A linear modulation-based stochastic resonance algorithm applied to the detection of weak chromatographic peaks

A simple stochastic resonance algorithm based on linear modulation was developed to amplify and detect weak chromatographic peaks. The output chromatographic peak is often distorted when using the traditional stochastic resonance algorithm due to the presence of high levels of noise. In the new algorithm, a linear modulated double-well potential is introduced to correct for the distortion of the output peak. Method parameter selection is convenient and intuitive for linear modulation. In order to achieve a better signal-to-noise ratio for the output signal, the performance of two-layer stochastic resonance was evaluated by comparing it with wavelet-based stochastic resonance. The proposed algorithm was applied to the quantitative analysis of dimethyl sulfide and the determination of chloramphenicol residues in milk, and the good linearity of the method demonstrated that it is an effective tool for detecting weak chromatographic peaks. Figure The linear modulation-based stochastic resonance algorithm (LSRA) improved the output chromatographic peak of chloramphenicol     

Linear Modulated Stochastic Resonance Algorithm Applied to Determination of Thidiazuron Residue in Water Using Stochastic Resonance

Abstract

The newly proposed linear modulated stochastic resonance algorithm (LSRA) was used to amplify and detect the weak chromatographic peaks of thidiazuron. The output chromatographic peak is often distorted when using the traditional stochastic resonance algorithm because of the existence of strong noise. In LSRA, the distortion of the output peak can be corrected by introducing a linear force into the nonlinear system. A two‐step optimization method was proposed to give attention to both the signal‐to‐noise ratio and the peak shape of output signal. The weak chromatographic peaks of thidiazuron can be amplified significantly and the distortion of the output peaks can be corrected using LSRA. The algorithm was used to detect thidiazuron residue in water with solid phase extraction‐high performance liquid chromatography. The limit of detection and limit of quantification were improved to 2.5 ng/l and 10 ng/l, respectively.     

UV-triggered main-component fraction collection method and its application for high-throughput chromatographic purification of combinatorial libraries

A maximum-seeking, algorithm-driven fraction collection method was developed to support high-throughput chromatographic purification, which provides new possibilities for off-line high-performance liquid chromatography mass spectroscopy (HPLC/MS) quality control experiments. The method is based on manipulation of a six-port valve that is installed downstream from the UV detector and equipped with a fraction collector loop. The detector signal is monitored by a programmable microcontroller that controls the state of the fraction collector valve. After detecting a chromatographic peak, the appropriate fraction is stored in the collector loop. The height of the next peak is compared to the previous one (using a maximum-seeking algorithm) and, depending on the result, the collected fraction is or is not exchanged with the new one. At the end of the run, the stored UV main component is pumped into the external fraction vial. This configuration was used for chromatographic purification of large compound libraries (the results of the purification of 5324 compounds are reported here), as well as for high-throughput off-line HPLC quality control experiments, where the collected main component fractions of an analytical-scale separation were subjected to further mass spectrometric molecular weight verification.     

Coupled stochastic resonance to improve chromatography determinations

Traditional bistable stochastic resonance has been demonstrated as an effective tool to detect the weak signal in a strong noise background. To achieve a better signal-to-noise ratio for the output signal, a coupled stochastic resonance was developed by nonlinearly coupling two double-well potential systems. The response characteristics of coupled stochastic resonance subjected to analytical signals have been investigated and compared with those of bistable stochastic resonance. The improvement of chromatographic determination with the proposed coupled stochastic resonance was validated by both simulated signals and chromatographic signals. The weak signals from both simulated data and plasma samples with different concentrations were all amplified significantly and the quantitative relationship between different concentrations and responses was kept well. It is reasonable to believe that coupled stochastic resonance could play an important role in applications where quantitative determination of low-concentration samples is crucial.     

一种有效提取弱信号的新方法

随机共振 ( Stochastic Resonance,简称 SR)最初由 Benzi[1] 于 1 981年提出 ,并在气象学领域中得到了成功的应用 .根据随机共振理论 ,通过加噪声可在某一“共振”点处大幅度提高信号的信噪比 .这种方法也已成功地应用于方波脉冲信号的恢复 [2 ] ,但在化学信号中的应用尚属空白 .我们首次将这种方法用于化学弱信号的检测 ,并在简单喇曼谱图的解析中获得成功 [3 ] .但是 ,加噪声的方法作为一种有效的信号分析手段还显得很不成熟 .具体表现为处理过程较繁 ,分析信号的峰位偏移明显 ,而且结果在一定程度上要依赖人为判断来决定 [3 ] .　　在…     

Stochastic resonance is applied to quantitative analysis for weak chromatographic signal of glyburide in plasma

Based on the theory of stochastic resonance, a new method carried on the quantitive analysis to weak chromatographic signal of glyburide in plasma, which was embedded in the noise background and the signal-to-noise ratio (SNR) of HPLC-UV is enhanced remarkably. This method enhances the quantification limit to 1 ng ml⁻¹, which is the same as HPLC-MS, and makes it possible to detect the weak signal accurately by HPLC-UV, which was not suitable before. The results showed good recovery and linear range from 1 to 50 ng ml⁻¹ of glyburide in plasma and the method can be used for quantitative analysis of glyburide.     

A Novel Approach to Improve the Detectability of CO2 by GC Analysis

A novel stochastic resonance algorithm was employed to enhance the signal-to-noise ratio (SNR) of signals of analytical chemistry.By using a gas chromatographic data set,it was proven that the SNR was greatly improved and the quantitative relationship between concentrations and chromatographic responses remined simultancously.The linear range was extended beyond the instrumental detection limit.     

Application of the stochastic resonance algorithm to the simultaneous quantitative determination of multiple weak peaks of ultra-performance liquid chromatography coupled to time-of-flight mass spectrometry

The stochastic resonance algorithm (SRA) has been developed as a potential tool for amplifying and determining weak chromatographic peaks in recent years. However, the conventional SRA cannot be applied directly to ultra-performance liquid chromatography/time-of-flight mass spectrometry (UPLC/TOFMS). The obstacle lies in the fact that the narrow peaks generated by UPLC contain high-frequency components which fall beyond the restrictions of the theory of stochastic resonance. Although there already exists an algorithm that allows a high-frequency weak signal to be detected, the sampling frequency of TOFMS is not fast enough to meet the requirement of the algorithm. Another problem is the depression of the weak peak of the compound with low concentration or weak detection response, which prevents the simultaneous determination of multi-component UPLC/TOFMS peaks. In order to lower the frequencies of the peaks, an interpolation and re-scaling frequency stochastic resonance (IRSR) is proposed, which re-scales the peak frequencies via linear interpolating sample points numerically. The re-scaled UPLC/TOFMS peaks could then be amplified significantly. By introducing an external energy field upon the UPLC/TOFMS signals, the method of energy gain was developed to simultaneously amplify and determine weak peaks from multi-components. Subsequently, a multi-component stochastic resonance algorithm was constructed for the simultaneous quantitative determination of multiple weak UPLC/TOFMS peaks based on the two methods. The optimization of parameters was discussed in detail with simulated data sets, and the applicability of the algorithm was evaluated by quantitative analysis of three alkaloids in human plasma using UPLC/TOFMS. The new algorithm behaved well in the improvement of signal-to-noise (S/N) compared to several normally used peak enhancement methods, including the Savitzky-Golay filter, Whittaker-Eilers smoother and matched filtration.     

The stochastic resonance algorithm with the direct current signal as external force and its application to the detection of weak chromatographic peaks

As a potential tool for amplifying weak chromatographic peaks, the stochastic resonance algorithm was developed based upon a counterintuitive physical phenomenon. Therefore, the essential step, parameter optimization, was perplexing and difficult for analysts. In order to avoid optimizing the system parameters on a case‐by‐case basis, an improved algorithm was proposed by introducing a constant or direct current signal into the signal to be measured as the external force. The weak chromatographic peak can be amplified and detected by the new algorithm using the same set of parameters. Two sets of our previous experimental data were reanalyzed by using the developed algorithm and the results were satisfactory. A generalized solution was expected to come into being on account of the new algorithm.     

Development of an obidoxime chloride reference material: a metrological approach to the determination of chromatographic purity

A metrological approach to determination of the chromatographic purity of obidoxime chloride and the corresponding obidoxime chloride reference material (RM) with a certified chromatographic purity value have been developed. This value was defined as the ratio of the sum of peak areas of obidoxime chloride isomers to the total peak area of detected substances including impurities (%) under specified HPLC–UV conditions. The RM homogeneity and stability were studied using HPLC with UV detection and evaluated as satisfactory. The certified value calculated from the results of an interlaboratory trial was equal to 99.9% with the expanded uncertainty of 0.6% at the level of confidence 0.95 and the coverage factor 2. The RM certified value, like other results of chromatographic purity determination traceable to the reference measurement procedure, is not traceable directly to the SI mole. However, the results are comparable in metrologically traceable environments, i.e. when relevant measuring laboratory instruments are calibrated with traceability chains to the corresponding SI units. Therefore, the RM can be used as a measurement standard (calibrator) for analytical instruments and as a control sample for quality control of HPLC obidoxime chloride assay results.     

Stochastic resonance algorithm applied to quantitative analysis for weak liquid chromatographic signal of pyrene in water samples

The phenomenon of stochastic resonance (SR), which was discovered in recent years, rendered an entirely new way for the detection of weak signals, and it has been widely studied in many different science fields. This phenomenon is manifest in nonlinear systems whereby a weak signal can be amplified when the noise, signal and nonlinear system attain the proper cooperation. The introduced algorithm was employed to detect pyrene in drinking water samples with solid-phase extraction–liquid chromatography. The weak chromatographic peak of the analyte was amplified significantly, and the profiles of the peaks were also satisfactory. The limit of detection and the limit of quantification were improved from 0.022?ng?mL^?1 and 0.08?ng?mL^?1 to 0.004?ng?mL^?1 and 0.01?ng?mL^?1, respectively. The results showed an excellent quantitative relationship between concentrations and chromatographic responses. It is expected that the SR will be an effective tool to detect weak chromatographic peaks quantitatively in trace analysis.     

A new single-well potential stochastic resonance algorithm to detect the weak signal

Based on the stochastic resonance theory, a new single-well potential stochastic resonance algorithm (SSR) to improve the signal-to-noise ratio (SNR) is presented. In the new algorithm, stochastic resonance takes place in a single-well potential driven only by the noise. The effect on the proposed algorithm is discussed. By using simulated and experimental data sets, it is proven that the signal-to-noise ratio (SNR) of the weak signal can be greatly enhanced by this method. The new single-well potential stochastic resonance algorithm (SSR) may be a promising tool to extend instrumental linear range and to improve the accuracy of trace analysis. The research enlarges the application scope of single-well potential to nonlinear signal processing.     

随机共振与仪器分析中弱信号的检测

样品分析过程中，往往得到背景噪声很强的信号，尤其在微量和痕量水平；当信号的信噪比很小时，通常的方法不能满足检测要求，该文基于随机共振理论提出了一种新的弱信号的检测方法并对相关参数进行了讲座主；方法是通过噪声的协调作用，获得系统的“共振”，从而实现弱信号的检测，应用于模拟和实验信号的处理结果证明了方法的可行性。     

Detection of the reduced forms of radical adducts on the ESR trace using HPLC‐electrochemical detector‐ultraviolet absorption detector‐electron spin resonance‐MS

To detect and identify the electron spin resonance (ESR) silent forms of the α‐(4‐pyridyl‐1‐oxide)‐N‐tert‐butylnitrone (4‐POBN) radical adducts, an electrochemical detector (ECD) was employed as a reactor in the HPLC‐ECD‐UV absorption detector‐ESR‐MS (HPLC‐ECD‐UV‐ESR‐MS). The ECD was employed to regenerate the radical forms from the reduced forms. The reduced forms of the 4‐POBN/pentyl radical adducts were analyzed using the HPLC‐ECD‐UV‐ESR‐MS. On addition of the ECD applied potential of +0.3 V, a peak appeared on the ESR trace of the HPLC‐ECD‐UV‐ESR‐MS analyses, indicating that the radical forms are regenerated from the reduced forms. The HPLC‐ECD‐UV‐ESR‐MS analyses were also performed for the reaction mixtures of phenylhydrazine with CuCl₂. Two peaks (peaks I and II) were detected on the UV trace (300 nm) of the HPLC‐ECD‐UV‐ESR‐MS. The mass spectra showed that the peak I and peak II compounds are radical and reduced forms of the 4‐POBN/phenyl radical adducts under the ECD applied potential of 0.0 V. Peak I was only detected on the ESR trace under the ECD applied potential of 0.0 V. In addition to peak I, peak II appeared on the ESR trace under the ECD applied potential of +0.3 V, indicating that the reduced forms are oxidized to the corresponding radical forms.     

Sequential simplex optimization and multichannel detection in HPLC: Application to method development

Summary The sequential simplex procedure for the optimisation of mobile phase composition in high-performance liquid chromatography (HPLC) is combined with multichannel detection. The operating software already available in a commercial LC system is exploited and extended to incorporate a number of new routines developed to facilitate HPLC method development. An efficient stop criterion for automated simplex procedures is proposed, based on continuous comparison of the chromatographic response function attained with that predicted. The theoretical basis is developed for a new peak homogeneity test, based on the wavelength sensitivity of the chromatographic peak maximum. An algorithm for assigning peak elution order, based on peak areas at multiple wavelengths, is developed for cases where multiple optima are recorded. The simplicity and practical utility of these techniques are demonstrated in the context of an HPLC separation method developed for a model system of six solutes.     

Application of Computer-Aided Spectral Deconvolution Technique in Validation of High Performance Liquid Chromatographic Peaks

Abstract

Reliable analysis with high performance liquid chromatography (HPLC) requires purity of the eluting peak. The present work has combined the advantages of the availability of full spectral data from HPLC photodiode array UV detector and computer algorithms to perform chromatographic peak purity check. A deconvolution technique based on multicomponent analysis has been applied to the UV spectra of co-eluting components. This method employs residual error (Relative-fit-error, RFE) between predicted spectrum and analyte's spectrum to detect presence of other component or contaminant. Typical RFE values for uncontaminated chromatographic peaks of norethisterone and ethynyloestradiol range between 1 and 3, while contaminated peaks have RFE values as large as 145. A systematic increase in ‘relative-fit error’ from 1.10 to 145 was observed for peaks of norethisterone when contaminated to varied extent with ethynyloestradiol. Extent of peak overlap in chromatogram was also mapped out with this technique. The co-prescribed oral contraceptive, norethisterone and ethynyloestradiol were used as model in this work. An advantage of the method is its applicability when the contaminant's spectrum is unavailable. The method, unlike several earlier techniques, is also applicable to chromatograms with concidental elution time for the components.     

强噪声背景中微弱信号检测的初步研究

为了提高信噪比,以往大都设法滤除噪声。根据随机共振理论,本文对用添加噪声来提高测量信号信噪比的方法进行了初步的尝试,并将此方法应用于强噪声背景中微弱信号的检测,得出了一些有意义的初步结构。     

Drug impurity profiling strategies

A general scheme is set up for the estimation of the impurity profile of bulk drug substances by the complex use of chromatographic, spectroscopic and hyphenated techniques. Several examples are presented as illustrations to the scheme from the authors' laboratory involving the use of chromatographic methods such as thin-layer-(TLC), gas-(GC), analytical and preparative high-performance liquid chromatography (HPLC), spectroscopic methods such as mass spectrometry (MS) and NMR spectroscopy as well as hyphenated techniques (HPLC/diode-array UV, GC/MS and HPLC/MS). In addition to summarizing earlier work, new examples are also presented: identification of an impurity (propyl 4-[diethylcarbamoyl(methoxy)]-3-methoxy phenylglyoxylate, II) in propanidid (I) and two unsaturated impurities in allylstrenol (VII) by GC/MS and HPLC/diode-array UV as well as estimation of the impurity profile of mazipredone (III) by HPLC/MS and HPLC/diode-array UV.     

阳极溶解电化学振荡体系中白噪声诱导随机共振的模拟

通过对电化学阳极溶解振荡模型加白噪声后引发的随机共振现象的模拟研究发现,在该体系的周期二振荡态时呈现显性内信号随机共振现象。当白噪声加在该电化学体系的周期二振荡态时,内信号的信噪比随着噪声的增大达到了最大值。同样噪声强度情况下,强信号的信噪比增加比弱信号的增加更加迅速。如果同时改变噪声强度,体系的信号频率也维持不变。研究表明,噪声对内信号的优化具有选择性,而体系的内信号也具有抵抗噪声和维持内在机制不变的性质。     

内噪声作用下的随机共振算法对弱信号的检测

基于随机共振理论提出了一种简便、有效地检测弱信号的方法。在内噪声协同作用下，通过调节输入噪声信号的大小能较好地提高系统输出信号的信噪比，从而实现检测背景噪声很强的弱信号的目的。应用于模拟信号和实验信号的结果证明了方法是可行的。