The stability of reference standard, i.e. impurity-free, heroin (diacetylmorphine) in methanol at room temperature (28 ± 2°C) over a period of approximately one year has been studied by HPTLC. The results indicate that the degradation of heroin starts on the second day after preparation of its solution in methanol and that decomposition is complete in approximately 38 weeks. The technique used for the study is simple and reliable. It enables understanding of the stability and degradation pattern of heroin and suggests a correct procedure for forensic use of this scarcely available reference standard in the analysis of heroin samples.
Authors:Věra Jedináková-Křížová, Josef Zeman, Hana Vinšová, and Eduard Hanslík
The contribution is focused on chemical, geochemical and mineralogical research of bentonite stability with the aim to determine
the effect of saturation medium composition and loading by heat on bentonite stability. The main part of the research is directed
to the experimental results of bentonite and bentonite leachate samples obtained for the bentonite interaction under laboratory
experiments. Computer-modeling methods were used to calculate equilibrium thermodynamic principles, the distributions of predominant
aqueous species, and potential solubility controls for the environmentally important oxidation states of each investigated
radioactive contaminants. The Eh–pH diagrams of individual chemical species of the tested radionuclides were calculated by
the geochemical software tool Geochemist’s Workbench that included the actual chemical compositions of the solid–liquid systems
under the given experimental conditions. It was confirmed that smectites are transformed to more stable silicate phases, such
as illite/smectite mixed layers, illite. The data obtained from the model calculations conform with experimental results.
The effect of the variable aqueous phase composition on bentonite stability using Ca–Mg and Na–Ca bentonites for the experiments
was studied. The synthetic granitic waters with the higher concentration of the K+ and Mg2+ cations were applied for the study of bentonite stability.
Authors:Małgorzata Starek, Monika Dąbrowska, Monika Bracha, and Włodzimierz Opoka
A study on the effect of oxidizing or reducing agents on the stability testing of piroxicam, tenoxicam, meloxicam, and isoxicam was performed. Detection of the formed oxidation and/or degradation products after reaction with factors such as iodine, potassium manganate( VII), hydrogen peroxide, and ascorbic acid was conducted by thin-layer chromatography (TLC)—densitometry technique. The reacting mixtures were also exposed to increasing temperatures. The chromatographic profiles showed the formation of several new peaks for all oxicams due to the presence of a number of degradation products formed in the presence of analyzed redox agents. The calculated kinetic parameters have confirmed the greatest stability of meloxicam and piroxicam and the smallest stability of isoxicam in the analyzed conditions. In the case of all the analyzed drugs, principal component analysis identified temperature as the main factor responsible for the speed of degradation and the shape of degradation profile.
Authors:R. Staník, J. Světlík, J. Karlovská, and I. Benkovský
The dimercaptosuccinic acid (DMSA) stability at pH = 3.8, 7.1, 8.8 and the interaction with SnCl2·2H2O were investigated. The degradation of DMSA is the most significant at alkali pH. There where observed oxidized and dimerized
forms of DMSA and fumaric acid presence. Progress of instability is less substantial and slower under neutral reaction conditions.
At acidic pH the concentration of soluble DMSA decreases with the time. The ligand forms with SnCl2 complex under alkali pH = 8.8 and its chemical formula was determined as Sn(DMSA)2.
Authors:Daniel Plano, Elena Lizarraga, María Font, Juan Palop, and Carmen Sanmartín
Thermal analysis of fusion and decomposition processes was carried out on organosulphur and organoselenium compounds in order
to establish thermal stability criteria. Degradation and fusion temperatures of 20 biological active compounds, synthesized
by our research group were determined using thermogravimetry (TG) and differential scanning calorimetry (DSC). Analysis of
the thermal data indicated that: (a) in general, sulphur compounds are more stable than selenium compounds; (b) the pyridine
ring diminished stability of sulphur and selenium compounds much more than the carbocyclic aromatic rings did (6a > 9a; 2b > 3b);
(c) selenomethyl derivatives are more stable than selenoethyl and selenoisopropyl compounds; (d) a chlorine atom on selenocompounds
has surprising effects.
Labeling of diethylenetriamine-N,N,N′,N″,N″-pentakis(methylenephosphonic) acid (DTPMP) with rhenium-188 using stannous chloride
as a reducing agent has been investigated. Dependence of the yield of the 188Re–DTPMP complex on the concentration of the reducing agent, pH, reaction time, temperature, ascorbic acid and amount of carrier
added has been studied. Under optimum conditions, the labeling yield of 188Re–DTPMP complex is 95% for the carrier-free 188Re but with the carrier-added 188Re the labeling yield is more than 97%. Furthermore, the stability of the 188Re–DTPMP complex against pH change and dilution with saline has been also studied. It is found that the addition of carrier
stabilizes the 188Re–DTPMP complex against pH change and dilution.
Authors:Nitin Dubey, Dinesh Jain, and Subhash Jadhawani
A stability-indicating high-performance thin-layer chromatographic (HPTLC) method has been developed for the determination of simultaneous determination of famotidine (FAMO), paracetamol (PCM), and ibuprofen (IBU) in tablet dosage forms. The separation was achieved on TLC aluminum plates precoated with silica gel 60F-254 using chloroform-methanol-ethyl acetate-acetic acid (21.5:16.1:59.1:3.2%, v/v/v/v) as the mobile phase. The densitometric analysis was carried out at 256 nm. Compact spots appeared at RF 0.21 ± 0.01, 0.80 ± 0.02, and 0.89 ± 0.01 for FAMO, PCM, and IBU, respectively. Linear regression analysis revealed linearity in the range of 160–960 ng per spot for FAMO, 400–2400 ng per spot for PCM, and 600–3600 ng per spot for IBU. Drugs were subjected to acid and alkali hydrolyses, forced oxidation, thermal and photodegradation treatments. The degraded products were well separated from the pure drugs. Statistical analysis proved that the method is precise, accurate, selective, and economical and may be used for routine analysis of FAMO, PCM, and IBU in tablet dosage forms.