Skimmer Cone Research Articles

Rubidium Isotope Measurements of Low‐Rb Geological Materials by MC‐ICP‐MS

The rubidium (Rb) isotope system has the potential to trace planetary evolution, magmatic‐fluid interaction and chemical weathering. These applications are based on Rb isotope measurement results with precisions fit for purpose, but measurements of low‐Rb geological materials are challenging due to large sample consumption and overload of ion‐exchange resin. Here we developed a measurement procedure for Rb isotope data (δ87RbSRM984) of low‐Rb geological materials using MC‐ICP‐MS. Using an Aridus III desolvator and Ni standard sampler + Ni X skimmer cone combination, the Rb loading amount was reduced significantly to 20 ng. A comparison between two methods for instrumental mass‐bias correction, the sample‐standard bracketing and combined sample‐standard bracketing and internal (Zr) normalisation (C‐SSBIN), shows that C‐SSBIN could produce Rb isotope data with better intermediate measurement precisions but strictly restricted to optimal Zr/Rb ratio. The robustness of this method was demonstrated by monitoring δ87RbSRM984 data of two in‐house Rb isotope standards, replicates, some reference materials with δ87RbSRM984 values previously reported, and element‐doped and matrix‐spiked synthetic solutions. Based on repeated measurements of Rb isotope standards and reference materials, the long‐term (over one year) intermediate precision was better than 0.05‰ (2s, standard deviations). We additionally recommend thirteen reliable reference materials for future Rb isotope ratio measurements.

Determination of Lu and Hf Mass Fractions and 176Hf/177Hf Ratios in Mafic‐Ultramafic Rock Reference Materials by Multi‐Collector Inductively Coupled Plasma‐Mass Spectrometry

Reported data for Lu, Hf mass fractions and 176Hf/177Hf isotopic ratios of mafic‐ultramafic rock reference materials (RMs) are rare at present, hampering the comparison of data quality between difference laboratories. Herein, we measured the Lu and Hf mass fractions and the 176Hf/177Hf isotopic ratios of ten mafic‐ultramafic rock RMs, including OKUM (komatiite), WPR‐1 (serpentinised peridotite), NIM‐N (norite), NIM‐P (pyroxenite), UB‐N (serpentinised peridotite), JP‐1 (peridotite), NIM‐D (dunite), MUH‐1 (serpentinised harzburgite), HARZ01 (harzburgite), DTS‐2b (dunite), which contain extremely low amounts of Lu and Hf (Lu, 2–150 ng g−1; Hf, 5–500 ng g−1). All measurements were conducted on a Neptune Plus multi‐collector inductively coupled plasma‐mass spectrometer employing an Aridus II desolvator inlet system and Jet sample/X skimmer cone configuration. The following RMs, OKUM, WPR‐1, UB‐N, JP‐1, NIM‐D, HARZ01 and DTS‐2b, have 176Hf/177Hf precision of less than 60 ppm (2s) at test portions of 0.06 to 0.3 g, and are good ultramafic RMs for Lu‐Hf systems. In contrast, significant Hf mass fraction and isotopic variability were observed in NIM‐N, NIM‐P and MUH‐1 at test portion masses of 0.1 to 0.3 g. Collectively, our study provides a new database that can be used by the geochemical community for evaluating the Lu‐Hf system of mafic‐ultramafic rocks.

Rapid Determination of Sulfur in Sixty Geological Reference Materials by High Resolution Inductively Coupled Plasma‐Mass Spectrometry

In this study, a rapid method for the quantification of sulfur mass fractions in geological materials using high‐resolution sector field‐inductively coupled plasma‐mass spectrometry (SF‐ICP‐MS) was developed. The effects of HNO3, Lefort, aqua regia, and HCl on the recoveries of sulfur in three different geological samples were evaluated. It was found that 0.5‐1 h digestion at 90 °C was enough to completely recover sulfur from BCR‐2 (basalt rock), GSS‐25 (loess), and GSD‐7 (stream sediment) using 2 ml aqua regia in both closed and open vessels. Compared with that of traditional digestion methods (e.g., HF‐HBr‐HNO3 acid digestion method), the efficiency of this proposed aqua regia digestion is improved by a factor of approximately 20. No loss of sulfur was observed because sulfur released from geological materials is directly oxidised to sulfate, which inhibits the volatilisation of sulfur. In addition, the effect of the heating‐condensing system combined with two different skimmer cones on the analytical sensitivity of sulfur was investigated. Compared with that of the normal sampling mode, the signal intensity of sulfur is enhanced by a factor of approximately 22 and 10 at a temperature of 140 °C using the S + X cone combination and S + H cone combination, respectively. This improvement is of importance for the determination of sulfur in samples with low sulfur content. The developed method was successfully applied to the determination of sulfur in geological reference materials. Most of the measured sulfur values of sixty geological materials, using both closed and open vessel digestion, are in good agreement with reference values. Compared with closed vessel digestion, the more flexible open vessel acid digestion is simple, fast, and shows great potential for the rapid quantification of sulfur in a large batch of geological and environmental samples.

Lithium Isotopic Ratios by Single‐Collector ICP‐SFMS: A Critical Evaluation Using Reference Materials

We deployed a procedure to measure Li isotope ratios on a single‐collector sector field inductively coupled plasma mass spectrometer (ICP‐SFMS) operated with a desolvation system and a high‐sensitivity skimmer cone. Under optimised instrumental acquisition conditions, chromatographically separated analyte solutions containing 1 ng g−1 of Li provided adequate sensitivity using analogue mode detection for both isotopes, without adverse memory effect. Unprecedented for this isotopic system, we estimated the expanded uncertainty (U; k = 2) associated with the obtained δ7Li values to validate the procedure. Were considered as potential contributors to the combined uncertainty estimation (uc) the measurement intermediate precision, sample digestion and homogeneity, chromatographic separation, procedural blanks and homogeneity of the bracketing measurement standard (IRMM‐016). The estimated U was on average (from results obtained with reference materials) 1.2‰ (k = 2). This is about twice the intermediate measurement precision (2s) of our data, highlighting the importance of evaluating other measurement uncertainty sources. The δ7Li values obtained for nineteen silicate rocks and one natural water agree with published values. We also provide the first δ7Li = (1.7 ± 1.2; 0.7)‰ (mean value ± U (k = 2); intermediate precision (2s); n = 13) for basalt RM BRP‐1.

Oxide Formation and Instrumental Mass Bias in MC‐ICP‐MS: An Isotopic Case Study of Neodymium

High rates of oxide formation affect the magnitude and behaviour of instrumental mass bias for Nd isotopic measurements performed with multi‐collector inductively coupled plasma‐mass spectrometry (MC‐ICP‐MS) instruments, causing the traditional correction methods (e.g., internal and external normalisation) to fail. Here, we investigate the instrumental conditions that govern oxide formation and provide an extensive data set describing how different oxide formation rates affect the measurement error of Nd isotopic ratios. Results are reported for several instrumental set‐ups including wet and dry plasma, different introduction methods, the addition of N2, and various sampler and skimmer cone geometries. The differences in the behaviour of Nd isotopic ratios observed for dry and wet plasma require several reaction mechanisms to explain why oxide formation is associated with a non‐linear mass bias for some rare earth elements. We developed a simple mathematical model to describe the behaviour of Nd isotopic ratios for a range of oxide formation rates and different instrumental settings and present a qualitative model that predicts the isotopic offsets of Nd ratios based on the cumulative contributions of the major sources of mass bias. A series of analytical recommendations for the determination of accurate and precise Nd ratios by MC‐ICP‐MS is presented.

A high-performance method for direct determination of ultra-trace REEs in geological samples by ICP-MS using a designed heating-condensing system

Our results firstly indicate that the geometry of the skimmer cone has an important effect on signal enhancement when using a heating-condensing system in ICP-MS.

Improved in situ zircon U–Pb dating at high spatial resolution (5–16 μm) by laser ablation–single collector–sector field–ICP–MS using Jet sample and X skimmer cones

High spatial resolution (5–16 μm) in situ zircon U–Pb dating using laser ablation–single collector–inductively coupled plasma–mass spectrometry (LA–SC–ICP–MS) is inherently challenging owing to the low signal intensities involved. In this study, we investigated the sensitivity of U and Pb using Jet sample and X skimmer cones in Ar plasma and Ar–N2 plasma compared with that standard sample and H skimmer cones. Our results indicate the sensitivity enhancement of Jet and X cones was required at the condition of Ar–N2 plasma. While maintaining a Th+/U+ ratio of 0.9–1.1 and a ThO+/Th+ ratio of <1.0%, the sensitivity of U and Pb using Jet and X cones in Ar–N2 plasma was a factor of two and five greater than using S and H cones in Ar–N2 and Ar plasmas, respectively. We also observed that increasing the flow of N2 did not change the maximum sensitivities of Pb and U using S and H cones, but led to a several-fold (4 for 206Pb and 7 for 238U) improvement using Jet and X cones. The increased sensitivity led to improved precision and accuracy of U–Pb dating at high spatial resolution, and we recommend using Jet and X cones for spatial resolutions of ∼5 μm. Using this improved LA–ICP–MS technique and spots of 16, 10, and 5 μm diameter, we obtained concordant U–Pb ages for the Phalaborwa, GJ-1, SA01, Temora, Plešovice, Qinghu, and SK10-2 zircons (2058–32 Ma). The accuracy and precision of weighted mean 206Pb/238U ages are better than 1.0% for 16 μm, 1.0% for 10 μm, and 1.5% for 5 μm spots.

Inductively coupled plasma with mass-spectrometry method development and validation for gadolinium in gadolinium-based contrast agents of pharmaceutical formulations

Gadolinium-based contrast agent interacts with the human body temporarily and improves the pictures of inside of the body produced by magnetic resonance imaging, computed tomography, X-rays and ultrasound and it also helps to distinguish the normal from abnormal conditions. In this study, the authors developed a simple, rapid, reliable and robust inductively coupled plasma mass-spectrometry method for estimation of gadolinium in gadolinium-based contrast agents to check the drug quality and ensure the patient safety. The samples were digested at 160°C using the microwave digestion system and the gadolinium was extracted in 0.4% (w/w) nitric acid. Interference of deposited gadolinium on sample cone and skimmer cone were investigated and evaluated. The developed method was validated as per ICH Q2 (R1) guideline and USP&lt;730&gt;. The precision was evaluated with six independent assays of gadolinium in each gadolinium-based contrast agent. The test method was found linear (r2 &gt; 0.999) with five different levels covered from 25~200%, and accurate, mean recoveries were 92.5~107.5% at three different levels covered from 50~150%. The robustness was performed by changing the nitric acid concentration (0.4±0.04%, w/w) in diluent system. This method is suitable to quantitatively determine the amount of gadolinium in gadolinium-based contrast agent of drug products in presence of excipients used in formulation and also in drug substance.

The Determination of Heavy Metals Concentration in Hair by Inductively Coupled Plasma Mass Spectrometry (ICP-MS)

Heavy metals are non-biodegradable pollutants in environment that can enter our bodies through different routes and accumulated in the body. Hair analysis is increasing in studies due to the advantage of results of any homeostatic mechanisms unlike blood sample. The aim of this was to develop an analytical method to determine the concentration of nickel (Ni), arsenic (As), cadmium (Cd) and lead (Pb) in hair sample by Inductively Coupled Plasma Mass Spectrometry (ICP-MS). The analysis was performed using ICP-MS ELAN 9000 (Perkin Elmer) that equipped with a Meinhard Concentric Quartz Nebulizer, Cyclonic Spray Chamber, Nickel Sampler and Skimmer Cones. The validation of each element was done using human hair Certified Reference Material (CRM), USA. Spike recovery of these elements was done by using CRM and the values were within 85% to 115% for validation. The linear calibration curves were established using concentration of 5, 10, 20, 50, 70 and 100 ppb of each element with good linearity (r2>0.999). The lowest limits of detection for Ni, As, Cd and Pb were 61.18 μg/g, 2.34 μg/g, 6.15 μg/g and 112.95 μg/g. The results prove that ICP-MS can provide better sensitivity and detection limit can be achieved down to 2.34 μg/g. This approach offers the advantages of simplicity and ease of use as no pre-analytical steps such as digestion or excretion. In conclusion, ICP-MS can offer the capability to performed sub part per billion levels of multi-elements measurement. Hence this study demonstrated that ICP-MS can be effectively used for determination of heavy metal in human hair.

Effects of cone combinations on accurate and precise Mg-isotopic determination using multi-collector inductively coupled plasma mass spectrometry.

High-precision determination of magnesium (Mg) isotopes can now be routinely achieved by multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). The analytical sensitivity and instrumental mass discrimination behavior of this method are, however, sensitive to the types of sample and skimmer cones used in these measurements, so it is important that these parameters should be investigated. Using the sample-standard-bracketing method in the wet-plasma mode, four available combinations of sample and skimmer cones [Jet sample cone + H skimmer cone (Jet + H), standard sample cone + H skimmer cone (Standard + H), standard sample cone + X skimmer cone (Standard + X), and Jet sample cone + X skimmer cone (Jet + X)] were systematically investigated for peak shape, sensitivity, mass discrimination, accuracy, and precision in Mg-isotopic ratio determination using a Neptune plus MC-ICP mass spectrometer. The results showed that different cone combinations do not affect peak shapes but would significantly change the sensitivities for Mg-isotopic determinations. Compared with using the Standard + H, the sensitivities of Mg-isotopic determinations were enhanced by approximately a factor of 1.3, 1.4, and 1.9 by using the Standard + X, the Jet + H, and the Jet + X combinations, with the most stable mass discrimination behaviors obtained by the Jet + H. The instrumental mass fractionation slope for any combination of a modified cone geometry (i.e. Standard + X, Jet + X, and Jet + H) is 0.500, while it is 0.510 for the Standard + H. In addition, the mass discrimination behavior is related to Mg concentrations once the combination is set, indicating the necessity of concentration match during Mg-isotopic determination. The precision and accuracy of the Jet + H combination are better than those of the other combinations, and this is further supported by the validation of the Mg-isotope data for four international reference materials: Cambridge-1, NASS-6, AGV-2, and BHVO-2. As the Jet + H combination also provides a high signal, this combination gives the most robust strategy for the highly precise and accurate determination of Mg isotopes.

Supersonic jet interactions with a micro-engineered skimmer

A micro-engineered, skimmer-based vacuum interface has been demonstrated and used to investigate gas dynamics on a sub-millimeter length scale. The interface is fabricated as a stacked assembly of silicon dies, based on an anisotropically etched inlet orifice and a pyramidal skimmer cone formed in electroplated nickel. Expansion of gas into vacuum, interaction of a supersonic jet with the skimmer and transmission of a collimated beam into a second vacuum stage have all been imaged with a schlieren microscope. Using a glass-walled vacuum chamber, flow patterns upstream and fully downstream of the skimmer have been imaged together for the first time. At low first-stage pressures, the 150–200 µm tall skimmers cannot fully penetrate the shock arising from interaction of the jet with the back wall. However, as the pressure is increased, a multiple shock cell structure evolves, the jet narrows and transmission rises sharply. Eventually, a collimated beam is transmitted to the second stage. When the skimmer aperture is smaller than the source aperture, a series of distinct peaks is evident in a plot of transmission against first-stage pressure. Imaging shows that at each successive peak, the number of shock cells increases by one and the skimmer inlet is coincident with a node.

Effects of different cone combinations on accurate and precise determination of Li isotopic composition by MC-ICP-MS

The multiple collector inductively coupled plasma mass spectrometer (MC-ICP-MS) is booming to be a high-precision, fast, and accurate instrument in measuring lithium (Li) isotopes. Modified highly sensitive Jet sample and X skimmer cones have largely upgraded analytical sensitivity and reduced sample consumption with distinct instrumental mass bias behaviors. Herein, four available combinations of the sample and skimmer cones [Jet sample cone + X skimmer cone (Jet + X), Standard sample cone + X skimmer cone (Standard + X), Standard sample cone + H skimmer cone (Standard + H), and Jet sample cone + H skimmer cone (Jet + H)] were tested for their effects on peak shape, sensitivity, mass bias behavior, and accuracy and precision of Li isotopic measurements in solution mode. The results showed that all four combinations were able to attain an ideal peak shape by adjusting the associated parameters, with a positively linear relation between 7Li (and 6Li) signals and Li concentrations. For a given Li concentration, the sensitivities were enhanced 3–7 times using the Standard + X, the Jet + H, and the Jet +X combinations compared to that of using the Standard + H. The enhanced sensitivity is attributable to more plasma ions introduced into the mass spectrometer through the Jet and X cones. Mass bias is distinct for different cone combinations, with a slight difference with various Li concentrations, indicating the neccesity of concentration match during measurement. Among the four cone combinations, the best reproducibility can be obtained by using the Standard + X cones to determine precise and accurate Li isotopes for samples. Furthermore, a pretreatment by 5% HNO3 and 0.1% HF, and then 2% HNO3 prior to analyses can minimize the memory effect of Li.

Multielement analysis of Zanthoxylum bungeanum Maxim. essential oil using ICP-MS/MS.

The concentrations of trace elements (Cr, Ni, As, Cd, Hg, and Pb) in Zanthoxylum bungeanum Maxim. essential oil (ZBMEO) were determined by inductively coupled plasma tandem mass spectrometry. The ZBMEO sample was directly analyzed after simple dilution with n-hexane. Aiming for a relatively high vapor pressure of n-hexane and its resultant loading on plasma, we used a narrow injector torch and optimized plasma radio frequency power and carrier gas flow to ensure stable operation of the plasma. An optional gas flow of 20% O2 in Ar was added to the carrier gas to prevent the incomplete combustion of highly concentrated organic carbon in plasma and the deposition of carbon on the sampling and skimmer cone orifices. In tandem mass spectrometry mode, O2 was added to the collision/reaction cell to eliminate the interferences. The limits of detection for Cr, Ni, As, Cd, Hg, and Pb were 2.26, 1.64, 2.02, 1.35, 1.76, and 0.97 ng L-1, respectively. After determination of 23 ZBMEO samples from different regions in China, we found that the average concentration ranges of trace elements in the 23 ZBMEO samples were 0.72-6.02 ng g-1, 0.09-2.87 ng g-1, 0.21-5.84 ng g-1, 0.16-2.15 ng g-1, 0.13-0.92 ng g-1, and 0.17-0.73 ng g-1 for Cr, Ni, As, Cd, Hg, and Pb, respectively. The trace elements in ZBMEO differed significantly when different extraction technologies were used. The study revealed that the contents of the toxic elements As, Cd, Hg, and Pb were extremely low, and hence they are unlikely to pose a health risk following ZBMEO ingestion. Graphical abstract The working mechanism of sample analysis by ICP-MS/MS.

Effects of cone combinations on the signal enhancement by nitrogen in LA-ICP-MS

The geometry of the skimmer cone is an important factor for signal enhancement and the reduction of oxides by the addition of nitrogen in LA-ICP-MS.

Analysis and Speciation of Lanthanoides by ICP-MS

AbstractInductively coupled plasma mass spectrometry (ICP-MS) is based on formation of positively charged atomic ions in a high-frequency inductively coupled Argon plasma at atmospheric pressure. The ions are extracted and transferred from the plasma source into a mass analyzer operated at high vacuum via an interface equipped with a sampling and a skimmer cone. The ions are separated in the mass analyzer according to their charge to mass ratio. The ions are converted at a conversion dynode and are detected by use of a secondary electron multiplier or a Faraday cup.From an analytical point of view, ICP-MS is a well-established method for multi-elemental analysis in particular for elements at trace- and ultra-trace levels. Furthermore, methods based on ICP-MS offer simple quantification concepts, for which usually (liquid) standards are applied, low matrix effects compared to other conventional analytical techniques, and relative limits of detection (LODs) in the low pg g−1range and absolute LODs down to the attomol range. For these applications, ICP-MS excels by a high sensitivity which is independent of the molecular structure and a wide linear dynamic range. It has found acceptance in various application areas and during the last decade ICP-MS is also more and more applied for detection of rare earth elements particularly in the life sciences.Due to the fact that all molecules introduced into the high temperature of the plasma in the ion source were completely dissociated and broken down into atoms, which are subsequently ionized, all elemental species information is completely lost. However, if the different species are separated before they enter the plasma by using adequate fractionation or separation techniques, then ICP-MS can be used as a very sensitive element-specific detector. We will discuss this feature of ICP-MS in this chapter in more detail at hand of the speciation of gadolinium-containing contrast agents.

The different cones combination enhanced sensitivity on MC-ICP-MS: The results from boron isotope analysis

The sensitivity of multi-collector inductively coupled plasma mass spectrometers (MC-ICP-MS) can be significantly improved using different sample and skimmer cones with different orifice diameters and angles. In this study, an MC-ICP-MS with three typical combinations of sample and skimmer cones [(H skimmer cone+standard sample cone (Standard+H), X skimmer cone+standard sample cone (Standard+X) and X skimmer cone+Jet sample cone (Jet+X)] was used to measure the boron isotopes, and the effect of the different combinations of sample and skimmer cones on the sensitivity of the MC-ICP-MS and the underlying physical principles were investigated. The results suggest that more ions can be introduced into sample cones with larger orifices, which results in increased sensitivity. Compared with standard skimmer cones (which have cylindrical entrances and trumpet-shaped exits), X skimmer cones (which have trumpet-shaped entrances and exits) can provide more space for ion beams to entrance the skimmer⿿s orifice after they are subjected to the space-charge effect.

In situ sulfur isotopes (δ34S and δ33S) analyses in sulfides and elemental sulfur using high sensitivity cones combined with the addition of nitrogen by laser ablation MC-ICP-MS

The sulfur isotope is an important geochemical tracer in diverse fields of geosciences. In this study, the effects of three different cone combinations with the addition of N2 on the performance of in situ S isotope analyses were investigated in detail. The signal intensities of S isotopes were improved by a factor of 2.3 and 3.6 using the X skimmer cone combined with the standard sample cone or the Jet sample cone, respectively, compared with the standard arrangement (H skimmer cone combined with the standard sample cone). This signal enhancement is important for the improvement of the precision and accuracy of in situ S isotope analysis at high spatial resolution. Different cone combinations have a significant effect on the mass bias and mass bias stability for S isotopes. Poor precisions of S isotope ratios were obtained using the Jet and X cones combination at their corresponding optimum makeup gas flow when using Ar plasma only. The addition of 4–8 ml min−1 nitrogen to the central gas flow in laser ablation MC-ICP-MS was found to significantly enlarge the mass bias stability zone at their corresponding optimum makeup gas flow in these three different cone combinations. The polyatomic interferences of OO, SH, OOH were also significantly reduced, and the interference free plateaus of sulfur isotopes became broader and flatter in the nitrogen mode (N2 = 4 ml min−1). However, the signal intensity of S was not increased by the addition of nitrogen in this study. The laser fluence and ablation mode had significant effects on sulfur isotope fractionation during the analysis of sulfides and elemental sulfur by laser ablation MC-ICP-MS. The matrix effect among different sulfides and elemental sulfur was observed, but could be significantly reduced by line scan ablation in preference to single spot ablation under the optimized fluence. It is recommended that the d90 values of the particles in pressed powder pellets for accurate and precise S isotope analysis should be less than 10 μm. Under the selected optimized analytical conditions, excellent agreements between the determined values and the reference values were achieved for the IAEA-S series standard reference materials and a set of six well-characterized, isotopic homogeneous sulfide standards (PPP-1, MoS2, MASS-1, P-GBW07267, P-GBW07268, P-GBW07270), validating the capability of the developed method for providing high-quality in situ S isotope data in sulfides and elemental sulfur.

Improvements in Cu–Zn isotope analysis with MC-ICP-MS: A revisit of chemical purification, mass spectrometry measurement and mechanism of Cu/Zn mass bias decoupling effect

A revised chemical purification procedure for Cu–Zn isotopes is proposed in this study. The handing time and amounts of chemicals, such as H2O2 and HCl are largely saved with this modification. The ionization efficiencies of Cu and Zn are investigated in detail in wet and dry plasma with two kinds of skimmer cones. The ionization efficiency of Zn is depressed by HNO3 in the matrix, while HCl affects Cu and Zn ionization efficiency similarly. Potential polyatomic interferences with 68Zn+ and 70Zn+ are 40Ar14N2+ and 40Ar14N16O+ respectively, which are highly dependent on the amount of N2 in dry plasma and on the HNO3 concentration in wet plasma. Use of the DNS sample introduction device without N2 gas provides the best conditions for Cu–Zn isotope measurement. A Cu/Zn mass bias decoupling effect has been revealed in this study, and this effect appears to be dependent on the presence of HNO3 and N2 in ionizing plasma.

Alkali element background reduction in laser ICP-MS

Abstract. Alkali backgrounds in laser ablation ICP-MS analyses can be enhanced by electron-induced ionisation of alkali contamination on the skimmer cone, reducing effective detection limits for these elements. Traditionally, this problem is addressed by isolating analyses of high-alkali materials onto a designated cone set, or by operating the ICP-MS in a "soft extraction" mode, which reduces the energy of electrons repelled into the potentially contaminated sampling cone by the extraction field. Here we present a novel approach, where we replace the traditional alkali glass tuning standards with synthetic low-alkali glass reference materials. Using this vitreous tuning solution, we find that this approach reduces the amount of alkali contamination produced, halving backgrounds for the heavy alkali elements without any change to analytical procedures. Using segregated cones is still the most effective method for reducing lithium backgrounds, but since the procedures are complimentary, both can easily be applied to the routine operations of an analytical lab.

Improved Inter‐calibration of Faraday Cup and Ion Counting for In Situ Pb Isotope Measurements Using LA‐MC‐ICP‐MS: Application to the Study of the Origin of the Fangshan Pluton, North China

A laser ablation multi‐collector inductively coupled plasma‐mass spectrometry (LA‐MC‐ICP‐MS) method was developed to obtain precise and accurate Pb isotopic ratio measurements in low‐Pb materials (&lt; 10 μg g−1) using a combination of Faraday cups and ion counters (FC–IC). The low abundance 204Pb (~ 1.4%) was collected using an IC. A NBS 981 standard solution was used to cross‐calculate the FC–IC gain and to investigate the signal response characteristics of the IC. A significant, continuous and linear decrease in the FC–IC gain was observed within 1 hr, but this drift could be corrected using the calibrator‐sample‐calibrator bracketing method. In addition, a non‐linear response of the IC used in this study was observed and corrected by a non‐linear correction algorithm, which was established by measuring a series of gravimetrically prepared NBS 981 standard solutions (NIST SRM 981). Compared with the conventional arrangement, the use of the newly designed X skimmer cone and Jet sample cone improved the signal intensities from Pb isotopes by a factor of 1.9. Compared with only Faraday cups, using a combination FC–IC array was found to enhance the measurement repeatability (RSD) of 20xPb/204Pb by approximately one order of magnitude when the 204Pb intensity was &lt; 8 mV. Eight natural glasses and the NIST SRM 612 reference material glass (as a calibration material) were measured to evaluate the new protocol for Pb isotope determination. The analytical results were in agreement with the reference values within 2s measurement uncertainties. For MPI‐DING ATHO‐G (5.67 μg g−1 total Pb), KL2‐G (2.07 μg g−1 total Pb) and ML3B‐G (1.38 μg g−1 total Pb), the typical accuracies of 20xPb/204Pb were 0.09% of preferred values with precisions of &lt; 0.33% (2RSD). The Pb isotope ratios in feldspars from granodiorite and within mafic microgranular enclaves (MMEs) from the Fangshan pluton, North China, were measured using the present method. The Pb isotopic compositions of feldspars from the whole host granodiorite show that that are radiogenic in the margin zone and gradually become less radiogenic. For the MMEs, the Pb isotopic compositions of feldspars are highly variable and overlap with those of the whole host granodiorite. For single‐grain feldspar, the strong rim‐core‐rim variations of the Pb isotopic compositions and trace elements are interpreted to have been generated via magma mixing. These results suggest that the Fangshan pluton underwent magma mixing of mantle‐derived mafic magmas with felsic magmas, and the proportion of the mafic magma influx decreased over time.