Interference Correction Research Articles

DIA-NN: neural networks and interference correction enable deep proteome coverage in high throughput.

We present an easy-to-use integrated software suite, DIA-NN, that exploits deep neural networks and new quantification and signal correction strategies for the processing of data-independent acquisition (DIA) proteomics experiments. DIA-NN improves the identification and quantification performance in conventional DIA proteomic applications, and is particularly beneficial for high-throughput applications, as it is fast and enables deep and confident proteome coverage when employed in combination with fast chromatographic methods.

Improvement of Wall-Corrections at the National Research Council’s Trisonic Wind Tunnel

The development of flow separation on a model tested at subsonic flow conditions reaching stall is not currently accounted for by the wall-correction methodology used at the National Research Council’s (NRC’s) 5 ft trisonic wind tunnel. Consequently, although this method provides accurate wall corrections during tests in prestall conditions, it is unable to generate reliable corrections in stall. The present paper investigates the possible improvements to the singularity representation of the model, which are paramount to the “one-variable” wall-correction methodology. This revision of the model representation is based on high-fidelity free-air computational fluid dynamics solutions for the NASA Common Research Model (CRM), which are validated by experimental datasets obtained from a semispan version of the CRM tested at the NRC’s 5 ft trisonic wind tunnel. The improved potential representation is tested on solid-wall experimental wind-tunnel data to present more reliable behavior of the wall interference correction estimates when substantial wing stalling is encountered.

Direct determination of Cr and Ni in oil samples by isotope dilution and external standard calibration using inductively coupled plasma mass spectrometry

In the present work, a method for the determination of Ni and Cr in crude oil samples and derivatives (petroleum asphalt cement (CAP) and malthene) through direct analysis of samples diluted in a mixture of organic solvents (xylene/butanol), by isotope dilution inductively coupled plasma mass spectrometry (ICP-MS), was developed. An exciting advantage of the proposed method was the addition of a polar solvent (butanol) to xylene, which has allowed the dilution of the samples, making possible the use of aqueous standards for the isotope dilution, without phase separation. For comparison, external standard calibration was carried out with organic standards and dilution in the same solvent. The spectrometer was set up and the instrumental parameters were optimized for the introduction of organic samples. Oxygen was introduced into the plasma to avoid carbon build-up at the interface. For interference correction from 40Ar12C+ over 52Cr+, the dynamic reaction cell was employed with CH4 as reaction gas. Accuracy evaluation was performed by analyzing the standard reference material NIST SRM 1084a (wear-metals in lubricant oil). The agreement between the obtained results and the SRM values were within the range of 95% to 106%. The RSDs were lower than 12% for the isotope dilution, and 10% for external standard calibration. The results obtained for Ni and Cr in crude oil and derivatives have shown that both calibration methods are statistically in agreement. Although isotope dilution is not commonly used for routine analysis, it has the potential to be. The time necessary for sample preparation could be reduced with the employment of an autodiluter, and the cost of enriched isotopes is a relative issue. The ID can also be employed as a primary method to verify the accuracy of external standard calibration methods.

Determination of the triple oxygen and carbon isotopic composition of CO2 from atomic ion fragments formed in the ion source of the 253 Ultra high-resolution isotope ratio mass spectrometer.

RationaleDetermination of δ17O values directly from CO2 with traditional gas source isotope ratio mass spectrometry is not possible due to isobaric interference of 13C16O16O on 12C17O16O. The methods developed so far use either chemical conversion or isotope equilibration to determine the δ17O value of CO2. In addition, δ13C measurements require correction for the interference from 12C17O16O on 13C16O16O since it is not possible to resolve the two isotopologues.MethodsWe present a technique to determine the δ17O, δ18O and δ13C values of CO2 from the fragment ions that are formed upon electron ionization in the ion source of the Thermo Scientific 253 Ultra high‐resolution isotope ratio mass spectrometer (hereafter 253 Ultra). The new technique is compared with the CO2‐O2 exchange method and the 17O‐correction algorithm for δ17O and δ13C values, respectively.ResultsThe scale contractions for δ13C and δ18O values are slightly larger for fragment ion measurements than for molecular ion measurements. The δ17O and Δ17O values of CO2 can be measured on the 17O+ fragment with an internal error that is a factor 1–2 above the counting statistics limit. The ultimate precision depends on the signal intensity and on the total time that the 17O+ beam is monitored; a precision of 14 ppm (parts per million) (standard error of the mean) was achieved in 20 hours at the University of Göttingen. The Δ17O measurements with the O‐fragment method agree with the CO2‐O2 exchange method over a range of Δ17O values of −0.3 to +0.7‰.ConclusionsIsotope measurements on atom fragment ions of CO2 can be used as an alternative method to determine the carbon and oxygen isotopic composition of CO2 without chemical processing or corrections for mass interferences.

Addressing Complex Matrix Interference Improves Multiplex Food Allergen Detection by Targeted LC-MS/MS.

The frequent use of precautionary food allergen labeling (PAL) such as "may contain" frustrates allergic individuals who rely on such labeling to determine whether a food is safe to consume. One technique to study whether foods contain allergens is targeted liquid chromatography-tandem mass spectrometry (LC-MS/MS) employing scheduled multiple reaction monitoring (MRM). However, the applicability of a single MRM method to many commercial foods is unknown as complex and heterogeneous interferences derived from the unique composition of each food matrix can hinder quantification of trace amounts of allergen contamination. We developed a freely available, open source software package MAtrix-Dependent Interference Correction (MADIC) to identify interference and applied it with a method targeting 14 allergens. Among 84 unique food products, we found patterns of allergen contamination such as wheat in grains, milk in chocolate-containing products, and soy in breads and corn flours. We also found additional instances of contamination in products with and without PAL as well as highly variable soy content in foods containing only soybean oil and/or soy lecithin. These results demonstrate the feasibility of applying LC-MS/MS to a variety of food products with sensitive detection of multiple allergens in spite of variable matrix interference.

ICP-MS AND ICP-AES ANALYSIS OF PLANT REFERENCE MATERIALS

Two methods — ICP-MS and ICP-AES are used for certification of the new reference material — needles of Siberian pine (NSP-1). Techniques of the analysis include decomposition of plant samples in two different ways: acid digestion in a microwave system MARS-5 and lithium metaborate fusion followed by ICP-MS and ICP-AES analysis of the solutions. Simultaneous determinations of all the elements were carried out in low, medium and high resolution using SF-mass-spectrometer ELEMENT and atomic-emission spectrometer IRIS Advantage with external calibrations and internal standards (In — ICP-MS, Sc —ICP-AES). Middle and high resolutions of ICP mass spectrometer were used for interference corrections. Data obtained by ICP-MS and ICP-AES with different decomposition techniques are in good agreement. The ICP-MS and ICP-AES techniques have been validated by the analysis of three plant reference materials: LB-1 (leaf of a birch), Tr-1 (grass mixture) and EK-1 (Canadian pondweed). These techniques were used for the determination of 38 elements in the new reference material NSP-1. Relative standard deviations for most of the determined elements were below 10%. Combination of ICP-MS and ICP-AES techniques for certification of the new reference material makes it possible to expand the set of elements to be determined and to reduce the total analysis time.

A Method to Suppress Isobaric and Polyatomic Interferences for Measurements of Highly Siderophile Elements in Desilicified Geological Samples

Sample decomposition using inverse aqua regia at elevated temperatures and pressures (e.g., Carius tube or high‐pressure asher) is the most common method used to extract highly siderophile elements (HSEs: Ru, Rh, Pd, Re, Os, Ir, Pt and Au) from geological samples. Recently, it has been recognised that additional HF desilicification is necessary to better recover HSEs, potentially contained within silicate or oxide minerals in mafic samples, which cannot be dissolved solely by inverse aqua regia. However, the abundance of interfering elements tends to increase in the eluent when conventional ion‐exchange purification procedures are applied to desilicified samples. In this study, we developed an improved purification method to determine HSEs in desilicified samples. This method enables the reduction of the ratios of isobaric and polyatomic interferences, relative to the measured intensities of HSE isotope masses, to less than a few hundred parts per million. Furthermore, the total procedural blanks are either comparable to or lower than conventional methods. Thus, this method allows accurate and precise HSE measurements in mafic and ultramafic geological samples, without the need for interference corrections. Moreover, the problem of increased interfering elements, such as Zr for Pd and Cr for Ru, is circumvented for the desilicified samples.

Improved in-situ Determination of Sr Isotope Ratio in Silicate Samples Using LA-MC-ICP-MS and Its Wider Application for Fused Rock Powder

The in-situ Sr isotope determination of solid samples has the advantages of high spatial resolution and convenient and rapid sample preparation. However, due to the lack of column chemistry separation of matrix elements from Sr, the interference correction (especially the isobaric interference from 87Rb on 87Sr) becomes a big issue for high precise in-situ Sr isotope analytical results. In this study, we evaluated the influence of isobaric interference systematically and adopted an improved strategy for isobaric interference correction of Rb. Specifically, as an external standard for data calibration, an in-house silicate standard (Rb-std) was fused from pure oxide powders. The new standard (Rb-std) shows very low contents of Sr (<1 ppm), Yb (<0.09 ppm) and Er (<0.05 ppm), which directly avoid the trouble of interference of doubly charged ions and isobar, when we determinate the mass fractionation factors of Rb (βRb). Our improved method can provide more accurate data than previous researches, in which the mass fractionation were calculated from an external reference material StHs6/80-G with high Rb (30.07 ppm), Sr (482 ppm), Yb (1.13 ppm) and Er (1.18 ppm). Then, these βRb from Rb-std were applied by linear interpolation to the unknown samples for correction of 87Rb on 87Sr. The analytical results of serial international reference materials (BIR-1G, BCR-2G, BHVO-2G, T1-G and ATHO-G) demonstrate that our improved method can raise the upper limit of Rb/Sr for in-situ Sr isotope determination and reduce the relative standard deviation of results. This improvement of the upper limit of Rb/Sr (<0.33) will expand not only range of microanalysis for silicate minerals, but also bulk Sr isotope determination of volcanic rock combining with rapid fusion technique.

An Effective Oxide Interference Correction on Sc and REE for Routine Analyses of Geological Samples by Inductively Coupled Plasma-Mass Spectrometry

Oxide interference correction plays a vital role in the accurate determination of trace element compositions of geological samples by inductively coupled plasma-mass spectrometry (ICP-MS). In this study, we found that the oxide production is mainly controlled by the gas flow of the ICP-MS and a constant oxide correction factor (OCF) can be measured during a routine analysis. Thus, we can obtain the oxide production by just investigating the gas flow for a fixed ICP-MS system with monitoring of OCF. Si, Ba and LREE oxide interferences on the Sc, Eu and Gd of four geological standard samples GSP-2, JP-1, GBW03112 and GBW03113 were corrected by such method and the results were in good agreement with the recommended values. Therefore, the present study provides a simple and fast correction method for the oxide interferences of the geological samples during the routine analyses. Furthermore, a Microsoft Excel spreadsheet template integrating the correction equations was developed in an in-house software (ICPMSDataCal) for effective calibration.

Weak localization in transition metal dichalcogenide monolayers and their heterostructures with graphene

We calculate the interference correction to the conductivity of doped transition metal dichalcogenide (TMDC) monolayers. Because of the interplay between valley structure and intrinsic spin-orbit coupling (SOC), these materials exhibit a rich weak localization (WL) behavior that is qualitatively different from conventional metals or similar two-dimensional materials such as graphene. Our results can also be used to describe graphene/TMDC heterostructures, where the SOC is induced in the graphene sheet. We discuss new parameter regimes that go beyond existing theories, and can be used to interpret recent experiments in order to assess the strength of SOC and disorder. Furthermore, we show that an in-plane Zeeman field can be used to distinguish the contributions of different kinds of SOC to the WL magnetoconductance.

In situ calcium isotopic ratio determination in calcium carbonate materials and calcium phosphate materials using laser ablation-multiple collector-inductively coupled plasma mass spectrometry

This study presents a highly precise and accurate Ca isotope analysis method using laser ablation multiple collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) in calcium carbonates and calcium phosphates. High-sensitivity cones and nitrogen gas were used to improve the performance of the LA-MC-ICP-MS. The experiment results show that at the N2 mode, the signal intensity of 44Ca+ in the high-sensitivity cones (Jet + X cones) was 5-fold higher than that in the normal cones (S + H cones), while the polyatomic interferences of 40Ar1H1H+ and 40Ar16O+ in the high-sensitivity cones were suppressed by factors of 6.1 and 10.6, respectively, after the addition of 8 ml min−1 N2. The combination of high sensitivity cones and N2 addition did not increase the production of double charged ions. Additionally, the interference correction of doubly charged Sr ions was investigated in detail. The experiment results demonstrate that the concentration ratio of Sr to Ca (represented as I87Sr++/I44Ca+), the 87Sr/86Sr ratio and the mass fractionation factor of Sr (fSr) during the measurement process were key parameters for in situ Ca isotope ratios analysis. The threshold values of these key parameters were evaluated and are recommended to ensure an accurate correction of doubly charged Sr ions. Using the optimized instrumental conditions and correction strategies, an excellent within-run precision (<0.06‰, 2SE) and external reproducibility (<0.15‰, 2SD) for the microanalysis of δ44/42Ca915b were obtained in natural calcium carbonates and calcium phosphates. These precisions are better than the values previously reported in the literature regarding using LA-MC-ICP-MS. Matrix effects were observed during the in situ Ca isotope analysis among calcium carbonates, hydroxy calcium phosphates and igneous apatites. Using the matrix-matching standards, accurate δ44/42Ca915b values in natural materials with various matrices were achieved, confirming the availability of the proposed method to resolve the spatial variation of δ44/42Ca in natural materials.

Comparison of methods for the geochemical determination of rare earth elements: Rock Canyon Creek REE–F–Ba deposit case study, SE British Columbia, Canada

Using the Rock Canyon Creek carbonate-hosted rare earth element (REE)–F–Ba deposit as an example, we demonstrate the need for verifying inherited geochemical data prior to reinterpretation. Inherited La, Ce, Nd and Sm data obtained by pressed pellet X-ray fluorescence (XRF), and La and Y data obtained by aqua regia digestion inductively coupled plasma atomic emission spectroscopy (ICP-AES) for more than 300 drill-core samples were analysed in 2009 and were subsequently compared to sample subsets re-analysed using lithium metaborate-tetraborate (LMB) fusion ICP mass spectroscopy (ICP-MS), Na 2 O 2 fusion ICP-MS, and LMB fusion-XRF. We determine that LMB ICP-MS and Na 2 O 2 ICP-MS accurately determined REE concentrations in control reference materials (CRM) SY-2 and SY-4, and provided precision of about 10%. Fusion-XRF was precise for La, Ce and Nd at concentrations greater than ten times the lower detection limit; however, accuracy of this method was not established because REE concentrations in SY-4 were below the lower detection limit. Analysis of the sample subset revealed substantial discrepancies for Ce concentrations determined by pressed pellet XRF in comparison to those determined by other methods due to Ba spectral interference. Samarium, present in lower concentrations than other REE that were determined, was consistently underestimated by XRF methods relative to ICP-MS methods. This may be the result of Sm concentrations approaching the lower detection limits of XRF methods, elemental interference or inadequate background corrections. Aqua regia dissolution results, reporting only for La and Y, are underestimated relative to the other methods. We highlight the importance of selecting the most appropriate analytical method and reference materials for determining the REE content of mineralized rock which may be several orders of magnitude higher than that of typical host rock.

More than Five Percent Ionization Efficiency by Cavity Source Thermal Ionization Mass Spectrometry for Uranium Subnanogram Amounts.

Numerous applications require the precise analysis of U isotope relative enrichment in sample amounts in the subnanogram to picogram range; among those are nuclear forensics, nuclear safeguards, environmental survey, and geosciences. However, conventional thermal ionization mass spectrometry (TIMS) yields U combined ionization and transmission efficiencies (i.e., ratio of ions detected to sample atoms loaded) of less than 0.1% or 2% depending on the loading protocol, motivating the development of sources capable of enhancing ionization. The new prototype cavity source TIMS at ETH Zürich offers improvements from 4 to 15 times in combined ionization and transmission efficiency compared to conventional TIMS, yielding up to 5.6% combined efficiency. Uranium isotope ratios have been determined on reference standards in the 100 pg range bound to ion-exchange or extraction resin beads. For natural U standards, n(235U)/ n(238U) ratios are measured to relative external precisions of 0.5-1.0% (2RSD, 2 < n < 11, conventional source) or 2.0% (2RSD, n = 6, cavity source) and accuracies of 0.2-0.7% (conventional source) or 0.4-0.9% (cavity source). Meanwhile, n(234U)/ n(238U) ratios are determined to relative external precisions of 1.7-3.6% (2RSD, 2 < n < 11, conventional source) or 5.6% (2RSD, n = 6, cavity source) and accuracies of 0.1-2.5% (conventional source) or 0.5-8.3% (cavity source), which would benefit further from in-run organic interference and peak tailing corrections.

Correction of Mass Spectrometric Interferences for Rapid and Precise Isotope Ratio Measurements of Calcium from Biological Samples Using ICP-Mass Spectrometry.

Stable isotope compositions of calcium (Ca) provide useful information concerning metabolic alterations of Ca in human and animal bodies. For the measurements of Ca isotope ratio, great care must be taken for the mass spectrometric interferences on Ca isotopes (42Ca+, 43Ca+, and 44Ca+) from doubly charged strontium (Sr) ions (84Sr2+, 86Sr2+, and 88Sr2+). To obtain reliable stable isotope data of Ca, we developed a new correction technique for the mass spectrometric interferences by mSr2+ ions based on standard addition method. Addition of a small fraction of Sr onto a Ca solution shifts the measured Ca isotope ratios on a three-isotope diagram (i.e., δ44Ca and δ43Ca) along a mixing line defined by both the true Ca isotope ratio and the Sr isotope ratio. Therefore, the true Ca isotope ratio of a sample can be obtained as the crossover point of mass dependent fractionation line and the mixing line. With the present correction technique, precise and accurate isotope ratio measurements can be made on analyte solutions having a CSr/CCa ratio (concentration ratio) of 0.03, which is 6 times higher than the CSr/CCa ratio applicable to the conventional correction technique.

Total evaporation technique for high-accuracy isotopic analysis of isotopically enriched molybdenum by negative thermal ionization mass spectrometry

The isotopic composition of isotopically enriched materials is essential for isotope dilution mass spectrometry and calibrated mass spectrometry, which are considered to be potential primary methods/authority methods of the highest metrological quality for the analysis of elemental content or isotopic compositions. In this study, a total evaporation (TE) technique was developed for accurate determination of isotopic compositions for seven enriched molybdenum materials with the utilization of negative ion-thermal ionization mass spectrometry (NTIMS). By using La(NO3)3 as an activator, the sample was efficiently ionized into for NTIMS measurement. To achieve highly precise results, the oxygen isotope interference in on Mo isotopic analysis was corrected by using the IUPAC recommended isotopic compositions for atmospheric O2. Various sources of uncertainty to TE-NTIMS, such as measurement repeatability, oxide interference correction, and the ion loss before and after measurement were discussed with respect to the determination of their uncertainty contribution and their influence on the results. As a result, the major isotope abundance for each enriched Mo material were determined as (k = 2): x(92Mo) = 0.974 69 ± 11 for enriched Mo-92, x(94Mo) = 0.920 26 ± 11 for enriched Mo-94, x(95Mo) = 0.965 50 ± 20 for enriched Mo-95, x(96Mo) = 0.967 59 ± 12 for enriched Mo-96, x(97Mo) = 0.942 06 ± 13 for enriched Mo-97, x(98Mo) = 0.984 56 ± 11 for enriched Mo-98, and x(100Mo) = 0.993 655 ± 12 for enriched Mo-100, respectively. These measurement results have been compared to those determined by a multi-collector inductively coupled plasma mass spectrometry via the mathematical iteration method in our previous work. Identical major isotope-abundance values were achieved within their combined standard uncertainties, indicating that the TE technique is a powerful and alternative tool for accurate determination of the isotopic composition for isotopically enriched materials. The potential influence owing to the variations of O isotopic compositions during NTIMS measurements were also investigated by applying the ‘In-run O’ isotope-abundance values reported in recent literatures for O isotope interference correction. The corrected Mo isotope abundances of either the major or the minor isotopes were in good agreement with that corrected by using the IUPAC atmospheric O2 isotopic compositions.

Preflight radiometric calibration of a carbon dioxide spectrometer

The first Chinese Carbon Dioxide Observation Satellite (TanSat), which is designed to make high-precision, high-spatial resolution measurements of carbon dioxide, was successfully launched on 22 December 2016. There are two instruments installed on the TanSat: the High Resolution Hyper-Spectral Sensor for carbon observation Grating Spectrometer, aiming at measuring the amount of carbon dioxide (CO2) in the atmosphere, and the cloud and aerosol polarimetric imager to identify the disturbance by clouds and to detect the impact of aerosol within the instrument instantaneous field of view. The two instruments work together to make global, high-precision CO2 measurements with exactly correction of cloud and aerosol interference. The major content of this paper is the laboratory radiometric calibration of ACGS. Both the gain coefficients and the dark current response of each channel were determined during instrument-level ground testing. The gain coefficients for the ACGS were characterized by measuring the instrument response to illumination by an integrating sphere at several light levels. The dark response was calibrated with additional thermal balance testing. This paper also identified bad pixels, recorded in a table of data elements, to be omitted in science data processing. The uncertainties achieved during the radiometric calibration were below 5% (k = 1), meeting the absolute calibration mission requirements.

Exploitation of hybrid anechoic wind tunnels for aeroacoustic and aerodynamic measurements

The last 10 years have seen the establishment of the hybrid anechoic wind tunnel as a significant tool for experimental aeroacoustics research. The hybrid anechoic wind tunnel features a test section which is effectively closed in the aerodynamic sense but open in the acoustic sense, this unique behavior being achieved by stretching fabric of high strength-to-weight ratio (such as Kevlar) over windows in the test section walls which open to anechoic chambers. The hybrid anechoic arrangement offers a number of advantages over the traditional open-jet test section, including low interference corrections that allow for testing of large models at higher Reynolds numbers—advantages well suited to aircraft noise source research. In this article, we review recent applications of hybrid anechoic tunnels for aircraft noise source studies. We discuss the established practice for acoustic and aerodynamic correction of measurements performed in these facilities, and assess some of the latest findings in aerodynamic behavior of hybrid anechoic tests sections.

Spectral interferences and their correction in atomic emission spectral analysis

The main sources of spectral interferences in atomic emission spectral analysis (AESA) are considered, including both wide-range (bremsstrahlung and recombination continuum, radiation of hot condensed particles and electrode ends, scattered light in the spectrometer, overlapping of the analytical line by the wings of the neighbor strong spectral lines of interfering elements, imposition of the components of molecular bands with the very close lines) and narrow-band (partial or complete overlapping of the analytical line with atomic or ionic lines of the sample elements, electrodes and discharge atmosphere; superposition of spectra from higher orders of reflection in conventional diffraction spectrometers and from neighboring orders in two-dimensional echelle spectrometers). The features of their manifestation in various sources of spectrum excitation (flames, DC arc, spark discharges, arc plasma discharges, inductively coupled plasma, microwave plasma, low-pressure electric discharges, laser spark) are considered. The possibilities of reducing the level of spectral interferences or elimination of the spectral noise at the stage of design and manufacturing of AESA devices, as well as upon selecting and adjusting of operation conditions of the analysis are shown. Much attention is paid to the most easily implemented in practice off-peak correction of wide-range spectral interferences. The modern methods of background correction under the spectral peak (under-peak) using a software for atomic emission spectrometers and providing creation of various mathematical models of the background signal in the vicinity of the analytical line at the stage of developing a specific AESA technique are considered. The issues of the choice of spectral lines for analytical measurements, tables and atlases of spectral lines, electronic databases used for this purpose are considered in detail. Specific features of application of the method of inter-element correction with direct spectral overlapping of the lines are given. The operating sequence for taking into account spectral interferences when developing the analysis techniques is proposed.

Multipoint Background Analysis: Gaining Precision and Accuracy in Microprobe Trace Element Analysis

Electron microprobe trace element analysis is a significant challenge. Due to the low net intensity of peak measurements, the accuracy and precision of such analyses relies critically on background measurements, and on the accuracy of any pertinent peak interference corrections. A linear regression between two points selected at appropriate background positions is a classical approach for electron probe microanalysis (EPMA). However, this approach neglects the accurate assessment of background curvature (exponential or polynomial), and the presence of background interferences, a hole in the background, or an absorption edge can dramatically affect the results if underestimated or ignored. The acquisition of a quantitative wavelength-dispersive spectrometry (WDS) scan over the spectral region of interest remains a reasonable option to determine the background intensity and curvature from a fitted regression of background portions of the scan, but this technique can be time consuming and retains an element of subjectivity, as the analyst has to select areas in the scan which appear to represent background. This paper presents a new multi-point background (MPB) method whereby the background intensity is determined from up to 24 background measurements from wavelength positions on either side of analytical lines. This method improves the accuracy and precision of trace element analysis in a complex matrix through careful regression of the background shape, and can be used to characterize the background over a large spectral region covering several elements to be analyzed. The overall efficiency improves as systematic WDS scanning is not required to assess background interferences. The method is less subjective compared to methods that rely on WDS scanning, including selection of two interpolation points based on WDS scans, because "true" backgrounds are selected through an exclusion method of possible erroneous backgrounds. The first validation of the MPB method involves blank testing to ensure the method can accurately measure the absence of an element. The second validation involves the analysis of U-Th-Pb in several monazite reference materials of known isotopic age. The impetus for the MPB method came from efforts to refine EPMA monazite U-Th-Pb dating, where it was recognized that background errors resulting from interference or strong background curvature could result in errors of several tens of millions of years on the calculated date. Results obtained on monazite reference materials using two different microprobes, a Cameca SX-100 Ultrachron and a JEOL JXA-8230, yield excellent agreement with ages obtained by isotopic methods (Thermal Ionization Mass Spectrometry [TIMS], Sensitive High-Resolution Ion MicroProbe [SHRIMP], or Secondary Ion Mass Spectrometry [SIMS]). Finally, the MPB method can be used to model the background over a large spectrometer range to improve the accuracy of background measurement of minor and trace elements acquired on a same spectrometer, a method called the shared background measurement. This latter significantly improves the accuracy of minor and trace element analysis in complex matrices, as demonstrated by the analysis of Rare Earth Elements (REE) in REE-silicates and phosphates and of trace elements in scheelite.

Research on the double-sided incremental forming toolpath planning and generation based on STL model

In order to take the advantages of the double-sided incremental forming (DSIF) that can freely switch the pressing and supporting functions of the two tools and realize the forming of the sheet parts with protruding features in both the positive and negative directions of the sheet (the sheet part with bidirectional protruding feature), a method for the double-sided incremental forming based on the stereo lithographic (STL) model was proposed. The method first classifies the forming features according to the protruding direction and the position relationship of the model into the different types of the features to be formed. The main forming surface and the supporting surface are determined by the types of the forming features, and the pressing and supporting tasks of the main tool and slave tool heads are assigned. Then, the cutter location points of the main tool and slave tool are generated, and the toolpath of the main tool and slave tool are planned out according to the forming sequence and the forming methods of the different forming features. Finally, a method of the interference detection and correction between the forming tool head and the sheet part is proposed. The finite element numerical simulation and the forming experiments of the sheet part with bidirectional protruding features show that the proposed toolpath generation method for the DSIF is applicable; the DSIF toolpath generated based on the STL model can fabricate the sheet part with the bidirectional protruding feature.