X-ray diffraction has been used in the pharmaceutical industry for some time. This is because it is non-destructive and very easy to use. The pattern that is created by x-ray diffraction offers a fingerprint, as such, that are required for patent descriptions. X-ray diffraction can also be used to identify a difference in batches of drugs.
Other uses for this method include:
- The detection of form impurities
- The monitoring of dosage uniformity
- The monitoring of a batch
- The crystal morphology
- The optimization of the process parameters
- Excipient compatibility
What is X-Ray Diffraction?
X-ray diffraction, also known as “XRD” is a non-destructive technique. This technique has the ability to provide a range of highly detailed information about a material’s chemical composition, crystallographic structure, and its physical properties.
X-ray diffraction peaks are created by the use of constructive interference or a beam of x-rays. These x-rays are monochromatic and they are always scattered at a range of angles. The angles used are very specific and they are arranged from every set of lattice planes that are found in a sample. The intensities of the peak are ultimately determined by each of the atomic positions that are within the lattice planes.
As a result of this, the pattern that is given is considered to be a fingerprint. It is, as such, a fingerprint of the periodic atomic arrangements that are in a specific material.
X-ray Diffraction and Bragg’s Law
X-ray diffraction is itself based on Bragg’s law. A beam of x-rays is sent to a sample and any reflected x-rays are detected. The pattern that is seen tends to be characteristic of the substance that is being investigated. X-ray diffraction is considered to be very useful when you need to determine how much crystallinity is in natural fibers both before and after chemical or physical treatment.
The sample involved is recorded on an x-ray diffractometer that is operated at a range of voltages and currents. Regions of the samples involved produce a broad peak however, crystalline regions always tend to produce sharp peaks. The degree of the crystallinity is determined by considering the intensities of the amorphous and the crystalline contents that are found in the sample.
X-Ray Diffraction and Drug Identification
It is vital that the identification of a drug is carried out effectively. Ideally, it would be in the most stable form. While some physical changes in the drug itself can affect its solubility and the ease at which it is manufactured, it can also affect its:
- Stability
- Bio-availability
While there are other techniques available such as mass spectrometry, solution NMR, and HPLC, they aren’t ideal for identifying crystal form. When you use XRD alongside these other techniques you’re likely to uncover a wealth of information.
The Stability of an Amorphous Drug
When there is poor water solubility of a drug there can be challenges for its formulation. Many pharmacists seek to overcome the issue by using a range of different approaches. The first approach that is used tends to be particle size reduction. However, there is always a chance that the substance will be contaminated by the equipment used to grind the drug.
Another method that is used involves preparing the drug as an amorphous form. This method increases the drug’s solubility. The difficulty with this is that this type of formulation is unstable. Its instability can cause the drug to crystallize. This is especially the case if it has been stored at a high humidity.
There is another difficulty with using the drug this way. This is because the drug might be precipitated from an amorphous form. In this case, bio-availability and drug dissolution could be compromised. This is why it is essential that you identify the on-set of any crystallization. It’s also recommended that a detection limit for the crystalline content is set.
A Wholly Useful Technique
X-ray diffraction application is very diverse and it can prove to be wholly useful in the world of pharmaceutical analysis. As a technique used on its own, x-ray diffraction is useful for solving a wide variety of issues and problems. However, it is essential that data interpretation and sample preparation are carried out with the utmost care. When x-ray diffraction is used alongside other techniques such as TGA, FTIR, DSC, and so on, it can help to provide greater clarity. In addition to this, x-ray diffraction can also help to provide a complete understanding of the events.
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