Selenium speciation analysis using inductively coupled plasma-mass spectrometry

Selenium exists in several oxidation states and a variety of inorganic and organic compounds, and the chemistry of selenium is complex in both the environment and living systems. Selenium is an essential element at trace levels and toxic at greater levels. Interest in speciation analysis for selenium has grown rapidly in this last decade, especially in the use of chromatographic separation coupled with inductively coupled plasma-mass spectrometry (ICP-MS). Complete characterization of selenium compounds is necessary to understand selenium's significance in metabolic processes, clinical chemistry, biology, toxicology, nutrition and the environment. This review describes some of the essential background of selenium, and more importantly, some of the currently used separation methodologies, both chromatographic and electrophoretic, with emphasis on applications of selenium speciation analysis using ICP-MS detection.     

Uranium colloid analysis by single particle inductively coupled plasma-mass spectrometry

Uranium single particle analysis has been performed by inductively coupled plasma-mass spectrometry (ICP-MS) and the performances are compared with that provided by scanning electron microsopy and single particle counting. The transient signal induced by the flash of ions due to the ionisation of an uranium colloidal particle in the plasma torch can be detected and measured for selected uranium ion masses (²³⁸U⁺, ²³⁵U⁺ or ²⁵⁴[²³⁸U¹⁶O]⁺) by the mass spectrometer. The signals recorded via time scanning are analysed as a function of particle size or fraction of the studied element or isotope in the colloid phase. The frequency of the flashes is directly proportional to the concentration of particles in the colloidal suspension. The feasibility tests were performed on uranium dioxide particles. The study also describes the experimental conditions and the choice of mass to detect uranium colloids in a single particle analysis mode.     

Thorium colloid analysis by single particle inductively coupled plasma-mass spectrometry

Thorium colloid analysis in water has been carried out by a single particle mode using inductively coupled plasma mass spectrometry (ICP-MS). The flash of ions due to the ionisation of a thorium colloidal particle in the plasma torch can be detected and measured in a time scan for ²³²Th⁺ or ²⁴⁸[ThO]⁺ according to the sensitivity required by the mass spectrometer. The peaks of the recorded intensity of the MS signal can be analysed as a function of the particle size or fraction of the studied element in the colloid phase. The frequency of the flashes is directly proportional to the concentration of particles in the colloidal suspension. After discussing Th colloid detection, on the basis of the intensity of the ion flashes generated in the plasma torch, tests were performed on thorium dioxide colloidal particles. This feasibility study also describes the experimental conditions and the limitation of the plasma design to detect thorium colloids in a single particle analysis mode down to about 10 fg.     

Multielemental determination in breast cancerous and non-cancerous biopsies by inductively coupled plasma-mass spectrometry following small volume microwave-assisted digestion

A microwave-assisted digestion method amenable to analysis of small size biological samples (<30 mg dry mass) has been optimized for determining twelve elements (Ag, As, Cd, Co, Cu, Cr, Mn, Mo, Ni, Pb, Se and Zn) by inductively coupled plasma-mass spectrometry (ICP-MS) in breast cancerous and non-cancerous biopsies. The use of three small volume PTFE closed vials (6-mL capacity) placed inside a conventional microwave vessel allows to drastically diminishing the volume of acid needed for digestion. A Plackett-Burman experimental design was used to evaluate the robustness of the digestion procedure. Effects of nitric acid volume, need for predigestion step, microwave power and digestion time were assessed. No significant effects were found, the digestion method being robust enough to be recommended for a routine practice. The method was successfully validated against CRM BCR 185 (bovine liver), CRM NRCC TORT-2 (lobster hepatopancreas), CRM NRCC DORM-2 (dogfish muscle) and CRM NRCC DOLT-2 (dogfish liver). Procedural detection limits ranged from 0.54 to 40 ng g(-1). Within-batch precision values were less than 3%, whereas between-batch precision values were in the range 2-11%. Forty-seven biopsies from thirty-nine women were analyzed: 20 samples corresponding to mammoplasties from healthy women and 27 samples from patients suffering from cancer pathology, 19 of which corresponded to tumour and 8 to adjacent normal tissue. After applying parametric and non-parametric statistical tests, a significant accumulation of Cu, Mn, Zn and Se in cancerous tissues was demonstrated.     

High-throughput determination of seven trace elements in food samples by inductively coupled plasma-mass spectrometry

A method was developed for high-throughput determinations of 7 elements in food samples, namely antimony (Sb), arsenic (As), cadmium (Cd), chromium (Cr), lead (Pb), mercury (Hg), and tin (Sn). The samples were digested by closed-vessel microwave-assisted digestion using concentrated nitric acid (HNO3) as the medium, followed by microwave- assisted evaporation to concentrate the sample solutions before dilution to the desired volume. The microwave-assisted evaporation procedure effectively reduced the final acid concentration to around 8% before analysis by inductively coupled plasma-mass spectrometry (ICP-MS). This reduction allows determination by ICP-MS to proceed without further sample dilution, which would affect the detection limit. The method was validated, and method recoveries for As, Cd, Cr, Pb, and Hg were within the certified ranges of the chosen certified reference materials. Recoveries of the 7 elements from spiked samples ranged from 93.1 to 103.6%. The standard uncertainties of precision for the 7 elements were between 3.1 and 4.3%. Interlaboratory comparison studies for As, Cd, and Pb gave z-scores ranging from -0.2 to 0.3.     

Comparative analysis of ancient ceramics by neutron activation analysis,inductively coupled plasma-optical-emission spectrometry,inductively coupled plasma-mass spectrometry,and X-ray fluorescence

The accurate measurement of the maximum possible number of elements in ancient ceramic samples is the main requirement in provenance studies. For this reason neutron activation analysis (NAA) and X-ray fluorescence (XRF) have been successfully used for most of the studies. In this work the analytical performance of inductively coupled plasma-optical-emission spectrometry (ICP-OES) and inductively coupled plasma-mass spectrometry (ICP-MS) has been compared with that of XRF and NAA for the chemical characterization of archaeological pottery. Correlation coefficients between ICP techniques and XRF or NAA data were generally better than 0.90. The reproducibility of data calculated on a sample prepared and analysed independently ten times was approximately 5% for most of the elements. Results from the ICP techniques were finally evaluated for their capacity to identify the same compositional pottery groups as results from XRF and NAA analysis, by use of multivariate statistics.     

Multielemental analyses of tree rings by inductively coupled plasma mass spectrometry

Inductively coupled plasma mass spectrometry (ICP-MS) was evaluated for major, minor, trace, and ultra-trace elemental analyses of individual tree rings. The samples were obtained from an old-growth Douglas fir (Pseudotsuga menziesii) growing 15 km northeast of Mount St. Helens volcano, Washington, USA and from trees at various other North American sites. Samples were brought into solution by microwave digestion in sealed Teflon vessels. Eightly percent of elements from Li to U had detection limits in the solid (wood) below 8.0 ng g^–1 (parts per billion, ppb). When selected element concentrations in the Mount St. Helens samples are plotted against time, two anomalous peaks occur at A. D. 1478 and 1490 that closely correlate with past eruptions of the volcano. These preliminary results show that ICP-MS is a rapid and sensitive analytical method for multielemental analyses of individual tree rings.     

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

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

Gold colloid analysis by inductively coupled plasma-mass spectrometry in a single particle mode

Analysis in a single particle mode of gold colloids in water has been performed by inductively coupled plasma-mass spectrometry (ICP-MS). The signal induced by the flash of ions due to the ionization of a colloid in the plasma torch can be measured for the ions ¹⁹⁷Au⁺ by the mass spectrometer without interferences. The intensity of the MS signal is recorded in time scan. The recorded peak distributions were analysed as a function of the colloid size for five monodisperse colloids (80-250 nm). This study describes the experimental conditions to analyse gold colloids in a single particle mode. The size detection limit is around 25 nm corresponding to 0.15 fg colloids and one particle per ml may be detected during a 1 min time scan within standard procedure.     

电感耦合等离子体质谱法测定地球化学样品中镉

采用HF-HClO4-HNO3-H2SO4分解样品,王水提取,选用4个国家一级标准物质制备成标准系列校准,ICP-MS法直接测定地球化学样品中的Cd。选择103Rh为内标,确定了仪器的最佳分析条件,研究了Zr,Sn对Cd的干扰,选择114Cd作为测定同位素,采用数学公式校正了Sn对Cd的同质异位素干扰,方法检测限(3s)为6.3×10-3μg/g,RSD(n=12)为3.9%～6.6%。经国家一级标准物质验证,测定值与标准值吻合较好。该方法适用于地球化学样品中的微量Cd的测定。     

On-line coupling of gel electrophoresis and inductively coupled plasma-mass spectrometry

The on-line coupling of gel electrophoresis with inductively coupled plasma-mass spectrometry (GE-ICP-MS) is a powerful tool for simultaneous separation, detection and quantification of bio-molecules, and has been applied to the determination of phosphorus in DNA, phosphoproteins, and phosphopeptides, gold in nano-particles, iron in metalloproteins, and iodine in aerosols, and cisplatin-oligonucleotide interactions. However, since the first report in 2005, relatively few papers have been published, perhaps reflecting the lack of familiarity with the benefits of this promising methodology. So, here for the first time, we critically review the applications of GE-ICP-MS, and explore the advantages and the limitations of the technique for various applications. Such scrutiny may be useful in not only the development of the technique but also highlighting its potential in proteomics, genomics and metallomics.     

Effects of sampler-skimmer separation in inductively coupled plasma-mass spectrometry

The effects of varying the sampler-skimmer spacing in an inductively coupled plasma-mass spectrometer are illustrated. The signals for a number of species were monitored including background ions (ArN⁺, ArO⁺, ArOH⁺, Ar₂⁺, Ar₂H⁺), background continuum, analyte ions (Cu⁺, Ce⁺, La⁺), analyte oxide ions (CeO⁺, LaO⁺), and matrix induced ions (ArNa⁺). As the sampler-skimmer spacing is increased over that normally used, the signal for some species decreases in intensity while the signal for others increases in intensity. There is a wide range of differential behavior and in some cases the signal changes are quite dramatic.

In addition to presenting results for an Ar plasma, measurements are also presented for a N₂-Ar mixed gas plasma. For some species, the signal changes observed when the sampler-skimmer spacing is increased are quite different with the N₂-Ar mixed gas plasma than with the Ar plasma and are, in some cases, opposite to signal changes observed with the Ar plasma. It appears that a larger sampler-skimmer spacing is more appropriate for a N₂ mixed gas plasma than the spacing normally used for a pure Ar plasma. Finally the effect of sampler-skimmer spacing on matrix effects is presented and it appears that matrix effects are not induced in the zone between the sampler and the skimmer.     

Determination of metals in composite diet samples by inductively coupled plasma-mass spectrometry

A study was conducted to evaluate the applicability of inductively coupled plasma-mass spectrometry (ICP-MS) techniques for determination of metals in composite diets. Aluminum, cadmium, chromium, copper, lead, manganese, nickel, vanadium, and zinc were determined by this method. Atmospheric pressure microwave digestion was used to solubilize analytes in homogenized composite diet samples, and this procedure was followed by ICP-MS analysis. Recovery of certified elements from standard reference materials ranged from 92 to 119% with relative standard deviations (RSDs) of 0.4-1.9%. Recovery of elements from fortified composite diet samples ranged from 75 to 129% with RSDs of 0-11.3%. Limits of detection ranged from 1 to 1700 ng/g; high values were due to significant amounts of certain elements naturally present in composite diets. Results of this study demonstrate that low-resolution quadrupole-based ICP-MS provides precise and accurate measurements of the elements tested in composite diet samples.     

Automatic selection of internal standards in inductively coupled plasma-mass spectrometry

The automatic selection of internal standards in inductively coupled plasma-mass spectrometry was performed using a cluster analysis algorithm. The samples contained 25 analytes, spanning the atomic mass and ionization potential ranges, and a single interfering element. The interferents examined were Na, Mg, K, Zn, Ba, and Pb. The cluster analysis algorithm used kinetic energy, ionization potential, oxide bond strength, hydride bond strength, and electronegativity, to group the analytes. These variables were weighted differently in the various matrices. The performance of the clustering method and selection of internal standards was good for most analytes in the various matrices.     

Determination of trace elements in organic material by inductively coupled plasma-mass spectrometry

Summary For purposes of trace element analysis of organic materials a combined analytical procedure is tested. It consists of a pressure decomposition by nitric acid at 220° C in quartz vessels. The measurements are performed in the diluted digests by inductively coupled plasma/mass spectrometry. Analytical figures of merit are given.Dedicated to Prof. Dr. Karl Winsauer on the occasion of his 60th birthday.     

高效色谱-电感耦合等离子体质谱法分析海藻类海产品中砷的形态

采用阴(Hamilton PRP-X100柱)阳(Dionex Ionpac CS-10柱)离子交换色谱-电感耦合等离子体质谱联用技术,分别以pH 10.3的20 mmol/L NH4HCO3和pH 2.0的5 mmol/L吡啶溶液为流动相,建立了As(Ⅲ)、As(Ⅴ)、一甲基砷酸(MMA)、二甲基砷酸(DMA)、砷甜菜碱AsB、砷糖PO4、砷糖OH、砷糖SO3、砷糖SO4砷形态的分析方法。采用微波消解法和超声溶剂提取法对不同海域10种紫菜和海带产品进行前处理,对As含量及其化学形态进行分析。实验表明,样品总砷的质量分数为1.7～38.7 mg/kg,样品萃取物中,As糖PO4和As糖OH为As的主要形态,其含量分别占可提取As的6.5%～67.7%和12.9%～86.2%,海带样品萃取物中还有As糖SO3和DMA被检测,其含量分别占可提取As的13.0%～52.1%和5.9%～17.4%。在紫菜和海带海藻类产品中,含As的化合物主要是毒性较低的有机砷。     

Controlled dissolution of silicon dioxide layers for depth resolved multielement analysis by inductively coupled plasma-mass spectrometry

Dissolution procedures were developed to control the number of surface layers removed, in an attempt to achieve depth resolved analysis by inductively coupled plasma-mass spectrometry (ICP-MS). NIST 612 glass was chosen because it is a homogeneous material with many elements at interesting concentrations, ~ 50 ppm. Varying dissolution time and HF concentration resulted in the reproducible removal of SiO₂ layers as thin as 70 Å deep. Dissolved trace metals were determined after dilution by inductively coupled plasma-mass spectrometry (ICP-MS) with a magnetic sector instrument. The amount removed was determined from the concentration of a major element, Ca. With the exception of Zn, trace metal concentrations agreed reasonably well with their certified values for removal depths of 500, 300 and 150 Å. Zinc concentration was significantly high in all dissolutions indicating either a contamination problem or that Zn is removed at a faster rate than Ca. For the dissolutions that removed 70 Å of SiO₂, Cr, Mn, Co, Sr, Cd, Ce, Dy, Er, Yb and U recovery results agreed with their certified values (~ 50 ppm); Ti, As, Mo, Ba, and Th could not be determined because net intensities were below 3σ of the blank; and measured concentrations for Cu, Pb and Zn were well above the certified values.     

Multielemental analysis in small amounts of environmental reference materials with inductively coupled plasma mass spectrometry

The lowest possible sample weight for performing multielemental trace element analysis on environmental and biological samples by ICP-MS has been investigated. The certified reference materials Bovine Liver NIST SRM 1577b, Human Hair NCS DC 73347 and Oriental Tobacco Leaves CTA-OTL-1 were applied at sample weights (1, 5, 20 and 50 mg aliquots, n = 10) which were significantly lower than those recommended with most recoveries in the range of 95-110%. Samples were digested in a mixture of nitric acid, hydrogen peroxide and hydrogen fluoride by closed-vessel microwave digestion. Multielemental analysis was performed with an optimized ICP-QMS method. Aqueous standard solutions were applied for external calibration with rhodium as the internal standard element. The detection limits varied between 0.02-0.38 microg/g for Li, Na, Cr, Mn, Ni, Cu, Zn, Sr, Cd, Ba and Pb, and up to 1.92 microg/g for Mg, Al, Ca, Fe and Ni. Digested human plasma samples were spiked with multielemental solution (0.5-10 microg/L) to test the analytical method and the recoveries were 95-105% for most analytes. Our results show that in the case of homogeneous SRMs it is possible to use them in very low amounts (1-5 mg) for method development and quality control.