Standard Calibration Research Articles

Extended Calibration of Charge Mode Accelerometers to Improve the Accuracy of Energy Systems

This paper presents an extended calibration procedure for mode accelerometers, which makes it possible to compare the accuracy of sensors of this type from different manufacturers. This comparison involves determining the upper bound on dynamic error for a given quality criterion, i.e., the integral square error and absolute error. Therefore, this article extends the standard calibration implemented in engineering practice using tests, providing a value for the upper bound on dynamic error as an additional parameter describing the accelerometer under consideration. This paper presents the theoretical basis for this type of solution, which is partly based on measurement data obtained from a standard calibration process and on the results of parametric identification. The charge mode accelerometer is considered here because this type of sensor is commonly used in the energy industry, as it can operate over a wide range of temperatures. The calculation results presented in this paper were obtained using MathCad 5.0 software, and the tests were carried out using an accelerometer of type 357B21. In the experimental part of this article (Results of Extended Calibration section), values for the upper bound of the dynamic error were determined for two error criteria and constrained simulation signals related to these errors. The impact of interference on the results of accelerometer tests was omitted in this paper.

Quantitative magnetization measurements of magnetic particles with FePt standard samples

Micrometer-sized magnetic particles have been widely used in magnetic force microscopy, magnetic resonance force microscopy, and bio-sensing. To quantitatively interpret the data obtained with magnetic particles, it is important to know the magnetic properties of the particles. However, the magnetic moment of individual particle is usually too small to be measured by common instruments for samples with large volume. Here, we present a method to characterize magnetic microspheres using patterned FePt thin films as standard samples. The FePt thin film in the L10 phase has perpendicular magnetic anisotropy, and the patterned features can be magnetized to near single-domain magnets, which make them suitable standards for magnetic sphere calibration with magnetic force microscopy. Multiple linear regression is used to analyze the frequency shift images and obtain the effective dipole moment of the spheres. The position of the dipole moment is obtained by minimizing the residuals in multiple linear regression with a gradient descent algorithm. Three NdFeB spheres of different diameters were measured. It was found that the magnetization increases with the increase in the diameter of the sphere, possibly due to the weakening of ferromagnetism on the surface.

Advancing PFAS characterization: Enhancing the total oxidizable precursor assay with improved sample processing and UV activation

Per- and polyfluoroalkyl substances (PFAS) encompass over 9000 chemicals utilized in various industrial and commercial applications. However, the quantification of PFAS using standard commercial analytical methods is currently limited to <50 selected compounds. To address this issue, the total oxidizable precursor (TOP) assay was developed, allowing for the oxidative conversion of previously undetectable PFAS precursors into measurable PFAS. This study investigated different sample processing methods to address post-oxidation PFAS loss identified in literature. Using PFOS as a probe molecule, up to 50 % loss of PFOS was identified during sample work-up. It was determined that the use of mass-labelled PFOS and methanolic acetic acid to chemically quench the sample post-oxidation improved PFOS recovery and allowed for correction of any remaining PFOS loss. The use of ultraviolet (UV) light was then investigated as an activator in contrast to the standard thermal activation method. A comparative evaluation was conducted to assess the recovery and conversion of perfluorooctanoic acid (PFOA), PFOS, and 6:2 fluorotelomer sulfonate (6:2 FTS) using both the heat-activated and UV-activated TOP assays. Results demonstrated that the UV-activated TOP assay achieved complete (100 %) oxidation of 6:2 FTS within 7.5 min, resulting in a total yield of generated perfluorinated carboxylic acids (PFCAs) at 108 ± 8 %. The study concluded by investigating the UV-activated TOP assay for its application on various aqueous film forming foam (AFFF) formulations and two AFFF samples drained from military aircraft rescue firefighting vehicles (ARFFVs). Analysis of these AFFF samples were supported by high resolution mass spectrometry and an expanded analytical suite, identifying several fluorotelomer precursors. The findings of this study provide compelling evidence that modifications in sample processing, work-up procedures, expansion of initial PFAS calibration standards, and UV-activation methods enhance the TOP assay, positioning it as a more reliable and quantitative analytical tool for PFAS characterization.

A Microfluidic Paper-based Analytical Device for Simultaneous Measurement of Albumin, Creatinine and Uric Acid in Urine based on Standard Addition Method

This work describes a simple method for the simultaneous measurement of urinary albumin, creatinine and uric acid using a standard addition approach on a microfluidic paper-based analytical device (µPAD). Hydrophobic barrier of the µPAD was created by stamping indelible ink onto a filter paper. The µPAD was designed with a flower-liked configuration. After aliquoting urine to a central sample zone, the sample flowed to ten surrounding channels, namely “the inner channels”, where the blank (water) or standard solutions had been added. The inner channels were connected to circular reagent zones where reagents had been immobilized. Tetrabromophenolphthalein ethyl ester, alkaline picrate, and a mixed solution of ferric chloride and ferric cyanide were used as the chromogenic reagents for the colorimetric detections of albumin, creatinine, and uric acid, respectively. Each reagent zone was linked with a circular detection zone through a second channel, namely “the outer channels”. The blue-, orange- and greenish-blue colored products were observed in the detection zones for the measurement of albumin, creatinine, and uric acid, correspondingly. A digital image of the µPAD was captured with a mobile phone. The color intensities were evaluated by ImageJTM and were employed for the quantitative analyses. The standard addition calibrations were found to be linear (r2 &gt; 0.99) for the spiked analyte concentrations up to 100 mg L-1 albumin, 1000 mg L-1 creatinine, and 50 mg dL-1 uric acid. The paper platform provided high precision (RSD &lt; 5 %) and good analytical recovery (91.8-109.7 %). Under paired t-test, the results obtained by the developed µPAD and the validating methods were not significantly different at 95 % confidence (albumin: tstat = -0.130, tcri = 3.182, creatinine: tstat = -0.133, tcri = 3.182, and uric acid: tstat = 1.119, tcri = 3.182).

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.

Opportunistic Screening With CT: Comparison of Phantomless BMD Calibration Methods.

Opportunistic screening is a new promising technique to identify individuals at high risk for osteoporotic fracture using computed tomography (CT) scans originally acquired for an clinical purpose unrelated to osteoporosis. In these CT scans, a calibration phantom traditionally required to convert measured CT values to bone mineral density (BMD) is missing. As an alternative, phantomless calibration has been developed. This study aimed to review the principles of four existing phantomless calibration methods and to compare their performance against the gold standard of simultaneous calibration (ΔBMD). All methods were applied to a dataset of 350 females scanned with a highly standardized CT protocol (DS1) and to a second dataset of 114 patients (38 female) from clinical routine covering a large range of CT acquisition and reconstruction parameters (DS2). Three of the phantomless calibration methods must be precalibrated with a reference dataset containing a calibration phantom. Sixty scans from DS1 and 57 from DS2 were randomly selected for this precalibration. For each phantomless calibration method first the best combination of internal reference materials (IMs) was selected. These were either air and blood or subcutaneous adipose tissue, blood, and cortical bone. In addition, for phantomless calibration a fifth method based on average calibration parameters derived from the reference dataset was applied. For DS1, ΔBMD results (mean standard deviation) for the phantomless calibration methods requiring a precalibration ranged from 0.1 2.7 mg/cm3 to 2.4 3.5 mg/cm3 with similar means but significantly higher standard deviations for DS2. Performance of the phantomless calibration method, which does not require a precalibration was worse (ΔBMD DS1: 12.6 13.2 mg/cm3 , DS2: 0.5 8.8 mg/cm3 ). In conclusion, phantomless BMD calibration performs well if precalibrated with a reference dataset. © 2023 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

The annealing setup and associated monitoring system of the ELIADE HPGe clover detectors at ELI-NP

We report a dedicated setup built in-house for the annealing of the HPGe clover detectors of the ELI-NP Array of DEtectors (ELIADE) γ-ray spectrometer, as well as the post-annealing testing of these detectors with the standard 60Co & 152Eu radioactive calibration sources employing conventional analog electronics. Both the design and assembly of the annealing setup were performed at the Extreme Light Infrastructure — Nuclear Physics (ELI-NP) facility, Măgurele, Romania. A `radiation damage annealing assembly kit' (NRK-200 unit) from the detector manufacturer Canberra is utilized in heating and controlling the temperature of the Ge crystals of the annealed detector. The vacuum inside the detector was maintained throughout the annealing process by constantly pumping the system using a turbo-molecular pumping station. The temperature of the germanium crystals, located inside a vacuum sealed chamber, of the detector and the vacuum level of this chamber were monitored throughout the annealing process, via both in-person observation and remote (online) monitoring. The Graphic User Interface (GUI) of an underlying LabVIEW script was utilized for running the monitoring process of the temperature and vacuum pressure values via a local network. To have the option of real-time online monitoring of the temperature, vacuum pressure, we coupled the web application Grafana with the Influx DB of the annealing data, as well as the backup time information of an Uninterruptible Power Supply (UPS) unit used in system.

X-ray Fluorescence Analysis of Waste Sm-Co Magnets: A Rational Approach

Determination of the chemical composition of waste Sm-Co magnets is required for their efficient recycling. The non-stereotypical composition of said magnets makes an analysis extremely challenging. X-ray fluorescence spectrometry is a promising analytical tool for this task. It offers high accuracy and simplicity of sample preparation as it does not require sample dissolution. However, a serious limitation of X-ray fluorescence analysis is the spectral interference of matrix elements and impurities. In this work, a two-stage technique has been developed for the determination of the main components (Sm, Co) and impurities (Fe, Cu, Zr, Hf, Ti, Ni, Mn, Cr) in samples of spent samarium–cobalt magnets using wavelength dispersive X-ray fluorescence spectrometry. In order to overcome the main limitation of the chosen method and to maximize its capabilities of qualitative and quantitative analysis, we propose an approach to the selection of analytical lines and experimental conditions, as well as a preparation method for the calibration standards. The obtained results have been shown to have a good correlation with ICP-OES. The limits of detection are in the range of 0.001–0.02 wt%, and the limits of quantification are 0.003–0.08 wt%.

Fading correction for calibration of a novel 2D OSL-film dosimeter

A new film dosimeter based on optically stimulated luminescence (OSL) was calibrated for high-resolution 2D dosimetry in the context of radiotherapy patient-specific quality assurance (PSQA). The OSL-film signal is linear with the dose and decays with time, in a process called fading. Two models were proposed to characterize the fading: (1) a linear model independent from the delivery and of practical use thanks to the straightforward signal-to-dose conversion, and (2) a delivery-dependent model, to investigate whether a more simplified model may be sufficient to accurately determine the fading independently from the specific-irradiation conditions. The models were used in a nonlinear regression over an experimental dataset acquired with a 6MV photon beam in standard calibration settings. Both models were accurate and showed an adjusted-R 2 of 0.98 (1) and 0.99 (2). The residual analysis on both models allowed to define the minimum scanning time to have a discrepancies between the models <1%. Under this condition the OSL fading can be assumed independent on the irradiation parameters. As a consequence, within these boundary conditions, the linear model can be used for the OSL-film calibration.

Hplc Method Development and Validation for the Simultaneous Estimation of Pitavastatin and Telmisartan

Method validation of both the compounds was done on the basis of ICH guidelines. Validation by HPLC method the wavelength was selected at the isobestic point at which the two drugs can be detected using UV detectors. The selected wavelength was 250nm. Optimized liquid chromatographic condition was obtained by performing many trials for the selection of mobile phase and column, for the separation of Pitavastatin &amp; Telmisartan. The method development was conducted with C18, 250 × 4.6 mm, 5µm particle size, Phenomenex with the flow rate of 1.0mL/min. the optimized mobile phase conditions were Acetonitrile and 10mM Ammonium acetate buffer containing 0.1% formic acid in the ratio of 65:35 v/v. Data of Simultaneous shows retention time for Pitavastatin 5.408 &amp; Telmisartan was 7.183. The method found to be linear, accurate, rugged and robust for validated parameters. The linearity range was determined by external standard calibration method in the concentration range of 10μg/ml to 60μg/ml. The amount of recovery was calculated as 98% – 101% and it was observed that all the values are within the limits. Further the precision of the method was confirmed by the repeatable analysis of sample. The results were found to be precise due to low values of the %RSD. It indicated that the method has good precision. Limit of quantification for Pitavastatin &amp; for Telmisartan 1.554μg/ml and 4.709μg/ml respectively. Similarly limit of detection for Pitavastatin &amp; for Telmisartan 0.647μg/ml and 1.959μg/ml respectively. In the robustness study %RSD obtained for change of flow rate and wavelength and ruggedness for change of analyst was found to be below 2, which was within the acceptance criteria. So, simple, sensitive, accurate, precise RP- HPLC methods were developed and validated for the simultaneous estimation of Pitavastatin &amp; Telmisartan.

A New and Rapid HPLC Method to Determine the Degree of Deacetylation of Glutaraldehyde-Cross-Linked Chitosan.

Chitosan is a linear biopolymer composed of D-glucosamine and N-acetylglucosamine units. The percentage of D-glucosamine in the polymeric chain can vary from one sample to another and is expressed as the degree of deacetylation (DDA). Since this parameter has an impact on many properties, its determination is often critical, and potentiometric titration is a common analytical technique to measure the DDA. Cross-linking with glutaraldehyde is one of the most explored modifications of chitosan; however, the determination of the DDA for the resulting reticulated chitosan resins can be challenging. In this paper, we report a new, rapid, and efficient method to determine the DDA of glutaraldehyde-cross-linked chitosan resins via HPLC. This method relies on the use of 2,4-dinitrophenylhydrazine (DNPH) as a derivatizing agent to measure the level of reticulation of the polymer (LR) after the reticulation step. In this study, we prepare three calibration curves (with an R2 value over 0.92) for three series of reticulated polymers covering a large range of reticulation levels to demonstrate that a correlation can be established between the LR established via HPLC and the DDA obtained via titration. The polymers are derived from three different chitosan starting materials. These standard calibration curves are now used on a routine basis in our lab, and the HPLC method has allowed us to change our DDA analysis time from 20 h to 5 min.

Exploring the impact of the extent of the partially edentulous area on the accuracy of two intraoral scanners

The accuracy of intraoral scans, particularly in edentulous areas, remains a concern despite the increasing use of digital technology, especially intraoral scanners. The purpose of this in vitro study was to assess the impact of the extent of an edentulous area on the accuracy (trueness and precision) of intraoral scans from 2 intraoral scanners. A KaVo dentoform with epoxy resin teeth was used to generate 9 groups with different numbers of teeth removed. A laboratory scanner served as the reference dataset, and 2 intraoral scanners (TRIOS 3 and Primescan AC) were evaluated. A single operator performed all scans following standardized protocols and calibration. Trueness and precision were assessed by using root mean square (RMS) values. Analysis of variance was used to compare trueness and precision values obtained from the 2 scanners and different partially edentulous conditions (α=.05). A significant difference was found in the trueness of intraoral scans of the 2 scanners and under different partially edentulous extensions. Primescan AC exhibited significantly lower trueness than TRIOS 3 (P<.001). For the individual edentulous conditions, Primescan had a significantly higher RMS mean than TRIOS 3 for G0, G3, G4, G6, G7, and G8 (P<.001) and a significantly lower RMS mean than TRIOS 3 for G1 and G4 (P<.001), while no significant difference in RMS mean was found between the 2 scanners for G2 (P=.999). For precision, no significant difference was found between the 2 scanners or different edentulous conditions [(F 8, 90)=1.82, P=.085]. The accuracy of intraoral scans was influenced by the length of edentulous areas and the scanner used. Primescan AC demonstrated lower trueness than TRIOS 3 for most partially edentulous conditions, while the scanners were similar in precision. These findings highlight the need for careful scanner selection in specific clinical situations, as scanning accuracy may vary depending on the scanner and edentulous condition.

A new direct extraction by gas-chromatography with flame ionization detector coupled to head space method for the determination of alcohol content of high matrix wine products

Detection, identification, and quantitation of alcohol in any matrix rich medium is a common practice although sample preparation is inevitable and time consuming. A sensitive, precise and ultimately wide range method for detection, identification and quantification of main content/residual/impurity alcohols without any matrix interference that can be used for production phase quality control, pharmaceutical and/or bio-technological refinement or toxicological evaluation and for forensics is always needed. Even for quality control also for toxicological considerations, ethanol (EtOH) and very similar compound methanol has to be detected and identified definitely becomes vital. However, with the fermented products, the matrix becomes a challenging process, makes the methods inefficient or more extraction methods have to be implanted. Here we propose a new simple and reliable direct extraction method has been developed for the determination of alcohol content of high matrix wine products using the gas-chromatography with flame ionization detector coupled to head space. The method was developed with a rich and complex component mixture of fermented alcoholic beverages (wine) with very high matrix effects. Isopropanol (IPA) was preferred as an internal standard, and Triton X-100 (TX-100) was used as diluting solution in this method. The amount of TX-100, extraction temperature, and the total volume of solution in head space vial (20 mL) were optimized. 2.5% TX-100, 80 °C extraction temperature, and 2.0 ml of total volume were used as optimum condition. Stationary phase was the fused silica, Agilent J&amp;W DB-624 column (30 m x 320 m x 1.8 m) and Helium was used as a mobile phase. GC oven temperature programme was 40C (5 min), 5C/min ramp to 60C (0 min) and 30C/min to 150C (1 min). Performance of the method was assessed by evaluating the recovery, accuracy, precision, linearity, limits of detection (LOD) and limit of quantification (LOQ). Calibration curve was drawn between the concentration of 2.5% to 15.0% EtOH (y = 1.572x – 0.702, R² = 0.9960, y; the ratio of peak area of EtOH to IPA, x: EtOH%). The slopes of standard addition and external calibration curve were statistically same. Recovery of the method was 97.5 ± 3.5 for tree different concentrations and the precision was %5.8 (n= 11). LOD and LOQ were calculated as 0.80% and 2.5%, respectively. The proposed method has a potential for application into the industry and academia with determination of the alcohol content/residual/impurity and also check the quality and content of the fermented medium without the effect of matrix.

Rapid and sensitive electrochemical detection of oxidized form of glutathione in whole blood samples using Bi-metallic nanocomposites

We report a facile one-pot synthesis of bimetallic nickel-gold (Ni–Au) nanocomposite for ultra-sensitive and selective electrochemical detection of oxidized glutathione (GSSG) by electrochemical deposition on fluorine doped tin oxide (FTO) substrate. The electrodeposition of Ni–Au nanocomposite on FTO was confirmed by various characterization techniques such as field emission scanning electron microscopy (FE-SEM), X-ray diffractometer (XRD) and Fourier transform infra-red (FTIR) spectroscopy. The cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) was utilized for the electrochemical characterization of glutathione reductase (GR)/Ni–Au/FTO working electrode at each stage of modification. The GR enzyme immobilized on the Ni–Au/FTO working electrode via glutaraldehyde cross-linking exhibited excellent selectivity against GSSG in the presence of nicotinamide adenine dinucleotide phosphate (NADPH). The immobilized GR enzyme breaks down the GSSG to reduced glutathione (GSH) and converting NADPH to NADP+ whereby generating an electron for the electrochemical sensing of GSSG. The synergistic behavior of bimetals and good electro-catalytic property of the fabricated sensor provided a broad linear detection range from 1 fM to 1 μM with a limit of detection (LOD) of 6.8 fM, limit of quantification (LOQ) of 20.41 fM and sensitivity of 0.024 mA/μM/cm2. The interference with other molecules such as dopamine, glycine, ascorbic acid, uric acid and glucose was found to be negligible due to the better selectivity of GR enzyme towards GSSG. The shelf-life and response time of the fabricated electrode was found to be 30 days and 32 s, respectively. The real sample analysis of GSSG in whole blood samples showed average recovery percentage from 95 to 101% which matched well with the standard calibration plot of the fabricated sensor with relative standard deviation (RSD) below 10%.

LC-MS accurate quantification of a tryptic peptide co-eluted with an isobaric interference by using in-source collisional purification.

Interferences from isobaric and isomeric compounds represent a common problem in liquid chromatography coupled to mass spectrometry (LC-MS). In this paper, in-source purification and chromatographic separation were combined with the aim of identifying isobaric contamination and quantifying accurately a compound despite the presence of an isobaric co-eluted interference. This is achieved by totally fragmenting in-source the precursor ions of the isobaric interference providing then LC-pseudo-MS2 capability, which allows an accurate quantification without the need for optimizing the chromatographic conditions to separate the co-eluted interference. To illustrate this concept, mixtures of tryptic and non-tryptic peptides were used. The ratio of peak areas of the tryptic peptide and its isotopically labelled internal standard was used not only for quantification with an internal standard calibration curve but also to know (1) if an isobaric interference co-eluted with the tryptic peptide; and (2) what is the minimum cone voltage necessary to ensure the complete removal of isobaric interference. This strategy was applied to quantify the tryptic peptide of two standards with known concentrations and, intentionally contaminated with the isobaric interference. The confidence intervals of the concentrations calculated with the internal standard calibration curve were 8.0 ± 0.5 μM (prepared at 8.0 μM) and 15.7 ± 0.5 μM (prepared at 16.1 μM) that confirm the tryptic peptide can be correctly quantified by in-source purification without the need for improving the chromatographic separation from its isobaric interference.

Technical note: Discrete in situ vapor sampling for subsequent lab-based water stable isotope analysis

Abstract. Methodological advancements have been made in in situ observations of water stable isotopes that have provided valuable insights into ecohydrological processes. The continuous measurement capabilities of laser-based analyzers allow for high temporal resolutions and non-destructive minimally invasive study designs of such in situ approaches. However, isotope analyzers are expensive, heavy, and require shelter and access to electrical power, which impedes many in situ assays. Therefore, we developed a new inexpensive technique to collect discrete water vapor samples in the field via diffusion-tight inflatable bags that can later be analyzed in the lab. In a series of structured experiments, we tested different procedural settings, bag materials, and closure types for diffusion tightness during storage as well as for practical handling during filling and extraction. To facilitate reuse of sampling bags, we present a conditioning procedure using ambient air as primer. In order to validate our method, direct measurements through hydrophobic in situ probes were compared to repeated measurements of vapor sampled with our bags from the same source. All steps are summarized in a detailed standard operating procedure (SOP). This procedure represents the preparation and measurement of calibration and validation vapor standards necessary for processing of unknown field-collected vapor samples in the foreseen application. By performing pertinent calibration procedures, accuracy was better than 0.4 ‰ for δ18O and 1.9 ‰ for δ2H after 1 d of storage. Our technique is particularly suitable when used in combination with minimally invasive water vapor sampling in situ probes that have already been employed for soils and tree xylem. It is an important step towards minimally invasive monitoring of stable isotope distributions and also time series in virtually undisturbed soils and trees without the need to have an analyzer in the field. It is therefore a promising tool for many applications in ecohydrology and meteorology.

Improved Calibration of Eye-in-Hand Robotic Vision System Based on Binocular Sensor.

Eye-in-hand robotic binocular sensor systems are indispensable equipment in the modern manufacturing industry. However, because of the intrinsic deficiencies of the binocular sensor, such as the circle of confusion and observed error, the accuracy of the calibration matrix between the binocular sensor and the robot end is likely to decline. These deficiencies cause low accuracy of the matrix calibrated by the traditional method. In order to address this, an improved calibration method for the eye-in-hand robotic vision system based on the binocular sensor is proposed. First, to improve the accuracy of data used for solving the calibration matrix, a circle of confusion rectification method is proposed, which rectifies the position of the pixel in images in order to make the detected geometric feature close to the real situation. Subsequently, a transformation error correction method with the strong geometric constraint of a standard multi-target reference calibrator is developed, which introduces the observed error to the calibration matrix updating model. Finally, the effectiveness of the proposed method is validated by a series of experiments. The results show that the distance error is reduced to 0.080 mm from 0.192 mm compared with the traditional calibration method. Moreover, the measurement accuracy of local reference points with updated calibration results from the field is superior to 0.056 mm.

A simple and rapid external standard calibration HPLC method for determination of lumefantrine in dried blood spot samples from malaria patients in Botswana.

A simple external calibration liquid chromatography-diode array detector method was developed, validated, and applied for the determination of lumefantrine (Lum) in dried blood spot (DBS) samples collected from malaria patients in Botswana. The samples were validated in accordance with the United States Food and Drug Administration guidelines for bioanalytical methods after sample preparation using solid-liquid extraction. Separation was achieved using an XTerra C18 column (50 × 4.6mm,5μm), and a binary solvent system of acetonitrile and water adjusted to pH2.3 was used as the mobile phase. The validated method was applied for the determination of Lum in DBS samples collected from malaria patients infected with Plasmodium falciparum in Botswana. The calibration curve was linear between 0.5 and 12 μg/mL with a coefficient of determination (R2 ) of 0.9996. The limit of detection and the lower limit of quantification were 0.5 and 1.4μg/mL, respectively. The efficiency of extraction measured as percentage recovery ranged between 84.2% and 107.8% at the three quality control (QC) levels, that is, low QC, mid QC, and high QC. In conclusion, data suggest that the method is suitable for the determination of trace Lum in biofluids and can also be used for therapeutic drug monitoring and pharmacokinetic profiling.

Study on the effect of calibration standards prepared with different matrix on the accuracy of bile acid quantification using LC-MS/MS

The transition from relative to absolute quantification of metabolites is the future development trend of mass spectrometry-based metabolomics research, which could fundamentally solve the problem of comparability of data between different laboratories. However, absolute quantification of endogenous molecules is largely hampered by the lack of analyte-free matrix, leading to uncertainty and inconsistency in the preparation of calibration standards. Bile acids (BAs) are an important class of biomarkers that play a key role in disease progression. In this paper, the quantitative accuracy of calibration curves prepared in neat solvent (NSCCs), charcoal stripped matrix (SMCCs) and authentic matrix (AMCCs) were validated using quality control samples (QCs) prepared in authentic matrix. Results suggested that AMCCs could largely minimize the confidence interval (C.I.) and the deviation in accuracy compared with NSCCs and SMCCs when measured concentration is higher than 20% of the background level. In addition, experimental data demonstrated that two-step calibration strategy proposed here is a promising and reliable alternative strategy to quantify endogenous BAs in biological sample.