Calibration-free Approach Research Articles

Stand-off laser induced breakdown spectroscopy on meteorites: calibration-free approach

In this work, LIBS (Laser Induced Breakdown Spectroscopy) capability to operate in stand-off configuration, without the need of a direct contact with the sample, has been coupled with the calibration-free (CF) approach to LIBS data analysis. The latter does not require the use of standard calibration. The feasibility of the calibration free method on stand-off LIBS spectra has been thereby tested. The quantitative analysis was performed on samples of two well-known meteorites, Toluca (iron meteorite) and Sahara 98222 (L6 chondrite) by using a stand-off configuration at a distance of 5 m. The plasma temperature and the electron number densities were determined for each sample and for each laser shot in order to apply the CF method. For the Toluca meteorite sample Fe, Ni and Co content was quantified during the depth profile. For the Sahara 98222 major and minor elements (Fe, Mg, Si, Na, Ti, Al, Cr, Mn, Ca, Ni, Co) were analysed by averaging different meteorite zones because of its strong inhomogeneity. Results demonstrate the possibility of remote analysis of minor bodies and space debris.

Model comparison for GLONASS RTK with low-cost receivers

GLONASS ambiguity resolution in differential real-time kinematic (RTK) processing is affected by inter-frequency phase biases (IFPBs). Previous studies empirically determined that IFPBs are linearly dependent on the frequency channel number and calibration values have been derived to mitigate these biases for geodetic receivers. The corresponding IFPB-constrained model is currently the de facto approach in RTK, but the growing market of GNSS receivers, and especially low-cost receivers, makes calibration and proper handling of metadata a complex endeavor. Since IFPBs originate from timing offsets occurring between the carrier phase and the code measurements, we confirm other studies that show that IFPBs are not exactly linearly dependent on the frequency channel number, but rather linearly dependent on the channel wavelength, which calls for a modification in the GLONASS functional model. As an alternative to calibration, we revisit a calibration-free method for GLONASS ambiguity resolution and provide new insights into its applicability. A practical experiment illustrates that the calibration-free approach can offer better ambiguity fixing performance when the uncertainty on the IFPB parameter is large, unless partial ambiguity resolution is performed.

Calibration-Free Robot-Sensor Calibration approach based on Second-Order Cone Programming

In order to overcome the restrictions of traditional robot-sensor calibration method which solve the tool-camera transformation and robot-world transformation rely on calibration target, a calibration-free approach that solve the robot-sensor calibration problem of the form AX = YB based on Second-Order Cone Programming is proposed. First, a Structure-From-Motion approach was used to recover the camera motion matrix up to scaling. Then rotation and translation matrix in calibration equation were parameterized by dual quaternion theory. Finally, the Second-Order Cone Programming method was used to simultaneously solve the optimal solution of camera motion matrix scale factor, the robot-world and hand-eye relation. The experimental results indicate that the calibration precision of rotation relative error is 3.998% and the translation relative error is 0.117% in defect of calibration target as 3D benchmark. Compared with similar methods, the proposed method can effectively improve the calibration accuracy of the robot-world and hand-eye relation, and extend the application field of robot-sensor calibration method.

Elemental Investigation of the Leaf and Seed of Coriander Plant by Synchrotron Radiation X-ray Fluorescence Spectroscopy

This study describes the potential of synchrotron radiation X-ray fluorescence spectroscopy technique for the investigation of elements present in the parts of the medicinally important coriander plant: leaf and seed. For this, X-ray fluorescence spectra of the leaf and seed of coriander plants have been recorded by exciting synchrotron radiation of energy 13 keV. The analyses of the procured spectrum show the presence of elements: potassium, calcium, titanium, chromium, manganese, iron, nickel, copper, zinc, and arsenic. A calibration free approach, PyMca has been used for the quantitative estimation of the detected elements in the leaf and seed of the coriander plant.

Determination of Metals Present in Textile Dyes Using Laser-Induced Breakdown Spectroscopy and Cross-Validation Using Inductively Coupled Plasma/Atomic Emission Spectroscopy

Laser-induced breakdown spectroscopy (LIBS) was used for the quantitative analysis of elements present in textile dyes at ambient pressure via the fundamental mode (1064 nm) of a Nd:YAG pulsed laser. Three samples were collected for this purpose. Spectra of textile dyes were acquired using an HR spectrometer (LIBS2000+, Ocean Optics, Inc.) having an optical resolution of 0.06 nm in the spectral range of 200 to 720 nm. Toxic metals like Cr, Cu, Fe, Ni, and Zn along with other elements like Al, Mg, Ca, and Na were revealed to exist in the samples. The %-age concentrations of the detected elements were measured by means of standard calibration curve method, intensities of every emission from every species, and calibration-free (CF) LIBS approach. Only Sample 3 was found to contain heavy metals like Cr, Cu, and Ni above the prescribed limit. The results using LIBS were found to be in good agreement when compared to outcomes of inductively coupled plasma/atomic emission spectroscopy (ICP/AES).

Quantitative analysis of metals in waste foundry sands by calibration free-laser induced breakdown spectroscopy

Laser-induced breakdown spectroscopy (LIBS) was applied for quantitative analysis of the elemental composition of waste molding and core sands produced from industry as part of the casting process. To perform the analysis, waste foundry sands (WFS) were collected from metalcasting foundries and prepared in the form of solid pellets with the addition of polyvinyl alcohol as binder. The measurements were carried out using the Mobile double pulse instrument for LIBS analysis (Modì). The spectral analysis was carried out with the calibration-free approach (CF-LIBS). Metal elements commonly found in WFS including Al, Ba, Fe, Li, Mg, Mn, Pb, Ti, Zr, and Zn, were detected and quantified. The metal concentrations for WFS were compared with virgin sand to assess the influence of the casting material as well as the binders used in the foundries to reclaim the sands. The results demonstrated the feasibility of LIBS method as an alternative or complementary technique for the chemical characterization of WFS.

Interband cascade laser-based optical transfer standard for atmospheric carbon monoxide measurements.

We report on an interband cascade laser (ICL)-absorption spectrometer for absolute, calibration-free, atmospheric CO amount fraction measurements, addressing direct traceability of the results. The system combines first-principles direct tunable diode laser absorption spectroscopy (dTDLAS) with a metrological validation. Using a multipath cell with 76 m path length, our detection limit is 0.5 nmol/mol at Δt=14 s. The system is highly linear (slope: 0.999±0.008) in the amount fraction range of 0.1-1000 μmol/mol and thus is interesting for industrial as well as environmental applications. The sensor repeatability at 300 nmol/mol is 0.06 nmol/mol (with Δt=10 min). The sensor's absolute response is in excellent agreement with the gravimetric values of a set of primary gas standards used to test the sensor accuracy. The relative expanded uncertainty (k=2) of the measured CO amount fraction is 2.8%. Due to this performance and the calibration-free approach, the spectrometer may be used as an optical transfer standard (OTS) if gas standards are for whatever reason not available or applicable, e.g., for airborne instruments. Our dTDLAS approach has shown excellent stability and accuracy in H2O detection [Appl. Phys. B116, 883 (2014)APPCDL0721-726910.1007/s00340-014-5775-4] even when compared to primary standards. We therefore deduce that the ICL spectrometer (after its adaptation to field conditions, similar to our H2O spectrometers) has good potential to meet the 2 nmol/mol compatibility goal stated by the World Meteorological Organization for atmospheric CO measurements, and serve as an OTS which does not need frequent calibrations using reference gases.

“Click” analytics for “click” chemistry – A simple method for calibration–free evaluation of online NMR spectra

Driven mostly by the search for chemical syntheses under biocompatible conditions, so called “click” chemistry rapidly became a growing field of research. The resulting simple one-pot reactions are so far only scarcely accompanied by an adequate optimization via comparably straightforward and robust analysis techniques possessing short set-up times. Here, we report on a fast and reliable calibration-free online NMR monitoring approach for technical mixtures. It combines a versatile fluidic system, continuous-flow measurement of 1H spectra with a time interval of 20s per spectrum, and a robust, fully automated algorithm to interpret the obtained data. As a proof-of-concept, the thiol-ene coupling between N-boc cysteine methyl ester and allyl alcohol was conducted in a variety of non-deuterated solvents while its time-resolved behaviour was characterized with step tracer experiments. Overlapping signals in online spectra during thiol-ene coupling could be deconvoluted with a spectral model using indirect hard modeling and were subsequently converted to either molar ratios (using a calibration-free approach) or absolute concentrations (using 1-point calibration). For various solvents the kinetic constant k for pseudo-first order reaction was estimated to be 3.9h−1 at 25°C. The obtained results were compared with direct integration of non-overlapping signals and showed good agreement with the implemented mass balance.

Quantitative Analysis of Shilajit using Laser-Induced Breakdown Spectroscopy and Inductively Coupled Plasma/Optical Emission Spectroscopy

Laser-induced Breakdown Spectroscopy (LIBS) was used for the quantitative study of Shilajit samples using first harmonic (1064 nm) of a Q-Switched Nd:YAG laser by an appropriate detection system. The samples were chosen from the northern Himalayan mountainous range at locations namely Skardu, Gilgit, Chilas, Chitral, and Muzaffarabad. The relative concentrations of detected species were measured via integrated intensity of the strongest line of an element and via Calibration-Free CF-LIBS approach. Our findings recommend the altitudinal variations in Physico-chemical properties of Shilajit. Different functional groups were identified using Fourier Transform infrared (FTIR)-Spectroscopy. The results of LIBS were compared to results of Inductively Coupled Plasma/Optical Emission Spectroscopy (ICP/OES) with fine harmony.

Approach for Self-Calibrating CO₂ Measurements with Linear Membrane-Based Gas Sensors.

Linear membrane-based gas sensors that can be advantageously applied for the measurement of a single gas component in large heterogeneous systems, e.g., for representative determination of CO2 in the subsurface, can be designed depending on the properties of the observation object. A resulting disadvantage is that the permeation-based sensor response depends on operating conditions, the individual site-adapted sensor geometry, the membrane material, and the target gas component. Therefore, calibration is needed, especially of the slope, which could change over several orders of magnitude. A calibration-free approach based on an internal gas standard is developed to overcome the multi-criterial slope dependency. This results in a normalization of sensor response and enables the sensor to assess the significance of measurement. The approach was proofed on the example of CO2 analysis in dry air with tubular PDMS membranes for various CO2 concentrations of an internal standard. Negligible temperature dependency was found within an 18 K range. The transformation behavior of the measurement signal and the influence of concentration variations of the internal standard on the measurement signal were shown. Offsets that were adjusted based on the stated theory for the given measurement conditions and material data from the literature were in agreement with the experimentally determined offsets. A measurement comparison with an NDIR reference sensor shows an unexpectedly low bias (<1%) of the non-calibrated sensor response, and comparable statistical uncertainty.

Online Classification of Mixed Co-Crystal and Solute Suspensions using Raman Spectroscopy

This work seeks to develop a calibration-free statistical approach based on Raman spectroscopy for online identification of impurities during co-crystallization. Caffeine-glutaric acid-acetonitrile was employed as the model system, which forms co-crystals from solution at appropriate conditions. Raman spectra were collected in three classes of suspensions with a solid mixture of caffeine crystals and co-crystals, pure co-crystals, and a mixture of glutaric acid crystals and co-crystals, respectively, at different temperatures. These suspensions were used to represent the possible products of co-crystallization processes during which single component could crystallize out concomitantly with the desired cocrystal. A statistical model combining principal component analysis (PCA) and discriminant analysis (DA) was developed to classify these suspensions. PCA was first performed for these spectra and the resulting first few principal components were subjected to DA. It was found that the three classes of suspe...

Frequency-Domain Photoacoustic Phase Spectroscopy: A Fluence-Independent Approach for Quantitative Probing of Hemoglobin Oxygen Saturation

In this paper, it is shown that the phase of the frequency-domain photoacoustic (PA) signal can be used to measure the absorption coefficient (μ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">α</sub> ) of the chromophore. This method can be referred to as a calibration-free approach in the sense that it is not affected by the attenuation of fluence in the tissue. This helps to enhance the accuracy of quantitative PA functional imaging. However, the premise for employing the aforementioned method is that chromophore geometry should be known a priori. As a proof of applicability of the theory, the method was applied to a simplified geometry and the extension of the method to more complicated geometries is discussed. One of the key subjects of functional imaging in medicine is blood. Parameters such as total hemoglobin concentration and hemoglobin oxygen saturation are valuable for diagnostics as well as for treatment of many diseases. The developed method was employed for in vitro monitoring of blood oxygenation on heparinized sheep blood and is applicable to characterization problems in biological tissues and other turbid media.

A calibration-free approach for on-site multi-element analysis of metal ions in aqueous solutions by electrodeposition-assisted underwater laser-induced breakdown spectroscopy

We investigate the possibility of on-site multi-element analysis of part-per-million order Cu2+ and Zn2+ in an aqueous solution by underwater laser-induced breakdown spectroscopy (underwater LIBS) of a Pt electrode on which Cu2+ and Zn2+ are electrodeposited in advance. Atomic emission lines of Cu and Zn are simultaneously observed. To apply a calibration-free LIBS (CF-LIBS) approach to the present system, we estimate the Zn/Cu ratio in the laser ablation plasma from the emission spectra. Although the Zn/Cu ratio in the deposit agrees with the ratio in the solution, the ratio in the plasma considerably deviates from the ratio in the deposit. We demonstrate the possibility of quantitative analysis even in such a case by correcting the deviation using a simple model considering heat propagation and thermal evaporation during liquid-phase laser ablation.

A calibration-free approach for measuring fracture aperture distributions using X-ray computed tomography

Various methods have been proposed to measure fracture aperture distributions, including X-ray computed tomography (CT) imaging, which has the advantage that it can be combined with dynamic flow experiments. In this paper, we present a calibration-free missing CT attenuation (CFMA) imaging method for measuring fracture apertures that avoids time-consuming calibration. In addition, this model does not assume a homogeneous matrix and thus provides a good estimate of fracture apertures even when rock properties are heterogeneous. The validity of the CFMA model is established by four approaches: comparing apertures calculated with the conventional calibration-based method; evaluating model predictability at different scanner voxel sizes; comparing with calibration coefficients in the literature from a number of experiments with different rocks and X-ray scanners; and comparing aperture measurements for dry and wet scans. We analyze the systematic error and the random error introduced by rock heterogeneities and CT scanning and show that by averaging 5 replicate scans, we reduce the aperture measurement error to ∼22 µm.

Normalization-Free Chipless RFIDs by Using Dual-Polarized Interrogation

A reliable encoding/detection scheme for chipless radio frequency identification (RFID) tags, free from any normalization procedure, is presented. The key strategy of the present approach consists in storing the information in the difference between vertically and horizontally polarized reflection coefficients of a completely passive tag. The measured reflection coefficients are preemptively filtered in the time domain to remove most of harmful effects due to the antenna coupling and environment multipath, and finally they are subtracted to obtain the differential response. A couple of chipless tag configurations suitable for providing the desired spectral response are presented. The resonators consist of an artificial impedance surface comprising either concentric rectangular loop resonators or square loop resonators loaded with stubs. The presented approach is experimentally verified in a non-anechoic environment, and its robustness is proved. This calibration-free approach could pave the way to practical applicability of chipless RFID tags in realistic scenarios with unknown response.

A Protocol for Diagnosing the Effect of Calibration Priors on Posterior Time Estimates: A Case Study for the Cambrian Explosion of Animal Phyla.

We present a procedure to test the effect of calibration priors on estimated times, which applies a recently developed calibration-free approach (RelTime) method that produces relative divergence times for all nodes in the tree. We illustrate this protocol by applying it to a timetree of metazoan diversification (Erwin DH, Laflamme M, Tweedt SM, Sperling EA, Pisani D, Peterson KJ. 2011. The Cambrian conundrum: early divergence and later ecological success in the early history of animals. Science 334:1091-1097.), which placed the divergence of animal phyla close to the time of the Cambrian explosion inferred from the fossil record. These analyses revealed that the two maximum-only calibration priors in the pre-Cambrian are the primary determinants of the young divergence times among animal phyla in this study. In fact, these two maximum-only calibrations produce divergence times that severely violate minimum boundaries of almost all of the other 22 calibration constraints. The use of these 22 calibrations produces dates for metazoan divergences that are hundreds of millions of years earlier in the Proterozoic. Our results encourage the use of calibration-free approaches to identify most influential calibration constraints and to evaluate their impact in order to achieve biologically robust interpretations.

Calibration-free laser induced breakdown spectroscopy as an alternative method for found meteorite fragments analysis

Calibration-free laser induced breakdown spectroscopy (CF-LIBS) was used for the determination of elemental composition and quantitative analysis of the Kosice meteorite by means of time resolved and broadband emission spectroscopy (200–1000 nm). The electron temperature was determined using the Saha-Boltzmann plot method and the electron density from Stark broadening of the hydrogen H α line (656 nm). Apart from magnesium, silicon and iron, which are the main elemental constituents of examined meteorite fragments, elements such as aluminum, nickel, potassium, sodium, chromium, calcium and manganese were also identified in the obtained LIBS spectra. Concentrations of Al, Ca, Cr, Fe, Mg, Mn, Na, Ni and Si were calculated using the calibration free approach and results were compared with ones obtained from the ICP-MS analyses. For the increase of the CF-LIBS accuracy, a selection of spectral lines was performed. Considering the transition probability, the population of absorbing level, the degree of ionization and predicted elemental concentration we calculated the probability of self-absorption and, consequently, spectral lines with highest self-absorption probability were rejected. CF-LIBS can be used as an alternative method for the meteorite fragments analysis (including the inner part and crust), because this method is quasi non-destructive and therefore analysis of all found fragments with minimal destruction is possible.

One-point calibration for calibration-free laser-induced breakdown spectroscopy quantitative analysis

We present a new method for improving the reliability of quantitative analysis by laser-induced breakdown spectroscopy (LIBS). The method can be considered as a variation of the calibration-free LIBS approach; although not completely standard-less, only one standard of known composition and similar matrix to the one to be analyzed is needed. On the other hand, the one-point calibration approach allows the empirical determination of essential experimental and spectroscopic parameters, whose knowledge is often imprecise or lacking; the result is a definite improvement of the trueness of LIBS analysis with respect to the traditional calibration-free approach.The characteristics and advantages of the proposed one-point calibration LIBS approach will be demonstrated on a set of copper-based samples of known composition.

Double-pulse laser-induced breakdown spectroscopy analysis of scales from petroleum pipelines

Pipeline scales from the Campos Bay Petroleum Field near Rio de Janeiro, Brazil have been analyzed by both Raman spectroscopy and by laser-induced breakdown spectroscopy (LIBS) using a double-pulse, calibration-free approach. Elements that are characteristic of petroleum (e.g. C, H, N, O, Mg, Na, Fe and V) were detected, in addition to the Ca, Al, and Si which form the matrix of the scale. The LIBS results were compared with the results of micro-Raman spectroscopy, which confirmed the nature of the incrustations inferred by the LIBS analysis. Results of this preliminary study suggest that diffusion of pipe material into the pipeline intake column plays an important role in the growth of scale. Thanks to the simplicity and relative low cost of equipment and to the fact that no special chemical pre-treatment of the samples is needed, LIBS can offer very fast acquisition of data and the possibility of in situ measurements. LIBS could thus represent an alternative or complementary method for the chemical characterization of the scales by comparison to conventional analytical techniques, such as X-ray diffraction or X-ray fluorescence.

Sequential Identification of Model Parameters by Derivative Double Two-Dimensional Correlation Spectroscopy and Calibration-Free Approach for Chemical Reaction Systems

A sequential identification approach by two-dimensional (2D) correlation analysis for the identification of a chemical reaction model, activation, and thermodynamic parameters is presented in this paper. The identification task is decomposed into a sequence of subproblems. The first step is the construction of a reaction model with the suggested information by model-free 2D correlation analysis using a novel technique called derivative double 2D correlation spectroscopy (DD2DCOS), which enables one to analyze intensities with nonlinear behavior and overlapped bands. The second step is a model-based 2D correlation analysis where the activation and thermodynamic parameters are estimated by an indirect implicit calibration or a calibration-free approach. In this way, a minimization process for the spectral information by sample-sample 2D correlation spectroscopy and kinetic hard modeling (using ordinary differential equations) of the chemical reaction model is carried out. The sequential identification by 2D correlation analysis is illustrated with reference to the isomeric structure of diphenylurethane synthesized from phenylisocyanate and phenol. The reaction was investigated by FT-IR spectroscopy. The activation and thermodynamic parameters of the isomeric structures of diphenylurethane linked through a hydrogen bonding equilibrium were studied by means of an integration of model-free and model-based 2D correlation analysis called a sequential identification approach. The study determined the enthalpy (ΔH = 15.25 kJ/mol) and entropy (TΔS = 13.20 kJ/mol) of C═O···H hydrogen bonding of diphenylurethane through direct calculation from the differences in the kinetic parameters (δΔ(‡)H, -TδΔ(‡)S) at equilibrium in the chemical reaction system.