Q: Are spectroscopic techniques (without chromatography) still important for pharmaceutical analysis?
The answer to this question depends on the purpose of the analysis. What type of information does the analyst aim for? A
separation step might not be needed when the compound is present as the only active pharmaceutical ingredient (API) in a pharmaceutical
mixture, and is simply dissolved in a simple matrix. In such cases, it may be possible to apply a stand-alone spectroscopic
One example is identity testing of a bulk pharmaceutical ingredient. This is most conveniently performed by infrared (IR)
spectroscopy. Indeed, the typical fingerprint region in the IR spectrum allows confirmation of the identity of a compound
after comparison with the spectrum of a standard.
When the purpose of an analysis is assaying the medicine, UV testing can be a good choice. Formulations containing a single
API can be conveniently analyzed with UV spectrophotometry if the excipients do not interfere in the UV absorbance. It may
or may not involve a simple sample preparation procedure, and the analysis could be applied routinely because of its simplicity.
It is also possible to carry out UV analysis in the form of a flow injection analysis (FIA). In FIA the samples are injected
into a flowing stream of liquid that continuously passes through a detector cell. UV measurement in the cell allows very fast
and automated analysis of all the samples.
When people are testing for the presence of impurities in medicines, in the majority of cases a separation technique will
be implemented. In this case sample preparation may be needed for the analysis of drug products containing the formulated
drug in the presence of excipients.
There are also areas in which the use of particular spectroscopic techniques (without chromatography) is emerging, such as
quick and initial detection of a counterfeit drug in suspicious medicines. Raman and near infrared (NIR) spectroscopy have
shown their strength in this field. These spectroscopic techniques could become as important as UV in the future.
Separation prior to detection generally results in higher specificity. However, since this is not always required, direct
application of spectroscopic techniques is therefore desired in cases where timely and cost-effective analysis is paramount.
Direct UV measurement is the preferred detection for dissolution testing. Vibrational spectroscopic techniques such as near
infrared (NIR) and Raman are used in process control and for anti-counterfeit analysis where fast and nondestructive analyses
are required. Implementation of quality-by-design (QBD) has resulted in a strong increase in the use of these techniques.
In addition, spectroscopic techniques can replace visual evaluation or comparison of colour against European Pharmacopoeia
reference standards, to make colour assessments more objective. These examples show that new opportunities can still be found
for applying direct spectroscopic techniques.
Maybe less so in small molecule pharmaceutical analysis, but in biopharmaceutical analysis, spectroscopic techniques (without
chromatography) still have a very important position in product release, stability testing, or characterization. A few examples
include: UV absorbance in the content analysis of protein products; absorbance or fluorescence in immune- and cell-based assays
(and even in some chemical assays like those that test for free SH groups); and fluorescence and circular dichroism in the
characterization of secondary and tertiary structure of proteins.
Ann Van Schepdael is a professor at the KU Leuven in Leuven, Belgium.
Tom van Wijk is a senior scientist at Abbott Healthcare BV in Weesp, the Netherlands.
Harm Niederlander was a project leader at Synthon Biopharmaceuticals in Nijmegen, the Netherlands, until August 2013.
This article is from The Column. The full issue can be found here: