Multi-point Calibration Research Articles

Concordant inter-laboratory derived concentrations of ceramides in human plasma reference materials via authentic standards

In this community effort, we compare measurements between 34 laboratories from 19 countries, utilizing mixtures of labelled authentic synthetic standards, to quantify by mass spectrometry four clinically used ceramide species in the NIST (National Institute of Standards and Technology) human blood plasma Standard Reference Material (SRM) 1950, as well as a set of candidate plasma reference materials (RM 8231). Participants either utilized a provided validated method and/or their method of choice. Mean concentration values, and intra- and inter-laboratory coefficients of variation (CV) were calculated using single-point and multi-point calibrations, respectively. These results are the most precise (intra-laboratory CVs ≤ 4.2%) and concordant (inter-laboratory CVs < 14%) community-derived absolute concentration values reported to date for four clinically used ceramides in the commonly analyzed SRM 1950. We demonstrate that calibration using authentic labelled standards dramatically reduces data variability. Furthermore, we show how the use of shared RM can correct systematic quantitative biases and help in harmonizing lipidomics. Collectively, the results from the present study provide a significant knowledge base for translation of lipidomic technologies to future clinical applications that might require the determination of reference intervals (RIs) in various human populations or might need to estimate reference change values (RCV), when analytical variability is a key factor for recall during multiple testing of individuals.

Facile barometric calibration of photoluminescence-based oxygen sensors on a standard rotary evaporator system with a digital vacuum pump

A simple setup and methodology for barometric calibration of quenched phosphorescence oxygen sensors are described, which utilize a standard rotary evaporator (Rotavap) system equipped with a digital vacuum pump. They were demonstrated with a panel of different sensing materials based on PtBP dye, including solid-state sensor coatings on different substrates (membrane inserts, stickers or inner wall of the vacuum flask), as well as liquid sensor formulations. The sensors inside the flask were exposed to different conditions created by the Rotavap system (dry or humid air, water, temperatures ranging 2°C-40°C, residual total pressure), and their intensity, lifetime or phase shift signals were measured with handheld sensor readers Optech (Mocon) and Firesting (PyroScience) in a contact-less manner to generate multi-point calibration curves. Several critical points of the method, which require careful consideration, have been revealed, including sensor mounting inside the Rotavap, its temperature control during calibration, choice of the reader. Finally, a detailed characterization of several sensor types was carried out and their key operational parameters (τ0, KSV, heterogeneity, T-coefficients), and calibration equations for the different conditions were determined and compared to each other and the results of conventional O2 calibration. Overall, barometric calibration method using Rotavap provides a useful alternative to conventional O2 calibration methods, being simple, accurate, convenient and versatile.

Limitations and insights regarding atmospheric mercury sampling using gold

BackgroundAtmospheric mercury (Hg) concentrations are quantified primarily through preconcentration on gold (Au) cartridges through amalgamation and subsequent thermal desorption into an atomic fluorescence spectrometry detector. This procedure has been used for decades, and is implemented in the industry-standard atmospheric Hg analyzer, the Tekran 2537. There is ongoing debate as to whether gaseous elemental mercury (Hg0) or total gaseous mercury (TGM, Hg0 + HgII) is measured using Au cartridges. The raw Hg signal processing algorithms for the Tekran 2537 analyzer have also been questioned. The objective of this work was to develop a better understanding of what forms of Hg are collected on gold cartridges through the use of permeation tube-based calibrators, that release known amounts of Hg0 and HgII. The potential differences between different Tekran analyzer models (i.e., 2537B versus 2537X) Hg signal processing algorithms, and Hg0 calibration methods were also investigated. ResultsExperiments were performed using Hg0 and HgII permeation calibrators. Validation tests showed that the HgII calibrator produced a reproducible and stable HgII permeation rate (2.2 ± 0.2 pg min−1). Results of HgII sampling and analysis using Au amalgamation showed the gold cartridges measured up to 75 % HgII, with the value at the beginning of the HgII measurement being much lower (as low as 10 %) due to HgII adsorption on analyzer surfaces and the Tekran particulate filter. Furthermore, thermal desorption of Hg from Au reduced only 80 % of HgII to Hg0, resulting in additional HgII that was not measured by the analyzer. By adding a thermolyzer upstream of the analyzer, 97 % of HgII was measured as Hg0. Additionally, Hg0 measurements using Tekran 2537 B and X models using a newly developed signal processing algorithm, different peak integration methods, and two Hg0 sources were compared. Results showed the 2537X model was not affected by the integration type, while the 2537B model was. Bell jar calibration based on the Dumarey equation resulted in 6 % ± 7 % (mean ± SD) underestimation of measured Hg0 concentrations compared to the calibration with a permeation calibrator. SignificanceGold cartridges measured an atmospheric Hg fraction somewhere between Hg0 and TGM due to HgII adsorption and inefficient reduction of HgII to Hg0 during thermal desorption from Au. Since HgII in ambient air can be 25 % of total Hg, distinguishing between Hg0 and TGM is important. The use of a thermolyzer or a cation exchange membrane upstream of gold cartridges is recommended to enable TGM or Hg0 measurements, respectively. Observations showed that traceable multipoint calibrations of atmospheric Hg measurements are needed for Hg quantification, and that different Hg0 calibration methods can produce significantly different results for measured atmospheric Hg concentrations.

Isotope dilution with isotopically labeled biomass: An effective alternative for quantitative metabolomics

BackgroundState-of-the-art quantitative metabolomics relies on isotope dilution using internal standards (IS) derived from fully 13C labeled biomass. By spiking samples and external standards with known amounts of IS, the spike characterization demands are kept to a minimum. In fact, it is sufficient to experimentally assess the isotopic enrichment of the IS. This study develops the yeast derived IS toolbox further, (1) by characterizing the concentration levels of hydrophilic metabolites in a yeast fermentation batch and (2) by exploring the analytical figures of merit of one-point IS versus multipoint external calibration using IS, the established gold-standard for quantitative metabolomics. ResultsIndependent reverse isotope dilution experiments using different chromatographic methods over a period of several months, delivered a list of 83 13C-labeled metabolites with fully characterized concentration and their uncertainty, covering 5 orders of magnitude, from the nanomolar to the low millimolar range. The 13C-labeled yeast-derived IS showed excellent intermediate stability with 92 % of molecules showing inter-method RSDs ≤30 % (75 % of molecules showed RSDs ≤15 %) over a timeframe of five months. One-point internal standardization with the characterized labeled biomass achieved figures of merit equivalent to multipoint calibrations for the majority of metabolites. SignificanceThe proposed calibration workflow rationalizes time and standard expenditure and is particularly beneficial for laboratories dealing with wide-target assays and small analysis batches. The present assessment serves as a seminal study for further developments of the concept towards absolute quantification from archive high-resolution MS data of U13C-biomass-spiked samples and the implementation of quick biomass recalibration with each experiment, promising seamless transition between internal standards derived from different fermentation batches.

Fast neonicotinoid quantification in honey using the one-point internal calibration approach

Neonicotinoids, a highly effective class of insecticides used worldwide, have been identified as a major cause of concern for biodiversity. To assess the ecological and environmental consequences of neonicotinoids' use, reliable analytical methodologies, including calibration approaches, are needed. Here, we compared the performance of internal calibration (IC) using a single concentration of stable isotope-labeled standard (SIL) with classical multipoint external calibration (EC) for the quantification of six neonicotinoids in honey. IC showed acceptable levels of trueness (86.3% - 116.0%) and precision (1.4% - 20.8%), although slight biases were observed at very low concentrations compared to EC. When applied to 32 original honey samples, both approaches showed strong agreement (R2 > 0.998) with proportional biases lower than 5%. These results highlight the possibility of implementing IC to simplify quantification in liquid chromatography-mass spectrometry-based pesticide applications.

Improving the Application of Prothrombin Time-Derived Fibrinogen Assay Through Value Transfer from the Von Clauss Method.

This study aimed to improve the accuracy of the fibrinogen (Fib) prothrombin time-derived (PT-der) method. To achieve this, a value transfer method was introduced for calibration, and its effectiveness was assessed. The PT-der Fib assay was calibrated by pooled samples (assigned by the von Clauss method) in three different ways: 1) multipoint calibration using an automatic dilution system, 2) multipoint calibration using a manual dilution method, and 3) manual calibration with multiple concentrations. Three calibration equations (1, 2, and 3) were obtained and an optimal equation was selected by comparing the detection results of the von Clauss method with the PT-der method. Subsequently, the optimal equation was assessed for an accuracy limit, and linear analysis and reference interval verification were performed following the guidelines (EP15-A and EP6-A) issued by the CLSI. Compared with the other two equations (equation 1 and 2), equation 3, available from manual calibration with multiple concentrations, showed a better performance for the PT-der determination in a primary cohort (n = 208), and a good agreement (99% of the results between 1.52 and 6.30 g/L were interchangeable) was validated (n = 3226). The reference interval was also verified in almost all healthy individuals (39/40). However, the discrep-ancy between the two methods was observed in several specific conditions, such as hyperfibrinolysis. Manual calibration with multiple concentrations is better for the Fib PT-der method assay. As a rapid, accurate, and economical test, the performance of the Fib PT-der method has been verified and may be more applicable than before.

Enhancing parameter calibration for micro-simulation models: Investigating improvement methods

Calibrating microscopic traffic simulation models is a prerequisite for simulation applications. This study proposes three novel methods to improve the accuracy and interpretability of the calibration model. The proposed approach involves selecting the calibration parameter, refining the model parameter system, and optimizing the calibration results. The first method expands the single-point mean into a multi-point distribution. The cumulative distribution curve of delay was selected as the calibration parameter. The second method divides the parameter system into global and local parameters. Global parameters were calibrated using NGSIM measured data, and local parameters were calibrated through intelligent algorithms. The third method proposes a methodology of parameter clustering recursion based on the genetic algorithm results, with information entropy selected as the analysis index. To evaluate the effectiveness of the proposed optimization methods, this study used NGSIM trajectory data as a case study. Eight simulation schemes based on the three optimization methods were designed, and simulation experiments were conducted using the VISSIM platform. The results show that the accuracy of the multi-point distribution calibration and parameter value optimization method is significantly higher than the default method. Additionally, the optimization method with calibration of both global and local parameters was more consistent with actual driving characteristics. This study provides a theoretical foundation for improving the practical application of traffic simulation technology, which has significant implications for transportation planning and management.

Characterization of calibration solution certified reference material for polycyclic aromatic hydrocarbons by exact matching isotopic dilution mass spectrometry: a case study from the Brazilian Metrology Institute

Abstract Recertification is a common practice in National Metrology Institutes whenever advances are made in certified reference material (CRM) characterization procedures, which play a key role in metrological traceability. This article compares measurements of 16 priority polycyclic aromatic hydrocarbons (PAHs) in toluene by gas chromatography isotopic dilution mass spectrometry (IDMS) using either an calibration curve or the exact matching approach. The multi-point IDMS calibration curve was used on the original CRM certification and the exact matching approach was carried out on its recertification. The measurement uncertainties by exact matching approach (0.3%–1.0%) were approximately 5 times smaller than those obtained using the calibration curve (1.5%–4.4%) for all PAHs, reducing the uncertainty component due to characterization of PAH CRM. This new characterization study added reliability, increased accuracy and reduced the measurement uncertainty of the Inmetro CRM, with metrological traceability to the International System of Units. The exact-matching isotope dilution is an important technique to value assign organic compounds in CRMs, an action that consolidates the chemical metrology in the Brazilian Metrology Institute.

Response of the TEROS 12 Soil Moisture Sensor under Different Soils and Variable Electrical Conductivity.

In this work, the performance of the TEROS 12 electromagnetic sensor, which measures volumetric soil water content (θ), bulk soil electrical conductivity (σb), and temperature, is examined for a number of different soils, different θ and different levels of the electrical conductivity of the soil solution (ECW) under laboratory conditions. For the above reason, a prototype device was developed including a low-cost microcontroller and suitable adaptation circuits for the aforementioned sensor. Six characteristic porous media were examined in a θ range from air drying to saturation, while four different solutions of increasing Electrical Conductivity (ECw) from 0.28 dS/m to approximately 10 dS/m were used in four of these porous media. It was found that TEROS 12 apparent dielectric permittivity (εa) readings were lower than that of Topp's permittivity-water content relationship, especially at higher soil water content values in the coarse porous bodies. The differences are observed in sand (S), sandy loam (SL) and loam (L), at this order. The results suggested that the relationship between experimentally measured soil water content (θm) and εa0.5 was strongly linear (0.869 < R2 < 0.989), but the linearity of the relation θm-εa0.5 decreases with the increase in bulk EC (σb) of the soil. The most accurate results were provided by the multipoint calibration method (CAL), as evaluated with the root mean square error (RMSE). Also, it was found that εa degrades substantially at values of σb less than 2.5 dS/m while εa returns to near 80 at higher values. Regarding the relation εa-σb, it seems that it is strongly linear and that its slope depends on the pore water electrical conductivity (σp) and the soil type.

Advancing High-Throughput MS-Based Protein Quantification: A Case Study on Quantifying 10 Major Food Allergens by LC-MS/MS Using a One-Sample Multipoint External Calibration Curve.

The LC-MS-based method has emerged as the preferred approach for quantifying food allergens. However, the preparation of a traditional calibration curve (MSCC) is labor-intensive and error-prone. Here, a sensitive and robust LC-MS/MS method for quantifying 10 major food allergens was developed and validated, where the one-sample multipoint external calibration curve (OSCC) was employed instead of MSCC. By employing the multiple isotopologue reaction monitoring (MIRM) technique with only one spiked level in the blank, OSCC can be effectively established. Results demonstrate that the proposed method exhibits excellent performance in selectivity, sensitivity, accuracy, and precision, comparable to that of the traditional MSCC. Additionally, this strategy allows for isotope sample dilution by monitoring the less abundant MIRM channel. Moreover, the developed method was successfully applied to investigate the contamination of 10 food allergens in commercial food products. With its high throughput and robustness, the MIRM-OSCC-LC-MS/MS methodology has many potential applications, especially in the MS-based protein quantification analysis.

Integrating a Multiple Isotopologue Reaction-Monitoring Technique and LC-MS/MS for Quantitation of Small Molecules: Ten Mycotoxins in Cereals as an Example.

Accurate quantification of mycotoxin in cereals is crucial for ensuring food safety and human health. However, the preparation of traditional multisample external calibration curves (MSCCs) is labor-intensive and error-prone. Here, a multiple isotopologue reaction-monitoring (MIRM)-LC-MS/MS method for accurate quantitation of ten major mycotoxins in cereals was successfully developed and validated, where a novel one-sample multipoint calibration curve (OSCC) strategy is used instead of MSCCs. The OSCC can be established by examining the correlation between the calculated theoretical isotopic abundances and the measured abundance across various MIRM channels. In comparison to the MSCC, the OSCC strategy exhibits outstanding performance including superior selectivity, accuracy (78.4-108.6%), and precision (<12.5%). Furthermore, the proposed OSCC-MIRM-LC-MS/MS method was successfully applied to investigate mycotoxin contamination in cereal samples in China. Considering the advantages of simplified workflows and improved throughput, the OSCC-MIRM-LC-MS/MS methodology holds great promise for accurately quantifying chemical contaminants in foods.

A correction method for radial distortion and nonlinear response of infrared cameras.

The key feature of non-contact temperature measurement provided by infrared (IR) cameras underpins their versatility. However, the accuracy of temperature measurements with IR cameras depends on imaging quality due to their non-contact nature, such as the lens, body temperature, and measurement environment. This paper addresses the correction of radial distortion and nonlinear response issues in IR cameras. To address radial distortion, we have designed a passive checkerboard calibration board specifically for infrared cameras. This board is used to calibrate the IR camera and derive the necessary camera parameters. Subsequently, these parameters are applied during the actual measurement process to rectify radial distortion effectively. Building on the radial distortion correction method mentioned above, we propose a multi-point segmented calibration approach that considers different temperature ranges and imaging regions. This method alleviates the issue of reduced temperature measurement accuracy due to variations in camera responses by computing gain and offset coefficient matrices for each temperature range. Experimental results demonstrate the effectiveness of the calibration board in correcting radial distortion in IR cameras, with a mean reprojection error of less than 0.16 pixels. Regarding the nonlinear response problem, the introduced method significantly reduces the relative error in temperature measurement. In the verification phase, spanning from 100 to 500 °C, the average relative error in temperature measurement decreases by 0.49% from 1.61% before and after correction, which highlights a substantial improvement in temperature measurement accuracy. This work gives a useful reference to improve the imaging quality and temperature measurement accuracy using infrared cameras.

Temperature-Corrected Calibration of GS3 and TEROS-12 Soil Water Content Sensors

The continuous monitoring of soil water content is commonly carried out using low-frequency capacitance sensors that require a site-specific calibration to relate sensor readings to apparent dielectric bulk permittivity (Kb) and soil water content (θ). In fine-textured soils, the conversion of Kb to θ is still challenging due to temperature effects on the bound water fraction associated with clay mineral surfaces, which is disregarded in factory calibrations. Here, a multi-point calibration approach accounts for temperature effects on two soils with medium to high clay content. A calibration strategy was developed using repacked soil samples in which the Kb-θ relationship was determined for temperature (T) steps from 10 to 40 °C. This approach was tested using the GS3 and TEROS-12 sensors (METER Group, Inc. Pullman, WA, USA; formerly Decagon Devices). Kb is influenced by T in both soils with contrasting T-Kb relationships. The measured data were fitted using a linear function θ = aKb + b with temperature-dependent coefficients a and b. The slope, a(T), and intercept, b(T), of the loam soil were different from the ones of the clay soil. The consideration of a temperature correction resulted in low RMSE values, ranging from 0.007 to 0.033 cm3 cm−3, which were lower than the RMSE values obtained from factory calibration (0.046 to 0.11 cm3 cm−3). However, each experiment was replicated only twice using two different sensors. Sensor-to-sensor variability effects were thus ignored in this study and will be systematically investigated in a future study. Finally, the applicability of the proposed calibration method was tested at two experimental sites. The spatial-average θ from a network of GS3 sensors based on the new calibration fairly agreed with the independent area-wide θ from the Cosmic Ray Neutron Sensor (CRNS). This study provided a temperature-corrected calibration to increase the accuracy of commercial sensors, especially under dry conditions, at two experimental sites.

Energy calibration of silicon drift detector - based spectrometer at ADITYA-U

The Tokamak plasma start-up is the first process to have a successful Tokamak plasma discharge. Considering the start-up condition, high electric field and neutral density with the absence of flux surfaces an enhanced electron transport to the Plasma-Facing Components (PFC) or the inner vessel wall is expected. Such electron excursion under an applied electric field induces electromagnetic emission, especially in the x-ray region. Such emission is important as it gives vital information about the initial condition of the plasma start-up and the potential for energy loss to the PFC/vessel walls. A Silicon Drift Detector (SDD) based soft x-ray (SX) spectrometer is installed at the ADITYA-U tokamak, operating within the range of 1–30 keV generating a 4 K channel spectrum. The energy calibration, spectra transformation from channel space to the energy space, is a pre-requisite for any spectroscopic measurement. The calibration is performed by natural radioactive sources 241Am, 109Cd, 133Ba, and 55Fe having micro-curie strength. Two-point and multipoint calibrations are applied to the SDD spectra. The results from the two processes establish that the multipoint calibration works well for the identification of the photon energy due to the realization of the detector linearity for a wider band.

Drift Characteristics of Sea-Bird Dissolved Oxygen Optode Sensors

Abstract The Sea-Bird 63 dissolved oxygen optode sensors used on various oceanographic platforms are known to drift over time. Corrections for drift are necessary for accurate dissolved oxygen measurements on the time scale of months to years. Here, drift on 14 Sea-Bird 63 dissolved oxygen optode sensors deployed on Spray underwater gliders over 5 years is described. The gliders with oxygen sensors were deployed regularly for 100-day missions as part of the California Underwater Glider Network (CUGN). A laboratory two-point calibration was performed on the oxygen sensor before and after glider deployment. Sensor drift during 100-day deployments was larger than during 100-day storage periods. Sensor behavior is modeled with a gain that asymptotically approaches 1.090 ± 0.005 with an e-folding time scale of 3.70 ± 0.361 years. At zero oxygen concentration, the sensor consistently reads around 3 μmol kg−1; a negative offset term is used in addition to the gain to correct the sensor oxygen. The correction procedure removes the error due to long time drift, one of the major sources of error, with an uncertainty of 0.5% (0.9% including outliers) or 0.5 μmol kg−1 depending on concentration, which improves the accuracy of the Sea-Bird 63 although uncertainty from other sources of error including the initial factory calibration and the sensor response time remain. Suggested procedures for implementing a two-point calibration procedure in the laboratory are discussed. Calibrations must be considered starting 6 months after initial factory calibration to keep error from sensor time drift under 1%. Significance Statement Dissolved oxygen measurements are widely used in oceanography. The optode sensors used to measure dissolved oxygen are known to drift over time. Here, the characteristics of drift for the oxygen optode sensor from Sea-Bird Scientific are described using a two-point calibration at zero and full saturation. The calibration procedure can be applied to oxygen optode sensors deployed on a variety of platforms when it is impractical to complete a multipoint calibration.

Measurements of volatile organic compounds in ambient air by gas-chromatography and real-time Vocus PTR-TOF-MS: calibrations, instrument background corrections, and introducing a PTR Data Toolkit

Abstract. Volatile organic compound (VOC) emissions and subsequent oxidation contribute to the formation of secondary pollutants and poor air quality in general. As more VOCs at lower mixing ratios have become the target of air quality investigations, their quantification has been aided by technological advancements in proton-transfer-reaction time-of-flight mass spectrometry (PTR-TOF-MS). However, such quantification requires appropriate instrument background measurements and calibrations, particularly for VOCs without calibration standards. This study utilized a Vocus PTR-TOF-MS coupled with a gas chromatograph for real-time and speciated measurements of ambient VOCs in Boulder, Colorado, during spring 2021. The aim of these measurements was to understand and characterize instrument response and temporal variability as to inform the quantification of a broader range of detected VOCs. Fast, frequent calibrations were made every 2 h in addition to daily multipoint calibrations. Sensitivities derived from the fast calibrations were 5 ± 6 % (average and 1 standard deviation) lower than those derived from the multipoint calibrations due to an offset between the calibrations and instrument background measurement. This offset was caused, in part, by incomplete mixing of the standard with diluent. These fast calibrations were used in place of a normalization correction to account for variability in instrument response and accounted for non-constant reactor conditions caused by a gradual obstruction of the sample inlet. One symptom of these non-constant conditions was a trend in fragmentation, although the greatest observed variability was 6 % (1 relative standard deviation) for isoprene. A PTR Data Toolkit (PTR-DT) was developed to assess instrument performance and rapidly estimate the sensitivities of VOCs which could not be directly calibrated on the timescale of the fast calibrations using the measured sensitivities of standards, molecular properties, and simple reaction kinetics. Through this toolkit, the standards' sensitivities were recreated within 1 ± 8 % of the measured values. Three clean-air sources were compared: a hydrocarbon trap, zero-grade air and ultra-high purity nitrogen, and a catalytic zero-air generator. The catalytic zero-air generator yielded the lowest instrument background signals for the majority of ions, followed by the hydrocarbon trap. Depending on the ionization efficiency, product ion fragmentation, ion transmission, and instrument background, standards' limits of detection (5 s measurement integration) derived from the catalytic zero-air generator and the fast calibration sensitivities ranged from 2 ppbv (methanol) to 1 pptv (decamethylcyclopentasiloxane; D5 siloxane) with most standards having detection limits below 20 pptv. Finally, applications of measurements with low detection limits are considered for a few low-signal species including sub-parts-per-trillion by volume (pptv) enhancements of icosanal (and isomers; 1 min average) in a plume of cooking emissions, and sub-parts-per-trillion by volume enhancements in dimethyl disulfide in plumes containing other organosulfur compounds. Additionally, chromatograms of hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, and decamethylcyclopentasiloxane (D3, D4, and D5 siloxanes, respectively), combined with high sensitivity, suggest that online measurements can reasonably be associated with the individual isomers.

A novel calibration method for continuous airborne metal measurements: Implications for aerosol source apportionment

Continuous metal monitors have been widely used in environmental monitoring due to the high temporal resolution, high detection limit, and necessity for near real-time source apportionment. However, the reliability of the conventional calibration method, the deviation caused by uncalibrated monitoring data, and the subsequent impact on source identification results are rarely discussed. In this study, a reliable multi-point calibration approach by Primary Standard Aerosol Mass Concentration Calibration System (PAMAS) for the Xact625i Ambient Metals Monitor was developed and applied. The measured data was almost meaningless in the low-concentration range with bias even exceeding 100 % by using the conventional single-point calibration method based on thin-film standards. PAMAS was utilized to generate aerosols with known concentrations of the 20 metal elements including Al, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, As, Sr, Cd, Sn, Sb, Ba, Tl, Pb, and Bi, in two concentration ranges of 150–1200 ng m−3 and 2.5–30 ng m−3 to validate the Xact625i Monitor. The results showed that the elemental concentrations were underestimated, especially in the low-concentration range, only for Cr, As, and Sr with slopes close to unity (1.00 ± 0.03). After calibration by PAMAS, the slopes of the linear relationships between measured and standard concentrations were all unity for the 19 elements in the high-concentration range, and close to unity for the 15 elements in the low-concentration range, and the accuracy of the remaining elements was also improved. After considering the calibration of aerosol metal data, it was found the number of source factors and their contributions to metals and PM2.5 in Chongming Dongtan, China, based on the PMF model significantly changed. This study highlighted the need of developing reliable calibration methods for online aerosol monitoring instruments and implied that the source apportionment results could be biased without careful data calibration.

Determination of glyphosate and aminomethylphosphonic acid residues in Finnish soils by ultra‐high performance liquid chromatography–tandem mass spectrometry

Glyphosate [N-(phosphonomethyl) glycine] (GLY) adsorbs strongly in Finnish soils. A new method for GLY and its main degradation product, aminomethylphosphonic acid (AMPA) residues in clay soils (Protovertic Luvisol) was developed and validated. A new method was necessary because the previous one required laborious cleaning pre-treatments, and its recovery was quite poor (<40%–70%). In the new method, the earlier method's extraction solvent, 0.1 M potassium hydroxide (KOH), was replaced by more effective 0.6 M KOH. The old post-column high-performance liquid chromatography and fluorescence (HPLC-FLD) method was replaced by the ultra-high performance liquid chromatography–tandem mass spectrometry (UHPLC-MS/MS) method. Compounds were identified as their fluorenyl methyl chloroformate (FMOC) derivatives by a multiple reaction monitoring (MRM) technique and quantified by an internal standard method utilising multipoint matrix-matched calibration. Glufosinate-ammonium (GLUF) was used to monitor the effectiveness of extraction with good recovery (80–119%). All calibration curves were found to be linear (R2 ≥ 0.98) in the studied calibration range (0.01–3.31 mg kg−1 in fresh soil). The repeatability and reproducibility were 25% and 28% for GLY, and 20% and 24% for AMPA in real research soil samples. The method was effective throughout the calibration range in all the studied Finnish agricultural soils.•An improved method was created to analyse glyphosate (GLY) and AMPA in Finnish clay soil.•The challenge caused by strong GLY adsorption on soil was solved by using multipoint matrix-matched calibration curve samples which were prepared identically with the research samples.•The method performed well in all tested clay, loam and sandy loam soils.

Variable microfluidic dosing valve for gas chromatography

Miniaturization coupled with the introduction of microfluidic systems and devices into the chromatograph hardware is one of the main approaches to the creation of modern gas chromatographic equipment. For variable sample dosing in automatic mode, a microfluidic dosing valve based on microelectromechanical systems was developed. The manufactured device provides multi-point calibration with a single calibration gas mixture. Two methods for constructing a calibration dependence were implemented using the developed dosing device: a calibrated loop for 250 μl taken as a constant dosing loop and calibration solutions (gas mixtures of propane in helium (GSO 10463–2014) with concentrations of 0.0025, 0.025, 0.25, 0.5б and 1.25 % vol.) were used in the first method, whereas in the second one a variable dosing provided by the developed microfluidic dosing valve which consisted in the possibility of introducing a different amount of the calibration gas mixture of propane in helium (2.5 % vol.) into the chromatographic column due to changing the time of sample injection at a constant pressure was implemented. The experiment was carried out on a PIA gas microchromatograph with a MEMS column (a sectional plane of 1 × 1 mm and a 1-m channel) with a Carbopak B adsorbent. It is shown that the use of the developed dosing device as part of the PIA gas microchromatograph makes it possible to carry out a metrologically assured quantitative analysis.

An accurate and efficient method for simultaneous determination of 16 trichothecenes in maize and wheat by UHPLC-Q-Orbitrap-HRMS combined one-step pretreatment with a novel isotope multipoint calibration strategy

Trichothecenes are mycotoxins generated by Fusarium species that are toxic to humans and animals and frequently contaminate cereals. Herein, we present an UHPLC-Q-Orbitrap-HRMS method using one-step pretreatment for simultaneous detection of 16 type A and B trichothecenes in maize and wheat. A calibration strategy based on natural isotopic distribution was adopted and validated to replace traditional time-consuming and laborious multipoint external calibration curves. Various conditions influencing the method were studied. The recoveries of spiked analytes at three different concentrations ranged from 74.2% to 105.3% and the inter-day relative standard deviations were 0.5–15.6%. The limits of quantitation were 4.4–108.8 μg/kg. Moreover, the current methodology was applied to the evaluation of type A and B trichothecenes present in samples from major wheat production areas in China. This study provides a facile methodology for type A and B trichothecenes analysis and presents promising applications for exposure risk assessment of trichothecenes in cereals.