了研究。估算了测定范围和检出限,探讨了内标元素对基体影响的校正作用,测定了加标回收率,对半定量法（ＴＱ）和定量法（ＱＡ）的结果作了比较。表明冷焰条件下,痕量Ｆｅ的测定是可行的,但Ｃａ的测定结果仍不理想;ＱＡ法明显优于ＴＱ法。