Baseline Correction Techniques Research Articles

Robust baseline correction for Raman spectra by constrained Gaussian radial basis function fitting

Accurate baseline correction is a fundamental requirement for extracting meaningful spectral information and enabling precise quantitative analysis using Raman spectroscopy. Although numerous baseline correction techniques have been developed, they often require meticulous parameter adjustments and yield inconsistent results. To address these challenges, we have introduced a novel approach, namely constrained Gaussian radial basis function fitting (CGF). Our method involves solving a curve-fitting problem using Gaussian radial basis functions under specific constraints. To ensure stability and efficiency, we developed a linear programming algorithm for the proposed approach. We evaluated the performance of CGF using simulated Raman spectra and demonstrated its robustness across various scenarios, including changes in data length and noise levels. In contrast to standard methods, which frequently require complicated parameter adjustments and may exhibit varying errors, our approach provides a simple parameter search and consistently achieves low errors. We further assessed CGF using real Raman spectra, leading to enhanced accuracy in the quantitative analysis of the Raman spectra of chemical warfare agents. Our results emphasize the potential of CGF as a valuable tool for Raman spectroscopy data analysis, significantly advancing sophisticated analytical techniques.

Baseline Correction for HPLC Chromatograms by Using Free Open-Source Software

Chromatograms with overlapping peaks and a baseline rise or upset constitute a great challenge for analysts. Such a case regarding the analysis of bupropion hydrochloride and its 5 impurities in a tablet formulation was used as a model. A baseline correction technique for liquid chromatography coupled with diode array detection is described by using Rstudio. The asymmetry least squares (ALS) algorithm was used as implemented in the “baseline” package, with parameters lambda and p set to 4 and 0.05, respectively. Peak deconvolution and subsequent integration and area quantification were accomplished through Fytik software. Chromatographic data from the validation procedure were utilized to demonstrate the feasibility of the suggested method and whether this correction affects the outcome of the validation study. Finally, a robustness study was carried out in order to shed light on the factors that have a more significant influence on the baseline correction, showing the reliability of this procedure through random changes in its parameters.

Evaluation of ensemble data preprocessing strategy on forensic gasoline classification using untargeted GC–MS data and classification and regression tree (CART) algorithm

The purpose of this work is to evaluate the ensemble data preprocessing (DP) strategy composing the selected variant of normalization, parametric time warping and baseline correction techniques in varying sequences for modelling a gas chromatography-mass spectrometry (GC–MS) data via classification and regression tree (CART) algorithm. Firstly, the relative merits between single-DP and ensemble-DP strategies were carefully compared using the best-performing sub-retention time (RT) windows reported elsewhere. Then, all the preprocessed sub-datasets were assessed based on predictive capability estimated via the CART algorithm. Performances of CART models were estimated from 50 pairs of training and testing samples that were prepared by a stratified random resampling method. Then, the three shortlisted sub-datasets were further evaluated using increased pairs of training and testing samples. Additionally, the most discriminative RT points were also identified using the three sub-datasets. Eventually, the most desired CART model was constructed using the shortlisted RT points after being treated by the most outstanding DP strategy. Results showed that 3-DP strategies tended to outperform the 1-DP and 2-DP strategies. However, the sequence of application must be carefully optimized as not all the 3-DP strategies induced positive impacts. It was found that the data aligned before baseline correction or normalization will likely outperform those being first normalized or baseline corrected. In conclusion, the untargeted GC–MS data of neat gasoline preferably be first aligned, followed by normalization, and ended by baseline correction.

Empirical predictive models for fling step and displacement response spectra based on the NESS database

The characterization of the fling-step represents a challenging task due to the shortage of near-source records with permanent tectonic displacement and the limitation in retrieving the fling-amplitude from accelerometric waveforms. In recent years, innovative ground-motion processing techniques have been developed for a more accurate estimation of both fling-displacements and spectral displacements in contrast to traditional bandpass filtering, although their application is still unusual. In this paper, we exploit the newly released dataset of the Near-Source Strong-motion records (NESS2) uniformly processed with the extended BASeline COrrection technique (eBASCO), against which we propose: (1) a new empirically-based ground motion model (GMM) for the prediction of the fling-step, and (2) an adjustment factor of the spectral displacements predicted by a reference GMM to account for the contribution of the fling-step at long periods. Such models are in agreement with observations and existing GMMs, and thus could be advantageously employed in seismic hazard analyses.

GMSS2.0: An Enhanced Software Program for Stochastic Finite-Fault Ground-Motion Simulation

AbstractThis article introduces an enhanced software program for stochastic ground-motion simulations using finite-fault sources, named Ground-Motion Simulation System version 2.0 (GMSS2.0). GMSS2.0 embodies an updated theoretical model of corner frequency and source duration, making the seismological model for defining the Fourier amplitude spectrum for each subfault more theoretically consistent. In addition, GMSS2.0 provides four rupture scaling relationships and five baseline correction techniques for end users to select the most suitable one for a specific application. For validation purposes, comprehensive comparisons between GMSS2.0 and EXtended SIMulation (EXSIM) for wide ranges of magnitude (M 4–8), distance (∼6–300 km) and spectral period (0.01–10 s) have been performed. The results show that GMSS2.0 can give remarkably close estimates to EXSIM with reasonable levels of accuracy. Finally, further validation is performed by comparing GMSS2.0 simulations with five Next Generation Attenuation-West2 ground-motion models for multiple scenario earthquakes with the updated site amplification for the generic California condition (VS30=500 m/s).

Microplastic Spectral Classification Needs an Open Source Community: Open Specy to the Rescue!

Microplastic pollution research has suffered from inadequate data and tools for spectral (Raman and infrared) classification. Spectral matching tools often are not accurate for microplastics identification and are cost-prohibitive. Lack of accuracy stems from the diversity of microplastic pollutants, which are not represented in spectral libraries. Here, we propose a viable software solution: Open Specy. Open Specy is on the web (www.openspecy.org) and in an R package. Open Specy is free and allows users to view, process, identify, and share their spectra to a community library. Users can upload and process their spectra using smoothing (Savitzky-Golay filter) and polynomial baseline correction techniques (IModPolyFit). The processed spectrum can be downloaded to be used in other applications or identified using an onboard reference library and correlation-based matching criteria. Open Specy's data sharing and session log features ensure reproducible results. Open Specy houses a growing library of reference spectra, which increasingly represents the diversity of microplastics as a contaminant suite. We compared the functionality and accuracy of Open Specy for microplastic identification to commonly used spectral analysis software. We found that Open Specy was the only open source software and the only software with a community library, and Open Specy had comparable accuracy to popular software (OMNIC Picta and KnowItAll). Future developments will enhance spectral identification accuracy as the reference library and functionality grows through community-contributed spectra and community-developed code. Open Specy can also be used for applications beyond microplastic analysis. Open Specy's source code is open source (CC-BY-4.0, attribution only) (https://github.com/wincowgerDEV/OpenSpecy).

Assessment of shifted excitation Raman difference spectroscopy in highly fluorescent biological samples.

Shifted excitation Raman difference spectroscopy (SERDS) can be used as an instrumental baseline correction technique to retrieve Raman bands in highly fluorescent samples. Genipin (GE) cross-linked equine pericardium (EP) was used as a model system since a blue pigment is formed upon cross-linking, which results in a strong fluorescent background in the Raman spectra. EP was cross-linked with 0.25% GE solution for 0.5 h, 2 h, 4 h, 6 h, 12 h, and 24 h, and compared with corresponding untreated EP. Raman spectra were collected with three different excitation wavelengths. For the assessment of the SERDS technique, the preprocessed SERDS spectra of two excitation wavelengths (784 nm-786 nm) were compared with the mathematical baseline-corrected Raman spectra at 785 nm excitation using extended multiplicative signal correction, rubberband, the sensitive nonlinear iterative peak and polynomial fitting algorithms. Whereas each baseline correction gave poor quality spectra beyond 6 h GE crosslinking with wave-like artefacts, the SERDS technique resulted in difference spectra, that gave superior reconstructed spectra with clear collagen and resonance enhanced GE pigment bands with lower standard deviation. Key for this progress was an advanced difference optimization approach that is described here. Furthermore, the results of the SERDS technique were independent of the intensity calibration because the system transfer response was compensated by calculating the difference spectrum. We conclude that this SERDS strategy can be transferred to Raman studies on biological and non-biological samples with a strong fluorescence background at 785 nm and also shorter excitation wavelengths which benefit from more intense scattering intensities and higher quantum efficiencies of CCD detectors.

Real-time dynamic displacement monitoring with double integration of acceleration based on recursive least squares method

Due to the difficulty of establishing fixed reference points, it is difficult to monitor displacement of a civil engineering structure in the field for long term. Although to integrate acceleration signals numerically is a common and low-cost displacement measurement method, the schemes proposed in the field of seismology are not suitable for long-term structural monitoring environment because of batch calculations of existing algorithms. In this paper, combining a baseline correction technique based on recursive least squares, a recursive high-pass filter and a recursive integrator, through multi-round baseline correction, filtering and integration, the authors develop an online and real-time acceleration integral scheme. This scheme is then applied to a numerical simulation case and a shaking table test, where the accuracy and reliability are proved. Finally, the applicability of the scheme in real monitoring environment is confirmed through utilizing it to monitor displacement of a real bridge.

The human task-evoked pupillary response function is linear: Implications for baseline response scaling in pupillometry.

The human task-evoked pupillary response provides a sensitive physiological index of the intensity and online resource demands of numerous cognitive processes (e.g., memory retrieval, problem solving, or target detection). Cognitive pupillometry is a well-established technique that relies upon precise measurement of these subtle response functions. Baseline variability of pupil diameter is a complex artifact that typically necessitates mathematical correction. A methodological paradox within pupillometry is that linear and nonlinear forms of baseline scaling both remain accepted baseline correction techniques, despite yielding highly disparate results. The task-evoked pupillary response (TEPR) could potentially scale nonlinearly, similar to autonomic functions such as heart rate, in which the amplitude of an evoked response diminishes as the baseline rises. Alternatively, the TEPR could scale similarly to the cortical hemodynamic response, as a linear function that is independent of its baseline. However, the TEPR cannot scale both linearly and nonlinearly. Our aim was to adjudicate between linear and nonlinear scaling of human TEPR. We manipulated baseline pupil size by modulating the illuminance in the testing room as participants heard abrupt pure-tone transitions (Exp. 1) or visually monitored word lists (Exp. 2). Phasic pupillary responses scaled according to a linear function across all lighting (dark, mid, bright) and task (tones, words) conditions, demonstrating that the TEPR is independent of its baseline amplitude. We discuss methodological implications and identify a need to reevaluate past pupillometry studies.

Achieving fast timing performance with multiplexed SiPMs

Using time of flight (ToF) measurements for positron emission tomography (PET) is an attractive avenue for increasing the signal to noise (SNR) ratio of PET images. However, achieving excellent time resolution required for high SNR gain using silicon photomultipliers (SiPM) requires many resource heavy high bandwidth readout channels. A method of multiplexing many SiPM signals into a single electronic channel would greatly simplify ToF PET systems. However, multiplexing SiPMs degrades time resolution because of added dark counts and signal shaping. In this work the relative contribution of dark counts and signal shaping to timing degradation is simulated and a baseline correction technique to mitigate the effect of multiplexing on the time resolution of analog SiPMs is simulated and experimentally verified. A charge sharing network for multiplexing is proposed and tested. Results show a full width at half maximum (FWHM) coincidence time resolution of ps for a single 3 mm × 3 mm × 20 mm LYSO scintillation crystals coupled to an array of sixteen 3 mm × 3 mm SiPMs that are multiplexed to a single timing channel (in addition to 4 position channels). A array of 3 mm × 3 mm × 20 mm LFS crystals showed an average FWHM coincidence time resolution of ps using the same timing scheme. All experiments were performed at room temperature with no thermal regulation. These results show that excellent time resolution for ToF can be achieved with a highly multiplexed analog SiPM readout.

Discriminative Measurement and Pharmacokinetic Evaluation of Choline Alphoscerate against Endogenous Choline in Human

This study aimed at the evaluation of plasma level profiles of choline produced after the oral administration of choline alphoscerate (CA). For this purpose, a high‐performance liquid chromatography/tandem mass spectrometry (HPLC/MS/MS) analytical method was developed and validated. Baseline correction technique was employed to monitor the CA‐related choline in plasma by subtracting background levels of choline from total choline levels measured after the drug administration. Choline was well separated in the plasma matrix under the analytical conditions employed for HPLC/MS/MS and the analytical method developed for the monitoring of choline in plasma was well validated. The endogenous choline levels in plasma under fasting condition were measured to be 7.78 ± 1.74 µmol/L for test period 1 and 7.88 ± 1.78 µmol/L for test period 2, respectively, and were considerably increased after consumption of meals. The corrected choline levels in plasma produced only by the oral administration of CA could be evaluated by subtracting the background levels of choline monitored before the drug was administered. The pharmacokinetic parameters estimated for test and control formulations were quite similar based on the comparison of C max, AUC12h , and T max, indicating that these are biologically equivalent dosage forms. The results of our study consequently suggest that the baseline correction method in evaluating plasma concentration profiles of endogenous substances is useful.

A fully automated iterative moving averaging (AIMA) technique for baseline correction

Baseline correction is one of the pre-processing steps in the analysis of metabolite signals from chemometric analytical instruments. Fully automated baseline correction techniques, although more convenient to use, tend to be less accurate than semi-automated baseline correction. A fully automated baseline correction algorithm, the automated iterative moving averaging algorithm (AIMA), is presented and compared with three recently introduced semi-automated algorithms, namely the adaptive iteratively reweighted penalized least squares (airPLS), Asymmetric Least Squares baseline correction (ALS) and a parametric method, using NMR, Raman and HPLC chromatograms. AIMA's potential in increasing the accuracy of multivariate analysis via SELTI-TOF and LCMS chromatograms was also assessed. The results show that the AIMA's accuracy is comparable to these semi-automated algorithms and has the advantage of ease of use. An AIMA plug-in for an open source metabolomics analysis tool, MZmine, was also developed. The AIMA plug-in is available at http://padel.nus.edu.sg/software/padelaima.

Application of Baseline Correction Techniques to the “Ratio Method” of DSC Specific Heat Determination

The measurement of specific heat by heat flux differential scanning calorimetry using the “ratio method” requires three consecutive runs (baseline, reference and sample) to be performed using identical temperature programs. Traditionally measurements are taken as the sample of interest is subjected to a controlled heating rate, but it is also possible to perform measurements on down-ramps, and this is often worthwhile as it provides a consistency check on the up-ramp data. In recent work a Netzsch DSC-404 has been used to investigate discrepancies observed between up- and down-ramp specific heat results. Based upon this experience several different “baseline correction” techniques have been developed, and have been applied to specific heat measurements on reference sapphire samples. The performance of these “baseline correction” techniques is shown to be extremely good, even up to 1400°C. An important conclusion is that, even in cases where agreement between up-ramp and down-ramp data is reasonable, a “baseline correction” method can still usefully be applied to improve the precision of the final results.

Drift-free electronic integrator for respiration studies.

A drift-free electronic integrator for phasic signals in the 0·08 to 20 Hz frequency range has been designed for respiratory studies in man, cat and rat. The integrator operates continuously without the need for any adjustments and uses a baseline correction technique which is controlled by the input signal and which allows a fast recovery from input signal transients.