Biomedical subjects

J Axel Zeitler

Publications and source records attributed to J Axel Zeitler.

4 recordsLinked to original sources

PubMed2007

Analysis of coating structures and interfaces in solid oral dosage forms by three dimensional terahertz pulsed imaging.

Three dimensional terahertz pulsed imaging (TPI) was evaluated as a novel tool for the nondestructive characterization of different solid oral dosage forms. The time-domain reflection signal of coherent pulsed light in the far infrared was used to investigate film-coated tablets, sugar-coated tablets, multilayered controlled release tablets, and soft gelatin capsules. It is possible to determine the spatial and statistical distribution of coating thickness in single and multiple coated products using 3D TPI. The measurements are nondestructive even for layers buried underneath other coating structures. The internal structure of coating materials can be analyzed. As the terahertz signal penetrates up to 3 mm into the dosage form interfaces between layers in multilayered tablets can be investigated. In soft gelatin capsules it is possible to measure the thickness of the gelatin layer and to characterize the seal between the gelatin layers for quality control. TPI is a unique approach for the nondestructive characterization and quality control of solid dosage forms. The measurements are fast and fully automated with the potential for much wider application of the technique in the process analytical technology scheme.

Capsules↗

PubMed2006

Drug hydrate systems and dehydration processes studied by terahertz pulsed spectroscopy.

Terahertz pulsed spectroscopy was used to distinguish between different hydrate systems. In the example of four pharmaceutical materials lactose, carbamazepine, piroxicam and theophylline it was demonstrated that all different hydrate and anhydrate forms exhibit distinct spectra in the far infrared. Furthermore the dehydration of theophylline monohydrate was characterised in situ. Here, a phase transition from the monohydrate to the anhydrous form was observed, followed by evaporation of the hydrate water in a second step. The rotational spectrum of water vapour is very characteristic in the far infrared and can easily be discerned from the terahertz spectrum of the solid state form.

Carbamazepine↗

PubMed2006

Characterization of temperature-induced phase transitions in five polymorphic forms of sulfathiazole by terahertz pulsed spectroscopy and differential scanning calorimetry.

The far-infrared properties of all five known polymorphic forms of the drug sulfathiazole have been studied by terahertz pulsed spectroscopy and low-frequency Raman spectroscopy. The observed spectra of the different polymorphs are distinctly different. Terahertz pulsed spectroscopy proves to be a rapid and complementary alternative to other physical characterization techniques reported in the literature for distinguishing between the five forms. Variable-temperature measurements (293-473 K) of all polymorphic forms have been performed. The phase transitions observed have been related to thermal analysis data. Form I is the form stable at high temperature of sulfathiazole with a melting point of about 475 K. Form II melts at around 470 K and recrystallizes at higher temperatures to form I. Forms III, IV, and V all convert to form I via a solid-solid phase transition at temperatures below 450 K. The phase transitions can be monitored by terahertz pulsed spectroscopy. Polymorphic impurities of the samples can be detected in the room temperature spectra and their effect on the phase transition behavior can be studied.

Calorimetry, Differential Scanning↗

PubMed2005

Using terahertz pulsed spectroscopy to quantify pharmaceutical polymorphism and crystallinity.

Terahertz pulsed spectroscopy (TPS) is a new technique that is capable of eliciting rich information when investigating pharmaceutical materials. In solids, it probes long-range crystalline lattice vibrations and low energy torsion and hydrogen bonding vibrations. These properties make TPS potentially an ideal tool to investigate crystallinity and polymorphism. In this study four drugs with different solid-state properties were analyzed using TPS and levels of polymorphism and crystallinity were quantified. Carbamazepine and enalapril maleate polymorphs, amorphous, and crystalline indomethacin, and thermotropic liquid crystalline and crystalline fenoprofen calcium mixtures were quantified using partial least-squares analysis. Root-mean-squared errors of cross validation as low as 0.349% and limits of detection as low as approximately 1% were obtained, demonstrating that TPS is an analytical technique of potential in quantifying solid-state properties of pharmaceutical compounds.

Carbamazepine↗