One-point Calibration Research Articles

Planar Laser Induced Fluorescence of OH for Thermometry in a Flow Field Based on Two Temperature Point Calibration Method

In view of the uncertainty in the calibration process of two-color plane laser-induced fluorescence (PLIF) temperature measurement, a new calibration method is proposed, in which the influence of fluorescence yield is considered. The calibration process was carried out at high and low temperature region, respectively. Then, the bias of thermometry results origin from quenching is restrained. This new calibration method is validated in a jet flame with temperature range of 1300–1800 K. Here, the temperature results from Coherent Anti-Stokes Raman scattering (CARS), single-point calibrated PLIF, and two-point calibrated PLIF are all acquired with the maximum standard errors of 13 K, 36 K, and 37 K, respectively. The temperature deviation between the average results from PLIF and Coherent Anti-Stokes Raman scattering (CARS) is 120 K and 10 K, when the two-point and one-point calibration methods are used. Therefore, the two-point calibrated PLIF is preferred in the combustion field, especially with a large temperature range and strong quenching coefficient.

In-line monitoring of protein concentration with MIR spectroscopy during UFDF.

Rapid increase of product titers in upstream processes has presented challenges for downstream processing, where purification costs increase linearly with the increase of the product yield. Hence, innovative solutions are becoming increasingly popular. Process Analytical Technology (PAT) tools, such as spectroscopic techniques, are on the rise due to their capacity to provide real-time, precise analytics. This ensures consistent product quality and increased process understanding, as well as process control. Mid-infrared spectroscopy (MIR) has emerged as a highly promising technique within recent years, owing to its ability to monitor several critical process parameters at the same time and unchallenging spectral analysis and data interpretation. For in-line monitoring, Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR) is a method of choice, as it enables reliable measurements in a liquid environment, even though water absorption bands are present in the region of interest. Here, we present MIR spectroscopy as a monitoring tool of critical process parameters in ultrafiltration/diafiltration (UFDF). MIR spectrometer was integrated in the UFDF process in an in-line fashion through a single-use flow cell containing a single bounce silicon ATR crystal. The results indicate that the one-point calibration algorithm applied to the MIR spectra, predicts highly accurate protein concentrations, as compared with validated offline analytical methods.

Self-absorption correction method for one-point calibration laser-induced breakdown spectroscopy.

As an important variant of calibration-free laser-induced breakdown spectroscopy (CF-LIBS), one-point calibration LIBS (OPC-LIBS) corrects the Boltzmann plot of the unknown sample by using one known sample and obtains higher quantitative accuracy than CF-LIBS. However, the self-absorption effect restricts its accuracy. In this work, a new self-absorption correction (SAC) method for OPC-LIBS is proposed to solve this problem. This method uses an algorithm to correct the self-absorption and does not require the calculation of the self-absorption coefficient. To verify the effectiveness of this SAC method, Ti, V, and Al elements in two titanium alloys were determined by classical OPC-LIBS and OPC-LIBS with SAC. The average relative errors (AREs) of all elements in the two samples were decreased from 8.78% and 9.28% to 8.07% and 7.56%, respectively. The results demonstrated the effectiveness of this SAC method for OPC-LIBS.

An Energy-Efficient BJT-Based Temperature Sensor with ±0.8 °C (3σ) Inaccuracy from −50 to 150 °C

This article presents an energy-efficient BJT-based temperature sensor. The output of sensing front-ends is modulated by employing an incremental Δ-Σ ADC as a readout interface. The cascoded floating-inverter-based dynamic amplifier (FIA) is used as the integrator instead of the conventional operational transconductance amplifier (OTA) to achieve a low power consumption. To enhance the accuracy, chopping and dynamic element matching (DEM) are applied to eliminate the component mismatch error while β-compensation resistor and optimized bias current are used to minimize the effect of β variation. Fabricated in a standard 180-nm CMOS process, this sensor has an active area of 0.13 mm2. While dissipating only 45.7 μW in total, the sensor achieves an inaccuracy of ±0.8 °C (3σ) from -50 °C to 150 °C after one-point calibration.

Facile Density Measurement Method for High-Concentration Sulfate Determination

In this study, a fast, facile and high accuracy method for high concentration sulfate determination is presented. The method is based on precipitation of sulfate ions with barium ions. The sulfate amount is quantified by measurement of the density of the barium and sulfate ion solutions before mixing, and the density of the supernatant after mixing. A calibration curve for sulfate concentration between 2.5 and 5.5 M in vanadium electrolyte was performed, obtaining a precision better than 0.7%, in agreement with a propagation-of-error analysis. Accuracy is determined by one-point calibration against a sample with known sulfate concentration and is at best the same as the precision. Within the precision of the method, no systematic effect of the presence of other ions/interferents (vanadium, phosphate) on the sulfate determination is observed.

Application of quantitative analysis for aluminum alloy in femtosecond laser-ablation spark-induced breakdown spectroscopy using one-point and multi-line calibration

To achieve the quantitative elemental analysis of aluminum alloy samples, the one-point and multi-line calibration (OP-MLC) method and femtosecond laser-ablation spark-induced breakdown spectroscopy (fs-LA-SIBS) were combined in this study. An ultrafast Ti: sapphire laser with high single-pulse energy and high repetition–rate operation was used as the laser source to ablate the sample at a 1k Hz pulse repetition rate and achieve re-excitation using spark discharge. Subsequently, an enhanced spectral peak intensity was achieved, which increased the sensitivity and analytical capabilities of laser-induced breakdown spectroscopy (LIBS) technique. Considering only one confirmed sample, the OP-MLC method was used to calculate the concentration ratios of trace elements Mg, Cr, Cu, Mn and Zn in four aluminum alloy samples to the calibration samples by the integral intensity ratio of the elemental characteristic lines between the two samples. The average relative errors with the identified concentrations were 3.99%, 15.13%, 8.76%, 9.30% and 9.64%, respectively. The results showed that the combination of OP-MLC method and fs-LA-SIBS has good accuracy in the quantitative analysis of elements, and has the advantages of simplicity, rapidity and high sensitivity.

Reducing matrix effects on the quantification of Ca, Mg, and Fe in soybean leaf samples using calibration-free LIBS and one-point calibration

Matrix effects are one of the most difficult analytical challenges in laser-induced breakdown spectroscopy (LIBS), since signal intensity depends on both element concentration and matrix. For instance, the measurement of nutrients in plant leaves using LIBS is notably impacted by matrix effects because of differences in fertilizer application, weather, soil properties, and health levels. Thus, to overcome matrix effects on the quantification of nutrients in plant leaves, we propose the use of CF-LIBS, in which the intensity of emission lines is corrected using the one-point calibration (OPC) method. In this study, we analyzed thirty soybean leaf samples of cultivars from various locations and health levels with 0.5 wt% TiO2 (internal standard), for which the matrix effects were visible in the calibration curves. Normalization using a Ti II line increased the average r2 of the calibration curves for Ca II, Mg II, and Fe II from 0.24 to 0.73, but this was insufficient to adjust for the variations in plasma temperature and for the degree to which the elements were ionized. With the proposed models and using just one sample to calibrate the OPC factors, we obtained an accuracy >92% and an average r2 of 0.87 for the quantification of Ca, Mg, and Fe in relation to the atomic absorption spectroscopy (AAS). We then concluded that CF-LIBS with the OPC corrections might mitigate matrix effects in LIBS analysis of soybean leaf samples. More studies are needed to assess whether the OPC factors calibrated with soybean leaf samples can be applied to other species.

Novel one-point calibration strategy for high-throughput quantitation of microcystins in freshwater using LC-MS/MS

Precise quantification of microcystins (MCs) in freshwater is crucial for environmental monitoring and human health. However, the preparation of traditional multi-sample external calibration curve (MSCC) is time consuming and prone to error. Here, a novel one-point calibration strategy including one sample multi-point calibration curve (OSCC) and in sample calibration curve (ISCC) is proposed for the quantitation of eight MCs in freshwater lakes using liquid chromatography tandem mass spectrometry (LC-MS/MS). The multiple isotopologue reaction monitoring (MIRM) of MCs and its 15N-labelled internal standards were used for OSCC and ISCC, respectively. The isotopic abundance of each MIRM channel could be calculated and measured accurately. Additionally, this strategy was comprehensively validated and showed good performance in selectivity, sensitivity, accuracy and precision as the traditional MSCC. Interestingly, OSCC could realize sample dilution by monitoring the less abundant MIRM transitions, while ISCC remove blank matrixes and generate calibration curve in each study samples. Furthermore, the proposed methodology was successfully applied to analyze several freshwater lake samples contaminated by MCs. Considering the advantages of excluding the MSCC preparation, simplified workflows and improved throughput, OSCC and ISCC will be favored for MCs monitoring and as an emerging approach in environmental pollutant control and prevention.

One-point calibration quantitative elemental analysis of Cu-Zn-Ag alloys with microchip laser-based SD-LIBS

Microchip laser-based spark-discharge assisted laser-induced breakdown spectroscopy (SD-LIBS) combined with one-point calibration (OPC) method was developed to realize quantitative elemental analysis of Cu-Zn-Ag alloy samples. OPC method makes it possible to use zinc atomic lines with unknown transition probabilities in the procedures of quantitative elemental analysis using a calibration-free algorithm. The relative errors of quantitative analysis of copper, zinc and silver in Cu-Zn-Ag alloy samples reached to 0.86%, 0.99% and 5.17% under current experimental condition, respectively. This work demonstrated that microchip laser-based SD-LIBS combined with OPC method can be used to realize convenient quantitative elemental analysis of zinc contained alloy samples with reliable accuracy.

Accurate elemental analysis with variant one-point calibration laser-induced breakdown spectroscopy capable of using analytical lines with unknown transition probabilities.

Calibration-free laser-induced breakdown spectroscopy (CF-LIBS) is a very useful elemental analysis technique. However, it requires knowledge of transition probabilities of the analytical lines. To solve this problem, a variant one-point calibration (OPC) LIBS method was proposed. Quantitative elemental analysis on Cu-Zn-Ag-Au alloys was realized with this method capable of using zinc analytical lines with unknown transition probabilities. The relative error was demonstrated to be less than 3.3%. This variant OPC method will be helpful for quantitative elemental analysis of different samples using CF-LIBS, no matter whether the transition probabilities of the observed lines are known or unknown.

Can postmortem toxicological findings be influenced by a further release of fentanyl from transdermal patches?–A pilot study using the pig model

Due to its high potency, fentanyl is increasingly misused by drug addicts. Yet, interpretation of PM toxicological results is challenging due to different issues leading to falsified higher fentanyl concentrations in blood. On the one hand, fentanyl has a high tendency for PM redistribution (PMR). On the other hand, a PM drug release from applied transdermal patches (TP) can alter blood concentrations. However, the latter has not yet been examined in a controlled manner. Thus, it should be investigated whether fentanyl is released from TP into adipose tissue (AT) or even blood near to or under a TP applied PM. In the context of another study, two fentanyl TP (TP 1: 100 μg/h and TP 2: 25 μg/h) were sticked PM to one pig each. TP 1 was applied to a shaved area on the left shoulder, TP 2 near the right groin. After 24, 48 and 72 h, AT was collected with a distance of approx. 5 (close), 10 (middle) and 15 cm (far) to the patch, respectively. In addition, peripheral blood (PB) and heart blood (HB) were sampled. After 72 hours, the TP was removed and AT was collected under the patch. HB and PB were analyzed after protein precipitation applying a one-point calibration. Regarding AT, quantification of fentanyl was performed after evaporation of the homogenates using a standard addition approach. All extracts were analyzed by LC-MS/MS. Highest fentanyl concentrations were detected in AT collected under the TP after 72 h, with concentrations of approx. 2,700 ng/g (TP 1) and 9,900 ng/g (TP 2). Regarding AT retrieved with a distance to TP 1, fentanyl could be found in every specimen collected after 24 h with highest concentrations of approx. 6.1 ng/g close to the TP, followed by 0.25 (middle) and 0.44 ng/g (far). After 48 h, analysis of AT was only positive for fentanyl in samples collected with a close (0.56 ng/g) and middle (0.19 ng/g) distance to the TP. Applying TP 2, only AT specimen retrieved after 48 were positive for fentanyl. Additionally, fentanyl could be detected in PB drawn after 48 h (0.14 ng/mL) applying TP 2. Screening of HB using patches 1 and 2 went negative for fentanyl. Independent of the dose, fentanyl appears to be released PM from TP into the underlying AT, with higher concentrations applying TP 2 despite a lower fentanyl releasing concentration. This effect might be explained by the respective skin conditions at the application sites, possibly leading to a different permeability of fentanyl. A small amount of the drug is distributed into surrounding AT. Yet, this effect seems to be more pronounced using TP with high releasing concentrations. Additionally, verification of fentanyl in PB could only be obtained after 48 h applying TP 2. The present study shows that fentanyl is released PM from sticked TP. This effect should be considered when interpreting PM findings. In addition, if fentanyl TP are applied chronically, PM blood concentrations of samples collected near to the TP could further be increased due to the subcutaneous fentanyl depot. In future studies, the extent of PMR after an antemortem application of fentanyl TP should be investigated to complement the data on interpretation of PM toxicological findings.

A One-Point Calibration Design for Hybrid Eye Typing Interface

We present an eye typing interface with one-point calibration, which is a two-stage design. The characters are clustered in groups of four characters. Users select a cluster by gazing at it in the first stage and then select the desired character by following its movement in the second stage. A user study was conducted to explore the impact of auditory and visual feedback on typing performance and user experience of this novel interface. Results show that participants can quickly learn how to use the system, and an average typing speed of 4.7 WPM can be reached without lengthy training. The subjective data of participants revealed that users preferred visual feedback over auditory feedback while using the interface. The user study indicates that this eye typing interface can be used for walk-up-and-use interactions, as it is easily understood and robust to eye-tracking inaccuracies. Potential areas of application, as well as possibilities for further improvements, are discussed.

Relative response factors and multiple regression models in liquid chromatography to quantify low-dosed components using alternative standards-proof of concept: total Δ9-THC content in cannabis flowers using CBD as reference.

A classical quantitative analysis in liquid chromatography is performed using either a one-point calibration or a calibration line, prepared using a reference standard of the compound(s) of interest. However, in some cases, adequate reference standards may be very expensive, rare to obtain, or have limited shelf-life properties. Also, in herbal matrices, multiple compounds could be necessary to be quantified, needing a whole series of different (related) reference standards. In these cases, the use of relative response (sometimes called relative correction factors) factors (RRFs) towards reference standards, different of the compound to be quantified, gained attraction. This study performed a comparison of the use of RRFs and linear relative response factor models (LRRFM) for the quantification of targeted low-dosed compounds using an alternative standard, since it is known that classical RRFs often fail in lower concentration ranges. For this purpose, the determination of the total Δ9-tetrahydrocannabinol (Δ9-THC + Δ9-THC-A) content in dried cannabis flowers, using UHPLC-DAD, was used as a case study. A chromatographic method was implemented and validated, and the use of classical calibration lines, classical RRF, and the LRRFM was applied and compared, with special focus on the concentration around 0.2% (w/w) total Δ9-THC, the legal limit (in most European countries) in these products. Results showed that the newly presented and validated LRRFM approach outperformed the classical RRFs, especially in the low-concentration ranges and that concentrations obtained with the LRRFM were in accordance with the interpolation results obtained with a calibration line.

Study of the effects of detection times in laser-induced breakdown spectroscopy and missed variation of plasma parameters with gate width

The time control of signal acquisition in laser-induced breakdown spectroscopy (LIBS) is critical to the quantification of elements in samples. Upon interacting with the laser pulse, the plasma expands and then cools rapidly in tens of microseconds, undergoing temperature variations of over 50,000 K. In the LIBS technique, the signal acquisition is controlled with the delay time, which is the time between the emission of the laser pulse and the reading of the spectrum, and the gate width, which is the integration time of the spectrometer. Although the relationship of the delay time with the measured plasma temperature and electron density is well-known in the literature, little is known about how these parameters vary with different gate widths. Thus, the objective of this work was to evaluate how the measured plasma parameters and the signal-to-noise ratio (SNR) of an atomic line change with different values of delay time and gate width. For this study, two sets of samples were prepared: i) pure NaCl and ii) NaCl with 20 wt% H3BO3, and at concentrations of 1 and 3 wt% Ca. TiO2 and CuSO4 were also added to these samples to facilitate plasma temperature and electron density calculations, which were carried out using a Saha-Boltzmann plot corrected with the one-point calibration method. The results of this study indicated that the measured plasma parameters did not vary with the gate width, even though the SNR of the Ca I line at 643.9 nm increased as the gate width did. Furthermore, the use of the concept of local thermodynamic equilibrium was verified even with long gate widths (≥ 20 μs), except for the 4 μs delay time. Studies with other samples and other combinations of LIBS system parameters, e.g., at sub atmospheric pressure, should be done to confirm and expand these findings.

High-Performance Thin-Layer Chromatography-Immunostaining as a Technique for the Characterization of Whey Protein Enrichment in Edam Cheese.

Whey protein-enriched cheese can be produced by means of a high-temperature treatment of a part of the cheese milk. In this way, the nutritional quality of the resulting cheeses can be increased while resources are conserved. High-performance thin-layer chromatography-immunostaining (HPTLC-IS) using specific β-lactoglobulin (β-LG) antibodies was applied to study the implementation and stability of β-LG in two different sample sets of whey protein-enriched Edam model cheeses, including industrial-scale ones. Two methods were compared for the extraction of the proteins/peptides from the cheese samples. By applying tryptic hydrolysis directly from a suspended cheese sample instead of a supernatant of a centrifuged suspension, a better yield was obtained for the extraction of β-LG. When applying this method, it was found that selected epitopes in the tryptic β-LG peptides remain stable over the ripening period of the cheese. For four of the tryptic β-LG peptides detected by immunostaining, the amino acid sequence was identified using MALDI-TOF-MS/MS. One of the peptides identified was the semi-tryptic peptide VYVEELKPTP. A linear relationship was found between the content of this peptide in cheese and the proportion of high-heated milk in the cheese milk. β-LG enrichment factors of 1.72 (n = 3, sample set I) and 1.33 ± 0.19 (n = 1, sample set II) were determined for the cheese samples containing 30% high-heated milk compared to the non-enriched samples. The relative β-LG contents in the cheese samples with 30% high-heated milk were calculated to be 4.35% ± 0.39% (sample set I) and 9.11% ± 0.29% (sample set II) using a one-point calibration. It can be concluded that the HPTLC-IS method used is a suitable tool for the analysis of whey protein accumulation in cheese, being therefore potentially directly applicable on an industrial scale. For more accurate quantification of the whey protein content in cheese, an enhanced calibration curve needs to be applied.

Accuracy Improvement for Minor Elements Determination Using Modified Self-Absorption Correction and One-Point Calibration in Calibration-Free Laser-Induced Breakdown Spectroscopy

Accuracy Improvement for Minor Elements Determination Using Modified Self-Absorption Correction and One-Point Calibration in Calibration-Free Laser-Induced Breakdown Spectroscopy

One-point calibration laser-induced breakdown spectroscopy for the quantitative analysis of EAST-like plasma-facing materials

An improved in vacuo in situ quantitative analytical method for the deposited impurities on the inner-wall of tokamak device is reported.

Development of a novel label-free all-fiber optofluidic biosensor based on Fresnel reflection and its applications

A novel, compact, cost-effective, and robust label-free all-fiber optofluidic biosensor (LF-AOB) based on Fresnel reflection mechanism was built through integrating single-multi mode fiber coupler and highly sensitive micro-photodetector. The Fresnel reflection light intensity detected by the LF-AOB greatly depended on the RI change on the end-surface of the fiber probe according to experimental and simulation results. The capability of the LF-AOB for real-time in situ detection in optofluidic system were verified by measuring salt and protein solution, and the lowest limit of detection was 1.0 × 10−6 RIU. Our proposed theory can effectively eliminate the influence of light intensity fluctuation, and one-point calibration method of sensor performance is conducive for rapid and convenient detection of targets. Label-free sensitive detection of SARS-Cov-2 Spike protein receptor-binding domain (S-RBD) and the binding kinetics assay between S-RBD and anti-S-RBD antibody were achieved using the LF-AOB. These contributed to the elegant design of all-fiber optical system with high efficiency, high resolution and sensitivity of micro-photodetector, and enhanced interaction between the light and the samples at the liquid-sensor interface because of the large surface area of the multi-mode fiber probe. The LF-AOB can be extended as a universal sensing platform to measure other factors associated with refractive index because its high sensitivity, low sample consumption (∼160 nL), and capability of real-time in situ detection.

Rapid stoichiometric analysis of calcium‑phosphorus ratio on hydroxyapatite targets by one-point calibration laser-induced breakdown spectroscopy

The calcium‑phosphorus ratio (Ca/P) has an important role in calcium phosphate applications, as a slight change in this ratio results in substantial modifications of their characteristics. Hydroxyapatite is a bioactive ceramic of the calcium phosphate family, and its composition and crystalline structure are similar to the human bone. For this reason, it is widely used to promote bone integration in prosthetics and scaffolds. Prosthetics are usually made of metal and coated with bioceramics and the some techniques used to make these coatings depositions conserve the stoichiometry from the target during deposition. Therefore, studying the target Ca/P is a way to guaranteeing the final deposition stoichiometry. In this study, we investigated the One Point Calibration – Laser Induced Breakdown Spectroscopy (OPC-LIBS) method for the measurement of the Ca/P of hydroxyapatite targets. This method is quantitative, based on the determination of correction parameters via analysis of a standard sample with known stoichiometry. Results were compared to well-established techniques of X-ray Fluorescence (XRF) and Atomic Absorption Spectroscopy (AAS) and showed that the deviation in the difference is less than 5%, proposing a substitute for elemental analysis. Moreover, this method has technical advantages such as rapid measurements, no need for sample preparation or destruction and easy automation.

A Digital Improvement-Trimming a Digital Temperature Sensor with EEPROM Reprogrammable Fuses.

An EEPROM (electrically erasable programmable read-only memory) reprogrammable fuse for trimming a digital temperature sensor is designed in a 0.18-µm CMOS EEPROM. The fuse uses EEPROM memory cells, which allow multiple programming cycles by modifying the stored data on the digital trim codes applied to the thermal sensor. By reprogramming the fuse, the temperature sensor can be adjusted with an increased trim variation in order to achieve higher accuracy. Experimental results for the trimmed digital sensor showed a +1.5/−1.0 ℃ inaccuracy in the temperature range of −20 to 125 ℃ for 25 trimmed DTS samples at 1.8 V by one-point calibration. Furthermore, an average mean of 0.40 ℃ and a standard deviation of 0.70 ℃ temperature error were obtained in the same temperature range for power supply voltages from 1.7 to 1.9 V. Thus, the digital sensor exhibits similar performances for the entire power supply range of 1.7 to 3.6 V.