峰形分析辅助色谱定性的研究

尝试建立了一种通过峰形分析进行色谱定性的方法。首先选择一组既易于测量,又能较好地表征色谱峰形特性的参数（峰宽、不对称因子）作为峰形分析的基础;其次,通过理论和实验证明：对于保留时间与标准物质非常接近的未知组分,可将样品与标准物质混合进样,得到重叠谱图（表观为单峰）,然后通过对重叠谱峰与标准物质谱峰的峰形分析与比较,达到对未知物定性的目的。     

一种变压器油色谱峰识别算法的设计

在变压器油色谱峰识别领域,传统的一阶导数法需要斜率阈值来实现色谱峰识别,因此自动化程度低及容易失真。针对这些缺点,本文在一阶导数法的基础上进行了改进,将迭代移动平均及归一化分析技术应用到色谱峰识别中,通过对信号曲线及方波曲线多次迭代移动平均确定最优的归一化识峰参数,结合色谱峰的绝对保留时间及识峰窗口实现对色谱峰的准确识别。实验结果表明：该算法可以准确识别色谱峰,对噪声、色谱峰的峰宽及峰形变化不敏感,具有很强的自适应性,满足变压器油中气体在线监测装置的现场使用要求。     

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。     

Modulation-induced error in comprehensive two-dimensional gas chromatographic separations

There is a fundamental difference between data collected in comprehensive two-dimensional gas chromatographic (GCxGC) separations and data collected by one-dimensional GC techniques (or heart-cut GC techniques). This difference can be ascribed to the fact that GCxGC generates multiple sub-peaks for each analyte, as opposed to other GC techniques that generate only a single chromatographic peak for each analyte. In order to calculate the total signal for the analyte, the most commonly used approach is to consider the cumulative area that results from the integration of each sub-peak. Alternately, the data may be considered using higher order techniques such as the generalized rank annihilation method (GRAM). Regardless of the approach, the potential errors are expected to be greater for trace analytes where the sub-peaks are close to the limit of detection (LOD). This error is also expected to be compounded with phase-induced error, a phenomenon foreign to the measurement of single peaks. Here these sources of error are investigated for the first time using both the traditional integration-based approach and GRAM analysis. The use of simulated data permits the sources of error to be controlled and independently evaluated in a manner not possible with real data. The results of this study show that the error introduced by the modulation process is at worst 1% for analyte signals with a base peak height of 10xLOD and either approach to quantitation is used. Errors due to phase shifting are shown to be of greater concern, especially for trace analytes with only one or two visible sub-peaks. In this case, the error could be as great as 6.4% for symmetrical peaks when a conventional integration approach is used. This is contrasted by GRAM which provides a much more precise result, at worst 1.8% and 0.6% when the modulation ratio (MR) is 1.5 or 3.0, respectively for symmetrical peaks. The data show that for analyses demanding high precision, a MR of 3 should be targeted as a minimum, especially if multivariate techniques are to be used so as to maintain data density in the primary dimension. For rapid screening techniques where precision is not as critical lower MR values can be tolerated. When integration is used, if there are 4-5 visible sub-peaks included for a symmetrical peak at MR=3.0, the data will be reasonably free from phase-shift-induced errors or a negative bias. At MR=1.5, at least 3 sub-peaks must be included for a symmetrical peak. The proposed guidelines should be equally relevant to LCxLC and other similar techniques.     

Recognizing chromatographic peaks with pattern recognition methods : Part 1. Development of a k-nearest-neighbour technique

Problems in automated peak recognition in chromatography are discussed. An algorithm based on the k-nearest neighbour technique is proposed. Recognition of a peak is done by comparing it with a predefined profile function (normally a Gaussian peak profile). The profile and a part of the chromatogram are both interpreted as points in a multi-dimensional pattern space. The distance between the two points gives the value of the peak recognition function. The effects of different properties of chromatographic peaks (i.e., peak width, peak height and noise) and of the profile parameter (i.e., dimension of the pattern space, shape and width of the function, and characteristics of the distance measure) are evaluated. The method has excellent properties for recognizing peaks with low signal/noise (S/N) ratios; an example with S/N = 1 is shown. Changing peak widths and drifting baselines have little effect on the recognition ability. Difficulties with changing peak heights can be compensated by range scaling. Problems occur when two peaks are not sufficiently separated.     

Improved computer algorithm for characterizing skewed chromatographic band broadening : II. Results and comparisons

A newly developed method using an exponentially modified Gaussian peak shape model produces results that are more precise and less subject to baseline noise than previous methods for characterizing chromatographic band broadening. The method requires only precisely measurable experimental peak parameters: peak retention time, peak height, peak area, and peak centroid (first moment). Accuracy and precision of the new method were compared with other digital approaches by using computer-synthesized peaks and experimental chromatographic data from many HPLC columns. The proposed method offers a reasonable compromise between accuracy, precision, and convenience. A rapid visual estimate of peak skew can be made by inspecting peak shape and referring to a calibration plot involving peak parameters. Peak variance and skew data from this method are also useful for finding column dispersion corrections in size-exclusion chromatography calibrations.     

Parametric studies of matched filters to enhance the signal-to-noise ratios of LC-MS-MS peaks

Chromatographic parameters of reference signals employed in matched filter methods have been studied using numerical experiments to improve the signal-to-noise (S/N) ratios of small liquid chromatography (LC) peaks obtained with electrospray tandem mass spectrometers (MS-MS). These parameters include the width, shape, and S/N ratios of chromatographic peaks used as the reference signal profiles. Our results show the effect of reference peak widths on improving the S/N ratio of chromatographic peaks; the influence of reference peak shapes is negligible. To verify simulation results, various reference signals, including analyte peaks of high concentration standards, internal standard peaks, and artificial Gaussian peaks of different widths, have been employed to enhance signal peaks on real liquid chromatography-tandem mass spectrometry (LC-MS-MS) chromatograms via matched filter methods. Our experimental results demonstrate that the S/N ratio enhancement of chromatographic peaks agree with the simulation predictions. These findings, therefore, suggest that regardless of peak shape, a well-smooth peak with a width close to that of the analyte peak is an adequate reference signal, when matched filter methods are used to improve LC-MS-MS chromatograms. Nevertheless, all methods processed LC-MS-MS peaks in this study do not achieve the ideal improvement ratios estimated with simulation results. We attribute this deficiency to spike-like noise, which have considerable low frequency components riding on LC-MS-MS chromatograms. Matched filtering, which works as a low-pass filter in the frequency domain, cannot effectively eliminate low frequency flicker noise contributed by these spikes. In addition, simple median filtering does not provide adequate improvement despite being able to smooth out most spikes in the chromatograms.     

Prediction of retention times and efficiency in linear gradient programmed pressure analysis on capillary columns

A method for the prediction of the retention time and the resolution of chromatographic peaks in different experimental conditions by starting from few experimental data measured in isothermal and isobaric analyses was published previously. In this paper, the same mathematical model was implemented for calculating the retention times and the column efficiency in programmed pressure runs. Some models originated from the Golay equation and reported in the literature are compared, and a new modified equation for the calculation of the peak width at half height is proposed. The procedure for the prediction of the retention time and the peak width at half height at programmed pressure of the carrier gas and different column temperature and linear gradient by using retention data of different compounds obtained in few isobaric runs is described. The prediction of the retention time and the separation efficiency of compounds with different polarity gave good results for the programmed pressure runs with linear gradient. The effect of the variation of the initial parameters of the experimental analyses and of the mathematical model on the accuracy of the prediction has been evaluated.     

Evaluation and prediction of the shape of gas chromatographic peaks

The evaluation and prediction of the shape of asymmetric gas chromatographic peaks is important as the knowledge of the amount of tailing permits to foresee the resolution between closely eluting peaks and to select the best analytical conditions for an efficient and rapid separation. A model function was tested in order to approximate the true peak shape obtained on non-polar column by injecting different compounds. The trend of the parameters involved in the used equation has been investigated as a function of column temperature and inlet pressure. The reproduction of the symmetrical or asymmetrical shape of gas chromatographic peaks is satisfactory and the method also permits to predict the shape of peaks obtained in different conditions of temperature and pressure.     

Peak area measurement of severely overlapped pairs

Summary Based on the ratio of two apparent heights and an empirical correction factor, a method is presented for quantitation of peak areas of severely overlapped pairs. This method can be applied to a wide range of area ratios and peak asymmetries, provided there exists a clear and precise valley-except for shoulder peaks. The relative errors of the first peak are usually within ±3% and theoretical relative error limits are −7.0% to +5.5%. Peak asymmetry of a severely overlapped pair can be determined using the ratio of the front half-width to the rear half-width at 10% peak height of an overlapping profile. The asymmetry so determined is an apparent one and the relative errors are −4% to +5.3% for peaks with 90% relative valley, depending on area ratio, degree of overlap and asymmetry. An empirical area equation for the first peak involving area ratio, asymmetry, resolution and the area measured by a perpendicular drop algorithm is also developed.     

Influence of the peak height distribution on separation performances: Discrimination factor and effective peak capacity

Summary A new index of performance of the chromatographic separation between two adjacent peaks, the discrimination factor, d₀, is defined. It is normalized between 0 and 1 and is directly and easily determined from the chromatogram. It does not depend on any assumption regarding peak shape, except that the peak profiles of individual sample components have a single mode. Its value depends on the relative heights of the two peaks as well as on their separation. The separation power of a chromatographic system is classically measured by its peak capacity, defined on the basis of constant resolution between adjacent peaks. A previously developed statistical theory of the composition of mixtures makes it possible to extend the concept of peak capacity by taking into account the peak height distribution in typical average chromatograms. A new parameter, the effective peak capacity, is defined for this purpose on the basis of a constant discrimination factor between adjacent peaks. It allows to take into account the distribution of peak heights in statistical theories of the evaluation of complex chromatograms and in the measurement of the limit of determination in quantitative analysis. The characteristics of the two new parameters, the discrimination factor and effective peak capacity, are discussed and compared with those of their classical homologs, resolution and peak capacity, in the case of gaussian component peaks of equal widths.     

Modeling of analytical peaks: peaks properties and basic peak functions

The general approach to the detailed characterizing of peak properties based on the use of characteristic points on a peak contour located at the certain levels is proposed. Three basic functions of peaks have been chosen which are submitted in normalized form on height and width. The ability to characterize a peaks shape of a certain analytical series is shown by an example of series of analytical peaks of thallium obtained by stripping voltammetry at linear and step potential sweep. Also the proposed shape parameters are studied for groups of stripping voltammetry and chromatographic peaks.     

Effect of injected sample amount on the shape of chromatographic peaks under condition of linear partition isotherm

In a previous paper a model function was tested in order to approximate the peak shape obtained on non-polar column by injecting different compounds. The simulation of the symmetrical or non-symmetrical shape of gas chromatographic peaks was satisfactory. In this paper, the influence of the amount of injected substance was investigated at different values of inlet pressure and carrier gas velocity, in order to evaluate the relative contribution to the total peak area and shape of the symmetrical distribution due to partition phenomena and of the non-symmetrical and tailing distribution due to adsorption-desorption kinetics. The effect of the molecular mass and of the chain length of compounds belonging to the homologous series of 1-alcohols and n-alkanes on the adsorption phenomena was evaluated.     

使色谱峰产生拖尾的一个因素--柱出口效应

使用塔板理论证明存在一种使正常色谱峰产生拖尾的因素－柱出口效应。证明符合线性分配的样品组分虽然在色谱内存在3种不同浓度的分布形态,但在流出色谱后却都因柱出口效应的影响而转变成拖尾峰。在不加任何近似处理的情况下,使用塔板理论直接对不同塔板数、容量因子的色谱峰不对称性进行了计算;计算结果同样支持了柱出口效应的存在。     

On-line graphite furnace atomic absorption spectrometry for liquid chromatographic detection Theoretical and experimental study

A simplified theory of on-line discontinuous detection in liquid chromatography is presented that makes provision for the effects of the interface measurement on peak shape. Optimum conditions were established: the detector time cycle and the retention time of the interface have to be consistent with the chromatographic peak width. Analytical use of the method necessitates measurement of the peak area, as the peak height is very sensitive to many parameters. Experimental verification of the theoretical conclusions is presented for a speciation method for butyltin compounds at trace levels.     

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。     

A novel approach of initial vectors construction in iterative target transformation factor analysis

The construction of the favorable initial iterative vectors is the key to iterative target transformation factor analysis (ITTFA). A tentative approach to construct the better initial vectors, which is based on the chromatographic information provided by evolving factor analysis (EFA), is proposed. A region, which contains the peak position at maximum height, is determined. Several elements in the region of each initial vector, instead of one element, are initialized as 1. The elements out of the region are initialized as 0. So it is not necessary to determine the exact peak position at maximum height for the resolution of partly overlapping chromatographic profiles, which may avoid the divergence brought by determination of the peak position at maximum height. In addition, it may give acceptable resolution for the embedded peaks. It is applied to resolve 2D-simulated data and experimental liquor GC/MS data, the resolutions are reasonable and improved.     

Mathematical correction for polyatomic interferences in the speciation of chromium by liquid chromatography–inductively coupled plasma quadrupole mass spectrometry

A procedure for overcoming polyatomic interferences in liquid chromatography–quadrupole inductively coupled plasma mass spectrometry based on the mathematical correction point by point along the chromatogram is described. Correction factors, that are part of the elemental equations used for mathematical correction, were calculated from the height or the area of the peaks obtained after measurement of interference stock solutions by flow injection. Due to the sequential nature of quadrupole mass spectrometers, the selection of the acquisition parameters with respect to the peak width and the number of isotopes monitorised is critical. A sampling frequency which allows getting a minimum of 20 points per peak is recommended to avoid artifacts in the corrected profiles of the peaks. The effect of polyatomic interferences from carbon and chlorine on the determination and speciation of chromium by high performance size exclusion chromatography coupled to quadrupole inductively coupled plasma mass spectrometry in compost lixiviates is studied. Biased results of + 50% are successfully corrected by the proposed procedure.