Thermal Analysis of Pharmaceuticals


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Perspectives in the use of spectroscopy to characterise pharmaceutical solids Int J Pharm ; 2 : In terahertz pulsed spectroscopy TPS Fig.

Real-Time Process Monitoring of Pharmaceuticals

The relatively low powered laser compared to Raman spectrometers also reduces the risk of thermal-induced changes or photodecomposition of the sample. Due to the large amount of complex data generated by spectroscopic techniques, chemometrics, a type of multivariate analysis is being increasingly used to analyse them. On the other hand, regression techniques such as multiple linear regression MLR , principal component regression PCR and partial least squares PLS regression are vital tools in quantifying and predicting drug content in pharmaceutical formulations.

The usefulness of chemometrics lie in its ability to filter out unnecessary information or noise and extract only the essential and relevant portions of the data for analysis. In a recent study on alkaloids of natural products in solid crystals, terahertz spectroscopy in combination with multiple linear regression were employed for qualitative and quantitative analysis [ 20 Ivanova BB, Spiteller M.

On the chemical identification and determination of flavonoids in solid-state Talanta ; Different mixtures of the alkaloids were investigated to determine the best combination that would give the lowest signal to noise ratio. Qualitative and quantitative mass spectrometry imaging of drugs and metabolites Adv Drug Deliv Rev ; 65 8 : In MSI, spectra are collected from the sample, creating a grid of points on the surface of the sample Fig.

The main advantage of MSI has been mass accuracy, mass resolution and spatial resolution. Spatial resolution is the minimum distance between two objects in an image at which they can be distinctly discerned. The drug is coated with a thin layer of matrix and irradiated with a laser beam.

To produce a good spectra, the matrix must absorb light at the laser wavelength and must not react with the analyte [ 22 Gut Y, Boiret M, Bultel L, et al. The tablet was first eroded to obtain a flat surface for higher quality and reproducibility of spectra acquisition. Then 2,5-dihydroxybenzoic acid and -cyanohydroxycinnamic acid were deposited by sublimation method onto the tablet before acquiring mass spectra images. This study demonstrated that the use of multivariate algorithms complemented MALDI MSI techniques for explicit identification and examination of drug distribution in tablets.

Time of flight secondary ion mass spectrometry ToF-SIMS imaging is a highly sensitive surface analytical technique which enables examination of complex surfaces of solid pharmaceutical dosage forms.

The investigation of pharmaceutical substances by thermal analysis

In ToF-SIMS, primary ion pulses are accelerated and focused onto the surface of a sample held under ultra-high vacuum. The bombarding particle impacts the surface and cause a sputter plume containing atoms, whole molecules and fragments of molecules.


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A certain portion of these will possess a charge that allows. Since each ion has equal kinetic energy, their drift velocity will be governed by the relation of kinetic energy to mass. Thus by measuring the time it takes for the secondary ions to reach the detector, the mass-to-charge ratio can be deduced and used to separate them.

This enables the study of any fragment within the mass spectrum, or to extract a spectrum from any region of interest from an image. In addition to that, depth profiling can offer very sensitive compositional and molecular information as a function of depth as well as provide full 3-dimensional distributions within the analysed volume [ 22 Gut Y, Boiret M, Bultel L, et al.

Time-of-flight instruments have resolving powers ranging from 10, to , and can routinely achieve less than 5 ppm mass accuracy [ 21 Lietz CB, Gemperline E, Li L. Several studies have used ToF-SIMS to map the distribution of drugs within solid state drug delivery systems by direct analysis of sample cross-sections. Cross-sections of three different controlled release pellet formulations paracetamol, theophylline and prednisone were studied with ToF-SIMS imaging and the distribution of drug, excipients and coating characterised [ 22 Gut Y, Boiret M, Bultel L, et al.

This methodology has also been successfully used to determine the distribution of different drug forms hydrated and non-hydrated within a controlled release pellet. One of the strategies to improving dissolution and bioavailability of poorly soluble drugs is by preparing them in nanoparticles from dried nanosuspensions. Characterization by conventional powder X-ray diffraction and differential scanning calorimetry DSC is limited due to their lack of sensitivity and spatial resolution. Thus nanothermal analysis nTA is an emerging technique which combines the high resolution imaging capabilities of atomic force microscopy AFM with the ability to characterize the thermal properties of drugs.

Compared to its predecessor, scanning thermal microscopy, it offers significantly enhanced spatial resolution. Nanoscale thermal analysis of pharmaceutical solid dispersions Int J Pharm ; : This imaging probe enables utilization of the most widely applied AFM imaging mode, tapping mode, to allow the analysis of softer samples, such as polymers, without damage from the imaging probe. NTA can be used to map thermal properties during imaging, or to carry out local thermal analysis at defined points on a surface.

In such analysis, the probe is heated in a temperature cycle similar to DSC whilst in contact with the sample, providing quantitative information on thermal phase transitions. The use of a microfabricated probes is advantageous because of their ability to measure samples down to femtograms and nanoliters. The stability of solid dispersions of felodipine in polyvinylpyrrolidone characterized by nanothermal analysis Int J Pharm ; : These studies showed that onset of crystallization can be detected, which is a critical consideration in the stability of poorly soluble drugs formulated in amorphous forms.

Oral controlled release dosage forms make up a large fraction of the pharmaceutical market due to the ease of administration and patient compliance. However, they do not provide any insight into the internal structure of the tablet cores.

Eventhough tight dissolution specifications are introduced to monitor the quality of the final products, a number of dosage forms fail after approval, and consequently have to be recalled from the market each year [ 26 Li H, Yin X, Ji J, et al. Microstructural investigation to the controlled release kinetics of monolith osmotic pump tablets via synchrotron radiation X-ray microtomography Int J Pharm ; 2 : Therefore, modern in vitro microtomography techniques are being utilised as new and efficient tools that can directly reveal the internal structure and dynamic characteristics of the controlled release tablet core at different stages of the drug release process.

Common Thermal Analysis Methods In the Pharmaceutical Sciences

In synchrotron radiation computed microtomography SR-CT , the sample is illuminated by an extended parallel x-ray beam and projection images of the sample are recorded with a 2D detector, commonly a camera coupled with x-ray scintillator. The sample is carefully rotated relative to the X-ray beam and the process is repeated to produce additional two-dimensional images from various viewpoints. Using a sophisticated Fourier transform algorithm, the 2D images are then combined to generate a complete 3D map of the sample.

X-ray microtomography of solid dosage forms. Pharm Technol Accurate sample structure can be reconstructed, given suitable angular sampling. Gray-scale images also can be manipulated using standard image analysis techniques to produce binary or multiple-coloured images and to obtain dimensional information about the sample.

An example of an application can be seen from a study on felodipine sustained release tablets observed at various time points during dissolution [ 26 Li H, Yin X, Ji J, et al. Quantification of swelling and erosion in the controlled release of a poorly water-soluble drug using synchrotron X-ray computed microtomography AAPS J ; 15 4 : In another study, tablet swelling behaviour of various in-house polymeric preparations was investigated over time using SR-CT. Synchrotron X-ray microtomographic study of tablet swelling Eur J Pharm Biopharm ; 75 2 : Investigation of internal structure of fine granules by microtomography using synchrotron X-ray radiation Int J Pharm ; : In the study, two granules were prepared: a bromhexine HCl granule coated with Kollicoat and a wax-matrix acetaminophen granule.

It was shown that SR-CT was capable of visualizing the internal structure as well as coating layer of the granules. Moreover, it successfully visualized the high talc regions of the Kollicoat layer that could not be detected by scanning electron microscopy. All these studies prove the high potency of SR-CT in elucidating internal and external shapes and structures of solid pharmaceutical dosage forms.

It is evident that recent advances in the analysis of solid-state pharmaceuticals are made possible with the improvement and adaptation of conventional techniques of NMR, Raman, mass spectrometry, thermal analysis and x-ray computed tomography. The progress of such techniques provides critical knowledge and understanding of complex phenomena such as polymorphism, disorder in the crystalline state, molecular-level interactions in crystalline and amorphous materials, and detection of phase impurities. It also enables accurate and vibrant mapping of solid dosage forms at high resolution and expands the capabilities for quantitative analysis of solid formulations even at low levels.

The various strengths and weaknesses of each technique can be exploited to achieve full and reliable characterization of solid drugs.

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Thermal Analysis – A Review of Techniques and Applications in the Pharmaceutical Sciences

It is hoped that the continual progress and advancement in analytical techniques will contribute to better understanding and ultimately effective quality control of solid pharmaceutical dosage forms. This is exactly what Open Access Journals provide and this is the reason why I support this endeavor.

Open Access publishing is therefore of utmost importance for wider dissemination of information, and will help serving the best interest of the scientific community. They offer accessible information to a wide variety of individuals, including physicians, medical students, clinical investigators, and the general public. They are an outstanding source of medical and scientific information.

1. INTRODUCTION

Indeed, the research articles span a wide range of area and of high quality. This is specially a must for researchers belonging to institutions with limited library facility and funding to subscribe scientific journals. They provide easy access to the latest research on a wide variety of issues. Relevant and timely articles are made available in a fraction of the time taken by more conventional publishers.

Articles are of uniformly high quality and written by the world's leading authorities. Open access journals are very helpful for students, researchers and the general public including people from institutions which do not have library or cannot afford to subscribe scientific journals. The articles are high standard and cover a wide area.


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    Thermal Analysis of Pharmaceuticals Thermal Analysis of Pharmaceuticals
    Thermal Analysis of Pharmaceuticals Thermal Analysis of Pharmaceuticals
    Thermal Analysis of Pharmaceuticals Thermal Analysis of Pharmaceuticals
    Thermal Analysis of Pharmaceuticals Thermal Analysis of Pharmaceuticals

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