Microconcentric Nebulizer Research Articles

Design, Optimization, and Application of a 3D-Printed Polymer Sample Introduction System for the ICP-MS Analysis of Nanoparticles and Cells

Commonly used sample introduction systems for inductively coupled plasma mass spectrometry (ICP-MS) are generally not well-suited for single particle ICP-MS (spICP-MS) applications due to their high sample requirements and low efficiency. In this study, the first completely 3D-printed, polymer SIS was developed to facilitate spICP-MS analysis. The system is based on a microconcentric pneumatic nebulizer and a single-pass spray chamber with an additional sheath gas flow to further facilitate the transport of larger droplets or particles. The geometry of the system was optimized using numerical simulations. Its aerosol characteristics and operational conditions were studied via optical particle counting and a course of spICP-MS measurements, involving nanodispersions and cell suspensions. In a comparison of the performance of the new and the standard (quartz microconcentric nebulizer plus a double-pass spray chamber) systems, it was found that the new sample introduction system has four times higher particle detection efficiency, significantly better signal-to-noise ratio, provides ca. 20% lower size detection limit, and allows an extension of the upper limit of transportable particle diameters to about 25 µm.

The influence of the sample introduction system on signals of different tin compounds in inductively coupled plasma-based techniques

The influence of the sample introduction system on the signals obtained with different tin compounds in inductively coupled plasma (ICP) based techniques, i.e., ICP atomic emission spectrometry (ICP–AES) and ICP mass spectrometry (ICP–MS) has been studied. Signals for test solutions prepared from four different tin compounds (i.e., tin tetrachloride, monobutyltin, dibutyltin and di-tert-butyltin) in different solvents (methanol 0.8% (w/w), i-propanol 0.8% (w/w) and various acid matrices) have been measured by ICP–AES and ICP–MS. The results demonstrate a noticeable influence of the volatility of the tin compounds on their signals measured with both techniques. Thus, in agreement with the compound volatility, the highest signals are obtained for tin tetrachloride followed by di-tert-butyltin/monobutyltin and dibutyltin.The sample introduction system exerts an important effect on the amount of solution loading the plasma and, hence, on the relative signals afforded by the tin compounds in ICP–based techniques. Thus, when working with a pneumatic concentric nebulizer, the use of spray chambers affording high solvent transport efficiency to the plasma (such as cyclonic and single pass) or high spray chamber temperatures is recommended to minimize the influence of the tin chemical compound. Nevertheless, even when using the conventional pneumatic nebulizer coupled to the best spray chamber design (i.e., a single pass spray chamber), signals obtained for di-tert-butyltin/monobutyltin and dibutyltin are still around 10% and 30% lower than the corresponding signal for tin tetrachloride, respectively. When operating with a pneumatic microconcentric nebulizer coupled to a 50°C-thermostated cinnabar spray chamber, all studied organotin compounds provided similar emission signals although about 60% lower than those obtained for tin tetrachloride. The use of an ultrasonic nebulizer coupled to a desolvation device provides the largest differences in the emission signals, among all tested systems.

Preliminary study on aerosol particle addition calibration method for on-line quantitative analysis of airborne radioactive particles with ICP-MS

An ambient aerosol concentration enrichment system coupled with ICP-MS for real-time monitoring of airborne radioactive particles is now under development. ICP-MS is very sensitive to sample introduction conditions, so it is necessary to develop an easy-use calibration method for on-line quantitative analysis in field application. In this paper, a calibration method using standard solution instead of monodisperse particles was established and validated preliminarily. First of all, four parameters for the method were determined experimentally, including: uptake flow rate and nebulisation efficiency of the Microconcentric nebuliser, nebulisation/transport efficiency of Aridus Desolvating Sample Introduction System, and Relative Sensitivity Factor between 159 Tb and 174 Yb. Then, monodisperse terbium nitrate particles were generated by a commercial Vibrating Orifice Aerosol Generator. Continuous aerosols of ytterbium nitrate droplets were nebulised from standard solution. They were mixed together, desolvated through the membrane dryer and introduced into ICP-MS for on-line analysis of terbium nitrate particles. The air sampled from nuclear environment was also introduced into ICP-MS to investigate the effect of flow rate on instrument responses. Finally, atom numbers of 159 Tb in discrete terbium nitrate particles were determined using the calibration method and compared to the calculated value. Results show that when air flow rate increase from 10 mL min−1 to 100 mL min−1, the ratio of 159 Tb ion count to 174 Yb ion intensity keeps constant although instrument sensitivity decreases by a factor of 25. The relative standard deviation of 159 Tb atom number measured is better than 18%. The discrepancy with the calculated value could be attributed to the over-estimation of atom number in the particles generated by VOAG because there was some liquid leakage in the VOAG.

Combined use of medium mass resolution and desolvation introduction system for accurate plutonium determination in the femtogram range by inductively coupled plasma-sector-field mass spectrometry

Formation of a polyatomic species made of an atom of a heavy element like lead, mercury or iridium, and atoms abundant in plasma (argon, nitrogen, oxygen, and hydrogen) when using an inductively coupled plasma-sector-field mass spectrometer (ICP-SFMS) may lead to false detection of femtograms (fg) of plutonium or bias in the measured concentrations. Mathematical corrections, based on the measurement of heavy element concentrations in the sample solutions and determination of the extents of formation of the polyatomic interferences, are efficient but time-consuming and degrade detection limits. We describe and discuss a new method based on the combination of, on the one hand, medium mass resolution (MR) of the ICP-SFMS to separate plutonium isotopes physically from interfering polyatomic species, and, on the other, use of a desolvation introduction system (DIS) to enhance sensitivity, thus partly compensating for the loss of transmission due to use of a higher resolution. Plutonium peaks are perfectly separated from the major interfering species (PbO 2, HgAr, and IrO 3) with a mass resolution of ~ 4000. The resulting nine-fold transmission loss is partly compensated by a five-fold increase in sensitivity obtained with the DIS and a lower background. The instrumental detection limits for plutonium isotopes, calculated for measurements of pure synthetic solutions, of the new method (known as MR-DIS method) and of the one currently used in the laboratory (LR method), based on a low mass resolution equal to 360, a microconcentric nebulizer and two in-line cooled spray chambers, are roughly equivalent, at around 0.2 fg ml − 1 . Regarding the measurement of real-life samples, the results obtained with both methods agree and the corresponding analytical detection limits for plutonium isotopes 239Pu, 240Pu and 241Pu are of a few fg·ml − 1 of sample solution, slightly lower with the MR-DIS method than with the current LR method. Although less sensitive than other plutonium ICP-MS measurement methods described in the literature, the main advantage of the MR-DIS method is that it is robust against the risk of false plutonium detection, even in the case of relatively high concentrations of heavy elements like lead, mercury or iridium.

Magnetic quantitative immunoanalysis of carcinoembryonic antigen by ICP-MS with mercury labels

The need of analytical methods for absolute quantitative protein analysis spurred research on new developments in recent years. In this paper, a sensitive and selective method based on mercury labeled magnetic immunoassay and inductively coupled plasma mass spectrometry (ICP-MS) detection was proposed for the quantification of carcinoembryonic antigen (CEA) in real human serum samples. Size exclusion chromatography (SEC) combined with ICP-MS was applied for the separation and detection of secondary antibody labeled with mercury and excess mercury. After a complete sandwich-type immunoreaction among primary antibody, CEA and secondary antibody labeled with mercury on magnetic nanoparticles (MNPs), the concentration of CEA was determined by microconcentric nebulizer (MCN)-ICP-MS analysis of mercury ion released from secondary antibody with an acid-dissolution (pH 1.0) step. With consumption of only 50 μL sample solution, the established method presented a limit of detection of 0.041 ng mL−1 for CEA, with the relative standard deviation (RSD) of 5.2% (c = 8 ng mL−1, n = 7). The response for CEA was linear over a dynamic range from 0.1 to 50 ng mL−1. The analytical results of CEA in three different human serum samples obtained by the proposed method are in good agreement with that obtained by the commonly used clinical method of chemiluminescent immunoassay (CLIA). The developed method was versatile and could be easily extended to other proteins quantitative analysis, especially for specific biomarker determination.

Determination of trace elements in biological samples treated with formic acid by inductively coupled plasma mass spectrometry using a microconcentric nebulizer

A simple and fast method for the determination of As, Ba, Cd, Co, Cu, Fe, Ga, Mn, Mo, Ni, Pb, Rb, Se, Sr, Tl, U, V and Zn in biological samples by inductively coupled plasma mass spectrometry (ICP-MS), after sample solubilization with formic acid and introduction by a microconcentric nebulizer, is proposed. The sample is mixed with formic acid, kept at 90 °C for one hour and then diluted with nitric acid aqueous solution to a 50% v/v formic acid and 1% v/v nitric acid final concentrations. The final sample solution flow rate for introduction into the plasma was 30 μL min −1. The optimized and adopted nebulizer gas flow rate was 0.7 L min −1 and RF power was 800 W. These conditions are very different than those normally used when a conventional nebulizer is employed. Rodhium was used as internal standard. External calibration against aqueous standard solutions, without formic acid, could be used for quantification, except for As, Se and Zn. However, external calibration with 50% formic acid allows the determination of all analytes with high accuracy and it is recommended. The detection limits were between 0.0005 (Tl) and 0.22 mg kg −1 (Fe) and the precision expressed by the relative standard deviations (RSD) were between 0.2% (Sr) and 3.5% (Ga). Accuracy was validated by the analysis of four certified reference biological materials of animal tissues, comparing the results by linear regressions and by the t-test at a 95% confidence level. The recommended procedure avoids plasma instability and carbon deposit on the cones.

Speciation analysis of arsenic and selenium compounds by CE‐dynamic reaction cell‐ICP‐MS

A dynamic reaction cell ICP-MS was used as a CE detector for the speciation analysis of arsenic and selenium. Samples containing arsenite, arsenate, monomethylarsonic acid, dimethylarsinic acid, arsenobetaine, selenite, selenate, selenocysteine, selenomethione, and Se-methylselenocysteine were subjected to electrophoretic separation before being introduced into the microconcentric nebulizer (CEI-100) for their determination by ICP-MS. The separation has been achieved in a 60 cm length x 75 microm id fused-silica capillary. The electrophoretic buffer used was 25 mmol/L CAPS, and 0.5 mmol/L SDS at pH 9.5, whereas the applied voltage was set at 25 kV. The potentially interfering (38)Ar(40)Ar(+) and (40)Ar(40)Ar(+) at the selenium masses m/z 78 and 80 were reduced in intensity by approximately three orders of magnitude by using 1.4 mL/min CH(4) as reactive cell gas in the dynamic reaction cell. Arsenic was determined as the adduct ion (75)As(12)CH(2) (+) at m/z 89. The LOD for arsenic and selenium was in the range of 0.6-1.8 ng/mL, and 0.5-1.4 ng/mL, respectively, based on peak height. This method has been applied to determine various arsenic and selenium compounds in NIST SRM 1633a Coal Fly Ash and NRCC DOLT-3 Dogfish Liver reference materials and a selenium dietary supplement. The arsenic and selenium compounds were extracted from fish liver and dietary supplement by using Protease XIV and Lipase, and from coal fly ash with HF solution. The spike recoveries were in the range 91-103% for all the species studied.

Immunoaffinity monolithic capillary microextraction coupled with ICP-MS for immunoassay with quantum dot labels

A sensitive and selective method of immunoaffinity monolithic capillary microextraction (CME) based on a sandwich immunoreaction with quantum dots (QDs) labels coupled with micro-concentric nebulizer inductively coupled plasma mass spectrometry (MCN-ICP-MS) was proposed for the determination of antigen human IgG in human serum. Aminopropyltriethoxysilane (APTES)-silica hybrid monolithic capillary which was prepared by room temperature ionic liquid (RTIL)-mediated sol–gel method was immobilized with primary goat-anti-human antibody. After a complete immunoreaction among primary antibody, IgG antigen and secondary antibody labeled with CdSe QDs in monolithic capillary, the concentration of IgG was quantified by MCN-ICP-MS simultaneous analysis of Cd and Se released from captured QDs labels with an acid-dissolution (pH 2.0) step. With consumption of only 50 μL sample solution, the established method presented a limit of detection of 0.058 μg L−1 based on the Cd signal and 0.097 μg L−1 based on the Se signal for human IgG antigen, with the relative standard deviations (RSDs) of 7.2% based on the Cd signal and 13% based on the Se signal (chumanIgGantigen = 5 μg L−1, n = 7), respectively. The response of CME-MCN-ICP-MS method for human IgG was linear over a dynamic range from 0.2 to 10 μg L−1 based on the Cd signal and from 0.5 to 10 μg L−1 based on the Se signal, respectively. The proposed method was successfully applied for the determination of IgG in real human serum with good recoveries. For validation, the same sample was also analyzed by the commonly used clinical method of immunoturbidimetry, and the analytical result obtained by the proposed method is in good agreement with that the result obtained by immunoturbidimetry. By using CdSe QDs labels, the quantification of human IgG antigen could be performed by ICP-MS determination of both Cd and Se, and the analytical results for human IgG antigen could be validated in one run. The developed method was fast, sensitive, selective, versatile and could be easily extended to other protein quantification schemes as well as in DNA analysis.

Comparison of microconcentric and membrane-desolvation sample introduction systems for determination of low rare earth element concentrations in surface and subsurface waters using sector field inductively coupled plasma mass spectrometry

Analytical performances of a microconcentric nebulizer (MCN) and a membrane-desolvation sample introduction system (Aridus) were compared for determination of low concentrations of rare earth elements (REEs) in surface and subsurface waters using a double focusing sector field inductively coupled plasma mass spectrometer. Conventional figures of merit were employed, such as sensitivities, limits of detection (LOD), REE–O + formation, matrix induced interferences, long term signal variations, and recovery from spiked sea water samples and a pristine water CRM. Sensitivity as a function of mass for the MCN was quite flat with the exception of light REE (LREE +) which was dependent on REE–O + generation. Signal responses using the Aridus were enhanced by factors of 4–10. Large sensitivity enhancements were observed for 139La +, 140Ce + and 141Pr +, due to the attenuation of their REE–O + (where the Aridus 140Ce 16O +/ 140Ce + was three orders of magnitude lower than that determined using the MCN) as a result of water analysis reduction in the plasma. Despite higher sensitivities, Aridus LODs were not significantly different from those obtained using the MCN, and values varied from 0.05 to 0.2 ng L − 1 and 0.1 to 0.2 ng L − 1 for the MCN and Aridus systems, respectively. When using the MCN, LREE + signals were closely associated with REE–O bond strengths, implying that LREE–O + production and breakdown are related to the strength of REE–O bonds in REE–O + ions suggesting that medium REE (MREE)–O + and heavy REE (HREE)–O + if formed, were thermally unstable in the plasma. In the presence of conservative Na concentrations, MCN LREE + signal suppressions varied from about 15 to 25% and about 5 to 10% for MREE + and HREE +. In contrast, regular 15% signal suppressions for all REE + were observed for the Aridus. In the case of the MCN, more than one internal standard is required for compensation for these different effects, whereas a single internal standard ( 159Tb +) compensated for REE + signal variations with the Aridus. Long term uncompensated REE + signal % RSDs using the MCN varied from about 2 to 5%, and % recoveries were about 95–110%. With internal standardization, % RSD varied irregularly from about 1 to 3% and % recoveries were not significantly improved. In contrast, with the Aridus, high % RSDs of about 8% and recoveries of about 80% were compensated with 159Tb + as the internal standard (< 0.5% and recoveries of about 100%, respectively). Accuracy was determined by analyzing spiked sea water CRM (NAAS-5) (1:100 v/v) spiked with 1 µg L − 1 REEs and CRM SLRS-4 using an external calibration procedure. With the Aridus system, REE recoveries were about 100% with 159Tb + as the internal standard. REE determinations of SLRS-4 were in good agreement with the reported values indicating that very low REE concentrations can be determined directly without matrix separation and analyte preconcentration.

Determination of Cobalamin in Nutritive Supplements and Chlorella Foods by Capillary Electrophoresis−Inductively Coupled Plasma Mass Spectrometry

A capillary electrophoresis-inductively coupled plasma mass spectrometric (CE-ICP-MS) method for the determination of cobalamin is described. Samples of cobalt-containing compounds were subjected to electrophoretic separation before injection into the microconcentric nebulizer (CEI-100) of ICP-MS. The Co-containing compounds studied include cyanocobalamin (CN-Cbl, vitamin B12), hydroxocobalamin (OH-Cbl), and Co(II). The species studied were well separated using a 70 cm lengthx75 microm i.d. fused silica capillary with the applied voltage set at +20 kV. A 25 mM Tris buffer (pH 9.0) containing 15 mM sodium dodecyl sulfate (SDS) was used as the electrophoretic buffer. The CE-ICP-MS detection limits were 0.3, 0.2, and 1.7 ng of Co mL(-1) for CN-Cbl, OH-Cbl, and Co(II), respectively. The concentrations of cobalamin compounds were determined in selected nutritive supplements and chlorella samples. A microwave-assisted extraction method was used for the extraction of these compounds. Over 92% of the total cobalt species was extracted using a 5% v/v HNO3 solution in a focused microwave field within a period of 10 min; spike recovery was in the range of 94-105% for various species. The major cobalt species in nutritive supplements and chlorella samples was cyanocobalamin.

Determination of trace elements in fuel ethanol by ICP-MS using direct sample introduction by a microconcentric nebulizer

The use of a microconcentric nebulizer in ICP-MS is proposed to allow the introduction of ethanol solutions. High gas flow rate and low RF power led to less interference and high sensitivity. It was possible to introduce solutions with up to 70% v/v ethanol. The ethanol increases the nebulization efficiency and transport, with a sensibility gain between 15 and 25 for most studied analytes. External calibration allowed low detection limits, adequate for fuel ethanol analysis. The Cu, Cd, Ni, Pb, Tl and Sn concentrations determined by isotope dilution were in accordance with those by external calibration. The precision was adequate, with RSD from 1 to 9% using external calibration with IS, and the recovery test showed the accuracy of the proposed method.

Determination of iodine and bromine compounds in foodstuffs by CE‐inductively coupled plasma MS

A CE-inductively coupled plasma mass spectrometric (CE-ICP-MS) method for iodine and bromine speciation analysis is described. Samples containing ionic iodine (I(-) and IO(3)(-)) and bromine (Br(-) and BrO(3)(-)) species are subjected to electrophoretic separation before injection into the microconcentric nebulizer (CEI-100). The separation has been achieved in a 50 cm length x 75 microm id fused-silica capillary. The electrophoretic buffer used is 10 mmol/L Tris (pH 8.0), while the applied voltage is set at -8 kV. Detection limits are 1 and 20-50 ng/mL for various I and Br compounds, respectively, based on peak height. The RSD of the peak areas for seven injections of 0.1 microg/mL I(-), IO(3)(-) and 1 microg/mL Br(-), BrO(3)(-) mixture is in the range of 3-5%. This method has been applied to determine various iodine and bromine species in NIST SRM 1573a Tomato Leaves reference material and a salt and seaweed samples obtained locally. A microwave-assisted extraction method is used for the extraction of these compounds. Over 87% of the total iodine and 83% of the total bromine are extracted using a 10% m/v tetramethylammonium hydroxide (TMAH) solution in a focused microwave field within a period of 10 min. The spike recoveries are in the range of 94-105% for all the determinations. The major species of iodine and bromine in tomato leaves, salt, and seaweed are Br(-), IO(3)(-), I(-), and Br(-), respectively.

A Metal-coded Affinity Tag Approach to Quantitative Proteomics

The quantitative analysis of protein mixtures is pivotal for the understanding of variations in the proteome of living systems. Therefore, approaches have been recently devised that generally allow the relative quantitative analysis of peptides and proteins. Here we present proof of concept of the new metal-coded affinity tag (MeCAT) technique, which allowed the quantitative determination of peptides and proteins. A macrocyclic metal chelate complex (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA)) loaded with different lanthanides (metal(III) ions) was the essential part of the tag. The combination of DOTA with an affinity anchor for purification and a reactive group for reaction with amino acids constituted a reagent that allowed quantification of peptides and proteins in an absolute fashion. For the quantitative determination, the tagged peptides and proteins were analyzed using flow injection inductively coupled plasma MS, a technique that allowed detection of metals with high precision and low detection limits. The metal chelate complexes were attached to the cysteine residues, and the course of the labeling reaction was followed using SDS-PAGE and MALDI-TOF MS, ESI MS, and inductively coupled plasma MS. To limit the width in isotopic signal spread and to increase the sensitivity for ESI analysis, we used the monoisotopic lanthanide macrocycle complexes. Peptides tagged with the reagent loaded with different metals coelute in liquid chromatography. In first applications with proteins, the calculated detection limit for bovine serum albumin for example was 110 amol, and we have used MeCAT to analyze proteins of the Sus scrofa eye lens as a model system. These data showed that MeCAT allowed quantification not only of peptides but also of proteins in an absolute fashion at low concentrations and in complex mixtures.

Determination of chloroplatinates by CE coupled to inductively coupled plasma sector field MS

In the present work the degradation of chloroplatinates emitted into the aquatic environment has been investigated in model studies. CE coupled to inductively coupled plasma sector field MS (ICP-SFMS) was employed as an analytical method of measurement. The CE-ICP-MS interface utilized the functional make-up flow design with a microconcentric nebulizer. [Pt(Cl(4))](2-) and [Pt(Cl(6))](2-) were separated within 5 min. During a measurement period of 6 h an excellent reproducibility of migration times (RSD 2.3%) could be achieved. The high sensitivity of ICP-SFMS resulted in an LOD of 80 ng/L platinum for the two compounds. External calibration using rhenium as internal standard was linear over three orders of magnitude. However, with external calibration a long-term drift of signal intensity was observed. In order to reduce the uncertainty of the obtained results, quantification of [PtCl(6)](2-) was performed for the first time by species-specific on-line isotope dilution MS using (194)[PtCl(6)](2-) as spike. The two different quantification strategies were compared in terms of their total combined uncertainty of measurement according to the EURACHEM guideline. The method was employed for monitoring the time-dependent degradation of [Pt(Cl(4))](2-) and [Pt(Cl(6))](2-) in water containing 0 and 2.8 mmol/L Cl(-) and river water. [Pt(Cl(6))](2-) was stable whereas [Pt(Cl(4))](2-) showed rapid degradation following pseudo first-order kinetics.

239 + 240Pu concentration and isotope ratio (240Pu/239Pu) in aerosols during high dust (Yellow Sand) period, Korea

Concentration and isotope ratio of Pu were analyzed for aerosols collected at Anmyeondo located in the western coast of Korea using multiple collector inductively coupled plasma mass spectrometer equipped with desolvated micro-concentric nebulizer. Aerosols were collected from June 2001 to April 2002 using high volume air sampler. The samples consist of high dust samples (Yellow Sand), and also low dust samples; maximum Al concentration was 74.2 μg/m3 and minimum was 0.17 μg/m3.Pu was concentrated using 0.1 ml TEVA resin columns after conc. HNO3 extraction. Isotope dilution using 242Pu spike and mass bias correction using 233U and 236U mixed solution enabled the quantification of Pu and measurement of isotope ratio simultaneously. The contribution of 238U from both spikes and samples was minimized by careful chemical separation and optimization of spike concentration. The 238U1H and tail contribution on 239Pu peak were about 0.75×10−5 and 1×10−5 of 238U intensity, respectively, and they were corrected from 239Pu using externally determined (238U1H+tailing)/238U ratio and 238U measurement during acquisition. The detection limits of this analytical procedure were 0.61 fg/ml and 0.56 fg/ml for 239Pu and 240Pu, respectively (4 nBq/m3 and 12 nBq/m3 for 239Pu and 240Pu, respectively). The precision of isotope ratio measurement was better than 2% for larger quantity than 20 fg of 239Pu.In spring, maximum concentration of 0.580 μBq/m3 for 239Pu and 0.404 μBq/m3 for 240Pu was observed when Al concentration was maximum, so called as Yellow Sand event. Pu concentrations in aerosols are well correlated with Al, a tracer of soil dust. The ratios of Pu/Al were 0.0082 (μBq/μg) and 0.0055 (μBq/μg) for 239Pu/Al and 240Pu/Al, respectively. Isotope ratios of Pu (240Pu/239Pu) in Yellow Sand samples show 0.191±0.014 close to those of global fallout. These facts indicate that Yellow Sand plays an important role in the behavior of Pu in the environment like other concomitant metals such as Al, Fe etc.

Nafion-Coated Bismuth Film and Nafion-Coated Mercury Film Electrodes for Anodic Stripping Voltammetry Combined On-Line with ICP-Mass Spectrometry

Nafion-coated bismuth film electrodes (NCBFEs) and Nafion-coated mercury film electrodes (NCMFEs) were used to electrochemically preconcentrate metal analytes for subsequent analysis by inductively coupled plasma-mass spectrometry (ICP-MS). Either type of electrodes is part of a thin-layer electrochemical flow cell that is positioned upstream of a microconcentric nebulizer for the ICP-MS. Performances of these electrodes were compared in terms of the analytical "figures of merit" (e.g., dynamic ranges, reproducibility, hydrodynamic stability, and elimination of matrix effects detrimental to ICP-MS). The coupled technique (ASV-ICP-MS) is found to possess a wide dynamic range (at least 4 to 5 orders of magnitude) and to be reproducible. Both electrodes are much more stable than the thin mercury film electrode (TMFE) traditionally used for ASV-ICP-MS, with the lifetime of the NCBFE exceeding 8 h. Adopting these electrodes for ASV-ICP-MS overcomes the problems associated with a TMFE, the erosion of which decreases the sample throughput, affects the analysis precision, and contaminates conventional glass nebulizers and spray chambers of the spectrometer. The medium exchange procedure inherent in ASV is successfully implemented with a two-valve flow injection system for the accumulation of trace Cd2+ into the electrode from a certified seawater sample, followed by stripping Cd into a solution that is compatible to the ICP-MS operation.

Capillary electrophoresis‐inductively coupled plasma‐mass spectrometry: A report on technical principles and problem solutions, potential, and limitations of this technology as well as on examples of application

This paper summarizes some basic principles of capillary electrophoresis (CE), inductively coupled plasma-mass spectrometry (ICP-MS), and coupling of both devices. Especially the interfacing is described in detail. A special focus is drawn to various interface developments reported in literature and technical problems, i.e., requirements to the interface setup and respective solutions. Nowadays, typically sheath flow-based interfaces are used. The sheath flow fulfills two requirements of hyphenation, (i) the closing of the electrical circuit of CE and (ii) the feeding of the used nebulizer with an adequate flow rate. In the beginning of CE-ICP-MS coupling predominantly home-made interface-nebulizer constructions were developed and tested for various speciation problems. Now increasingly such laboratory-constructed interfaces are left. Mostly commercial nebulizers are employed being combined with commercially available tee or cross fittings to connect the CE capillary to the electrode, the additional sheath flow, and the nebulizer. Due to the low sample amounts and low flow rates from CE, such nebulizers are typically low-flow nebulizers like, e.g., the microconcentric nebulizer (MCN) and the direct injection nebulizer (DIN). However, there are also reports on couplings using standard Meinhard systems. Still the control and reduction of a siphoning sucting flow and sufficient detection limits are the major problems in hyphenating CE to ICP-MS. Different solutions are reported on these problems and summarized here. Finally numerous applications are reported. Mostly, applications are performed on speciation of selenium, arsenic, metallothionein isoforms, mercury, or cobalt.

Radial ICP characteristics for ICP-AES using direct injection or microconcentric nebulisation

Radial analyte signal intensities, fundamental plasma parameters, and non-spectral interference effects were characterized for inductively coupled plasma atomic emission spectrometry (ICP-AES) using a direct injection nebuliser (Vulkan DIN) or a microconcentric nebuliser (MCN) coupled to a cyclonic spray chamber for sample introduction. Radial analyte signal intensity profiles for atomic and ionic lines with energy sum (Esum) between 1.85 and 15.41 eV were used. When using the MCN system, for all lines the signal intensity profiles were parabolic with maxima at the axial centre of the plasma. For the Vulkan DIN, the shapes of the profiles were dependent on their Esum showing minimum intensities at the axial centre of the plasma for lines with high Esum values. The ionisation temperature, electron number density and magnesium ion-atom line intensity ratio determined indicated that ionisation and excitation capabilities were deteriorated at the centre of the plasma when using the Vulkan DIN compared with the MCN. This was found to be not simply a result of high aerosol load when using the Vulkan DIN, but because of poor plasma–aerosol interaction, possibly caused by the confined distribution of aerosol in the plasma and high nebuliser gas velocity. Indeed, for the Vulkan DIN, electron number density and ionisation temperature increased with liquid flow rate, which could be explained by plasma shrinkage, or the thermal pinch effect, which increased the aerosol–plasma interaction at increased liquid flow rates. As a consequence, when increasing the liquid flow rate in the range 20–90 μL min−1: (i) analyte sensitivity increased linearly; (ii) the plasma became unstable; (iii) the magnitude of matrix effects remained almost unaffected. These results are partly in contrast to observations made with other types of direct injection nebulisers and ICP instruments.

Quantitative determination of selenium metabolites in human urine by LC-DRC-ICP-MS

Two selenium metabolites, Se-methylseleno-N-acetylgalactosamine (SeGal-N-Ac) and Se-methylselenogalactosamine (SeGal-NH2), were quantified in human urine by LC-DRC-ICP-MS. Urine samples were analysed after 1 + 1 dilution in a reversed phase chromatographic system using an eluent consisting of 200 mM ammonium acetate and 5% methanol with a pH of 9.25 and quantified by standard addition. Samples were collected from 8 volunteers before and after 5 days ingestion of 100 μg Se day−1 in form of selenized yeast. The average concentration of (SeGal-NH2) before and after selenium intake was 1.4 and 1.9 μg Se L−1, respectively, while the average concentration of Se-Gal-N-Ac increased from 2.6 to 11.6 μg Se L−1 before and after selenium consumption. Detection limits calculated on basis of three times the standard deviation on peak areas of 2 μg Se L−1 solutions were 0.1 μg Se L−1 for SeGal-NH2 and 0.2 μg Se L−1 for SeGal-N-Ac based on peak areas and monitoring 80Se. The precision expressed as the relative standard deviation (n = 6) at the 2 μg Se L−1 level was 3.1 and 1.7% for SeGal-NH2 and SeGal-N-Ac, respectively, while the corresponding values were 1.0 and 0.7% at the 10 μg Se L−1 level. Linearity in urine matrix was examined in the range 0.5–100 μg Se L−1 and correlation coefficients better than 0.999 were obtained. As the cationic compound SeGal-NH3+ may be confounded with the trimethylselenonium ion (TMSe+), urine samples were also analysed in a cation exchange chromatographic system in which SeGal-NH3+ was separated from the trimethylselenonium ion. None of the samples contained TMSe+ in detectable amounts. Three sample introduction systems were compared—a microconcentric nebuliser in combination with a cyclonic spray chamber (MCN), a direct injection nebuliser (DIN) and an ultrasonic nebuliser (USN). The MCN was most suitable for this purpose.

Sample introduction systems for reversed phase LC-ICP-MS of selenium using large amounts of methanol—comparison of systems based on membrane desolvation, a spray chamber and direct injection

Three sample introduction systems were compared for their efficiency in introducing a variety of biologically relevant selenium species in organic solutions with the purpose of mimicking the effluent from a chromatographic system. The sample introduction systems consisted of a microconcentric nebuliser (MCN) in combination with a membrane desolvator (MD), a MCN in combination with a cyclonic spray chamber (CS) and a direct injection nebuliser (DIN), respectively. Thirteen selenium standards diluted in 50% methanol were introduced in each system at a flow rate of 50 μl min−1. Except for the selenite and methaneseleninic acid standards that were lost in the MCN-MD system, similar normalized response factors were achieved for the standards regardless of the sample introduction system. When trimethylselenonium and selenate standards were continuously infused in a linear methanol gradient from 10 to 90%, the signal was almost unaffected when the MCN-MD was used as interface. The signals from the MCN-CS introduction system were almost unaffected in methanol concentrations between 10 and 40%, after which they slowly declined. The signal from the DIN showed a plateau in signal intensity at methanol concentrations between 35 and 70%. Detection limits in flow injection analysis, expressed as the concentration that would result in a signal equivalent to three times the peak to peak noise of the baseline, were estimated to be 200, 150 and 100 ng Se L−1 for the MCN-CS, MCN-MD and DIN, respectively. The independence of the signal from the methanol concentration in the eluent allowed quantification of human selenoprotein P isoforms by gradient microbore reversed phase chromatography (μRPC) on the basis of an internal trimethylselenonium standard. The MCN-MD system was applied for μRPC analysis of 77Se enriched yeast samples and more than 30 selenium containing compounds were separated using a linear gradient from 5% to 95% methanol, some of the selenium species eluting in 85% methanol.