LED-array photocalorimetry: Instrument design and application to photostability of nifedipine

A photocalorimeter was designed to analyse quantitatively the photostability of pharmaceuticals. Its application is demonstrated with reference to two solution phase test systems; the photodegradations of 2-nitrobenzaldehyde (2-NB) and nifedipine. Light emitting diode (LED) arrays were used to illum...

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Bibliographic Details
Published in:Journal of pharmaceutical and biomedical analysis 2008-12, Vol.48 (5), p.1316-1320
Main Authors: Dhuna, Meena, Beezer, Anthony E., Connor, Joseph A., Clapham, David, Courtice, Chris, Frost, John, Gaisford, Simon
Format: Article
Language:English
Subjects:
2-Nitrobenzaldehyde
Analysis
Analytical, structural and metabolic biochemistry
Biological and medical sciences
Calorimetry - instrumentation
Drug Stability
Electronics
Equipment Design - instrumentation
Fundamental and applied biological sciences. Psychology
General pharmacology
Hydrogen-Ion Concentration
Isothermal calorimetry
Light
Light emitting diode (LED)
Medical sciences
Nifedipine
Nifedipine - chemistry
Nifedipine - radiation effects
Pharmacology. Drug treatments
Photocalorimetry
Photochemistry - instrumentation
Thermodynamics
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Description
Summary:A photocalorimeter was designed to analyse quantitatively the photostability of pharmaceuticals. Its application is demonstrated with reference to two solution phase test systems; the photodegradations of 2-nitrobenzaldehyde (2-NB) and nifedipine. Light emitting diode (LED) arrays were used to illuminate the sample and reference channels of the calorimeter. Five LEDs were used to create an array from 360 to 700 nm. A power supply system was constructed that zeroed the instrument by supplying a preset voltage to the sample side LEDs and varying that supplied to the reference LEDs until a zero calorimetric signal was obtained. The photodegradation of 2-NB was zero-order and varied in proportion to the input voltage supplied to the LED array. Analysis of the data (the rate of reaction was determined to be equal 1.04 × 10 −6 mol dm −3 s −1 by pH titration) determined a reaction enthalpy of 5.0 ± 0.6 kJ mol −1. In the case of nifedipine, the LEDs in the array were operated individually in order to determine the causative wavelength of degradation. This was found to be 360 nm, in agreement with the literature.
ISSN:0731-7085
1873-264X
DOI:10.1016/j.jpba.2008.09.007