Effect of sampler and skimmer orifice size on analyte and analyte oxide signals in inductively coupled plasma-mass spectrometry

The size of the orifice in the sampling cone of the interface in an inductively coupled plasma-mass spectrometer (ICP-MS) has a major impact on signal characteristics. In particular, for oxide forming elements, the MO⁺/M⁺ ratio is very dependent on orifice size. This is illustrated for a range of elements (La, Ho and Yb) as a function of nebulizer gas flow and for sampling cone orifice sizes ranging from 0.51 to 0.94 mm. In addition the size of the sampling orifice changes the shape of the signal vs nebulizer flow rate plot and this is illustrated. A curious and important observation is that the signal dependence on nebulizer flow rate is essentially identical for all analytes at any one orifice size if the analyte and analyte oxide (when observed) responses are summed. This indicates that the sampling orifice is the primary location of oxide formation in ICP-MS. Finally the effect of the skimmer orifice diameter on analyte signals is also illustrated for orifice diameters of 0.76, 0.89 and 1.0 mm in conjunction with sampling orifice sizes ranging from 0.51 to 0.94 mm.     

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.     

The effect of plasma operating parameters on analyte signals in inductively coupled plasma-mass spectrometry

Utilizing the SCIEX ICP-MS an extensive study of the effects that plasma operating parameters have on analyte ion signals in ICP-MS has been carried out. Parameters studied included aerosol flow rate (nebulizer pressure), auxiliary flow rate, power and sampling depth (sampling position from the load coil). The two key parameters are aerosol flow rate (nebulizer pressure) and power. Elements can be grouped into characteristic behaviour patterns based on the overall dependence of their ion count signal on these two parameters. The nebulizer pressure-power behavior patterns allow a sensible selection of compromise operating conditions and significantly clarify single parameter observations which often indicate confusing trends in behavior. In addition to characterizing analyte ion signals the parameter behavior plots have also been used to study oxide species and plus two ions in ICP-MS. While aerosol flow rate and power appear to be the key ICP parameters in ICP-MS, ion signals are dependent on sampling depth and auxiliary flow rate and some data are also presented illustrating the signal dependence on these two parameters.     

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.     

Correction for non-spectroscopic matrix effects in inductively coupled plasma-mass spectrometry by common analyte internal standardization

The Common Analyte Internal Standardization (CAIS) chemometric technique is extended to correct for non-spectroscopic matrix effects in inductively coupled plasma-mass spectrometry (ICP-MS). The approach is based on using an internal reference element to correct for the matrix effect. Unlike the conventional internal reference method, the CAIS technique allows for the analyte to behave differently from the internal reference under the influence of the matrix. With the CAIS technique a single internal reference element is sufficient to correct for all the analytes. Experimental tests with 13 analytes in four different matrices using different ICP-MS instruments demonstrate that the CAIS is efficient and general for matrix effect correction. Not only is the corrected concentration more accurate, but the precision is significantly better. The capability of CAIS to correct for the effect of a mixture of two matrices was also established experimentally, and 20–30% matrix suppression was eliminated. Furthermore, the developed technique was used as a simple diagnostic quality assurance procedure to evaluate the performance of the mass spectrometer.     

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.     

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.     

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.     

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.     

Ti in dilute slurries of TiO2 nanoparticles by in-torch vaporization sector field inductively coupled plasma-mass spectrometry☆

A Re coil-filament in-torch vaporization (ITV) sample introduction system was interfaced to a sector field inductively coupled plasma-mass spectrometry (SFICP-MS) system. In this first report on an un-optimized ITV-SF-ICP-MS system, detection limits were established using 5 μL volumes of 100 pg mL^− 1 standard solutions, translating to 0.5 pg absolute. Such absolute amounts of a dried solution are near or below the detection limit of many ICP-based techniques. The absolute detection limits for Cd, Eu, Pb, Ti, U and Zn were in the 0.2–2 fg range (or, in the 10's of millions to millions of atoms for Pb, Cd, Zn and Ti, about one million atoms for U and about 800 thousand for Eu). These absolute detection limits along with the ability of ITV to handle minute amounts of discrete samples (thus eliminating memory effects from nanoparticles adhering to the walls of pneumatic nebulization sample introduction systems and from clogging of the mass spectrometer orifice), use of sonicated water-based slurries (that eliminated contamination from acid digestion reagents or from slurry stabilization reagents), and elimination of oxygen containing molecular ion interferences due to use of dry samples enabled concentration determinations of Ti (and consequently of TiO₂) in pg mL^− 1 concentrations of slurries of manufactured, 20 nm diameter TiO₂ nanoparticles.     

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。     

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.     

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.     

Multielemental analysis of food and agricultural matrixes by inductively coupled plasma-mass spectrometry

The suitability of quadrupole inductively coupled plasma-mass spectrometry (ICP-MS) for multielemental analysis of food following microwave closed vessel digestion of samples was evaluated in relation to analytical challenges presented by some major food and agricultural matrixes. Fifteen key analytes (Al, As, Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb, Se, Sn, V, Zn) were determined in 9 reference materials representative of 3 major groups of staple foods (cereals, seafood, and meat). For all measurements, the method of external calibration was used and Rh was selected as internal standard. Matrix-induced interferences were evaluated for each material, and suitable methods to overcome them were applied. Spectral interferences caused by C, Cl, and Ca content of digestates were quantitated and corrected by entering a simple system of mathematical correction equations into the instrument software before each analytical run. Full mastering of interferences together with adoption of a series of measures to control the reliability of analytical measurements produced accurate results for all the analytes. A standard analytical protocol is outlined for the benefit of both research and routine high-throughput laboratories that perform ICP-MS analyses of food.     

An improved interface for inductively coupled plasma-mass spectrometry (ICP-MS)

Adiabatic sampling of the plasma from an inductively coupled plasma (ICP) torch is a crucial first step for inductively coupled plasma-mass spectrometry (ICP-MS) to reach its full potential as a trace multi-element analysis system. Previous results in the literature are reviewed, and a series of experiments reported, which indicate that a discharge, previously called a “pinch” effect, can be present in which the plasma properties are strongly altered by a constricted current flowing between the plasma and the sampling orifices, i.e. a secondary discharge. Measurements and calculations indicate that this mechanism is consistent with previously reported deleterious effects—abnormal production of doubly ionized species, a wide kinetic energy distribution for the ions sampled into vacuum, formation of ions from metal eroded from the sampling orifices, and a decreased orifice life-time. The mechanism producing the effect was found to be an unwanted capacitive coupling between the voltage on the induction coil and the plasma. Results are included which show that by centre-grounding the coil, the “pinch” effect can be reduced to negligible proportions. The resulting improvements for ICP-MS operation are described.     

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.     

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.