Solid-state study of mepivacaine hydrochloride.

Different crystalline forms of the local anaesthetic mepivacaine hydrochloride (MH) were revealed by Fourier transform infrared spectroscopy (FT-IR), not by conventional differential scanning calorimetry (DSC). The existence of two polymorphic anhydrous modifications was discovered and further characterized by X-ray powder diffraction and thermal analysis: Form II, the commercial one, and the more stable Form I, obtained by re-crystallization from Form II. Two pseudopolymorphs were also obtained: Form III, a solvate crystallized from ethanol and Form IV, a solvate crystallized from methanol. Single crystal X-ray diffraction data for both solvates were collected and their structures were determined. Form II, metastable and monotropically related to Form I, generates through desolvation of Form III, very often present in industrial processing, where crystallization from ethanol solution is a common practice. For the sake of clarity, the presence of polymorphic forms should be reported in the drug master files of MH. However, since MH is readily water soluble, the observed polymorphism has no relevance to its typical clinical use as aqueous solutions.

Improving gas chromatographic determination of residual solvents in pharmaceuticals by the combined use of headspace solid-phase microextraction and isotopic dilution.

Cyclohexane and toluene were gas chromatographically determined via headspace solid-phase microextraction both in ketoprofen drug substance and ketoprofen capsules by a procedure relying on isotopic dilution (ID), an analytical tool derived from mass spectrometry (MS). This approach, using an internal standard method, gave mean precision and accuracy (RSD 2.56%, 2.97% and bias 0.21%, -0.99% for cyclohexane and toluene, respectively) not obtainable by the more commonly used external standard ones in the presence of real sample matrices. Optimisation of the operative conditions was also supported by experimental design. More generally, the proposed method, exploiting ID without resort to the costly MS instrumentation, could be recommended whenever opportune deuterated analogues of the target analytes and GC capillary columns able to separate all the peaks involved are ready available on the market.

Characterization of Sanguinaria canadensis L. fluid extract by FAB mass spectrometry.

Positive-ion fast atom bombardment mass spectrometry was used for the rapid characterization of commercial Sanguinaria canadensis L. fluid extracts. Quaternary and non-quaternary benzophenanthridine alkaloids afford persistent peaks due to [M]+ and [M+H]+ ionic species, respectively, and their relative abundances are in good agreement with previously reported per cent analytical data. The procedure allowed sanguinarine, chelerythrine, chelirubine, sanguilutine, protopine, allocryptopine and the isomers sanguirubine and/or chelilutine to be effectively detected by means of persistent and intense peaks in all the samples examined.

Development of a densitometric method for the determination of cephalexin as an alternative to the standard HPLC procedure.

A HPTLC-densitometric method was developed in order to obtain a reliable procedure for routine analysis of cephalexin in pharmaceutical formulations. Optimization of TLC conditions for the densitometric scanning was reached by eluting HPTLC silica gel plates in an horizontal developing chamber. Quantitation of cephalexin was performed in single beam reflectance mode by using a computer-controlled densitometric scanner and applying a five-point calibration. A linear regression has been found in the 200-1000 ng range. The setup method is precise, reproducible and accurate. Recovery was also assessed by comparison with the HPLC USP XXIII alternate method. In this case HPTLC-densitometry appears worth of consideration as being relatively inexpensive and time-saving (up to 12 samples can be determined simultaneously in less than 15 min with a solvent consumption of about 15 ml). The results suggest that the proposed method may be used in place of HPLC for the routine quantitation of cephalexin in both pure and dosage forms.

Direct quantitation of antiseptic quaternary ammonium compounds by fast atom bombardment mass spectrometry.

The medicinally important quaternary ammonium salts benzyldimethyltetradecylammonium chloride (BDTA), cetylpyridinium chloride and benzethonium chloride, all afford, under fast atom bombardment (FAB) mass spectrometric conditions, abundant and persistent [M-Cl]+ species usefully amenable to quantitative analysis with the aid of thioglycerol as a liquid FAB matrix. The use of BDTA as an internal standard allowed a direct, precise and accurate determination of cetylpyridinium and benzethonium chlorides, either as pure samples or in dosage forms, in the concentration range 0.05-2 mg/ml.

Determination of benzalkonium chloride in contact lens solutions by positive-ion fast atom bombardment mass spectrometry.

Under positive-ion fast atom bombardment (FAB) mass spectrometric conditions, benzalkonium chloride (BAK) afforded intense peaks at m/z 304 and 332, corresponding to the intact cations [M--Cl]+ of C12 and C14 homologues, respectively. The use of benzethonium chloride as an internal standard and thioglycerol as a FAB matrix allowed the direct and specific determination of the BAK content (0.004-0.020%) in commercial hard contact lens solutions through the individual assay of the two alkyl homologues. A linear relationship between the homologue concentration and the peak-area ratio was observed over the concentration range 3-180 micrograms ml-1.

Evaluation of some benzyl and benzylidene monosubstituted gamma-butyrolactones and tetrahydrofurans as platelet activating factor antagonist agents.

Some benzyl and benzylidene monosubstituted gamma-butyrolactones and tetrahydrofurans were applied as platelet activating factor (PAF) antagonist agents. The results indicated that, whereas all benzyl derivatives are completely inactive, benzylidene substitution is the key feature for obtaining moderate activity. Molecular modeling and molecular electrostatic potential mapping are applied in conjunction with the most recent PAF-receptor model to rationalize the results.

Revealing the mammalian lignan precursor secoisolariciresinol diglucoside in flax seed by ionspray mass spectrometry.

Ionspray mass spectrometry allowed the rapid detection and unambiguous identification of secoisolariciresinol diglucoside, an important mammalian lignan precursor occurring in flax seed. It was observed that this compound is embedded in a complex form, probably a complex glucoside of still undisclosed structure, among the polar solvent extractables of flax seed from which it could not be released as such without the intervention of alkaline methanolysis. Comparison of ionspray mass spectra of untreated and methanolysed flax-seed extracts confirmed methanolysis as the crucial step in setting up any further analytical or preparative procedure concerned with secoisolariciresinol diglucoside.

Investigation of Pinus mugo essential oil oxygenated fraction by combined use of gas chromatography and dry column chromatography.

The oxygenated compounds of Pinus mugo Turra essential oil were investigated by a combination of GC and dry column chromatography (DCC) coordinated by GC data processing. The collected data resulted in a bar graph ("normalized" gas chromatogram) giving the RRT's and relative amounts of 68 components; 38 of them were identified by MS and IR. The described procedure may be used for essential oil analysis in general.