The research consisted of investigation of non-freezable bound water (NFW) contents of raw hydroxypropylcellulose (HPC) Klucel^® Pharm HF, MF, and LF by differential scanning calorimetry. Polymers (HF, MF and LF) used in the research differed significantly in their molecular mass and viscosity. Mixtures of HPC and low soluble salicylic acid or highly soluble sodium salicylate were used to examine the effect of counter-ions presence and drug solubility on NFW contents. The dependencies of determined enthalpies of melting (ΔH) and respective contents of water W_c (water fraction in the dry mass of HPC or HPC mixture) ΔH = f(W_c) were linear. The sought values of non-freezing water were calculated (by extrapolation) as the concentration at which ΔH = 0. It was found that the viscosity and molecular mass of the raw HPCs did not affect the contents of non-freezing water, which ranged between 0.54 and 0.51 g g⁻¹ for all types LF, MF, HF. Poorly soluble salicylic acid (SA) reduced the non-freezing water content to 0.19–0.17 g g⁻¹. On the other hand, matrices composed of highly soluble sodium salicylate (NaSA) showed variable decrease of NFW content—0.44 g g⁻¹ for HF and 0.54–0.51 g g⁻¹ for LF and MF. It was also found that the maximum temperature T_max of melting was strongly influenced by the solubility of the drug. Highly soluble NaSA shifted T_max toward the lower negative values, while SA toward the higher positive values. Assessing NFW contents in hydrated HPC matrices may contribute to a better understanding of the drug release and dissolution mechanisms of tablet formulations.

Ciprofloxacin (CIP), moxifloxacin (MOX), norfloxacin (NOR) and ofloxacin (OFL), are the antibacterial synthetic drugs, belonging to the fluoroquinolones group. Fluoroquinolones are compounds susceptible to photodegradation process, which may lead to reduction of their antibacterial activity and to induce phototoxicity as a side effect. This paper describes a simple, sensitive UPLC-MS/MS method for the determination of CIP, MOX, NOR and OFL in the presence of photodegradation products.

Photostability of moxifloxacin (MOXI) after UVA irradiation in solutions and solid phase, with and without participation of Cu(II), Zn(II), Al(III), and Fe(III) was tested. The studies were carried out by the TLC-densitometric method and LC-MS/MS method. Elaborated and validated chromatography-densitometric method was used for assaying. It was shown that the number and type of photoproducts depend on the environment and type of the metal ion. The studied ions enhanced the degradation of MOXI in solutions, and the influence of Cu(II) and Fe(III) ions was higher than that of Zn(II) and Al(III) ions. In solid phase, in contrast to solutions, all metal ions decreased the photodegradation, however the influence of ions, Al(III) and Zn(II), was weaker than that of Cu(II) and Fe(III) ions. Identification of the degradation products performed with LC-MS/MS and ¹H NMR identified them as: 1-cyclopropyl-6-fluoro-7-amino-8-methoxy-4-oxo-1,4-dihydroquinoline-3-carboxylic acid, 1-cyclopropyl-6-fluoro-8-methoxy-4-oxo-7-(2-oxo-octahydro-6H-pyrrolo[3,4-b]pyridine-6-yl)-1,4-dihydroquinoline-3-carboxylic acid, 7-[3-hydroxyamino-4-(2-carboxyethyl)pyrrolidin-1-yl]-1-cyclopropyl-6-fluoro-8-methoxy-4-oxo-1,4-dihydroquinoline-3-carboxylic acid.

A new derivative spectrophotometric method was developed for determination of gentamicin beside methyl and propyl hydroxybenzoates in injection solutions. The determination was carried out after modifying the gentamicin molecule by reaction with o-phthal aldehyde. The obtained spectrum of product in methanol solution was converted into a third-derivative spectrum. The measurements were made at wavelength λ = 281 nm, where a linear relationship between D3 and antibiotic concentration occurs, when no coexisting constituents are present. The method is of high specificity to gentamicin in the presence of methyl and propyl hydroxybenzoates and has good accuracy. The recovery is from 99.38% to 100.16%, and wide linearity ranges from 0.004% to 0.008%. The method has satisfactory precision (RSD = 2.52%) as well as high sensitivity (LOD = 1.66 · 10⁻⁴% and LOQ = 5.04 · 10⁻⁴%).

The lipophilicity of fifteen fluoroquinolones has been investigated. Reversed-phase thin layer chromatography with densitometric detection was applied to determine the R_M0 factor. The RP-TLC investigations were performed in mixtures of organic modifier–water. The partition coefficients of examined fluoroquinolones were also calculated with computational programs. All the obtained data, from experimental methods and theoretical calculations, were compared and a suitable conclusion was reached. The received results demonstrate that the RP-TLC method may be the only reliable technique for fluoroquinolones in describing their lipophilic nature as well as the activity.