Laser ablation inductively coupled plasma mass spectrometry: a new tool for trace element analysis in ice cores

A new method for the detection of trace elements in polar ice cores using laser ablation with subsequent inductively coupled plasma mass spectrometry analysis is described. To enable direct analysis of frozen ice samples a special laser ablation chamber was constructed. Direct analysis reduces the risk of contamination. The defined removal of material from the ice surface by means of a laser beam leads to higher spatial resolution (300-1000 microm) in comparison to investigations with molten ice samples. This is helpful for the detection of element signatures in annual layers of ice cores. The method was applied to the successful determination of traces for the elements Mg, Al, Fe, Zn, Cd, Pb, some rare-earth elements (REE) and minor constituents such as Ca and Na in ice cores. These selected elements serve as tracer elements for certain sources and their element signatures detected in polar ice cores can give hints to climate changes in the past. We report results from measurements of frozen ice samples, the achievable signal intensities, standard deviations and calibration graphs as well as the first signal progression of 205Pb in an 8,000-year-old ice core sample from Greenland. In addition, the first picture of a crater on an ice surface burnt by an IR laser made by cryogenic scanning electron microscopy is presented.     

Analytical evaluation of electrothermal vaporization/low-pressure inductively coupled plasma atomic emission spectrometry for trace elemental analysis in microliter samples

A novel method for the determination of trace elements in microliter samples using the tantalum filament electrothermal vaporization/low-pressure inductively coupled plasma (ETV/LP-ICP) atomic emission spectrometry has been developed. An improved tantalum filament ETV was directly coupled with LP-ICP system for efficient vaporization of microliter samples and further quantitative analysis. The experimental parameters including ETV current, rf power and mass flow rate of argon carrier gas were optimized using the copper emission signal produced by 5 μl of standard solution (5 μg/ml). Under the optimized condition, the analytical performances including linearity, precision and detection limit for the developed system were investigated. Absolute detection limits in the range of 22–391 pg for selected eight elements (Fe, Cu, Cr, Mn, Pb, K, Zn and Mg) were obtained with satisfactory precision (<8.9% RSD). The feasibility of the developed system has been demonstrated by analyzing wheat gluten NIST standard sample.     

A comparison of neutron activation analysis and inductively coupled plasma mass spectrometry for trace element analysis of biological materials

Fifty individual food types were analysed by instrumental and radiochemical neutron activation analysis as well as inductively coupled plasma mass spectrometry after testing all techniques by analysing IAEA mixed human diet, H-9. The performance of these trace element techniques and their limitations were evaluated under normal, routine, multi-element surveys of a large range of solid biological materials.South Australian Department of Agriculture, 21 Divett Place, Adelaide, SA, Australia.     

Hollow-fiber liquid-phase microextraction prior to low-temperature electrothermal vaporization ICP-MS for trace element analysis in environmental and biological samples

A new method of hollow-fiber liquid-phase microextraction (HF-LPME) prior to electrothermal vaporization (ETV) inductively coupled plasma mass spectrometry (ICP-MS) determination of trace Cu, Zn, Pd, Cd, Hg, Pb and Bi, based on gaseous compounds introduction into the plasma as their diethyldithiocarbmate (DDTC) chelates, was developed. The use of the reagent DDTC as chemical modifier could not only enhance the analytical signals, but also decrease the vaporization temperature. At a temperature of 1300 degrees C, trace Cu, Zn, Pd, Cd, Hg, Pb and Bi can be vaporized completely into the ICP. The factors affecting the formation of the chelates and their vaporization behaviors were investigated in detail, and the microextraction conditions were optimized. Under the optimized conditions, the detection limits of the proposed method were 12.4, 28.7, 7.9, 4.5, 3.3, 4.8 and 1.6 pg ml(-1) for Cu, Zn, Pd, Cd, Hg, Pb and Bi, respectively. Enrichment factors of 305, 284, 24, 29, 20, 73 and 43 could be achieved within 15 min of extraction time, and the relative standard deviations (RSDs) for the seven determinations of 0.5 ng ml(-1) of target analytes were 8.8, 6.9, 7.1, 9.4, 10.2, 6.1 and 10.8%, respectively. The newly developed method has been applied to the determination of trace Cu, Zn, Pd, Cd, Hg, Pb and Bi in environmental water and human serum samples, and the recoveries for the spiked samples were in the range of 88-116%. In order to validate this method, two certified reference materials, GBW08501 peach leaves and GBW(E)080040 seawater, were analyzed, and the determined values were in good agreement with the certified values.     

Analysis of fish otoliths by electrothermal vaporization inductively coupled plasma mass spectrometry: aspects of precipitating otolith calcium with hydrofluoric acid for trace element determination

A method is developed for determination of trace elements, including Ag, As, Cd, Co, Cr, Cu, Mn, Ni, Se, Tl and Zn, in fish otoliths by electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS). Hydrofluoric acid was used to precipitate calcium resulting from acid dissolution of otolith calcium carbonate. Initial acidity of the sample solution influenced the precipitation efficiency of calcium fluoride. Up to 99.5% of Ca was precipitated in solutions that contained less than 2% (v/v) HNO₃. Recoveries of the elements obtained from spiked artificial otolith solutions were between 90 and 103%. Stabilization of the elements within the ETV cell was achieved with 0.3 μg Pd/0.2 μg Rh chemical modifier that also afforded optimum sensitivity for multielement determination. The method was validated by the analysis of a fish otolith reference material (CRM) of emperor snapper, and then applied to the determination of the trace elements in otoliths of several fish species captured in Raritan Bay, New Jersey. Results indicated that fish physiology and biological processes could influence the levels of Cu, Mn, Se and Zn in the otoliths of fish inhabiting a similar aqueous environment. Otolith concentrations of Cr and Ni did not show any significant differences among different species. Concentrations for Ag, As, Cd, Co and Tl were also not significantly different, but were very low indicating low affinity of otolith calcium carbonate to these elements.     

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.     

Multiplexed electrothermal vaporization sample introduction system for inductively coupled plasma spectrometry

A multiplexed electrothermal vaporization (ETV) system for sample introduction into an inductively coupled plasma was designed in an effort to increase sample turn-around time. Tungsten filaments (300 W), originally designed for overhead projectors, were chosen for use as ETVs to avoid the high power requirements associated with other ETV devices, e.g. graphite furnaces (2–3 kW). In short, we have multiplexed the thermal stages have been multiplexed such that a vaporization event can take place every 20 s. This represents a significant increase in the throughput typically associated with ETV-ICPMS, which is normally approximately 20–30 samples/h. Evaluated with respect to common figure of merit criteria, the performance of the multiplexed ETV system is similar to that seen with conventional graphite furnace ETV systems. However, several mass spectral interferences can be introduced by the presence of W into the plasma, which hinder the analysis of certain metals (Hg, Mo, etc.). Thus, other low power vaporizers (e.g. Re, Ta) should be considered for use in future systems.     

Direct solid sampling electrothermal vaporization of alumina for analysis by inductively coupled plasma optical emission spectrometry

A procedure based on electrothermal evaporation (ETV) and inductively coupled plasma atomic emission spectrometry (ICP-OES) for the determination of trace impurities in Al₂O₃ powders without any sample pretreatment is presented. With the aid of matrix modifier the transport and the evaporation efficiency for refractory compounds could be increased by forming halides with a lower boiling point. As calibration is still a problem in direct solid sample analysis, different calibration approaches including the use of certified reference materials from NIST and standard addition of aqueous solutions of analytes were discussed. The accuracy obtained with calibration and with the standard addition method was shown up for the elements Ca, Fe, Ga, Mg, Mn, Na, Ni and V for the case of Al₂O₃ NIST standard reference material (SRM 699). The ETV–ICP-OES method was used for the analysis of Al₂O₃ powders with impurities in the low μg/g range and the results for the elements Ca, Fe, Ga, Mg, Mn, Na, Ni and V obtained with evaporation of discrete powder amounts with ETV–ICP-OES and slurry evaporation under the use of ultrasonic homogenization during the sampling and ETV–ICP-MS were shown to be in a good agreement.     

Recent trends in trace element determination and speciation using inductively coupled plasma mass spectrometry

During the past decade, inductively coupled plasma mass spectrometry (ICPMS) has evolved from a delicate research tool, intended for the well-trained scientist only, into a more robust and well-established analytical technique for trace and ultra-trace element determination, with a few thousand of instruments used worldwide. Despite this immense success, it should be realized that in its ’standard configuration’– i.e. equipped with a pneumatic nebulizer for sample introduction and with a quadrupole filter – ICPMS also shows a number of important limitations and disadvantages: (i) the occurrence of spectral interferences may hamper accurate trace element determination, (ii) solid samples have to be taken into solution prior to analysis and (iii) no information on the ‘chemical form’ in which an element appears can be obtained. Self-evidently, efforts have been and still are made to overcome the aforementioned limitations to the largest possible extent. The application of a double focusing sector field mass spectrometer in ICPMS instrumentation offers a higher mass resolution, such that spectral overlap can be avoided to an important extent. Additionally, in a sector field instrument, photons are efficiently eliminated from the ion beam, resulting in very low background intensities, making it also very well-suited for extreme trace analysis. Also the combination of the ICP as an ion source and a quadrupole filter operated in a so-called ‘alternate’ stability region, an ion trap or a Fourier transform ion cyclotron resonance mass spectrometer allows high(er) mass resolution to be obtained. With modern quadrupole-based instruments, important types of spectral interferences can be avoided by working under ‘cool plasma’ conditions or by applying a collision cell. The use of electrothermal vaporization (ETV) or especially laser ablation (LA) for sample introduction permits direct analysis of solid samples with sufficient accuracy for many purposes. The application range of LA-ICPMS has become very wide and the introduction of UV lasers has led to an improved spatial resolution. Solid sampling ETV-ICPMS on the other hand can be used for some specific applications only, but accurate calibration is more straightforward than with LA-ICPMS. Limited multi-element capabilities, resulting from the transient signals observed with ETV or single shot LA, can be avoided by the use of a time-of-flight (TOF) ICPMS instrument. Finally, when combined with a powerful chromatographic separation technique, an ICP-mass spectrometer can be used as a highly sensitive, element-specific multi-element detector in elemental speciation studies. Especially liquid (HPLC-ICPMS) and – to a lesser extent – gas (GC-ICPMS) chromatography have already been widely used in combination with ICPMS. In speciation work, sample preparation is often observed to be troublesome and this aspect is presently receiving considerable attention. For GC-ICPMS, new sample pretreatment approaches, such as headspace solid phase microextraction (headspace SPME) and the purge-and-trap technique have been introduced. Also supercritical fluid chromatography (SFC) and capillary electrophoresis (CE) show potential to be of use in combination with ICPMS, but so far the application ranges of SFC-ICPMS and CE-ICPMS are rather limited. It is the aim of the present paper to concisely discuss the aforementioned recent ’trends’ in ICPMS, using selected real-life applications reported in the literature.     

Recent trends in trace element determination and speciation using inductively coupled plasma mass spectrometry

During the past decade, inductively coupled plasma mass spectrometry (ICPMS) has evolved from a delicate research tool, intended for the well-trained scientist only, into a more robust and well-established analytical technique for trace and ultra-trace element determination, with a few thousand of instruments used worldwide. Despite this immense success, it should be realized that in its ’standard configuration’– i.e. equipped with a pneumatic nebulizer for sample introduction and with a quadrupole filter – ICPMS also shows a number of important limitations and disadvantages: (i) the occurrence of spectral interferences may hamper accurate trace element determination, (ii) solid samples have to be taken into solution prior to analysis and (iii) no information on the ‘chemical form’ in which an element appears can be obtained. Self-evidently, efforts have been and still are made to overcome the aforementioned limitations to the largest possible extent. The application of a double focusing sector field mass spectrometer in ICPMS instrumentation offers a higher mass resolution, such that spectral overlap can be avoided to an important extent. Additionally, in a sector field instrument, photons are efficiently eliminated from the ion beam, resulting in very low background intensities, making it also very well-suited for extreme trace analysis. Also the combination of the ICP as an ion source and a quadrupole filter operated in a so-called ‘alternate’ stability region, an ion trap or a Fourier transform ion cyclotron resonance mass spectrometer allows high(er) mass resolution to be obtained. With modern quadrupole-based instruments, important types of spectral interferences can be avoided by working under ‘cool plasma’ conditions or by applying a collision cell. The use of electrothermal vaporization (ETV) or especially laser ablation (LA) for sample introduction permits direct analysis of solid samples with sufficient accuracy for many purposes. The application range of LA-ICPMS has become very wide and the introduction of UV lasers has led to an improved spatial resolution. Solid sampling ETV-ICPMS on the other hand can be used for some specific applications only, but accurate calibration is more straightforward than with LA-ICPMS. Limited multi-element capabilities, resulting from the transient signals observed with ETV or single shot LA, can be avoided by the use of a time-of-flight (TOF) ICPMS instrument. Finally, when combined with a powerful chromatographic separation technique, an ICP-mass spectrometer can be used as a highly sensitive, element-specific multi-element detector in elemental speciation studies. Especially liquid (HPLC-ICPMS) and – to a lesser extent – gas (GC-ICPMS) chromatography have already been widely used in combination with ICPMS. In speciation work, sample preparation is often observed to be troublesome and this aspect is presently receiving considerable attention. For GC-ICPMS, new sample pretreatment approaches, such as headspace solid phase microextraction (headspace SPME) and the purge-and-trap technique have been introduced. Also supercritical fluid chromatography (SFC) and capillary electrophoresis (CE) show potential to be of use in combination with ICPMS, but so far the application ranges of SFC-ICPMS and CE-ICPMS are rather limited. It is the aim of the present paper to concisely discuss the aforementioned recent ’trends’ in ICPMS, using selected real-life applications reported in the literature. Received: 30 November 1998 / Revised: 22 March 1999 / Accepted: 24 March 1999     

Determination of trace element concentrations in meteorites by inductively coupled plasma — Mass spectromety

Determination of 25 trace elements in the meteorites Allende and Murchison by ICP-MS is described. Samples are digested using HF, HNO₃, and HClO₄ at 140°C and diluted into HNO₃. Element concentrations were determined using USGS terrestrial rocks as standards for calibration. Precision and accuracy of the technique, evaluated based on measurements of samples of known composition, are for 16 elements better than 10%.     

Direct analysis of tantalum powders by electrothermal vaporization inductively coupled plasma atomic emission spectrometry

A direct inductively coupled plasma atomic emission method for the determination of Ag, Al, As, Ca, Cd, Co, Cu, Fe, Ga, K, Li, Mg, Na and Pb in high-purity tantalum powders has been developed. The electrothermal vaporization technique using a modified longitudinally-heated Grün-ETAAS furnace with sample introduction on a platform and an automated sampling workstation provided the possibility of in situ analyte-matrix separation, freedom of blank, and applicability to routine analysis. Hard- and software were modified to allow signal recording and data processing independent of the spectrometer software. The extent of spectral interferences by Ta-emission at the analyte wavelengths used was determined and the analyte signals of each sample run were automatically corrected. Limits of detection ranging from 5 ng/g (Ag, Cu) to 250 ng/g (K, Pb) were obtained using optimized furnace and spectrometer conditions. The method was applied to the analysis of two tantalum samples and the results for Cu, Fe, K, Mg and Na were compared with those obtained by liquid and solid-samping ETAAS, showing satisfactory agreement.     

Analyte transport efficiencies in electrothermal vaporization for inductively coupled plasma mass spectrometry

A modified graphite furnace for solid-sampling atomic absorption spectrometry as an electrothermal vaporizer (ETV) was coupled to a Perkin–Elmer/Sciex ELAN 6000 ICP mass spectrometer. The integrals obtained from electrothermal vaporization of aliquots containing As, Cd, Cu, Co, Fe, Mn, Pb, Se, and Zn were compared with those obtained from pneumatic nebulization of the same aqueous standard solution. The pneumatic nebulizer was calibrated by weighing the mass of aqueous aerosol trapped on a filter. With “wet plasma” conditions maintained also for measurements with the ETV and reference signals for analyte signals obtained with the calibrated pneumatic nebulization, the transport efficiency of the ETV system, e.g. the ratio of the analyte amount introduced into the plasma to that amount dosed into the vaporizer, was determined. The transport efficiency of two different tube and interface designs has been evaluated. Investigations with and without the use of trifluoromethane as reactive gas, with different furnace heating rates, and with varying gas flows were performed. In general, the tube equipped with a nozzle led to generally higher transport efficiency than the standard tube. Without trifluoromethane transport efficiencies ranged from 10% to 35% with the standard tube and from 15% to 50% with the nozzle-type tube. With addition of 2 mL min^–1 trifluoromethane to the argon flow of 400 mL min^–1 through the tube, transport efficiencies from 20% to 70% and from 70% to100% were achieved with the standard and nozzle-type tubes, respectively.     

Analyte transport efficiencies in electrothermal vaporization for inductively coupled plasma mass spectrometry

A modified graphite furnace for solid-sampling atomic absorption spectrometry as an electrothermal vaporizer (ETV) was coupled to a Perkin-Elmer/Sciex ELAN 6000 ICP mass spectrometer. The integrals obtained from electrothermal vaporization of aliquots containing As, Cd, Cu, Co, Fe, Mn, Pb, Se, and Zn were compared with those obtained from pneumatic nebulization of the same aqueous standard solution. The pneumatic nebulizer was calibrated by weighing the mass of aqueous aerosol trapped on a filter. With "wet plasma" conditions maintained also for measurements with the ETV and reference signals for analyte signals obtained with the calibrated pneumatic nebulization, the transport efficiency of the ETV system, e.g. the ratio of the analyte amount introduced into the plasma to that amount dosed into the vaporizer, was determined. The transport efficiency of two different tube and interface designs has been evaluated. Investigations with and without the use of trifluoromethane as reactive gas, with different furnace heating rates, and with varying gas flows were performed. In general, the tube equipped with a nozzle led to generally higher transport efficiency than the standard tube. Without trifluoromethane transport efficiencies ranged from 10% to 35% with the standard tube and from 15% to 50% with the nozzle-type tube. With addition of 2 mL min(-1) trifluoromethane to the argon flow of 400 mL min(-1) through the tube, transport efficiencies from 20% to 70% and from 70% to 100% were achieved with the standard and nozzle-type tubes, respectively.     

Capabilities of high resolution inductively coupled plasma mass spectrometry for trace element determination in plant sample digests

The analytical performance of inductively coupled plasma mass spectrometry (ICP-MS) for the analysis of plant sample digests was evaluated using double focusing sector field ICP-MS (ICP-SMS). Instrumental detection limits of ICP-SMS are superior to those obtained by quadrupole systems (ICP-QMS) and reach the fg mL^–1 range for elements with high m/z ratios. Matrix effects caused by a plant digest after sample preparation resulting in 200-fold dilution were found to be negligible. The usefulness of high mass resolution for overcoming some spectral interferences is demonstrated. Mathematical correction possibilities could be necessary to improve accuracy. The concentrations of more than 20 elements can be determined in 5 min and only one internal standard is necessary to correct for instrumental drift. Received: 30 March 1998 / Revised: 4 May 1998 / Accepted: 16 May 1998     

Electrothermal vaporization inductively coupled plasma atomic emission spectrometry for the analysis of solid samples: contribution to instrumentation and methodology

Summary A commercially available graphite furnace was modified in order to use it as an electrothermal vaporization device for solid sample analysis with an inductively coupled plasma atomic emission spectrometer. An evaluation of two different ETV systems has been made. This paper mainly describes the different aspects which must be taken into account when coupling an ETV system to an ICP. Cu was chosen as an element easy to determine and Cd and Pb as elements with more difficulties. From the optimization it was found that the transport efficiency for Cd in solution and solid is different, whereas for Cu and Pb the efficiencies are in good agreement for both sample types. Calibration with solids and liquids was attempted for Cu. The paper gives preliminary results on the determination of Cu in solid reference materials. In some cases (e.g. Pb) a background correction based on a linear interpolation seemed not satisfactory. Detection limits and limits of determination for Cu, Cd and Pb in different solid samples are given.Presented at the 5th International Colloquium on Solid Sampling with Atomic Spectroscopy, May 18–20, 1992; Geel, Belgium. Papers edited by R. F. M. Herber, Amsterdam     

Capabilities of high resolution inductively coupled plasma mass spectrometry for trace element determination in plant sample digests

The analytical performance of inductively coupled plasma mass spectrometry (ICP-MS) for the analysis of plant sample digests was evaluated using double focusing sector field ICP-MS (ICP-SMS). Instrumental detection limits of ICP-SMS are superior to those obtained by quadrupole systems (ICP-QMS) and reach the fg mL^–1 range for elements with high m/z ratios. Matrix effects caused by a plant digest after sample preparation resulting in 200-fold dilution were found to be negligible. The usefulness of high mass resolution for overcoming some spectral interferences is demonstrated. Mathematical correction possibilities could be necessary to improve accuracy. The concentrations of more than 20 elements can be determined in 5 min and only one internal standard is necessary to correct for instrumental drift. Received: 30 March 1998 / Revised: 4 May 1998 / Accepted: 16 May 1998     

Practical aspects of routine trace element environmental analysis by inductively coupled plasma-mass spectrometry

Since the appearance, in the early eighties, of first publications describing plasma source mass spectrometry as a viable analytical technique, there has been a rapid increase in the number of papers detailing its possible applications, instrumental developments and fundamental studies. In the laboratories involved in the environmental or food monitoring problematics, inductively coupled plasma-mass spectrometry (ICP-MS) systems are usually acquired in order to analyze large series of samples. At our knowledge, very rare are works dedicated to the sum of factors and additional problems usually encountered in the routine analysis using this analytical technique. In this work, we will try to fill in these gaps by discussing the main factors that may strongly influence the analysis of large series of samples. Firstly, there are uncertainties associated to the choice of measurement parameters: calibration blanks, curve algorithms and their long-term validity, selection of internal standards, recalibration blocks and usefulness of correction equations. Secondly, we will discuss analytical parameters that concern samples themselves: their appropriate dilution and acidification as well as the knowledge of matrix effects possibly produced. Finally, there is also a very important point concerning appropriate definition of the procedure blank as well as its utilization. Only the careful consideration of all these aspects permits to obtain accurate results during routine analysis. Aim of this work is not oriented to discussion of typical and well-documented ICP-MS individual problems but rather to means that allow to overcome main uncertainties resulting in an improvement of the whole routine analysis.