Quantitative chiral analysis in capillary electrophoresis from unresolved peaks using derivative electropherograms,experimental design,and artificial neural networks

Quantitative capillary electrophoretic analysis of chiral compounds might be difficult or even impossible when baseline separation is not reached. In this work, the use of n-th derivative of the electropherogram was studied and examined on model and experimental data. The electropherograms should be first smoothed using Savitzky-Golay method and the quantitative analysis is then possible using either a graphical method or multivariate calibration applying a combination of experimental design (ED) and artificial neural networks (ANNs). The best results were obtained for the first derivative, higher derivatives are not suitable because of noise accumulation. The method was applied to real experimental data to quantify chiral amino acids from unresolved peaks, but it is applicable for quantitative analysis of any other chiral analytes from poorly resolved peaks. Precision of analysis from partially resolved peaks reached was about +/- 3.2% relative standard deviation.     

Quantitative Dünnschicht-Chromatographie: Numerische Peakerkennung und Auswertung mit Digitalrechnern

The paper describes the principles of a programm for numerical peak detection and numerical integration for area determination by digital computers with respect to thin-layer chromatography. Integrating analog to digital conversion and digital smoothing will improve the signal to noise ratio. The first derivative will be found by smoothed numerical differentiation and is used for peak detection. The actual base line is corrected by eomparision of the tangents between the minima of the peaks.     

Matched filtering with background suppression for improved quality of base peak chromatograms and mass spectra in liquid chromatography-mass spectrometry

A time domain filter that combines the properties of matched filtering and two-fold differentiation is presented. The filter coefficients are given by the second derivative of a Gaussian model peak, controlled by the setting of two parameters related to the chromatographic system. The fundamental characteristics of the filter were derived, and its applicability demonstrated for real liquid chromatography-mass spectrometry (LC-MS) data. The filter is primarily intended as a fast pre-processing step, for a mass chromatogram with 320 scans over 700 mass channels the computation time was 0.6 s on a standard PC. Base peak chromatograms with improved peak detection capability and mass spectra useful for compound identification were obtained with filtered data. The most significant effect of the described filter is background reduction due to the differentiation, which in combination with the matched filter can be performed with maintained or even improved signal-to-noise ratio.     

Computerized detection and evaluation of peaks in survey spectra from photoelectron spectroscopy

The computer program described is written in Algol-60 and allows a fast data analysis of photoelectron peaks in survey spectra (0–1500 eV). Additional peak parameters such as area, background and peak width are also determined. The assumptions about peak shape are kept to a minimum. In spectra with good counting statistics, it is possible to detect peaks with peak/background ratio down to 0.01.     

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.

     

固相微萃取-电感耦合等离子体质谱联用接口及其分析性能研究

本文设计了集热解析和进样功能为一体的固相微萃取-电感耦合等离子体质谱(SPMP-ICP-MS)联用的接口单元。利用I2在常温下连续稳定升华的物理特性,进行联用系统的气路调节的最佳化。以四乙基铅溶液为例探讨了SPME—ICP—MS接口的分析性能。采用峰面积的数据采集方式,获得了较好的重现性以及线性范围,其检出限为0．009ng／mL。     

Separation and determination of active components in Schisandra chinensis Baill. and its medicinal preparations by non-aqueous capillary electrophoresis

A simple, economical and effective non-aqueous capillary electrophoresis separation and detection method was developed for the quantification of deoxyschizandrin and gamma-schizandrin in Schisandra chinensis Baill. and its medicinal preparations for the first time. After optimization of separation conditions, a buffer of 140 mmol/L sodium cholate in methanol was selected for separating the two analytes, but baseline separation of SA and SB in real samples was not obtained. Therefore second-order derivative electropherograms were applied for resolving overlapping peaks. Regression equations revealed good linear relationships (correlation coefficients 0.9975--0.9988) between peak heights in second-order derivative electropherograms and concentrations of the two analytes. The relative standard deviations (RSD) of the migration times and the peak height of the two constituents were in the ranges 0.62--0.79% and 0.25--2.17% (intra-day) and 1.43--2.06 and 4.08--5.72% (inter-day), respectively. The recoveries of the two constituents ranged from 93.2 to 103.0%. The results indicated that baseline separation of the analytes was sometimes hard to obtain in real samples and second-order derivative electropherograms were applicable for the resolution and analysis of overlapping peaks.     

Chemometrics‐assisted chromatographic fingerprinting: An illicit methamphetamine case study

The volatile chemical constituents in complex mixtures can be analyzed using gas chromatography with mass spectrometry. This analysis allows the tentative identification of diverse impurities of an illicit methamphetamine sample. The acquired two‐dimensional data of liquid–liquid extraction was resolved by multivariate curve resolution alternating curve resolution to elucidate the embedded peaks effectively. This is the first report on the application of a curve resolution approach for chromatogram fingerprinting to identify particularly the embedded impurities of a drug of abuse. Indeed, the strong and broad peak of methamphetamine makes identifying the underlying peaks problematic and even impossible. Mathematical separation instead of conventional chromatographic approaches was performed in a way that trace components embedded in methamphetamine peak were successfully resolved. Comprehensive analysis of the chromatogram, using multivariate curve resolution, resulted in elution profiles and mass spectra for each pure compound. Impurities such as benzaldehyde, benzyl alcohol, benzene, propenyl methyl ketone, benzyl methyl ketone, amphetamine, N‐benzyl‐2‐methylaziridine, phenethylamine, N ,N ,α‐trimethylamine, phenethylamine, N ,α,α‐trimethylmethamphetamine, N‐acetylmethamphetamine, N‐formylmethamphetamine, and other chemicals were identified. A route‐specific impurity, N‐benzyl‐2‐methylaziridine, indicating a synthesis route based on ephedrine/pseudoephedrine was identified. Moreover, this is the first report on the detection of impurities such as phenethylamine, N ,α,α‐trimethylamine (a structurally related impurity), and clonitazene (as an adulterant) in an illicit methamphetamine sample.     

Evaluation of peak overlap in migration-time distributions determined by organelle capillary electrophoresis: Type-II error analogy based on statistical-overlap theory

Organelles commonly are separated by capillary electrophoresis (CE) with laser-induced-fluorescence detection. Usually, it is assumed that peaks observed in the CE originate from single organelles, with negligible occurrence of peak overlap. Under this assumption, migration-time and mobility distributions are obtained by partitioning the CE into different regions and counting the number of observed peaks in each region. In this paper, criteria based on statistical-overlap theory (SOT) are developed to test the assumption of negligible peak overlap and to predict conditions for its validity. For regions of the CE having constant peak density, the numbers of peaks (i.e., intensity profiles of single organelles) and observed peaks (i.e., maxima) are modeled by probability distributions. For minor peak overlap, the distributions partially merge, and their mergence is described by an analogy to the Type-II error of hypothesis testing. Criteria are developed for the amount of peak overlap, at which the number of observed peaks has an 85% or 90% probability of lying within the 95% confidence interval of the number of peaks of single organelles. For this or smaller amounts of peak overlap, the number of observed peaks is a good approximation to the number of peaks. A simple procedure is developed for evaluating peak overlap, requiring determination of only the peak standard deviation, the duration of the region occupied by peaks, and the number of observed peaks in the region. The procedure can be applied independently to each region of the partitioned CE. The procedure is applied to a mitochondrial CE.     

A continuous wavelet transform algorithm for peak detection

Contactless conductivity detector technology has unique advantages for microfluidic applications. However, the low S/N and varying baseline makes the signal analysis difficult. In this paper, a continuous wavelet transform-based peak detection algorithm was developed for CE signals from microfluidic chips. The Ridger peak detection algorithm is based on the MassSpecWavelet algorithm by Du et al. [Bioinformatics 2006, 22, 2059-2065], and performs a continuous wavelet transform on data, using a wavelet proportional to the first derivative of a Gaussian function. It forms sequences of local maxima and minima in the continuous wavelet transform, before pairing sequences of maxima to minima to define peaks. The peak detection algorithm was tested against the Cromwell, MassSpecWavelet, and Linear Matrix-assisted laser desorption/ionization-time-of-flight-mass spectrometer Peak Indication and Classification algorithms using experimental data. Its sensitivity to false discovery rate curve is superior to other techniques tested.     

一阶导数停流法测定药物和饮用水中的铁

本文利用Ｆｅ＾３＋离子催化Ｈ２Ｏ２氧化四甲基对苯二胺的反应，将采用停流技术获得的动力学曲线转换成一阶导数曲线，根据导数峰高值与Ｆｅ＾３＋离子浓度的线性关系测定药物和自来水中的含量，本方法的线性范围为４．０－４０．０ｎｇＦｅ＾３＋／ｍｌ，相对标准偏差小于２．５％，标准加入回收率在９８．７％－１０１％之间，检测限为１．９２ｎｇＦｅ＾３＋／ｍｌ。对照实验结果表明，导数动力学法比一般非导数动力学法具有线关     

基于无基底扣除的数据趋势累积谱峰检测算法

谱峰的检测分析在色谱技术研究中具有十分重要的作用,但在色谱数据采集、传输的过程中,不同程度的噪声干扰给谱峰检测带来了极大的困难。目前传统的谱峰检测算法普遍通过基底扣除的方式对谱峰的形态进行预定义,将谱峰分为单峰、重叠峰等多个种类。针对不同种类的谱峰采用不同的检测方法,这就导致了传统的谱峰检测算法具有高复杂度、低自动化程度以及容易失真等缺点。因此,该文从另一个角度出发提出了一种新型的谱峰检测算法。该算法取消基底扣除以及谱峰分类这一步骤,直接在源数据曲线的基础上进行谱峰检测,主要分为离散差分、趋势累积以及遍历寻峰3个步骤。首先通过信号量表征数据升降趋势;然后进行数据趋势累积,根据累积总和定位谱峰,采用三点定位的方式,即峰起点、极值点和峰终点描述一个谱峰的位置;最后根据遍历排序的方式进行谱峰的筛选。此外,通过谱峰扣除的方式得到曲线基底部分。采用C语言设计编写了算法程序,并对多个动态比表面积分析仪测定的色谱图进行了检测分析,结果显示使用该算法可以精准区分谱峰部分与基底部分,受数据曲线毛刺、震荡等噪声干扰很小,谱峰的三点定位十分准确,且不受其复杂形态的影响,具有很强的普适性。与其他算法相比,该算法定位准确,结构清晰,具有较好的稳定性以及可靠性。该文报道了无基底扣除以及趋势累积等新型谱峰检测思想在吸脱附色谱曲线中的应用,证明了其在吸脱附色谱峰检测中的有效性和良好的应用前景。     

基于非接触式电导信号的土壤速效钾含量检测方法

该文针对土壤中速效钾含量采用传统测定法操作复杂、检测时效滞后的问题,建立了基于非接触式电导检测信号快速检测土壤速效钾含量的分析方法。采用高效毛细管电泳/非接触式电导检测仪获取河南潮土的非接触式电导检测信号,并使用导数法与高斯曲线拟合法相结合进行初步峰谱识别,按条件进行峰值过滤后,引入基于Levenberg-Marquardt(L-M)的高斯分峰拟合算法,实现了单峰和重叠峰的拟合计算,得到高斯峰和相应的特征参数,包括峰位、峰高、半峰宽和峰面积;最后将拟合得到的高斯峰及相应的特征参数表征原始非接触式电导检测信号离子峰谱信息结合偏最小二乘法(PLS),确定特征参数与土壤速效钾含量的关系,建立模型,实现了对土壤中速效钾含量的预测。结果表明,将基于L-M的高斯分峰拟合算法结合偏最小二乘法应用于非接触式电导检测信号测定土壤速效钾含量时具有较高精度,回归模型决定系数(R~2)为0.856 4,相对分析误差(RPD)为2.639,适用于土壤速效钾的快速检测分析。     

Calibration of solid sampling Zeeman atomic absorption spectrophotometry by extrapolation to zero matrix

Summary A new method is described for the calibration of solid sampling Zeeman atomic absorption spectrophotometry, which can be applied independently of the use of certified reference materials. The specific signal (peak height divided by analyte mass or peak height divided by sample mass, for standard and sample, resp.) is plotted as a function of the analyte or the sample mass, and the line is extrapolated to zero mass. It is believed that this gives a specific signal not influenced by deviations from linearity of the calibration curve and free from matrix effects. The method yielded good results for Zn, Cd and Pb in several certified reference materials.Presented at the 5th International Colloquium on Solid Sampling with Atomic Spectroscopy, May 18–20, 1992; Geel, Belgium. Papers edited by R. F. M. Herber, Amsterdam     

Determination in gas chromatography—mass spectrometry data of mass spectra free of background and neighboring substance contributions

The determination in a g.c.—m.s. data matrix by singular value analysis and least squares of the mass spectra of the substances present and of their corresponding resolved g.c. peak profiles has been supplemented by the determination of a background for each mass, assumed to be constant over 10–12 contiguous scans. The norm for the g.c. peaks has been changed to a maximum of one so that the mass spectral intensities are proportional to the true ion currents at the respective g.c. peak maxima. Complete resolved spectra are computed by using all measured masses. Examples are given of close resolutions (less than one scan separation) and multiple overlap resolution (8 overlapping substances). The method is compared with other published clean-up methods.     

First-order derivative resolution of overlapped PAH peaks with common mass spectra in gas chromatography-mass spectrometry

First-order derivative of 15 points smoothed chromatograms of mixtures of benzo(b)fluoranthene (BbF) and benzo(k)fluoranthene (BkF) for the m/z 252 ion obtained using two microscans has been proposed as a simple alternative to the resolution of overlapped chromatographic peaks of these two compounds which have identical mass spectra. The procedure provides limits of detection of 12 and 29ngg(-1) for BbF and BkF, respectively and offers the possibility to use the 250 and 248 ions to confirm the identity of these analytes.     

Comparative analysis of peak-detection techniques for comprehensive two-dimensional chromatography

Comprehensive two-dimensional gas chromatography (GC×GC) is a powerful technology for separating complex samples. The typical goal of GC×GC peak detection is to aggregate data points of analyte peaks based on their retention times and intensities. Two techniques commonly used for two-dimensional peak detection are the two-step algorithm and the watershed algorithm. A recent study [4] compared the performance of the two-step and watershed algorithms for GC×GC data with retention-time shifts in the second-column separations. In that analysis, the peak retention-time shifts were corrected while applying the two-step algorithm but the watershed algorithm was applied without shift correction. The results indicated that the watershed algorithm has a higher probability of erroneously splitting a single two-dimensional peak than the two-step approach. This paper reconsiders the analysis by comparing peak-detection performance for resolved peaks after correcting retention-time shifts for both the two-step and watershed algorithms. Simulations with wide-ranging conditions indicate that when shift correction is employed with both algorithms, the watershed algorithm detects resolved peaks with greater accuracy than the two-step method.     

True ion pick (TIPick): a denoising and peak picking algorithm to extract ion signals from liquid chromatography/mass spectrometry data

Liquid Chromatography ‐ Time of Flight Mass Spectrometry has become an important technique for toxicological screening and metabolomics. We describe TIPick a novel algorithm that accurately and sensitively detects target compounds in biological samples. TIPick comprises two main steps: background subtraction and peak picking. By subtracting a blank chromatogram, TIPick eliminates chemical signals of blank injections and reduces false positive results. TIPick detects peaks by calculating the S(CC_INI) values of extracted ion chromatograms (EICs) without considering peak shapes, and it is able to detect tailing and fronting peaks. TIPick also uses duplicate injections to enhance the signals of the peaks and thus improve the peak detection power. Commonly seen split peaks caused by either saturation of the mass spectrometer detector or a mathematical background subtraction algorithm can be resolved by adjusting the mass error tolerance of the EICs and by comparing the EICs before and after background subtraction. The performance of TIPick was tested in a data set containing 297 standard mixtures; the recall, precision and F‐score were 0.99, 0.97 and 0.98, respectively. TIPick was successfully used to construct and analyze the NTU MetaCore metabolomics chemical standards library, and it was applied for toxicological screening and metabolomics studies. Copyright © 2013 John Wiley & Sons, Ltd.     

Decisive problems of zone-circulating flow injection analysis and its solution

Although experiment and computer analysis of zone-circulating flow injection analysis (ZCFIA) data have been investigated, there are still some essential problems inherent to ZCFIA. Computer program of high dimensional modified simplex method was used for resolving peaks of ZCFIA damped response curves. Peaks are resolved on the basis of the criterion that each area of the peak surrounded by the curve and the abscissa is equal, because each sample zone circulates repeatedly in the manifold in equal volume. As a result, the peaks of the damped response curve have been resolved into each component and the curve obtained by summing these components has been proved to be equal to the original response curve. By following up the data analysis of ZCFIA, it was found that there were many conflicts in the manual analysis of data by Li. At least, the dispersion in a flow system should not be investigated by ZCFIA, and it might be studied by the single-line manifold of FIA.