A high-efficiency cross-flow micronebulizer for inductively coupled plasma mass spectrometry

A pneumatically driven, high-efficiency cross-flow micronebulizer (HECFMN) is introduced for inductively coupled plasma (ICP) spectrometries. The HECFMN uses a smaller nozzle orifice for nebulizer gas (75 microm in diameter) and a replaceable and adjustable fused-silica capillary for sample uptake. The HECFMN is optimally operated over a wide range of sample uptake rate (5-120 microL/min) at a rf power of 1100 W and nebulizer gas flow rates of 0.8-1.0 L/min when a 50 microm i.d. by 150 microm o.d. capillary is used. The aerosol quality is qualitatively examined in a simple manner, and the transport efficiencies are determined by direct filter collection. Compared with conventional cross-flow nebulizers (CFNs), the HECFMN produces much smaller and more uniform droplets and thus provides much higher analyte transport efficiencies (generally 24-95%) at the sample uptake rates of 5-100 microL/min. Several analytical performance indexes are acquired using an Ar ICPMS system. The sensitivities and detection limits measured with the HECFMN at 50 microL/min sample uptake rate are comparable to or improved over those obtained with a conventional CFN consuming 1 mL/min sample, and the precisions with the HECFMN (typically 1.1-1.7% RSDs) are slightly better than those with the CFN (1.6-2.3% RSDs). The ratios of refractory oxide ion-to-singly charged ion (CeO+/Ce+) are typically in the range from 0.7 to 3.3% for the sample uptake rates of 5-100 microL/min. The free aspiration rate of the HECFMN is 8.9 microL/min for distilled deionized water at the nebulizer gas flow rate of 1.0 L/min without any effect of pressure. The features of the HECFMN suggest good potential for HECFMN use in interfacing ICPMS with capillary electrophoresis and microcolumn high-performance liquid chromatography.     

Chemical reaction interface mass spectrometry with high efficiency nebulization

A high efficiency nebulizer (HEN) coupled to a heated spray chamber and a membrane desolvator is used for liquid sample introduction in chemical reaction interface mass spectrometry (CRIMS). Compared to the conventional thermospray nebulizer operated at solvent flow rate of 1 mL/min, the HEN provides small droplets at lower flow rates (10-100 microL/min), improving the desolvation and analyte transport efficiency. As a result, the sensitivity for carbon detection by CRIMS is improved by a factor of 4. The new arrangement offers an easy-to-use and robust interface, facilitating the availability of a variety of liquid chromatographic techniques to the CRIMS. Separation and detection of labeled peptides in a mixture of unlabeled biopolymers is illustrated at a solvent flow rate of 45 microL/min as an example of new possibilities offered by the improved liquid introduction interface.     

A large bore-direct injection high efficiency nebulizer for inductively coupled plasma spectrometry

A large bore-direct injection high efficiency nebulizer (IB-DIHEN) is introduced that is less prone to capillary blockage and optimally operates at low nebulizer gas pressures compared with the conventional DIHEN used for inductively coupled plasma (ICP) spectrometries. The aerosol quality is examined using a two-dimensional phase Doppler particle analyzer (2D PDPA), and analytical figures of merits are acquired by ICP mass spectrometry. Compared with the DIHEN, the LB-DIHEN produces larger droplets, but the velocity distributions and mean droplet velocities are narrower and lower, respectively, providing longer residence times for the droplets in the plasma. High RF power (1500 W), low nebulizer gas flow rates (0.25-0.35 L/min), and low solution uptake rates (80-110 microL/min) are required to operate the LB-DIHEN at optimum conditions for ICPMS. Detection limits and sensitivities measured with the LB-DIHEN are superior to those of a conventional nebulizer-spray chamber combination, but precision is inferior. The performance of the LB-DIHEN is further explored in the determination of trace elements in an herbal extract.     

Improvements in LC/Electrospray Ion Trap Mass Spectrometry Performance Using an Off-Axis Nebulizer

Charged residues from the electrospray process have been hypothesized to limit the sensitivity and dynamic range of an ion trap mass spectrometry operation. Incorporation of an off-axis nebulizer (positioned 90-95° from the sampling orifice) was found to drastically reduce the detrimental effects caused by the charged particles or droplets compared to typical on-axis nebulization configurations (spraying 10-20° from sampling orifices). The off-axis nebulizer reduced total ion currents that enter the ion trap (through the reduction of charged residues) by a factor of 5-7 while resulting in an increase of analyte [M + H](+) signal by a factor of 6 compared to an on-axis sprayer at flow rates of 20 μL/min. At higher flow rates (e.g., 800 μL/min) these enhancements are more evident. At flows greater than 200 μL/min, off-axis nebulization reduced total ion current that enters the ion trap by a factor of 30 and resulted in a factor of more than 20 increase in [M + H](+) signal relative to on-axis nebulization. Incorporation of the off-axis nebulizer improved the detection limit and precision for determination of dihydroxyvitamin D(3) in plasma compared to on-axis nebulization. The LC/MS/MS detection limits obtained for the off-axis nebulizer on the ion trap was within a factor of 2 from the detection limit determined by the triple quadrupole. The relative standard deviation of the dihydroxyvitamin D(3) determination was less than 8% for both off-axis ion trap and triple-quadrupole determinations.     

A high-efficiency cross-flow micronebulizer interface for capillary electrophoresis and inductively coupled plasma mass spectrometry.

A pneumatic nebulizer interface for capillary electrophoresis (CE) and inductively coupled plasma mass spectrometry (ICPMS) is reported. The interface is constructed using a high-efficiency cross-flow micronebulizer (HECFMN) and has the following features. (1) Makeup solutions can be fed to the interface by nebulizer self-aspiration and liquid gravity pressurization. (2) The liquid dead volume of the interface is approximately 65 nL, much smaller than those (200-2500 nL) reported for other interfaces. (3) The interface can be stably operated at a liquid flow rate down to 5 microL/min with a high analyte transport efficiency up to 95% to the plasma and (4) does not induce noticeable laminar flow in the CE capillary at typical nebulizer gas flow rates of 0.8-1.2 L/min. Because of these features, baseline resolution of 10 lanthanides with a CE-ICPMS system using the HECFMN interface is achieved, and detection limits and peak asymmetry are 0.05-1 microg/L and 0.93-1.23, respectively, improved significantly over those reported previously for a CE-ICPMS system using a high-efficiency nebulizer interface. Peak precision for the 10 lanthanides is in the range of 6.2-12.3% RSD (N = 5). Peak widths are from 9.1 s for 139La to 17.9 s for 175Lu. The effects of nebulizer gas flow rate, makeup solution flow rate, and spray chamber volume on CE-ICPMS signal intensity and separation are also evaluated for the HECFMN interface by the separation of Cr3+ and Cr2O7(2-).     

Ultratrace and isotope analysis of long-lived radionuclides by inductively coupled plasma quadrupole mass spectrometry using a direct injection high efficiency nebulizer

The direct injection high efficiency nebulizer (DIHEN) was explored for the ultrasensitive determination of long-lived radionuclides ((226)Ra, (230)Th, (237)Np, (238)U, (239)Pu, and (241)Am) and for precise isotope analysis by inductively coupled plasma mass spectrometry (ICPMS). The DIHEN was used at low solution uptake rates (1-100 μL/min) without a spray chamber. Optimal sensitivity (e.g., (238)U, 230 MHz/ppm; (230)Th, 190 MHz/ppm; and (239)Pu, 184 MHz/ppm) was achieved at low nebulizer gas flow rates (0.16 L/min), high rf power (1450 W), and low solution uptake rates (100 μL/min). The optimum parameters varied slightly for the two DIHENs tested. The detection limits of long-lived radionuclides in aqueous solutions varied from 0.012 to 0.11 ng/L. The sensitivity of the DIHEN was improved by a factor of 3 to 5 compared with that of a microconcentric nebulizer (MicroMist used with a minicyclonic spray chamber at a solution uptake rate of 85 μL/min) and a factor of 1.5 to 4 compared with that of a conventional nebulizer (cross-flow used with a Scott type spray chamber at a solution uptake rate of 1 mL/min). The precision of the DIHEN ranged from 0.5 to 1.7% RSD (N = 3) for all measurements at the 10 ng/L concentration level (～3 pg sample size). The sensitivity decreased to 10 MHz/ppm at a solution uptake rate of 1 μL/min. The precision was about 5% RSD at a sample size of 30 fg for each long-lived radionuclide by the DIHEN-ICPMS method. The oxide to atom ratios were less than 0.05 (except ThO(+)/Th(+) ) and decreased under the optimum conditions in the following sequence: ThO(+)/Th(+) > UO(+)/U(+) > NpO(+)/Np(+) > PuO(+)/Pu(+) > AmO(+)/Am(+) > RaO(+)/Ra(+). Atomic and oxide ions were used as analyte ions for ultratrace and isotope analyses of long-lived radionuclides in environmental and radioactive waste samples. The analytical methods developed were applied to the determination of long-lived radionuclides and isotope ratio measurements in different radioactive waste and environmental samples using the DIHEN in combination with quadrupole ICPMS. For instance, the (240)Pu/(239)Pu isotope ratio was measured in a radioactive waste sample at a plutonium concentration of 12 ng/L. This demonstrates a main advantage of DIHEN-ICPMS compared with α-spectrometry, which cannot be used to selectively determine (239)Pu and (240)Pu because of similar α energies (5.244 and 5.255 MeV, respectively).     

Rotation planar chromatography coupled on-line with atmospheric pressure chemical ionization mass spectrometry

The coupling of a rotation planar preparative thin-layer chromatography system on-line with mass spectrometry is demonstrated using a simple plumbing scheme and a self-aspirating heated nebulizer probe of a corona discharge atmospheric pressure chemical ionization source. The self-aspiration of the heated nebulizer delivers approximately 20 microL/min of the 3.0 mL/min eluate stream to the mass spectrometer, eliminating the need for an external pump in the system. The viability of the coupling is demonstrated with a three-dye mixture composed of fat red 7B, solvent green 3, and solvent blue 35 separated and eluted from a silica gel-coated rotor using toluene. The real-time characterization of the dyes eluting from the rotor is illustrated in positive ion full-scan mode. Other self-aspirating ion source systems including atmospheric pressure photoionization, electrospray ionization, and inductively coupled plasma ionization, for example, might be configured and used in a similar manner coupled to the chromatograph to expand the types of analytes that could be ionized, detected, and characterized effectively.     

Study of the Technological Parameters of Ultrasonic Nebulization

The principle of an ultrasonic nebulizer is based on the vibrations of a piezoelectric crystal driven by an alternating electrical field. These periodic vibrations are characterized by their frequency, their amplitude, and their intensity, which corresponds to the energy transmitted per surface unit. When the vibration intensity is sufficient, cavitation occurs, and droplets are generated. Ventilation enables airflow to cross the nebulizer and to expel the aerosol droplets. For a given nebulizer, the vibration frequency of the piezoelectric crystal is fixed, often in the range 1–2.5 MHz. In most cases, an adjustment in vibration intensity is possible by modifying vibration amplitude. The ventilation level is adjustable. The vibrations may be transmitted through a coupling liquid—commonly water—to a nebulizer cup containing the solution to be aerosolized. In this work, we studied the influence of the technological parameters of ultrasonic nebulization on nebulization quality. Our study was carried out with a 9% sodium chloride solution and a 2% protein solution (α1 protease inhibitor). Three different ultrasonic nebulizers were used. An increase in vibration frequency decreased the size of droplets emitted. The coupling liquid absorbed the energy produced by the ultrasonic vibrations and canceled out any heating of the solution, which is particularly interesting for thermosensitive drugs. An increase in vibration intensity did not modify the size of droplets emitted, but decreased nebulization time and raised the quantity of protein nebulized, thus improving performance. On the other hand, an increase in ventilation increased the size of emitted droplets and decreased nebulization time and the quantity of protein nebulized because more drug was lost on the walls of the nebulizer. High intensity associated with low ventilation favors drug delivery deep into the lungs.     

Study of the technological parameters of ultrasonic nebulization.

The principle of an ultrasonic nebulizer is based on the vibrations of a piezoelectric crystal driven by an alternating electrical field. These periodic vibrations are characterized by their frequency, their amplitude, and their intensity, which corresponds to the energy transmitted per surface unit. When the vibration in tensity is sufficient, cavitation occurs, and droplets are generated. Ventilation enables airflow to cross the nebulizer and to expel the aerosol droplets. For a given nebulizer, the vibration frequency of the piezoelectric crystal is fixed, often in the range 1-2.5MHz. In most cases, an adjustment in vibration intensity is possible by modifying vibration amplitude. The ventilation level is adjustable. The vibrations may be transmitted through a coupling liquid--commonly water--to a nebulizer cup containing the solution to be aerosolized. In this work, we studied the influence of the technological parameters of ultrasonic nebulization on nebulization quality. Our study was carried out with a 9% sodium chloride solution and a 2% protein solution (alpha1 protease inhibitor). Three different ultrasonic nebulizers were used. An increase in vibration frequency decreased the size of droplets emitted. The coupling liquid absorbed the energy produced by the ultrasonic vibrations and canceled out any heating of the solution, which is particularly interesting for thermosensitive drugs. An increase in vibration intensity did not modify the size of droplets emitted, but decreased nebulization time and raised the quantity of protein nebulized, thus improving performance. On the other hand, an increase in ventilation increased the size of emitted droplets and decreased nebulization time and the quantity of protein nebulized because more drug was lost on the walls of the nebulizer. High intensity associated with low ventilation favors drug delivery deep into the lungs.     

Atmospheric pressure photoionization-mass spectrometry with a microchip heated nebulizer

A novel, microfabricated heated nebulizer chip for atmospheric pressure photoionization-mass spectrometry (APPI-MS) is presented. The chip consists of fluidic and gas inlets, a mixer, and a nozzle etched onto silicon wafer that is anodically bonded to a Pyrex glass wafer, on which an aluminum heater is sputtered. A krypton discharge lamp is used as the source for 10-eV photons to initiate the photoionization process. Dopant, delivered as part of the sample solution, is used to achieve efficient ionization. The use of the microfabricated heated nebulizer with APPI in the analysis of four analytes is demonstrated, and the spectra are compared to those obtained with a conventional APPI source. Ionization in positive and negative ion modes was successfully achieved and the spectra were mainly similar to those obtained with conventional APPI, indicating that the ionization in microfabricated and conventional APPI sources takes place by the same mechanisms. The flow rates with conventional APPI are approximately 100 muL/min, whereas the microchip heated nebulizer allows the use of flow rates 0.05-5 muL/min, thus being compatible with microfluidic separation systems or micro- and nano-LC. A stable signal was demonstrated throughout a 5-h measurement, which proved the excellent stability of the micro-APPI. The same heated nebulizer chip can be used for weeks.     

Anodic stripping voltammetry coupled on-line with inductively coupled plasma mass spectrometry: optimization of a thin-layer flow cell system for analyte signal enhancement

Parameters affecting analyte signal enhancement in anodic stripping voltammetry-inductively coupled plasma mass spectrometry (ASV-ICP-MS), using a thin-layer ASV cell and microconcentric nebulization (MCN), have been examined. Silver was used as a test analyte and was deposited at a glassy carbon working electrode. The MCN allowed use of solution flow rates that were beneficial to optimum electrolytic performance of the thin-layer cell. High analyte deposition efficiencies obtained with the thin-layer cell, combined with minimal sample consumption of the MCN, allowed substantial signal enhancement (>400 times higher than continuous nebulization level) to be obtained with 2-3 mL of sample and deposition times of less than 30 min. Signal enhancement was strongly influenced by the opposing effect of flow rate on the electrolytic deposition efficiency (deposition efficiency decreases with increasing flow rate) and on the quantity of analyte delivered to the cell (analyte mass throughput increases with increasing flow rate). Excellent linearity for stripping peak heights was demonstrated for a wide range of analyte deposition times and for peak heights and peak areas (r > 0.999) over a wide concentration range (25 ng/L-20 μg/L). Precision was good (RSD typically <3% for n = 3-6) except for a high Ag blank contributed to by corrosion of the counter electrode and by Ag diffusion from the reference electrode into the cell. Details of the flow manifold and ASV cells are discussed, along with relevant performance characteristics of the MCN.     

Capillary-based multi nanoelectrospray emitters: improvements in ion transmission efficiency and implementation with capillary reversed-phase LC-ESI-MS

We describe the coupling of liquid chromatography (LC) separations with mass spectrometry (MS) using nanoelectrospray ionization (nano-ESI) multiemitters. The array of 19 emitters reduced the flow rate delivered to each emitter, allowing the enhanced sensitivity that is characteristic of nano-ESI to be extended to higher flow rate separations. The signal for tryptic fragments from proteins spiked into a human plasma sample increased 11-fold on average when the multiemitters were employed, due to increased ionization efficiency and improved ion transfer efficiency through a newly designed heated multicapillary MS inlet. Additionally, the LC peak signal-to-noise ratio increased approximately 7-fold when the multiemitter configuration was used. The low dead volume of the emitter arrays preserved peak shape and resolution for robust capillary LC separations using total flow rates of 2 microL/min.     

Performance-enhanced "tunable" capillary microwave-induced plasma mass spectrometer for gas chromatography detection

Improvements in the stability and performance of a capillary microwave-induced plasma-mass spectrometer (MIP-MS) were achieved by optimizing power transfer to the cavity using a tunable coaxial MIP. The MIP, operating at atmospheric pressure, was sustained with 30 mL/min He and 60 W of power. Measurement precision and sensitivity for the standard waveguide and coaxial systems were determined using 16 organochlorine pesticide solutions separated by gas chromatography (GC). The linear dynamic range obtained with the tunable MIP-MS extended over 3 orders of magnitude, a 10 time improvement with respect to the standard MIP. Detection limits were between 3 and 19 pg of Cl mol(-1) s(-1), 7 times lower than the detection limits obtained with the nontunable MIP-MS. Analysis of pesticides containing sulfur atoms was also possible, further demonstrating multielement MIP-MS detection. Excellent accuracy (10% recovery) and precision (5% RSD) were found for the detection of the pesticides in a petroleum-contaminated reference soil. By placing the GC column at the plasma expansion stage, molecular fragmentation of a mixture of volatile organic compounds was also demonstrated. With the MS operated in the selected ion monitoring mode, measurement sensitivity was approximately 500 pg/s per compound.     

Determination of folates in human plasma using hydrophilic interaction chromatography-tandem mass spectrometry

Folic acid is an essential nutrient, and folate deficiency is associated with a variety of disorders including neural tube defects (during pregnancy) and heart disease. A fast, sensitive, and robust HPLC-tandem mass spectrometry (LC-MS-MS) method was developed for the quantification of free folic acid, tetrahydrofolate, 5'-methyltetrahydrofolate, and 5'-formyltetrahydrofolate in human plasma. Sample preparation required only acetonitrile precipitation of proteins followed by filtration instead of solid-phase extraction or solvent-solvent extraction as in other methods. The rapid and streamlined sample handling procedure minimized degradation of the highly unstable folate species. Hydrophilic interaction chromatography was used for additional sample cleanup on-line, and baseline separation and detection of all four folate species was achieved in less than 30 min. The folate species were detected using negative ion electrospray-tandem mass spectrometry with multiple reaction monitoring of the diagnostic fragment ions of each deprotonated molecule. The predominately organic (hydrophobic) solvent system combined with the microbore flow rate (50 microL/min) used for the chromatography resulted in enhanced electrospray signal response compared to reversed-phase HPLC using a wider bore column. The recovery of all folate species (from spiked plasma) was >97% over a concentration range from 300 pg/L to 12 mg/L with intraday precision (RSD, n = 5) of 3.7-6.5%. Stability studies were carried out for spiked samples in order to define storage and handling conditions. The folic acid limit of quantification (LOQ) in human plasma was 80 pmol/L +/- 10%, and the limit of detection (LOD) was 37.5 pmol/L. The LOQ and LOD for tetrahydrofolate, 5'-methyltetrahydrofolate, and 5'-formyltetrahydrofolate were 1250, 400, and 360 pmol/L of plasma and 425, 165, and 140 pmol/L of plasma, respectively.     

Capillary liquid chromatography/electrospray mass spectrometry for analysis of steroid sulfates in biological samples

A new procedure for capillary liquid chromatography-electrospray (CLC-ES) mass spectrometry is described. Using this procedure, coupling of a CLC column to a low-flow-rate ES interface is made simple. A 5-cm precolumn and a 35-cm analytical column, both fused-silica capillaries with an i.d. of 100 microm and packed with 3-microm octadecylsilane-bonded material, are coupled in series to a sheathless ES emitter. One solvent splitter is positioned between the loop injector and the precolumn, and a second, between the precolumn and the analytical column. By opening and closing the splitters in the appropriate order, this arrangement permits the injection of 1-20 microL of sample solution with analyte focusing onto the top of the precolumn, followed by isocratic or gradient elution at a flow rate of 0.2-0.3 microL/min through the analytical column. The relative standard deviation of the retention times of reference compounds was <3.5% (n = 5). The potential of the system in metabolome analysis, in which numerous isomeric compounds will require identification, is illustrated by the application of the system to the analysis of steroid sulfates in plasma.     

Microchip atmospheric pressure chemical ionization source for mass spectrometry

A novel microchip heated nebulizer for atmospheric pressure chemical ionization mass spectrometry is presented. Anisotropic wet etching is used to fabricate the flow channels, inlet, and nozzle on a silicon wafer. An integrated heater of aluminum is sputtered on a glass wafer. The two wafers are jointed by anodic bonding, creating a two-dimensional version of an APCI source with a sample channel in the middle and gas channels symmetrically on both sides. The ionization is initiated with an external corona-discharge needle positioned 2 mm in front of the microchip heated nebulizer. The microchip APCI source provides flow rates down to 50 nL/min, stable long-term analysis with chip lifetime of weeks, good quantitative repeatability (RSD < 10%) and linearity (r(2) > 0.995) with linear dynamic rage of at least 4 orders of magnitude, and cost-efficient manufacturing. The limit of detection (LOD) for acridine measured with microchip APCI at flow rate of 6.2 muL/min was 5 nM, corresponding to a mass flow of 0.52 fmol/s. The LOD with commercial macro-APCI at a flow rate of 1 mL/min for acridine was the same, 5 nM, corresponding to a significantly worse mass flow sensitivity (83 fmol/s) than measured with microchip APCI. The advantages of microchip APCI makes it a very attractive new microfluidic detector.     

Comparison of laser ablation and dried solution aerosol as sampling systems in inductively coupled plasma mass spectrometry

This paper describes a study designed to determine the possibility of using a dried aerosol solution for calibration in laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The relative sensitivities of tested materials mobilized by laser ablation and by aqueous nebulization were established, and the experimentally determined relative sensitivity factors (RSFs) were used in conjunction with aqueous calibration for the analysis of solid steel samples. To such a purpose a set of CRM carbon steel samples (SS-451/1 to SS-460/1) were sampled into an ICP-MS instrument by solution nebulization using a microconcentric nebulizer with membrane desolvating (D-MCN) and by laser ablation (LA). Both systems were applied with the same ICP-MS operating parameters and the analyte signals were compared. The RSF (desolvated aerosol response/ablated solid response) values were close to 1 for the analytes Cr, Ni, Co, V, and W, about 1.3 for Mo, and 1.7 for As, P, and Mn. Complementary tests were carried out using CRM SS-455/1 as a solid standard for one-point calibration, applying LAMTRACE software for data reduction and quantification. The analytical results are in good agreement with the certified values in all cases, showing that the applicability of dried aerosol solutions is a good alternative calibration system for laser ablation sampling.     

Development of a sheathless interface between reversed-phase capillary HPLC and ICPMS via a microflow total consumption nebulizer for selenopeptide mapping

A sheathless interface based on a total consumption micronebulizer operating at flow rates in the range 0.5-7.5 microL min(-1) was developed between capillary HPLC and ICPMS. It allowed the efficient nebulization and transport into the plasma of mobile phases containing up to 100% organic solvent without either cooling the spray chamber or oxygen addition. The coupled system was applied to selenopeptide mapping in a protein fraction isolated from a selenized yeast extract. The detection limits were 150 (80Se) and 200 fg (82Se) for a quadrupole instrument with and without a collision cell, respectively, which is a factor 100-150 less than that reported elsewhere for HPLC-ICPMS. The minimal peak broadening ( approximately 5 s at the half-height) allowed baseline resolution of a mixture containing more than 30 selenopeptides, many of which could not be separated using the conventional HPLC-ICPMS coupling.     

Magnetic Sector ICPMS with Desolvating Micronebulization: Interference-Free Subpicogram Determination of Rare Earth Elements in Natural Samples

A new method has been developed combining desolvating micronebulization with magnetic sector inductively coupled plasma mass spectrometry (ICPMS) for the analysis of all 14 stable rare earth elements (REEs) in small samples of marine particulate matter. Application is demonstrated for REEs in suspended particles from a deep ocean hydrothermal vent plume and a geological reference material. A 100-fold reduction in oxide formation, relative to standard nebulizer-spray chamber sample introduction, makes oxide interference correction negligible, even for samples that are very enriched in Ba and light REEs. Enriched isotopes for one light and one heavy REE ((145)Nd and (171)Yb) are used as both isotope dilution and internal standards, providing determination of all the REEs in one analysis. This standardization scheme eliminates the need for multimass drift correction used previously to achieve acceptable accuracy with external standardization techniques. Instead, the method exploits capabilities for accurate and precise determination of isotope ratios, a principal strength of ICPMS, and the mass-independent sensitivity of electric field scans on our double-focusing instrument. We demonstrate overall precision of ≤2% (1σ) and accuracy better than 6% for all the REEs (except Er = 8.7%), based on comparison to recommended values for USGS certified reference material BHVO-1 (basalt). This performance is similar to that obtained by full isotope dilution mass spectrometric techniques, but the new method is far simpler, requires 5 min sample(-)(1), and avoids interferences introduced by complex mixtures of enriched isotopes. Sensitivity of (1.2-1.4) × 10(6) counts s(-)(1) ppb(-)(1) and background intensities of 2-60 counts s(-)(1) provide excellent detection limits of 1-40 ppq, a 100-fold improvement on established ICPMS methods. The low sample introduction rate (100 μL min(-)(1)) allows unprecedented absolute detection limits of 1-20 fg.     

Sample preconcentration using ion-exchange polymer film for laser ablation sampling inductively coupled plasma atomic emission spectrometry

An efficient sample pretreatment/introduction technique for the inductively coupled plasma atomic emission spectrometry (ICP-AES) using ion exchange for analyte preconcentration and matrix separation and laser ablation sampling for sample introduction has been developed. Ammonium pyrrolidine dithiocarbamate (APDC)-polystyrene films are coated on glass plates for analyte preconcentration. Repetitive laser ablation sampling of the polymer film removes the ion-exchanged metal ions from the polymer film as fine particles for sample introduction into the ICP. After immersing the sample probe in a sample solution for 5 min, the ICP emission intensity for laser ablation of the polymer film is a few times larger than that after solution nebulization. The sample probe removes only a small fraction of the sample solution and, therefore, in principle, does not disturb the original solution significantly. Single-pulse laser ablation of the polymer film shows that the ion-exchanged metal ion concentration in the film reduces exponentially with the depth of the polymer film. Ion exchange to the polymer film is probably limited by the rate of metal ion diffusion into the film. Calibration curves for Cu, Hg, Pb, and Zn show linear dynamic range of ～1-2 orders of magnitude. The linear dynamic range for Cu increases to >3 orders of magnitude when using Pb as an internal standard. RSD of the ICP emission intensity is ～8%.