Effects of sample probe insertion on plasma conditions in direct sample insertion-inductively coupled plasma-atomic emission spectrometry

The effects of sample probe insertion on plasma excitation conditions in direct sample insertion-inductively coupled plasma-atomic emission spectrometry (DSI-ICP-AES) were investigated. Graphite sample probes in the form of a cup and a rod (with or without undercut) were used. Molybdenum rods were also used for comparison. A dark central channel is created in the plasma when a sample probe is inserted. The diameter of the central channel correlates with the diameter of the sample probe. In addition, the plasma excitation conditions were monitored using repetitive laser sampling to introduce a steady flow of Zn or Fe particles into the ICP. Changes in the relative excitation temperature and electron number density of the plasma were deduced from the ratios of the emission intensities of Fe line pair and Zn line pair, respectively. The temperature and electron number density of the plasma decreased when a sample probe was inserted. The degree of changes in the plasma conditions depends on the diameter of the sample probes, regardless of the form and material of the probe. The diameter of the sample probe instead of its mass plays a significant role in perturbing the plasma excitation conditions.     

A computer-controlled direct sample insertion device for inductively coupled plasma-mass spectrometry

A direct sample insertion (DSI) device has been developed for application to inductively coupled plasma-mass spectrometry (ICP-MS). In a DSI device for use with ICPs, the sample is placed into or onto a probe with subsequent introduction of the sample carrying probe, via the central tube of the ICP torch, into the plasma. A mechanical, stepper-motor driven, computer controlled DSI device and software support system has been designed and developed that can easily be attached to a commercial ICP-MS system (Perkin-Elmer/SClEX Elan). This system allows the direct introduction of microliter volumes of liquids and milligram quantities of powdered/solid samples into the ICP-MS with little or no sample pre-treatment.     

Elimination of some spectral interferences and matrix effects in inductively coupled plasma-mass spectrometry using direct sample insertion techniques

Two key problem areas in inductively coupled plasma-mass spectrometry (ICP-MS) are spectral interferences from analyte and matrix based molecular ions, particularly oxide species; and non-spectroscopic matrix effects where an excess of an element, particularly heavier elements, suppresses the signal of lighter elements. It is shown that direct sample insertion (DSI) techniques can be used to eliminate some of these problems. With the absence of water in a DSI system, oxide species are reduced to a very low level ( .1%). Examples are shown for BaO⁺, CeO⁺ and ClO⁺. In addition, by relying on differential thermal volatilization, the suppressive matrix effect of U on Zn can be eliminated. Chemical modification with NaF is a key operational factor in achieving these benefits.     

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.     

Inductively coupled plasma-mass spectrometry: Capabilities and applications

Researchers in the field of trace elements analysis are continuously in search of new instrumental solutions for obtaining better results in terms of analysis speed, precision, accuracy, detection power, and applicability to a wider range of analytical problems. One of the more recent innovations in this field is the inductively coupled plasma (ICP) source coupled with a mass spectrometry (MS). An ICP-MS system consists of an ICP torch which ionizes the species present and a mass spectrometer for the separation under vacuum of the different species. The main advantages of this technique with respect to graphite furnace atomic absorption spectrometry (GFAAS) and to ICP atomic emission spectrometry (ICP-AES) are: (a) detection limits better than those obtained with graphite furnace, i.e., down to the ng g⁻¹ level, due to the high sensitivity of the channel electron multiplier, which transforms the mass of each ion into an electric signal; (b) the possibility of detecting refractory elements, lanthanides, and all the other elements including halogens, C, and S; (c) high analysis speed (up to 90 elements in 5 min) due to the velocity of the quadrupole mass spectrometer in selecting different masses with respect to the speed necessary to scan different wavelengths; (d) spectral simplicity, because spectra have peaks only at the mass of each isotope and all elements have at least one isotope free from spectral overlap of other analytes; (e) capability of determining individual isotopes of each element. The instrument, therefore, allows not only quantitative elemental analyses to be carried out, but also semiquantitative assays of all the elements present and isotopic ratio analyses to determine quantitatively two or more isotopes of the same element. The most interesting application fields of this technique are in environmental chemistry, geochemistry, oil chemistry, technology of semiconductors, and biochemistry.     

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.     

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.     

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。     

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.     

Determination of trace lead by hydride generation-inductively coupled plasma-mass spectrometry

A newly developed hydride generation-inductively coupled plasma-mass spectrometry (HG-ICP-MS) system was employed to determine trace amounts of lead in geological and biological samples. Laboratory-made single-stage and double-stage gas-liquid separators (GLSs) were investigated in order to replace the consumable membrane-GLS. Possible reasons were given why double-stage GLSs were superior over the single-stage ones according to the factors such as GLS volume and configuration, carrier gas inlet mode and flow rate. Interferences in liquid and vapor phase from concomitant ions and their products were investigated employing different flow mani-folds. Memory effects contributed to the blank values, but could be reduced employing a special wash protocol. Internal and external standardization were combined to improve the accuracy of the method, with bismuth as the internal standard according to its similarity with lead in the HG-ICP-MS system. Compared with ICP-MS and hydride generation-atomic fluorescence spectrometry (HG-AFS) methods, the system performance of HG-ICP-MS was characterized with improved detection limit to 0.002 ng/ml and acceptable short- and long-term stabilities. The linear dynamic range of this method was up to 50 ng/ml lead. Three Chinese national certified reference materials: poplar leaves, human hair and copper ore, were analyzed for method validation, and the results agreed well with the certified values. At last, the method was also employed to determine wide range of lead concentrations in lightweight limestone and nervous tissue samples from infants of albino rats with recoveries between 95 and 105% (n=10).     

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.     

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.     

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。     

电感耦合等离子体质谱法检测氧化镓中杂质元素

建立了电感耦合等离子体质谱法(ICP-MS)测定氧化镓中杂质元素的检测方法,采用微波消解技术溶样,以5 ng/mL Rh为内标补偿校正镓基体的抑制效应,采用碰撞室技术(CCT)消除多元素分子离子的干扰.方法的检出限为0.10～1.0 ng/mL,加标回收率在85%～110%之间,RSD为0.6%～7.1%.该方法能满足99.95%～99.995%氧化镓中杂质元素的分析要求.     

Signal enhancement effect of halogen matrix in electrothermal vaporization-inductively coupled plasma-mass spectrometry

In tungsten furnace electrothermal vaporization(ETV)-inductively coupled plasma mass spectrometry(ICP-MS), the presence of halogen matrices caused a signal enhancement for volatile elements such as Zn, Cd and Pb, whose halides melting and boiling points were relatively low. In order to clarify the mechanism of signal enhancement in ETV-ICP-MS, the effects of chemical interaction between analytes and halogen matrices on the surface of ETV furnace, the transport efficiency of vaporized analytes from the furnace into the ICP and the physical properties of the ICP itself and of the micro plasma (interface plasma) in the interface region between the sampling and the skimmer cones were investigated by atomic absorption and atomic emission spectrometry. Among the effects mentioned above, neither the chemical interaction on the surface of the ETV furnace nor the transport efficiency of vaporized analytes could be related to the analyte signal enhancements. The degree of enhancement was found to depend on the ionization potential of the coexisting halogen and was not caused by a variation in the physical properties of the ICP but rather by a variation of those of the interface plasma. These results suggest that the halogen matrices may affect the physical properties of the interface plasma, contributing to the promotion of the ionization of analytes.     

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.     

Using inductively coupled plasma-mass spectrometry for calibration transfer between environmental CRMs

Multielement analyses of environmental reference materials have been performed using existing certified reference materials (CRMs) as calibration standards for inductively coupled plasma-mass spectrometry. The analyses have been performed using a high-performance methodology that results in comparison measurement uncertainties that are significantly less than the uncertainties of the certified values of the calibration CRM. Consequently, the determined values have uncertainties that are very nearly equivalent to the uncertainties of the calibration CRM. Several uses of this calibration transfer are proposed, including, re-certification measurements of replacement CRMs, establishing traceability of one CRM to another, and demonstrating the equivalence of two CRMs. RM 8704, a river sediment, was analyzed using SRM 2704, Buffalo River Sediment, as the calibration standard. SRM 1632c, Trace Elements in Bituminous Coal, which is a replacement for SRM 1632b, was analyzed using SRM 1632b as the standard. SRM 1635, Trace Elements in Subbituminous Coal, was also analyzed using SRM 1632b as the standard.     

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.