Metal Complexes as Self-Indicating Titrants for Acid-Base Reactions in Chloroform

The paper reports an unprecedented spectrophotometric determination of amines in chloroform, in which amines are not transformed into colored derivatives. This result has been achieved by exploiting the acid-base properties of the tight-ion-paired metal complexes [(HR₂DTO)Pt(H₂R₂DTO)][Cl], which are able to donate a HCl molecule to an amine, giving rise to an ammonium salt and to the neutral complexes [(HR₂DTO)₂Pt]. The circumstance that [(HR₂DTO)Pt(H₂R₂DTO)][Cl] and [(HR₂DTO)₂Pt] species show different absorptions in the visible region of the electromagnetic spectrum enables the aforementioned platinum complexes to behave as self-indicating titrants in the spectrophotometric determination of aliphatic amines, which are known to be UV-vis transparent. The new method has been tested by determining a series of fatty amines in the bulk and gave excellent results. The limits of applicability of this method (pK_a > 4) were found by testing a series of benzodiazepines.

Synthesis of Nimetazepam - Molecularly Imprinted Polymer and SPE Application

The synthesis and performance of a molecularly imprinted polymer (MIP) designed to enable the clean-up of the interferences existing in alprazolam (Alpra) drug samples is described. The MIP was synthesized using non-covalent molecularly imprinted method. Nimetazepam (Nimet), which has a similar chemical structure as the major impurities in Alpra drug samples, was used as the dummy template. Methacrylic acid was used as the monomer. Both the affinity and selectivity of the MIP for Nimet and structurally related compounds were examined through batch-rebinding studies. The specific binding amount of Nimet was determined to be 11.4 mg•g-1. The MIP was used as the sorbent in solid phase extraction (MI-SPE) and methanol was used as the washing solvent for the clean-up of Nimet in the Alpra complex samples. The effective clean-up of Nimet was achieved, with a recovery > 90% for Alpra, in the stimulated samples.

Quality control Fourier transform infrared determination of diazepam in pharmaceuticals

A quality control procedure has been developed for the determination of diazepam in pharmaceuticals using Fourier transform infrared (FTIR) spectroscopy. The method involves the off-line extraction of diazepam with chloroform by sonication and direct determination in the extracts through peak area measurement in the interval between 1672 and 1682 cm(-1) using a baseline correction defined between 1850 and 1524 cm(-1). For standardization it was used an external calibration line established from standard solutions of diazepam in chloroform. The method provides a limit of detection of 0.04 mg per tablet (n=5), a relative standard deviation (R.S.D.) of 0.5% for 5 independent measurements of a standard solution at a concentration level of 0.76 mg g(-1) and a sampling frequency of the whole procedure of 4 h(-1), being required only 45 s for the measurement step. Results obtained by FTIR agree with those obtained by a reference methodology based on ultraviolet spectrometry and thus the developed procedure offers a good alternative for the determination of diazepam in pharmaceuticals.