Combined use of algorithms for peak picking, peak tracking and retention modelling to optimize the chromatographic conditions for liquid chromatography-mass spectrometry analysis of fluocinolone acetonide and its degradation products

A strategy for rapid optimization of liquid chromatography column temperature and gradient shape is presented. The optimization as such is based on the well established retention and peak width models implemented in software like e.g. DryLab and LC simulator. The novel part of the strategy is a highly automated processing algorithm for detection and tracking of chromatographic peaks in noisy liquid chromatography-mass spectrometry (LC-MS) data. The strategy is presented and visualized by the optimization of the separation of two degradants present in ultraviolet (UV) exposed fluocinolone acetonide. It should be stressed, however, that it can be utilized for LC-MS analysis of any sample and application where several runs are conducted on the same sample. In the application presented, 30 components that were difficult or impossible to detect in the UV data could be automatically detected and tracked in the MS data by using the proposed strategy. The number of correctly tracked components was above 95%. Using the parameters from the reconstructed data sets to the model gave good agreement between predicted and observed retention times at optimal conditions. The area of the smallest tracked component was estimated to 0.08% compared to the main component, a level relevant for the characterization of impurities in the pharmaceutical industry.     

全二维气相色谱/飞行时间质谱用于烟叶中酸性成分的分离与分析

建立了烟叶中酸性化合物(挥发性、 半挥发性羧酸类和酚类)组成研究的全二维气相色谱/飞行时间质谱(GC×GC-TOFMS)分析方法, 并用此方法对香料烟中的酸性化合物进行了表征. 用同时蒸馏萃取样品的前处理方法, 采用TOFMS谱图库检索结合全二维特有的包含结构信息的二维谱图, 通过族分离和结构谱图, 鉴定出了香料烟中143种挥发性及半挥发性酸性组分, 包括10种酸酐和呋喃二酮, 43种有机酸和90种酚类化合物. 同时对不同类别的化合物在二维气相色谱上的分布模式进行了研究. 结果表明, 全二维气相色谱飞行时间质谱的高分辨率非常适合于烟叶这类复杂体系的分离分析.     

五味子提取物高效液相色谱分析方法的优化

针对五味子乙醇提取物的复杂体系,借助于复杂样品分析系统软件(CSASS),根据组分在4次简单线性梯度下42个峰的保留时间,快速准确地计算出各组分的液相色谱保留参数a,c值和峰形参数σ,W1/2。借助这些参数,对五味子色谱的分离情况进行高精度仿真预测。在此基础上,应用移动重叠分辨分离图和谱图仿真技术,发展了计算机辅助的五味子提取物的高效液相色谱全局优化方法。在优化条件下,五味子提取物的高效液相色谱分析可在40 min内完成,且常量成分和部分低含量成分都能够得到较好的分离。所建立的方法已成功地用于五味子中化合物保留时间及峰形的预测,并在此基础上对其色谱分离条件进行优化。     

Determination of volatile components in peptic powder by gas chromatography-mass spectrometry and chemometric resolution

Gas chromatography-mass spectrometry (GC-MS) coupled with chemometric resolution upon two-dimensional data was proposed as a method for the analysis of volatile components in a traditional Chinese medicinal preparation peptic powder which contains Rhizoma Atractylodis, Pericarpium Citri Reticulatae, Cortex Magnoliae Officinalis and Radix Glycyrrhizae. Ninety-three components were separated and 65 of them were qualitatively and quantitatively analyzed which represented about 90.28% of the total content. With the help of chemometric resolution, the data were resolved into a pure chromatogram and a mass spectrum of each chemical component. The accuracy of qualitative and quantitative results was greatly improved by using the two-dimensional comprehensive information of chromatograms and mass spectra. The example showed that chemometric resolution could greatly enhance separation ability. This makes it possible to analyze complicated practical systems like traditional Chinese medicinal preparations with the help of coupled instruments and chemometric resolution methods.     

Bayesian peak tracking: A novel probabilistic approach to match GCxGC chromatograms

A novel peak tracking method based on Bayesian statistics is proposed. The method consists of assigning (i.e. tracking) peaks from two GCxGC-FID data sets of the same sample taken in different conditions. Opposed to traditional (i.e. deterministic) peak tracking algorithms, in which the assignment problem is solved with a unique solution, the proposed algorithm is probabilistic. In other words, we quantify the uncertainty of matching two peaks without excluding other possible candidates, ranking the possible peak assignments regarding their posterior probability. This represents a significant advantage over existing deterministic methods. Two algorithms are presented: the blind peak tracking algorithm (BPTA) and peak table matching algorithm (PTMA). PTMA method was able to assign correctly 78% of a selection of peaks in a GCxGC-FID chromatogram of a diesel sample and proved to be extremely fast.     

GC—TOF／MS及主成分投影法用于安息香膏的成分分析

利用气相色谱-飞行时间质谱,对安息香膏的挥发性成分进行分析,并用峰面积归一化法计算各成分相对含量。利用在两种不同极性色谱柱上的比较试验,确定了适合安息香膏分析的色谱柱条件。在最适合安息香膏分离的色谱条件下对4种不同批次安息香膏的微差样品进行分析。通过质谱库检索,辅助英文版精油库（ES02006版）比对,解析并确定出精油中的24种组分,主要成分是苯甲酸苄酯（25．52％）、苯甲酸（23．12％）、乙基香兰素（14．93％）、苯甲醇（14．50％）、肉桂酸肉桂酯（13．41％）、肉桂酸苄酯（7．54％）等。用主成分投影分析法对4种微差样品进行分类区分,结果证明,用主成分分析法辅助GC—TOF／MS能较快速准确地对微差样品进行区分。该方法可用于安息香膏的产品开发及其品质控书1。     

Mutual peak matching in a series of HPLC–DAD mixture analyses

One of the largest challenges in high performance liquid chromatography (HPLC) method development is the necessity for tracking the movement of peaks as separation conditions are changed. Peak increments are then used to build a mathematical model capable of minimizing the number of experiments in an optimization circuit. Method optimization for an unknown mixture is, moreover, complicated by the absence of any a priori information on component properties and retention times when direct signal assignment is not possible. On the contrary, achievement of the maximum separation becomes an important factor for successful identification or quantitation. In this case, the optimization may be based on assigning peaks of the same component chosen from different experiments to each other. In other words, mutual peak matching between the HPLC runs is required.

A new method for mutual peak matching in a series of HPLC with diode array detector (HPLC–DAD) analyses of the same unknown mixture acquired at varying separation conditions has been developed. This approach, called mutual automated peak matching (MAP), does not require any prior knowledge of the mixture composition. Applying abstract factor analysis (AFA) and iterative key set factor analysis (IKSFA) on the augmented data matrix, the algorithm detects the number of mixture components and calculates the retention times of every individual compound in each of the input chromatograms. Every candidate component is then validated by target testing for presence in each HPLC run to provide quantitative criteria for the detection of “missing” peaks and non-analyte components as well as confirming successful matches. The matching algorithm by itself does not perform full curve resolution. However, its output may serve as a good initial estimate for further modeling. A common set of UV-Vis spectra of pure components can be obtained, as well as their corresponding concentration profiles in separate runs, by means of alternating least-square multivariate curve resolution (ALS MCR), resulting in reconstruction of overlapped peaks.

The algorithms were programmed in MATLAB^® and tested on a number of sets of simulated data. Possible ways to improve the stability of results, reduce calculation time, and minimize operator interaction are discussed. The technique can be used to optimize HPLC analysis of a complex mixture without preliminary identification of its components.     

Development of a three-dimensional topographic map display for capillary electrophoresis/mass spectrometry with an ion trap/reflectron time-of-flight mass spectrometer detector: Applications to tryptic digests of isoforms of myelin basic protein

A three-dimensional (3-D) contour map format has been developed to display the large amount of data continuously collected throughout an on-line capillary separation using an ion trap storage/reflectron time-of-flight detector (IT/reTOF). The resulting data are displayed on a single computer screen with a mass-to-charge ratio value-elution time-intensity representation. The intensity of various components is represented by 16 different colors so that the mass-to-charge ratio value, the elution time, and the intensity can be conveniently determined for each component. In addition, the mass spectrum and total ion chromatogram or total ion electropherogram (TIE) are shown on the same screen as the 3-D map that enables the correlation of a single spot in the 3-D map to the peaks in the TIE and the corresponding mass spectrum. The 3-D map has been used to identify various posttranslational modification sites of bovine myelin basic protein charge isomers, where the datafiles of tryptic digests of proteins analyzed by capillary electrophoresis/mass spectrometry were processed by this software and a comparison could be performed among the isoforms. The feature of in-screen integration over both the separation domain and the mass domain makes the acquisition of the selected ion chromatogram very convenient and greatly improves the ability to detect modified components present in low amounts.     

基于图论的色谱指纹图谱谱峰的全局匹配

以色谱工作站的积分数据为基础,定义了允许匹配峰组的域,提出了在域内根据色谱峰面积、保留时间计算各匹配峰组之间距离矩阵的公式,从而形成有向图。采用图论中的最短路径算法寻找可能的匹配峰组中的最佳匹配峰组。采用优化的匹配参数,对珍菊降压片、丹参提取物、柴胡皂苷提取物、人参皂苷提取物的HPLC谱图进行匹配并将有关结果与国家药典委员会推出的指纹图谱软件自动匹配结果作了比较。结果表明:本算法可最大程度地匹配可能的色谱峰并极少出现错配、漏配峰组,无需手动校正。     

Identification of structures of nitrogen-containing compounds in crude oils in conjunction with chemometric resolution

A universal method was established for the systematically structural identification of nitrogen-containing compounds in crude oils. Pre-fractionation of the non-hydrocarbons in a crude oil sample into 7 fractions was performed by di-adsorption column chromatography using neutral aluminum oxide and silica gel; subsequent high-resolution separation of individual components was achieved by using capillary column gas chromatography, and compound types were detected by mass spectrometer. The two-dimensional data from the compounds in the fractions were further resolved by a chemometric method to obtained the deconvoluted chromatogram and mass spectrum of every compound, and then, the nitrogen-containing compounds were identified in combination with the retention indices. This method could relieve the difficulty of classical analysis in identifying those species with very low contents or incompletely separation, particularly in the cases where the authentic standards were not available for addition into the unknown samples in order to reveal what indeed existed in them. The structures of 168 nitrogen-containing compounds in a crude oil sample were determined by this method with satisfactory results.     

Resolution and identification of the acidic fraction of a petroleum ether extract ofRadix Rehmanniae Preparata by an evolving chemometric approach

Summary An evolving approach is described for analyzing the acidic components of a petroleum ether extract of Radix Rehmanniae Preparata. The latter was extracted, separated and derivatized. The subsequent separation of the individual components was characterized by GC-MS. The two-way data were resolved into a pure chromatogram and a mass spectrum of each chemical component. The reliability and accuracy of the qualitative results were greatly improved and the degree of the chromatographic separation could be enhanced to a certain extent. This enabled the analysis of complicated practical systems by hyphenated instruments and these advanced methods.     

全二维气相色谱/飞行时间质谱(GC×GC/TOFMS)用于烟叶中挥发、半挥发性碱性化合物的组成研究

建立了烟叶中挥发性、半挥发性碱性化合物组成研究的全二维气相色谱/飞行时间质谱(GC×GC/TOFMS)分析方法, 并用所建立的方法对香料烟中碱性化合物进行了表征. 对比了一维气相色谱和全二维色谱方法用于烟叶碱性组分组成分析的效果. 一维色谱质谱方法共鉴定出45种碱性化合物. 用所建立的全二维气相色谱方法, 采用TOFMS谱图库检索结合全二维特有的包含结构信息的二维谱图, 通过族分离和结构谱图鉴定, 鉴定出了香料烟中挥发性、半挥发性碱性组分共92种. 包括吡咯类化合物6种, 吡啶类化合物39种, 吡嗪类化合物10种, 苯胺类化合物11种, 喹啉类化合物11种, 吲哚类4种和其他类化合物11种. 同时对不同类别的化合物在二维气相色谱上的分布模式进行了研究. 研究结果表明, 全二维色谱飞行时间质谱的高分辨率和特有的定性手段适合于烟叶这类复杂植物体系的化学组成研究.     

沉香的高效液相色谱-四极杆-飞行时间质谱数字化指纹图谱研究

采用高效液相色谱-四极杆-飞行时间质谱联用(HPLC-Q-TOF-MS)技术,研究构建了一种沉香数字化色谱-质谱指纹图谱的新方法。沉香药材经乙醇提取后,采用HPLC-Q-TOF-MS测定,并同时采集HPLC-Q-TOF-MS及液相色谱-紫外数据,得到液相色谱-紫外检测(HPLC-UV)色谱图和高分辨飞行时间质谱(TOF-MS)总离子流色谱图。对色谱图中的各个色谱峰进行精确质量数识别,建立数字化指纹图谱,以精确质量数结合保留时间表征沉香中的化学成分,即为每个色谱峰给出具有唯一性的数字信息,以数字化的形式反映其化学成分,并根据精确质量及同位素推算出分子式,结合二级质谱及文献资料共鉴定出30个化学成分。该方法对沉香的每种化学成分给出了类似于身份认定的数字化信息,具有唯一性,能全面反映沉香的物质成分,可为沉香的药理、药效及质量标准研究提供科学的数据。     

Evaluation of novel sample identification approach based on chromatographic fingerprint set correlation homogeneity analysis

Instead of usual rationale for chromatographic fingerprint based sample identification which relies upon visual inspection or principal component analysis of raw or aligned chromatograms novel nonparametric statistical measure of fingerprint set homogeneity is proposed. Randomization test is applied for significance analysis of fingerprint set homogeneity while average maximum crosscorrelation is used as a merit function. Chromatogram sets generated by random selection from standard and unknown sample chromatogram collections are compared with respect to merit function values with set of chromatograms that represents standard and/or unknown sample. In that instance fingerprint homogeneity significance is represented by the fraction of random chromatogram sets that have higher merit values than the standard and/or unknown sample sets. A set of peptide maps corresponding to different haemoglobin variants has been selected for evaluation of proposed test. This approach is compared to chromatogram alignment based on correlation optimized warping coupled with principal component or cluster analysis. Proposed method is simple i.e. straightforward sample identification procedure which reliability has been evaluated here. Impact of this approach on peptide mapping validation and system suitability analysis is discussed.     

Anion exchanger as a reaction/separation medium-absorptiometric determination of trace amounts of boron in waters by on-line complexation with chromotropic acid presorbed on the anion-exchange column

A novel method of on-line absorptiometric determination for trace amounts of boron was developed based on the complexation with chromotropic acid presorbed on an anion-exchange column. On-line reaction and separation were achieved by controlling pH conditions in solutions to accelerate the 1:2 complex formation in the concentration process at pH 3 and to stabilize the complex in the separation process at pH 8. About 75% of the boron introduced into the stream was kinetically collected as the 1:2 complex on the column under the experimental conditions. The 1:2 complex was satisfactorily separated from excess reagent and matrix components by changing the concentration of NaClO4 in the eluent and its peak height on the chromatogram monitored at 350 nm was used for calibration. The sensitivity could be enhanced by increasing the sample amount introduced and the detection limits (3sigma) were 162 ng dm(-3) and 45 ng dm(-3) of boron, when 5.0 cm3 and 13.4 cm3 of the samples were used, respectively. The method has been successfully applied to the determination of boron in samples of river water, tap water and ion-exchanged water.     

气体色谱分析的多图谱归一定量法和气体组分的相对校正因子

本文报道一种扩展的气相色谱归一化定量分析方法，使两台或两台以上色谱仪对同一样品的诸多组分所完成的多张色谱力痛应用归一定量法进行计算，从而在进行多组分测定（尤其是气体样品的分析）时大大减少工作量，本方法的关键是样品中某一组分在多张图谱中均有分离很好的峰。     

New peak broadening parameter for the characterization of separation capability in capillary electrophoresis

The influence of separation conditions on peak broadening is usually estimated by the number of theoretical plates. Using the data available in literature and experimental data, it is shown that in pressure‐assisted capillary electrophoresis the plate number is not directly related to the separation capability of conditions used. The experiments at different electrolyte flow velocities demonstrate that a higher plate number (the best separation efficiency) can be obtained with a lower peak resolution. Since ions are separated by electrophoresis due to the difference in electrophoretic mobilities, the peak width in terms of electrophoretic mobility is suggested as a new peak broadening parameter describing the separation capability of the conditions used. The parameter can be calculated using the tailing factor and the temporal peak width at 5% of the peak height. A simple equation for the resolution calculation is derived using the parameter. The advantage of the peak width in terms of mobility over other parameters is shown. The new parameter is recommended to be used not only in pressure‐assisted capillary electrophoresis but also in general capillary electrophoresis when in a number of runs the virtual separative migration distance and separation capability of the conditions used change widely.     

Essential peak area normalisation for quantitative impurity content determination by capillary electrophoresis

Summary A number of papers have been published [1–5] which mention that normalisation of CE peak areas (ie division of peak areas by migration time) is necessary to ensure correct quantitation. However, there is a general unawareness of the impact of not performing this simple data manipulation upon impurity results when expressed as % area/area. An exercise has been conducted to exemplify the need for this normalisation using the separation of selected pharmaceuticals as illustrative examples. The impact of normalisation on % area/area results was demonstrated using the pharmaceutical ranitidine, and a synthetic precusor, as test solutes. The UV absorbance of each compound was determined and found to be equivalent. A solution of ranitidine hydrochloride was the spiked with a weighed amount of precursor. The % area/area CE results, when normalised, mateched the known weighed radio. Use of uncorrected peak area data in this instance would have resulted in a severe underestimation of impurity levels. A quantitative analysis of drug related impurities was conducted at three levels of operating voltage whilst keeping all other operating parameters constant. This produced electropherograms having identical peak profiles but each peak having a different retention time and peak area. However, when normalised, the results were identical at each level of operating voltage confirming the validity and necessity of normalisation. A chiral separation of a racemic pharmaceutical was conducted. The uncorrected peak area data indicated the test sample was not racemic whilst the corrected data correctly confirmed that the compound was racemic. The significance and impact upon reported purity data of not normalising peak area data has been clearly demonstrated in this paper.     

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.     

Determination of Teucrium chamaedrys volatiles by using direct thermal desorption-comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry

The direct qualification and quantification of the volatile components of Teucrium chamaedrys was studied using a direct thermal desorption (DTD) technique with comprehensive two-dimensional (2D) gas chromatography-time-of-flight mass spectrometry (GC x GC-TOF/MS). The GC x GC separation chromatographically resolved hundreds of components within this sample, and with the separation coupled with TOF/MS for detection, high probability identifications were made for 68 compounds. The quantitative results were determined through the use of internal standards and the desorption of differing amounts of raw material in the injector. The highest yield of volatile compounds (0.39%, w/w) was obtained at 150 degrees C thermal desorption temperature using 1.0mg of dried sample placed in a glass injector liner when studied over the range 1.0-7.0mg. Lowest yield of 0.33% (w/w) was found for the largest sample size of 7.0mg. Relative standard deviation (RSD) for 10 replicates at each size sample were in the range 3.9-21.6%. The major compounds identified were beta-pinene, germacrene D, alpha-pinene, alpha-farnesene, alpha-gurjunene, gamma-elemene and gamma-cadinene. All identified compounds were quantified using total ion chromatogram (TIC) peak areas. DTD is a promising method for quantitative analysis of complex mixtures, and in particular for quantitative analysis of plant samples, which can yield data without the traditional obligation for costly and time-consuming extraction techniques.