Determination of arsenic by inductively coupled plasma mass spectrometry – comparison of sample introduction techniques

A comparison is made of four sample introduction techniques for the determination of As by inductively coupled plasma mass spectrometry. The techniques studied were 1) flow injection with pneumatic nebulization (FIA-PN), 2) direct electrothermal vaporization (ETV), 3) continuous hydride generation (HG) and 4) hydride generation with in situ trapping followed by electrothermal vaporization (HG-ETV). It was found that FIA-PN and ETV gave similar detection limits in concentration units (about 20 pg mL^–1), although ETV had a much lower absolute detection limit (0.2 pg). Sample introduction by hydride generation gave an inferior detection limit (100–200 pg mL^–1), also in combination with in situ trapping and ETV, owing to the blank signal from traces of As in NaBH₄ which is difficult to eliminate. The results indicate that the more elaborate sample introduction techniques based on ETV and HG may not offer significant advantages compared to normal solution nebulization for the determination of As in simple sample matrices such as natural fresh waters, where matrix removal is not required.     

Determination of uranium in urine – measurement of isotope ratios and quantification by use of inductively coupled plasma mass spectrometry

For analysis of uranium in urine determination of the isotope ratio and quantification were investigated by high-resolution inductively coupled plasma mass spectrometry (HR ICP-MS). The instrument used (ThermoFinniganMAT ELEMENT2) is a single-collector MS and, therefore, a stable sample-introduction system was chosen. The methodical set-up was optimized to achieve the best precision for both the isotope ratio and the total uranium concentration in the urine matrix.Three spiked urine samples from an European interlaboratory comparison were analyzed to determine the (235)U/(238)U isotope ratio. The ratio was found to be in the range 0.002116 to 0.007222, the latter being the natural uranium isotope ratio. The first ratio indicates the abundance of depleted uranium.The effect of storage conditions and the stability for the matrix urine were investigated by using "real-life" urine samples from unexposed persons in the Netherlands. For samples stored under refrigeration and acidified the results (range 0.8 to 5.3 ng L(-1) U) were in the normal fluctuation range whereas a decrease in uranium concentration was observed for samples stored at room temperature without acidification.     

Ultra-sensitive quantification of lysozyme based on element chelate labeling and capillary electrophoresis–inductively coupled plasma mass spectrometry

In this study, an ultra-sensitive method for the quantification of lysozyme based on the Gd³⁺ diethylenetriamine-N,N,N′,N″,N″-pentaacetic acid labeling and capillary electrophoresis–inductively coupled plasma mass spectrometry (CE–ICP–MS) was described. The Gd³⁺-tagged lysozyme was effectively separated by capillary electrophoresis (CE) and sensitively determined by inductively coupled plasma mass spectrometry (ICP–MS). Based on the gadolinium-tagging and CE–ICP–MS, the lysozyme was determined within 12 min with an extremely low detection limit of 3.89 attomole (3.89 × 10⁻¹¹ mol L⁻¹ for 100 nL of sample injection) and a RSD < 6% (n = 5). The proposed method has been successfully used to detect lysozyme in saliva samples with a recovery of 91–106%, suggesting that our method is sensitive and reliable. The success of the present method provides a new potential for the biological assays and sensitive detection of low-abundant proteins.     

A systematic study on the influence of carbon on the behavior of hard-to-ionize elements in inductively coupled plasma–mass spectrometry

A systematic study on the influence of carbon on the signal of a large number of hard-to-ionize elements (i.e. B, Be, P, S, Zn, As, Se, Pd, Cd, Sb, I, Te, Os, Ir, Pt, Au, and Hg) in inductively coupled plasma–mass spectrometry has been carried out. To this end, carbon matrix effects have been evaluated considering different plasma parameters (i.e. nebulizer gas flow rate, r.f. power and sample uptake rate), sample introduction systems, concentration and type of carbon matrix (i.e. glycerol, citric acid, potassium citrate and ammonium carbonate) and type of mass spectrometer (i.e. quadrupole filter vs. double-focusing sector field mass spectrometer). Experimental results show that P, As, Se, Sb, Te, I, Au and Hg sensitivities are always higher for carbon-containing solutions than those obtained without carbon. The other hard-to-ionize elements (Be, B, S, Zn, Pd, Cd, Os, Ir and Pt) show no matrix effect, signal enhancement or signal suppression depending on the experimental conditions selected. The matrix effects caused by the presence of carbon are explained by changes in the plasma characteristics and the corresponding changes in ion distribution in the plasma (as reflected in the signal behavior plot, i.e. the signal intensity as a function of the nebulizer gas flow rate). However, the matrix effects for P, As, Se, Sb, Te, I, Au and Hg are also related to an increase in analyte ion population caused as a result of charge transfer reactions involving carbon-containing charged species in the plasma. The predominant specie is C⁺, but other species such as CO⁺, CO₂⁺, C₂⁺ and ArC⁺ could also play a role. Theoretical data suggest that B, Be, S, Pd, Cd, Os, Ir and Pt could also be involved in carbon based charge transfer reactions, but no experimental evidence substantiating this view has been found.     

Characterization of a sealed Americium–Beryllium (AmBe) source by inductively coupled plasma mass spectrometry

Two Americium–Beryllium neutron sources were dismantled, sampled (sub-sampled) and analyzed via inductively coupled plasma mass spectrometry (ICP-MS). Characteristics such as “age” since purification, actinide content, trace metal content and inter and intra source composition were determined. The “age” since purification of the two sources was determined to be 25.0 and 25.4 years, respectively. The systematic uncertainties in the “age” determination were ±4% 2σ. The amount and isotopic composition of U and Pu varied substantially between the sub-samples of Source 2 (n = 8). This may be due to the physical means of sub-sampling or the way the source was manufactured. Source 1 was much more consistent in terms of content and isotopic composition (n = 3 sub-samples). The Be–Am ratio varied greatly between the two sources. Source 1 had an Am–Be ratio of 6.3 ± 52% (1σ). Source 2 had an Am–Be ratio of 9.81 ± 3.5% (1σ). In addition, the trace element content between the samples varied greatly. Significant differences were determined between Sources 1 and 2 for Sc, Sr, Y, Zr, Mo, Ba and W.     

Metabolomic approach to Alzheimer’s disease diagnosis based on mass spectrometry

Alzheimer??s disease is the most common neurodegenerative disease, but there is still no cure and early diagnosis remains very difficult. For this reason, the discovery of new biomarkers is of great importance. The application of metabolomics is emerging in this field, based on the use of mass spectrometry as a technique of analysis. In this work, blood serum samples (from Alzheimer??s disease patients and healthy controls) were analysed by mass spectrometry in order to search for potential metabolomic biomarkers. The application of multivariate statistical tools (PLS-DA) enabled us to discriminate between groups. In addition, some phosphatidylcholine compounds were identified as markers of the disease.     

A mathematical model for continuous hydride generation with inductively coupled plasma spectrometry analysis—I. Hydride transfer

A mathematical model for the continuous hydride generation technique with inductively coupled plasma (ICP) spectrometry during hydride transfer between generation and ICP is proposed. Experimental results for As, Pb, Sn and Te hydrides are compared with model calculations, and deviations between them are evaluated statistically. The main parameters affecting the hydride transfer, such as the carrier flow rate and the gas-liquid separator volume, are studied both theoretically and experimentally.     

Classifying wine according to geographical origin via quadrupole-based ICP–mass spectrometry measurements of boron isotope ratios

The potential of quadrupole-based ICP–MS as a tool for B-isotopic analysis of wines and its usefulness in provenance determinations were assessed. A precision of 0.1–0.25% RSD (corresponding to a relative standard deviation of the mean of three replicate measurements of 0.06–0.12%) was sufficient to establish small differences in the B isotope ratios in wines from different geographical origins. Each sample measurement was bracketed by measurements of a standard and mass bias drift correction made by interpolation. Sample preparation was kept to a minimum to avoid possible fractionation. Dilution of the wine samples by a factor of 100 with 0.65% HNO₃ was found to reduce matrix-induced mass discrimination substantially. Wines from three wine-producing regions, Stellenbosch, Robertson, and Swartland, in the Western Cape Province of South Africa, and wines from specific regions in France (Bergerac) and Italy (Valpolicella) were analyzed by ICP–QMS for their B-isotopic compositions. It was concluded that the ¹¹B/¹⁰B ratios can be used to characterize wines from different geographical origins. Average ¹¹B/¹⁰B ratios in red wines from South Africa (Stellenbosch), France (Bergerac), and Italy (Valpolicella) were found to differ by between 0.5 and 1.5%.     

Use of a multi-tube Nafion® membrane dryer for desolvation with thermospray sample introduction to inductively coupled plasma-atomic emission spectrometry

A multi-tube Nafion^® membrane dryer used as a part of a desolvation system in conjunction with thermospray nebulization was optimized and characterized with inductively coupled plasma-atomic emission spectrometry (ICP-AES). Either argon or nitrogen could be used as the sweep gas, and optimum conditions were found to be at low temperature and low sweep gas flow rate. Analyte sensitivity was not significantly affected by placing the membrane between the plasma and the nebulizer, although about 20% of the analyte entering the dryer is lost within the dryer. A dual role of the membrane dryer was demonstrated. As a secondary step within the desolvation system, it enabled a high desolvation efficiency of 99.94% for aerosols from 1% (v/v) nitric acid. Plasma solvent load could be reduced to 0.9 mg min⁻¹ with a tap water cooled condenser combined with the membrane dryer, compared to 21 mg min⁻¹ with the normal chilled condenser desolvation system. Meanwhile, the membrane was also found to act as a pulse dampener, eliminating the plasma pulsation in the central channel caused by thermospray nebulization and thus improving the analytical performance of the system. The average relative standard deviations (RSD) with the optimized membrane/thermospray system were 0.83% and 0.60% for the background and analyte signals, respectively, which were reduced by a factor of 1.9 and 2.7 for the background and analyte signals, respectively, compared to thermospray without the membrane desolvation, and were essentially identical to those obtained with pneumatic nebulization sample introduction. The improvements in detection limits with the membrane/thermospray system were 1.2–3.0 times with an average factor of 1.8 compared to thermospray without the membrane dryer, and 18–68 times with an average factor of 39 compared to the standard pneumatic nebulization sample introduction system without a desolvation unit. The detection limits for Mn, Mg, Cr and Cd with the present thermospray/membrane system were comparable to those reported for pneumatic nebulization ICP mass spectrometry.     

Determination of isotope ratios of metals (and metalloids) by means of inductively coupled plasma-mass spectrometry for provenancing purposes — A review

Since considerable time, isotopic analysis of different elements present in a sample, material or object (such as the ‘light’ elements H, C, N, O and S and ‘heavy’ elements, such as Sr and Pb), has been used in provenancing studies, as several factors — defined by “the environment” or origin of the sample — can lead to measurable differences in their isotopic composition. For the light elements, traditionally, (gas source) isotope ratio mass spectrometry (IR-MS) is used, while for a long period of time, thermal ionization mass spectrometry (TIMS) was considered as the only technique capable of detecting subtle variations in the isotopic composition of the ‘heavier’ elements. However, since the introduction of the first inductively coupled plasma mass spectrometers (ICP-MS), considerable attention has been devoted to the development of methodologies and strategies to perform isotopic analysis by means of ICP-MS. While the relatively modest isotope ratio precision offered by single-collector ICP-MS may already be fit-for-purpose under some circumstances, especially the introduction of multi-collector ICP-MS instruments, equipped with an array of Faraday detectors instead of a single electron multiplier, has lead to tremendous improvements in the field of isotopic analysis. As a result, MC-ICP-MS can be seen as a very strong competitor of TIMS nowadays, while it even provides information on the small isotopic variations shown by some elements, that are not or hardly accessible by means of TIMS (e.g., elements with a high ionization energy). Owing to these new instrumental developments, the application field of isotopic analysis by means of ICP-MS is continuously growing, also in the field of provenance determination. This paper is intended as a review of the developments in and the recent applications of isotopic analysis by means of ICP-MS in this specific research field.     

Simultaneous or scanning data acquisition? A theoretical comparison relevant to inductively coupled plasma sector-field mass spectrometers

The benefits of simultaneous multichannel detection over single-channel scanning detection are well established in analytical chemistry. Multichannel detection increases duty cycle, which leads to enhanced sensitivity, detection limits, and reduced analysis time. Also, multichannel detection used with either isotope-ratio or internal-standard techniques provides a mechanism to reduce the effect of multiplicative or flicker noise prevalent in plasma sources. An additional benefit of simultaneous detection is superior analysis of short-lived transient signals. Presented here is a theoretical comparison between simultaneous/continuous multichannel acquisition and single-channel scanning acquisition. To conduct this comparison, reported sensitivity, single-channel precision, and background values for commercial inductively coupled plasma sector-field mass spectrometers (ICP-SFMS) are used to generate theoretical figures of merit for both acquisition methods. Among the figures of merit that will be considered are detection limits, precision, and analysis time, particularly for multi-element or multi-isotope analysis.     

Evaluation of measurement uncertainty in the elemental analysis of sintered silicon carbide using laser ablation in liquid—inductively coupled plasma mass spectrometry with external calibration and isotope dilution

Accreditation and Quality Assurance - The goal of this study was to evaluate the uncertainty of elemental analytical methods that use laser ablation in liquid (LAL) as a pretreatment. After LAL...     

β-Cyclodextrin-cross-linked polymer as solid phase extraction material coupled with inductively coupled plasma mass spectrometry for the analysis of trace Co(II)

A sensitive method for the separation/analysis of Co(II) was described. The β-cyclodextrin cross-linked polymer (β-CDCP) was synthesized and used as solid phase extraction material (SPE) to separate/pre-concentrate trace cobalt coupled with inductively coupled plasma mass spectrometry (ICP-MS) for the analysis of Co(II). The method was based on α-pyridylazo-β-naphthol (PAN) as the complexing agent for Co(II)-PAN at neutral condition and the adsorption behavior of Co(II)-PAN on β-CDCP was studied. Further, p-octylpolyethylene-glycolphenyl ether (Triton X-100) as environment-friendly eluant was used. The linear range, detection limit (DL) and the relative standard deviation (R.S.D.) was 5.0-160.0 ng/mL, 5.84 ng/L and 2.27% (n = 3, c = 30.0 ng/mL) respectively. The enhancement factor was 10. Moreover, the β-CDCP could be used repeatedly and offered better recovery and estimation of standard samples.     

Characterization of a recycling nebulization system for inductively coupled plasma spectrometry—II. Matrix and memory effects

The matrix and memory effects in a recycling nebulization system for ICP spectrometry were investigated. The emission signals from Cu and Mn in the presence of different concentrations of aluminium, sodium and magnesium chlorides were compared during long-term (40 min) nebulization. The experimental results indicate a complex matrix effect which may depend upon analyte concentration enhancement and altered nebulization efficiency or clogging. With water presaturated carrier gas, the salt effects were minimized, and the emission signals of Cu and Mn were stable (1–2% RSD) during long-term nebulization in the presence of different matrices.     

Online analysis of europium and gadolinium species complexed or uncomplexed with humic acid by capillary electrophoresis–inductively coupled plasma mass spectrometry

Detailed information on the geochemical behavior of radioactive and toxic metal ions under environmental conditions (in geological matrices and aquifer systems) is needed in order to assess the long-term safety of waste repositories. This includes knowledge of the mechanisms of relevant geochemical reactions, as well as associated thermodynamic and kinetic data. Several previous studies have shown that humic acid can play an important role in the immobilization or mobilization of metal ions due to complexation and colloid formation. In our project we investigate the complexation behavior of (purified Aldrich) humic acid and its influence on the migration of the lanthanides europium and gadolinium (homologs of the actinides americium and curium) in the ternary system consisting of these heavy metals, humic acid and kaolinite (KGa-1b) under almost natural conditions. Capillary electrophoresis (CE, Beckman Coulter P/ACE MDQ), with its excellent separation performance, was hyphenated with a homemade interface to inductively coupled plasma mass spectrometry (ICP–MS, VG Elemental PlasmaQuad 3) giving a system that is highly sensitive to the rare-earth element species of europium and gadolinium with humic acid. The humic acid used was also halogenated with iodine, which acted as an ICP–MS marker. To couple CE to ICP–MS, a fused silica CE capillary was flexibly fitted into a MicroMist 50 μl nebulizer with a Cinnabar cyclonic spray chamber in the external homemade interface. The chamber was chilled to a temperature of 4 °C to optimize the sensitivity. 200 ppb of cesium were added to the CE separation buffer so that the capillary flow could be observed. A make-up fluid including 4 ppb Ho as an internal standard was combined with the flow from the capillary within the interface in order to get a fluid throughput high enough to maintain continuous nebulization. Very low detection limits were achieved: 125 ppt for ¹⁵³Eu and 250 ppt for ¹⁵⁸Gd. Using this optimized CE–ICP–MS coupling system it was possible to quantify metal concentrations from the detection limit up to approximately 1 ppm (the linear range). This set-up was used to separate metal/humic acid-species in a 100 mM acetic acid/10 mM acetate buffer system. Using humic acid as the complexing ligand, uncomplexed metal ion species could be separated from metal–humate complexes on a time-resolved scale.      

Depth profile analysis of various titanium based coatings on steel and tungsten carbide using laser ablation inductively coupled plasma –“time of flight” mass spectrometry

A homogenized 193 nm ArF* laser ablation system coupled to an inductively coupled plasma-”Time of Flight”-mass spectrometer (LA-ICP-TOFMS) was tested for depth profiling analysis on different single-layer Ti based coatings on steel and W carbides. Laser parameters, such as repetition rate, pulse energy and spatial resolution were tested to allow optimum depth related calibration curves. The ablation process using a laser repetition rate of 3 Hz, 120 μm crater diameter, and 100 mJ output energy, leads to linear calibration curves independent of the drill time or peak area used for calibrating the thickness of the layer. The best depth resolution obtained (without beam splitter) was 0.20 μm per laser shot. The time resolution of the ICP-TOFMS of 102 ms integration time per isotope was sufficient for the determination of the drill time of the laser through the coatings into the matrix with better than 2.6% RSD (about 7 μm coating thickness, n = 7). Variation of the volume of the ablation cell was not influencing the depth resolution, which suggests that the depth resolution is governed by the ablation process. However, the application on the Ti(N,C) based single layer shows the potential of LA-ICP-TOFMS as a complementary technique for fast depth determinations on various coatings in the low to medium μm region.     

Platinum determination by inductively coupled plasma–sector field mass spectrometry (ICP–SFMS) in different matrices relevant to human biomonitoring

The analytical challenges of Pt determination by ICP-SFMS posed by different human tissues and fluids have been critically assessed. Investigated samples were (1) urine, (2) serum of cancer patients sampled during chemotherapy with carboplatin, (3) microdialysates (20 micro L sample volume) collected from tumor and non-tumor tissue, and, finally-for the first time-(4) human lung tissue to study background concentrations of inhaled platinum. Sample preparation involved microwave digestion and open vessel treatment or simple dilution (microdialysates). Depending on the sample preparation and introduction systems used (microconcentric nebulization, ultrasonic nebulization with and without membrane desolvation) excellent procedural detection limits (3s criterion) of 0.35 pg g(-1) for urine, 420 pg g(-1) for serum, 400 pg g(-1) for lung tissue and 13 pg g(-1) for microdialysates could be obtained. Ultratrace concentrations of 1-40 pg g(-1), and 1000-3000 pg g(-1) were measured in urine and human lung tissue, respectively, as typical for samples in environmental studies. Quantification was carried out by IDMS and standard addition in the case of urine samples. Internal standardization could not correct for non-spectral interferences in external calibration. In the serum and microdialysates of patients during chemotherapy with carboplatin, elevated Pt levels ranging between 0.01 and 10 micro g g(-1) were determined by external calibration ((195)Pt isotope). For all investigated samples spectral interferences could be excluded by following different strategies. High-resolution control measurements ((194)Pt, (195)Pt) were performed in the case of elevated Pt levels, i.e. for microdialysates and serum samples. An Hf/Pt ratio of 0.4 was determined in human lung samples. An HfO formation ratio of 0.2% was assessed for standard solutions at the present experimental conditions, revealing that the contribution of (179)Hf(16)O, (178)Hf(17)O, (177)Hf(18)O to the (195)Pt isotope signal used for quantification was not significant.     

Elemental fingerprint profile of beer samples constructed using 14 elements determined by inductively coupled plasma–mass spectrometry (ICP-MS): multivariation analysis and potential application to forensic sample comparison

Determination of elemental fingerprint profile of 40 commercial beer samples was performed using inductively coupled plasma–mass spectrometry combined with principal component analysis and receiver operating characteristic (ROC) analysis. Fourteen trace elements, ⁵¹V, ⁵²Cr, ⁵⁹Co, ⁶⁰Ni, ⁷⁵As, ⁸²Se, ⁹⁵Mo, ¹¹¹Cd, ¹¹⁵In, ¹²¹Sb, ¹³³Cs, ²⁰⁸Pb, ²⁰⁹Bi, and ²³⁸U, were monitored. All 40 beer samples are distinguishable by using the proposed method. ROC analysis showed that individual beer samples can be correctly identified via the magnitude of its correlation coefficient with respect to the other beers with low false positive rate. The obtained results suggested that the elemental fingerprint technique is feasible for sample differentiation and comparison.     

Determination of macro and trace elements in canned marine products by inductively coupled plasma—optical emission spectrometry (ICP-OES) and ICP—mass spectrometry (ICP-MS)

This study determined the concentration of eight macroelements (Na, K, Mg, P, S, Ca, Fe, Zn) and nineteen trace elements (Li, Be, Cr, Mn, Co, Ni, V, Cu, Ga, Se, Rb, Sr, In, Sn, Cs, Ba, Tl, Bi, U) in commonly consumed canned marine products from South Korea. The samples were wet-digested using nitric acid and hydrogen peroxide by a microwave system and analyzed for macroelements using inductively coupled plasma—optical emission spectrometry (ICP-OES) and for trace elements by inductively coupled plasma—mass spectrometry (ICP-MS). The analytical methods were validated by the correlation coefficients, limits of detection and quantification, correlation variance, spiking recovery tests, and analyzing a NIST 1566?b oyster tissue certified reference material. The concentrations of macro and trace elements varied among the canned marine products. The macroelements were present in the order of Na?>?K?>?P?>?S> Mg?>?Ca?>?Fe?>?Zn. In general, the concentrations of macro and trace elements were within the specified limits of Food and Nutrition Board, Joint Food and Agriculture Organization/World Health Organization Expert Committee on Food Additives, and Ministry of Food and Drug Safety, Korea. The results suggest that the analyzed canned marine products are safe in terms of the analyzed elements and their consumption therefore does not cause any threat to human health.