Assessing chromatographic peak purity using condition index and singular value evolving profiles

A new method for determining chromatographic peak purity is presented. The method uses condition index evolving profiles (CIEPs) and singular value evolving profiles (SVEPs). To produce a CIEP or a SVEP, singular value decompositions are performed on data matrices containing the analyte's pure-component spectrum and sample spectra as they evolve over a chromatographic time profile. Visual inspection of condition indices and singular values as they evolve over time enables detection of less than 0.5% of a spectrally similar impurity with no chromatographic resolution (R_s = 0). Additionally, the CIEPs and SVEPs allow estimation of chromatographic pure regions. This method represents an extension of CIEPs which have been used in successful library searches of multicomponent mixtures based on gas chromatography-Fourier transform infrared spectra and liquid chromatography-UV-visible spectra.     

Semi-automated peak trapping recycle chromatography instrument for peak purity investigations

A peak trapping recycle chromatography system has been developed and optimized for peak purity assessment of active pharmaceutical ingredients analyzed by high performance liquid chromatography (HPLC). After being analyzed using a reversed phase analytical column, peaks of interest are trapped and are subsequently introduced to a recycle chromatography system. In addition to the increased effective length afforded the recycling system, the small selectivity difference between the analytical and recycling methods help separate potential impurities under the main peak. For more difficult to separate components, the increased efficiency of recycle chromatography provides the necessary resolution. Over 227,000 theoretical plates have been obtained in the recycle dimension for some compounds. The sensitivity of the system fell short of the target (0.1%), but it did show sensitivity (0.5%) comparable to other peak purity techniques commonly used in the pharmaceutical industry. The recovery and repeatability have also been shown to be adequate for peak purity assessment. The system has also been automated using a Visual Basic macro, simplifying the interface allowing it to be used as an open access instrument.     

Probabilistic peak detection for first-order chromatographic data

We present a novel algorithm for probabilistic peak detection in first-order chromatographic data. Unlike conventional methods that deliver a binary answer pertaining to the expected presence or absence of a chromatographic peak, our method calculates the probability of a point being affected by such a peak. The algorithm makes use of chromatographic information (i.e. the expected width of a single peak and the standard deviation of baseline noise). As prior information of the existence of a peak in a chromatographic run, we make use of the statistical overlap theory. We formulate an exhaustive set of mutually exclusive hypotheses concerning presence or absence of different peak configurations. These models are evaluated by fitting a segment of chromatographic data by least-squares. The evaluation of these competing hypotheses can be performed as a Bayesian inferential task. We outline the potential advantages of adopting this approach for peak detection and provide several examples of both improved performance and increased flexibility afforded by our approach.     

Chemometric quality control of chromatographic purity

It is common practice in chromatographic purity analysis of pharmaceutical manufacturing processes to assess the quality of peak integration combined by visual investigation of the chromatogram. This traditional method of visual chromatographic comparison is simple, but is very subjective, laborious and seldom very quantitative. For high-purity drugs it would be particularly difficult to detect the occurrence of an unknown impurity co-eluting with the target compound, which is present in excess compared to any impurity. We hypothesize that this can be achieved through Multivariate Statistical Process Control (MSPC) based on principal component analysis (PCA) modeling. In order to obtain the lowest detection limit, different chromatographic data preprocessing methods such as time alignment, baseline correction and scaling are applied. Historical high performance liquid chromatography (HPLC) chromatograms from a biopharmaceutical in-process analysis are used to build a normal operation condition (NOC) PCA model. Chromatograms added simulated 0.1% impurities with varied resolutions are exposed to the NOC model and monitored with MSPC charts. This study demonstrates that MSPC based on PCA applied on chromatographic purity analysis is a powerful tool for monitoring subtle changes in the chromatographic pattern, providing clear diagnostics of subtly deviating chromatograms. The procedure described in this study can be implemented and operated as the HPLC analysis runs according to the process analytical technology (PAT) concept aiming for real-time release.     

An empirical expression for the full energy peak efficiency of an N-type high purity germanium detector

An empirical expression for the full energy peak efficiency (ε) in terms of the gamma-ray energy (E) and the vertical distance from the detector surface (z) (i.e.,ε=ε(z,E)) has been obtained for an N-type high purity germanium (HPGE) detector using an extended mixed standard radionuclide solution. Comparison of the calculated efficiencies and the experimentally measured values for the energy range of 59.5–1332.5 keV and a source-to-detector distance of 1.2–7.2 cm showed that the theoretical values agree with that of the experiment within 1.5–3.7% standard deviations. This shows a good agreement between the theory and the experiment.     

便携式气相色谱仪中嵌入式谱峰识别算法设计

设计了嵌入式气相色谱谱峰识别算法,用于便携式气相色谱仪的数据分析处理,现场使用时能够不连接计算机就得出分析结果。该算法提出了用于谱峰识别的序列映射方法,减小了对斜率阈值的依赖,增强了谱峰分析的准确性和稳定性。通过实验对比可知,即使对于复杂组分的样本谱图,该嵌入式分析算法也能较好地分析提取出样品的谱峰数据,其分析结果与实验室色谱工作站软件分析结果非常接近,能够满足用户现场使用的分析需求,提高了便携仪器在现场使用的快捷性和便利性。     

Binary diffusion coefficients of phenolic compounds in subcritical water using a chromatographic peak broadening technique

Infinite dilution diffusion coefficients of certain phenolic compounds were measured as a function of temperature in water slightly acidified with formic acid using the Taylor dispersion method. The diffusion coefficients calculated using the chromatographic peak broadening technique were found to increase exponentially with an increase in the temperature. The diffusion coefficients of the selected phenolic compounds did not vary as a function of their molecular weights and the diffusion coefficients of the phenolic compounds increased as a function of temperature (from 2.16 × 10⁻¹⁰ m² s⁻¹ at 298 K to 5.79 × 10⁻¹⁰ m² s⁻¹ at 413 K for malvidin-3,5-diglucoside). However, for some phenolic compounds such as gallic acid monohydrate, quercetin-3-β-d-glucoside, protocatechuic acid and (−)-epicatechin, there were difficulties in making measurements above temperatures of 352 K, 372 K, 392 K and 413 K, respectively, due to thermal degradation of the phenolic compounds in water above these temperatures. The experimentally measured diffusion coefficients of the phenolic compounds were correlated as a function of temperature and solvent viscosity and were compared with those predicted using theoretical models. The validity of the Stokes-Einstein diffusion model in predicting the diffusion coefficients of the phenolic compounds in hot pressurized water was also evaluated.     

An ion chromatographic method for the estimation of tresyl groups on activated supports

Summary A simple and sensitive ion chromatographic method for the estimation of tresyl groups on several activated supports (tresylated diol silica, tresylated Sepharose 4B and Tresyl-5PW) has been developed. The method involves the hydrolysis of tresyl groups on the supports followed by ion chromatographic determination of the liberated 2,2,2-trifluoroethanesulfonic acid. It is useful for the prediction of the immobilization efficiency of proteins.     

Fast liquid chromatographic determination of radiochemical and chemical purity of [11C]methionine by UPLC technique

Salinity, water logging, high nitrate, fluoride and dissolved uranium concentration in drinking water of southwest Punjab has impacted the local population leading to health issues and additional burden on economy. Though it was known that both U and its daughter products especially Rn contribute to radiological dose to the population through drinking water, there were no correlation studies carried out between these radioactive elements in U impacted regions of southwest Punjab. In this study, an initiative has been taken to assess the doses due to dissolved radon in drinking water. In addition, the U–Rn couple is evaluated in detail along with other hydrochemical parameters. The radon concentration ranges from 360–1700 Bq/m³ for Faridkot and 140–1400 Bq/m³ for Muktsar for both seasons and the related average total dose due to radon for both season of Faridkot and Muktsar are 9.79 µS/year and 7.74 µS/year respectively. The total dissolved uranium is in range of 16–350 µg/L for Faridkot and 14–106 µg/L for Muktsar for both seasons. An inverse correlation was observed between Rn and U, which could be attributed to diverse geochemistry of U and Rn in groundwater.

     

An estimation of the column efficiency made by analyzing tailing peak profiles

It has been shown previously that most columns are not radially homogeneous but exhibit radial distributions of the mobile phase flow velocity and the local efficiency. Both distributions are best approximated by fourth-order polynomial, with the velocity in the column center being maximum for most packed columns and minimum for monolithic columns. These distributions may be an important source of tailing of elution peaks. The numerical calculation of elution peaks shows how peak tailing is related to the characteristics of these two distributions. An approach is proposed that permits estimations of the true efficiency and of the degree of column radial heterogeneity by inversing this calculation and using the tailing profiles of the elution peaks that are experimentally measured. This method was applied in two concrete cases of tailing peak profiles that had been previously reported and were analyzed by applying this new inverse approach. The results obtained prove its validity and demonstrate that this numerical method is effective for deriving the true column efficiency from experimental tailing profiles.     

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。     

Characterization of peak purity by fast multiscan circular dichroism detection

Summary A method has been developed to detect inhomogeneity of apparently homogeneous peaks of very similar analytes. The method utilizes the rapid scan feature of state-of-the-art spectrometers/detectors that allow the recording of up to 30 spectra in a single chromatographic peak. Sensitivity and selectivity are enhanced by chiroptical/optical detection. Thus, identification of “front” and “rear” components of the peak can be carried out. The method is exemplified by mixtures of codeine, hydrocodone and oxycodone as analytes. Presented at: Balaton Symposium on High-Performance Separation Methods, Siófok, Hungary, September 3–5, 1997     

Numerical technique and computational procedure for isotachophoresis

This paper presents a new numerical method for computation of solutions of prototypical equations of isotachophoresis. Numerical computation is complicated because the Poisson equation, which relates electrostatic potential to space charge density, contains a small parameter. This parameter is usually assumed to have the value of zero. Under this assumption the Poisson differential equation is replaced by an algebraic equation, which is often called the equation of electroneutrality, because it indeed states that the electrolyte is electrically neutral this assumption were not studied in the past. Here we propose an iterative procedure which allows for computation of solutions without the assumption of electroneutrality. The accuracy is controlled by a number of iterations and is limited by a computer round-off error only. The method is based on our previously published theory of existence and uniqueness of solutions of isotachophoretic equations. Details of the computational algorithm for prototypical equations of isotachophoresis are given. A numerical example and comparison with previously published data are also provided.     

Gas chromatographic determination of inorganic gases in high purity ethylene

Summary A simple and sensitive gas chromatographic method using the single column technique without an extreme working temperature range for the separation of O₂, N₂, CO and CO₂ was developed. The analysis was performed on micropacked columns filled with active charcoal with particle size distribution smaller than 20 m, using a microthermal conductivity detector. The results obtained show that such a column is capable of good separation of O₂, N₂ and CO at room temperature. To shorten the elution time of CO₂ the temperature has to be elevated above ambient temperature by about 100°C. Employing for ethylene removal the subtraction method introduced in gas chromatography very early by Ray, the achieved separation of inorganic gases was usefully applied for the determination of inorganic gases traces in high purity ethylene.     

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.     

Estimation of chromatographic peak shape parameters in Fourier domain

A number of models in chromatography have analytical solutions in the Laplace or Fourier domain. Often, the moments of the Laplace domain solutions are calculated to characterize the peak shape. Nonlinear fitting in the Fourier domain can be performed to exploit the entire peak shape rather than the moments only. Curve fitting in the Fourier domain offers an attractive alternative for parameter estimation. In this study we will show - with some simple applications - the possibilities of estimation of chromatographic peak shape parameters in Fourier domain. Various models are fitted to different transient signals.