An approach for measuring peak area of an overlapped peak pair

Summary Based on the exponentially modified Gaussian (EMG) function, a new approach is presented for the quantitation of a partially overlapped peak pair. This approach can be employed in a wide range of peak area ratio and asymmetry, provided that the relative valley between the two peaks is not greater than 55%. The first peak area is calculated by the use of the ratio of the front half-width at height fraction 0.1 to that at heigt fraction 0.5. The second peak area is calculated by subtracing the first peak area from the total area which is provided by a microprocessor-based integrator. The relative error for the first peak never exceeds ±5%, but this is not always the case for the second peak. The relative error for the second peak depends not only on the accuracy of the total area and that of the first peak area but on area ratio as well.     

2nd-order spline wavelet convolution method in resolving chemical overlapped peaks

A 2nd-order spline wavelet convolution method in resolving overlapped peaks is developed. It determines the number of peaks, peak positions and width through wavelet's convolution, then uses spline function to construct the resoluter, which is used to resolve overlapped peaks. Theoretical proof is given, and the selections of wavelets and parameters are discussed. It is proven that baseline separation can be achieved after processed, the relative errors of peak position and area are less than 0.2% and 4.0% respectively. It can be directly applied to seriously overlapped signals, noisy signals and multi-component signals, and the results are satisfactory. It is a novel effective method for resolution.     

Study on spline wavelet self‐convolution in filtering and resolving overlapped voltammetric signals simultaneously

The normal distribution function is used as resolving factor and spline wavelet self‐convolution is used to resolve the overlapped peaks containing noise. The resolution of several kinds of overlapped peaks (SNR from 5 to 50) simulated by computer has been discussed in details. It is known that the overlapped peaks with noise can be separated (SNR > 50) directly and the noise is removed at the same time in time domain. Base‐line separation can be achieved. The relative errors of peak area and position are less than 5.0%. The satisfactory results are also obtained in resolving voltammetric overlapped signals by this method.     

Recursive Wavelet Peak Detection of Analytical Signals

A novel algorithm, entitled recursive wavelet peak detection (RWPD), is proposed to detect both normal and overlapped peaks in analytical signals. Recursive peak detection is based on continuous wavelet transforms (CWTs), which can be used to obtain initial peak positions even for overlapped peaks. Genetic algorithm (GA) and Gaussian fitting are used to refine peak parameters (peak positions, widths, and heights). Finally, area of peaks can be calculated by numeric integration. Simulated and ultrahigh performance liquid chromatographic ion trap time-of-flight mass spectrometry (UPLC-IT-TOF-MS) data sets have been analyzed by RWPD, MassSpecWavelet, and peakfit package by Tom O’Haver. Results show that RWPD can obtain more accurate positions and smaller relative fitting errors than MassSpecWavelet and peakfit, especially in overlapped peaks. RWPD is a convenient tool for peak detection and deconvolution of overlapped peaks, and it has been developed in R programming language and is available at https://github.com/zmzhang/RWPD.

     

三元重叠色谱峰面积的定量方法

本从色谱峰的ＥＭＧ模型出发，通过对重叠色谱峰的模拟和回归分析，提出了一种三元重叠色谱峰的面积的定量方法，三元重叠色谱峰的每一个峰面积可以由峰面积比和总面积求得，此法所需的数据都由实验色谱图上测得，峰面积计算结果的相对误差小于±５％，适用于相对峰谷为５０％－９５％的三元重叠色谱峰面积的定量。     

Correction method for quantitative area determination of overlapping chromatographic peaks based on the exponentially modified Gaussian (EMG) model

A simple method is presented for peak area correction of overlapping peaks. This correction is necessary for the normal approach of dealing with overlapping peaks by a vertical line at the valley point. The relative area errors caused by this vertical line are calculated as the correction factors in three dimensions of peak separation, peak ratio, and peak tailing skew. The calculation is based on the exponentially modified Gaussian asymmetric peak model.     

Simultaneous voltammetric determination of ascorbic acid and uric acid using a Nafion/multi-wall carbon nanotubes composite film-modified electrode

A Nafion/multi-wall carbon nanotubes (MWNT) composite film-modified electrode was fabricated. The modified electrode showed excellent electrocatalytic activity toward ascorbic acid (AA) and uric acid (UA) in 0.1-mol L⁻¹ NaCl medium (pH 6.5). Compared to the bare electrode that only displayed a broad and overlapped oxidation peak, the Nafion/MWNT film-modified electrode not only remarkably enhanced the anodic peak currents of AA and UA but also avoided the overlapping of the anodic peaks of AA and UA with a 320-mV separation of both peaks. Under the optimized conditions, the peak currents of AA and UA were proportional to their concentration at the ranges of 8.0 × 10⁻⁵ to 6.0 × 10⁻³ mol L⁻¹ and 6.0 × 10⁻⁷ to 8.0 × 10⁻⁵ mol L⁻¹, respectively. The proposed method was used for the detection of AA and UA in real samples with satisfactory results.     

High-throughput automated post-processing of separation data

The development of an efficient method for high-throughput analysis of multiple electropherograms or chromatograms collected in series is presented. The method, encoded in a computer program designated "Cutter", utilizes batch processing for determining chromatographic figures of merit (CFOM) including peak centroid times, heights, areas, signal-to-noise ratios (S/N), variance (sigma2), skew, excess, and plate number (N) across a set of separations collected serially. The software was validated using simulated data with varying S/N, skew, and excess. The accuracy of the analysis was comparable to or improved over commercial software with area calculation relative errors (RE) below 5% for simulated data with S/N = 5. File sets containing 1300 electropherograms were analyzed in 5 min, representing a nearly 200-fold reduction in analysis time from other methods. Incorporated within the program is a novel method for automated peak deconvolution using an Empirically Transformed Gaussian function. Area measurements of deconvoluted peaks were within 3% of the true value of a simulated data set with S/N = 5 and resolution (R(S)) = 1 for equivalent peaks, and within 10% when the ratio of the overlapped peak heights was 10:1.     

Spline wavelet in the resolution of overlapping voltammetric peaks

Spline wavelet transform is used to resolve overlapping voltammetric peaks. A suitable resolving factor is chosen to multiply the filters of spline wavelet and make it a peak resoluter. Simulated overlapping voltammetric peaks are processed by the peak resoluter and satisfactory results are obtained. Base-line separation can be achieved, the relative errors of peak position are less than 3.0%, and the relative errors of peak area are less than 5.0%. The effect of different resolving factors and spline wavelet basis are discussed. To test the procedure, two systems, cadmium (Ⅱ)-indium (Ⅲ) and lead (Ⅱ)-thallium (Ⅰ), are used.     

Computerized separation of chromatographically unresolved peaks

A computerized peak deconvolution software and mass spectra were successfully applied for the deconvolution of overlapped peak cluster in the chromatogram obtained separating the complex mixture of pesticides by retention time locking gas chromatography-mass spectroscopy. The method based on the unique fragment ions in the spectra can be used for deconvolution of peak clusters if mass spectra of overlapped peaks differ. This method allows determining actual retention times of overlapped peaks. Peak areas found by this method however, cannot be used naturally for the quantitative purposes as the abundance of fragment ions used for this deconvolution procedure can dramatically differ. Computer assisted deconvolution of peaks in the peak clusters gives more realistic peak area ratios as at this method it is supposed equal response for all peaks overlapped in a cluster.     

Relaxation in Unsaturated Polyester Resins Studied by Thermally Stimulated Depolarization Currents

Investigations involving thermally stimulated depolarization currents were performed on unsaturated polyester resins cured with styrene. Samples containing different amounts of Co octoate promoter were studied. The complex spectra revealed the classical β and the α dipolar relaxations. The peak characterizing the α dipolar relaxation was overlapped by a ρ peak of appreciable magnitude, due to the presence of impurities in the promoter solution [1]. However, study of the elementary spectra as concerns both α and β peaks for various samples containing different amounts of Co octoate demonstrated that the relaxation kinetics, and particularly the values of the apparent activation energies, do not depend on these impurities. This revised version was published online in August 2006 with corrections to the Cover Date.     

The use of derivatives for establishing integration limits of chromatographic peaks

Summary The paper deals with composite peaks in which the resolution is not sufficient to allow simple area determinations with conventional integrator procedures. It is proposed to use the second derivatives of composite peaks, since the derivatives accentuate envelope perturbations due to overlapped peaks. In particular, when there are two solutes in the composite, and when the peak separation is between 2 and 4σ, the second derivative of the composite has two minima and three maxima. The second maximum is indicative of the cross point of the two solutes. This point can be used to initiate and/or terminate the integration of the components in the composite. Similarly, the second minimum occurs at a point close to the true maximum of the second peak in the composite. This point can also be used for the quantitative determination of the second component in the composite. The second derivative traces can also be integrated, but their utility in quantitative analysis of the peaks is questionable. An inversion procedure is given in which the second derivative trace is inverted to yield a trace similar to the conventional chromatograms but with better apparent resolution. In special circumstances, the inverted derivatives can be used for integration purposes.     

In-source decay and fragmentation characteristics of peptides using 5-aminosalicylic acid as a matrix in matrix-assisted laser desorption/ionization mass spectrometry

The use of 5-aminosalicylic acid (5-ASA) as a new matrix for in-source decay (ISD) of peptides including mono- and di-phosphorylated peptides in matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS) is described. The use of 5-ASA in MALDI-ISD has been evaluated from several standpoints: hydrogen-donating ability, the outstanding sharpness of molecular and fragment ion peaks, and the presence of interference peaks such as metastable peaks and multiply charged ions. The hydrogen-donating ability of several matrices such as α-cyano-4-hydroxycinnamic acid (CHCA), 2,5-dihydroxybenzoic acid (2,5-DHB), 1,5-diaminonaphthalene (1,5-DAN), sinapinic acid (SA), and 5-ASA was evaluated by using the peak abundance of a reduction product [M + 2H + H]⁺ to that of non-reduced protonated molecule [M + H]⁺ of the cyclic peptide vasopressin which contains a disulfide bond (S-S). The order of hydrogendonating ability was 1,5-DAN > 5-ASA > 2,5-DHB > SA = CHCA. The chemicals 1,5-DAN and 5-ASA in particular can be classified as reductive matrices. 5-ASA gave peaks with higher sharpness for protonated molecules and fragment ions than other matrices and did not give any interference peaks such as multiply-protonated ions and metastable ions in the ISD mass spectra of the peptides used. Particularly, 1,5-DAN and 5-ASA gave very little metastable peaks. This indicates that 1,5-DAN and 5-ASA are more “cool” than other matrices. The 1,5-DAN and 5-ASA can therefore be termed “reductive cool” matrix. Further, it was confirmed that ISD phenomena such as N-Cα bond cleavage and reduction of S-S bond is a single event in the ion source. The characteristic fragmentations, which form a− and (a + 2)-series ions, [M + H − 15]⁺, [M + H − 28]⁺, and [M + H − 44]⁺ ions in the MALDI-ISD are described.     

基于稀疏模型的气相色谱-质谱数据解析及其在严重重叠峰解析中的应用

提出一种气相色谱-质谱（GC-MS）数据解析算法。以色谱峰顶点处的质谱作为待测谱,在谱库中检索一定量相关参考谱,求解关于各纯组分色谱响应值的方程。质谱检索采取分步策略,先利用质谱碎片规律建立高速索引进行粗选,然后使用强峰高概率出峰准则和耐挤压性准则排除无关质谱。为求解色谱响应值方程,提出基于稀疏模型的回归算法,相比传统算法,稀疏算法利于提取待测谱的主要结构,避免"过拟合"。实验结果表明,该质谱检索算法具有较高的精度和规模较小的剩余参考谱集,而所提稀疏模型算法可有效解析严重重叠峰。该算法可作为GC-MS重叠峰解析,特别是严重重叠峰解析的一种有效解决方案。     

严重重叠的色谱峰对的解析

本文根据指数修正的高斯函数模型(EMG),并利用回归分析提出了一种解析严重重叠的色谱峰对的方法。此法可适用于相对峰谷在50％～95％的严重重叠的色谱峰对的解析。     

Bi-quadratic surface response for quantitative determination of analytes leading to partially overlapped chromatographic peaks

A simple analytic approach is described for the accurate determination of the concentration of components which give rise to partially overlapped chromatographic peaks. This method requires neither deconvolution processes nor chromatographic separation of the peaks. From the empirical point of view a bi-quadratic function has been found relating the area of an unresolved peak with the concentrations of the related analyte and of the interfering one. Such concentrations are then computed by solving the related non linear system of equations by the Newton-Raphson method.     

Multivariate curve resolution in liquid chromatography—resolving two-way multi-component data using a Varimax extended rotation

The Varimax extended rotations (VER) have been proposed as a new method to mathematically resolve severely overlapped peaks in chromatographic experiments that produce bilinear data. VER employs a four-step procedure to determine the relative concentration and identity of the components that comprise a severely overlapped chromatographic peak. In the first step, the data are pre-processed to ensure that they are in a form suitable for multivariate curve resolution. The second step involves principal component analysis, which reduces the dimensionality of the data matrix while simultaneously retaining the information present in the data. In the third step, a new coordinate system is developed for the data using a Varimax rotation followed by a so-called extended rotation, which assists in identifying the so-called pure regions in the peak. Identifying these regions is crucial to rotating the concentration and spectral matrices towards a solution. The fourth step utilizes alternating least squares (ALS) to improve the estimates of the concentration and spectral profiles of each component. Results from real and simulated data are used to illustrate the efficacy and simplicity of the proposed method.     

Voltammetry of resazurin at a mercury electrode

Electrochemical behavior of resazurin on HMDE in Britton-Robinson (B-R) buffers (pH 2.0–10.0) was studied using the square-wave voltammetry (SWV), square-wave adsorptive stripping voltammetry (SWAdSV), and cyclic voltammetry (CV) techniques. The voltammogram of resazurin in B-R buffer at pH < 4.0 exhibited two cathodic reduction peaks. The voltammetric peaks were obtained at −0.144 V (reversible) and −1.250 V (irreversible) at pH 3.2, and correspond to the reduction of resorufin to dihydroresorufin and to the catalytic hydrogen wave, respectively. At pH > 4.0, a new irreversible cathodic reduction peak, assigned to the protonation of N-oxide on the phenoxazin ring, was observed. Electrochemical parameters (I _p/E _p, I _p/v, I _p/pH, I _p/t _acc) of the compound were determined. From the voltammetric data, electrochemical reduction mechanisms for all peaks have been suggested. Maximum peak current for the reversible peak was obtained at pH 4.1. A linear relationship between the current and concentration was determined, and also the lowest detection limit was found as 3.25 × 10⁻⁸ mol L⁻¹ and 1.98 × 10⁻¹⁰ mol L⁻¹ for SWV and SWAdSV, respectively.     

Epithermal neutron activation analysis of uranium by neptunium-239 using high resolution gamma-spectrometry

The possibility to use the most intensive gamma-peak of²³⁹Np for INAA of uranium with epithermal neutrons and high resolution Ge(Li)-spectrometry is evaluated. A way for calculation of the peak area of overlapping peaks of¹⁵³Sm and²³⁹Np is proposed. This can be used in other similar cases in the practice of NAA. On this basis a scheme for NAA of uranium in geological objects is proposed. Lower detection limit is 8·10⁻⁸ g U the precision 5–10% (relative standard deviation). The accuracy is demonstrated by the analysis of some geological standard reference materials.     

Biosorption of metal ions with Penicillium chrysogenum

Biosorption of metal ions with Penicillium chrysogenum mycelium is described in this article. Alkaline pretreatment was used to remove proteins and nucleic acids from cells, and this treatment increased the adsorption capacities, for Cr³⁺ from 18.6 mg g⁻¹ to 27.2 mg g⁻¹, for Ni²⁺ from 13.2 mg g⁻¹ to 19.2 mg g⁻¹, for Zn²⁺ from 6.8 mg g⁻¹ to 24.5 mg g⁻¹. The adsorption of metal ions was strongly pH dependent. The mycelium could beused for large-scale removal of Cr³⁺ from tannery wastewater. The results show that this inexpensive mycelium adsorbent has potential in industry because of its high adsorption capacity. The main chelating sites are amino groups (−NH₂) of chitosan in the mycelium. A new model is established, which describes the relation of adsorption of metal ions on pH according to amino group chelating with metal ions and H⁺. The relative errors of simulation for Cu²⁺, Ni²⁺, Zn²⁺, and Cr³⁺ are 4.66%, 5.45%, 11.55%, and 1.69%, respectively.