A densitometric thin-layer chromatographic method has been established for the analysis of celecoxib, etoricoxib, and valdecoxib in pharmaceutical formulations. TLC was performed on silica gel 60 F
plates with chloroform-acetone-toluene 12:5:2 (
) as mobile phase. UV detection was performed by densitometric scanning at 254 and 290 nm. The method was validated by determination of linearity, precision, limits of detection, and determination (from 0.0017 to 0.0848 μg per band) and accuracy (from 99.16 to 100.48%).
A sensitive, selective, precise, and stability-indicating high-performance thin-layer chromatographic (HPTLC) method has been established for densitometric analysis of flurbiprofen in pharmaceutical tablets. Chloroform-acetone-xylene 5.0:2.0:1.0 (
) was used as mobile phase. Regression analysis of the calibration data revealed a good linear relationship between peak-area response and amount of flurbiprofen in the range 50–600 ng per band (
= 0.9993 ± 0.0004). The limits of detection (LOD) and quantification (LOQ) were 10 and 32 ng per band, respectively. Flurbiprofen was subjected to different stress conditions. An
plot was constructed for degradation under acidic conditions and the activation energy was calculated.
Authors:R. Bettini, G. Bertolini, E. Frigo, A. Rossi, I. Casini, I. Pasquali, and F. Giordano
The aim of this work was to study the solubility in supercritical CO2 of the hydrated phase of three model drugs, namely theophylline, carbamazepine, and diclofenac sodium, in comparison with
the respective anhydrous form. Possible solid-state modifications, stemming from the interaction with supercritical CO2, were investigated by differential scanning calorimetry, thermogravimetric analysis, hot stage microscopy, Fourier Transform
infrared spectroscopy and Karl-Fischer titrimetry. It was found that all three pharmaceutical hydrates exhibited higher solubility
in supercritical CO2 than the relevant anhydrous phases. In the case of theophylline monohydrate, the instability of the crystal phase at the
experimental temperature adopted has been evidenced. Diclofenac sodium tetrahydrate represents a peculiar case of chemical
interaction with the acid supercritical fluid, mediated by crystal water.
Isothermal titration calorimetry (ITC) has been used to develop a method to construct the solid-liquid equilibrium line in
ternary systems containing the solute to precipitate and an aqueous mixed solvent. The method consists in measuring the heat
of dissolution of a solid component (the solute) during successive additions of the liquid solvent. The cumulated heat, resulting
from the successive heat peaks obtained for the different injections of known volumes of solvent, plotted vs. the ratio of the numbers of moles nsolvent /nsolute is represented by two nearly straight lines. The intersection of the two lines gives the solubility limit and the corresponding
enthalpy of dissolution of the solute in the solvent.
Phase diagrams have been established at 303.15 K in binary mixed solvents ethanol-water over the whole concentration range
for four components of pharmaceutical interest, namely: caffeine, nicotinamide, nicotinic acid and salicylic acid.
Procedures for measuring sublimation rates of pharmaceutical compounds by isothermal thermogravimetry are discussed. Experimental
data was obtained using the Mettler TA4000 thermogravimetric system. The sublimation rate is measured directly from the mean
weight loss per unit time in the linear region of the monitored TG profile at a set isothermal temperature. This data when
fitted to the Arrhenius equation yields the sublimation enthalpy. For the benzoic acid reference, the enthalpy so calculated
is 99% of the value obtained from direct vacuum TG measurements. Thermal degradation in the solid state or pre-melting can
effect a departure from the characteristic linear mass loss-time sublimative profile. Data pertaining to several established
Merck drugs is discussed. Examples where loss of residual solvent, onset of thermal degradation and pre-melting phenomena
affect the measurement, are presented.
A thin-layer chromatographic method has been established for quantification of aloenin in aloe (
Mill.) pharmaceuticals. Chromatographic separation was performed on silica gel plates with ethyl acetate-ethanol (95%)-water, 20:3:1 (
), as mobile phase. The plates were scanned densitometrically at 365 nm. The method was validated for precision, repeatability, and accuracy. It was found to be precise — intra-day and inter-day
were 2.21% and 3.15%, respectively. Instrumental precision and repeatability for the method were 0.42 and 1.94 (
[%]), respectively. Accuracy was checked by measurement of recovery at three levels; average recovery was 97.86%. The method was used for analysis of aloenin in aloe juice, aloe tablets and aloe liquid extract for injections and was confirmed to be suitable for this purpose.
Authors:Anna Kwiecień, Jan Krzek, and Łukasz Biniek
A thin-layer chromatographic method with densitometric detection has been established for quantification of azithromycin in pharmaceutical preparations. Silica gel plates with fluorescence indicator F
were used with chloroform-ethanol-ammonia 6:14:0.2 (
) as mobile phase. Chromatograms were visualized by spraying with 1:4 (
) sulfuric acid-ethanol and heating at 120C for 5 min. Scanning and densitometric analysis was performed at 483 nm. The
of azithromycin under these conditions was 0.53. The method was characterized by high sensitivity (LOD = 40 ng/zone and LOQ = 80 ng/zone), wide linear range (from 0.08 to 1.2 μg/zone,
= 0.9965), and high precision, accuracy (mean percentage recovery 102.73%), and specificity.
DSC purity analysis is based on thermodynamic phase diagrams for substances (purity ≥98%) which undergo a melting point. Impurities
which have eutectic behaviour with the analyte are determined together.
DSC purity analysis obtained from a single melting event of a 1–2 mg sample is, therefore, extremely attractive for the global
assessment of eutectic impurities. The main advantages in early development lie in the very small amount of material necessary
and the very fast analysis time.
However, the DSC purity analysis cannot replace chromatographic methods which deliver specific individual levels of impurities.
Furthermore, a complete validation of a DSC purity method is difficult and time consuming. Despite these limitations, DSC
is the best support for the development of chromatographic methods, for purity profile and stability assessment during pharmaceutical
Parameters of purity determination and validation aspects are discussed. Examples of use in pharmaceutical development are
Thermal analysis methods are well-established techniques in research laboratories of pharmaceutical industry. The robustness
and sensitivity of instrumentation, the introduction of automation and of reliable software according to the industrial needs
widened considerably the areas of applications in the last decade. Calibration of instruments and validation of results follow
the state of the art of cGMP as for other analytical techniques. Thermal analysis techniques are especially useful for the
study of the behavior of the poly-phasic systems drug substances and excipients and find a unique place for new delivery systems.
Since change of temperature and moisture occur by processing and storage, changes of the solid state may have a considerable
effect on activity, toxicity and stability of compounds. Current requirements of the International Conference of Harmonisation
for the characterization and the quantitation of polymorphism in new entities re-enforce the position of thermal analysis
techniques. This challenging task needs the use of complementary methods. Combined techniques and microcalorimetry demonstrate
their advantages. This article reviews the current use of thermal analysis and combined techniques in research and development
and in production. The advantage of commercially coupled techniques to thermogravimetry is emphasized with some examples.