Application of attenuated total reflectance Fourier transform infrared spectrometry to the determination of cephalosporin C in complex fermentation broths

Correcting attenuated total reflection-Fourier transform infrared spectra for water vapor and carbon dioxide

Fourier transform infrared (FT-IR) spectroscopy is a valuable technique for characterization of biological samples, providing a detailed fingerprint of the major chemical constituents. However, water vapor and CO(2) in the beam path often cause interferences in the spectra, which can hamper the data analysis and interpretation of results. In this paper we present a new method for removal of the spectral contributions due to atmospheric water and CO(2) from attenuated total reflection (ATR)-FT-IR spectra. In the IR spectrum, four separate wavenumber regions were defined, each containing an absorption band from either water vapor or CO(2). From two calibration data sets, gas model spectra were estimated in each of the four spectral regions, and these model spectra were applied for correction of gas absorptions in two independent test sets (spectra of aqueous solutions and a yeast biofilm (C. albicans) growing on an ATR crystal, respectively). The amounts of the atmospheric gases as expressed by the model spectra were estimated by regression, using second-derivative transformed spectra, and the estimated gas spectra could subsequently be subtracted from the sample spectra. For spectra of the growing yeast biofilm, the gas correction revealed otherwise hidden variations of relevance for modeling the growth dynamics. As the presented method improved the interpretation of the principle component analysis (PCA) models, it has proven to be a valuable tool for filtering atmospheric variation in ATR-FT-IR spectra.

Real-time endpoint monitoring and determination for a pharmaceutical salt formation process with in-line FT-IR spectroscopy

An application of Fourier transform infrared (FT-IR) spectroscopy equipped with an attenuated total reflectance (ATR) probe for in-line monitoring of a hydrochloride (HCl) salt formation process of 4-{1-methyl-2-piperidin-4-yl-4-[3-(trifluorometryl)phenyl]-1H-imidazol-5-yl}-N-[(1S)-1-phenylethyl]pyridine-2-amine (freebase), an active pharmaceutical ingredient as a P38 MAP kinase inhibitor, is described. The freebase forms both mono- and bis-HCl salts due to its structural features. The mono-HCl salt is the desired product but the bis-salt is an impurity. The key to maximizing the product yield and minimizing the impurity level is to monitor the salt-forming reaction and to terminate it at the correct HCl charge amount. The process analytical technology (PAT) provided real-time data for process control and overcame the limitations that had been previously encountered by other analytical instrumentations, such as high-performance liquid chromatography and titration. Two qualitative approaches for reaction endpoint determination were employed. In the first approach, changes in the concentration of the freebase and bis-salt were monitored via the first derivative concentration profiles. The flat point in the freebase profile and the rise in the bis-salt profile were used as a detection bracket for the endpoint of HCl charging. In the second approach, principal component analysis (PCA) was used to classify the status of the process based on a spectral library consisting of spectra collected around the endpoint. Results indicated that both methods provided adequate accuracy for endpoint control in a small window between 1.0 and 1.05 HCl to freebase mole ratio. Both methods were used to support a scaled up process. Three batches of MAP mono-HCl salt formation were successfully controlled and prepared.